Effect Of Soil-structure Interaction On Torsional Irregularity In A Multistorey Building: An Etabs Response-spectrum Study

Abstract

Soil-structure Interaction (SSI) Modifies The Effective Boundary Conditions Of Multistorey Buildings Through Foundation Translation, Rocking And Torsional Flexibility. These Effects Are Especially Important In Plan-irregular Reinforced-concrete Buildings, Where Eccentricity Between The Centres Of Mass And Rigidity Produces Coupled Lateral-torsional Response. This Paper Evaluates The Seismic And Torsional Behaviour Of An Irregular Multistorey RC Building Using Three-dimensional ETABS Modal And Response-spectrum Analysis In Accordance With IS 1893 (Part 1): 2016. Three Result Sets Identified In The Source Report As Hard-, Medium- And Soft-soil Spectrum Cases Are Compared Without Altering The Reported Values. Maximum Storey Displacement Increases From 36.065 Mm To 53.793 Mm And 70.296 Mm, While Maximum Storey Drift Increases From 0.000417 To 0.000621 And 0.000811. Maximum Storey Shear Rises From 3393.381 KN To 4475.290 KN And 5495.392 KN. Governing Torsional Irregularity Ratios Remain Nearly Unity In The X Direction But Increase From 1.235 To 1.267 In The Y Direction, Indicating Directional Torsional Irregularity And A Governing Soft-soil Case. The Paper Also Identifies An Inconsistency Between The Stated Seismic Weight And Reported Base Shear. Results Are Interpreted As Soil-spectrum-dependent Outputs Because Verified Foundation-spring Assignments And Matched Fixed-base/SSI Models Are Unavailable. The Study Provides A Transparent Framework For Future SSI Verification And Torsional Assessment.

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