ABSTRACT
ABSTRACT: A relatively simple approach for the probabilistic seismic performance assessment of building structures has been proposed. It combines the SAC-FEMA method, which is a part of the broader PEER probabilistic framework and enables probability assessment in closed form, with the N2 method. The N2 method, which has been implemented in Eurocode 8, is based on nonlinear pushover analysis and inelastic response spectra. The most demanding part of the PEER probabilistic framework, i.e. the Incremental Dynamic Analysis (IDA), is replaced by the much simpler Incremental N2 (IN2) analysis. Predetermined default values for dispersion measures are needed for the practical implementation of this approach. In the paper, this simplified approach is summarized and applied to two variants of a four storey reinforced concrete frame: a bare frame and the frame with masonry infill with openings. Both structures, representing old building not designed for earthquake resistance, were pseudo-dynamically tested in full-scale in the ELSA laboratory in ISPRA. The most common analytical modeling technique, which employs compressive diagonal struts for modeling of masonry infill, and one-component lumped plasticity elements for modeling the flexural behavior of beams and columns, was applied. The mathematical models were validated by comparing the results of nonlinear dynamic analyses with test results. The probabilities of exceedance of the near collapse limit state are estimated and discussed. The results of analyses indicate that the infills can completely change the distribution of damage throughout the structure. The probability of failure of the infilled frame is smaller than that of the bare frame. As expected, it is larger than acceptable for both structures.
One of the methods developed for the seismic risk evaluation of structures is the SACFEMA method, which enables probability assessment in closed form (Cornell et al. 2002), and represents a part of a broader PEER probabilistic framework (Deierlein 2004). Within the framework of SAC-FEMA method, the relationship between the seismic intensity measure and the engineering demand parameter is usually determined by Incremental Dynamic Analysis (IDA) developed by Vamvatsikos & Cornell (2002). IDA is a powerful tool for estimation of seismic demand and capacity for multiple levels of intensity. However, it requires a large number of inelastic time-history analyses (and corresponding detailed data on ground motion time-histories and hysteretic behavior of structural elements) and is thus very time-consuming. Often it is possible to create summarized IDA curves with less input data, with less effort, but with still acceptable accuracy. One possible approach is to determine seismic demand for multiple levels
