Abstract
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.
Highlights
Strenghtening reinforced concrete beams by adding concrete and steel bars presents the advantages of relatively low cost and no need for a highly qualified workforce, making it an interesting alternative when it is possible to increase the cross-section dimensions of the element to be strengthened
In view of the practicality of using expansion bolts at the beam-jacket connection, an experimental study was developed aiming to contribute to the understanding of the behavior of beams strengthened with this technique when they are subjected to cyclic loading
Some cracks on the jackets were observed during the two static loading cycles before the cyclic loading
Summary
Strenghtening reinforced concrete beams by adding concrete and steel bars presents the advantages of relatively low cost and no need for a highly qualified workforce, making it an interesting alternative when it is possible to increase the cross-section dimensions of the element to be strengthened. In case of cyclic loading, increasing the ratio of this reinforcement decreases the interface damage resulting from such loading, minimizing the loss of stiffness of the strengthened element, and increases the number of cycles it can withstand. One of the main factors that can reduce the interface shear strength is the effect of cyclic actions, which cause a decrease in the stiffness of the element, associated to a greater propagation of cracks, leading to strains in the structural elements larger than those verified under short-term static loading, and to different stress redistribution. In view of the practicality of using expansion bolts at the beam-jacket connection, an experimental study was developed aiming to contribute to the understanding of the behavior of beams strengthened with this technique when they are subjected to cyclic loading. This study, detailed in [1], is summarized here
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