Tutorial for design of foundations using safe

BY: ASAYE CHEMEDA (E-mail: asayechemeda@yahoo.com)
AMBO UNIVERSITY CIVIL ENGINEERING DEPARTMENT 2016
TUTORIAL FOR
DESIGN OF
FOUNDATIONS
USING
CSI-SAFE
SOFTWARE

1 BY: ASAYE CHEMEDA (E-mail: asayechemeda@yahoo.com)
Contents
1. Introduction.......................................................................................2
2. Isolated (Single) Footing.....................................................................3
2.1. From the Built-in Model................................................................3
2.2. Using Grids.................................................................................38
2.3. From AutoCAD..........................................................................74
3. Combined Footing ..........................................................................106
3.1. From the Built-in Model.............................................................106
3.2. Using Grids................................................................................139
3.3. From AutoCAD.........................................................................176
4. Mat Foundation.............................................................................. 207

1. Introduction
Foundations are components of a structure which ultimately transfer loads from
the superstructure safely into the soil. Foundations are alternatively named as
footings. Depending on the mechanism and the depth of the soil to which the loads
are transferred, foundations can be broadly categorized into shallow foundations
and deep foundations. Shallow foundations are those where the foundation loads
are transferred to a soil at shallow depth and where the load transfer mechanism is
predominantly through resistance of the soil at the bottom of the foundations. The
depth of shallow foundations is usually less than their largest dimension.
Foundations which transfer the superstructure load to a soil layer found a large
depth are said to be deep foundations. The resistance soil force on deep
foundations is generated through two mechanisms; namely, tip resistance and side
friction. This tutorial is entirely about shallow foundations.
Depending on the number and arrangement of columns they support and their
geometry, shallow foundations can be classified into isolated, combined, strip and
mat.
Isolated footings (or as sometimes called spread or single footings) are footings
which support only one column. The load from the column may be only
concentrated load, only moment or a combination of concentrated load and
moment. The shape of the footings may be square, rectangular or circular.
Combined footings are footings which support a number of columns along a single
row. The number of columns is usually two. However, more than two columns can
also be present on combined footings all aligned along a single row. The ratio of
the longer side to the shorter side of these foundations shouldn’t be considerably
large. The shape of combined foundations can be either rectangular or trapezoidal.
Strip foundations are those foundations where the shorter dimension of the
foundation is negligible as compared to the longer dimension. The load on strip
foundations may come either from a number of columns are from a long wall.
Mat foundations are foundations which support many columns arranged in more
than one row i.e. in two dimensions. These foundations may support all the
columns of the entire building or a number of columns from portion of the
building.
During this tutorial, it is assumed that the user has prior knowledge about the
theoretical design process of shallow foundations.

2. Isolated (Single) Footing
In this part of the tutorial, an isolated footing will be designed in three different
ways. First, a square isolated foundation will be designed using the built-in model
of the software itself. Then a rectangular isolated foundation will be designed using
grids. Lastly, a circular foundation will be designed by importing the geometry from
AutoCAD. In all sections, a design problem will be given first and the procedures
which will be followed to carry out the design process in SAFE program will be
detailed.
2.1. From the Built-in Model
STEP
1:
Creating the Model
To create a footing model from the built-in program, there are three ways.
a. Go to File menu and click on New Model …
b. Click on the icon . This icon is the first among the list of icons just
below the menu bar.
c. Simply click on the Ctrl and N keys simultaneously (Ctrl+N).
Performing one of the above three ways results in the popping-up of the
following ‘New Model Initialization’ window.
Design a square isolated footing with the following parameters:
• Dimension of the footing: 2.5mX2.5m
• Dimension of the column: 0.5mX0.5m
• Ultimate bearing capacity of the soil : 100kN/m2
• Maximum allowable settlement of the foundation: 10mm
• Concentrated load (DL) : 300kN
• Concentrated load (LL): 140kN
• Grade of concrete: C-25 (25MPa 28-day characteristics cube strength)
• Grade of reinforcement bar (rebar): S-300 (300MPa characteristics yield
strength)
• Overall thickness of the foundation: 500mm
• Concrete cover : 50mm
• There are no bending moments on the column

Figure 1
This window consists of two parts: the ‘Design Data’ part and the ‘Initial Model’
part. In the ‘Design Data’, there are ‘Design Code’, ’Design Preferences’,
‘Project Information’ and ‘Units’.
The ‘Design Code’ consists of a list of selected design codes from many countries.
Depending on the suitability of the code for your country, you may select one
among the list of codes. The design code which follows similar design philosophy
to my country code is BS 8110-1997. So, this design code is selected.
After selecting the design code, it is better to first select the units to be used in the
design and analysis process. These units can be selected by clicking on the
‘Modify/Show’ button in front of ‘Units’. The following window pops up when
the button is clicked. To choose metric units, click on ‘Metric Defaults’ button.
The click results is metric units for best practices to be selected. It can be observed
that, even though all the units are metric, they are not consistent. To select a
preferred consistent unit, click on the ‘Consistent Units’ button. In this ‘Units’

window, the decimal places and minimum number of significant digits for any
quantity can also be modified.
Figure 2
By clicking on the ‘Modify/Show’ button in front of the ‘Project Information’,
information regarding the project, the company and the model can be entered.
By clicking on the ‘Modify/Show’ button in front of the ‘Design Preferences’,
the user preferences regarding the design code, concrete cover for slabs and beams,
post-tensioning can be changed. The following ‘Design Preferences’ window
pops-up when the button is clicked. The ‘Min. Cover Slabs’ tab of the window
may be of interest for this particular problem as footings will be modelled as slabs.

Thus, click on this tab. This is the tab where the concrete cover and preferred rebar
size will be entered.
Figure 3.
In the ‘Min. Cover Slabs’ tab, for ‘Non-Prestressed Reinforcement’ , both the
‘Clear Cover Top’ and ‘Clear Cover Bottom’ should be set to 50mm as the
concrete cover in this design problem stated to be 50mm. The ‘Preferred Bar Size’
can be set to any reasonable value. Here, the ‘Preferred Bar Size’ is set to 20 which
is the diameter of the rebar in mm which will be used as the main reinforcement in
the foundation. Leave the rest at they are.
Once everything is set correctly in the ‘Design Data’ box, go to the ‘Initial Model’
box and select the suitable model. Since, an isolated (single) footing will be designed
click on the big square button just above ‘Single Footing’. The button itself shows
a plan view of an isolated footing. When the button is clicked, the following ‘Single
Footing’ window will pop up. In this window, there are three boxes: ‘Plan
Dimensions’, ‘Load’ and ‘Properties’.

In the ‘Plan Dimensions’ box, the footing and column dimensions will be entered.
While entering the footing dimension, it is the distance from the center of the
column to each of the edge which will be entered not the actual dimension of the
footing. Since the column is located centrally on a 2.5mX 2.5m square footing, the
distance from the center of the column to all the edges of the footing will be 1.25m.
Thus, set all the values of ‘Left Edge Distance’, ‘Right Edge Distance’, ‘Top
Edge Distance’ and ‘Bottom Edge Distance’ to be 1.25m. These values may be
accordingly changed depending on the location of the column on the footing.
Figure 4.
The text field in front of the ‘Load Size (Square)’ is the field where the column
size for square columns will be entered. Since in this design problem, the column
is of dimensions 500mmX500mm, enter 500 in the text field as the unit is already
in mm. For column shapes other than square, just enter a preliminary column
dimension and you can change both the shape and size of columns at a later time.
In the ‘Load’ box, enter the concentrated loads and moments in the column
depending on their type as ‘Dead’ or ‘Live’. In this particular problem, there is
300kN concentrated dead load and 140kN concentrated live load with no
moments. Thus, enter these values as shown in Fig. 4.
In the ‘Properties’ box, the footing thickness and the subgrade modulus of the soil
will be entered. The footing thickness of the footing is given to be 500mm. Thus,
enter this value as shown in fig. 4. However this value may be revised depending
on the punching shear requirements at a later time. The subgrade modulus of a soil
is the ratio of the increment of contact pressure to the corresponding change in
settlement. In the absence of a supportive test to determine its value, it can also be
safely approximated by the ratio of the bearing capacity of the soil to the maximum

permissible settlement in the soil. In this particular problem, the subgrade modulus
can be approximated by 100kN/m2
/10mm = 10000kN/m3
. Thus enter this value
in the text field in front of the ‘Subgrade Modulus’. Then press the ‘OK’ button.
This exits the ‘Single Footing’ window and a plan view of the foundation will be
displayed on the main screen. You can zoom in and zoom out using the wheel of
your mouse or using the tool bar under the menu bar.
Figure 5
The column shape and dimensions can be changed at this stage. The column is
shown at the center of the plan view in Fig.5 with somewhat darker color. Changing
the originally square column to rectangular column is a pretty easy process and
there are different options to do that. The simplest one is to draw the column from
the ‘Draw’ menu. For this, delete the existing column with unwanted shape and go
to ‘Draw’ menu and click on ‘Quick Draw Areas Around Points’. Or simply click
on the equivalent icon on the left hand side tool bar and the following window
will pop up.
Figure 6

In this window, change the ‘Shape of Object’ to the shape that you want and the
property to ‘STIFF’, enter the dimensions and click on the footing where you want
the column.
The other way to change the shape of columns is to left click on any edge, then
right click on the left clicked edge and a ‘Point Object Information’ window pops
up. In the ‘Geometry’ tab of this window, you can change the X,Y,Z coordinates
of the corner to any desired value. Through similar process on other corners of the
column, the shape of the column can be converted into any desired quadrilateral or
triangular shape. To change the column into other shapes and sizes, hover over the
column in the plan view and right click on any point inside the column. On the
right click, the following window pops up.
Figure 7

Then by clicking on the ‘Geometry’ tab, any edge of the originally ‘Straight’ side of
the square can be changed to some selected geometric shapes.
STEP 2: Defining Material Properties
The materials which are involved in the design of the footing should be defined
before the analysis. These materials are the concrete, the reinforcement bar (rebar)
and the soil which is already defined. Thus, the concrete property and the rebar
property will be defined here.
The material definition can be carried out in two ways.
The first one is through the ‘Define’ menu in the menu bar. The other one through
the model explorer on the left hand side of the home window. To define material
properties through the former method, click on ‘Define’ menu and again click on
‘Materials…’ resulting in the following window depending on prior material
definitions.
Figure 8
The list in the ‘Materials’ box may not be exactly as it appears in your widow.
However, that doesn’t bring any change in the outcome of the design process as
you can customize this list any time.
The ‘Add New Material Quick…’ button allows you to define materials quickly
from a list of pre-defined materials. The ‘Add New Material’ button allows you
to define materials by changing their properties. The ‘Add Copy of Material’
button allows you to define a material with same property as an already defined
material. The ‘Modify/Show Material’ button displays the property of an already

defined material with the possibility of modification. The ‘Delete Material’ button,
when active, deletes a defined material property.
For this particular problem, we will define concrete and rebar properties through
the ‘Add New Material’ button. Thus, click on this button. This can also be
achieved by right clicking on ‘Materials’ on the model explorer and selecting ‘New
Material’. The following window pops up in ether cases.
Figure 9
This is the window where material properties are defined. First, let us define the
concrete property which will be used in the design. Put any name for the material
in the text field in front of ‘Material Name’. But, it is important to make sure that
the concrete with the defined material name is assigned for the footing. For this
particular problem, let the name of the concrete to be used be ‘C25’. Since we are
defining a concrete, the ‘Material Type’ should be set to ‘Concrete’.

