Seismic Analysis of RC Frame – A Parametric Study

Seismic Analysis of RC Frame – A Parametric Study

Sakshi A. Manchalwar, Asst. Professor Civil Engineering Department Priyadarshini's J.L. College of Engineering Nagpur, India

Abstract The analysis of high rise building is quite complicated in view of large number of redundants involve. There are different methods by which a frame of multistory can be analysed, and the design of such frame is affected more by lateral loads than by gravity forces. Present study deals with the analysis of multistoried building (upto14 story) subjected to earthquake force. A complete parametric study is carried out for this frame. Effect of column stiffness, effect of number of bays, and building height etc. is studied. This building is assumed to be located in Mumbai. The earthquake load analysis is carried out using software namely SAP2000.

KeywordsSeismic Analysis, Stiffness, RC frame

1. INTRODUCTION

   Due to spiraling rise in cost of land, tall structures are being constructed in present day. These multistorey high structures require a small size of costly land and provide required floor area. The analysis of high rise building is quite complicated in view of large number of redundants involve. There are different methods by which a frame of multistory can be analysed, and the design of such frame is affected more by lateral loads than by gravity forces. Tall buildings are generally those buildings whose lateral dimension are less than or comparable to height of structure. The response of such type of structure to lateral loading becomes critical since stability of structure against lateral loading governs the design. For a structural designer a multistory building can be defined as one whose structural system must be modified to make it sufficiently economical to resist lateral forces due to wind or earthquake within prescribed criteria for strength, drift and comfort of the occupant.

2. STUDY OF BUILDING FRAME Parameters studied are pertaining to 14 storey building frame

   1. sizes of column are varied as

      0.3 x 0.3, 0.3 x 0.4, 0.3 x 0.6, 0.3 x 0.7, 0.3 x 0.8, 0.3 x

      1.0, 0.3 x 1.2, 0.3 x 1.4

   2. No. of bays considered are

   Single, Two bay, Three bay

   The 14th storey single bay, two bays and three bays are also studied with and without diaphragm as shown in fig. 2.1

   Fig 2.1 Intermediate frame considered for the analysis

   Fig 2.2 Frame model considered for the analysis

3. EFFECT OF COLUMN STIFFNESS

   1. Single bay frame (without diaphragm):

      Column moment: With the increase in stiffness of column the moment in column increases continuously from negative value towards positive value. If each model of different column stiffness considered separately the column moment decreases from bottom floor column towards top floor column up to certain floor and then again increases toward negative value. As shown in fig 2.3

      Beam moment: With the increases in stiffness of column the moment in beam decreases continuously. If each model of different column stiffness considered separately the beam moment increases from bottom floor beam towards top floor beam up to certain floor and then again decreases continuously. As shown in fig 2.4

      Fig.2.3 comparison of column moment

      Fig.2.4 comparison of beam moment

   2. Single bay frame (with diaphragm):

      Fig 2.5 Comparison of column moment

      Fig.2.6 Comparison of beam moment

   3. Two bay frame (without diaphragm):

      Fig.2.7 Comparison of column moment

   4. Two bay frame (with diaphragm):

      Fig.2.8 Comparison of column moment

   5. Three bay frame:

   Fig.2.9 Comparison of column moment

4. CONCLUSION

As the stiffness of column increases the moment in the same floor level beam decreases. However if 14 story frame is considered, the beam moment increases up to certain floor, in

middle portion moment nearly constant and then again reduced up to top story.

As the stiffness of column increases the moment in same floor level column increases continuously from negative value towards positive value. However if 14 story frame is considered, the column moment decreases up to certain floor, then again increases up to top story.

REFERENCES

1. Aschheim et al, Theory of principal components analysis and applications to multistory frame buildings responding to seismic excitation, Engineering Structures 24, 2002, p. 10911103.

2. Fintel M. Hand book of Concrete Engineering, second edition, CBS Publisher and Distributors, 1986.

3. IS-1893-2002, part-I, Indian Standard criteria for Earthquake Resistance Design of Structure, Bureau of Indian Standards, 2002, New Delhi.

4. Ji et al, An analytical framework for seismic fragility analysis of RC high-rise buildings, Engineering Structures 29, 2007, p. 31973209.

5. Lee et al, Evaluation of seismic performance of multistory building structures based on the equivalent responses, Engineering Structures 28, 2006, p. 837856.

6. Zou and Chan, Optimal seismic performance-based design of reinforced concrete buildings using nonlinear pushover analysis, Engineering Structures 27, 2005, p. 12891302.