An Investigation on Design of Tall building Structures with a Hexagrid System using Staad pro
Ashish Panthi1, Dr. Aslam Hussain2
1Research Scholar, Department of Civil Engineering, UIT Bhopal2Asst, Prof., Department of Civil Engineering, UIT Bhopal
Abstract: The advancement of technology and development of economy of the world have
brought the new era of tall buildings. The most efficient building system for high rises has
been the tube-type structural systems. Now-a-days, a particular structural system called a
hexagrid system has caught the attention of engineers. In order to improve the efficiency of
tube-type structures in tall buildings, as both structural and architectural requirements are
provided well, a new structural system, called "Hexagrid", is introduced in this study. It
consists of multiple hexagonal grids on the face of the building. However limited academic
researchers have been done with focus on the structural behaviour, design criteria and
performance assessment of this structural system. This study investigated the tall hexagrid
buildings, focusing on size and pattern of diiferent hexagrid modules.
Keywords: Hexagrid (Beehive), Structural systems
1. Introduction
The most important issue in the design of high-rise buildings is the lateral load system that
accordingly, the selection of a structural systems that can ductility, stiffness, and sufficient
resistance based on valid regulations provide is the most important principle in the field of
high-rise building because the parameters of stiffness, ductility and structural resistance
system will change with variation the type of lateral load systems a relatively large amount.
Therefore, in this study, new structural system has been extended that nominated new
Hexagrid.
More recently, the diagrid structural system with tubular behaviour is being employed as
structurally efficient as well as architecturally satisfying structural system for tall buildings.
Perimeter diagonals act as a facade, which governs the aesthetics of the building to a great
degree. In order to improve the efficient of tube-type structures in tall buildings, a new
structural system called Hexagrid (Beehive) is introduced in this paper. In the hexagrid
structure system, almost all the conventional vertical columns are eliminated. Hexagrid
structural system consists of Hexagrid perimeter which is made up of a network of multi-
storey tall hex-angulated truss system. Hexagrid is formed by intersecting the diagonal and
horizontal components. The project is focused to horizontal hexagrid pattern which aims to
investigate the optimal angle and a topology of diagonal members in a hexagrid frame using
finite element analysis and to study the structural properties of hexagonal structures so as to
compare their potential efficiency with the conventional systems. This effect can be better
appreciated by analyzing the results in terms of inter storey drift, time period and
displacement. The horizontal hexagrid pattern is given in Fig. 1.1.
Fig. 1: Horizontal hexagrid
2. REVIEW OF PAST RESEARCH
Mathew Thomas (2018) performed the seismic analysis of the building is conducted for
hexagrid buildings with vertical and horizontal orientation of the hexagrid module. The size
of the hexagrids are varied to obtain optimum module size in both orientation. The study is
conducted for 60-stored steel building with symmetric floor plan by using same the volume
of steel. Equivalent static analysis of the buildings is conducted in SAP 2000 software to
optimum module size.
Han-Ul Lee and Young Chan Kim (2017) investigated the characteristics of tall hexagrid
tubular buildings, focusing on the size and pattern of the hexagrid modules, and proposed a
sizing formula based on stiffness- design criteria of members in preliminary design stage.
Saeed Kia Darbandsari (2017) estimated the seismic performance of horizontal hexagrid
concerning the combined horizontal and vertical hexagrid, tubular and diagrid structural
systems. First 30 and 50 story buildings are modeled using ETABS, then pushover and
nonlinear dynamic analyses are performed on buildings using PERFORM 3D. Results
indicate that the horizontal hexagrid system under nonlinear dynamic analysis has the least
roof displacement; buildings capacity curves also demonstrate that the horizontal hexagrid is
the most efficient system, as it brings lowest roof displacement along with high energy
dissipation.
Divya M. S. (2017) analysed 48 storied Steel building with diagrid system and hexagrid
system is presented. Modelling and analysis of structural member is done using finite element
software ETABS. Loads, load combinations and seismic data are provided according to IS
875:1987and IS 1893:2002 respectively. Comparison of analysis results with conventional
system is done in terms storey displacement, storey shear, storey drift and time period.
