Effect of Horizontal Tied Rebars on Precast Reinforced Concrete Core Walls

Abstract eng:
In the core wall system in high-rise buildings, the four L-shaped core walls at the center effectively reduce seismic vibration. The axial load of the core wall is very high under the action of seismic force. In particular, the corner and the area near the corner of L-shaped core walls are subjected to high compressive stress. On the other hand, precast core walls are effective for construction because they can be built more quickly than cast-in-place core walls. In this study, lateral loading tests were conducted on four full precast wall columns and a monolithic wall column simulating the corner and the area near the corner of the L-shaped precast core wall. Each specimen represented the lower three stories of a high-rise building of approximately 25 stories. The specimens had rectangular cross sections, were the flexural type. The precast specimen consisted of four square-section precast columns. The vertical joints between the precast columns were grouted with high-strength mortar without cotter bars. Each precast column had cotters at the vertical joint. The horizontal tied rebars were concentrated at the second and third floor levels, and at the mid height level of the first story of some specimens to connect the precast columns. The specified design strength of the concrete was 60 N/mm2, and that of the grout was 80 N/mm2. The loading test was a cantilever type, and the loading was cyclic lateral loading. A constant axial loading force was applied to represent the axial stress at the center core. The relative displacement was measured by displacement transducers, such as the relative sliding and opening displacement in the vertical joints. Based on a comparison of the results of lateral loading tests, the effect of the horizontal tied rebars and the structural performance of these wall columns were clarified. Major findings are as follows. The precast columns were unified without the cotter bars by the sufficient horizontal tied rebars and cotters in the vertical joint. The unified precast wall column showed the required strength and ductility. When the precast columns are unified by the horizontal tied rebars, the horizontal strength can be calculated approximately by the equation for bending of the column. Failure of the vertical joint occurred at the specimen having a small quantity of horizontal tied rebars or a small number of cotters in the vertical joint. The specimen showed independent movement of the precast columns, and the strength and ductility of the specimen decreased. The shear strength of the vertical joint calculated by the equation matched the failure mode of the specimens.

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