The unit weight of reinforced concrete may vary depending of the design code of
your country. Thus, enter the unit weight of reinforced concrete stipulated in your
country code in the text field in front of ‘Weight per Unit Volume’. For this
particular example, we will use 25kN/m3
.
For C-25 concrete, the modulus of elasticity according to BS 8110-1197 is around
29GPa. Thus, enter this value in the text field in front of ‘Modulus of Elasticity,
E’. If you selected another design code in step 1 while creating the model, you
should refer to actual value of this parameter from the code and enter it accordingly.
Be aware of the units though.
The values of Poisson’s ratio and coefficient of thermal expansion may also be
defined in the design code and should be entered accordingly. For this particular
problem, a value of 0.2 for ‘Poisson’s Ratio, U’ and a value of 10x10-6
/o
C for
‘Coefficient of Thermal Expansion, A’ will be entered. The ‘Shear Modulus, G’
will be automatically calculated in an uneditable text field.
The grade of concrete for this particular problem is C-25 which is a concrete with
28 day characteristics cube compressive strength of 25MPa. The concrete
designation may be different for different country codes but the concept is the
same. Therefore, enter 25 in the text field in front of ‘Concrete Cube
Compressive Strength, fcu’.
If a lightweight concrete is used, check on ‘Lightweight Concrete’ and enter the
corresponding ‘Shear Strength Reduction Factor’ in the space provided.
When you press on ‘OK’, a concrete material with the above properties will be
added to the list of materials. This material will be assigned for the footing before
the analysis.
After defining the concrete property, the program returns to the window shown in
Fig. 5. To define a rebar property, we will follow the same procedure as we followed
while defining the concrete property. Since a new rebar property will be defined,
click on the ‘Add New Material…’ button. A ‘Material Property Data’ window
pops up and when you change the ‘Material Type’ to ‘Rebar’, the window appears
to look like the following.

Figure 10
Change the ‘Material Name’ to any name you want. Here, we name it ‘S300’. The
material type should be ‘Rebar’. The weight per unit volume of steel is stipulated
in the design code. For BS 8110-1197, the weight per unit volume is 77.0085kN/m3
.
Thus, enter this value in the text field in front of ‘Weight per Unit Volume’. The
modulus of elasticity for reinforcement bars according to the same design code is
200GPa. Thus enter this value in the text field in front of ‘Modulus of Elasticity,
E’ considering the unit.
In the ‘Other Properties for Rebar Materials’ box, two quantities are mentioned:
minimum yield stress and minimum tensile stress for the reinforcing material. The
values of these parameters will be specified in the design code which you defined
earlier. If the code assumes that the rebar material exhibits elastic perfectly plastic
behavior, the values of these two quantities will be the same. The grade of steel to
be used for this particular example is S-300. The yield stress for this type of
reinforcement bar is 300MPa. Since the design code of my country assumes that
rebars exhibit elastic perfectly plastic behavior, the minimum tensile stress will also
be 300MPa. Thus enter 300 in both text fields in front of the ‘Minimum yield

stress, Fy’ and ‘Minimum Tensile Stress, Fu’. Then press ‘OK’ in both
‘Material Property Data’ and ‘Materials’ windows concluding the material
definition step.
STEP 3: Defining Footing and Column Properties
After defining the material properties, the footing and column properties can be
defined. This definition can take place in two ways: from the menu bar and from
the model explorer. In SAFE software, footings are modelled as ‘footings’ and
foundation columns are modelled as ‘stiff’.
To define footing and column properties from the menu bar, go to ‘Define’ menu
and click on ‘Slab Properties…’. The following window will pop up.
Figure 11
In the ‘Slab Property’ box, two foundation components are listed. The names in
this box for your particular design may be different from the list of names in the
box. The ‘FOOTING’ corresponds to the bottom slab portion of the foundation
and ‘STIFF’ corresponds to the foundation column. The ‘Add New Property…’
button prompts the user to enter new properties for the footing and foundation
column while the ‘Add Copy of Property…’ copies the property of an existing
slap. The ‘Modify/Show Property…’ allows the user to show the property of an
existing component with the possibility of modification. When the ‘Delete
Property’ button is active, it allows the user to delete an existing slab property.
In this case, we use the ‘Modify/Show Property…’ button. However, one can
also use the ‘Add New Property…’ button. To use ‘Modify/Show Property…’

button, highlight the foundation component to be modified like the ‘FOOTING’
is highlighted in Fig. 8 and click on this button. Since ‘FOOTING’ is highlighted,
we will be modifying the footing property. The following window appears after the
click.
Figure 12
The ‘Property Name’ will be automatically assigned to ‘FOOTING’. The ‘Slab
Material’ should be set to the concrete grade which is defined in step 2. Since the
name of the concrete material defined in step 2 for this particular problem is ‘C25’,
a material with this name should be selected from the list.
In the ‘Analysis Property Data’ box, ‘Type’ should be set to ‘Footing’ as we are
modifying the footing property. The ‘Thickness’ value should be set to the same
value as the one which is used while creating the model. Since the thickness of the
footing is 500mm, this value is entered in the text field corresponding to
‘Thickness’. As footings are modelled as thick plates, check the ‘Thick Plate’

option. The ‘Orthotropic’ check box is selected when a footing with irregular
dimension is to be used.
When you press ‘OK’, the ‘Slab Property Data’ window will be exited and the
‘Slab Properties’ window in Fig. 11 gets activated. Now, the property of the
foundation column will be modified. To do this, highlight ‘STIFF’ in the ‘Slab
Property’ box and click on the ‘Modify/Slab Property…’ button. The following
window appears after the click.
Figure 13
The ‘Property Name’ will be automatically assigned to ‘STIFF’. The ‘Slab
In the ‘Analysis Property Data’ box, ‘Type’ should be set to ‘Stiff’ as we are
foundation column and the footing are equal, the thickness of the ‘Stiff’ is 500mm,
this value is entered in the text field corresponding to ‘Thickness’. As foundation
columns are modelled as thick plates, check the ‘Thick Plate’ option. The
‘Orthotropic’ check box is selected when a column with irregular dimension is to
be used.

‘Slab Properties’ window in Fig. 8 gets activated. Again press ‘OK’ and exit the
window for defining the footing and foundation column.
STEP 4: Defining Load Patterns, Load Cases and Load Combinations
The loads on the foundation should be defined accordingly before the analysis.
First, the load pattern should be defined. This can be done from the ‘Define’ menu
or from the ‘Model Explorer’. This time, we will do it from the model explorer.
In the model explorer, expand ‘Load Definitions’ and you will see ‘Load
Patterns’. When you expand ‘Load Patterns’, you will see ‘DEAD’ and ‘LIVE’.
At the end, the model explorer appears to look like:
Figure 14
Now, right click on ‘Load Patterns’ and click on ‘New Load Pattern’ and the
following window pops up.

Figure 15
In the ‘Load Patterns’ window, two load patterns are already defined: ‘DEAD’
and ‘LIVE’. The ‘Type’ of the ‘Load’ should also be changed accordingly. There
are many options for type of loading. The ‘Type’ for dead loads should be set to
‘DEAD’ and for live loads ‘LIVE’. If there are other types of load patterns on the
foundation such as earth quake load, you can add the load pattern with the ‘Add
Load Pattern’ button. You can also delete any undesirable load pattern using the
‘Delete Load Pattern’ button. Since in this example, we have only dead and live
loads, we will leave the existing load patterns as they are. The ‘Self Weight
Multiplier’ value should also be changed accordingly. This value imparts the option
whether to include or exclude the self-weight of the foundation in addition to
external loads. If the self-weight of the foundation is already included as an external
dead load or if you want to exclude the effect of self-weight from the analysis, the
value under ‘Self Weight Multiplier’ should be set to zero. In this example, we
will consider the self-weight as an additional load to the external dead load. Thus,
the value under ‘Self Weight Multiplier’ for the ‘DEAD’ load is one. For the
‘LIVE’ load, it will be zero. Press ‘OK’ and the window will be exited.
After this, the load cases will be defined. Load cases are used to dictate the way the
loads are applied (statically or dynamically) or the way the structure responds
(linearly or non-linearly) for the defined load patterns. To define a load case, go to
‘Define’ menu and click on ‘Load Cases…’. The following window will pop up
after the click.

Figure 16
The load patterns which were defined earlier will automatically appear in the list of
‘Load Case Name’ of the ‘Load Cases’ window. The ‘Load Case Type’ column
shows the way in which each load pattern will be applied during analysis. If you
want to modify this, highlight the load pattern for which you are going to change
the load case type and click on the ‘Modify/Show Case…’ button. If you click
this button, the following window will appear. In this window, you can change the
way the load is applied from the ‘Load Case Type’ box. The way the structure
responds can also be selected from the ‘Analysis Type’ box. This problem ‘Static’
is for the ‘Load Case Type’ and ‘Linear’ is selected for the ‘Analysis Type’ since
the load is static and the foundation responds linearly. The scale factor for the dead
load in the ‘Loads Applied’ box will be left as one. Press ‘OK’ and exit the window.
The load case type for the live load should also be ‘Linear Static’. Otherwise, it
should be changed by clicking the ‘Modify/Show Case…’ button to linear static
case. If both the load case types are as desired click ‘OK’ and exit the ‘Load Cases’
window.

Figure 17
Definition of the load combinations will be the next step. Two load combinations
will be considered in this example for ultimate limit state and serviceability limit
state. To define load combinations, go to ‘Define’ menu and click on ‘Load
Combinations…’ and the following window pops up.
Figure 18

New load combinations will be added through the ‘Add New Combo…’ button.
Here, two load combinations will be added; one for the ultimate limit state the other
for the serviceability limit state. When the ‘Add New Combo…’ button is clicked,
the following window appears.
Figure 19
In the ‘Load Combination Data’ window, any name can be given for the load
combination. The ‘Combination Type’ should be set to ‘Linear Add’ as the
component loads (dead and live) will be added linearly. However, there are also
other options from the drop down menu in front of ‘Combination Type’. In the
window shown in Fig. 19, the two loads (dead and live) should be activated below
the ‘Load Name’ column of the ‘Define Combination of Load Case/Combo
Results’ box. The values in the ‘Scale Factor’ column correspond to the partial

safety factors for load for the failure mode under consideration. These partial safety
factors are specified in the design code of your country. In the design code of my
country, the partial safety factor for dead loads for ultimate limit sate case is 1.3 and
for serviceability limit state is 1 for the cases where there are only dead and live
loads. For such load patterns, the partial safety factor for live loads for ultimate
limit sate case is 1.6 and for serviceability limit state is 1. Thus, enter a value of 1.3
in front of ‘DEAD’ and 1.6 in front of ‘LIVE’ in ‘Scale Factor’ column. The
failure condition which is being under consideration can be defined by selecting
and deselecting the check boxes in the ‘Design Selection’ box. Since the above
scale factors are for the ultimate limit state, check on ‘Strength (Ultimate)’. The
‘Load Combination Data’ window for the serviceability limit state looks like the
following window.
Figure 20

STEP 6: Drawing Design Strips
Design strips determine the way in which different quantities related to the
reinforcement calculation are calculated. Forces are integrated across the design
strips. Thus, the larger the width of coverage of the design strips within the given
structure, the higher will be the calculated values of the bending moments and shear
forces. Thus, an optimum width of strip is required compromising the safety and
economical requirements. The width of the design strip will be specified in the
design code. According to the code of my country, the width of design strips for
isolated foundations is 1m. Thus, a one meter design strip will be drawn in both X
and Y directions on the foundation. These design strips in X and Y direction are
usually defined in SAFE software as layer A and layer B.
Before drawing design strips, existing design strips, if any, should be deleted. To do
this, follow the following command: ‘Select’>’Select’>’Properties’>’Design
Strip Layers’. This results in the following ‘Select Design Strip Layers’ window.
Figure 21
In this window, select all layers and press ‘OK’ and the window will be exited while
any existing design strips are selected. Then press the ‘Delete’ key. This deletes any
existing design strips. After this, new layers of design strips in both X and Y
directions will be drawn.
To draw the design strip, go to the ‘Draw’ menu and click on ‘Design Strips’ and
the following window pops up.

