International Concrete Abstracts Portal

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.

SP123 This volume is a collection of technical papers on the aspects of design of beam-column joints for seismic resistance. Nineteen papers are divided into the following groups. - Tests conducted on specimens designed using current codes but with the same general geometry and a specified loading history. (4 papers) - Design recommendations -- Japan. (1 paper) - Influence of joint geometry on strength and deformation characteristics. (8 papers) - Influence of bond on joint performance. (4 papers) - Joint in precast systems and with high-strength materials. (2 papers)

Two series of experiments on the performance of beam-column joints in reinforced concrete frames were carried out. In Series I, the influence of the transverse reinforcement in the joint and/or the portion of the beam end connected to the column was investigated. From the test results, it is derived that heavy transverse joint reinforcement may reduce the slippage of beam bars in the joint and enhance the joint stiffness after cracking, and the similar transverse shear type reinforcement in the beam end has little effect on relieving the stiffness after degradation of a frame due to the deterioration of bond along the beam bars within the joint. In Series II, the effects of locating a plastic hinge in the beam away from the column face were examined. The test results show that the bond deterioration of beam bars within the joint may be prevented effectively by plastic hinge relocation, but shear-sliding deformation may occur at the plastic hinge away from the column face owing to the inevitable increased shear force in the beam. A new arrangement of beam bars to improve the behavior of the plastic hinge is proposed.

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.

Proposes mechanisms of the transfer of forces to beam-column joints, generated under typical seismic actions in cast-in-place reinforced concrete slabs. One of the main objectives of the paper is to review behavioral models that should assist designers in visualizing the flow of internal forces in beam-column-slab subassemblages. It is postulated that membrane forces play a dominant role and that contributions of other actions, such as bending in slabs and torsion in transverse beams, are relatively unimportant, particularly when significant ductility demands arise during seismic motions. Locations at which slab reinforcements transmit tensile forces by means of bond to the surrounding concrete are considered to be particularly important in the assessment of the enhancement of beam flexural strength. The description of these phenomena is related to observations made during the testing of isolated reinforced concrete beam-column subassemblages with slabs simulating one-and two-way cast-in-place floor systems. Subsequently, the findings are extended to describe the perceived behavior of continuous floor slabs supported by beams of multibay ductile frames. The relevance of the flexural strength enhancement of beams to the design of beam-column joints and columns is briefly examined. Design recommendations are made, particularly with respect to the effective width of the tension flanges.