Behaviour under cyclic loading of strengthened beams

Abstract This work presents a study on the behavior of reinforced concrete beams strengthened in bending by the addition of concrete and steel on their tension side and having expansion bolts as shear connectors at the junction between the beam and the jacket, subjected to a cyclic loading. The experimental program included tests on six full scale reinforced concrete beams, simply supported, initially with rectangular cross section 150 mm wide and 400 mm high, span of 4000 mm and total length of 4500 mm. All the beams, after receiving two cycles of static loading in order to create a pre-cracking condition, were strengthened in bending by partial jacketing and then subjected to cyclic loading until the completion of 2x106 cycles or the occurrence of fatigue failure. Following the cyclic loading, the beams that did not fail by fatigue were subjected to a static load up to failure. The main variables were the beam-jacket interface condition (smooth or rough), the flexural reinforcement ratio in the beam and in the jacket, and cyclic load amplitude. On the basis of the obtained test results and the results of previous studies of similar beams tested only under static loading, the behavior of the strengthened beams is discussed and a proposal for the beam-jacket connection design is presented, for the cases of predominantly static and cyclic loading.

摘要 本研究针对受拉侧增设混凝土与钢板进行受弯加固、且梁与加固套之间采用膨胀螺栓作为抗剪连接件的钢筋混凝土梁，开展循环荷载作用下的受力行为研究。本实验方案包含6根足尺钢筋混凝土梁的试验，所有梁均为简支梁，初始截面为矩形，宽150mm、高400mm，跨度4000mm，总长度4500mm。所有梁先经历两次静载循环以形成预开裂状态，随后通过局部套箍加固实现受弯加固，之后承受循环荷载直至完成2×10⁶次循环或发生疲劳破坏。未发生疲劳破坏的梁，在循环荷载试验结束后将被施加静载直至破坏。本次试验的主要变量包括：梁与加固套的界面条件（光滑或粗糙）、梁本体及加固套的受弯配筋率，以及循环荷载幅值。基于本次试验所得结果，并结合此前仅在静载条件下测试的同类梁的研究成果，本研究对加固后梁的受力行为展开讨论，并针对以静载为主和以循环荷载为主的两类工况，提出了梁-加固套连接节点的设计方案。