Design and analysis of RC structures with flat slab

Outline
Introduction
Load & combinations
Steps in a project
Drawings
Materials Used
Conclusion
Analysis & design

3
Introduction
In the Project work, we were assigned a job of reading
important code books used
• IS 456-2000 “Indian Standard code of practice for plain and reinforced
Cement
• IS: 875 (Part 1 DEAD LOADS) 1987 “Indian Standard Code of Practice for
Design Loads (other than Earthquake) for buildings and structures.
• IS: 875 (Part 2 LIVE LOADS) 1987 “Indian Standard Code of Practice for
Design Loads (other than Earthquake) for buildings and structures”
• IS: 875 (Part 3 WIND LOADS) 1987 “Indian Standard Code of Practice for
Design Loads (other than Earthquake) for buildings and structures”
• IS 1893:2002 – Part I, “Criteria for Earthquake Resistant Design of
structures”

4
Introduction
 About the Software :

 About the Project:
• NET MAGIC FOR IT, ITIES & ELECTRONIC DATA
CENTRE
• SBC of Soil = 300 kN/sq.m
• Architectural drawings provided
• Designed as per IS 456-2000*
• Loads are worked out as per IS 875-1987.
• Analysis is done using the STADD.Pro software.
• Design aids of SP-16 are considered.
Tuesday, June 15, 2021 5
Introduction

Details of the “NET MAGIC”:
 Name of the Project : NET Magic
 Location of the project : Plot No-88/A, Electronic
City, 1st Phase, Bangalore.
 Total plot Area : 5052.2 sq. m
 Ground floor built up area : 3003.0sq.m
 First built up area : 3003.0sq.m
 Second floor built up area : 3003.0sq.m
 Total Build up Area : 9009.0sq.m
6
Introduction

4.ANALYSIS OF STRUCTURE
1.PLANNING
STEPS involved in a Project
2.IDEALISATION OF STRUCTURE
3.LOAD CALCULATION
8.SUPERVISION OF THE WORK
5.DESIGNING OF STRUCTURE
6.DETALING
7.EXECUTION

DEAD LOAD
LOADS
LIVE LOAD
SESMIC LOAD
IS: 875 (Part 2 LIVE LOADS) 1987
IS: 875 (Part 1 DEAD LOADS) 1987
IS 1893:2002 – Part I

DEAD LOAD:
The densities of different materials considered for design
are as follows:-
• Density of reinforced concrete = 25 kN/ cu.m
• Density of soil = 20 kN/ cu.m
• Density of steel = 78.5 kN/ cu.m
• Density of plain concrete = 24 kN/ cu.m
• Density of finishes(plastering) = 20 kN/ cu.m
• Density of Granite = 26 kN/ cu.m
• Density of Solid blocks = 18 kN/ cu.m
• Density of Cinder for filling = 08 kN/ cu.m
• Density of Brickbat filling = 20 kN/ cu.m
• Partition wall load on slab = 1.0 kN/sq.m
• False Ceiling = 0.5 kN/sq.m

Tuesday, June 15, 2021
DEAD LOAD:
DL on intermediate floors:
• DL of slab (thickness 0.275 M) = 0.275 x 25 = 6.875 kN/sq.m

DEAD LOAD:
Floor finishes (DL):
• Floor finishes(general) = 1.80 kN/sq.m
• Partition load = 1.00 kN/sq.m
Total Load = 3.30 kN/ sq.m
DL on terrace floor:
• Floor finishes = 1.00 kN/sq.m
• Water Proofing = 2.00 kN/sq.m
Total load = 3.50 kN/sq.m
DL on Sunken Slab:
• Filled with brick batten of
• 8 kN/m3 of .2m depth = 1.60 kN/sq.m

DEAD LOAD:
DL on Sunken Slab(utility):
• False Ceiling = 0.50 kN/ sq.m
• Partition load = 1.00 kN/sq.m
• Filled with brickbat of
• 8 kN/m3 of .2m depth = 1.60 kN/sq.m
DL on corridors:
DL on roof of lift and stairs:

