SEISMIC BEHAVIOR OF BUILDINGS WITH FRICTION ISOLATORS IN THE LAKEBED ZONE OF MEXICO CITY

Abstract

Historically, it has been established that using base isolation in the Lakebed Zone of Mexico City is not a feasible alternative. This is due to the existing soft soil deposits in that area and their predominant long periods of vibration. However, recent technology developments, such as friction pendulum isolators (FPI), are an interesting alternative worth to explore, which can help to improve the City's seismic resilience. In that sense, this paper explores the use of FPI on medium- and low-rise steel buildings in the Lakebed Zone of Mexico City. Three-, six- and nine-storey high models, in 2D, were studied for three different cases. Case 0, which was taken as a benchmark, corresponded to conventional fixed-base buildings (i.e. without FPI), designed to resist both gravitational loads and seismic demands. Case 1 corresponded to the same structures of Case 0, but the structures were mounted on FPI. Case 2 corresponded to the buildings of Case 1 with FPI, but their superstructure was redesigned considering gravitational loads only. The seismic behavior of the buildings was evaluated in terms of: i) maximum inter-storey drift; ii) maximum lateral displacements; iii) maximum floor velocities; iv) maximum floor accelerations; v) maximum inter-storey shear; and vi) maximum overturning moment. Twelve synthetic and two historic seismic ground motions were used for a site with a predominant period of vibration close to 2 s. They were scaled to different intensities in order to conduct incremental dynamic analysis (ADI). Finally, the probability of collapse of the studied buildings was estimated. The results indicate that the probability of collapse on isolated buildings with FPI was lower than that for conventional buildings. Advantages of using FPI in the Lakebed Zone of Mexico City are presented and discussed, while some significant differences between cases 1 and 2 were identified.