Parametric Study on Diagrid Structural System with and without Shear Walls

International Journal of Civil, Mechanical and Energy Science, 7(3)
May-Jun, 2021
Available: https://aipublications.com/ijcmes/
Peer-Reviewed Journal
ISSN: 2456-2319
https://dx.doi.org/10.22161/ijcmes.73.1 1
Parametric Study on Diagrid Structural System with and
without Shear Walls
Anshuman R. Prajapati1
, Ashwin G. Hansora2
1
P.G. Student, Applied Mechanics Department, L. D. College of Engineering, Ahmedabad, Gujarat, India.
2
Assistant Professor,
Applied Mechanics Department, L. D. College of Engineering, Ahmedabad, Gujarat, India.
Received: 05 Mat 2021; Received in revised form: 20 Apr2021; Accepted: 09 May 2021; Available online: 25 May 2021
©2021 The Author(s). Published by Infogain Publication. This is an open access article under the CC BY license
(https://creativecommons.org/licenses/by/4.0/)
Abstract— Among the various lateral load resisting systems of the tall structures, diagrid structural system
is a unique structural system and found effective compared to other bracing systems, which is increasingly
popular from the past decades. The diagrids are perimeter structural configurations characterized by a
grid of diagonal members which are involved both in gravity and in lateral load resistance. The diagrid
structure ensures the overall stiffness and strength of the building only engaging the diagonal members in
a purely axial behaviour and fully braces the interior gravity columns for stability only at joints of diagrid.
The intermediate floors, are not laterally restrained by the global behaviour of the diagrid system, means if
diagonals are continuous throughout the module height, the floors would derive a certain degree of lateral
stiffness only from the flexural stiffness of the diagrids. Although diagrid system is good enough to perform
well in lateral load resisting compare to other simple frame and shear wall building, we can combined the
diagrid structure with shear walls for optimum design. The present study aimed to understand the
behaviour of the diagrid structural system with shear walls at core. For this study a regular square plan of
30m × 30m diagrid structure considering different storey module (i.e. 4, 6, 8 & 12) with and without core
Shear Walls is modelled and analyzed. For minimum displacement and drift different plan shape of shear
wall are taken and one of them with optimum results is used for further analysis. Then behaviour of diagrid
structure with and without shear wall along the height is also studied considering 24, 36 and 48 storey.
ETABS software is used for modelling and analysis. Parameters such as inter storey drift-ratio, storey
displacement, base shear and reduction in lateral load on diagrid are taken into consideration.
Keywords— Diagrid structure, Inter storey drift ratio, Shear wall, Storey module, Storey displacement,
Tall building.
I. INTRODUCTION
The lateral loading due to wind and earthquake is
governing factor that causes the design of high-rise
buildings. These lateral loads are resisted structural by
different structural system provided. The lateral load
resisting systems that are used mainly shear wall, wall-
frame, braced tube system, outrigger system, diagrid
system and tubular system.
Diagrid is an exterior structural system in which all
perimeter vertical columns are removed and replaced by
inclined columns on which is called diagrids. Shear and
over-turning moment developed due to lateral loads are
resisted by axial action of these diagonals. As most diagrid
structures have core as partial lateral stability. The diagrid
structure is an extension of the tube-in-tube structure,
where the outer tube is comprised of diagrids. There is bit
confusion between the conventional exterior braced frame
structure and diagrid structure but the major difference
between them is that in a diagrid structure, peripheral
columns are eliminated. This is because in diagrid
structures, diagrids are also takes the gravity load in
addition to the lateral load by triangulated configuration,
while the conventional bracing system could not take any
gravity load.[14]
Structural systems of tall buildings can be divided into two
broad categories: core structures and exterior/peripheral
structures, which is based on the distribution of the
components of the primary lateral load-resisting system
over the building. A system is categorized as an core
structure when the major part of the lateral load resisting
system is located at core of the structure. Similarly, if the