DEAD LOADS :
WALL LOADS:
• DL of wall (clear ht. 4.2m) = 4.2x.2x20 = 16.8 kN/m
• DL of Double wall
• (thickness .25m) = 4.2x.25x20 = 21.0 kN/m
• DL of Double wall
• (thickness .325m) = 4.2x.325x20 = 27.3 kN/m
• DL of Double wall (@ plinth) = 4.2x.230x20 = 19.32 kN/m
• DL of wall (@ plinth) = 4.2x0.1x20 = 08.40 kN/m
• DL of parapet wall(on terrace)= 1.2x.15x20 = 03.60 kN/m
(* density includes plastering of wall)

LIVE LOADS :
• Commercial Office Floors = 4.0 kN/ sq.m
• Stack Area = 12.0 kN/ sq.m
• Toilets/Utility = 2.0 kN/ sq.m
• Staircase, Corridors, Balconies = 5.0 kN/ sq.m
• Terrace Floors(Access provided) = 1.5 kN/ sq.m
• Lift Machine slab = 10.0 kN/ sq.m
• Fire tender movement = 15.0 kN/ sq.m
• AHU = 10.0 kN/ sq.m
• Service corridors = 6.25 kN/ sq.m
• UPS, battery rooms = 10.0 kN/ sq.m
• Staging rooms = 10.0 kN/ sq.m
• Precision AC = 8.0 kN/ sq.m
• Chiller platform = 10.0 kN/ sq.m
• FSS, MM and Wan Rooms = 5.0 kN/ sq.m

SESMIC LOADS :
According to IS 1893 (Part 1): 2002
• Zone factor, Z = 0.1
• Response reduction factor, RF = 3.0
• Importance factor, I = 1.0
• Rock and soil site factor, SS = 2.0
• Damping ratio, DM = 0.05 (5%)
• Period in X direction, Px = 0.622 s
• Period in Z direction, Pz = 0.622 s

LOAD COMBINATIONS :
• DL + LL
• 1.5(DL + LL)
• 1.2(DL + LL + EQX)
• 1.2(DL + LL – EQX)
• 1.2(DL + LL + EQZ)
• 1.2(DL + LL – EQZ)
• 1.5(DL + EQX)
• 1.5(DL – EQX)
• 1.5(DL + EQZ)
• 1.5(DL – EQZ)
• 0.9DL + 1.5 EQX
• 0.9DL - 1.5 EQX
• 0.9DL + 1.5 EQZ
• 0.9DL - 1.5 EQZ
o DL = Dead Load
o LL = Live Load
o EQX = Seismic Load in X direction
o EQZ = Seismic Load in Z direction

MATERIALS USED:
Concrete Item Grade Max size of
aggregate (mm)
Type of Cement
Footings M25 20 OPC
Columns, Core walls &
Shear walls
M40 20 OPC
Slab & beams M35 20 OPC
Retaining Walls M30 20 OPC
Plinth Beams M25 20 OPC
Water Retaining structure M30 20 OPC
Grade of Steel : Fe500
Grade of Concrete:

DRAWINGS :
ARCHITECTURAL DRAWING:
 Ground Floor Plan
 First Floor Plan
 Second Floor Plan
STRUCTURAL DRAWING:
 Arrangements in Ground floor(Plinth)
STAAD MODEL:
 Column and beam model
 Layout of flat slabs, beams and columns
 STAAD Model for G+2 Building

SITE PLAN

Designs:
Column Design
Staircase
Continuous Beam
Isolated Footing
Flat Slab
Combined Footing

FOOTING Design:
Foundation should be designed:
• To transmit the load of the structure safely onto a sufficient
area of the soil so that stresses induced in the soil are within
safe limits.
• To ensure uniform settlements i.e., the intensity of soil
reaction should be the same under all the footings of a
structure.
• The foundation area should be designed such that the center
of gravity of loads in plan coincides with the center of gravity
of the foundation area.