Figure 22
In this window, the ‘Strip Layer’ should be selected to be either ‘A’ or ‘B’. But if
‘A’ is for design strip in X direction ‘B’ should be for Y direction and vice versa.
Since we are drawing a strip around the column to consider maximum moment and
shear forces, the ‘Strip Design Type’ should be set to ‘Column Strip’. The width
of the strip will be 1m in both directions and since the column will be centrally
located, all the widths will be set to 0.5m. To draw the design strip in the X
direction, without closing the window, left click at the center of one side of the
footing on the plan view parallel to the Y axis and again left click at the center of
the parallel side and right click. This creates a design strip in X direction. In doing
so, if you can’t snap to the center of the side of the footing, you can modify the
snap options by clicking on the ‘Snap Options…’ command from the ‘Draw’
menu and adjusting the options which you want to snap to. The design strip in Y
direction can also be drawn in a similar procedure after changing the ‘Strip Layer’
to ‘B’.
You can display the design strips by setting the display options by clicking on ‘Set
Display Options…’ from the ‘View’ menu or by simultaneously clicking on ‘Ctrl’
and ‘W’ keys or by just clicking on the set display options icon from the tool
bar below the menu bar. This results in the following window:

Figure 23
Then, check on ‘Labels’, ‘Show Width’ and ‘Show Stations’ in the ‘Design Strip
Objects’ box and press ‘OK’ and the following window appears displaying the
design strips in the two directions.
Figure 24

STEP 7: Assigning Slab Data, Support Data and Load Data
The slab data, support data, and load data which are defined in the previous steps
should be assigned to the corresponding structural component. The way to do this
is first to select the component and next to assign the slab property, support
property or loads accordingly. The selection can be done by clicking on the
component from the plan view or through the ‘Select’ menu. The latter option
assures that the component is selected exactly as selection by clicking may result in
incorrect selection. Thus, all the selections here will be done from the ‘Select’
menu. The assignments will be discussed as follows:
a. Assigning slab data to the footing
Select the footing through the following strings of commands
‘Select’>’Select’>’Properties’>’Slab Properties…’. Then select ‘Footing’ and
press ‘OK’. Then assign the footing property through the following strings of
commands ‘Assign’>’Slab Data’>’Properties…’. Then select ‘FOOTING’ and
press ‘OK’.
b. Assigning slab data to the foundation column
Select the foundation column through the following strings of commands
‘Select’>’Select’>’Properties’>’Slab Properties…’. Then select ‘Stiff’ and press
‘OK’. Then assign the footing property through the following strings of commands
‘Assign’>’Slab Data’>’Properties…’. Then select ‘STIFF’ and press ‘OK’.
c. Assigning support data to the footing
commands ‘Assign’>’Support Data’>’Soil Properties…’. Then select ‘SOIL’
and press ‘OK’.
d. Assigning reinforcement data to the design strips
Select each design strip through the following strings of commands
‘Select’>’Select’>’Properties’>Design Strip Layers…’. Then select ‘A’ or ‘B’
(one at a time) and press ‘OK’. When you right click on the selected strip layer, the
‘Slab-Type Area Object Information’ window pops up. In the ‘Design’ tab of
this window, set the ‘Rebar Material’ to ‘S300’ and press ‘OK’. Do this for both
strips.
e. Assigning load on the foundation column

To assign load on the foundation column, right click on the point at the center of
the foundation column and a ‘Point Object Information’ window pops up. In this
window, click on the ‘Loads’ tab. Then click on ‘Reset All’ button to delete any
existing loads.
Figure 25
The dead load and the live load can be assigned through the ‘Assign Load…’
button. The procedure is: click on ‘Assign Load…’ button, then select ‘Force
Loads’ then press ‘OK’ then select either ‘DEAD’ or ‘LIVE’ depending on which
load you want to enter its value then enter its value accordingly and in the right
direction (axis), then select ‘Add to Existing Loads’ and press ‘OK’. While doing
this, the foundation column dimensions should be entered in the ‘Size of Load for
Punching Shear’ box of ‘Point Loads’ window. You can also delete any forces
which are wrongly entered through ‘Delete Existing Loads’ radio button option.
In this example, since the dead load is 300kN and the live load is 140kN, these
values are entered in the Gravity Direction.

STEP 8: Running the Analysis
After this, the analysis can be run. But, make sure that the footing and the
foundation column are assigned with the correct rebar material. To do this, right
click anywhere in the plan view of the footing and the ‘Slab-Type Area Object
Information’ window will pop-up.
Figure 26
In the ‘Design’ tab of this window, set the value of ‘Rebar Material’ to ‘S300’.
Do this for the column foundation, and both design strips as well. After this, go to
the ‘Run’ menu and click on the ‘Run Analysis’ command.
STEP 9: Displaying the Output
Once the analysis is run, the output will be displayed. Particularly, the punching
shear design is of great importance as the footing cannot be designed without the
punching shear requirement being adequately satisfied. To do this, go to the ‘Run’
menu and click on ‘Run Analysis & Design’ command or simply click on the ‘F5’
key. When you do this, you will be prompted to save the model, if you haven’t
already don this. When you save the model, the following window showing the
displacement of the soil in a banded figure will be displayed.

Figure 27
To display the punching shear ratio, go to the ‘Display’ menu and click on ‘Show
Punching Shear Design’. After this, the punching shear ratio will be displayed in
the plan view around the foundation column as in the following figure.
Figure 28
As can be noticed from the figure, the punching shear ratio is 0.3088. Generally, a
punching shear ratio less than one indicates the concrete thickness is adequate to

resist punching shear and a value greater than one indicates that the punching shear
capacity is exceeded somewhere along the critical section. For economical design,
it is recommended to keep the punching shear ratio between 0.95 and 1 as very
small values of punching shear ratio means excess concrete thickness is used.
However, if the punching shear ratio is greater than one, the thickness of the
concrete should be increased and the foundation should be re-designed. A detailed
quantitative description of the foundation design can also be obtained by right
clicking on the plan view shown in Fig 28 as shown below. Several trial may be
made by zooming in and out to get the quantitative description.
Figure 29
Through the ‘Display’ menu, relevant quantities can be displayed on the screen.
For instance, the ‘Display’>’Show Strip Forces’ command or by simply clicking
the ‘F8’ key, the following window will be displayed.

Figure 30
In this window, the ‘Load Case/Load Combination’ box provides with radio
buttons to select for which particular load case or load combination that we want
to display the output. The ‘Component’ box contains four radio buttons to select
which quantity to display. The ‘Show Forces For These Strip Layers’ box allows
us to select the strip layer for which the quantity is displayed. Both strip layers can
be selected at the same time. From the ‘Scaling’ box, we can select whether
automatic scaling or user defined scaling is used while displaying the diagram. The
‘Display Options’ box allows us to fill or not to fill the diagram and to display or
not to display the values on the diagram. For the preferences shown in Fig. 30, the
following diagram will be displayed.

Figure 31
The ‘Display’>’Show Slab Design…’ command results in the window shown in
Fig 32. In this window, several options can be set in order to display the footing
design in the way we wanted to. The ‘Choose Display Type’ box allows us to
select the ‘Design Basis’ between ‘Strip Based’ and ‘Finite Element Based’.
Unless some differences in the way the design is displayed, there is no difference in
the amount of reinforcement between these selections. Through the ‘Display
Type’ in the same box, it can be selected whether to display flexural reinforcement
or shear reinforcement. This box also allows us to impose or not to impose
minimum reinforcement during the design. The ‘Rebar Location Shown’ box
allows us to select which reinforcement, top or bottom or both, to be displayed.
The ‘Reinforcing Display Type’ box allows us to set the manner in which the
amount of reinforcement is displayed. The option whether to show the reinforcing
envelop diagram and the reinforcing extent can be set by the check boxes in the
‘Reinforcing Diagram’ window. The strip layer direction for which the amount
of reinforcement is displayed can be chosen from the ‘Choose Strip Direction’
box. The ‘Display Options’ box allows us whether to display output in filled
diagram or not and whether the values at controlling stations will be displayed or
not. If we want to display the amount of reinforcement above some specified
reinforcement bar area or spacing, we can use the options in the ‘Show Rebar

Above Specified Value’ box. When the ‘Typical Uniform Reinforcing
Specified Below’ radio button is selected, the ‘Typical Uniform Reinforcing’
box get activated. In this box, we can set a specific value above which the
reinforcement amount will be displayed. The reinforcement diagram output, for the
options set in Fig. 32, will be shown below in fig. 33.
Figure 32

Figure 33
As can be noticed from the footing design diagram in fig. 33, the top reinforcement
across strip layer A is 0mm2
/m for top reinforcement and 1090mm2
/m for bottom
reinforcement.
The design outputs can also be displayed in tabular format by clicking on the ‘Show
Tables…’ menu item from the ‘Display’ menu or by just clicking on the equivalent
icon from the tool bar below the menu bar and the following window will
pop up.

Figure 34
In this window, we can select any of the model definitions or analysis results or
design results and press ‘OK’ to display the quantity which we want to have a look
at. By using the right hand side buttons in the window, the load patterns and the
load cases can be selected.
STEP 10: Detailing
After running the analysis and after checking that the results are reasonable, the
detailing will be done. However, before running the detailing, the detailing
preferences can be set from the ‘Detailing’ menu. From the ‘Detailing
Preferences…’, the likes of dimensional units and material quantity units can be
selected. From ‘Slab/Mat Detailing Preferences…’, the likes of rebar
curtailment options, the rebar detailing options, rebar selection rules and preferred
rebar sizes can be selected. The ‘Drawing Sheet Set-up…’ menu allows us to set-
up the contents of the drawing sheet. The ‘Drawing Format Properties…’ allows
us to set some formats in which the output displayed.

To run the detailing, go to ‘Run’ menu and click on ‘Run Detailing…’ or
simultaneously press ‘Shift’ and ‘F5’ keys or just click on the run detailing icon
from the tool bar just below the menu bar. Then, the ‘Run Detailing
Options’ window pops up so that we set the detailing options. Set the detailing
options which you want and click ‘OK’.
Once the detailing is run, the detailing can be displayed. The detailing display
options can be best accessed from the ‘Model Explorer’. When expanded in full,
the ‘Detailing’ tab of the model explorer looks like:
Figure 35
By clicking on any of the options from the detailing tab, a desired detailing can be
displayed. For instance, by double clicking on the ‘Footing Table’, the following
detail of footing can be shown.

