Earthquake Resistant Performance of Reinforced Concrete Building Retrofitted by Multi-Story Steel Braces

对多层钢支撑加固的钢筋混凝土平面框架进行了反复荷载试验。测试了两个与实际建筑比例为四分之一的试件，其中三个开间跨度为1000 mm，两层高度为800 mm，在中央开间放置多层钢支撑。选取含多层钢支撑的钢筋混凝土单元框架的破坏类型作为试验参数。1号试件的设计目的是考虑多层钢支撑上浮引起的基础转动。相反，2号试件被设计为导致第一层钢支撑底部的弯曲破坏，这是由于支撑的RC受拉边缘柱中的整个纵筋屈服和连接钢支撑水平弦杆与RC地基梁之间的锚杆拔出(称为类型3的破坏)。某钢支撑横截面为H型，宽60 mm，深60 mm，采用WELDI…厚度为6 mm的NG平板较多。混凝土水平位置采用金属浇注模板浇筑。圆柱体试验测得混凝土抗压强度为30 Mpa，框架试件中心用两个油压千斤顶单独施加顶侧向力，使每根柱子的轴力保持恒定。对于2号试件的基础，用PC筋连接到RC反应楼板上。对于设计用于引起多层支撑上浮的1号试件，钢支撑下的两个基础没有连接到楼板上，而是通过在受轴压的RC基础和反力楼板之间插入圆形钢筋来支撑横向反力，对于1号试件，在顶部漂移角为0.2%时，基础作用发生上浮。顶板倾角为0.7%时形成倒塌机制，在边梁端部和底层裸柱底部发展弯曲屈服。试件1在顶部倾角为1%处达到最大强度后，由于铰区混凝土受压破坏，试件1的抗侧能力逐渐衰减。试验中多层支撑以底座转角为主的抗侧能力与快速分析计算结果吻合较好，同时考虑了边梁和地基梁对上拔的约束作用。对于2号试件，在顶部漂移角为0.3%时，支撑的RC边柱中的所有纵筋都处于受拉状态。在顶部漂移角为1%时，各梁端均形成塑性铰，抗侧力达到最大。此后，由于混凝土的受压破坏和钢支撑两边柱底部纵筋的断裂，抗侧力急剧减小。较少

Reversed cyclic loading tests were carried out for RC plane frames strengthened by multi-story steel braces. Two specimens with a quarter scale to actual buildings were tested which had three bays with each 1000 mm span length and two stories with the height of 800 mm, placing multi-story steel braces at the center bay. The failure type of RC unit frame containing multi-story steel brace was chosen as a test parameter. Specimen No. 1 was designed to develop the rotation of base foundation due to the uplift of multi-story steel braces. On the contrary, Specimen No. 2 was designed to result in flexural failure at the base of steel brace in a first story which is caused by both yielding of whole longitudinal bars in a RC tensile edge column of the brace and pull-out of anchorage bars bridging between horizontal chord of steel brace and RC foundation beam (called as the failure of Type 3). Cross section of a steel brace was H-shape with 60 mm width and 60 mm depth, which was built by weldi … More ng flat plates with 6 mm thickness. Concrete was cast in the horizontal position using metal casting form. Concrete compressive strength was 30 Mpa by cylinder tests.Top lateral force was applied alone at the center of the frame specimen by two oil jacks, keeping each column axial force constant. For footings of Specimen No. 2 were connected to RC reaction floor by PC tendons. For Specimen No. 1 designed to cause the uplift of multi-story braces, on the other hand, two footings under the steel brace were not connected to the floor, but lateral reaction force was supported through round steel bar inserted between RC footing subject to axial compression and steel reaction plate settled on reaction floor.For Specimen No. 1, uplift of base function occurred at the top drift angle of 0.2 %. Collapse mechanism was formed at the top drift angle of 0.7 %, developing flexural yielding at the end of boundary beans and the bottom of first story bare columns. Lateral resistance capacity in Specimen No. 1 decayed gradually due to concrete compressive failure at these hinge regions after attaining the maximum strength at the top drift angle of 1 %. Lateral resistance capacity dominated by base rotation of multi-story braces in the test agreed well with that computed by quick analysis taking the confining effect of both boundary beams and foundation beams on uplifting into account. For Specimen No. 2, all longitudinal bars in RC edge column of a brace yielded in tension at the top drift angle of 0.3 %. Lateral force resistance reached the maximum, forming plastic hinges at all beam ends at the top drift angle of 1 %. Hereafter lateral resistance diminished abruptly by the concrete compressive failure and the fracture of column longitudinal bars at the bottom of both edge columns of steel brace. Less