Shear Retrofit of Single-layered RC Squat Wall with Section Enlargement

Abstract

The single-layered squat wall has very poor performance in all aspects. Therefore, various retrofitting strategies have been researched can be applied to it to improve its seismic performance. The concrete section enlargement retrofitting method is one of the seismic retrofitting strategy generally used in working place due to its economic efficiency and practical reason. The insufficiency of flexural capacity of the single-layered squat wall can be retrofitted by providing column element at the both ends of the wall as giving boundary elements to single-layered squat wall. In addition, the insufficiency of shear capacity can be retrofitted by web section enlargement with reinforcements in that section. However, in the case of the former one, consideration of shear strength of the retrofitted member is also needed. If the enlarged flexural capacity excesses the shear strength of it, unexpected brittle failure could be occurred. Therefore, this study proposed the analytical way to predict shear strength and initial stiffness of the retrofitted squat wall by revising existing shear strength model. The revised model considered not only reinforcement details of the column member, also compatibility condition between the column and the single-layered squat wall. Based on the test result of this study, the validity of the proposed analytical way is proved. Moreover, it was verified that the proposed method also could predict not only shear strength, also initial stiffness of the infilled RC squat wall in RC frame by comparing the results of the test and that of the proposed method. In the case of the latter one, there occurs space waste problem due to large area of the concrete section enlargement casted with normal strength concrete within reinforcements. Therefore, this study planned to use UHPFRC which has higher stiffness, tensile stress, and compressive stress than that of the normal strength concrete for the section enlargement retrofitting method. By using the UHPFRC for this method, it is supposed that its possible to obtain required strength with much thinner section enlargement. However, since there exists few researches related to this topic, this study planned experimental and analytical approach to verify retrofitting effect of the single-layered squat wall retrofitted with the UHPFRC web section enlargement method. Therefore, this study proposed an algorithm for deriving shear stress-shear strain curve of the retrofitted squat wall. By this method, it is able to determine failure mode of the retrofitted squat wall, and find out that the ratio of thickness of the RC squat wall and that of the UHPFRC section can affect behavior and failure mode of the retrofitted member. In addition, the maximum stress occurred in the interface of the retrofitted squat wall can be determined based on the failure mode of it, and this study suggested design stress depending on the thickness ratio for preventing interface failure of retrofitted squat wall. Moreover, this study applied the method to the web retrofitted single – layered squat wall with the single - layered panel, and compared it with the double – layered squat wall. Therefore, the validity of the method also can be confirmed. Therefore, it is able to verify shear retrofitting effect of the section enlargement retrofitting method by using the analytical and the experimental results of this study. Furthermore, the results of this study can be used for the guidelines of the section enlargement retrofitting method.