Experimental Study on Prestressed Concrete Beam-Column Joints Which Have Column-To-Beam Strength Ratios Near 1

Abstract eng:
For beam-column joints of reinforced concrete in moment resisting frames, a new type of failure is recently identified, which is called joint hinging mechanism. In the joint hinging failure mechanism, a beam-column joint reaches its maximum strength after tensile yielding of longitudinal bars passing through the joint for both horizontal and vertical direction. The joint hinging failure occurs typically in beam-column joints with low column-to-beam flexural strength ratios near one, regardless of the joint shear margin. The joint hinging mechanism causes lower strength mechanism and lower energy dissipation compared to beam hinging mechanism. Meanwhile, beam-column joints of prestressed concrete are usually designed according to provisions with joint shear equations to prevent the joint failure before yielding of reinforcing bars or tendons. However, there is no guarantees that the joint hinging mechanism never occurs in beam-column joints of prestressed concrete. Hence, an experimental program on seismic performance of prestressed concrete beam-column joints with low column-to-beam flexural strength ratio was carried out. This paper reports the test results. The test series consists of six specimens of one third scale. For four of the specimens, geometries and bar arrangements of beams and columns are identically and column-to-beam flexural strength ratios are one. These four specimens include one prestressed concrete beam-column joint without non-prestressed reinforcement, two prestressed reinforced concrete joints and one prestressed concrete without grout of tendons. In addition to them, two specimens in which column-to-beam strength ratio were 1.4 were loaded. The test results show that: 1) joint hinging mechanism is occurred in beam-column joints which have column-to-beam strength ratios equal to one even for prestressed concrete and maximum story shear in cases of joint hinging mechanism are lower than cases of beam hinging mechanism, 2) larger column-to-beam strength ratio improves moment capacities of beam-column joints and leads beam hinging mechanism, 3) effects of location of tendons on strength are slight, 4) bondless between tendons and concrete reduce maximum strength of beam-column joints and 5) calculated moment capacities of prestressed concrete beam-column joints according to the theory for moment capacities of reinforced concrete beam-column joints in which dealt with prestress on beams and columns as axial forces agree with the test results.

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