A Comparative Study on Behaviour of High Rise Building with Shear Wall Under Seismic Analysis

A Comparative Study on Behaviour of High Rise Building with Shear Wall Under Seismic Analysis

M. Durga Prasanna1

1 PG Student (Department of Civil Engineering,

V.R.Siddhartha Engineering college, Vijayawada)

Dr. B. Panduranga Rao2

2Professor& Dean

( Department of Civil Engineering, V.R.Siddhartha Engineering college, Vijayawada)

Abstract:- Earthquakes have been the cause of great disasters, right from the evaluation of earth, causing destruction to property, injury and loss of life. Due to rapid industrial development and concentration of population in cities, the effective design and construction of earthquake resistant structures plays a major part in the reduction of losses due to earthquakes. In this thesis , the earthquake response of 12 storied asymmetric building was studied using two methods- "Seismic coefficient method and modal analysis is using Response spectrum method". Analysis carried out in both the methods manually and by using software's( E tabs), For modal analysis in response spectrum method, natural frequencies and mode shape coefficients are determined by MAT LAB Program. A comparative study has been made on responses obtained from the both the methods.

INTRODUCTION:

Considering the past information of earthquake, there is need in the demand of earthquake resisting building which can be fulfilled with the aid of supplying the shear wall structures inside the building. The decision regarding provision or shear wall to face up to lateral forces play maximum critical function in deciding on the suitable structural device for given structure. Generally systems are subjected to two types of forces i.e. Static and Dynamic. Static forces are steady even as dynamic forces vary with time.

In majority civil structures most effective static forces are considered at the same time as dynamic forces arent calculated due to the fact the calculations are more complicated. This might also purpose disaster specifically during Earthquake because of seismic waves. By presenting shear wall in multi-storied building we can face up to seismic waves. By presenting shear wall in multi- storied building we can face up to seismic forces triggered due to earthquake. The masses are calculated by means of manually and ETABS software by offering shear wall of total structure.

METHODS OF EARTHQUAKE ANALYSIS:

Two broad approaches of earthquake analysis of multi storied structures are

1. Equivalent static force analysis.

2. Dynamic analysis.

   1. Equivalent Static Force Analysis :

      Seismic analysis of most structures is still carried out on the assumption that the lateral force is equivalent to the actual dynamic loading . This method requires less

      effort because, expect for the fundamental period, the periods and shapes of higher natural modes of vibration are not required. The base shear which is the total horizontal force on the structure is calculated on the basis of the structures mass, its fundamental period of vibration, and corresponding shape. The base end shear is distributed along the height of the structure, in terms of lateral forces, according to the code formula., Planar models appropriate for each of the two orthogonal lateral directions are analysed separately; the results of the two analyses and the various effects, including those due to torsional motions of the structure, are combined. This method is usually conservative for low to medium height buildings with a regular conformation.

   2. Dynamic analysis:

Static methods of seismic analysis are not accurate for complex structures which demand dynamic analysis for accuracy. Various methods of varying complexity have been developed for dynamic seismic analysis of structure. The two main methods currently used for dynamic analysis are

1. Response spectrum analysis

2. Time history analysis

Response Spectrum Analysis :

It is dynamic method analysis. This method is also known as modal method or mode superposition method. The method is applicable to those structures where modes other than the fundamental one significantly affect the response of the structure. Generally, the method is applicable to analysis of the dynamic response of structures, which are asymmetrical or have areas of discontinuity irregularity, in their linear range of behaviour. In particular, it is applicable to analysis of force and deformations in multi-storey buildings due to medium intensity ground shaking, Which causes a moderately large but essentially linear response in the structure. In the calculation of structural response, the structure should be so represented by miss of an analytical or computational model that reasonable and rational results can be obtained by its behaviour. Where response spectrum method is used with modal analysis procedure, at least 3 modes of response of the structure should be considered expect in those cases where it can be shown qualitatively that either third mode or second mode produces negligible.

Time History Analysis:

It is a dynamic method analysis. This method is a useful technique for the elastic analysis of structure. A

linear time history analysis overcomes all the disadvantages of a modal response spectrum analysis provided non-linear behaviour is not involved. In this method, the mathematical model of the building is subjected to accelerations from earthquake records that present the expected earthquake at the base of the structure. The method consists of a step-by-step direct integration over a time interval. This method is applicable to both elastic and in elastic analysis.

METHODOLOGY:

1. Seismic analysis of 12 storeyed building of complete shear wall was considered.

2. Analysis on seismic coefficient method & response spectrum method as given in

   IS 1893(Part-1):2002

3. Seismic coefficient method (manually & E tabs) 4.Response Spectrum method( By using modal analysis & Mat lab)

5.The lateral load distribution, the shear forces, the bending moments and drifts at various floor levels of the building are worked out.

