COMPARATIVE STUDY ON THE SEISMIC RETROFIT OF A MID‐RISE STEEL BUILDING: STEEL BRACING VS ENERGY DISSIPATION

Abstract

The paper presents a comparative study of an existing retrofit for a mid-rise steel building using additional stiff steel braced-frames against an alternate retrofit using ADAS (Added Damping and Stiffness) passive energy dissipation devices. The subject building, located near Alameda Park in downtown Mexico City, is a ten-storey office building that was built in the 1950s. The structure was damaged during the 1985 Michoacan Earthquake because of resonant response with the site. The building was later retrofitted using additional braced frames according to the seismic provisions of Mexico's 1987 Federal District Code. The retrofit scheme was planned to take the structure away from resonant responses and to inhibit structural damage. A proposed upgrade using ADAS energy dissipation devices was studied to compare energy dissipation against traditional stiffening using steel braces as retrofit options for mid-rise buildings in Mexico City's lake-bed zone. Different sets of analyses were carried out to compare both alternatives: (a) three-dimensional elastic analyses; (b) limit analyses and; (c) nonlinear dynamic analyses for postulated site ground motions for a M 5 = 8.1 earthquake. Initial costs of the retrofit schemes were also studied. The comparative studies suggest that a retrofit using ADAS devices would have a better dynamic performance than the one using steel braces. However, the steel bracing retrofit provides more strength and its initial cost of retrofit is less than that of the ADAS retrofit.