COLLAPSE SEISMIC RISK ASSESSMENT FOR IRREGULAR MID-RISE BUILDINGS

Mid-rise buildings, which may be used as office or apartment buildings, are very common structures in urban areas. Because these buildings are usually heavily populated, the casualty caused by the collapse of these structures in an earthquake could not be overestimated. Therefore, developing a suitable assessment method to identify these buildings with high collapse risk is an important issue. This paper presents a probabilistic assessment method, which involves nonlinear response-history analysis together with incremental dynamic analysis (IDA), to assess the collapse risk of a mid-rise building, so high-risk buildings and their damage patterns can be identified. This methodology is developed based on the procedure of collapse fragility analysis proposed by FEMA P-58, while the local and damage global criteria that define collapse failure are adopted from ASCE 41-13 and PEER-TBI, respectively. Finally, for demonstration, the proposed procedure is applied to assess the collapse risk of a mid-rise RC building that collapsed in a major earthquake occurred in Taiwan, 2016.

Incremental dynamic analysis of the long-span continuous beam bridge considering the fluctuating frictional force of rubber bearing

In the seismic design of long-span bridges, the classic bi-linear model was used to simulate the frictional restoring force of the rubber bearings. However, in actual earthquake, the rubber bearing suffered fluctuating axial pressure in earthquake, even separated from the beam when vertical component of the earthquake was too strong. Employing the bi-linear model for the bearing may incorrectly estimate the seismic response of the bearings, as well as the whole bridge. This paper developed a nonlinear frictional bearing model, which can consider the variation of the frictional restoring force in the bearings, even the separation with the beam in vertical directions. A typical continuous beam bridge was modeled in ABAQUS, and incremental dynamic analysis was conducted for the quantitative comparison of the seismic responses using different bearing models. The intensity measure was selected as the ratio of the peak ground acceleration (PGA) in the vertical direction to the PGA in the horizontal direction. The analysis results indicated that the different bearing model led to the significant different seismic response for the bearings and piers, even the vertical component was small. The bi-linear bearing model would underestimate the seismic demand of the bearing and piers.

Bidirectional Energy-based Pushover Procedure as a Fast Approach to Establish Approximate IDA Curves under Biaxial Seismic Excitations: An Evaluation for Medium- and High-rise Buildings

Bidirectional energy-based pushover (BEP) procedure is expanded in this paper to predict approximate incremental dynamic analysis (IDA) results of medium- and high-rise structures. BEP is a unique approach in the sense that it provides approximate IDA curves under the simultaneous effect of two horizontal components of ground motions and is applicable to both symmetric- and asymmetric-plan buildings. The method has already proved to be useful in low-rise buildings, and this study aims to evaluate its suitability for mid- and high-rise structures. Six structural models were considered in this evaluation in two groups of 9- and 20-story buildings, with each group consisting of a symmetric, a one-way asymmetric, and a two-way asymmetric-plan building. The results revealed that the method was sufficiently accurate to provide approximate IDA curves for all structural models. The method had similar accuracy in the asymmetric models as it did in the symmetric models, although the accuracy slightly decreased as the height of the building increased. BEP also provided good estimates of the demands in both ‘flexible’ and ‘stiff sides’ of the asymmetric buildings as well as the demands over the height of the buildings.