Experimental testing on the structural capacity of coupling beams with non-anchored longitudinal rebars

Abstract

Coupling beams are structural elements which connect shear walls to improve the lateral stiffness and allow to transfer shear forces, while possessing sufficient ductility to dissipate the energy produced due to the lateral displacement. An error in the construction of a 16-story buildings resulted in that only the bottom layer of the longitudinal reinforcement bars in all coupled beams are anchored into the lateral walls, the upper longitudinal bars are cut before anchored to the lateral walls. The reconstruction of all coupled beams in the building is technical and economically non-feasible therefore, to propose a more efficient and less costly retrofit procedure, an experimental study is undertaken to analyze the real structural capacity of these coupling beams. Carbon fiber reinforced polymer (CFRP) is chosen as the reinforcement material for the upper part of the beams. A total of three specimens are tested, two of them under cyclic quasi-static load to determine the flexural capacity of the cross section in the interface wall-coupling beam, and one of them under monotonic loading to determine the shear capacity of the cracked cross section. The results of the cyclic test showed a very limited contribution of the CFRP in the flexural capacity when the fiber is in tension. However, the flexural behavior of the section with the lower reinforcement in tension is not affected by the upper non-anchored bars and showed a flexural capacity and energy dissipation according to the existing rate of the steel reinforcement. The experimental results are used to develop a finite element model which reproduce the structural behavior of the beams with the construction error.