روش انرژي تعميم‌يافته جهت برآورد پاسخ قاب‌هاي خمشي فولادي تحت تحريك لرزه‌يي

Modified Energy Method for Evaluation of Steel Moment-Resisting Frame Response under Seismic Excitation

براساس نوع نگرشي كه به حركت لرزه‌يي زمين مي‌توان داشت، روش‌هاي طراحي لرزه‌يي سازه‌ها متفاوت مي‌شوند. يكي از اين روش‌ها كه بر پايه‌ي تحليل غير خطي سازه‌هاست، از ديدگاه انرژي به زلزله شكل مي‌گيرد. با توجه به ضعف‌هايي كه در روش‌هاي ديگر طراحي از جمله: روش نيرو و جابجايي وجود دارد، به‌نظر مي‌رسد كه در آينده‌ي نزديك روش انرژي با رشد و تكامل مناسب جايگزين تمامي روش‌هاي فعلي طراحي لرزه‌يي سازه‌ها شود. در اين مطالعه، دقت اين روش در تخمين نياز تغييرمكاني قاب‌هاي خمشي تحت ركوردهايي با خصوصيات نزديك و دور از گسل بررسي مي‌شود. با توجه به تاثيرگذاري طيف سرعت ركورد در ميزان انرژي انتقالي از زمين به سازه، در ابتدا خصوصيات طيف سرعت ركوردهاي دور و نزديك گسل بررسي مي‌شوند. با انجام اين بررسي‌ها، راهكاري وابسته به شدت طيفي (SI) جهت تخمين دقيق‌تري از انرژي انتقالي ركورد پيشنهاد شده است. در پايان با بررسي دقت اين راهكار مشاهده مي‌شود كه به‌كارگيري آن در افزايش دقت نتايج تاثير قابل توجهي دارد.

From the viewpoints of the building response to the seismic ground motions, there are different seismic design methodologies. Currently seismic design codes are based on force method. However, disadvantages of this method in neglecting important parameters including structure vulnerability potential as well as characteristics of strong motions cause improper performance of structures in past catastrophic earthquakes. Thus, the seismic design methodology shifted to nonlinear methods based on performance concepts. Consequently, new methods based on displacement were proposed in the recent years for better evaluation of structural performance. Due to the inherent weaknesses such as dependency accuracy to ground motion characteristics incorporated in these design methods, it is expected that the energy method will advance and supersede the current structural seismic design methods. Since the damage value caused by an earthquake to a structure is in close relationship with the energy dissipation capacity of the structure, it can be anticipated that the energy based method will be a proper technique for evaluation of performance structure. In this study, the accuracy of the energy-based method in predicting displacement demand of steel moment resisting frames of different storey numbers under near-field and far-field earthquake records is studied. To capture accuracy of the energy-based method, the obtained results have been compared with the results of the non-linear time-history analysis. Taking into account the amount of energy transformed from ground to structures has directed correlation to spectrum velocity, its characteristics for near and far-field records are studied first. A new method which depends on spectrum intensity (SI) is proposed for more accurate prediction of energy transferred from earthquake record to the structures. Finally, by examining the accuracy of this method, it is observed that the proposed method in predicting displacement demand of frames can significantly increase the result accuracy for any type of seismic excitation.