بهسازي لرزهيي ساختمان‌هاي بتن‌مسلح با تغيير محل تشكيل مفصل خميري به كمك دستك فولادي

Rehabilitation of RC Buildings using Plastic Hinge Relocation with Knee Brace

بسته به‌شدت نيروي زلزله، نواحي با تغييرشكل غيركشسان يا به بيان ديگر، مفاصل خميري در تيرها و ستون‌هاي بتن‌مسلح شكل مي‌گيرند. بعد از زلزله، به منظور حفظ يك‌پارچگي سازه و عملكرد مورد انتظار از سازه، اين اجزا سازه‌يي بايد ترميم و يا تعويض شوند. به‌دليل هزينه بالاي تعويض، معمولاً گزينه‌ي ترميم انتخاب مي‌شود. سيستم مهاربند فولادي مي‌تواند به‌طور موثر در ترميم ساختمان‌هاي بتن‌مسلح آسيب‌ديده و بهسازي سازه‌هاي موجود مورد استفاده قرار گيرد. در اين پژوهش، به صورت تحليلي و عددي به بررسي پارامترهاي مختلف تاثير دستك فولادي در مقاوم‌سازي و ترميم قاب‌هاي خمشي بتن‌مسلح از قبيل: درصد جذب برش، تغييرمكان جانبي نسبي، و محل تشكيل مفاصل خميري پرداخته شده است. همچنين تاثير محل قرارگيري دستك فولادي، سطح مقطع دستك و اندازه‌ي دهانه‌ها در مدل‌هاي مختلف با تحليل ديناميكي طيفي و تحليل بارافزون مورد مطالعه قرار گرفته است. نتايج تحليل نشان مي‌دهند كه روش پيشنهادي تغيير محل تشكيل مفصل خميري به كمك دستك فولادي، مشكلات ضعف سختي، كاهش مقاومت، و ظرفيت تغييرمكان سازه‌هاي ضعيف و آسيب‌ديده را در حين زلزله جبران مي‌كند.

Depending upon the severity of the earthquake, regions of inelastic deformation, or plastic hinges, may form in the components of reinforced concrete buildings. These components must then be replaced or retrofitted in order to restore the structural integrity of the structure to its originally intended design performance. Due to the high cost of replacement, retrofit is often an efficient and viable option. For large earthquakes, the formation of plastic hinges in columns can lead to the buckling and rupture of longitudinal steel. Traditionally, once initial buckling occurs, columns are generally replaced, as the cost of replacing portions of bars can be prohibitive. Replacement is deemed necessary since the inelastic strain capacity of reinforcing bars is severely diminished once buckling occurs, making the structure vulnerable to collapse during the next seismic event. Past research on RC member retrofit has focused on issues related to deficiencies in shear, lap splices, or confinement. Numerous techniques have been developed for retrofitting, including, steel, concrete or advanced composite jackets. These retrofit techniques can also be utilized to repair elements with deficiencies exposed during seismic loading, or to retrofit well designed members that have formed mild plastic hinges (without any signs of bar buckling). However, once buckled or ruptured bars are observed, it is assumed that repair is no longer feasible. It is the objective of this paper to challenge this assumption via relocation of the plastic hinge to a position where the member remained essentially elastic during the initial seismic attack. This is accomplished through the use of a knee brace. In this study, the influence of different parameters of a knee brace on the strengthening of RC frames is investigated, analytically and numerically. Also the effect of knee brace location and cross section is investigated by dynamic and pushover analysis. The results show that the proposed hinge relocation technique is able to restore the lost strength and displacement capacity of RC members.