Design of Isolated Footing:
Axial load P = 3810 KN
Moment MX = -11 KN-m
Moment MY = 5 KN-m
Size of Column = 750 x 750 m
Size of the footing: (3810 X 1.1)/300
Assuming a Square footing of side 4 m, Then area of the
footing=16 Sq.m > Areq.
Bearing Pressure = (P/A) ± (Mx/Zx) ± (My/Zy)
MAX = 200.25 KN/Sq.m
MIN = 197.25 KN/Sq.m
Both less than SBC, So safe.
Design Forces:
PU = 4770 KN
Mxx = 11 kN-m
Myy = 5 KN-m
Therefore Pe max = 300.375 KN/Sq.m

Design of Isolated Footing:
CAL of Depth:
BM consideration:
Mu= (Wl2)/2 = 793 KN-m
Depth Required = Mu/bd2 = 0.138 fck
Therefore d = 479 mm = 500 mm (say)
2 Way shear check:
Total downward stresses = permissible stresses X area of
resistance
From above, on solving we get d = 700.7 mm
REINFORCEMENT:
Mu / bd2 = 1.573
Pt= 0.482
One Way Shear:
Vu = Pu X b X d = 85.60 KN
τc = Vu/(b X d) = 0.063 < .015
Therefore Pt = .482
Ast = 3423 mm2
So providing 22 mm dia bars @ 100 mm center to center both
the ways.

COMBINED FOOTING (6 footings):

Place
Req. Ast
Top column strip Top MS Middle CS Bottom MS Bottom CS
Left end
Column Strip
N N N N N
Middle Strip 830 N 860 N 809
Right end
Column Strip
N N N N N
X Direction reinforcements (TOP):
X Direction reinforcements (Bottom):
Place
Req. Ast
Left end
Column Strip
N N N N N
Middle Strip N N N N N
Right end
Column Strip
N N 820 N 2043

Y Direction reinforcements (TOP):
Place
Req. Ast
Left end
Column Strip
N 1536 N N N
Middle Strip N 1424 840 N N
Right end
Column Strip
N 1393 N N N
Y Direction reinforcements (Bottom):
Place
Req. Ast
Left end
Column Strip
N N N N 1630
Middle Strip N N N N 1266
Right end
Column Strip
N N N 834 2729

Nominal Reinforcements=0.12X1000X650=78000sq.mm=780
sq.cm
Reinforcement in X direction
Top: Providing 12 T @125 c/c overall length.
Bottom: Providing 12 T @125 c/c From top to bottom column strip
and later on 16T@100c/c
Reinforcement in Y direction
Top: Providing 12 T @125 c/c overall length with 16T 125 c/c in
top and bottom strips as in dwg.
Bottom: Providing 10 T @100 c/c From Left to Right and 20 T @100
c/c in bottom column strip with sufficient lap length.

Column Design:
Consider column no C-29 for design:
Column size = 750 x 750 mm
Column No as in Staad.pro = 49146
Characteristic strength of concrete, fck = 40 N/mm2
Characteristic strength of Steel, f y = 415 N/mm2
Height of the floor = 4200 mm.
Depth of the column about X-axis = 750 mm
Depth of the column about Z-axis = 750 mm
Factored load PU = 1217 KN
Factored moment, MUX = 163 KN-m
Factored moment, MUY = 12 KN-m

Column Design:
COLUMN REINFORCEMENT DETAILS
Percentage of Steel required (Pt) = 0.8 %
Ast Reqd. = 0.8 x 750 x 750 / 100 = 4500 mm2
Steel Provided 16 TOR 32mm
Ast provided = 16 x (π x 320 x 20 / 4) = 5026.5 mm2
Percentage of Steel Provided (Pt) = 0.893 %
Providing 8T @ 300 c/c lateral ties

Continuous Beam Design:
Considering a continuous beam:
Span of the beam = 32.24 m
Size of Beam = 200 x 1200 mm
Characteristic strength of concrete, fck = 35 N/mm2
Characteristic strength of Steel, fy = 415 N/mm2
BEAM

Continuous Beam Design
Mu (@ Support) = 205.71 KN-m
Mu (@ Middle) = 102.86 KN-m
Vu = 153.14 KN
Ast1 (@Top) = 497.38 mm2.
Ast2 (@Bottom) = 245.5 mm2.
But, Ast min is .2% of cross section, i.e., 480 mm2
So, provide 4-20T (throughout the length)
Providing 2LVS, #10 @300mm c/c.

Staircase Design
Total load is 14.9 KN/m
Moment Mu = 59 KN-m
Mu limit = 0.138 x fck x b x d = 148 KN-m > Mu So Safe…!
Ast = 1001.77 sq.mm
Therefore provide 16mm T @ 200 c/c
Distribution steel of min .12% is provided as 8 T @ 200 c/c
A detailed drawing is shown in the following figure.