Anshuman R. Prajapati et al. Parametric Study on Diagrid Structural System with and without Shear Walls
ISSN: 2456-2319
major part of the lateral load-resisting system is located at
the perimeter of structure, a system is called as an exterior
structure.[11]
The major types of lateral load-resisting systems in
category of core structures are the moment-resisting
frames and shear walls. These systems are usually
arranged as planar assemblies in two principal orthogonal
directions and may be used as a combined system. The
building perimeters has more structural significance in tall
buildings due to their very tallness, which means greater
vulnerability to lateral forces, especially wind loads.
Therefore, it is quite desirable to concentrate as much
lateral load-resisting system components as possible on the
perimeter of tall buildings to increase their structural
depth, and, in turn, their resistance to lateral loads.[11]
The design of the modules comes first among the items to
be decided while planning the diagrid structure. The
criteria for design of the modules are the suitability of the
gap angle, topographic conditions, strength, height of the
structure, loads, etc. How many floors there will be
between node numbers of each modules, the angle and
dimensions of the structural tubes vary as per requirements
of design.[12]
1.1 Drawbacks (Local issue) of Diagrid Structural
System
The structural behaviour of systems with mega-diagonals
could be assimilated to a vertical truss with panel points
(diagrid nodes) located multiple floors apart in
Fig.1.1(a)[7] is sketched a typical diagrid system. The
diagrid structure ensures the global stiffness and strength
of the overall building by considering diagonal members
as truss member in design(purely axial behaviour) and
braces the interior gravity columns for stability only at
panel points. The intermediate floors in Fig. 1.1(a)[7], are
not laterally restrained by the global behaviour of the
diagrid system; in other words, if diagonals are continuous
throughout the module height, the floors would derive a
certain degree of lateral stiffness only from the flexural
stiffness of the diagonals Fig. 1.1(b).[7]
Fig. 1: (a) Typical diagrid system (b) Mega-diagonal
elements between panel points.[7]
Within given the module height, the diagrid members
provide a partial lateral restraint with the help of their
flexural stiffness. This partial restraining could be or not
sufficient to brace the internal columns, activating a single
floor buckling mode, and to limit inter storey drifts.[7]
Fig. 2: (a) Lateral deformation of diagrid module (b) The
diagrid diagonals under horizontal forces.[7]
(a)
(b)
(a)
(b)

ISSN: 2456-2319
II. METHODLOGY
First step is to find optimum plan shape/placement of shear
wall at core, for which parameters such as displacement
and inter- drift ratio is taken into consideration. For this
RC bare frame structure with four different placement/plan
shape shear walls at core is taken and analysis is carried
out and lateral loads (Seismic and Wind) are considered.
After analysis, one case with optimum/minimum
displacement and inter- drift ratio will taken into
consideration for further analysis for diagrid structure with
and without shear walls.
In second part of work diagrid structure with four different
module (i.e. 4, 6, 8, 12 module ; Angle of diagrid θ=
67.38°, 74.47°, 78.23°, 82.09° respectively) taken into
consideration with and without shear walls at core of
structure. Each case is also analyzed with three different
height (i.e. 24 , 36 and 48 ).
Square RC framed structure with steel pipe section
diagrids at periphery is considered for modeling. Lateral
loads are seismic and winds are taken into consideration as
per Indian Standard codes IS 1893 (Part 1) : 2016 and IS
875 (Part 3) : 2015 respectively.
2.1 Placement/Plan-Shape of Shear Wall At Core
Fig. 3: Shear Walls at core (a) Case 1 (b) Case 2 (c)
Case 3 (d) Case 4
2.2 Diagrid Structure with and Without Shear Walls
Fig.4 : Plan of Building (a) without shear wall (b) with
shear wall
Fig.5: 4, 6, 8 and 12 storey diagrid Module
Fig. 6: 4 Module : 24, 36, 48 Storey
III. GEOMETRIC DATA
Table 1: Model Details
PLAN 30m × 30m
HEIGHT 3.6m
MEMBER
SIZE
BEAM 300mm X 500mm
SLAB 120mm

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SHEAR
WALL
250mm
MATERIAL
TYPE
CONCRETE
BEAM-M30
COLUMN-M40
SLAB-M30
SHEAR WALL-
M30
STEEL
REBAR-HYSD 500
DIAGRID-Fe345
LOAD
DEAD(FF) 1.0 KN/m2
LIVE 3.0 KN /m2
MATERIAL
DENSITY
CONCRETE 25kN/m3
STEEL 78.5kN/m3
SOIL TYPE MEDIUM OR STIFF SOILS
RESPONSE
REDUCTION
FACTOR (R)
5
IMPORTANCE
FACTOR (I)
1.2
ZONE III
BASIC WIND
SPEED
39 m/s
TERRAIN
CATEGORY
III
Table 2 : Column section details for 24, 36, 48 storey
height
STOREY SECTION SIZE
24 950mm X 950mm
36 1150mm X 1150mm
48 1350mm X 1350mm
Table 3 :Diagrid (Diagonal) pipe section details
STOREY MODULE
SECTION SIZE
(OUTER DIAMETER-
THICKNESS)
24
4 350 mm - 15mm
6 400 mm - 20mm
8 450 mm - 25mm
12 550 mm - 30mm
36 4 350 mm - 25mm
6 420 mm - 25mm
8 500 mm - 25mm
12 620 mm - 30mm
48
4 370 mm - 30mm
6 450 mm - 30mm
8 550 mm - 40mm
12 650 mm - 40mm
Table 4 : Nomenclature for cases considered
STOREY/
MODULE
4 6 8 12
24 A1 A2 A3 A4
36 B1 B2 B3 B4
48 C1 C2 C3 C4
IV. RESULT AND DISCUSSION
4.1 Placement/Plan-Shape Of Shear Wall At Core
Fig. 7: Maximum Story Displacement in mm
Fig. 8: Maximum Inter-Story Drift Ratio

