RESPONSE ANALYSIS OF PLUS SHAPED TALL BUILDING WITH … · 2020. 4. 2. · related to bracings focused on seismic load analysis; hence, a need to study the response of tall buildings

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International Journal of Advanced Research in Engineering and Technology (IJARET) Volume 11, Issue 3, March 2020, pp. 371-380, Article ID: IJARET_11_03_032

Available online athttp://www.iaeme.com/IJARET/issues.asp?JType=IJARET&VType=11&IType=3

ISSN Print: 0976-6480 and ISSN Online: 0976-6499

© IAEME Publication Scopus Indexed

RESPONSE ANALYSIS OF PLUS SHAPED TALL BUILDING

WITH DIFFERENT BRACING SYSTEMS UNDER WIND

LOAD

Dr. Ritu Raj

Assistant Professor, Department of Civil Engineering

Delhi Technological University

Shubhangi Jha, Shreyansh Singh and Siddhant Choudhary

Bachelor of Technology, Department of Civil Engineering

Delhi Technological University

ABSTRACT

This paper aims at response study and analysis of plus shaped tall building with

different orientations of bracing systems under wind loads. The effect of wind load on

building becomes very critical with increase in height of tall buildings. As not much

encouraging information is available in the standard codes of practice regarding tall

buildings with irregular plans and cross-sectional shapes, hence, more research needs

to be done in the given area. With the same objective, the present study focuses on a

different plan i.e. plus shaped tall building exposed to 0o, 30

o and 60

o angles of attack

of wind. Isolated condition (without bracing system), V bracing, Cross bracing, Single

Diagonal bracing and Inverted V bracing system have been considered to analyse the

effectiveness of various bracing systems as structural system against wind loads in tall

buildings. Bentley STAAD Pro software v8i module was used to carry out response

study. Prototype buildings are presumed to be constituted of RCC beams and columns.

The prototype building was designed as G+35 with 4.5 m ground floor height and 3.3

m remaining floors’ height. Mean response of prototype building at windward position

and leeward position for 0o, 30

o and 60

o wind incidence angles including base shear

(Fx), moment about y axis (My), twisting moment (Mz) and deflection in x direction has

been obtained to study the outcome under wind loads of plus shape and different

bracing systems.

Key words: Wind Loads, Tall Buildings, Plus shaped buildings, Cross Bracing, Single

Diagonal Bracing, V Bracing, Inverted V Bracing

Cite this Article: Dr. Ritu Raj, Shubhangi Jha, Shreyansh Singh and Siddhant

Choudhary, Response Analysis of Plus Shaped Tall Building with Different Bracing

Systems Under Wind Load, International Journal of Advanced Research in

Engineering and Technology (IJARET), 11(3), 2020, pp 371-380.

http://www.iaeme.com/IJARET/issues.asp?JType=IJARET&VType=11&IType=3

Dr. Ritu Raj, Shubhangi Jha, Shreyansh Singh and Siddhant Choudhary


1. INTRODUCTION

Tremendous rise in population over past few years has added undue stress on the limited land

for accommodation resulting in shift from horizontal to vertical mode of expansion. As a

result, tall buildings and their judicious design has become an imperative answer to the

question of efficiently utilizing land for residential, industrial, recreational, educational and

other purposes. During the design of tall buildings, the correct estimation of lateral loads

especially wind loads becomes very crucial as wind is a complicated occurrence that varies

randomly.

However, various standard codes of practices being used worldwide for estimation of

wind loads although provide some information but are not exhaustive. [1-5] They deal with

no shapes other than standard cross-sectional shapes including square shape and rectangular

shape and give very minimal information on pressure distribution on tall buildings under wind

loads at skew angles of attack.

Review of research work done in the field shows that so far majority of the focus has been

on pressure distributions of the tall building models only. S. Chakraborty et al, 2014 used

wind tunnel experiment to study mean wind pressure coefficients on an irregular plus shaped

tall building at wind incidence angle 0o and 45

o respectively. Yi Yi et al, 2017 derived a

formula for estimation of wind induced torques on L shaped tall buildings. R. Sheng et al,

2018 studied effects of global and local wind loads on high-rise building through wind tunnel

tests and concluded that wall pressure forces depend on the location. [6-9]

A.K. Mulla and B.N. Srinivas, 2015 executed response analysis of a tall R.C. structure

with outrigger system and steel bracing using ETABS program under static and dynamic

loads. [10] M. Boostani et al, 2018 contemplated an experimental program using fem (finite

element method) numerical examination to propose supporting frameworks called 'o' grid

bracing systems, for seismic tremor safe steel structures. [11] A. Arzeytoon and V. Toufigh,

2018 conducted probabilistic seismic performance assessment of ribbed bracing systems. [12]

A. Rahimi and M.R. Maheri, 2018 considered the impacts of retrofitting rc frames by x-

bracing on the performance of columns under earthquake loads. [13] Since, most of the work

related to bracings focused on seismic load analysis; hence, a need to study the response of

tall buildings with different types of concentric bracing systems under wind loads was

realized.

