Study of Seismic Behaviour of Multi-Storied R.C.C. …ijer.irponline.in/ijer/publication/v5si3/37.pdf · 2017-10-12 · building without bracings and regular building on plain ground

International Journal of Engineering Research ISSN:2319-6890)(online),2347-5013(print) Volume No.5 Issue: Special 3, pp: 690-697 27-28 Feb. 2016

NCASE@2016 doi : 10.17950/ijer/v5i3/037 Page 690

Study of Seismic Behaviour of Multi-Storied R.C.C. Buildings Resting on Sloping Ground and Considering Bracing System

D. J. Misal, M. A. Bagade

Civil Engineering Department, Dr.D.Y.Patil School of Engineering and Technology, Charholi (Bk), Pune,412105, Maharashtra, India. Email: [email protected]

Abstract: In hilly areas buildings are built on sloping grounds. When the hilly areas come under the seismic zones, these buildings are highly vulnerable to earthquakes. The dynamic analysis is carried out using response spectrum method to the step back and step back and set back building frames. The dynamic response that is fundamental time period, storey displacement and base shear action induced in columns have been studied for buildings of different heights. These results show that the performance of step back and set back building frames are more suitable in comparison with step back building frames. But after considering bracings to the step back building frames, a better performance can be observed when compared with step back and set back building frames. Three dimensional space frame analysis is carried out for four different configurations such as step back buildings without bracings, step back buildings with bracings, step back and set back building without bracings and regular building on plain ground of buildings ranging from eight, ten and twelve storey resting on sloping ground. Building models are analyzed by Etabs software to study the effect of time period, storey displacement and base shear. Keywords Earthquake, Sloping Ground, Response spectrum method, step back frames, step back and set back frames, step back with bracings, ETABS software.

1. Introduction

Seismology is the study of vibrations of earth, mainly caused by earthquakes. The study of these vibrations by various techniques, understanding the nature and various physical processes that generate them from the major part of seismology. From the seismic history of our country, it is observed that majority of the devastating earthquakes have been occurred in northern and north-eastern states of India. Most of this region is the hilly area which lies in the seismically active belt of Himalaya Range. In the last decade, all these regions have gone under rapid changes due to economic development. Being the frontier states rapid urbanization is going on these boundary of country, states with growing real estate development. Due to this, population density in hill region has increased enormously and all types of construction practices are followed. During past earthquakes reinforcement concrete frame buildings that have columns of different heights within one storey, suffered more damage in shorter columns as compared to taller columns in the same storey. First example of buildings on sloping ground and

building with a mezzanine floor can be seen in Figure 1.1

Figure 1.1 Building frame with short columns

Poor behavior of shorter columns is due to the fact that in an earthquake, a tall column and a short column of same cross section move horizontally by same amount. Second example of structural behaviour of short column under lateral loading which can be seen in Figure 1.2

Figure 1.2 Structural behaviour of short column under lateral loading

However the short column is stiffer as compared to tall column and it attracts larger earthquake force. Stiffness of a column means resistance to deformation the larger is the stiffness, larger force required to deform it. If a short column is not adequately designed for such a large force, it can suffer significant damage during an earthquake. This effect is called short column effect.

1.1. Bracings



Figure 1.3 Cross or X-Bracing

Bracing systems are used to resist horizontal forces like wind load, seismic action and to transmit to the foundation. The bracing members are arranged in many forms, which carry solely tension, or alternatively tension and compression. The bracing is made up of crossed diagonals, when it is designed to resist only tension. Based on the direction of wind, one diagonal takes all the tension while the other diagonal is assumed to remain inactive. One of the most common arrangements is the cross bracing. Bracings hold the structure stable by transferring the loads sideways (not gravity, but wind or earthquake loads) down to the ground and are used to resist lateral loads, thereby preventing sway of the structure.

2. Objective of the Present Study

It is observed from the past earthquakes, buildings in hilly regions have experienced high degree of demand leading to collapse though they have been designed for safety of the occupants against natural hazards. Hence, while adopting practice of multi-storey buildings in these hilly and seismically active areas, utmost care should be taken, making these buildings earthquake resistant. In these areas buildings with step back configuration frames may sometimes give worst results so bracing system is used for these buildings and comparing the results with other configuration. The objectives of this work are as follows

1. The dynamic analysis is carried out using response spectrum method to the step back and step back, step back building frames and regular building on plain ground.

2. To carry out modeling and response spectrum analysis of seismic behaviour of multi-Storied R.C.C. buildings resting on sloping ground and considering bracing system by analytically and compared the same using Etabs software.

3. Three dimensional space frame analysis is carried out for four different configurations of buildings ranging from eight, ten and twelve storey’s resting on sloping ground under the action of seismic load by using Etabs software.