ISSN: 2456-2319
Results and plot of displacement and inter-storey drift ratio
are showing that Case 1 which is square box type
placement of shear wall at core is having minimum
displacement and inter drift ratio in both directions and
also in seismic and wind loads. Therefore shear wall of
Case 1 (square) will be used for diagrid structure modeling
with shear walls at core for optimum results.
4.2 Diagrid Structure With And Without Shear Walls
4.2.1 Maximum Displacement Results
Fig. 9: Maximum Story Displacement in mm 24 Storey
Fig. 13:Maximum Story Displacement in mm 48 Storey

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4.2.2 Inter Drift Ratio Results
Fig. 15: Inter storey drift ratio : 24 storey (EQ)
As mentioned above within the diagrid storey module
intermediate floors are partialy restrained and having less
storey stiffness which results in high inter storey drift ratio,
but after providing shear wall at core, that increases the
stiffness and imparts the lateral stability with help of their
large in plane stiffness. From results it is clear that in
almost all the cases of diagrid structure, major issue is of
excessive inter storey drift ratio, which is eliminated with
help of shear walls at core.
4.2.3 Percentage Reduction In Maximum Inter Drift Ratio
Table 4: Reduction in maximum IDR(%)
EQ
24 Storey 36 Storey 48 Storey
4 Module 22.52 13.41 13.83
6 Module 29.00 16.91 15.71
8 Module 40.43 24.03 17.72
12 Module 50.33 37.43 21.98
WL
24 Storey 36 Storey 48 Storey
4 Module 53.18 13.81 12.65
6 Module 35.41 17.30 12.43
8 Module 42.57 26.27 14.66
12 Module 49.74 37.07 24.93
It is found that shear walls at core in diagrid structure will
almost eliminate the local stability and flexibility issue
within the diagrid module. This happens because when
shear walls are provided at core due to their large in plane
stiffness they increase the stiffness of overall diagrid
structure and not only at node points.
From result and plot of percentage reduction in maximum
inter drift ratio it is found that decrement in inter drift
with increase in module, increases significantly and in
steep angle diagrid building it is giving maximum
reduction.
4.2.4 Reduction In Reaction On Diagrid
Fig. 16: 4 Story diagrid module

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4.2.5 Base Shear With & Without Shear Wall under EQ
Fig. 20: Base shear 4 Story Module

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4.2.6 Percentage Increase In Quantity With Shear Wall
Fig. 24: % Increase In Quantity With Shear Wall
V. CONCLUSION
In this paper a regular square plan of 30m × 30m diagrid
structure considering different storey module (i.e. 4, 6, 8 &
12) with and without core Shear Walls is analysed and 24,
36 and 48 storey buildings are also considered. Parameters
such as inter storey drift-ratio, storey displacement, base
shear and reduction in lateral load on diagrid are taken into
consideration.
▪ As results shows incorporation of shear walls at core
of the diagrid structure is advantageous in many ways
with very small increase in material quantity.
▪ By providing shear wall at core of diagrid structure
maximum displacement reduced by 15-30% and
maximum inter-storey drift ratio reduced by 15-50%
(Higher decrement observed as the storey module
increase) under both seismic and wind load.
▪ Shear walls almost eliminate the local stability issue
and also eliminate the problem of large inter storey
drift within storey module, by increasing the stiffness
of structure.
▪ Shear wall takes most of lateral loads and results in
reduction in load on diagrid about almost half (45%-
55%) compared to structure without shear wall.
▪ By incorporation of shear wall at core of diagrid
structure, the increase in base shear is around 5 to 6%
and material quantity is around 8-11% for concrete
and 3-4% for steel which is considerably small.
▪ Further, shear wall takes 30% to 65% of lateral loads
which reduces the lateral loads on diagrid at periphery
which ultimately results in economical diagrid section
compared to diagrid structure without shear walls at
core.
▪ As per studies with increase in diagrid angle (higher
storey module), material requirement for diagrid is
less and for those structure inter storey module drift
are large and stiffness reduced significantly therefore
if shear wall is provided than large inter-storey drift
and displacement are reduced and stiffness will
increase.
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