International Concrete Abstracts Portal

SP-228CD This CD-ROM of Special Publication 228 contains the papers presented at the Seventh International Symposium on the Utilization of High-Strength/High- Performance Concrete that was held in Washington, D.C., USA, June 20-24, 2005. The symposium continued the success of previous symposia held in Stavanger, Norway, (1987); Berkeley, California (1990); Lillehammer, Norway, (1993); Paris, France, (1996); Sandefjord, Norway, (1999); and Leipzig, Germany, (2002). The symposium brought together engineers and material scientists from around the world to discuss topics ranging from the latest applications to the most recent research on high-strength and high-performance concrete. In the years since the first symposium was held in Stavanger, there has been worldwide growth in the use of both high-strength and high-performance concrete. In addition to more research and applications of traditional types of high-performance concrete, the use of self-consolidating concrete and ultra-high-performance concrete has moved from the laboratory to practical applications. This publication offers the opportunity to learn the latest about these developments.

To improve the toughness and shear resistance of high strength concrete, steel fiber was induced into the reinforced high strength concrete beams. 39 steel fiber reinforced high strength concrete (fcu=52.4~84.7MPa) beams with stirrups and 5 control beams were tested. The test program was divided into two series. One series was tested under two symmetrical point loads, and the other was tested under an equivalent uniformly distributed load simulated by eight symmetrical point loads. The main variables were steel fiber volume fraction, steel fiber type, stirrup content and concrete strength. The test results showed that deformation properties, diagonal cracking strength and shear strength of the beams were improved significantly by the addition of steel fibers. Based on the test results, some empirical formulas are given to predict the diagonal cracking strength and shear strength of steel fiber reinforced high strength concrete beams. Results are also coordinated with those for reinforced concrete beams.

Three 96-ft (29.3-m) long, 72-in. (1.83-m) deep, pretensioned bulb-tee girders were tested to evaluate behavior under static shear loadings. The three girders had a design concrete compressive strength of 10,000 psi (69.0 MPa) and incorporated 0.6-in. (15.2mm) diameter, Grade 270, low relaxation prestressing strands. One of the girders was designed based on the AASHTO Standard Specifications for Highway Bridges and the other two were designed based on the AASHTO LRFD Bridge Design Specifications. The shear designs incorporated the use of either welded wire fabric or conventional bars for reinforcement. Prior to testing, a 10-ft (3.05m) wide reinforced concrete deck slab was added to each girder and a fatigue test was performed. After the fatigue test, each girder was cut in half and both ends were tested to evaluate static shear strength performance. Measured strengths consistently exceeded the design strengths calculated by both AASHTO design approaches using both design and measured material properties.

Coupling beams in earthquake-resistant wall structures have long represented a design challenge due to the high shear stress and distortion demands imposed by strong earthquakes. Currently, the design of reinforced concrete coupling beams, particularly those with low span-to-depth ratios, involves substantial reinforcement detailing to ensure a stable behavior during earthquakes, leading to reinforcement congestion and construction difficulties. As a design alternative, the use of strain-hardening or high-performance fiber reinforced cement composites (HPFRCCs) in coupling beams was experimentally investigated. The use of composite materials with large strain capacity and damage tolerance was aimed at reducing transverse reinforcement requirements while maintaining adequate seismic behavior, making the construction of coupling beams more feasible. To validate this alternative, three HPFRCC coupling beam specimens and one control reinforced concrete coupling beam were tested. The main variables investigated were the type of material used in the coupling beams, fiber type, and reinforcement detailing. Test results indicate that in order to achieve large displacement capacity, diagonal reinforcement must be provided in the proposed HPFRCC coupling beams. However, the use of an advanced fiber cementitious material allowed the elimination of the transverse reinforcement required to provide confinement and diagonal bar support in RC coupling beams, thus, significantly simplifying the reinforcement details.

In the last decades, a large number of experimental campaigns on the behaviour of high-strength reinforced and/or prestressed concrete beams failing in shear have been published. With the aim of taking into account this large amount of information and to re-evaluate the current codes of practice an extensive research was performed. New expressions are proposed for the design of high and normal-strength reinforced and prestressed concrete beams. For beams with web reinforcement, the procedure is based on a truss model with variable angle of inclination of the struts plus a concrete contribution. The angle is obtained by compatibility, based on the MCFT, and it is able to predict the interaction with axial load, bending and torsional moment. Different databases published after the development of this procedure are used to test the ability of this proposal. It correlates with the empirical tests better than any current code of practice does.