DIRECT ESTIMATION OF THE SEISMIC DEMAND AND CAPACITY OF MDOF SYSTEMS THROUGH INCREMENTAL DYNAMIC ANALYSIS OF AN SDOF APPROXIMATION

Introducing a fast and accurate method to estimate the seismic demand and capacity of first-mode-dominated multi-degree-of-freedom systems in regions ranging from nearelastic 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 multi-degree-of-freedom system with a single-degree-of-freedom oscillator whose backbone matches the structure’s 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 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 limit-states such as immediate occupancy or global dynamic instability. Using three multistory buildings as case studies, the methodology is favorably compared to the full IDA. CE Database keywords: Nonlinear analysis; Static analysis; Dynamic analysis; Seismic response; Earthquakes; Performance evaluation; Buildings, multistory; Approximation methods.