ارزيابي عملكرد روش هاي فرم و مونت كارلو در محاسبه احتمال خرابي لغزشي سد بتني وزني تحت بارهاي استاتيكي

Performance Evaluation of Monte Carlo Simulation and FORM Method to Calculate Probability of Failure for Concrete Gravity Dams in Sliding Failure Mode under Static Loading

بدون شك خرابي يك سد بتني خسارات مالي و جاني جبران ناپذيري را به يك جامعه وارد خواهد كرد. در اين پژوهش با انتخاب سد بتني وزني Sariyar واقع در تركيه، بعنوان مطالعه موردي، احتمال خرابي اين سد در مود لغزشي محاسبه شده است. مهم ترين عامل در خرابي لغزشي يك سد، افزايش سطح آب مخزن بوده كه با افزايش نيروي جانبي و آپليفت، احتمال خرابي نيز افزايش خواهد يافت. لذا براي درنظر گرفتن حالات مختلف كه ممكن است براي يك سد پيش بيايد، تمامي ارتفاع هاي محتمل براي درياچه اين سد شبيه سازي شده و احتمال خرابي و شاخص قابليت اطمينان در اين حالات با استفاده از دو روش مونت كارلو و فرم بدست آمد و با يكديگر مقايسه شده است. همچنين تاثير تعداد نمونه هاي توليد شده بر پاسخ هاي بدست آمده در روش مونت كارلو نيز مورد بحث قرار گرفته است. نتايج نشان دادند روش مونت كارلو در برخي حالات كه مقاومت سيستم بسيار بيشتر از بار موجود مي باشد و تابع شرايط حدي فاصله زيادي با اجتماع نمونه ها دارد، ممكن است با هر تعداد نمونه قادر به ارائه احتمال خرابي نباشد. در اين حالات مي توان با استفاده از روش فرم، مقاديري براي شاخص قابليت اطمينان محاسبه نمود، اما مشخص شد كه اين مقادير فاصله زيادي با واقعيت خواهند داشت. با افزايش نيروهاي وارده، پاسخ هاي بدست آمده از روش مونت كارلو از دقت بالايي برخوردار خواهند بود ولي روش فرم، ميزان احتمال خرابي را كمتر از آنچه كه هست نشان خواهد داد.

Failure of a concrete gravity dam will cause unavoidable human loss and financial damages. In this study SARIYAR concrete gravity dam, located in turkey was chosen as a case study and its probability of sliding failure in various condition was studied. The most important reason in sliding failure of a concrete dam was lateral and uplift loads, caused by increase in the level of reservoir water. Different scenarios were considered in which might happen for a dam, all the possible height of reservoir water simulated. Afterward, Probability of failure and reliability index was calculated with Monte Carlo simulation and FORM method in all conditions and comparison with each other. The influence of the Number of Simulations (NOS) in the Monte Carlo method was also discussed. Results showed that, in some cases, the resistance of the system was much more than the loads and limit state function had a significant distance from samples. In such states, Monte Carlo was unable to calculate the probability of failure with each NOS but FORM method obtained the Reliability Index (β) in these situations. It became clear that these values were far from reality. With increase in the forces, responses from Monte Carlo had a high degree of precision. The probability of failure generated by FORM method was less than a reality. Failure of a concrete gravity dam will cause unavoidable human loss and financial damages. In this study SARIYAR concrete gravity dam, located in turkey was chosen as a case study and its probability of sliding failure in various condition was studied. The most important reason in sliding failure of a concrete dam was lateral and uplift loads, caused by increase in the level of reservoir water. Different scenarios were considered in which might happen for a dam, all the possible height of reservoir water simulated. Afterward, Probability of failure and reliability index was calculated with Monte Carlo simulation and FORM method in all conditions and comparison with each other. The influence of the Number of Simulations (NOS) in the Monte Carlo method was also discussed. Results showed that, in some cases, the resistance of the system was much more than the loads and limit state function had a significant distance from samples. In such states, Monte Carlo was unable to calculate the probability of failure with each NOS but FORM method obtained the Reliability Index (β) in these situations. It became clear that these values were far from reality. With increase in the forces, responses from Monte Carlo had a high degree of precision. The probability of failure generated by FORM method was less than a reality. Failure of a concrete gravity dam will cause unavoidable human loss and financial damages. In this study SARIYAR concrete gravity dam, located in turkey was chosen as a case study and its probability of sliding failure in various condition was studied. The most important reason in sliding failure of a concrete dam was lateral and uplift loads, caused by increase in the level of reservoir water.