رفتار لرزه اي تير همبند فولادي تعويض پذير در ديوار برشي بتني مسلح

Seismic Behavior of Replaceable Steel Coupling Beam in Reinforced Concreat Shear Wall

كاربرد تيرهاي همبند فولادي در ديوارهاي برشي بتن مسلح به علت عملكرد لرزه اي و انعطاف پذيري بهتر و همچنين اجراي راحت تر و ابعاد كوچكتر آن نسبت به تيرهاي بتني رو به گسترش مي باشد. جهت اجتناب از خرابي ماندگار اتصال تير فولادي به ديوار بتني، مي توان از تير فولادي داراي المان تعويض پذير استفاده نمود. در اين مقاله يك تير همبند فولادي طراحي شده بر اساس استاندارد 2800 و مبحث دهم مقررات ملي ساختمان طراحي و ساخته شده است. همچنين المان تعويض پذير و بخش هاي كناري آن بر اساس ضوابط تير پيوند مبحث دهم مقررات ملي ساختمان طراحي و ساخته شده است. مجموعه دو ديوار طرفين تير و تيرهمبند تعويض پذير با مقياس 1 به 3 ساخته شده و با تاريخچه جابجايي چرخه اي بر اساس تغيير شكل نسبي طبقات مورد آزمايش قرار گرفته است. با توجه به نتايج بدست آمده، رفتار غير خطي تير همبند به المان تعويض پذير محدود شده است اما با توجه به مقاطع استفاده شده و نيروهاي موجود در تيرها، رابطه استفاده شده از مبحث دهم جهت طراحي تيرهاي كناري نياز به اصلاح دارد. همچنين بر اساس سختي محاسباتي و سختي اندازه گيري شده سيستم و بر ميناي طول مهاري تير فولادي در ديوار بتن مسلح، روشي براي محاسبه سختي واقعي اين مجموعه براي طراحي سازه ها و محاسبه جابجايي طبقات پيشنهاد شده است.

Reinforced concrete shear walls are frequently used as lateral load resisting systems because of their ductile response and very good energy dissipation. When openings in RC shear walls are used due to architectural requirements, coupling beams are forming to connect two adjacent walls. The behavior of coupled shear walls is governed by coupling beams and they are the most vulnerable parts of coupled shear wall systems and were seriously damaged due to severe past earthquakes. To avoid construction difficulties and huge size of the RC coupling beams and better seismic performance an ductility, steel coupling beams in reinforced concrete shear walls have been mostly used during last years. Steel coupling beams connections to concrete shear walls are vulnerable and it is practically difficult and economically waste to repair damaged coupling beams, which would cause the building life cycle cost increasing. Therefore, it is necessary to transform traditional design approach to a design method in which some important parts would be replaceable rather than repairable. In this paper a building with special shear walls with steel coupling beams as lateral force resisting system is designed based on Iranian Standard 2800 and Iranian National Building Code. One of the 5th to 8th floor steel coupling beams section considered as fuse element and side beams and stiffeners of I-shaped beams designed based on eccentrically braced frames link beam criteria of Iranian National Building Code (part 10). Experimental specimen containing two RC shear walls that connected to each other with designed replaceable steel coupling beam in 1 to 3 scale is constructed and assembled in strong floor lab. For providing one degree of freedom movement of load wall four TBI Motion Company TRH65VE linear supports used. Cyclic displacement history of experiment calculated based on story drift and amplitudes of loading determined using Iranian Standard 2800 limit for story drift. Based on experimental results side beams remained in the border of elastic range and inelastic behavior of system concentrated in fuse element so the goal of system is satisfied. The side beam section is stronger and different with that was obtained from link beam criteria of Iranian National Building Code (part 10) because of available steel sheet size and since the side beam force is almost equal to elastic capacity of beam, the criteria for designing side beams is modified. Total system stiffness and fuse beam stiffness that obtained from experiment are fewer than analytical stiffness of system and fuse beam. Stiffness degradation of system occurs due to partially fixed performance of steel coupling beam connection to RC shear wall and micro cracks of wall in the connection zone. Different between real and analytical stiffness of system is very important and it is necessary to repeat the building design with modified stiffness and recalculate story drifts and distributed forces in structural elements. In this paper modifying method of stiffness is developed with moving fixed end point of steel coupling beam and increase of beam length. Effective fixed point of beam is defined by adding a portion of embedment length of steel beam in RC shear wall to both steel coupling beam ends.