4. Dynamic response of these buildings, in terms of base shear, fundamental time period and displacement are find out and compared within the considered configuration as well as with other configurations.

3. Scope of Study

1. Three dimensional space frame analysis is carried out for four different configurations such as step back buildings without bracings, step back buildings with bracings, step back and set back building without bracings and regular building on plain ground of buildings ranging from eight, ten and twelve storey resting on sloping ground.

2. Dynamic response of these buildings, in terms of base shear, fundamental time period and displacement are find out and compared within the considered configuration as well as with other configurations.

3. The only RC framed buildings are considered for the analysis

4. The buildings considered (8-12 storey buildings) without basement, shear wall.

5. The contribution of infill walls are considered as non-integral with RC frames.

6. The out of plane action of masonry walls are neglected in the analysis.

7. The effect of the supporting foundation medium on the motion of structure gives soil structure interaction but this effects may not considered in the seismic analysis for structures supported on rock or rock like materials.

8. The Flexibility of floor diaphragms are neglected and considered as rigid diaphragm.

9. The base of the column is assumed to be fixed in the analysis.

10. Secondary effect P-shrinkage and creep are not considered.

11. The contribution of infill wall to the stiffness was not considered.

4. Building Configuration 4.1 Model Description

1. In the present study, four groups of building configurations are considered,

a.Step back buildings without bracings. b.Step back buildings with bracings. c.Step back and set back building without bracings. d. Regular building on plain ground. 2. Three dimensional space frame analysis is carried out

for four different configurations of buildings ranging from eight, ten and twelve storey resting on sloping ground under the action of seismic load by using Etabs software.

3. The height and length of building in a particular pattern are in multiple of blocks (in vertical and horizontal direction), the size of block is being maintained at 7 m x 5 m x 3.5 m.

4. The height of all floors is 3.5m 5. The depth of footing below ground level is taken as 1.8

m where, the hard stratum is available. 6. The slope of ground is 27 degree with horizontal,

which is neither too steep or nor too flat. 7. Basically model consists of two bays with four groups

of building configurations. 8. The dynamic analysis is carried out using response



spectrum method to the step back and step back and step back building frames.

9. The buildings shown in Figure 4.1 having Step back buildings without bracings frames of 8 storey, 10 storey and 12 storey buildings, Step back buildings with bracings frames of 8 storey, 10 storey and 12 storey buildings are shown in Figure 4.2, Step back and set back building without bracings frames of 8 storey, 10 storey and 12 storey buildings are shown in Figure 4.3 and Regular building on plain ground frames of 8 storey, 10 storey and 12 storey buildings are shown in Figure 4.4.

Figure 4.1 Step back buildings without bracings frames of 8 storey, 10 storey, and 12 storey buildings.

Figure 4.2 Step back buildings with bracings frames of 8 storey, 10 storey, and 12 storey buildings.

Figure 4.3 Step back and set back building without bracings frames of 8 storey, 10 storey, and 12 storey buildings.

Figure 4.4 Regular building on plain ground frames of 8 storey, 10 storey, and 12 storey buildings.

Figure 4.5 3D view of Step back buildings without bracings

frame

Figure 4.6 3D view of Step back buildings with bracings frame

Figure 4.7 3D view of Step back and set back building frame



Figure 4.8 3D view of Regular building on plain ground frame

4.2 Geometrical Properties of Members Table 4.1 Geometrical properties of members for different configurations of building

Building Configurations

Number of Storey

Size of Column in mm

Size of Beam in

mm Step Back Building

STEP8 to STEP9

300X680 300 X530

STEP10 to STEP12

400X830

Step Back and Set Back Building

STEP-SET8 to STEP-SET9

300X680 300 X530

STEP-SET10 to STEP-SET12

400X830

Regular Building on Plain Ground

REG8 to REG9

300X680 300 X530

REG10 to REG12

400X830

Bracing STEP8 to STEP12

230X380

4.3 Assumed Preliminary Data Required for Analysis of Frame

i. Types of structure: multi-storey rigid joined plane frame (special RC moment resisting frame)

ii. Number of stories: four different configurations of buildings ranging from G+8, G+10, G+12.

iii. Infill wall: 230 mm thick for all floors iv. Specific weight of R.C.C :25 kN/m3 v. Specific weight of infill :20 kN/m3

vi. Materials: Concrete grade is M25 and Steel reinforcement is Fe500

vii. Depth of slabs are taken as 225 mm thick for all floors. viii. Height of parapet:1.2m

ix. Response spectra: As per IS 1893 (Part 1):2002

4.4 Load Analysis Table 4.2 Load analysis for different configurations of building

A.Dead Load IS 875 Part 1:-1987 1.Wall load on each Floor 13.66 kN/m 2.Wall load on roof floor 5.52 kN/m 3.Floor finish on each floor 1.5 kN/m2 B.Live Load IS 875 Part 2:-1987 1.Live load on each floor 4 kN/m2 2.Live load on roof floor 2 kN/m2 C.Secismic Load IS 1893(Part-1)-2002 1.Zone factor 0.16 (Zone-III) 2.Soil type I 3.Importance factor 1

