Shear Behavior of Unbonded Precast Prestressed Concrete Beam-Column Joints Caused Volume Loss in Joint Panel By Sheath Tubes

Abstract eng:
The beam-column joint shear strength (called as Vj) for prestressed concrete (called as P/C) structures is almost depended on a concrete strength in joint panel. Apertures in joint panel are formed by sheath tubes for unbonded precast prestressed concrete (called as unbonded PCaP/C) structures. There are not these apertures for reinforced concrete structures (called as R/C). It is expected that the volume loss with apertures in joint panel causes the decrease of Vj. Conveniently a seismic design expression of the beam-column joint ultimate shear strength for the unbonded PCaP/C structures is applied that of the “Design Guidelines for Earthquake Resistant Reinforced Concrete Buildings Based on Inelastic Displacement Concept” [reference 1]. This guideline is the seismic design provision published by Architectural Institute of Japan (called as AIJ). So the reduction of the beam-column joint ultimate shear strength by apertures formed with sheath tubes isn't considered at present. Therefore, this paper focuses on the effect of joint-panel shear behavior caused volume loss rate (called as Rvl) by sheath tubes for unbonded PCaP/C structures. The Rvl divided the volume of the apertures formed with a sheath tube by the beam-column joint effective volume. And if the Rvl is 0%, it means that there is no aperture in beam-column joint. Previous test results of five specimens in references 2 and 3 were used for cruciform beam-column subassemblages in this paper. The Rvl of five specimens were from 0% to 12.1%. All specimens were beam-column joint shear failure. When the Rvl were smaller than 6.1%, the joint shear strengths were larger than lower R/C strength of seismic design provisions by AIJ. On the other hand when the Rvl were greater than 6.1%, the tendency of the joint shear strengths was smaller than that. It was obvious that the volume loss by apertures in joint panel causes the decrease of Vj. When the Rvl were smaller than 6.1%, the joint-panel area expanded both to the lateral and vertical direction after the peak. On the other hand when the Rvl were greater than 6.1%, the joint-panel area expanded to the lateral direction and shrunk to the vertical direction after the peak. From above mention it is found that the beam- column joint panels were failed in the horizontal shear force when the Rvl was smaller than 6.1%, and the beam- column joint panels were failed in the vertical (an axial direction) shear force when the Rvl was greater than 6.1%. The reduction coefficient considered with apertures in a beam- column joint about the beam-column joint ultimate shear strength is proposed under a simple method in this paper. The reduction coefficient calculated by a detail method was published in references [2 and 3]. The simple method and the detail method is compared with the seismic R/C design expression. The reduction coefficient proposed the simple method about the beam-column joint ultimate shear strength agreed well with referred test results. And it is an useful expression that the simple method is applied every kind of sheath tube shape.

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