Seismic fragility functions for lightly reinforced concrete columns according to failure modes

The aim of this study is to develop seismic fragility functions for lightly reinforced concrete (RC) columns according to column failure mode. Four different damage states ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>D</mml:mi> <mml:mi>S</mml:mi> </mml:mrow> <mml:mn>1</mml:mn> </mml:msub> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>D</mml:mi> <mml:mi>S</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>D</mml:mi> <mml:mi>S</mml:mi> </mml:mrow> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>D</mml:mi> <mml:mi>S</mml:mi> </mml:mrow> <mml:mn>4</mml:mn> </mml:msub> </mml:mrow> </mml:math> ) are considered when developing seismic fragility functions. In addition, to readily calculate the fragility of the columns, empirical equations computing the central and dispersion values of drift ratios associated with individual damage states are proposed based on a database containing the test data of 193 lightly reinforced concrete columns. Because it is observed that column property variables and column failure mode distinctively affect fragility curves, they are explicitly considered in the proposed equations. The PSO algorithm was used to determine the coefficients of the proposed equations to improve accuracy. It is shown that the seismic fragility curves of the columns are accurately predicted with the proposed empirical equations.