كليدواژه :
شاخص شدت و شاخص تقاضا , سطوح خطر زلزله , سطوح عملكرد , مقدار ميانه ظرفيت فروريزش
چكيده فارسي :
به‌منظور تعيين و پيش‌بيني ميزان خسارت وارد برسازه‌ها استانداردهاي مبتني بر عملكرد، سطوح و حدود مشخصي را ارائه نموده‌اند. هدف از تحقيق حاضر ارزيابي اين سطوح، با استفاده از مقايسه‌ي شاخص‌هاي تقاضاي لرزه‌اي (DM) و شاخص شدت (IM)، و همچنين بررسي نحوه‌ي عملكرد مباحث ششم و دهم از مقررات ملي و استاندارد 2800 در محدود نمودن خسارت وارد برسازه‌ها است. بدين منظور با طراحي دو قاب خمشي فولادي ويژه ده و بيست طبقه و مدل‌سازي آن‌ها در نرم‌افزار OpenSees و انجام تحليل ديناميكي افزايشي IDA با استفاده از ركوردهاي معرفي‌شده توسط NGA براي حوزه‌هاي دور و نزديك، منحني‌هاي شكنندگي فروريزش قاب‌ها در سه سطح عملكردي IO،CP و GI رسم شده است. در ادامه با استفاده از منحني‌هاي مزبور مقادير احتمال متناظر با وقوع فرا گذشت قاب‌هاي موردمطالعه از 3 سطح خطر با دوره‌هاي بازگشت 75، 475 و 2475 ساله به‌دست‌آمده و به ارزيابي و مقايسه‌ي خسارت وارد بر اين قاب‌ها پرداخته‌شده است. نتايج اين تحقيق نشان مي‌دهد به‌طوركلي قاب‌هاي خمشي ويژه موردمطالعه تحت اثر ركوردهاي حوزه دور و نزديك در سطوح عملكردي IO، CP و GI، ايمن بوده و بنابراين هدف آيين‌نامه‌هاي بارگذاري و طراحي لرزه‌اي تأمين‌شده است و بيشترين ضريب اطمينان را قاب ده طبقه و تحت اثر ركوردهاي حوزه دور و كمترين ضريب اطمينان را سازه بيست طبقه و تحت اثر ركوردهاي حوزه نزديك دارد كه اين موضوع، علاوه بر ارائه تأثير افزايش ارتفاع سازه بر احتمال فروريزش سازه‌ها، به‌وضوح اثر ركوردهاي حوزه نزديك را نيز نشان مي‌دهد.
چكيده لاتين :
In order to determine and predict the possible damage imposed on the structures, performance-based standards have presented certain levels and limits. The current study aimed to make a probabilistic evaluation of the process of the special steel moment frames exceeding these levels through comparing the demand measure (DM) and the intensity measure (IM). It further tried to examine the performance of the sixth and tenth issues of the national regulations and standard 2800 in confining the damage imposed on this type of structure. The results of DM probabilities analysis based on IM parameter could be expressed in two ways: 1) the fragility curve of the probability exceeding the limit states, and 2) assessment of the probability of the mean annual exceeding the limit states. Among numerous types of limit states, the global collapse of the structure is of utmost significance. The present study utilized both forms of this analysis. In the first phase of the research, cumulative distribution function curves (CDF) were used to assess the performance of the structures subjected to the records of various risk levels according to FEMA-350 guideline. To this end, a ten-story and a twenty-story special steel moment frame were modeled in OpenSees software. Then, fragility curves of frames collapse were drawn at three performance levels of immediate occupancy (IO), collapse prevention (CP), and global instability (GI) through using the incremental dynamic analysis (IDA) by means of the records introduced in The Next Generation Attenuation (NGA) for near and far fault records. Then, in the second phase of the study, the collapse probability of the structures under the study was estimated for Tehran city, which is located at a high seismicity zone. It is worth noting that these structures were designed and loaded according to the existing guidelines and were considered at the risk level 2 (risk level 2 according to the FEMA 356 and 360 guidelines) under the influence of the earthquake, Moreover, the median collapse capacity intensity (S ̂_CT) was calculated indicating the acceleration in which the structure collapse probability equals to 50%. Finally, the aforementioned curves were used and the probability values corresponding to the exceeding occurrence of the frames under the study were obtained from three risk levels with the return periods of 75, 475 and 2475 years old and the damage imposed on these frames were assessed and compared. The findings indicated that the special moment frames influenced by the far and near faults records were safe at the performance levels of IO, CP, and GI and hence, the purpose of the seismic designing and loading guidelines was fulfilled. The highest certainty coefficient belonged to the ten-story frame under the influence of far fault records and the lowest certainty coefficient belonged to the twenty-story structure under the influence of near fault records. This clearly demonstrated the influence of increasing the structure height on the collapse probability of the structures and the impact of near fault records. avbsbsb nncj nzzka naakk anaak kxlcl llajsj lsppddi aappais ppwwieu pkakanlssppd plssldj. opqpqqnznz llkksnx xm..nxmla l;aa;a ncmckc.
