Analysis of change in dynamic properties of a frame-resistant test building

Abstract

This paper introduces and employs a damage detection methodology applied specifically to frame-resistant buildings designed according to the capacity criterion. The proposed technique assesses the effectiveness of the ductile resistant mechanism, following the occurrence of an earthquake. The method is based on the observation that, for ductile frames, the damage resulting from a strong earthquake should be limited to the plastic hinge zones, typically distributed throughout the structure, according to the weak-beam/strong-column principle. This damage distribution results in negligible changes in damping and global mode shapes, but large changes in frequencies and local response. From the operational point of view, the procedure makes use of a modal characterization of the building, utilizing well-established experimental techniques, focused on both the overall behaviour of the building as well on the local behaviour of single joints, where major damage might be expected to occur. Damage evaluation is based on measured local changes in the mode shapes. Two sets of damage indexes are calculated: the first is related to the overall behaviour of the structure, while the other is related to the effectiveness of the local ductile mechanisms. In this paper, application of this methodology to a 60 per cent scale, 5-storey precast concrete test building (9.14 m by 9.14 m in plan, 11.43 m high) is presented. This building was subjected to dynamic testing before and after the application of pseudo-dynamic loads, simulating a 1.5 g PGA earthquake. The damage evaluation indicated a significant loss in stiffness of the whole structural system (of the order of 70%) and shed light on the effectiveness of the ductile resistant mechanisms. These results are consistent with the data recorded during the pseudo-dynamic test and the observed visual damage.