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SP-121 The Second International Symposium on the Utilization of High Strength Concrete was held in Berkeley, CA, May 1990. A substantial amount of research work and project construction with high strength concrete was completed since the last Symposium. Recent findings were presented and discussed.

Two bridges, the Joigny and Pertuiset, have recently been built in France using high-strength concrete. It was necessary to measure the shrinkage and creep deformation of the concretes for their design. Two series of samples were taken, corresponding to the two kinds of concretes (one with and one without silica fume). The specimens were loaded at different levels and ages (including early ages). Some cylinders were carefully sealed to avoid any drying. Besides the mathematical equations deduced from these trials and detailed in the paper, the following results were discovered: the nonsilica fume high-strength concrete (HSC) is quite comparable to the normal strength concrete (NSC); during the setting, the silica fume HSC exhibits a certain autogenous shrinkage which is higher than that of the NSC concrete; for the silica fume HSC, the magnitude of the creep deformation is highly dependent on the age of concrete at loading, compared with elastic strains, so that the creep is much lower than for NSC (except when loading occurs at a very early age); regarding NSC, the theory of superposition applies fairly to the creep of high-strength concrete for nondecreasing loadings; and, finally, the desiccation creep is reduced for nonsilica fume HSC and entirely cancelled for silica fume HSC, meaning that creep does not depend on size for these materials. Some physical models are proposed at the paper's conclusion to explain these phenomena.

The object of this study is to investigate the possibility of improving ductility of high-strength concrete columns with the lateral reinforcement. Eight column specimens confined by lateral reinforcements having 328.4 and 792.3 MPa in yield strength were tested under reversed cyclic lateral loads with constant axial compressive load levels from 0.254 to 0.629. The concrete compressive strengths were 85.7 and 115.8 MPa, respectively. Volumetric ratio of lateral reinforcement was 1.6 percent in all specimens. Test results indicated that the very large ductility could be achieved by using high yield strength lateral reinforcement, even for such high-strength concrete columns. Modifications of previously proposed stress-strain models on confined concrete were also made for applying them extensively into the calculation of moment-section curvature relationships of high-strength concrete columns with lateral confining reinforcement.

Three earthquake-type loading tests of reinforced concrete (RC) columns, short beams, and beam-column joints using high-strength concrete were carried out. The main objectives of this program were to investigate the seismic behavior of RC members using high-strength concrete, and to obtain guidelines for their design in high-rise buildings. Concretes having three levels of compressive strength, 400, 600, and 800 kg/cmý (39, 59, and 78 MPa), were used. High-strength reinforcing bars with nominal yield strengths of 8500 and 14,000 kg/cmý (834 and 1370 MPa) were provided for lateral reinforcement. Longitudinal reinforcement with a yield strength of 6000 kg/cmý (588 MPa) was also used for beam-column joint test. Emphasis was put on the combination of high-strength concrete and high-strength reinforcing bars. The seismic behavior of columns, short beams, and beam-column joints under high axial load, high beam shear, and high joint shear, respectively, were observed. The relationship between ductility and amount of lateral reinforcement were particularly discussed in the column and short beam tests. In the beam-column joint test, several joint details were considered, and their behavior was investigated. The design guidelines for these high-strength concrete members were also presented in this paper. The results of this experimental program show that the combination of high-strength concrete and high-strength steel bars can be quite effective in improving strength and ductility of RC members of high-rise buildings.

Six reinforced concrete beams and four slabs with different reinforcement ratios were tested to failure. The behavior of specimens manufactured with normal strength concrete (fc = 36 MPa) and high-strength concrete (fc = 83 MPa) was compared with respect to cracking and deflections. It was found that crack widths and crack spacings were fairly comparable for both concrete types in the region of stabilized cracking. Deflections decreased by using high-strength concrete due to the increased modulus of elasticity and cracking moment. However, for the beams, this gain diminishes at higher load levels.