4.Reponse reduction factor 5 (SMRF) 5.Damping percent 5 %

5. Method of Seismic Analysis 5.1 Response Spectrum Analysis The seismic analysis of all buildings are carried out by response spectrum method by using IS 1893 (Part-I)-2002, The other parameters used in seismic analysis are, moderate seismic zone (III), zone factor 0.16, importance factor 1.0, 5 % damping, response reduction factor 5, presuming special moment resistant frame for all configurations and height of buildings. For each building case, adequate modes (minimum eight) were considered, in which, the sum of modal masses of all modes was at least 99 % of the total seismic mass. The member forces for each contributing mode due to dynamic loading were computed and the modal responses were combined using CQC method. The following design spectrum was utilized in response spectrum analysis.

Sa/g = 1+15 T when 0.00 ≤ T ≤0.10 seconds 2.50 0.10 ≤ T ≤0.40 seconds

1/T 0.40 ≤ T ≤4.00 seconds 6. Results and Discussions 6.1 Analysis of Results of R.C.Frames Building Configurations (2D) for 8 Storey 6.1.1 Comparison of time period between step back without bracings, step back with bracings, step back and set back without bracing and regular building on plain ground frames of 8 storey building

Figure 6.1 Time period variation with respect to Number of Storey for 8 Storey Result Conclusion: from the above graph time period for step back without bracings and with bracings frames and regular building on plain ground are more than step-set back frames. 6.1.2 Comparison of storey shear between step back without bracings, step back with bracings, step back and set back without bracing and regular building on plain ground frames of 8 storey building



Figure 6.2 Storey shear variation with respect to Number of Storey for 8 Storey Result Conclusion: from the above graph storey shear for first stories step back without bracings and step-set frames are less than step back with bracings frames and regular building on plain ground. 6.1.3 Comparison of displacement between step back without bracings, step back with bracings, step back and set back without bracing and regular building on plain ground frames of 8 storey building

Figure 6.3 Displacement variation with respect to Number of Storey for 8 Storey Result Conclusion: from the above graph displacement for Top stories step back without bracings, step-set and regular building on plain ground frames are more than step back with bracings frames. 6.2 Analysis of Results of R.C.Frames Building Configurations (2D) for 10 Storey 6.2.1 Comparison of time period between step back without bracings, step back with bracings, step back and set back without bracing and regular building on plain ground frames of 10 storey building





Figure 6.6 Displacement variation with respect to Number of Storey for 10 Storey Result Conclusion: from the above graph displacement for Top stories step back without bracings, step-set and regular building on plain ground frames are more than step back with bracings frames. 6.3 Analysis of Results of R.C.Frames Building Configurations (2D) for 12 Storey 6.3.1 Comparison of time period between step back without bracings, step back with bracings, step back and set back without bracing and regular building on plain ground frames of 12 storey building



Figure 6.9 Displacement variation with respect to Number of Storey for 12 Storey Result Conclusion: from the above graph displacement for Top stories step back without bracings, step-set and regular building on plain ground frames are more than step back with bracings frames. 6.4 Analysis of Results of Maximum Torsional Moment with Respect To Column Force of R.C.Frames Building Configurations (2D) for 8, 10, 12 Storey



Figure 6.10 Maximum Torsional Moment variation with respect to Number of Storey for 8, 10, 12 Storey Result Conclusion: from the above graph Maximum Torsional

Moment for step-set and regular building on plain ground frames are less than step back with bracings and step back without bracings frames.

7. Conclusions 1. As per IS1893(Part-1)-2002 buildings with dual system consist of shear walls or bracing frames so that these are designed to resist the total design lateral force in proportion to their lateral stiffness. 2. Storey shear for first stories step back without bracings and step-set building frames are less than step back with bracings frames. 3. The step back building frames without bracings give higher values of time period as compared with step back and set back frames. 4. The step back building frames without bracings give higher values of top storey displacement as compared with step back and set back frames. 5. The performance of step back frames without bracings during seismic excitation can be effected more than other configurations of building frames. Hence, step back building frames without bracings on sloping ground are not desirable. However, it may be adopted by providing bracing system to control displacements. 6. Maximum torsional moment for step-set and regular building on plain ground frames are less than step back with bracings and step back without bracings frames. 7. As number of storey increases time period and top storey displacement also increases. 8. Step back frames with bracings gives less displacements compared with Step back frames without bracings and also Step and Set back frames.

