Comparative assessment of nonlinear static and dynamic methods for analysing building response under sequential earthquake and tsunami

Abstract

Summary This paper presents a comprehensive comparison of different dynamic and static approaches for assessing building performance under sequential earthquakes and tsunami. A 10‐storey reinforced concrete seismically designed Japanese vertical evacuation structure is adopted as a case study for the investigation. The case study building is first assessed under sequential earthquake and tsunami nonlinear response history analyses: the first time this is done in the literature. The resulting engineering demand parameters are then compared with those obtained when the analysis procedure is systematically simplified by substituting different static approaches for the nonlinear response history analyses in both the earthquake and tsunami loading phases. Different unloading approaches are also tested for the cases when an earthquake pushover is adopted. The results show that an earthquake nonlinear response history analysis, followed by a transient free vibration and a tsunami variable depth pushover, provides the best alternative to full dynamic analyses in terms of accuracy and computational efficiency. This structural analysis combination is recommended and has the advantage that it does not require the tsunami inundation time history to be known in advance. The proposed double pushover approach is instead deemed only suitable for the collapse assessment of regular low to mid‐rise buildings and for the development of collapse fragility functions. An important observation made is that sustained earthquake damage seems not to affect the tsunami resistance of the case study building when the fully dynamic analysis is carried out for the sequential loading. This observation will be the subject of future work.

Advances in the Assessment of Buildings Subjected to Earthquakes and Tsunami

“…In Rossetto et al (2018a), we systematically change the analysis approach used in each of the three phases involved in the assessment of structural behavior under sequential earthquakes and tsunami, namely the earthquake loading phase, unloading of the structure until at-rest condition and the tsunami loading phase. In the earthquake loading phase non-linear response history analysis (DY) was considered as well as a static nonlinear pushover (PO) with a typical lateral load distribution following the shape of the first mode response of the structure (e.g.…”

“…For brevity, in this section only the main results of the comparison of DY-TDY with DY-VHPO and PO-VHPO are presented. The reader is referred to Rossetto et al (2018a) for the complete comparison of approaches and the sensitivity analyses performed. It is highlighted that the double pushover approach (PO-VHPO), illustrated schematically in Figure 7, presents significant computational savings as compared to DY-TDY.…”

“…Else, a capacity spectrum based method, (for instance, FRACAS as described in Rossetto et al 2016), can be used to determine the structure performance point under a given earthquake ground motion or spectrum. However, in order to eliminate the effect of estimation errors in the earthquake performance point arising from, for instance, the use of a capacity spectrum based assessment, Rossetto et al (2018a) decided to stop the PO analysis when the maximum inter-storey drift ratio experienced by the structure in the corresponding DY analysis (IDRmax, DY ) was achieved in a matching floor within the structure subjected to the PO analysis. It is acknowledged that this matching procedure can lead to different estimates of the overall damage distribution on the structure (with the exception of the matched floor), as the response under dynamic excitation differs from the one under static pushover.…”

Fragility functions for a reinforced concrete structure subjected to earthquake and tsunami in sequence

“…Static analysis is performed considering an equivalent tsunami force according to design prescriptions. Rossetto et al [12] present a comprehensive comparison of several numerical analyses for a tsunami vertical evacuation building. They presented different analysis typologies that can be used to assess the response of a structure and evaluated the bias associated to each approach in predicting the structural response.…”

“…Hence, this study builds on the paper by Rossetto et al [12], and aims to assess the impact of the preceding ground motion on the tsunami response and fragility of structures. A reinforced concrete structure designed to the Japanese Seismic Codes is subjected to consistent ground motion and tsunami loads, i.e.…”