The influence of openings on lateral behaviour of low-shear strength masonry infilled reinforced concrete frames is investigated. The design of the reinforced concrete frames in this study are aimed to reflect common seismic design deficiencies, such as location of lap splices at bottom of columns, insufficient transverse reinforcements at column and beam ends and lack of stirrups at beam-column joints. Six half-scale single-storey, single-bay frame specimens were tested under in-plane lateral loading. The investigated parameters include shape (window and door), size (regular and large windows) and location of the openings (eccentric and central).The results indicate that presence of openings alters the failure mode, increases the damage level and reduces ductility, strength and stiffness of the infilled frame. The door opening led to reductions of 29% in strength, 34% in the effective stiffness and 23% in the energy dissipation capacity. The window openings led to average reductions of 23% in strength, 8% in effective stiffness and 11% in the energy dissipation capacity. Empirical equations are proposed for estimating overall reductions in stiffness and strength of infilled frames because of the presence of openings, which take into account the effects of size, shape and location of openings. Copyright
Concrete buildings reinforced by plain (smooth) bars are one of the special types of old reinforced concrete buildings that were generally built before the 1970s. As columns are generally the most important structural members of a framed structure, understanding their realistic seismic behavior is very helpful in estimating structural deformations, forces and energy dissipation capacities. Furthermore, in most of old-framed building structures, columns play a key role in the fi nal behavior because of strong beam-weak column conditions. This article reports the results of experimental monotonic and cyclic tests on four concrete column specimens reinforced by plain bars and with various types of splices. Through the experimental results, it tried to obtain more clarifi cation on the complicated behavior of such old reinforced members as well as the differences compared with relevant results of columns reinforced by deformed bars. It was realized that slip (fi xed-end rotation) contribution is the major source of deformation in all specimens independent from type of splices. Moreover, general mode of behavior was restrained-rocking action independent of type of splice detailing. A simple theory for the explanation of hysteresis force-displacement response was proposed. The theory assumes a concrete block rocking element that is restrained with plain bars at both ends. Figure 13. Cumulative hysteresis energy dissipation for specimens. (a) WOS-C specimen; (b) SOS-C specimen; (c) HOS-C specimen; and (d) normalized dissipated energy per cycle.
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