Figure 36
Apart from this detail, other details can also be shown.
STEP 11: Reporting
The last step of foundation design is reporting. Before creating the report, the
report preferences should be set up. To do this, go to the ‘File’ menu and click on
‘Report Set-up…’ and the following window pops up.
In this ‘Report Setup Data’ window, the user preferences regarding the reporting
such as the report output type, the report page orientation and the report items can
be set along with the load patterns and load combinations. Once the preference is
set, the report can be created by clicking on ‘Create Report’ command in the ‘File’
menu. The ‘Advanced Report Writer’ command in the same menu can be used to
set some advanced reporting formats.

Figure 37
This concludes the tutorial for the design of single footing using the built-in model.
2.2. Using Grids
STEP 1: Creating the Model
Design a rectangular isolated footing with the following parameters:
• Dimension of the footing: 2mX3m
• Dimension of the column: 0.4mX0.6m
• Allowable bearing capacity of the soil : 100kN/m2
• Bending moment (dead) in the long direction (My, DL):50kNm
• Bending moment (live) in the long direction (My, LL):25kNm
strength)

To create a footing model by using a grid, there are three ways. Go to ‘File’ menu
and click on ‘New Model …’ or just click on the icon . This icon is the first
among the list of icons just below the menu bar or simply click on the ‘Ctrl’ and
‘N’ keys simultaneously (Ctrl+N).
The click results in metric units for best practices to be selected. It can be observed

Figure 38

Figure 39

Figure 40.
box and select the suitable model. Since an isolated (single) footing will be designed
from grids click on the big square button just above ‘Grid Only’. The button itself
shows crossing grids. When the button is clicked, the following ‘Coordinate
System Definition’ window will pop up.
The footing in this example is rectangular with centrally located column. The grid
which will be created will be boundaries of the outer edges of the footing and the
outer edges of the foundation column. As a result, there is uneven spacing between
the grids. To create such grids with uneven spacing, it is better to create it by
clicking the ‘Edit Grid’ button. When you click this button, a ‘Coordinate System’
window will pop up. In the ‘Display Grid Data as’ box, two radio buttons are
there to choose between ‘Ordinate’ and ‘Spacing’. These are the options how the
location of different grids is defined. If the ‘Ordinate’ option is selected, the X and
Y-coordinates of the grids will be entered. If the ‘Spacing’ option is selected, the
spacing between the grids will be entered. If the grids are irregular in shape with
non-vertical and non-horizontal grids, they can be defined in the ‘General Grid
Data’ box by entering the XY coordinates of the starting and ending points.
Regular grids can also be defined by this option too.

Figure 41
In this example, the length of the footing is 3m and the column dimension is 0.6m
in x direction. The distance between the left face of the footing and the left face of
the foundation column is 1.2m. The same is true for the distance between the right
face of the footing and the right face of the foundation column. To limit the footing
and the column in x-direction, the grids should have x-coordinates of 0, 1.2, 1.8
and 3.
The length of the slab is 2m and the column dimension is 0.4m in y direction. The
distance between the bottom face of the footing and the bottom face of the
foundation column is 0.8m. The same is true for the distance between the top face
of the footing and the top face of the foundation column. To limit the footing and
the column in y-direction, the grids should have x-coordinates of 0, 0.8, 1.2 and 2.

Figure 42
The ‘Model Datum’ is the level of the model in z-direction. Any value can be set
to this. Set the ‘Story Height Above’ value to some reasonable non zero value, say
2, and set the ‘Story Height Below’ to 0 as there will be no story below the footing.
Then press ‘OK’ and the grids will be displayed on the ‘Plan View’ window as
below:

Figure 43
and the soil support. Thus, these properties will be defined here.
definitions.

Figure 44
For this particular problem, we will modify the existing ‘C30’ concrete using the
‘Modify/Show Material’ button and define a new rebar property through the
‘Add New Material’ button.
Highlight ‘C30’ in the ‘Materials’ box and click on the ‘Modify/Show Material’
button. This can also be achieved by right clicking on ‘Materials’ on the model
explorer. The following window will pop up.
This is the window where concrete properties will be modified. Put any name for
the material in the text field in front of ‘Material Name’. But, it is important to
make sure that the concrete with the defined material name is assigned for the
footing. For this particular problem, let us keep the name of the concrete as ‘C30’.
Since we are defining a concrete, the ‘Material Type’ should be set to ‘Concrete’.
.

Figure 45
/o
C for
will be automatically calculated in an un-editable text field.

the analysis.
After modifying the concrete property, the program returns to the window shown
in Fig. 44. To define a rebar property, we will follow the same procedure as we
followed while defining the concrete property. Since a new rebar property will be
defined, click on the ‘Add New Material…’ button. A ‘Material Property Data’
window pops up and when you change the ‘Material Type’ to ‘Rebar’, the window
appears to look like the following.
Figure 46

.
definition step.
The other property which should be defined is the soil support. To define the soil
properties, go to the ‘Define’ menu and click on ‘Soil Subgrade Properties’ menu
item and the following window appears.
Figure 47
By using the buttons in this window, a new soil property or copy of soil property
can be added. An existing soil property can also be modified or deleted. For this

problem, let us add a new soil property by using the ‘Add New Property…’
button. Thus, click on this button and the following window pops up.
Figure 48
In this window, set the property name to ‘SOIL’ and change the subgrade modulus
to 10,000kN/m3
. Because, the subgrade modulus which can be assume by the ratio
of the bearing capacity by the allowable settlement for this particular example is so.
Then press ‘OK’ in both the ‘Soil Subgrade Property Data’ and ‘Soil Subgrade
Properties’ windows.
The ‘Add New Property…’ button prompts the user to enter new properties for
the footing and foundation column while the ‘Add Copy of Property…’ copies
the property of an existing slap. The ‘Modify/Show Property…’ allows the user
to show the property of an existing component with the possibility of modification.
When the ‘Delete Property’ button is active, it allows the user to delete an existing
slab property.

Figure 49
In this case, we use the ‘Add New Property…’ button to add new slab properties
for the footing and foundation column. Click the button and the following window
will pop up.
Figure 50
The ‘Property Name’ can be assigned with any name; but, in this case, the property
name which will be used is ‘FOOTING’. The ‘Slab Material’ should be set to the
concrete grade which is defined in step 2. Since the name of the concrete material
defined in step 2 for this particular problem is ‘C30’, a material with this name
should be selected from the list.
In the ‘Analysis Property Data’ box, ‘Type’ should be set to ‘Footing’. The
‘Thickness’ value should be set to the thickness of the footing defined in the

example. Since the thickness of the footing is 500mm, this value is entered in the
text field corresponding to ‘Thickness’. As footings are modelled as thick plates,
check the ‘Thick Plate’ option. The ‘Orthotropic’ check box is selected when a
footing with irregular dimension is to be used.
‘Slab Properties’ window gets activated. Now, the property of the foundation
column will be added. To do this, again click on the ‘Add New Property…’ button.
The following window appears after the click.
Figure 51
The ‘Property Name’ can be any name but we use ‘STIFF’. The ‘Slab Material’
should be set to the concrete grade which is defined in step 2. Since the name of
the concrete material defined in step 2 for this particular problem is ‘C30’, a material
with this name should be selected from the list.
defining the property of column. The ‘Thickness’ value should be the foundation
column thickness which is equal to the footing thickness. Thus, a value of 500 will
be entered in the text field corresponding to ‘Thickness’. As foundation columns

are modelled as thick plates, check the ‘Thick Plate’ option. The ‘Orthotropic’
check box is selected when a column with irregular dimension is to be used.
‘Slab Properties’ window gets activated. Again press ‘OK’ and exit the window for
defining the footing and foundation column.
Figure 52

Figure 53
whether to consider or ignore the self-weight of the foundation in addition to
after the click.

Figure 54
window.

Figure 55
Figure 56

Figure 57

following window.
Figure 58

STEP 6: Drawing the Footing Components and Design Strips
The footing, the foundation column and a point where the loads will be applied on
the foundation column should now be drawn on the grid.
i. Drawing the footing
Since the footing will be drawn around points and since the footing is
rectangular, go to the ‘Draw’ menu and click on ‘Draw Rectangular
Slabs/Areas’ or simply click on the equivalent icon on the left hand
side tool bar. The following window will appear on the screen after the click.
Figure 59
Making sure that the ‘Property’ is set to ‘FOOTING’, first click on the grid
where one corner of the footing will be located. Then, without releasing the
click, drag into the opposite corner of the footing to draw the footing.
ii. Drawing the foundation column
While the window in fig 59 is active, change the ‘Property’ to ‘STIFF’ and
click on the grid where one corner of the foundation column will be located.
Then, without releasing the click, drag into the opposite corner of the
foundation column to draw the foundation column.
iii. Drawing the point on the foundation column where the load will be applied
Go to ‘Draw’ menu and click on ‘Draw Points’, then click on the mid-point
of the footing and the point will be created. If the cursor could not snap to
the midpoint, you can adjust the ‘Snap Options’ from the ‘Draw’ menu.
After this, the design strips will be drawn. Design strips determine the way in which
different quantities related to the reinforcement calculation are calculated. Forces
are integrated across the design strips. Thus, the larger the width of coverage of the
design strips within the given structure, the higher will be the calculated values of
the bending moments and shear forces. Thus, an optimum width of strip is required
compromising the safety and economical requirements. The width of the design
strip will be specified in the design code. According to the code of my country, the
width of design strips for isolated foundations is 1m. Thus, a one meter design strip
will be drawn in both X and Y directions on the foundation. These design strips in
X and Y direction are usually defined in SAFE software as layer A and layer B.

To draw the design strip, go to the ‘Draw’ menu and click on ‘Design Strips’ or
simply click on the equivalent icon from the left hand sided tool bar and the
Figure 60
direction, without closing the window, left click at the center of one side of the
menu and adjusting the options which you want to snap to. The design strip in Y
direction can also be drawn in a similar procedure after changing the ‘Strip Layer’
to ‘B’.

Figure 61
Objects’ box and press ‘OK’ and after drawing dimension lines by using the
command ‘Draw’>’Draw Dimension Lines’, the following window appears
displaying the design strips in the two directions.
Figure 62

a. Assigning support data to the footing
‘Select’>’Select’>’Properties’>’Slab Properties…’. Then select ‘FOOTING’
and press ‘OK’. Then assign the footing property through the following strings of
and press ‘OK’.
b. Assigning reinforcement data to the design strips
strips.
c. Assigning load on the foundation column
window, click on the ‘Loads’ tab.
loads you want to enter their values then enter their values accordingly (both the
concentrated load and the bending moment) and in the right direction (axis), then
select ‘Add to Existing Loads’ and press ‘OK’. While doing this, the foundation

column dimensions should be entered in the ‘Size of Load for Punching Shear’
box of ‘Point Loads’ window.
Figure 63
You can also delete any forces which are wrongly entered through ‘Delete
Existing Loads’ radio button option. In this example, since the dead concentrated
load is 275kN and the dead bending moment is 50kNm about y-axis and since the
live concentrated load is 175kN and the live bending moment is 25kNm about y-
axis, these values are entered in the Gravity Direction for the concentrated load and
along y-axis for the bending moment.

