كليدواژه :
تيرپيوند قائم , تغييرمكان ماندگار , زلزله حوزه نزديك گسل , زلزله حوزه دور از گسل
چكيده فارسي :
بحثي كه بين مهندسان زلزله وجود دارد اين است كه خرابي سازه اي و غيرسازه اي در ابتدا در اثر بارهاي جانبي ناشي از تحريك زلزله ايجاد مي گردد. در آيين نامه هاي آمريكا از جمله FEMA356 عملكرد سازه اي با استفاده از حداكثر تقاضاي تغيير شكل تخمين زده مي شود. در هر حال علاوه بر تغيير شكل هاي حداكثر، تغييرشكل هاي ماندگار نقش مهمي را در تعريف عملكرد سازه اي دارند و مي توانند نتايج مهمي را داشته باشند. دامنه تغييرشكل هاي ماندگار در بررسي سازهاي و اقتصادي بهسازي سازه هاي آسيب ديده، بسيار مهم مي باشند. علاوه بر اين، تغييرمكان هاي ماندگار به عنوان يكي از مهمترين پارامترها در ارزيابي ظرفيت باقي مانده سازه هاي آسيب ديده براي تحمل پس لرزه ها معرفي شده اند. در اين پژوهش تغييرمكان ماندگار يك قاب فولادي پنج طبقه كه با در نظر گرفتن تير پيوند قائم طراحي شده است، مورد بررسي قرار گرفته و تاثير طول تير پيوند قائم بر روي تغييرمكان ماندگار سازه انجام شده است. نتايج بدست آمده نشان دهنده مناسب بودن طول 20 سانتي متر براي داشتن تغييرمكان ماندگار كم تر و همچنين كنترل بهتر حداكثر تغييرمكان سازه براي زلزله هاي حوزه نزديك گسل و زلزله هاي حوزه دور از گسل مي باشد.
چكيده لاتين :
There is a debate among earthquake engineers that the structural and non-structural damages initially occur due to lateral loads caused by earthquake excitation. American provisions, including FEMA356 estimate structural performance by means of maximum deformation demand. However, in addition to the maximum deformation, residual displacement plays an important role in structural performance. Amplitude of residual displacement is an important parameter in technical and economical determination of rehabilitation needs for damaged structures to resist aftershocks. In this study, residual displacements of five and eight-story steel frames with Vertical Link Beam, VLB, are investigated in which the effect of VLB length is concerned. For VLB, the IPE sections with typical steel are considered, instead of using boxes and H-shaped cross-section. The IPE section has some advantages compared to box section such as lower cost, easier installation and replacement. The VLBs with IPE cross-section are studied in 5 separate models with lengths of 20, 25, 30, 35 and 40 cm. In this paper, experimental results of a frame model with vertical link beam tested in structural laboratory of Building and Housing Research Center (BHRC) is used for verification of numerical model. As one of the fastest nonlinear software, OpenSees (Open System for Earthquake Engineering Simulation) is used for structural modeling. The steel material used in this model is uniaxial material steel 02. In the following, seven near field and seven far field earthquake acceleration time histories are scaled using 2800 standard and imposed to five-story and eight-story five-bay frames with chevron bracing system. According to the seismic design of structures if ductile elements are used in a structure, beams and columns should remain elastic during earthquake while ductile elements dissipate input energy by nonlinear behavior of ductile members.
Based on obtained results, the VLB with length of 20 and 25 cm for far field earthquakes and 20 cm for near field earthquakes have the best performance. The Bam earthquake is selected to investigate hysteresis diagram of the VLB energy dissipation. Results for near field earthquake like the Bam earthquake show that VLB with the length of 40 cm, has low energy dissipation capability. Furthermore, the VLB with 40 cm length causes more residual displacement and yielding. By considering the station with 104.28 km distance from center of Bam earthquake, the reported record at this station is used as a far field earthquake. In this case, link beams with more than 25 cm length have moment behavior. However, the link beams with the length of 20 and 25 cm have better seismic performance. Considering the RMS (Root Mean Square) parameter as a controller criterion, the VLB with the length of 20 cm is more suitable for near and far field earthquakes. Considering the seismic performance parameters of VLB, i.e. appropriate stiffness, high stability, energy dissipation capability, appropriate control of maximum response of structure and less residual displacement, the VLB with the length of 20 cm also has the best seismic performance for near and far field earthquakes compared to the other cases.
