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The objective of this paper is to show that the use of high-strength concrete (HSC) (especially concrete with silica fume) can notably reduce the long-term deformations of reinforced concrete (RC) slabs. This may be achieved by reducing creep deformation, increasing the elastic modulus, the tensile strength, and the steel-concrete bond properties. Moreover, this paper shows that the CEB (Comite Euro-International du Beton) moment-curvature relationship established for ordinary concrete is still valid for HSC. A procedure for the nonlinear finite element analysis of RC beams and slabs is briefly described. The proposed procedure is based on the nonlinear CEB moment-curvature relationship incorporated into an iterative secant stiffness algorithm. Predicted deflections from the proposed procedure are compared with experimental results from slabs made with ordinary or HSC.

When high-strength concretes are used in high-rise buildings, long-span bridges, and offshore structures, special attention must be given to the dimensional changes that occur in the concrete members. For design purposes, the length changes are usually considered to consist of instantaneous shortening, shrinkage, and creep. Instantaneous shortening depends on stress level, cross-sectional dimensions of the member, and modulus of elasticity of steel and concrete at the age when the load is applied. Shrinkage deformations generally depend on type and proportions of concrete materials, quantity of water in the mix, size of member, amount of reinforcement, and environmental conditions. Creep deformations depend on concrete stress, size of member, amount of reinforcement, creep properties of concrete at different ages, and environmental conditions. In recent years, questions have been raised about the validity of methods for calculating deformations in high-strength concrete members and the in-place properties of high-strength concrete members. These properties include compressive strength, modulus of elasticity, shrinkage, and creep. This paper reviews existing state-of-the-art technology concerning instantaneous shortening, shrinkage, and creep of high-strength concrete members.

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.

A series of 28 reinforced concrete beams without shear reinforcement have been tested in shear by two-point loading. The main test parameters were: longitudinal reinforcement ratio (1.8 and 3.2 percent); shear span ratio (2.3, 3.0, and 4.0); size (b/h = 150/250 and b/h = 300/500 mm); and concrete type (normal density concrete of cylinder strength 54, 78, and 98 MPa and lightweight aggregate concrete, 58 MPa). The results are compared with other test results and concrete codes. For members made of normal density concrete of compressive cylinder strength exceeding 80 MPa, the diagonal cracking strength remained constant or showed a minor decrease in spite of the increasing tensile splitting strength of the concrete. A more significant decrease in ultimate shear strength was observed. A probable explanation is the increasing brittleness of the material with increasing strength. The new Norwegian Concrete Code, which includes provisions for high-strength concrete, predicts the influence of concrete compressive strength and aggregate types on the diagonal cracking shear strength fairly well. The influence of dimensional scale was, however, larger than expected. The shear strength formula in CEB-FIP Model Code generally overestimates the diagonal cracking strength of high-strength concrete slabs or beams with moderate longitudinal reinforcement ratios. An improved shear strength prediction formula for high-strength concrete has been adopted by the Norwegian Code. The lightweight aggregate concrete beams had relatively low diagonal cracking strength, as expected, but high ultimate shear strength. The tests confirm the results (except for one test series) found by Ahmad et al.

An equation is proposed for predicting the ultimate shear capacity of reinforced concrete columns and beams composed of high-strength concrete having a compressive strength of up to 90 MPa, and high-strength reinforcing bars having a tensile strength of 1000 MPa. Six beams and ten columns with and without shear reinforcement were tested to determine their diagonal cracking strengths and ultimate shear capacities. The shear span-depth ratio was 1.0 for the beams and 1.14 for the columns. The quantity pw åy (pw: shear reinforcement ratio; åy: yield strength of shear reinforcement) was varied from 0 to 11.2 MPa. The axial stress in the columns was varied at 0, 18.4, and 36.8 MPa. The current ACI Building Code equation for predicting shear capacity of deep beams was found to be applicable to the beams fabricated with high-strength concrete. However, it cannot be applied to the members with high axial load stress. The equation proposed in this paper accurately predicts the ultimate shear capacity of reinforced concrete columns as well as the beams made with high-strength concrete and high-strength steel bars.