Zeba J. Sayyed (2017) gives a newly evolved technique which is done on the normal
conventional structure and also the effect on the building due to seismic forces is studied in
this paper. For comparing the results of conventional structure over hexagrid structure
software based analysis has been carried out by considering various seismic parameters to
check the effect of seismic forces on the structure.
Kiran. T (2017) carried out linear dynamic response spectrum analysis on a multi-storied RC
building with Bare frame, Shear wall and Hexagrid system of bracings. For this purpose RC
frame is designed using ETABS V.13. The behavior of the structure is studied based on the
maximum displacement, maximum drift, maximum storey shear and maximum overturning
moment. The study includes the consideration of the effect of base shear and displacement
for RC frames with and without Hexagrid bracings and with shear wall. Comparison is made
for result parameters such as maximum storey displacement, maximum storey drift,
maximum storey shear and maximum overturning moment between various models for
zones-III and comparison is made for result parameters such as maximum storey
displacement, maximum storey drift, maximum storey shear and maximum overturning
moment between seismic zones of India (Zone-III) for different models. ETABS V13 was
used for the purpose and the desired information was achieved.
Deepa Varkey and Manju George (2015) focused on the concept of diagrid structural system,
structural performance of a steel tall building and compare the complex shape of high rise
building for diagrid system using SAP2000. The resulting diagrid structures were assessed
under gravity, wind and seismic loads and various performance parameters were evaluated on
the basis of the analysis results. The comparisons are in terms of lateral displacement, base
shear and inter storey drift.
Rohit Kumar Singh (2014) studied a regular five storey RCC building with plan size 15 m ×
15 m located in seismic zone V is considered for analysis. STAAD.Pro software is used for
modelling and analysis of structural members. All structural members are designed as per IS
456:2000 and load combinations of seismic forces are considered as per IS 1893(Part 1):
2002. Comparison of analysis results in terms of storey drift, node to node displacement,
bending moment, shear forces, area of reinforcement, and also the economical aspect is
presented. In diagrid structure, the major portion of lateral load is taken by external diagonal
members which in turn release the lateral load in inner columns.
3. RESEARCH METHODOLOGY
In this study comparison of size and pattern of hexagrid modules under seismic forces is
presented. Here 15 storey is taken and same dead load and live load [Han-Ul Lee and Young
Chan Kim (2017)] is applied in all the buildings for its behaviour and comparison. As we all
know that buildings are always subjected to vibrations because of earthquake and therefore
seismic analysis is essential for the buildings. So in our work we also conduct vibration
analysis of all the buildings along with storey drift in seismic zone IV are analysed by means
of Staad. Pro software. The response of all the building frames is studied for useful
interpretation of results.
3.1 STEPS FOR COMPARISON
The foremost performance parameters in this research work are different size of the hexagrid
modules and the hexagrid shape. However in this investigation only vertical hexagrids in
orientations are used. 15 storey buildings have been designed using Staad Pro. Analysis of
results in terms of moments, displacements, shear force, axial force and drift has been
presented in the last chapter
Following steps are adopted in this study:‐
Step‐1 Selection of floor plan and Seismic zone. As in previous discussions we have designed
our models for Zone IV as per IS code 1893 (Part 1): 2002 for which zone factor (Z) taken is
0.24. According to our assumptions we modelled 15 storey building with different module
size and pattern of hexagrid is taken. Floor to floor height is 3m.
Step‐2 Modelling of buildings using STADD. Pro software
Step‐3 Investigation of all the building frames was done under seismic zone IV
Step‐4 Presentation of results with regard to maximum moments in columns and beams,
storey displacement, shear force, axial force and drift.
3.2 STRUCTURAL MODELS
A square floor plan of 20 m x 20 m is considered for all the models. Storey height taken was
3m. The dead load and live load obtained from the base paper [Han-Ul Lee and Young Chan
Kim (2017)] are 4 KN/m2 and 2.5 KN/m2 correspondingly. All the models are investigated
for seismic zone IV only. Seismic parameters definitions are taken from Indian code IS 1893
(Part 1): 2002.
