A Review on Seismic Analysis Of a Building on sloping ground

A Review on Seismic Analysis Of a Building on sloping ground

Dr. Sanjaya Kumar Patro 1, Susanta Banerjee 1, Debasnana Jena 2, Sourav Kumar Das 2 1 Prof. & Dean, Department of Civil Engineering,KIIT University,Bhubaneswar,India.

1M.Tech scholar, Department of Civil Engineering, KIIT University, Bhubaneswar,India.

2M.Tech scholar, Department of Civil Engineering, KIIT University, Bhubaneswar,India.

Abstract

During earthquake, torsionally coupled & irregular buildings in hilly areas serves more damage.Dynamic characteristics of hill buildings are somewhat different than the buildings on flat ground.Torsional effect of such buildings is demanded for having the difference stiffness and mass along horizontal and vertical plane during earthquake ground motion.Short column of RC frame building serves damage because of attracting more forces during earthquake.

1. Introduction

   Many irregular configured buildings with different foundation levels are constructed with locally available traditional material in hilly slopes due to lack of flat land in hilly regions.Becuse of population density,demand of such type of building in hilly slopes is increased.The study of earthquake resistant building on slopes becomes popular to prevent the loss of life,property during earthquake ground motion.Different height of columns are present in building on hilly slopes in a same storey,as a reslt more forces are attracted during earthquake ground motion by short columns and damage occurs.

2. Significance

   It is observed from past earthquakes that the buildings on slopes serves more damage and collapse occurs.This review paper aims to analyse the dynamic characteristics of these type of buildings with three different configuration such as a) Step back,b) Step back-Setback,and c) Setback.

3. Previous Study

   B.G. Birajdar1, S.S. Nalawade considered two buildings on sloping ground and one building is on flat soil. The first two are step back buildings and step back-setback buildings; and third is the set back building.The slope is taken 27 degree with horizontal.Depth of footing was taken 1.75m below

   ground level and the block size was considered as 7 m x 5 m x 3.5 m.The properties of beam and column is shown in table 1.

   Table 1

   S.M.Nagargoje and K.S.Sable considered same configuration of building and first two configuration of building was resting on slope soil and third configuration was taken on flat soil.Block size is taken as 7 m x 5 m x 3.4 m.Footing depth was taken as 1.6m below ground level.The properties of beams and columns were taken is shown in table 2.

   Table 2

4. Method of analysis

   B.G. Birajdar1, S.S. Nalawade1 took the materials isotropic,homogeeous in nature.Floor diaphragms are taken as rigid.M25 concrete was used and P-delta effects,creep & shrinkage effects were not considered.Axial deformation was considered for columns. Torsional effect was considered as per IS- 1893:2002.Seismic analysis was performed by Response Spectra Method as per IS 1893:2002.Ordinary moment resistins frame was taken for all these types of buildings in seismic zone III.Response reduction factor and importance factor was taken as 3 and 1 respectively.5% of damping was considered.

   S.M.Nagargoje and K.S.Sable3 analysed the seismic behaviour of these building located in seismic zone III by Seismic Coefficient Method as per IS 1893:2002.Response reduction factor and importance factor was taken as 5 and 1 respectively.Minimun six modes were analysed for each type of building.

5. Analysis of Result

B.G. Birajdar1, S.S. Nalawade1 observed that the along x direction time period and top storey displacement is increased for step back building as the height increases.Dynamic response i.e fundamental time period,base shear,top storey displacemnt for step back building along x direction is shown in table 3.

Table 3

The value of fundamental time period estimated by empirical formula as per IS 1893:2002 is lower than

the value of fundamental time period obtained in dynamic analysis.

The value of base shear,fundamental time period is higher in Y direction than the corresponding values when earthquake force acts in x direction.Time period in dynamic analysis is greater than that calculated by empirical formula as per IS 1893:2002.The value of normalized shear force in columns,base shear,top storey displacement,time period for step back building along Y direction is shown in table 4.

Table 4

In case of Step Back Set Back Buildings,the value of base shear ratio obtained in X direction from dynamic and static analysis are almost same. Time period in dynamic analysis in X direction is greater than that calculated by empirical formula as per IS 1893:2002 for Step Back Set Back Buildings.The value of time period,base shear ratio,top storey displacement in X direction is shown in table 5.

Table 5

In Y direction,variation of shear force is found less significant.Time period in dynamic analysis of this type of building is not affected by the height of building.Uniform section for columns from top to bottom is sufficient. The value of time period,base shear ratio,top storey displacement in Y direction is shown in table 6.

Table 6

For Set Back Buildings on Plain Ground,time period is increased in dynamic analysis in X direction and base shear varies between 1.862 to 2.140.Table 7 shows the results for set back building in X direction.

Table 7

Earthquake in Y direction in case of set back building on plane ground top storey displacement is 3.5 times the higher than the corresponding values in X direction. The base shear ratio has been found significantly high. Table 8 shows the results for set back building in Y direction.

Table 8

S.M.Nagargoje and K.S.Sable3 observed the base shear,top storey displacement in X and Y direction for step back,step back-set back and stepback building is shown in table 9,table 10,table 11 respectively.

Table 9

Table 10

Table 11

The relationship between displacemnt and storey of Step,Step-Set,Set buildings is observed and shown in fig.1

1. Extreme left short column at ground level are damaged most during earthquake in case of Step back and Step back-Set back buildings.

2. Less damage occurs in case of Set back building in flat soil.Detailed study of economic cost for levelling sloping soil and other issues need to be studied.

3. Bse shear is higher for Step back-Setback building and lower for Setback building.

4. Lateral displacement of top storey is maximum for Step back building.

5. On sloping soil Setback- Stepback building is favored.

7.References

1. B.G. Birajdar, S.S. Nalawade," SEISMIC ANALYSIS OF BUILDINGS RESTING ON SLOPING GROUND", 13th World Conference on Earthquake Engineering,Vancouver, B.C., Canada,August 1-6, 2004,Paper No. 1472.

2. Satish Kumar and D.K. Paul., Hill buildings configuration from seismic consideration, Journal of structural Engg., vol. 26, No.3, October 1999, pp. 179- 185.

3. S.M.Nagargoje and K.S.Sable," Seismic performance of multi-storeyed building on sloping ground", Elixir International Journal, 7 December 2012.

4. S.S. Nalawade., Seismic Analysis of Buildings on Sloping Ground, M.E. Dissertation, University of Pune, Pune Dec-2003.

5.D.S.R.Murthy & K.Latha Journal of Structural Engineering ,Vol 37,No 4,Octomber-November 2010 pp256-262.

6.Cnclusion

Fig. 1

1. Murthy C.V.R. Learning earthquake design.

2. IS 13920:1993,"Indian Standard Code of Practice for Ductile Detailing of Reinforced Concrete Structures Subjected to Seismic Forces",Bureau of Indian Standards,New Delhi.

   Different types of building configuration are analysed and the following conclusion can be made:

   a) During earthquake,STEP back buildings are more vulnerable than other building configuration.

3. IS:1893 (I)-2002., Criteria for Earthquake Resistant Design of Structures BIS, New Delhi.

4. IS 456:2000,"Indian Standard Code of Practice for Plane and Reinforced concrete",Bureau of Indian Standards,New Delhi.