Effects of Beam Prestressing Force on the Strength and Failure Mode of Reinforced Concrete Exterior Beam-Column Joints

Hitoshi Shiohara, Afonso Toshiiti Sato, Shunsuke Otani, and Taizo Matsumori
The University of Tokyo, Graduate School of Engineering, Department of Architecture.

The number of past experimental investigation on reinforced concrete exterior beam-column joints with prestressing is limited, and more limited is the number of studies related specifically to evaluate the joint strength [1]. Six reinforced concrete exterior beam-column joints with and without post tensioning in the beam were tested under static lateral load reversals. The objectives of this study are to study the effects of (a) post tensioning force in the beam, (b) location of anchorage plates for beam longitudinal bars and/or post tensioning steel bars, (c) amount of lateral reinforcement in beam-column joint, and (d) mid layer longitudinal bars in column on the joint failure.

From this study, it was concluded as follows:

(1) All specimens showed joint shear failure initiated after beam bar reached yielding strength. The story shear capacity of the beam-column sub-assemblage was much smaller than that calculated based on the flexural strength of beam section or column section using bending theory;

(2) In post tensioned specimens the story shear, joint shear force and column bar stress were higher than that of the normal reinforced concrete test specimens;

(3) In the case that the end plates of beam bars and/or post tensioning were anchored outside of the outer column reinforcing bar, bond condition is improved due to the confinement by the anchorage plate, and consequently the column bar stress and bond stress were increased;

(4) In the test specimen, which did not have joint lateral reinforcement, the story shear-story drift relation was almost the same until the maximum story shear was reached, it showed severe strength deterioration at larger deflection;

(5) In the test specimen, which did not have intermediate column reinforcing bar, maximum story shear, the joint shear force and column outer reinforcing bar bond stress was lower than that of the specimens with intermediate column bars.

References

Sato, A. T., Yang, C., Shiohara, H., Otani, S., “Shear resisting mechanism of R/C exterior beam-column connections with post tensioned beams,” Transactions of the JCI, Japan Concrete Institute, Vol.23 (to be published in February 2002).

Architectural Institute of Japan, “AIJ Design guidelines for earthquake resistant reinforced concrete buildings based on inelastic displacement concept,” AIJ, August 1999. (in Japanese)

American Concrete Institute (ACI), “Building code requirements for structural concrete and commentary,” ACI 318-99, Farmington Hills, Mich., 1999.