2. METHODOLOGY

2.1 Response study technique

The present study is focused on wind load response analysis of a plus shaped tall building.

Data from boundary layer wind tunnel testing experiments was used to calculate forces acting

on the models of uniform area along the height. The different cases considered for study

included isolated condition (plus shaped building without any bracing system), plus shaped

building with single diagonal bracing, V-bracing, cross bracing and inverted V-bracing

respectively.

The columns under study of the building were named Column A (Column at windward

position) and column B (column at leeward position) as shown in Figure 1.

Response Analysis of Plus Shaped Tall Building with Different Bracing Systems Under Wind

Load


Figure 1. Windward (Column A) and Leeward (Column B) positions in the plus shaped building.

Prototype buildings were subjected to 0o, 30

o and 60

o angles of attack and parameters such

as Base Shear (Fx), Moment in the y-direction (My), Twisting moment (Mz) and Deflection in

the x-direction (X) was studied at windward side and leeward side, respectively. Readily

available software package STAAD Pro v8i was used for analysis.

2.2. Details of the Prototype Building

Floor Area = 1600 m2

Height = 120 m

Number of floors = 36 (G+35)

3. RESULTS AND DISCUSSION

Figure 2. Impact of different wind attack angles on Fx at Windward Side (column A) in a Plus shaped

Building



Figure 3. Impact of different wind attack angles on Fx at Leeward Side (column B) in a Plus shaped

Building

Base shear at 0o was higher than 30

o and 60

o angles of attack in both cases i.e. windward

side and leeward side of the building. However, at 0o wind incidence angle, cross bracing

exhibited maximum base shear at windward side (7462.84 kN) while V bracing exhibited

maximum base shear at leeward side (12480.57 kN). At 30o and 60

o wind incidence angles,

single diagonal bracing system exhibited maximum value of base shear at both windward and

leeward positions of the building.

For windward position of the building (column A), V bracing system showed minimum

values of base shear at all angles of attack with least value of base shear being 4722.85 kN at

30o angle of attack, whereas for leeward position of the building (column B), isolated

condition (without any bracing system) showed minimum values of base shear at all angles of

attack with least value of base shear as 5685.17 kN at 60o angle of attack.

Figure 4. Effect of 0o incidence angle on moment (My) at Windward Side (column A) in a Plus shaped

Building


Load


Figure 5. Effect of 0o incidence angle on moment (My) at Leeward Side (column B) in a Plus shaped

Building

Base moment was seen to be maximum at 0-degree angle of wind attack for both column-A (windward position) and Column B (Leeward position), as observed in Figures 4 and 5. It

was gauged that base moment (My) in an isolated condition was maximum at 60 degree angle

of attack for column-A (windward position) and at 30 degree angle of attack for Column B

(Leeward position).

Figure 6. Effect of 30o incidence angle on moment (My) at Windward Side (column A) in a Plus

shaped Building


Building



Figure 8. Effect of 60o incidence angle on moment (My) at Windward Side (column A) in a Plus

shaped Building


Building

At all angles of attack, Inverted V bracing showed minimum values of My at windward

position and maximum values of My at leeward position while V bracing showed maximum

values of My at windward position and minimum values of My at leeward position.

Figure 10. Effect of 0o incidence angle on moment (Mz) at Windward Side (column A) in a Plus

shaped Building


Load


Figure 11. Effect of 0o incidence angle on moment (Mz) at Leeward Side (column B) in a Plus shaped

Building

For windward position of the building (Column A), Inverted V bracing system showed

maximum values of twisting moment at all angles of attack (with maximum value being

108.20 kN-m at 0o

wind incidence angle and 25% building height), while V bracing system

showed minimum values of twisting moment at all angles of attack (with least value being -

62.32 kN-m at 30o wind incidence angle and 33.34% building height).


shaped Building

Figure 13. Effect of 30o incidence angle on moment (Mz) at Leeward Side (column B) in a Plus

shaped Building

For leeward position (Column B), isolated condition (without any bracing system) and V

bracing system showed similarly high values of twisting moment at all angles of attack (with



maximum value of V bracing system as 152.80 kN-m at 0o

wind incidence angle and 33.34%

building height), while Inverted V bracing system showed minimum values of twisting

moment at all angles of attack (with least value being -99.67 kN-m at 0o wind incidence angle

and 33.34% building height).


shaped Building

Figure 15. Effect of 60o incidence angle on moment (Mz) at Leeward Side (column B) in a Plus

shaped Building

Numerical values obtained for twisting moment were negligible in all conditions as

compared to corresponding values of base moment about Y-axis. It was hence concluded that

a section designed for maximum axial force or base moment is safe and can take care of the

twisting moment. Therefore, there is no need to design the section of a column separately for

twisting moment.


