A research program has been promoted in order to study the compositions and properties of High Performance Concretes to be produced in France. Concretes with a characteristic compressive strength of 50 to 60 MPa (7 000 to 8 500 psi) on cylinders tests may be fabricated every where in France at a reasonnable cost, by selecting aggregates, cement and superplasticizers. The Brittle behaviour of such concretes under loads action needs a reevalua-tion and a possible adaptation of the codes of design. The other characteristics of this material are significantly improved : reduction of creep and shrinkage, increase of compacity. The gain to be expected from a generalized use of such concretes results from short time characteristic, by decreasing the member sections and improving the rate of utilization of shuttering, and from long time characteristic by increasing durability. However a complementary program is now in progress in order to clear some uncertain-ties and to design an experimental structure.

In the prestressed, precast concrete industry high-strength concretes are widely used for axially loaded piles and columns, but also increasingly for flexural members such as double tee beams and girders. Use of high-strength concretes permits fabrication of longer, more slender spans and economic mild and prestressed reinforcing steel patterns. And, for plant-produced members the necessary high strength may be achieved easily and consistently without out-of-the-ordinary quality control procedures9 and this is documented here. To facilitate designs using high-strength concretes a number of design aids have been developed, and selected examples are persented. Finally, by its very nature, where high early strengths are required prestressed precast concrete members frequently have a substantial amount of long-term reserve capacity and excellent deflection control.

The basic philosophy of the current ACI Code for confining concrete in earthquake design is that the increase of the strength of the core of the column due to confinement must offset the loss of strength due to spalling of the unconfined cover. The equatians given in the code are based on the assumption that when a reinforced concrete column is subjected to uniaxial load the maximum capacity of the confined core is reached when the unconfined cover starts spalling. It is not clear whether this assumption is applicable for high strength concrete. The strains at which the cover concrete and confined concrete -will reach their maximum capacities will depend on their respective stress-strain curves. In this paper, based on several sets of experimental data, analytical expressions are proposed for the stress-strain curves of confined and unconfined high-strength concrete. Using these analytical expressions, moment-curvature relationships are predicted. The predicted curves were compared with the experimental data of columns subjected to reversed lateral loading. Rased on the satisfactory comparison for normal strength concrete columns, the theoretical model is then applied to high‘ strength concrete.

Higher strength concrete which is defined to be that with uniaxial, 12000 psi compressive strength in the range of 6000 psi

High-strength concrete (8000 pounds per square inch or above) requires that a high level of structural integrity be achieved because of the demanding applications for which it is generally selected. natural limitations of As the inher-approached, the product are close control of materials production and placement is increasingly important. Statistical methods to provide such control are outlined in this paper.