International Concrete Abstracts Portal

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.

Presents a critical review of current design provisions for shear and anchorage in beam-column joints subjected to large seismic actions. When current design limits are compared with experimental data, the results indicate that if short anchorage lengths and large shear stress are used simultaneously, large losses of bond transfer capacity and stiffness will occur. The performance of joints based on different levels of joint shear stress and anchorage lengths is discussed, and an empirical formula linking anchorage and shear is proposed based on the limited tests data available on bar slip.

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.

Geometrical configurations of reinforced concrete beam-column joints in actual building structures are quite varied because the configurations depend upon the number of structural members connecting the joints, the shapes of cross section of the members, the eccentricity among the axes of members, and so on. Focusing the interest mainly on the eccentricity from these factors, studies on seismic behavior of reinforced concrete interior beam-column joints in one-way frames with eccentricity are carried out with a classificatory examination, an investigation of a building destroyed by a strong earthquake, and a survey of previous studies and the authors' experiments. From the investigation of the destroyed building, it is suggested that the heavy eccentricity between columns and beams caused torsional moments in the columns and joints, causing severe damage. From the survey of three previous experiments in which one-sided eccentric joint specimens with wide columns and deep beams were subjected to lateral loading, it is shown that effective width and/or torsional moment should be considered for calculating the strength and stiffness of frames. Experimental results indicate that such eccentricities caused twisting of the columns and joints, resulting in reduction of the shear strength of the members. From the results of the classification examination and of the authors' tests in which five beam-column subassemblages with several types of eccentricity and beam width were subjected to cyclic lateral forces, it is observed that joints with one-sided eccentric beams suffer larger torsional moment around column axes, narrowing the effective joint width. Therefore, the shear cracking stress and the deformability of joints are reduced.