Load


Figure 16. Impact of different wind attack angles on Deflection at Windward Side (column A) in a

Plus shaped Building

Figure 17. Impact of different wind attack angles on Deflection at Leeward Side (column B) in a Plus

shaped Building

Deflection in isolated condition was seen to be maximum at all angles of attack with

highest value of deflection as 161.46 mm at leeward position and 0o wind incidence angle. For

both i.e. leeward and windward positions of the building, inverted V bracing had the

minimum value of deflection at all angles of attack with least value of 42.35 mm at 60o

wind

incidence angle at windward position.

At windward position, reduction of sway by 44.8%, 46.33% and 18.29% while at leeward

position, reduction of sway by 41.37%, 48.61% and 53.17% at 0o, 30

o and 60

o wind incidence

angles respectively was observed due to Inverted V bracing.

5. CONCLUSIONS

1. Single diagonal bracing system reflected lesser axial force values. The axial force

values show a very slow decrease from bottom to 30% height of the building and then a rapid

decrease to the top.



2. Twisting moment was observed to be negligible in all systems, except in the case of

inverted V-bracing system for column B (Leeward position) at 60-degree angle of attack.

3. It was concluded that, at 0-degree, 30 degree and 60-degree angle of wind attack, V and

inverted V-bracing systems gave comparable values with minimum sway of 67%, 50% and

54% respectively.

REFERENCES

[1] AS/NZS: 1170.2 (2002), “Structural Design Actions, Part-2: Wind Action”

[2] ASCE: 7-02 (2002), “Minimum Design Loads for Buildings and Other Structures”

[3] BS: 63699 (1995), “Loading for Buildings: Part 2 – Code of Practice for Wind Loads”

[4] EN 1991-1-4 (2005), “Euro code 1: Actions on Structures - Wind Actions”

[5] IS:875-Part-3 (2015), “Code of Practice for Design Loads (other than Earthquake Loads) for Buildings and Structures- Wind Loads”

[6] Chakraborty, S., Dalui, S.K. and Ahuja, A.K., 2014. Wind load on irregular plan shaped tall building-a case study. Wind and Structures, 19(1), pp.59-73.

[7] Raj, R., Sharma, A. and Chauhan, S., 2018. Response of Square and Plus Shaped Buildings on Varying Wind Loads. Journal of Structural Engineering.

[8] Li, Y., Li, Q.S. and Chen, F., 2017. Wind tunnel study of wind-induced torques on L-shaped tall buildings. Journal of Wind Engineering and Industrial Aerodynamics, 167, pp.41-50.

[9] Sheng, R., Perret, L., Calmet, I., Demouge, F. and Guilhot, J., 2018. Wind tunnel study of wind effects on a high-rise building at a scale of 1: 300. Journal of Wind Engineering and

Industrial Aerodynamics, 174, pp.391-403.

[10] Mulla, A.K. and Srinivas, B.N., 2015. A study on outrigger system in a tall RC structure with steel bracing. International Journal of Engineering Research and, 4.

[11] Boostani, M., Rezaifar, O. and Gholhaki, M., 2018. Introduction and seismic performance investigation of the proposed lateral bracing system called “OGrid”. Archives of civil and

mechanical engineering, 18(4), pp.1024-1041.

[12] Arzeytoon, A. and Toufigh, V., 2018. Probabilistic seismic performance assessment of ribbed bracing systems. Journal of Constructional Steel Research, 148, pp.326-335.

[13] Rahimi, A. and Maheri, M.R., 2018. The effects of retrofitting RC frames by X-bracing on the seismic performance of columns. Engineering Structures, 173, pp.813-830.

[14] IS:456 (2000), “Plain and Reinforced Concrete – Code of Practice”

[15] IS:875-Part-1 (1987), “Code of Practice for Design Loads (other than Earthquake Loads) for Buildings and Structures- Dead Loads”

[16] IS:875-Part-2 (1987), “Code of Practice for Design Loads (other than Earthquake Loads) for Buildings and Structures- Imposed Loads”

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RESPONSE ANALYSIS OF PLUS SHAPED TALL BUILDING WITH … · 2020. 4. 2. · related to bracings focused on seismic load analysis; hence, a need to study the response of tall buildings