Five types of different shear reinforcement, namely single-bend, U-stirrup, double-bend, shear stud, and T-headed shear reinforcement are evaluated numerically. Emphasis is placed on the evaluation of their contribution to the punching shear capacity of high-strength concrete plates. The numerical investigation was conducted by using finite element analysis. The finite element analysis reported here is an application of the nonlinear analysis of reinforced concrete structures using three-dimensional solid finite elements. The purpose of this application is to demonstrate that three-dimensional elements represent a way to model out-of-plane shear reinforcement in the slab. Hence, the three-dimensional 20-node brick element with 2 x 2 x 2 Gaussian integration rule over the element faces and a plasticity-based concrete model were employed in a finite element program.

Single-bend and double-bend shear reinforcements were modeled with the smeared layer method, while the U-stirrup, shear stud, and T-headed shear reinforcement were depicted individually in the mesh. Reasonable agreement has been obtained between the numerically predicted behavior and experimental test results. Finite element analysis confirmed the experimental test results, that the double-bend, shear stud, and T-headed reinforcements are the most efficient types of shear reinforcement, and the U-stirrup is the least effective type of shear reinforcement. Transverse shear stress was evaluated by the finite element analysis in terms of shear stress distribution, and compared with the ultimate punching shear resistance specified by the ACI 318 design code.

The 1989 Loma Prieta earthquake and subsequent studies resulted in higher design requirements for transverse reinforcement in reinforced concrete bridge beam-column joints constructed in California. The resulting reinforcement details can be congested and difficult to construct. An experimental investigation examined four large-scale interior joints with details typical of those required in California. The experimental program included tied square cross-section columns and spirally reinforced circular cross-section columns. Both conventional and headed joint reinforcement configurations were investigated. Experimental results show that current design requirements produce joints that remain essentially elastic to relatively large drifts, whereas the columns develop inelastic rotations adjacent to the joints. The use of headed reinforcement within the joint regions was shown to be effective in reducing congestion and thereby improving construct-ability while maintaining comparable structural behavior.

Columns supporting bridge structures may be expected to respond inelastically during strong earthquake shaking. Restoration to serviceable conditions may require repair or replacement of damaged regions, which may entail considerable cost and operational delay. To evaluate the feasibility of available repair techniques, an experimental study to evaluate repair techniques for damaged bridge columns was undertaken. The original columns were reinforced with spirals conforming to modern bridge requirements for regions of high seismic risk. Three of the test columns were severely damaged; the fourth column was moderately damaged. Repairs for the severely damaged columns used headed reinforcement, mechanical couplers, and newly cast concrete. The moderately damaged column was repaired by cover replacement and epoxy injection. The success of each scheme was evaluated by comparing the behavior of the repaired column with that of the original column as well as the repair intent.

Six 1/2-scale cantilevered pier walls were loaded in the weak direction under cyclic loading and taken to (near) destruction. Five of the damaged pier walls were repaired with two alternating crossties at each crosstie location, whereas one of the damaged pier walls was repaired with T-headed reinforcing bars in place of regular crossties. The six repaired pier walls were retested under the same test protocol as the original samples to compare their performance. Whereas a regular crosstie restrains the longitudinal steel against the core, a T-headed reinforcing bar provides confinement by the heads of the reinforcing bars bearing directly against the concrete. This additional confinement provides a partial explanation of why the T-headed reinforcing bars provided better structural performance in the one repaired pier wall than five other pier walls repaired with the crossties. The experimental setup and the results are also presented.

Testing of concrete walls and columns subjected to axial compression shows that double head studs used as cross ties are more effective than conventional stirrups with 90 and 180 degree hooks in confining the concrete, thus improving strength and ductility. Unlike conventional stirrups, the studs with heads sufficiently large enough to develop yield strength do not require hooks and bends which must engage the longitudinal bars. It is proposed that because of the superiority of studs in increasing strength and ductility of columns and walls, design codes should allow reduced cross-sectional areas and/or larger spacing when studs are used as cross ties.