آسيب‌پذيري لرزه‌يي ديوارهاي ساحلي كيسوني به روش احتمالاتي: مطالعه‌ي موردي (بندر كوبه)

Probabilistic Seismic Vulnerability of Caisson Quay Walls: Case Study of Kobe Port

در اين نوشتار با استفاده از تحليل‌هاي عددي غيرخطي، آسيب‌پذيري لرزه‌يي يكي از مقاطع ديوار ساحلي بندر كوبه، كه در زمين‌لرزه‌ي كوبه (1995) به علت وقوع روان‌گرايي خسارت‌هاي زيادي به آن وارد شده است، مورد بررسي قرار گرفته است. در ابتدا پاسخ عددي به‌دست‌آمده نسبت به جابه‌جايي‌هاي افقي و قايم گزارش‌شده پس از زلزله و همچنين با نتايج به‌دست‌آمده توسط ديگر پژوهشگران اعتبارسنجي شده است. سپس با تحليل‌هاي احتمالاتي، منحني‌هاي شكست براي سطوح مختلف عملكردي همچون سرويس‌پذيري، تعميرپذيري، و نزديك به واژگوني به‌دست آمده‌اند، تا احتمال خسارت براساس پارامترهاي مختلف شدت براي سطوح خسارت مذكور بررسي شود و نشان داده شده است كه در هر زمين‌لرزه، پارامترهاي مختلف لرزه‌يي، احتمال خسارت‌هاي مختلفي را به‌دست مي‌دهند و منحني شكست فقط براساس يك پارامتر خاص نمي‌تواند معرف احتمال شكست سيستم سازه‌يي باشد.

Ports and marine facilities play important roles in global transportation and commercial activities. Earthquakes can create significant damage to ports and other marine facilities because such systems commonly rely on geological units containing problematic soils. Several sections of the quay walls constructed in Kobe Port were reportedly damaged during the catastrophic Kobe 1995 earthquake. This paper deals with the seismic vulnerability of a damaged section of this port via the results of fully nonlinear numerical analyses and subsequent probabilistic analysis. Numerical analyses were carried out using the finite difference method, contributing a constitutive model capable of simulation of liquefaction occurrence. Results of the preliminary numerical analyses were compared with those observed in the field, as well as the findings of previous researchers in terms of lateral and vertical permanent displacements. This preliminary benchmark analysis provided satisfactory results in order to confirm the numerical modeling for the subsequent runs. Several subsequent analyses were then performed using many input motions recorded during different earthquakes. To investigate the seismic vulnerability of the wall subjected to several input motions, probabilistic analyses were carried out on the pool of the numerical results for evaluation of system fragility curves. Fragility curves for different levels of damage; "serviceable", "repairable", and "near collapse", were drawn, based on various intensity parameters including PGA, PGV, and Ia. It is shown that different damage probability can be obtained from various seismic parameters in every earthquake. A fragility curve based on a single intensity measure cannot appropriately represent the probability of failure in such structural-geotechnical systems. According to the results of this study, the probability of exceedence from the upper performance level, i.e. "near collapse", when PGA, PGV, and Ia are chosen as intensity measures, are 46%, 51%, and 40% percent, respectively.