Behaviour of steel special moment resisting frame buildings designed using current Indian code

Abstract

Seismic design codes recommend Force-Based Design method for design of Steel Special Moment Resisting Frame (SMRF) buildings. FBD relies on capacity design principles to contain inelastic action primarily in beams in SMRFs during strong earthquake shaking. Therefore, in line with the strength hierarchy required in capacity design, seismic design codes recommend guidelines/procedures for the design of capacity-protected components (such as connections, panel zones, and columns) in SMRFs. Although, the intent of the recommended procedures is same across various seismic design codes in this regard, few critical differences persist between the procedures outlined in Indian seismic design code and other seismic design codes (more specifically, the American and the European ones). The key differences are: (a) in recognising the expected increase in material yield stress from the minimum specified, or characteristic, yield strength of the material, (b) in estimating the demand on and the capacity of panel zones, and (c) in recommending a minimum column to beam strength ratio (CBSR) for the design of columns in SMRFs. To assess the implication of the identified critical differences, two buildings, a 3-storey and a 9-storey with steel SMRFs, are designed compliant to the Indian code; then, the performance of the two buildings is evaluated using nonlinear static and dynamic analyses. The performance assessment of the designed buildings indicates undesirable behaviour wherein conventional expectation of resisting strong earthquake ground motion through ductile flexural plastic hinge formation at the beam ends is not realised. Finally, the two buildings are redesigned to account for the three issues mentioned above. The redesigned buildings are seen to demonstrate acceptable earthquake behaviour. Hence, a need is perceived to update the seismic design provisions of the current Indian code for steel SMRFs to ensure acceptable behaviour of such buildings during earthquake shaking.