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The article presents the results of a research study that was conducted at the American University of Beirut (AUB) on the effect of transverse reinforcement crossing the critical hooked bars region of normal strength concrete (NSC) beam-column joints on the bond strength and ductility of the mode of failure of the hooked bars. Nine full-scale beam-column joint specimens were tested. The specimen simulated the rigid connection of a cantilever vertical beam to a base column. The load was applied near the tip of the beam while the column was fixed to the strong floor. The tensile beam bars were anchored in the column using hooked-bar anchorages. In previous research, confinement to the joint was provided either by carbon fiber reinforced polymer (CFRP) sheets externally confining the joint or steel fibers incorporated in the concrete mix. Results revealed that the transverse reinforcement crossing the hooked bars region was effective in increasing the anchorage capacity and the ductility of the load-deflection history of the specimens. Correlation of the effects of the three different confinement modes is presented. [ABSTRACT FROM AUTHOR]

The paper presents a correlation study of the results of three research programs conducted on hooked bars anchored in highstrength concrete (HSC) beam-column joints at the American University of Beirut (AUB). The specimen simulated the rigid connection of a cantilever beam to a column. In two previous programs, the beam-column joint was confined either externally with carbon fiber-reinforced polymer (CFRP) sheets or internally by steel fibers incorporated in the concrete mix. Although stirrups were included in the beam and column elements of the specimens of the two programs, the column stirrups were not extended in the beam-column joint. It was necessary to conduct a third program where confinement of the joint was provided internally by stirrups crossing the critical hooked bars region. Results of the three programs indicated positive effect of the different confining modes on bond strength of the anchored bars and ductility of the load-deflection history. Comparison of the results of the three programs is presented. [ABSTRACT FROM AUTHOR]

The effect of steel fibers in improving the bond performance of hooked-bar anchorages and the ductility of the failure mode of beam-column connections was evaluated by testing 12 beam-column-type specimens. The specimen simulated the rigid connection of a vertical cantilever beam to a base column. The tensile beam reinforcement consisted of two bars anchored in the column outside the column reinforcement cage using hooked-bar anchorages. The variables used in the study were the beam bar size (16, 25, or 32 mm [No. 5, No. 8, or No. 10]) and the volume fraction of steel fibers added and dispersed in the concrete mixture (0, 0.5, 1.0, or 1.5%). The analysis of the test results revealed that steel fibers were effective in increasing the anchorage capacity and the ductility of the load-deflection history of specimens with steel fibers as compared with companion specimens identical in geometry and bar size but without steel fibers. [ABSTRACT FROM AUTHOR]

Abstract: In 2001, a multi-phase research program was started at the American University of Beirut (AUB) to evaluate the effect of steel galvanizing on bond strength of reinforcement in concrete structures. This paper reports on the fourth phase of the program designed to assess the effect of steel galvanizing on bond strength of hooked bars anchored in high strength concrete structures. Twelve specimens, each simulating the rigid connection of two cantilever beams to a column, were tested. The variables included bar size and the confinement mode of the beam bars anchored in the column. Test results indicated that galvanizing caused a consistent reduction in bond strength of hooked bars ranging from 6% to 17% with an average of 13%. This is contrary to the results of the earlier phase of the AUB program which indicated strength concrete structures. Based on analysis of test results of all four phases of the AUB research program, design recommendations insignificant effect of steel galvanizing on bond strength of hooked bars anchored in normal are provided concerning the anchorage length of galvanized reinforcing bars in normal and high strength concrete structures. [Copyright &y& Elsevier]

Abstract: In 2001, a multi-phase research program was started at the American University of Beirut (AUB) to evaluate experimentally the effect of hot dip galvanizing on bond strength of reinforcement in concrete structures. In the first two phases, 24 full-scale beam specimens were tested in positive bending to evaluate the effect of galvanizing on bond strength of tension lap splices in normal and high strength concrete specimens. The variables were bar size, concrete strength, the amount of transverse reinforcement confining the splice region, and whether the bars were galvanized or not. Test results indicated that galvanizing had a negligible effect on bond strength of reinforcement in normal strength concrete. However, galvanizing caused an average of 20% decrease in bond strength of reinforcement in high strength concrete regardless of the amount of transverse reinforcement confining the splice region. This paper reports on a third phase of the AUB program, designed to evaluate the effect of galvanizing on anchorage performance of hooked bars in normal strength concrete structures. Up to date there has been no research work done in this area. Twelve specimens were tested. The specimen simulated the rigid connection of two cantilever beams to a column. The variables were bar size, the confinement mode of the beam bars anchored in the column, and whether the bars were galvanized or not. The effect of galvanizing was evaluated by comparing the performance of galvanized bars with black bars based on the mode of failure, ultimate load, and the general load–deflection behavior. Test results indicated that effect of galvanizing on the bond strength of hooked bars in normal strength concrete was not significant. [Copyright &y& Elsevier]

Abstract: Hot-dip galvanizing is one of the methods used to solve the problem of corrosion of reinforcement in concrete structures. The few research reported in the literature on the effect of galvanizing on bond strength of reinforcing bars anchored in pullout specimens, indicates contradictory results. The primary objective of this paper is to evaluate experimentally the effect of hot dip galvanizing on the bond capacity of tension lap splices. The test results may have an implication on the development length and splice length design provisions of galvanized bars in building design codes. To achieve the objective, six concrete beam specimens were tested in positive bending. For each of three bar sizes 20, 25, and 32 mm, two companion beams identical except for whether the bars were black or galvanized, were tested. Each beam was designed with bars spliced at midspan in a constant moment region. The nominal concrete strength was 28 MPa. The mode of failure was splitting of the concrete cover in the splice region. The test results indicated that the use of galvanized bars has a negligible negative effect on bond strength of reinforcement in normal strength concrete. [Copyright &y& Elsevier]

This paper presents the results of two phases of a research program conducted at the American University of Beirut (AUB) to examine the effect of confinement provided by fiber-reinforced polymer (FRP) sheets on the bond strength of tension lap splices anchored in high-strength concrete (HSC) beams. Ten beams with a nominal concrete strength of 68.95 MPa (10 ksi) were tested in positive bending. Each beam was reinforced on the tension side with three 20 mm (No. 6) bars spliced at midspan in a constant moment region. U-shaped FRP sheets were used to externally confine the splice region. The main test variables were the types of FRP sheets: glass or carbon (GFRP or CFRP), the FRP configuration in the splice region (one strip, two strips, or a continuous strip), and the number of FRP layers confining the splice region (one layer or two layers). Except for the epoxy adhesive, no additional anchorage mechanism or bonding procedure was applied for the FRP sheets on the concrete beam. Test results indicated that GFRP and CFRP wraps were effective in improving the bond strength of the lap splices and the ductility of the mode of failure. The experimental results were used to propose a new FRP confinement parameter [ktr,f that accounts for the presence of FRP sheets confining tension lap splices in HSC beams. This parameter was calculated based on: area, spacing and ultimate strength of the FRP sheets, and the number and diameter of steel bars being developed. [ABSTRACT FROM AUTHOR]