Table 1: Geometry and load consideration
Type of structure Residential buildingPlan dimension 20 x 20 m
Total height of building 45 mHeight of each storey 3 m
Diagrid section Steel sectionSeismic load (as per IS code 1893 part-1) Zone IV
Dead load (4 KN/m2) 875- part 1Live load (2.5 KN/m2) 875- part 2
Thickness of slab 150 mmBeam size 400 x 400 mm
Column size 400 x 300 mm
Table 2 Material properties considered in the modelling
Description Value
Steel table Standard section (l100012B50016)
Young’s modulus of steel, Es 2.17x104 N/mm2
Poisson ratio 0.17
Tensile Strength, Ultimate Steel 505 MPa
Tensile Strength, Yeild Steel 215 MPa
Elongation at Break Steel 70 %
Modulus of Elasticity Steel 193-200 GPa
4. GENERATION OF THE STRUCTURE
The structure may be generated from the input file or mentioning the co-ordinates in the GUI.
The figure below shows the GUI generation method.
(a) HP1 (b) HP2 (c) HP 3 (d) HP 4 (e) HP5 (f) HP6
Fig. 2: Models
5. VIBRATION EFFECT ON DIFFERENT MODELS
The vibration analysis of a structure suggested a lot of implication in its designing and
performance over a period of time. The lowest frequency was in 1st mode. The frequency
was increasing with each subsequent mode of vibration and also increases with hexagrid
module size.
Fig. 3: Mode shape of conventional frame
Fig. 4: Mode shape hexagrid pattern 1
Fig. 5: Mode shape hexagrid pattern 2
Fig. 6: Mode shape hexagrid pattern 3
Fig. 7: Mode shape hexagrid pattern 4
1 2 3 4 5 605
101520253035404550
HP6HP5HP4HP3HP2HP1
Mode
Freq
uenc
y (c
ycle
s/sec
)
Fig. 8: Variation of frequency with different shape
6. SUPPORT REACTION
Magnitude of support reaction for various models has been plotted in figure number 9, it is
determined that in this comparative study maximum support reaction is in HP4 whereas HP 1
shows minimum support reaction value.
HP1 HP2 HP3 HP4 HP5 HP60
100002000030000400005000060000700008000090000
Supp
ort R
eact
ion,
KN
Fig. 9: Support reaction
7. SHEAR FORCE
Magnitude of shear force for various models has been plotted in figure number 10, result
suggest that maximum shear force is in HP4. HP2 shows minimum shear force value which
consequences in balanced structure.
HP1 HP2 HP3 HP4 HP5 HP60
500
1000
1500
2000
2500
Shea
r Fo
rce,
KN
Fig. 10: Maximum shear force
8. BENDING MOMENT
Magnitude of bending moment for various models has been plotted in figure number 11, it is
determined that in this comparative study maximum bending moment is in HP4 whereas HP2
shows minimum bending moment value which results in balanced section.
HP1 HP2 HP3 HP4 HP5 HP60
200400600800
10001200140016001800
Ben
ding
mom
ent,
KN
m
Fig. 11: Maximum bending moment
Here result shows that bending moment is low in HP2 structure which means less
reinforcement is required.
9. DISPLACEMENT
Magnitude of maximum displacement for various models has been plotted in figure number
12, below it is determined that deflection is maximum in HP 3 whereas minimum in HP 2
which indicates that HP 3 will require more supports as compared to other cases.