Figure 64

Figure 65
Figure 66

However, if the punching shear ratio is greater than one, the thickness of the
concrete should be increased and the foundation should be re-designed. A detailed
Figure 67

Figure 68

Figure 69

Figure 70
Figure 71
across strip layer A is around 0mm2
/m for
bottom reinforcement.

pop up.
Figure 72
STEP 10: Detailing

Figure 73

Figure 74
In this detail, the diameter of the reinforcement which is used is 10mm. If you want
to change the diameter….
STEP 11: Reporting

Figure 75
This concludes the tutorial for the design of single footing using the grids.

2.3. From AutoCAD
STEP
1:
Creating the Model
To create a footing model from an AutoCAD file, first draw the plan view of the
foundation on AutoCAD. In this case, it will be two concentric circles one with a
radius of 0.3m (foundation column) and another with a radius of 1.2m (footing).
When you draw the plan view on AutoCAD, make sure that you are drawing it on
a new layer. If you want the origin of the SAFE mode to coincide with the center
of the circular foundation, make the center of the circle coincide with the global
origin of the AutoCAD file when you draw it. Then save the AutoCAD file in DXF
format. To save an AutoCAD file in DXF format, go to ‘File’ menu in the
AutoCAD file and click on ‘Save As’. At the bottom of the upcoming window, just
below the text field where you will enter the file name, you will see ‘Files of type’
with a drop-down menu list. From the drop down menu list, select the option which
has ‘(.dxf)’ at the end. Then enter the file name and save it at any location in your
computer where you can easily remember close it. This saves the file in DXF
format.
Once you saved the AutoCAD file in DXF format, open the SAFE software and
when you use the command ‘File’>’Import’>’.DXF/.DWG Architectural Plan’
or when you simultaneously click on ‘Ctrl’+’Shift’+’I’ keys, and you will be
prompted to open a file. Open the DXF file from the location where you saved it
and the following window will pop up.
In this window, just change the ‘CAD Drawing Units’ to ‘m’ since in the
AutoCAD file is the model is drawn in meter units. Then press ‘OK’.
Design a circular isolated footing with the following parameters:
• Radius of the footing: 1.5m
• Radius of the column: 0.3m
• Allowable bearing capacity of the soil : 150kN/m2
strength)

Figure 76
Then, the following model appears in the plan view.
Figure 77

After the model is created, the preferences regarding the units, the design codes
and concrete cover should be entered. To change the units, click on ‘Units…’
button which is found in the right bottom corner of the main window and the
following widow will pop up. In this window, click on ‘Metric Defaults’ and press
‘OK’ as we will be using metric units. If you want to use U.S. units click on ‘U.S.
Defaults’ and if you want to use a particular metric or U.S. unit consistently click
on ‘Consistent Units…’ and select that particular unit which you want to use
consistently.
Figure 80
To select the design code and other design preferences, go to ‘Design’ menu and
click on ‘Design Preferences…’ and the following window will pop up. In the
‘Code’ tab of this window, change the ‘Design Code’ to ‘BS 8110-1997’ or any
other code which you want to design the circular foundation with. In the ‘Min.
Cover Slabs’ tab, for ‘Non-Prestressed Reinforcement’ , both the ‘Clear Cover

Top’ and ‘Clear Cover Bottom’ should be set to 50mm as the concrete cover in
this design problem stated to be 50mm. The ‘Preferred Bar Size’ can be set to any
reasonable value. Here, the ‘Preferred Bar Size’ is set to #14 which is the bar
number which will be used as the main reinforcement in the foundation. Leave the
rest as they are and press ‘OK’.
Figure 81.
definitions.

Figure 82
For this particular problem, we will add new concrete and a rebar materials using
the ‘Add New Material…’ button. Thus click on this button and the following
window will pop up.
footing. For this particular problem, let us use the name of the concrete as ‘C20’.
.

Figure 83
/o
C for
the analysis.
After adding a new concrete property, the program returns to the window shown
in Fig. 82 To define a rebar property, we will follow the same procedure as we

Figure 84
.

definition step.
Figure 85
Figure 86

to 15,000kN/m3
slab property.
Figure 87
will pop up.

Figure 88

Figure 89
defining the property of column. The ‘Thickness’ value should be the footing
thickness which is equal to 600mm. As foundation columns are modelled as thick
plates, check the ‘Thick Plate’ option. The ‘Orthotropic’ check box is selected
when a column with irregular dimension is to be used.

Figure 90
Figure 91

after the click.
Figure 92

window.
Figure 93

Figure 94
Figure 95

following window.

Figure 96
i. Drawing the footing
circular, go to the ‘Draw’ menu and click on ‘Quick Draw Areas Around
Points’ or simply click on the equivalent icon on the left hand side tool
bar. The following window will appear on the screen after the click.
Figure 97

Since the footing has circular shape, change the ‘Shape of Object’ to
‘Circular Slab’. Make sure that the ‘Property’ is set to ‘FOOTING’. The
value of the ‘Diameter [m]’ should be set to ‘3’ as the footing diameter is
3m.Then, with great care take the cursor to exactly the center of the footing,
and just make one left click. This draws the footing.
ii. Drawing the foundation column
the ‘Diameter [m]’ to 0.6. Then, with great care take the cursor to exactly
the center of the column and just make one lift click. This draws the
foundation column.
iii. Drawing the point on the foundation column where the load will be applied
of the footing and the point will be created. If the cursor could not snap to
the midpoint, you can adjust the ‘Snap Options’ from the ‘Draw’ menu.

Figure 98
direction, without closing the window, left click at the extreme left side of the
footing on the plan view and again left click at the extreme right side of the footing
and right click. This creates a design strip in X direction. In doing so, if you can’t
snap to the extreme points on the footing, you can modify the snap options by
clicking on the ‘Snap Options…’ command from the ‘Draw’ menu and adjusting
the options which you want to snap to. The design strip in Y direction can also be
drawn in a similar procedure after changing the ‘Strip Layer’ to ‘B’.

Figure 99
Figure 100

a. Assigning support data to the footing
and press ‘OK’.
b. Assigning reinforcement data to the design strips
strips.
c. Assigning load on the foundation column

Figure 101
Existing Loads’ radio button option. In this example, since the dead concentrated
load is 500kN and since the live concentrated load is 250kN, these values are
entered in the Gravity Direction for the concentrated load and along y-axis for the
bending moment.

Figure 102

Figure 103
Figure 104

However, if the punching shear ratio is greater than one, like in this example, the
thickness of the concrete should be increased or the grade of the concrete should
be increased and the foundation should be re-designed. A detailed quantitative
description of the foundation design can also be obtained by right clicking on the
plan view shown in Fig 104 as shown below. Several trial may be made by zooming
in and out to get the quantitative description.
Figure 105

Figure 106
not to display the values on the diagram. For the preferences shown in Fig. 106,
the following diagram will be displayed.

Figure 107

Figure 108
Figure 109

/m for
bottom reinforcement.
pop up.
Figure 110
STEP 10: Detailing

Figure 111

Figure 112
STEP 11: Reporting

Figure 113
This concludes the tutorial for the design of single footing using a model
imported from AutoCAD.

3. Combined Footing
In this part of the tutorial, a combined footing will be designed in three different
ways. First, a rectangular combined foundation will be designed using the built-in
model of the software itself. Then a trapezoidal isolated foundation will be designed
using grids. Lastly, a rectangular combined foundation will be designed by
importing the geometry from AutoCAD. In all sections, a design problem will be
given first and the procedures which will be followed to carry out the design process
in SAFE program will be detailed.
3.1. From the Built-in Model
STEP
1:
Creating the Model
To create a footing model from the built-in program, there are three ways.
d. Go to File menu and click on New Model …
e. Click on the icon . This icon is the first among the list of icons just
below the menu bar.
f. Simply click on the Ctrl and N keys simultaneously (Ctrl+N).
Design a rectangular combined footing with the following parameters:
• Dimension of the footing: 2.9mX5.8m
• Dimension of first column: 0.3mX0.3m
• Dimension of second column: 0.35mX0.35m
• Distance between the columns: 4.5m
• Distance between the center of the first column to the left edge: 0.15m
• Concentrated ultimate load on the first column : 650kN
• Concentrated ultimate load on the second column: 1000kN
strength)
• There are no bending moments on the column

Figure 114

The click results is metric units for best practices to be selected. It can be observed
Figure 115

Figure 116.
box and select the suitable model. Since, an isolated (single) footing will be designed
click on the big square button just above ‘Combined Footing’. The button itself
shows a plan view of a combined footing. When the button is clicked, the following

‘Combined Footing’ window will pop up. In this window, there are three boxes:
‘Plan Dimensions’, ‘Load’ and ‘Properties’.
In the ‘Plan Dimensions’ box, the footing and column dimensions will be entered.
While entering the footing dimension, it is the distance from the center of the
columns to each of the edge which will be entered not the actual dimension of the
footing. Since the distance from the left edge to the center of the column is 0.15m,
the ‘Left Edge Distance’ is set to 0.15m. The distance from the center of the
second column to the right edge, if you calculate it from the dimensions of the
footing, is 1.15m. Thus, the value of set all the values of ‘Right Edge Distance’ is
set to 1.15m. Since the column is centrally located in y-direction, the values of ‘Top
Edge Distance’ and ‘Bottom Edge Distance’ are set to be 1.45m.
The radio button below ‘Load Spacing and Size’ should be set to ‘X Direction’
as the columns will be aligned in x-direction. The value of the ‘Spacing’ should be
set to 4.5 as the distance between the columns is 4.5m. For the ‘Load Size
(square)’, the dimensions of any of the columns can be entered and later it can be
changed depending on the actual footing dimensions.
Figure 117
Since in this design problem, the dimension of the first column is 300mmX300mm,
enter 300 in the text field as the unit is already in mm. For column shapes other
than square, just enter a preliminary column dimension and you can change both
the shape and size of columns at a later time.
In the ‘Load Values’ box, enter the concentrated loads and moments in the
column depending on their type as ‘Dead’ or ‘Live’. In this particular problem, the

loads on each column are factored or ultimate loads comprised of dead and live
loads. But, the self-weight is not included. Since, the self-weight is regarded as a
dead load and should be multiplied by a partial safety factor. Thus, it is better if we
define the factored loads as live loads with partial safety factor of unity. Thus, set
the value for ‘P’ of ‘Load1’ to be 650 and the value for ‘P’ of ‘Load2’ to be 1000
in the live load column.
In the ‘Properties’ box, the footing thickness and the subgrade modulus of the soil
will be entered. The footing thickness of the footing is given to be 500mm. Thus,
enter this value as shown in fig. 117. However this value may be revised depending
on the punching shear requirements at a later time. The subgrade modulus of a soil
is the ratio of the increment of contact pressure to the corresponding change in
settlement. In the absence of a supportive test to determine its value, it can also be
safely approximated by the ratio of the bearing capacity of the soil to the maximum
permissible settlement in the soil. In this particular problem, the subgrade modulus
can be approximated by 100kN/m2
/10mm = 10000kN/m3
. Thus enter this value
in the text field in front of the ‘Subgrade Modulus’. Then press the ‘OK’ button.
This exits the ‘Combined Footing’ window and a plan view of the foundation will
be displayed on the main screen. You can zoom in and zoom out using the wheel
of your mouse or using the tool bar under the menu bar.
Figure 118

and the soil which is already defined. Thus, the concrete property and the rebar
property will be defined here.
definitions.
Figure 119
For this particular problem, we will define concrete and rebar properties through
the ‘Add New Material’ button. Thus, click on this button. This can also be
achieved by right clicking on ‘Materials’ on the model explorer. The following
window pops up in ether cases.

