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.

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.

The present research evaluates the performance of reinforced concrete buildings made of high performance materials in earthquake prone areas through the parametric analysis of twenty-two buildings using a finite element approach. The concrete strength in the buildings varied from 50 MPa to 90 MPa and the reinforcement consisted of 500 MPa, 800 MPa and 1200 MPa steel. Among the building combinations considered, there were two that involved varying concrete strengths between the beam and column elements and different combinations of reinforcement steel. The design of the buildings was carried out for peak ground acceleration 0.25g according to the Eurocodes 2 and 8 for both ductility class ‘’Medium’’ and ‘’High’’. The nonlinear static (pushover) analysis technique was employed to assess the behavior of the RC buildings. The performance of the buildings designed for ductility class ‘’Medium’’ and ‘’High’’ under the design earthquake level corresponding to 0.25g and a selected collapse prevention level corresponding to 0.50g was very satisfactory. Considering the financial benefits resulting from the use of mixed concrete strengths in the beams and columns and their general performance under the two seismic events, the construction of RC buildings incorporating different material strengths appears to offer several potential benefits.

Four one-bay and one-story high-strength concrete frames were made and tested under reversed cyclic lateral force while subjected to high axial compression. Test results have indicated that confinement of high-strength concrete columns in frame by steel tube in stead of conventional hoop and use of high-strength steels as longitudinal rebars of the frame members could not only assure ductile seismic performance to the frame under high axial compression, but also reduce the residual story deformation to acceptable level. The damages in hoop-confined reinforced concrete beam were also significantly mitigated. In addition, a design formula was proposed to evaluate the ultimate lateral load capacity of the confined high-strength concrete frame. Good agreement between the theoretical ultimate lateral loads and the measured results verified validity of the proposed formula.

Three series of tests were carried out to investigate the behavior and strength of high and normal strength concrete spiral columns under uniaxial compressive loading. Five columns with normal strength and fourteen high strength spiral columns were tested. Normal strength and high strength steel were used as spiral reinforcement. The main variables investigated were; (a) volumetric ratio (varied from 0.008 to 0.038) and spacing of spiral reinforcement, (b) ratio of gross to core area (varied between 1.05 and 1.45), and (c) strength of spiral reinforcement. Strength increase and ductility due to the presence of spiral reinforcement were investigated. When high strength concrete is used, the minimum spiral reinforcement required by ACI 318-02 results in extremely small spacing as the ratio of the gross to core area increases. Spacing of the spiral reinforcement can be increased to reasonable values if higher strength steel is used. During the tests it was observed that the columns having high strength spiral reinforcement behaved well, and had adequate ductility.