In this article, the fragility of reinforced concrete and steel structures in Bucharest, a city of high seismic hazard, designed using the recent building codes in Romania, is assessed. A total of 24 reinforced concrete and steel structures with heights varying from five stories to 13 stories were analyzed. Their seismic fragility was evaluated using two procedures from the literature. In the first procedure (SPO2FRAG), the fragility was derived based on the pushover curves using the SPO2IDA algorithm, while in the second procedure (FRACAS), the fragility was derived from nonlinear time-history analyses. The analyzed structures were designed for three levels of peak ground accelerations, corresponding to mean return periods of 100, 225, and 475 years. Subsequently, the damage assessment of the analyzed structures was performed using ground motions generated from a Monte-Carlo simulated earthquake catalogue for the Vrancea intermediate-depth seismic source. The damage degrees that were estimated using the SPO2FRAG approach are higher than those estimated using the FRACAS approach. The life-cycle analysis of the structures shows that a further increase of the design peak ground acceleration for Bucharest is feasible from an economic point of view using the SPO2FRAG results. However, based on the FRACAS results, the opposite conclusion can be drawn. Finally, generic lognormal fragility functions are proposed as a function of building height and structural system.
During earthquakes, a structure may undergo torsional effects even if it is perfectly symmetrical. One of the causes is that seismic waves do not arrive in‐phase in each point of the infrastructure. Moreover, there are always eccentricities between the mass centre, where the seismic forces are considered to be acting, and the stiffness centre, around which the building rotates, this contributing as well to the occurrence of torsional effects. These eccentricities are generated by asymmetries of the structure itself, position of non‐structural elements, asymmetrically applied loading or other factors. Seismic design codes usually take into account torsional effects by means of an equivalent eccentricity that is added to the actual distance between the centres of mass and stiffness. In ordinary design, to analyse the behaviour of a structure subjected to seismic actions, when establishing the mass of the building, a fraction of the variable loads is considered to be uniformly distributed on each floor. This obviously does not happen in reality. The present paper focuses on estimating the limits of the possible actual variation of internal forces in structural members caused by torsional effects. To this aim, two eccentrically braced steel structures were considered. In each case, the variable loads were redistributed in the plan of the building according to different loading schemes, but keeping their total amount constant, equal to the value corresponding to the uniform arrangement on each floor.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.