Pushover-Based Seismic Capacity Evaluation of Uto City Hall Damaged by the 2016 Kumamoto Earthquake

Abstract

The seismic capacity of the main Uto City Hall building, which was severely damaged by the 2016 Kumamoto Earthquake, was evaluated by the proposed pushover-based procedure. In this procedure, the seismic capacity index of the building is defined as the maximum scaling factor of the seismic input, for which the local responses do not exceed their limit values. From the pushover analysis result, the displacement limit of the equivalent single-degree-of-freedom model was determined. Then, the seismic capacity index was evaluated using an equivalent linearization technique. The evaluated index was re-evaluated by considering the bidirectional excitation. The pushover analysis result revealed that the torsional response is significant in the nonlinear behavior of this building. The evaluated seismic capacity implied that some structural damages, including the yielding of the beam-column joint, may have occurred during the first earthquake on 14 April 2016.Buildings 2019, 9, 140 2 of 37 the nonlinear seismic behavior of buildings. In recent years, the author and other researchers have worked to extend these simplified procedures and improve the seismic performance estimates of buildings with plan and/or elevation irregularities [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].These extended simplified procedures have been verified by comparison to nonlinear dynamic analysis results. However, it is challenging to verify them using existing irregular buildings that were damaged during an actual seismic event. Therefore, verifying these simplified procedures by considering the main Uto City Hall building is an important benchmark of their ability. Brief Review of Related StudiesThe author has determined that there are four possible approaches toward predicting the peak response of an asymmetric building with consideration given to the torsional effects. The first one is the extended N2 method [10][11][12][13][14]; the second one is a modal pushover analysis [15][16][17][18][19][20][21][22]; the third one consists of combining two pushover analyses and the envelope of the results, as proposed by Bosco et al. [23,24]; the fourth one consists of combining the analyses of two independently equivalent SDOF models (representing the first and second modes) with the envelope of four pushover analyses (including the effect of bidirectional excitation) [25][26][27][28][29].The first approach, namely, the extended N2 method, is an extended version of the simplified procedure proposed by Fajfar and Fischinger [4]. This approach involves the estimation of the peak response for each frame in the pushover analysis results multiplied by a correction factor, which is defined using the linear dynamic analysis and pushover analysis results [10][11][12][13].The second approach, namely, modal pushover analysis (MPA), was proposed by Chopra and Goel for regular buildings and considers the effect of higher modes. Subsequently, this approach was extended to asymmetric buildings [15]. Then, it was extended further ...

Predicting Maximum and Cumulative Response of A Base-isolated Building Using Pushover Analysis

“…The pushover analysis of the N-story base-isolated frame building model is carried out by considering the change in the first mode's shape at each nonlinear stage. Displacement-based mode-adaptive pushover (DB-MAP) analysis is applied [27,28]. Then, the nonlinear equivalent-acceleration-equivalentdisplacement (A 1 * -D 1 * ) relationship of the equivalent SDOF model is determined based on the pushover analysis results.…”

Prediction of the Maximum Seismic Member Force in a Superstructure of a Base-Isolated Frame Building by Using Pushover Analysis

“…The two buildings are modelled as three-dimensional spatial frames, wherein the floor diaphragms are assumed to be rigid in their own planes without out-of-plane stiffness. For numerical analyses, the nonlinear analysis program for spatial frames developed by the author in a previous study [24] is upgraded for the base-isolated buildings. The beams are modelled as an elastic line element with a rigid zone at each end and a length assumed as half the depth of the intersected column minus one-fourth the depth of the considered beam.…”

“…Carry out the pushover analysis of the base-isolated frame building model considering the change in the first mode's shape at each nonlinear stage. Displacement-based mode-adaptive pushover (DB-MAP) analysis [24,29] φ at each loading step: Note that this procedure is based on the procedure proposed by Kuramoto [28] for traditional reinforced concrete moment-resisting frame building structures. The outline of the calculation is:…”

“…The procedure for a set of pushover analyses is described as follows. Note that the basic idea of a set of pushover analyses herein is the same as mode-adaptive bidirectional pushover analysis (MABPA) proposed previously by the author [24,29] for the consideration of combination of bidirectional excitation. 1.…”

“…Carry out the pushover analysis of the base-isolated frame building model considering the change in the first mode's shape at each nonlinear stage. Displacement-based mode-adaptive pushover (DB-MAP) analysis [24,29] is adopted. The first mode vector at each loading step n, n Γ 1n ϕ 1 , is calculated assuming that the displacement vector at each loading step, n d, is proportional to the first-mode vector n Γ 1n ϕ 1 at each loading step:…”