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 trend in offshore and marine concrete is to use higher strength concretes (HSC) than have been used in the past. These concretes provide both additional strength and improved durability due to their improved microstructure. This is achieved by using greater cement content, supplementary cementing materials, and a low water-cementitious material ratio. HSC is more brittle than normal strength concrete and requires additional confining reinforcement to insure ductile behavior of the structural members. Higher strength steels and special methods of confinement, such as the use of T-headed bars, can contribute to the ductility of the concrete.

The use of HSC creates some constructability problems such as high concrete temperatures due to a large amount of cement present and significant thermal gradients. Reinforcing bar congestion in HSC requires concrete with smaller coarse aggregate sizes and very high slumps to satisfactorily place the concrete. Lap splicing in HSC can produce problems of concrete splitting unless the splices are properly confined. The use of mechanical couplers for splicing has some advantages in HSC. Proper curing with HSC is essential.

Presents information regarding highly confined, high-strength lightweight aggregate (LWA) concrete specimens, tested as part of a proprietary research program for which Phase I results have recently been released. The program specifically investigated the ultimate and post-ultimate behavior of members designed to resist high-intensity bending/punching shear loads, such as those imparted by massive ice features against offshore oil/gas platforms. Two special steel confining systems were utilized to confine the high-strength (compressive strengths nominally between 8000 and 9000 psi) LWA concrete; these were T-headed stirrup bars for use in reinforced concrete, and overlapping button-headed studs for use in plate-steel/concrete/plate-steel sandwich composites. These two confining systems both allowed the LWA concrete to exhibit extreme ductility prior to failure.

Flexural, deflection, and ductility factors of over 40, and axial compressive strains of over 8 percent, were achieved, while maintaining essentially 100 percent of the ultimate capacity of the test specimens The tests were performed on 1- to 3.5-scale specimens, using a 4 million-lb capacity testing machine. Three approximately 16 x 16 x 42-in. prisms--two of reinforced concrete and one of sandwich composite concrete--were tested in axial compression. Also, four continuous beam specimens (one reinforced concrete and three sandwich composite concrete) were tested in bending/punching shear. These beam specimens were approximately 153 in. long, 36 in. wide, and had effective depths of approximately 13 in. Nonlinear finite element analyses of the beam specimens were also performed as part of the study.

The behavior and load-deformation response of reinforced concrete exterior beam-column joints constructed with headed reinforcement is evaluated. The evaluation is based on the experimental results of two exterior joint specimens, one representative of construction for high seismic regions and one representative of construction for wind loads. An overview of the experimental study is presented prior to evaluating the effectiveness of the specimens constructed using headed reinforcement. Headed reinforcement lessens congestion in beam-column joints. Use of headed reinforcement eased specimen fabrication and concrete placement. Excellent behavior was observed for both specimens constructed to meet current ACI-ASCE Committee 352 design recommendations.

Disturbed strain regions are areas within a concrete member where plane sections do not remain plane after the member is deformed. Disturbed strain regions occur in portions of all reinforced concrete members. Typically, the disturbed regions are at the boundary regions, concentrated loading points, geometric discontinuities, and in members with relatively small span-to-depth ratios such as deep beams. Recently, more rational procedures have been developed for design of the disturbed regions of reinforced concrete, including strut-tie and compressive field procedures. Such design procedures combined with recent test results have indicated that the traditional design rules and guidelines are frequently unnecessarily conservative. This is particularly so where efficient reinforcing details are adopted such as the headed reinforcement discussed in this article.

At the ACI 1997 Spring convention in Seattle, WA., ACI Committee 439, Steel Reinforcement, sponsored a full day technical session comprised of two parts. Both parts were a mix of various reinforcement products and systems. The presentations provided state-of-the-art coverage of important developments in reinforcing systems that have occurred in recent years. Seven papers submitted for this symposium volume that cover welded wire reinforcement applications and design approaches, headed reinforcing bar applications and mechanical reinforcement splice system design, and performance standards.

These papers will provide engineers and contractors with up-to-date information on new technologies that are available now to improve the performance of reinforced concrete structures, especially in zones of high seismicity and to make design and construction more cost effective.

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.