Figure 120
This is the window where material properties are defined. First, let us define the
concrete property which will be used in the design. Put any name for the material
in the text field in front of ‘Material Name’. But, it is important to make sure that
the concrete with the defined material name is assigned for the footing. For this
particular problem, let the name of the concrete to be used be ‘C25’. Since we are
defining a concrete, the ‘Material Type’ should be set to ‘Concrete’.
.

/o
C for
will be automatically calculated in an uneditable text field.
the analysis.
After defining the concrete property, the program returns to the window shown in
Fig. 119. To define a rebar property, we will follow the same procedure as we

Figure 121
.

definition step.
Figure 122
In the ‘Slab Property’ box, two foundation components are listed. The names in
this box for your particular design may be different from the list of names in the
box. The ‘FOOTING’ corresponds to the bottom slab portion of the foundation
and ‘STIFF’ corresponds to the foundation column. The ‘Add New Property…’
button prompts the user to enter new properties for the footing and foundation
column while the ‘Add Copy of Property…’ copies the property of an existing
slap. The ‘Modify/Show Property…’ allows the user to show the property of an
existing component with the possibility of modification. When the ‘Delete
Property’ button is active, it allows the user to delete an existing slab property.
In this case, we use the ‘Modify/Show Property…’ button. However, one can
also use the ‘Add New Property…’ button. To use ‘Modify/Show Property…’

button, highlight the foundation component to be modified like the ‘FOOTING’
is highlighted in Fig. 122 and click on this button. Since ‘FOOTING’ is
highlighted, we will be modifying the footing property. The following window
appears after the click.
Figure 123
The ‘Property Name’ will be automatically assigned to ‘FOOTING’. The ‘Slab
In the ‘Analysis Property Data’ box, ‘Type’ should be set to ‘Footing’ as we are
footing is 500mm, this value is entered in the text field corresponding to
‘Thickness’. As footings are modelled as thick plates, check the ‘Thick Plate’

option. The ‘Orthotropic’ check box is selected when a footing with irregular
dimension is to be used.
‘Slab Properties’ window in Fig. 11 gets activated. Now, the property of the
foundation column will be modified. To do this, highlight ‘STIFF’ in the ‘Slab
Property’ box and click on the ‘Modify/Slab Property…’ button. The following
window appears after the click.
Figure 124
The ‘Property Name’ will be automatically assigned to ‘STIFF’. The ‘Slab
value as the thickness of the footing which is 500mm, this value is entered in the
text field corresponding to ‘Thickness’. As foundation columns are modelled as
thick plates, check the ‘Thick Plate’ option. The ‘Orthotropic’ check box is
selected when a column with irregular dimension is to be used.

‘Slab Properties’ window in Fig. 122 gets activated. Again press ‘OK’ and exit the
window for defining the footing and foundation column.
Figure 125

Figure 126
whether to include or leave the self-weight of the foundation in addition to external
loads. If the self-weight of the foundation is already included as an external dead
load or if you want to exclude the effect of self-weight from the analysis, the value
under ‘Self Weight Multiplier’ should be set to zero. In this example, we will
consider the self-weight as an additional load to the external dead load. Thus, the
value under ‘Self Weight Multiplier’ for the ‘DEAD’ load is one. For the ‘LIVE’
load, it will be zero. Press ‘OK’ and the window will be exited.
after the click.

Figure 127
window.

Figure 128
Figure 129

Figure 130
country, the partial safety factor for dead loads for ultimate limit sate case is 1.3 for
the cases where there are only dead and live loads. For such load patterns, the partial
safety factor for live loads for ultimate limit state case is 1.6. In this particular
problem, the loads are already factored and for convenience, they are defined as

live loads. The only un-factored load is the self-weight which will be considered as
dead load. The self-weight is considered as a dead load while defining the load
patterns by making the self-weight multiplier to be equal to one. Thus, enter a value
of 1.3 in front of ‘DEAD’ and 1 in front of ‘LIVE’ in ‘Scale Factor’ column. The
scale factors are for the ultimate limit state, check on ‘Strength (Ultimate)’.
STEP 6: Drawing Actual Column Dimensions and Design Strips
The column shape and dimensions can be changed at this stage. The column is
shown at the center of the plan view in Fig.118 with somewhat darker color. Since
a single column dimension is entered and since, in this problem, there are two types
of column sizes, the column dimensions should be revised. The dimension of the
second column should be adjusted to 350X350mm.
To change the dimensions of the second column, the existing column should be
deleted and another column with the right dimension should be drawn. So, carefully
select the second column. At the bottom left corner of the window, it should
display, ‘1 Areas, 4 Edges selected’. Otherwise, you should press the ‘Esc’ key
and select again. Once, the column is selected, delete it using the ‘Delete’ key.
To draw a new column of actual dimensions, go to the ‘Draw’ menu and click on
‘Quick Draw Slabs/Areas Around Points’ or simply click on the equivalent icon
from the left hand side toolbar. After the click, the following window will be
displayed.
Figure 131
In this window, the ‘Shape of Object’ should be ‘Rectangular Slab’ and set the
‘Property’ to ‘STIFF’ as we will be drawing a foundation column. The dimension
of the column are 0.35m in both x-direction and y-directions. Thus, set the ‘X
Dimension [m]’ and ‘Y Dimension [m]’ values to 0.35. With great care, move

the cursor to the center of the second column and when you see a small red cross,
make one left click and close the ‘Quick Draw Areas Around Points’ window.
Design strips determine the way in which different quantities related to the
reinforcement calculation are calculated. Forces are integrated across the design
strips. Thus, the larger the width of coverage of the design strips within the given
structure, the higher will be the calculated values of the bending moments and shear
forces. Thus, an optimum width of strip is required compromising the safety and
economical requirements. The width of the design strip will be specified in the
design code. According to the code of my country, the width of column strips for
combined foundations should extend up to a distance of 0.5 times the depth from
the face of the support in the direction of the line connecting the two columns (x-
direction). The area between the column strips in y-direction should be covered
with middle strips. In the transverse direction (x-direction), the whole length should
be covered with a column strip. These design strips in X and Y direction are usually
defined in SAFE software as layer A and layer B. Thus, the column strip at the first
column in y-direction will have the following dimensions when the strip is drawn
from bottom to top: ‘Start Width Left [m]’ = 0.15m, ‘Start Width Right [m]’ =
0.15+0.5/2=0.40m, ‘End Width Left [m]’ = 0.15m, ‘End Width Right [m]’ =
0.15+0.5/2=0.40m.
For combined footings, the existing design strips drawn by the program itself can
be used. You can display the design strips by setting the display options by clicking
on ‘Set Display Options…’ from the ‘View’ menu or by simultaneously clicking
on ‘Ctrl’ and ‘W’ keys or by just clicking on the set display options icon from
the tool bar below the menu bar. This results in the following window:

Figure 132
Objects’ box and check both ‘Design Strip Layer A’ and ‘Design Strip Layer B’
and press ‘OK’ and the following window appears displaying the design strips in
the two directions.
Figure 133

f. Assigning slab data to the footing
commands ‘Assign’>’Slab Data’>’Properties…’. Then select ‘FOOTING’ and
press ‘OK’.
g. Assigning slab data to the foundation column
Select the foundation column through the following strings of commands
‘Select’>’Select’>’Properties’>’Slab Properties…’. Then select ‘Stiff’ and press
‘OK’. Then assign the footing property through the following strings of commands
‘Assign’>’Slab Data’>’Properties…’. Then select ‘STIFF’ and press ‘OK’.
h. Assigning support data to the footing
and press ‘OK’.
i. Assigning reinforcement data to the design strips
strips.
j. Assigning load on the foundation column

The loads are already assigned on the foundation column. However the dimension
of the second column should be modified. To do this, right click at the center of
the second column. In the ‘Loads’ tab of the appearing window, click on ‘Assign
Loads’ button then select ‘Force Loads’ then press ‘OK’.
Figure 134
Then select ‘LIVE’, enter its value accordingly and in the right direction (axis), then
select ‘Replace to Existing Loads’ and press ‘OK’. While doing this, the
foundation column dimensions should be entered in the ‘Size of Load for
Punching Shear’ box of ‘Point Loads’ window. In this example, since the live
load is 1000kN for the second column, this should be entered in the Gravity
Direction and the values of ‘Load Size in X Dimension (mm)’ and ‘Load Size
in Y Dimension (mm)’ should both be set to 350.

Figure 135
the ‘Run’ menu and click on the ‘Run Analysis & Design’ command or simply
click on the ‘F5’ key. When you do this, you will be prompted to save the model, if
you haven’t already don this. When you save the model, the following window
showing the displacement of the soil in a banded figure will be displayed.
After the analysis is run the following output will be displayed on the plan view
window.

Figure 136
Figure 137
As can be noticed from the figure, the punching shear ratio is 1.5443 for the first
column and 0.9814 for the second column. Generally, a punching shear ratio less
than one indicates the concrete thickness is adequate to resist punching shear and
a value greater than one indicates that the punching shear capacity is exceeded
somewhere along the critical section. For economical design, it is recommended to
keep the punching shear ratio between 0.95 and 1 as very small values of punching
shear ratio means excess concrete thickness is used. However, if the punching shear
ratio is greater than one, the thickness of the concrete should be increased and the

foundation should be re-designed. In this problem, since the punching shear ratio
at column 1 is greater than one, the footing depth should be revised. However,
since this is just an illustration of how to design foundations with SAFE, we will
proceed as if the depth of the footing was adequate for punching shear. A detailed
Figure 138

Figure 139

Figure 140

Figure 141
Figure 142

As can be noticed from the footing design diagram in fig. 142, the top
reinforcement across strip layer A is 1834mm2
/m and 0mm2
/m for bottom
reinforcement at the location indicated by the vertical line.
pop up.
Figure 143
STEP 10: Detailing

Figure 144

Figure 145
STEP 11: Reporting

Figure 146
This concludes the tutorial for the design of single footing using the built-in model.

