تحليل ديناميكي غيرخطي افزايشي قاب هاي فولادي با مهاربندهاي كمانش‌تاب ‌برون‌محور تحت ركوردهاي نزديك گسل

Incremental Inelastic Dynamic Analysis of a Buckling-Restrained Braced Frames in Eccentric Configuration Subjected To Near Fault Earthquakes Records

در سيستم هاي مهاربندي كمانشتاب، تسليم هسته‌ي فولادي به كشش و فشار به جذب مقادير بالايي از انرژي كمك ميكند. پيكربندي متداول اين سيستم ها هم‌محور است، با استفاده از تيرهاي شكل پذير وصله‌شده به همراه مهاربندي كمانش تاب با پيكربندي برون‌محور مي توان هم از مزاياي معماري مهاربندي برون‌محور و هم از مزاياي طراحي مهاربندهاي كمانش تاب بهره برد. هدف اين نوشتار، ارزيابي و مقايسه‌ي عملكرد ديناميكي سيستم مهاربندي برون‌محور متداول و مهاربندي كمانش‌تاب با پيكربندي برون‌محور تحت اثر ركوردهاي حوزه‌ي دور و نزديك است. بدين منظور تحليل ديناميكي غيرخطي افزايشي قاب‌هاي دوبعدي با طول دهانه و تعداد طبقات مختلف انجام و پارامترهايي مختلف براي دو سيستم مهاربندي تعيين شده است. نتايج نشان ميدهد كه سيستم مهاربندي كمانش‌تاب برونمحور در مناطقي با لرزهخيزي بالا و در نزديكي گسل هاي لرزه زا نسبت به سيستم مهاربندي برون‌محور متداول عملكرد بهتري از خود نشان مي دهد.

Near-fault earthquakes have different properties compared to far-fault earthquakes because of forward-directivity, long-period pulses and fling-step motion. Near-fault ground motion can cause extensive structural damage compared to far-fault ground motion. The concentration of energy at short intervals and in pulses of near-fault ground motion causes impulsive movement. Application of systems with high ductility and energy absorption subjected to near-fault earthquakes is inevitable. In the buckling-restrained braced frames, yielding of steel core, either in tension or compression, helps to absorb the high magnitude of energy. The usual configuration of these systems is concentric. Application of ductile beam splices and buckling-restrained braces in eccentric configurations makes it possible to use the architectural benefits of eccentrically braced frames and also the design benefits of buckling-restrained braced frames. In this bracing system, brace elements provide the lateral stiffness of steel frames and are designed to undergo large inelastic axial deformations. Link beams should remain elastic, while transferring ultimate brace forces into the columns. In addition to the properties of the eccentric buckling-restrained frames, such as appropriate dynamic performance and ductility ratio, the system has the capability to be easily repaired after an earthquake because the structural damage is concentrated in the braces and not in the link beam. Evaluation and comparison of the dynamic performance of these eccentrically braced frames and buckling-restrained braced frames subject to near-fault and far-fault ground motion is the aim of this thesis. To reach the objective, incremental inelastic dynamic analyses of 2D frames with different heights and length of span are performed, and parameters, such as average maximum inter story drift, input energy and limit states, from the incremental dynamic analysis curves for both bracing systems are compared. Results indicate that eccentric buckling restrained braced frames for high seismic regions and subject to near-fault ground motion have better dynamic performance compared to eccentrically braced frames.