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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