EARTHQUAKE RESISTANT PERFORMANCE AND FAILUREMECHANISM OF PRECAST PRESTRESSED CONCRETE BEAMCOLUMNJOINTS ASSEMBLED BY POST-TENSIONING STEEL BARS

摘要

Prestressed concrete beam-column subassemblage specimens, which were prefabricated by passing posttensioningrntendons through precast RC beams and columns, were tested under reversed cyclic loading.rnBeam-column joint panel failed in shear for specimens provided bond between post-tensioning bars andrnconcrete by grout injection, whereas concrete compressive failure due to flexural moment was observed atrnbeam ends for unbonded specimen. To study on horizontal shear force input to joint panel, concreterncompressive stress distribution acting on beam critical section was researched through measuring concreternnormal strains by gauges stuck on beam surface. Central region of joint panel concrete in some height wasrnsubjected to horizontal compression by concrete stress blocks on beam critical sections on both sides of arnjoint. This means that all concrete compressive force at beam and column critical section is not necessarilyrnintroduced to a joint panel. The horizontal and vertical joint input shear force, which were computed usingrnmeasured tensile forces of post-tensioning steel beam and column bars and accounting for noncontributionrnof the compressive force in middle region of a joint to horizontal and vertical shearrnrespectively, deteriorated with the decrease in story shear force. Shear strength in interior beam-columnrnjoint obtained by above-mentioned method agreed well with average shear strength predicted by AIJrnprovision proposed for RC beam-column joints. The measured joint shear cracking strength was almostrnequal to two-thirds of the computed results based on the principal stress field taking account of thernprestress to a beam.