Acknowledgements This gives me an immense pleasure in submitting the

project paper on “Study of Seismic Behaviour of Multi-Storied R.C.C. Buildings Resting on Sloping Ground and Considering Bracing System”. I am thankful to my internal guide, our M.E-Coordinator Prof.Mahesh A.Bagade and my external guide Prof. P. B. Daigavhane and Prof. S.B. Kharmale for his valuable guidance and kind help during completion of my project paper.

I would like to thank Principal Dr. Ashok S.Kasnale and H.O.D Dr.Sanjay K.Kulkarni of Dr. D. Y. Patil School of Engineering and Technology lohegaon and also thankful to our library staff for allowing me to have all the stuff that I needed.

I wish to acknowledge our Dr.Nagesh L.Shelke and Prof.Pallavi K.Pasnur for his valuable support throughout this project paper.

Last but not least, I am deeply grateful to my family members, all my friends and well-wishers for encouraging and helping me directly or indirectly, throughout my project paper. REFERENCES

i. R. Nagarjuna, and S.B.Patil, “Lateral Stability of Multistorey

Building on Sloping Ground”, International Research Journal of Engineering and Technology, Vol.02, pp.2395-0072, 2015.

ii. N. Kalsulkar, and S.Rathod, “Seismic Analysis of R.C.C Building Resting on Sloping Ground with varying Number of Bays and Hill Slopes”, International Journal of Current Engineering and Technology, Vol.5, No.3, pp.2347-5161, 2015.

iii. A.S.Swathi, G.V.Rama Rao, and R.A.B.Depaa, “Seismic Performance of Buildings on Sloping Grounds”, International Journal of Innovative Research in Science, Engineering and Technology, Vol.4, pp.1756-1761, 2015.

iv. S.K.Deshmukh, and F.I.Chavan “Seismic Analysis of R.C.C. Building Resting on Sloping Ground”, International Journal of Pure and Applied Research in Engineering and Technology, Vol. 3, pp.119-133, 2015.

v. G.Suresh, and E.Arunakanth, “Seismic Analysis of Buildings Resting on Sloping Ground and Considering Bracing System”, International Journal of Engineering Research and Technology, Vol. 3, pp. 2278-0181, 2014.

vi. B.Shivanand, and H.S.Vidyadhara, “Design of 3D R.C. Frame on Sloping Ground”, International Journal of Research in Engineering and Technology, Vol.03, pp. 2321-7308, 2014.

vii. S.Kumar, V.Garg, and A.Sharma, “Effect of Sloping Ground on Structural Performance of R.C.C. Building under Seismic Load”, International Journal of Science, Engineering and Technology Vol. 2, pp. 2348-4098, 2014.

viii. S.K.Patro, S.Banerjee, D.Jena, and S.K.Das, “A Review on Seismic Analysis of a Building on Sloping Ground”, International Journal of Engineering Research and Technology, Vol. 2, pp. 2278-0181, 2013.

ix. S.M.Nagargoje, and K.S.Sable, “Seismic Performance of Multi-Storeyed Building on Sloping Ground”, Elixir International Journal, 53 11980-11982, 2012.

x. B.G.Birajdar, and S.S.Nalawade, (2004). “Seismic Analysis of Buildings Resting on Sloping Ground”, 13th World Conference on Earthquake Engineering, Vancouver, B.C., Canada, Paper No. 1472, 2004.



xi. S.Kumar, and D.K.Paul, “Hill buildings configuration from seismic consideration”, Journal of Structural Engineering, vol. 26, No.3, pp.179-185, 1999.

xii. Structural and Earthquake Engineering Software, “ETABS 2015”, Computers and structures, Inc.

xiii. S.K.Duggal, “Earthquake-Resistant Design of Structures”, Oxford university press, India, 2007.

xiv. A.K.Chopra, “Dynamics of structures theory and applications to earthquake engineering”, Prentice- Hall, Englewood Cliffs, California, 1995.

xv. P.Agrawal, and M.Shrikhande, “Earthquake Resistant Design of Structures”, Prentice-Hall of India Learning Private limited, India, 2012.

xvi. IS: 1893 (Part-1)-2002, “Indian Standard Criteria for Earthquake Resistant Design of Structures,” Bureau of Indian Standards, India.

xvii. IS: 456-2000, “Indian Standard code of practice for Plain and Reinforced concrete,” Bureau of Indian Standards, India.

Documents

Study of Seismic Behaviour of Multi-Storied R.C.C. …ijer.irponline.in/ijer/publication/v5si3/37.pdf · 2017-10-12 · building without bracings and regular building on plain ground