HP1 HP2 HP3 HP4 HP5 HP60
20406080
100120140160180200
Ben
ding
mom
ent,
KN
m
Fig. 12: Displacement comparison
10. LATERAL DISPLACEMENT
It represents the total displacement of the floor w.r.t ground. The lateral forces (wind or
seismic) acting on building are the main reason for it. As per code IS: 800:2007, the
maximum top storey displacement due to lateral load should not exceed H/500, where H =
total height of the building. The displacement results obtained from our analysis for all the
models are within the permissible limit.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 150
2
4
6
8
10
12
14
16
18
HP6HP5HP4HP3HP2HP1
No. of floor
Lat
eral
disp
lace
men
t, cm
Fig. 13: Lateral displacement of models
In above figure Y axis represent the value of storey displacement and X axis represent
number of floor. Structure undergoes maximum displacement at the top storey level in case
of HP6. The maximum displacement in HP1, HP2, HP3, HP4, HP5 and HP6 is 3.9372 mm,
2.2436 mm, 1.4372 mm, 1.3140 mm, 1.3429 mm and 5.5382 mm respectively. As module
size increases displacement of vertical hexagrid increases. Also the hexagrid structure whose
module size are small it offers more stiffness to the structural system which reflects the less
top storey displacement
11. STOREY DRIFT
According to IS: 1893-2002, the storey drift in any storey should not exceed 0.004 times
storey height. The storey drift values obtained in our analysis is within the permissible limit.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 150
0.20.40.60.8
11.21.41.61.8
2
HP6HP5HP4HP3HP2HP1
No of floor
Stor
et d
rift,
cm
Fig. 14: Storey Drift of different models
Above graph shows the variation of drift in the all structural systems. With reference to
lateral load resisting system drift is of interest. Now X axis characterizes number of floor and
Y axis signifies Storey drift. We noticed that drift for HP6 is higher compared to HP1, HP2,
HP3, HP4 and HP5. We also observed that drift increases with increase in module size. So it
is desirable to have vertical hexagrids with greater module size.
12. TIME PERIOD
By performing the dynamic analysis, time period is found out by considering 6 mode shapes
for all models.
1 2 3 4 5 60
0.2
0.4
0.6
0.8
1
1.2
1.4
HP6HP5HP4HP3HP2HP1
Mode shape
Tim
e pe
riod
, sec
Fig. 15: Time period
As we know time period depends upon the mass and stiffness of the structure. If the time
period is more, the modal mass is more but the stiffness of the building is less vice versa. We
observed that the time period is minimum for HP1, hence the stiffness is more when
associated to other models. Also in case HP1 as time period is less, lesser is mass of structure
and hence more is the stiffness.
The time period for different models is shown in Fig. 5.13. The first mode time period of HP1
is 0.16331 seconds and for HP2 is 0.16137 seconds, HP3 is 0.27432 seconds, HP4 is 0.31036
seconds, HP5 is 0.16539 seconds and for HP6 is 0.16243 seconds respectively. The time
period of HP1 structure is the least suggesting that it has higher stiffness compared to other
structures
13. CONCLUSION
This study investigated the structural performance of a building structure using a hexagrid
system through the analyses of 15 storey buildings.
The main conclusion obtained from the analysis of building frames are:
1. The lateral load carrying capacity increases with increase in module size of vertical
hexagrids, in static analysis the vertical hexagrids show better performance in higher
module size.
2. We noticed that as module size increases the displacement of vertical hexagrid also
increases. Also the hexagrid structure whose module size are small it offers more
stiffness to the structural system which reflects the less top storey displacement
3. We observed that the time period is minimum for HP1, hence the stiffness is more as
associated to other cases we considered. Also in case HP1 as time period is less, lesser
is the mass of structure and hence more is the stiffness.
4. The time period for different models suggest that the first mode time period of HP1 is
0.16331 seconds and for HP2 is 0.16137 seconds, HP3 is 0.27432 seconds, HP4 is
0.31036 seconds, HP5 is 0.16539 seconds and for HP6 is 0.16243 seconds
respectively. The vibration analysis of a structure embraces a lot of impact in its
designing and performance over a period of time. The lowest frequency was in 1st
mode. The frequency was increasing with each subsequent mode of vibration and also
increases with hexagrid module size.
5. In this comparative study maximum support reaction is in HP4 whereas HP 1 shows
minimum support reaction value.
6. Here result shows that bending moment is low in HP2 structure which means less
reinforcement is required.
7. It is observed that drift in case of HP6 is higher as compared to HP1, HP2, HP3, HP4
and HP5. In vertical hexagrids the drift increases with increase in module size. So it is
desirable to have vertical hexagrids with larger module size.
8. Therefore HP1 is best with respect to its performance.
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