3.2. Using Grids
To create a footing model by using a grid, there are three ways. Go to ‘File’ menu
and click on ‘New Model …’ or just click on the icon . This icon is the first
among the list of icons just below the menu bar or simply click on the ‘Ctrl’ and
‘N’ keys simultaneously (Ctrl+N).
Design a trapezoidal combined footing shown in the figure below
• Ultimate bearing capacity of the soil : 100kPa
• Allowable settlement of the soil : 10mm
strength)

The click results in metric units for best practices to be selected. It can be observed
Figure 147

Figure 148

Figure 149
box and select the suitable model. Since an isolated (single) footing will be designed
from grids click on the big square button just above ‘Grid Only’. The button itself
shows crossing grids. When the button is clicked, the following ‘Coordinate
System Definition’ window, shown in fig. 150, will pop up.
The footing in this example is trapezoidal with two columns. The grids which will
be created will be boundaries of the outer edges of the footing and the outer edges
of the foundation column. As a result, there is uneven spacing between the grids
and there will be slanting grids. To create such slanting grids with uneven spacing,
it is better to create it by clicking the ‘Edit Grid’ button. When you click this button,
a ‘Coordinate System’ window will pop up. In the ‘Display Grid Data as’ box,
two radio buttons are there to choose between ‘Ordinate’ and ‘Spacing’. These
are the options how the location of different grids is defined. If the ‘Ordinate’
option is selected, the X and Y-coordinates of the grids will be entered. If the
‘Spacing’ option is selected, the spacing between the grids will be selected. If the
grids are irregular in shape with non-vertical and non-horizontal grids, they can be
defined in the ‘General Grid Data’ box by entering the XY coordinates of the
starting and ending points of the grids. Regular grids can also be defined by this
option too. For this particular example, we will use the ‘General Grid Data’ box.
To use this ‘General Grid Data’ box, first delete the existing coordinates from ‘X

Grid Data’ and ‘Y Grid Data’ by clicking on the left hand side arrow and pressing
the ‘Delete’ key.
Figure 150
In this example, the values which will be entered are shown in the coordinates of
the starting point (X1, Y1) and the coordinates of the ending point (X2, Y2) for all
the grid lines in the following table. Here, the bottom left corner of the footing will
be considered as the origin of the coordinate system.
Grid
ID.
X1 Y1 X2 Y2 Description
1 0 0 5 1 Bottom edge
2 0 1.55 5 1.55 Bottom grid for column1
3 0 2.15 5 2.15 Top grid for column1
4 0 3.7 5 2.7 Top edge
5 0 1.65 5 1.65 Bottom grid for column2
6 0 2.05 5 2.05 Top grid for column 2
A 0 0 0 3.7 Left edge
B 0.6 0 0.6 3.7 Right grid for column1
C 4.6 0 4.6 3.7 Left grid for column2
D 5 0 5 3.7 Right edge

Figure 151
The ‘Model Datum’ is the level of the model in z-direction. Any value can be set
to this. Set the ‘Story Height Above’ value to some reasonable non zero value, say
2, and set the ‘Story Height Below’ to 0 as there will be no story below the footing.
Then press ‘OK’ and the grids will be displayed on the ‘Plan View’ window as
below:

Figure 152
definitions.

Figure 153
For this particular problem, we will modify the existing ‘C30’ concrete using the
‘Modify/Show Material’ button and define a new rebar property through the
‘Add New Material’ button.
Highlight ‘C30’ in the ‘Materials’ box and click on the ‘Modify/Show Material’
button. This can also be achieved by right clicking on ‘Materials’ on the model
explorer. The following window will pop up.
footing. For this particular problem, let us keep the name of the concrete as ‘C30’.
.

Figure 154
/o
C for
The grade of concrete for this particular problem is C-30. C-30 is a concrete with

the analysis.
After modifying the concrete property, the program returns to the window shown
Figure 155

.
definition step.
Figure 156

Figure 157
to 10,000kN/m3
slab property.

Figure 158
will pop up.
Figure 159

Figure 160

defining the property of column. The ‘Thickness’ value should be equal to the
footing thickness which is 600mm. This value should be entered in the text field
corresponding to ‘Thickness’. As foundation columns are modelled as thick plates,
column with irregular dimension is to be used.

Figure 161
Figure 162
after the click.

Figure 163
window.

Figure 164
Figure 165

Figure 166

following window.
Figure 167

iv. Drawing the footing
rectangular, go to the ‘Draw’ menu and click on ‘Draw Slabs/Areas’ or
simply click on the equivalent icon on the left hand side tool bar. The
following window will appear on the screen after the click.
Figure 168
Making sure that the ‘Property’ is set to ‘FOOTING’, and the ‘Edge
Drawing Type’ to ‘Straight Line’, click on the grid where the four corners
of the footing will be located. Repeating the click at the first click point will
draw a trapezoidal foundation.
v. Drawing the foundation column
click on the grid where the four corners of the foundation columns will be
located. Repeating the click at the first click for both foundation columns
will draw the foundation columns with their respective sizes. Note that, the
first column is 0.6mX0.6m while the second column is 0.4mX0.4m.
vi. Drawing the point on the foundation column where the load will be applied
of the foundation columns and the points will be created. If the cursor could
not snap to the midpoint, you can adjust the ‘Snap Options’ from the
‘Draw’ menu.

Figure 169
shear forces, the ‘Strip Design Type’ should be set to ‘Column Strip’. Since the
whole footing area should be covered with design strip in x-direction, the width of
the strip in x-direction will be 3.7m at the start and 1.7m at the end. Since, the
footing is symmetrical about the centerline in x-direction, the ‘Start Width Left [m]’
and ‘Start Width Right [m]’ values will be 1.85 while the ‘End Width Left [m]’ and
‘End Width Right [m]’ values will be 0.85. To draw the design strip in the X
direction, without closing the window, left click at the center of left side of the
menu and adjusting the options which you want to snap to.
The design strip in Y direction can also be drawn in a similar procedure after
changing the ‘Strip Layer’ to ‘B’. The design strips in y direction extend for a

distance of half of the depth from the face of the support for each column. Thus,
the widths of the strips for each column 1 and column 2 are shown in Fig. 170(a)
and 170(b) respectively. When you make the click to draw the strips make sure that
you click at the bottom first and then at the top for both design strips.
(a) (b)
Figure 170
Middle strips should also be drawn between the column strips in y-direction
(transverse direction). To draw middle strips, change the ‘Strip Design Type’ in
the ‘Draw Design Strips’ window to ‘Middle Strip’ and enter the right values of
the widths of the middle strips to the right and to the left of the point from which
you will start drawing the strips. For this example, if we start drawing the middle
strip from x = 2.5m, the values of ‘Start Width Left [m]’, ‘Start Width Right
[m]’, ‘End Width Left [m]’ and ‘End Width Right [m]’ are 1.6,1.8,1.6 and 1.8
respectively. So, enter these values and draw the middle strip between the two
column strips.

Figure 171
Figure 172

d. Assigning support data to the footing
and press ‘OK’.
e. Assigning reinforcement data to the design strips
strips.
f. Assigning load on the foundation columns
To assign load on the foundation columns, right click on the point at the center of
each foundation column (one at a time) and a ‘Point Object Information’ window
pops up. In this window, click on the ‘Loads’ tab.

Figure 173
Existing Loads’ radio button option. In this example, the dead concentrated load
is 439kN and the live load is 125kN for the column1. For the second column, the
dead concentrated load is 380kN and the live concentrated load is 100kN for the
second column. These values are entered accordingly and the final values for the
second column are shown in Fig 173.

Figure 174
the ‘Run’ menu and click on ‘Run Analysis & Design’ command or simply click
on the ‘F5’ key. When you do this, you will be prompted to save the model, if you
haven’t already done this.
After running the analysis the following output diagram will be displayed on the
plan view window.

Figure 175
Figure 176
As can be noticed from the figure, the punching shear ratio is for the first column
is 1.0826 and for the second column is 1.1421. Generally, a punching shear ratio
less than one indicates the concrete thickness is adequate to resist punching shear

and a value greater than one indicates that the punching shear capacity is exceeded
somewhere along the critical section. For economical design, it is recommended to
keep the punching shear ratio between 0.95 and 1 as very small values of punching
shear ratio means excess concrete thickness is used. However, if the punching shear
ratio is greater than one, the thickness of the concrete should be increased and the
foundation should be re-designed. Since the objective of this tutorial is to show you
how to design foundations with SAFE, we will proceed with the design process as
if the depth was adequate for punching shear requirement. A detailed quantitative
description of the foundation design for each column can also be obtained by right
clicking on the plan view. The detailed description for the first column is shown in
Fig 177. Several trial may be made by zooming in and out to get the quantitative
description.
Figure 177

Figure 178

Figure 179

Figure 180

Figure 181
/m for bottom reinforcement and 1348mm2
/m
for top reinforcement.
pop up.

Figure 182
STEP 10: Detailing

Figure 183
detail of footing can be shown. In the detail, the foundation is displayed as a
rectangular footing, which is not in accordance with the actual geometry. Thus,
good judgment is required while utilizing the design results.

Figure 184
STEP 11: Reporting

Figure 185
This concludes the tutorial for the design of single footing using the grids.

3.3. From AutoCAD
STEP
1:
Creating the Model
foundation on AutoCAD. In this case, it will be a rectangle with dimensions of
5.6mX1.8m (footing) and three squares (foundation columns). When you draw the
plan view on AutoCAD, make sure that you are drawing it on a new layer. If you
want the origin of the SAFE mode to coincide with the center of the circular
foundation, make the center of the circle coincide with the global origin of the
AutoCAD file when you draw it. Then save the AutoCAD file in DXF format. To
save an AutoCAD file in DXF format, go to ‘File’ menu in the AutoCAD file and
click on ‘Save As’. At the bottom of the upcoming window, just below the text
field where you will enter the file name, you will see ‘Files of type’ with a drop-
down menu list. From the drop down menu list, select the option which has ‘(.dxf)’
at the end. Then enter the file name and save it at any location in your computer
where you can easily remember close it. This saves the file in DXF format.
Design the combined foundation shown below with the given parameters:
strength)
• All the given loads are factored (ultimate) loads.

Figure 186
Then, the following model appears in the plan view. As can be noted, the left
bottom corner of the footing coincides with the origin of the coordinate system.
To achieve this, make sure that that this corner coincides with the origin of the
Global coordinate system while drawing the plan view on the AutoCAD.

Figure 187
consistently.
.
Figure 188

Figure 189

definitions.
Figure 190
window will pop up.

.
Figure 191
/o
C for
The grade of concrete for this particular problem is C-20. C-20 is a concrete with

the analysis.
Figure 192
.

definition step.
Figure 193

Figure 194
to 10,000kN/m3
slab property.

Figure 195
will pop up.
Figure 196

Figure 197

defining the property of column. The ‘Thickness’ value should be thickness of the
footing which is 600mm. This value should be entered in the text field
corresponding to ‘Thickness’. As foundation columns are modelled as thick plates,
column with irregular dimension is to be used.
Figure 198

Figure 199
after the click.

Figure 200
window.

