سازه بتنی مسلح در معرض زلزله و سونامی پشت سر هم
Abstract
1- Introduction
2- Case-study application
3- Results and discussion
4- Conclusions
References
Abstract
Many coastal regions lying on subduction zones are likely to experience the catastrophic effects of cascading earthquake and tsunami observed in recent events, e.g., 2011 Tohoku Earthquake and Tsunami. The influence of earthquake on the response of the structure to tsunami is difficult to quantify through damage observations from past events, since they only provide information on the combined effects of both perils. Hence, the use of analytical methodologies is fundamental. This paper investigates the response of a reinforced concrete frame subjected to realistic ground motion and tsunami inundation time histories that have been simulated considering a seismic source representative of the M9 2011 Tohoku earthquake event. The structure is analysed via nonlinear time-history analyses under (a) tsunami inundation only and (b) earthquake ground motion and tsunami inundation in sequence. Comparison of these analyses shows that there is a small impact of the preceding earthquake ground shaking on the tsunami fragility. The fragility curves constructed for the cascading hazards show less than 15% reduction in the median estimate of tsunami capacity compared to the fragility functions for tsunami only. This outcome reflects the fundamentally different response of the structure to the two perils: while the ground motion response of the structure is governed by its strength, ductility and stiffness, the tsunami performance of the structure is dominated by its strength. It is found that the ground shaking influences the tsunami displacement response of the considered structure due to the stiffness degradation induced in the ground motion cyclic response, but this effect decreases with increasing tsunami force.
Introduction
Tsunami have contributed to 250,125 deaths between 1994 and 2013 [1]. They are the deadliest natural hazard, with an average of 79 deaths for every 1000 people affected, compared to four deaths per 1000 for other natural hazards. Past tsunami have caused widespread damage and economic losses, with a direct loss of US$211 billion being estimated for the 2011 Tohoku event alone [2]. Exposure to this hazard is high, as 6 out of the 10 most populous megacities are at risk of being severely affected by storm surge and tsunami [3]. Moreover, regions at highest risk lie on subduction zones around the Pacific “Ring of Fire” (e.g., Japan, Indonesia, Pacific Northwest), and hence are likely to experience strong ground shaking as well as tsunami inundation [4]. An important component in the evaluation of tsunami impact or risk is the estimation of building response due to tsunami onshore flow. To date the majority of research on this topic has focussed on the development of fragility functions based on post-tsunami damage observed at a given location, so-called “empirical fragility functions”, e.g. Suppasri et al. [5] among many others. Empirical tsunami fragility functions are by their nature specific to the event represented in the post-event damage data as well as the local building stock, and are limited by the typical absence of locally recorded tsunami intensity measures, such as the flow velocity. They commonly adopt building damage observations from locations that have been affected by both earthquake and tsunami hazards, implicitly including the response of buildings to the combined hazards. Assessment of structural performance through numerical analyses is therefore essential to overcome these limitations. Analytical fragility functions are therefore needed to complement empirical assessments for a physical understanding of structural behaviour under cascading earthquake and tsunami.