A Modal Pushover Analysis Procedure Using Adaptive Load Distribution
摘要
This study aims to extend the modal pushover analysis (MPA) procedure to the displacement based adaptive modal pushover analysis (A-MPA) procedure by integrating the concept of the modal pushover analysis procedure advocated by (Chopra and Goel, 2002), the displacement-based adaptive pushover procedure introduced by (Antoniou and Pinho, 2004), and the proposed iterative procedure developed herein to determine the target displacement (the peak roof displacement). In this study, to consider the effect of structural yielding on the lateral load distributions in relation to the mode shapes, the MPA procedure is modified by using a variant (adaptive) load distribution for the significant modes. The iterative procedure proposed here to determine the target displacement significantly reduces the computational demand compared to other adaptive procedures that necessitate a preliminary adaptive pushover analysis, assuming constant spectral displacement or repeating adaptive pushover analysis multiple times, as is the case for the adaptive modal combination (AMC), variant of modal pushover analysis (VMPA) and multi-mode adaptive pushover analysis (MADP) procedures, respectively. It utilizes only the nth mode pushover curve, and either the equation of motion for the nth mode inelastic single-degree-of-freedom (SDF) system or the inelastic response (or design) spectrum to determine the target displacement iteratively. A comparative evaluation of adaptive MPA (A-MPA) and MPA procedures in estimating seismic demands for a 9-story steel building is conducted, considering eleven different ground motions with six ground motion multipliers applied to each, resulting in a total of 66 ground motions. This analysis is performed in conjunction with a rigorous non-linear response history analysis (non-linear RHA). It is concluded that the A-MPA procedure demonstrates superior performance compared to the MPA procedure in estimating the seismic demands of story drifts and plastic hinges of the structure, particularly in the upper half of the frame. Furthermore, the fundamental mode has a relatively minor impact; instead, it is the contributions from the higher modes that create a notable difference between the two procedures.