Staircase Design:
ROW OF CHAIRS
500 mm
500 mm
GL
Wall
FOUNDATION
GROUND FLIGHT
MAIN STEEL
# 16 @ 200
DIST. STEEL
# 8 @ 200
150
Ld =564
REINFORCEMENT
FROM BM
FLOOR LEVEL
LANDING FIRST FLIGHT
R=165
T= 275
LAP L

Flat Slab Design:
A flat slab is a reinforced concrete slab supported directly over
columns without beams generally used when head room is limited
such as in cellars and warehouses.
The different types of flat slabs are
• Slab without drop and column head
• Slab with drop and without column head
• Slab with drop and column head.
Here in this case the design is done using the second type of flat slab
that is Slab with drop and without column head.

Flat Slab Design:
Design Process:
Data available:
Live load = 12 KN/sq.m
Dead loads:
Floor finishes = 1.8 KN/sq.m
Partitioning = 1.0 KN/sq.m
False ceiling = 0.5 KN/sq.m
Grade of steel = Fe 500
Grade of concrete = M35
Column size = .75 x .75 m
Length of column strip = 4.014 m
Length of middle strip = 4.014 m
Length b/w face to face of column in y axis = 7.278 m
C/c distance of columns in y axis = 8.028 m

Flat Slab Design:
Proportioning:
Slab depth: L/d = (36 to 40)
So, L/d = 40 = d 200.7mm
Adopt a depth of 355 mm with a cover of 20 mm.
so total depth D = 375mm.
Drop > 230/4 = 57.5 mm
Or ≥ 100 mm, so let depth at drop as 375mm
Length and width of drop = equal to the size of column strip = 4.014 m
Loads:
LL =12 KN/sq.m FF= 1.8 KN/sq.m FC= 0.5 KN/sq.m
Partitioning = 1 KN/sq.m
Self-weight = 0.375 X 25 = 9.375 KN/sq.m
Total load = 24.675 KN/sq.m
Ultimate load = Total X 1.5 = 37.0125 KN/sq.m

Flat Slab Design:
Column strip Middle strip
Negative 961 320
Positive 413.5 275.5
Moments:
Max Mo = (Wu x L2 x Ln
2)/8 = 1970 KN-m
Distribution:
-Ve BM = 0.65 x 1970 = 1280.5 KN-m
+Ve BM = 0.35 x 1970 = 689.5 KN-m

Flat Slab Design:
Column strip Middle Strip
Neg. BM Pos. BM Neg. BM Pos. BM
Moment 961 413.5 320 275.5
Breadth(b) 4014 4014 4014 4014
Depth(d) 355 230 230 230
Mu/bd2 1.954 1.947 1.507 1.297
Ast 8172.27 5349.46 4067.96 3474.31
Pt 0.582 0.579 0.441 0.376
Spacing 246.13 376.01 494.46 578.94
PROVIDE
16 T @ 250
C/C
16 T @ 380
C/C
16 T @ 510
C/C
16 T @ 580
C/C

References:
 Nilson, David Darwin, Charies W. Dolan, “Design of Concrete
Structures” Tata McGraw - Hill, Publishing Company Limited,
New Delhi
 S N Sinha, “Handbook of Reinforced Concrete Design” Tata
McGraw-Hill, Publishing Company Limited, New Delhi
 IS 1893:2002 – Part I, “Criteria for Earthquake Resistant
Design of structures”, Bureau of Indian Standards, New Delhi
 IS 456-2000 “Indian Standard code of practice for plain and reinforced
Cement ”, Bureau of Indian Standards, New Delhi

References:
 IS: 875 (Part 1 DEAD LOADS) 1987 “Indian Standard Code
of Practice for Design Loads (other than Earthquake)
for buildings and structures”, Bureau of Indian Standards,
New Delhi.
 IS: 875 (Part 2 LIVE LOADS) 1987 “Indian Standard Code
of Practice for Design Loads (other than Earthquake)
for buildings and structures”, Bureau of Indian Standards,
New Delhi.
 SP: 16-1980 “Design aids for Reinforced Concrete to IS:
456-1978”, Bureau of Indian Standards, New Delhi

Design and analysis of RC structures with flat slab

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