Determining the effective level of outrigger in preventing collapse of tall buildings by IDA with an alternative damage measure

Abstract Outrigger and belt truss have been successfully applied in reducing the lateral displacement of tall buildings under wind and earthquake conditions. Limited number of researches that have considered the inelastic seismic behavior of tall buildings with braced core-outrigger system, have just examined outrigger efficiency in reduction of drift or core moment and have not studied its efficiency in preventing “collapse” of tall buildings under severe earthquakes. This paper presents the results of an analytical study on the capability and effective level of outrigger in preventing collapse of tall buildings with braced core system during two sets of far and near field earthquakes. Results of NLTHA showed that tall buildings with braced core consisting of stronger braces, designed in accordance with UBC97, will collapse under severe near-field records as a result of failure of their columns. Similar buildings with either optimized braces, designed according to AISC341-16, or RC shear wall core could survive same earthquakes. Various levels were examined for the outrigger location along building height to prevent their collapse. By performing the incremental dynamic analysis on the studied structural models, the achieved enhancement due to the outrigger addition was investigated. A new damage measure was proposed to be used in IDA that can describe the point of structural collapse, more precisely. It was observed that in order to successfully prevent the collapse of studied structures under severe near-field records, two outriggers must be used, one at the second story and the other at about 0.14 height of structure.