Direct Estimation of Seismic Demand and Capacity of Multidegree-of-Freedom Systems through Incremental Dynamic Analysis of Single Degree of Freedom Approximation

Introducing a fast and accurate method to estimate the seismic demand and capacity of first-mode-dominated multidegree-of-freedom systems in regions ranging from near-elastic to global collapse. This is made possible by exploiting the connection between the static pushover (SPO) and the incremental dynamic analysis (IDA). While the computer-intensive IDA would require several nonlinear dynamic analyses under multiple suitably scaled ground motion records, the simpler SPO helps approximate the multidegree-of-freedom system with a single-degree-of-freedom oscillator whose backbone matches the structureʹs SPO curve far beyond its peak. Similar methodologies exist but they usually employ oscillators with a bilinear backbone. In contrast, the empirical equations implemented in the static pushover 2 incremental dynamic analysis (SPO2IDA) software allow the use of a complex quadrilinear backbone shape. Thus, the entire summarized IDA curves of the resulting system are effortlessly generated, enabling an engineer-user to obtain accurate estimates of seismic demands and capacities for limitstates such as immediate occupancy or global dynamic instability. Using three multistory buildings as case studies, the methodology is favorably compared to the full IDA.