International Concrete Abstracts Portal

A set of shear-resistant actions is presented to analyze reinforced concrete interior beam-column joints in weak beam-strong column ductile frames. The proposed analysis explains the results of experiments of beam-column joints with and without bond at beam bars and with various horizontal shear reinforcement. Local bond strength at beam bars affects horizontal hoop stress. Under or up to the limit of enough bond, larger local bond strength demands larger horizontal hoop stress. Over this limit, larger local bond strength demands smaller horizontal hoop stress. Joint shear reinforcement improves anchorage of beam bars because horizontal hoop stress guarantees bond stress outside diagonal strut. This results in smaller compressive stresses of joint concrete, preventing compressive shear failure.

Bond and/or anchorage performances of longitudinal bars in reinforced concrete beam-column joints were outlined, based on the investigations performed in the United States, New Zealand, and Japan in the past 10 years. The effects of joint size-bar diameter ratio, development length, geometry of bent bar, column axial force, and transverse reinforcement were discussed. The bond deterioration caused such undesirable phenomena as pinching in force-story drift hysteresis curves, increasing the slip deformation at the beam-column interface, changing the shear transfer mechanism in the joint core, and decreasing the flexural strength of the adjoining members. Bars passing through an interior joint and bent bars in an exterior joint were treated separately to make the discussion clear.

Describes two types of prefabricated beam-column joints designed to save manpower requirements in construction work. The first type consists of making precast subassemblages with beam-column joints and integrated beams. Through-holes are provided in the vertical direction in the beam-column joint to accommodate column reinforcing bars (Type 1). The second type consists of precast subassemblages with beam-column joints and columns integrated. Through holes are provided in the horizontal direction in the beam-column joint to accommodate beam reinforcing bars (Type 2). Column or beam reinforcing bars are passed through the holes in these precast subassemblages; the parts are integrated by subsequent grouting of the holes with high-strength mortar. The earthquake resistance of these precast subassemblages was investigated with cyclic loading tests. The systems are intended for use in a 13-story reinforced concrete building, designed so that its collapse mechanism would be of the beam-yielding type. With Type 1 precast subassemblages, column reinforcing bars grouted and fixed inside sleeve-pipe holes are not subject to stresses extending into the plastic range. Therefore, by suitably designing the anchorage lengths of beam reinforcing bars inside the joints, there will be no slippage of the beam bars. A ductility of more than six times the yielding displacement may be attained. With Type 2 subassemblages, the beam reinforcing bars grouted and fixed inside sleeve-pipe holes are subjected to repeated stresses extending into the plastic range, such that bond deterioration occurs inside the joints. Strength declines at large deformations exceeding three times the yield displacement, and satisfactory ductility is not obtained. Taking test results into consideration, precast subassemblages of the first type are recommended for adoption in the 13-story building.

Three reinforced concrete beam-column connections, each with a slab were tested under the U.S.-Japan-New Zealand-China cooperative research program on design of beam-column connections. Two of the specimens were subjected to both unidirectional and bidirectional cyclic loads. Results of the tests are described with the aid of story shear drift angle relations, story shear orbits, measured joint shear deformations, and plots of drift angle components. Various methods for calculating joint shear strength are evaluated in light of the test results. Test data are also used to determine slab effective widths for use in calculation of uncracked beam stiffness and beam flexural capacity.

The results of three full-scale reinforced concrete beam-column joint specimens subjected to one- and two-directional reversed loading are presented in this paper. The influences on aseismic behavior of beam-column joints with different loading systems and monolithic slabs have been analyzed. Also, the relevant provisions for joints in the Chinese design code for reinforced concrete structures have been checked by test results, and some recommendations for beam-column joint design are given.