Figure 201
Definition of the load combinations will be the next step. Since the loads are
factored, only one load combination will be considered. To define load
combination, go to ‘Define’ menu and click on ‘Load Combinations…’ and the
Figure 202

The load combination which will be considered is factoring only the self-weight
which is considered as a dead load and the other factored loads will be considered
as live loads for convenience and the scaling factor for the live loads will be one.
When the ‘Add New Combo…’ button is clicked, the following window appears.
Figure 203
the case where there are only dead and live loads. For such load patterns, the partial

safety factor for live loads for ultimate limit sate case would have been 1.6. But, in
this case, since the loads are already factored and for convenience reason since the
factored loads are considered as live loads, a scaling factor of unity will be used.
Thus, enter a value of 1.3 in front of ‘DEAD’ and 1 in front of ‘LIVE’ in ‘Scale
Factor’ column. The failure condition which is being under consideration can be
defined by selecting and deselecting the check boxes in the ‘Design Selection’ box.
The serviceability limit state will not be considered for this case.
j. Drawing the footing
The footing will be drawn as a rectangular slab. Thus, go to the ‘Draw’ menu
and click on ‘Draw Rectangular Slabs/Areas…’ or click on the equivalent
icon from the left hand side tool bar and the following window will pop
up.
Figure 204
Make sure that the ‘Property’ is set to ‘FOOTING’ and click at one corner
of the footing. Then, without releasing the click, drag into the opposite
corner and release the click. This draws a rectangular footing.
iv. Drawing the foundation column
draw the three columns by following a similar procedure which you used
while drawing the footing.
v. Drawing the points on the foundation columns where the load will be applied
of each of the footing and the points will be created. If the cursor could not
snap to the midpoint, you can adjust the ‘Snap Options’ from the ‘Draw’
menu.

width of design strips for combined foundations in the longitudinal direction
should cover the whole area of the footing. In this particular problem, the width of
the strips in x-direction is 1.8m. The design strips in the transverse direction will be
defined for each column and should extend to a distance of half the depth of the
footing from the face of the column on each side. These design strips in X and Y
direction are usually defined in SAFE software as layer A and layer B.
Figure 205
The window in fug 205 is for the design strip in X direction. The ‘Draw Design
Strips’ windows for column1 and column3 in the transverse direction are shown
in fig. 206(a) and for column2 in the same direction is shown in fig. 206(b).
(a) (b)

Figure 206
shear forces, the ‘Strip Design Type’ should be set to ‘Column Strip’. While
drawing the design strips, if you can’t snap to the intended points on the footing,
you can modify the snap options by clicking on the ‘Snap Options…’ command
from the ‘Draw’ menu and adjusting the options which you want to snap to. Or
you can use other ways to draw the design strips. The design strip in Y direction
can also be drawn in a similar procedure after changing the ‘Strip Layer’ to ‘B’.
Figure 207

Figure 208
d. Assigning support data to the footing
and press ‘OK’.
e. Assigning reinforcement data to the design strips
strips.
f. Assigning load on the foundation column

Figure 209
Existing Loads’ radio button option. In this example, since the factored
concentrated load is 100kN and since the bending moment about y-axis is 10kNm,
these values are entered in the Gravity Direction for the concentrated load and

along y-axis for the bending moment and the final values are shown in the above
figure.
Figure 210

Figure 211
Figure 212
column, 0.1564 for the second column and 0.0537 for the third column. Generally,
a punching shear ratio less than one indicates the concrete thickness is adequate to
However, if the punching shear ratio is greater than one, like in this example, the

thickness of the concrete should be increased or the grade of the concrete should
be increased and the foundation should be re-designed. A detailed quantitative
description of the foundation design can also be obtained by right clicking any of
the columns shown in Fig 213 as shown below. Several trial may be made by
zooming in and out to get the quantitative description.
Figure 213

Figure 214

Figure 215

Figure 216
Figure 217
/m for top reinforcement and 1008smm2
/m
for bottom reinforcement.

pop up.
Figure 218
STEP 10: Detailing

Figure 219

Figure 220
STEP 11: Reporting

Figure 221

4. Mat Foundation
In this part of the tutorial, a mat foundation will be designed by using an imported
model from AutoCAD. This is an advantageous procedure because geometrical
asymmetries, different sizes of columns and different loadings can be
accommodated by drawing a single AutoCAD drawing. Designing mat foundations
from the built-in model is beneficial when the column dimensions and loadings are
identical which may not often be the case. Thus, this procedure of designing
foundations will not be considered in this tutorial. Of course, there is a possibility
for modification of the inbuilt model once it is created. And creating mat
foundation models by using grids may involve creating several grid lines especially
when the geometry is asymmetrical and column dimensions are not identical. Thus,
this way of creation of models will not be discussed. However, if these ways of
creating the model are mandatory, the procedure of creating is no different from
that of combined foundations which are discussed earlier.
Design the mat foundation shown below with the given parameters:
• Grade of reinforcement bar (rebar): S-400 (400MPa characteristics yield strength)
• All the given loads are factored (ultimate) loads.

foundation on AutoCAD. In this case, a rectangle with dimension of 10mX20m
and a number of squares representing the foundation columns. When you draw the
plan view on AutoCAD, make sure that you are drawing it on a new layer. If you
want the origin of the SAFE mode to coincide with the center of the circular
foundation, make the center of the circle coincide with the global origin of the
AutoCAD file when you draw it. Then save the AutoCAD file in DXF format. To
save an AutoCAD file in DXF format, go to ‘File’ menu in the AutoCAD file and
click on ‘Save As’. At the bottom of the upcoming window, just below the text
field where you will enter the file name, you will see ‘Files of type’ with a drop-
down menu list. From the drop down menu list, select the option which has ‘(.dxf)’
at the end. Then enter the file name and save it at any location in your computer
where you can easily remember close it. This saves the file in DXF format.

Figure 222
Then, the following model appears in the plan view.
Figure 223

consistently.
Figure 224

Figure 225

definitions.
Figure 226
window will pop up.

.
Figure 227
/o
C for

the analysis.
in Fig. 226 To define a rebar property, we will follow the same procedure as we
Figure 228
.

definition step.
Figure 229

Figure 230
to 10,000kN/m3
slab property.

Figure 231
will pop up.
Figure 232
name which will be used is ‘Mat’. The ‘Slab Material’ should be set to the concrete
grade which is defined in step 2. Since the name of the concrete material defined in
step 2 for this particular problem is ‘C25’, a material with this name should be
selected from the list.

In the ‘Analysis Property Data’ box, ‘Type’ should be set to ‘Mat’. The
Figure 233
defining the property of column. The ‘Thickness’ value should equal to the
thickness of the mat. As foundation columns are modelled as thick plates, check

the ‘Thick Plate’ option. The ‘Orthotropic’ check box is selected when a column
with irregular dimension is to be used.
Figure 234

Figure 235
after the click.

Figure 236
window.

Figure 237
Definition of the load combinations will be the next step. Since the loads are
factored, only one load combination will be considered. To define load
combination, go to ‘Define’ menu and click on ‘Load Combinations…’ and the
Figure 238

The load combination which will be considered is factoring only the self-weight
which is considered as a dead load and the other factored loads will be considered
as live loads for convenience and the scaling factor for the live loads will be one.
When the ‘Add New Combo…’ button is clicked, the following window appears.
Figure 239
the case where there are only dead and live loads. For such load patterns, the partial

safety factor for live loads for ultimate limit sate case would have been 1.6. But, in
this case, since the loads are already factored and for convenience reason since the
factored loads are considered as live loads, a scaling factor of unity will be used.
Thus, enter a value of 1.3 in front of ‘DEAD’ and 1 in front of ‘LIVE’ in ‘Scale
Factor’ column. The failure condition which is being under consideration can be
defined by selecting and deselecting the check boxes in the ‘Design Selection’ box.
The serviceability limit state will not be considered for this case.
k. Drawing the mat
The footing will be drawn as a rectangular slab. Thus, go to the ‘Draw’ menu
and click on ‘Draw Rectangular Slabs/Areas…’ or click on the equivalent
icon from the left hand side tool bar and the following window will pop
up.
Figure 240
Make sure that the ‘Property’ is set to ‘Mat’ and click at one corner of the
footing. Then, without releasing the click, drag into the opposite corner and
release the click. This draws a rectangular footing.
vi. Drawing the foundation column
draw the three columns by following a similar procedure which you used
while drawing the footing.
vii. Drawing the points on the foundation columns where the load will be applied
of each of the footing and the pointss will be created. If the cursor could not
snap to the midpoint, you can adjust the ‘Snap Options’ from the ‘Draw’
menu.

width of design strips for combined foundations in the longitudinal direction
should cover the whole area of the footing. In this particular problem, the width of
the strips in x-direction is 1.8m. The design strips in the transverse direction will be
defined for each column and should extend to a distance of half the depth of the
footing from the face of the column on each side. These design strips in X and Y
direction are usually defined in SAFE software as layer A and layer B.
following window pops up. Column strips of width 2m around each column will
be drawn in both directions. The remaining spaces between the columns strips will
be filled with middle strips.
Figure 241
The window in fug 241 is for the column strip in Y direction. The column strip in
X direction can be drawn by just changing the ‘Strip Layer’ to ‘B’. The ‘Draw
Design Strips’ windows for middle strips in X and Y directions are shown in fig.
242(a) and fig. 2242(b) respectively.

(b) (b)
Figure 242
Figure 243

Figure 244
g. Assigning support data to the footing
and press ‘OK’.
h. Assigning reinforcement data to the design strips

this window, set the ‘Rebar Material’ to ‘S400’ and press ‘OK’. Do this for all
strips.
i. Assigning load on the foundation column
Figure 245

Existing Loads’ radio button option. In this example, for column 1, since the
factored concentrated load is 500kN and since the bending moments about x-axis
and y-axis respectively are 70kNm and 100kNm, these values are entered in the
Gravity Direction for the concentrated load and along the respective axes for the
bending moment and the final values are shown in the above figure. The loading
for the rest columns will be entered in a similar way.
Figure 246
Do this for all column foundations, and all design strips as well. After this, go to

Figure 247
Figure 248

column, ‘N/C’ for the second, fifth and eighth columns. This usually happens
when the column dimension is not entered when the loads are assigned or when
the mat thickness is inappropriate. In this example, all the column dimensions are
entered correctly and the reason for the appearance of ‘N/C’ on some of the
columns is due to inappropriate mat thickness. For the rest columns, the punching
shear ratio is well below unity. Generally, a punching shear ratio less than one
indicates the concrete thickness is adequate to resist punching shear and a value
greater than one indicates that the punching shear capacity is exceeded somewhere
along the critical section. For economical design, it is recommended to keep the
punching shear ratio between 0.95 and 1 as very small values of punching shear
ratio means excess concrete thickness is used.
Thus, to get an acceptable punching shear ratio, change the thickness of the slab to
600mm. To do this, first unlock the model by pressing button from the list of
buttons below the menu bar. Then, go to the ‘Define’ menu and click on ‘Slab
Properties’. After this, highlight ‘Mat’ and ‘STIFF’ one at a time and click on
‘Show/Modify Properties’ button and change the value for ‘Thickness’ to ‘600’.
After this, if you click on ‘Run’ > ‘Run Analysis & Design’, the following window
will appear.
Figure 249

If you click on ‘Display’ > ‘Show Punching Shear Design’, the following will be
displayed on the screen.
Figure 250.
It can be seen from the above punching shear design diagram that all the punching
shear ratios are acceptable.

Figure 251
not to display the values on the diagram. For the preferences shown in Fig. 251,
the following diagram will be displayed.

Figure 252

Figure 253
Figure 254

pop up.
Figure 255
STEP 10: Detailing

Figure 256

displayed. For instance, by double clicking on the ‘Rebar Plan’, the following detail
of footing can be shown.
Figure 257
STEP 11: Reporting

Figure 258

Tutorial for design of foundations using safe

More Related Content

What's hot (20)

Similar to Tutorial for design of foundations using safe (20)

Recently uploaded (20)

Tutorial for design of foundations using safe