A Simplified nonlinear method for progressive collapse analysis of moment resisting frames

Abstract

The Alternate Load Path Method (APM) that is presented in several standards is the widely followed method for the assessment of progressive collapse potential. In particular, the Linear Static APM is popular since it is simple and easy to implement compared to nonlinear methods. Although nonlinear approaches can give us a wider range of structural responses, they are not widely used since they involve complex procedures. We present here a nonlinear dynamic analysis approach for the post column loss behaviour in buildings that combines the simplicity of the linear methods with the comprehensiveness of the nonlinear ones. The method involves defining a special hinge that captures the specifications of the General Services Administration (GSA) guidelines, and reduces the complexities involved in nonlinear procedures. In addition to the collapse potential, the method is able to obtain the point of collapse initiation, collapse path and final extent of collapse relatively easily. A 3D concrete moment resisting frame under the short side face middle column removal case yielded similar results to the linear APM recommended by the GSA guidelines; but the proposed method was also able to identify that failure was initiated with the double spanned beam directly over the removed column yielding in flexure and progressed upwards, finally resulting in an overall collapse of all beams on the short side face that frame into the columns vertically in line with the removed column.