ANALYSIS& RESULTS:

Seismic coefficient method( manual Calculation):

Design Parameters:

For seismic zone 3, the zone factor Z is 0.16(Table 2 of IS: 1893). Being an office building, the importance factor, I, is

1.2 (Table 6 of IS: 1893). Building is required to be provided with moment resisting frames detailed as per IS: 13920-1993. Hence, the response reduction factor, R, is 5. (Table 7 of IS: 1893 Part 1)

Number of bays along x direcion-3=14.505m Number of bays along y direction-7=22m Number of floors=12@3.6m ht/floor

Slab thickness:150mm Floor finishes=1.0kN/m^2 Live load=3kN/m^2

Soil type=medium Seismic zone=3

STEP 1: Calculation of lumped masses to various floor levels

Slab weight=22×14.505×0.15×25=1196.6KN Floor finish=22×14.505×1 =319.11KN

Live load on floor =22×14.505×3/4 =239.3 KN

Seismic weight on each floor = 1196.6+319.11+239.3=1755.01KN Seismic weight on roof floor=1196.6+319.11=1515.71KN

Weight of walls= 3.45×0.165x(3.845(8)+7.2(8)+3.46(8)+5.035(4)+4.15(4)+2.98(4)+3.76(4)+3.42(4)+1.535(4)+1.12(4))

=2903.744KN

Weight of wall on roof=1451.872KN

lumped weight at each floor=1196.6+319.11+239.3+2903.744=4658.754KN lumped weight at roof level=1196.6+319.11+1451.872=2967.582KN

Total seismic weight=4658.754(11)+2967.58=54213.874KN

STEP 2: Determination of fundamental natural period

Ta=0.09*43.2/22 ( For medum stiffness soil )

=0.828 ( as per IS 1893:2002) Sa/g=1.642

STEP 3: Determination of design base shear

VB=Ah*W

Ah= Z/2 * I/R * Sa/g

= 0.16/2 *1.2/5 *1.642

=0.0315264

VB=0.0315264*54213.874=1704.168KN VB= 1704.168KN

STEP4: Vertical distribution of base shear:

Seismic coefficient method : ( Etabs)

Comparison of Seismic Lateral Load Values: ( Manually and E tabs)

Response Spectrum Method:

Seismic Response of 12 storeyed building by Seismic Coefficient Method :(Manually)

Seismic Response of 12 storeyed building by Seismic Coefficient Method : (Etabs)

Seismic Response of 12 storeyed building Response spectrum Method :

Graphs: Lateral Forces:

1500

1500

1000

1000

seismic coefficient method(manually)

seismic coefficient method(manually)

500

500

seismic coefficient method(Etabs)

seismic coefficient method(Etabs)

0

0

Storey shear in KN

Storey shear in KN

Storey shear :

2000

2000

12 11 10 9 8 7 6 5 4 3 2 1

Storey number

12 11 10 9 8 7 6 5 4 3 2 1

Storey number

Storey Moment:

Storey moment in Kn-m

Storey moment in Kn-m

60000

50000

40000

30000

20000

10000

0

12 11 10 9 8 7 6 5 4 3 2 1

Storey number

Seismic coefficient method

Response spectrum method

CONCLUSIONS:

Based on the work presented in the thesis , the following conclusions are:

1. The seismic coefficient method is conservative at top floors compared to response spectrum method and vice- versa.

2. The base shear is high in seismic coefficient method when compared to the response spectrum method

3. The lateral load distribution is decreasing from a higher value to top floors to bottom floors in both seismic coefficient method and response spectrum method 4.Gradual increase in storey moments are observed from top storey to lower storey in both the methods.

1. Storey moments are high in seismic coefficient method compared to response spectrum method.

2. It is suggested to relay on response spectrum method even in asymmetric multi-storeyed buildings for seismic analysis and design.

REFERENCES:

1. Clough, R.W. and Penzein, J., Dynamics of Structures, McGra Hill KogaKusha Ltd., Tokyo,Japan 1975

2. Dowrick ,D.J. Earthquake Resistant Design .John wiley & sons,London,1977.

3. Duggal,S.K., Earthquake Resistant Design of structures, Oxford University press2007

4. IS 1893(part 1) :2002, Criteria for earthquake Resistant Design of structures,Fifth Revision,New Delhi, 2002

5. Jaya Krishna & Chandra Sekaran, A,R. Elements of Earthquake Engineering . 1st Ed., Savitha Prakashan, Merut, India,1976.

6. Pankaj Agarwal and Manish Shrinkande, Earthquake Resistant Design of Structures PHI Learning Private Ltd., New Delhi, India 2010.

7. Pravin B. Waghmare, P.S.Pajadge and N.M.Kahe, Response spectrum analysis of a shear frame structure by using MATLAB, Int. Journal of Applied Sciences and Engineering Research, vol.1,

   No.2,2012

8. S.S.Patil, S .A.Ghadge, C.G.Konapure, and C.A.Ghadge, Seismic Analysis of high- Rise Building by Response Spectrum Method, international Journal Of Computational Engineering Research Vol.3 Issue.3