International Concrete Abstracts Portal

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.

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.

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.

In structures subjected to lateral loading, slab reinforcement acting as effective tensile reinforcement of the beams has been found to increase significantly the beam flexural strength. The enhanced beam flexural strength has several effects on the structural behavior, including a shift in the ratio of strengths between the beams and other members. This may result in a failure mechanism different from that anticipated. The slab contribution depends on several variables, including the connection type (interior or exterior), lateral deformation level, and lateral load history (uniaxial or multiaxial). This paper summarizes general behavior observed during isolated and multiple beam-column-slab connection tests. An approximation is given for estimating the amount of slab reinforcement to be considered as effective tensile reinforcement of the beams.

Describes a theoretical investigation into the hysteretic behavior of hinges in reinforced concrete members subjected to seismic loading. The most important feature of this study is the quantitative evaluation of bond deterioration process between the main reinforcement steel and concrete. An analytical procedure is formulated and a computer program for assessing bond deterioration is developed. End hinges and adjacent bond regions in reinforced concrete members are represented by mathematical models that consist of steel elements, concrete fiber elements, and bond links. Assuming appropriate constitutive curves for these elements, the equilibrium condition of section forces in a hinge is obtained iteratively. This analytical method is applied to the problem of slippage of beam bars in reinforced concrete cruciform beam-column joint subassemblages. The analytical results aptly explain the transient processes of structural behavior observed in experiments, and the quantitative assessment of bond deterioration processes is accomplished satisfactorily.