International Concrete Abstracts Portal

Experimental and theoretical studies on shear strength of large reinforced concrete beams are presented. The shear strength of a reinforced concrete beam without shear reinforcement gradually decreases as an effective depth d of a beam increases, and is generally called the size effect. From the result of the experiment on large beams, the size effect of a beam exists even for a beam deeper than 100 cm which had been outside of the scope of past experiments, and the size effect at d ò 100 cm may be considered to be inversely proportional to the fourth root of the effective depth. According to the result of a nonlinear finite element analysis, the size effect on flexural tensile strength of concrete and shear transfer across crack surfaces must be considered in estimating the shear strength of a large reinforced concrete beam.

The stress-deformation relation now generally accepted for tensile fracture, i.e., with the descending branch described by means of a stress-displacement relation in a localized band, has been applied to the compressive stresses in a bent, reinforced beam. The displacement in this band is averaged over a length, which is proportional to the depth of the compression zone. The resulting average stress-strain relation, which is strongly size-dependent, is used for the analyses of the stresses in a rectangular beam section, and for the corresponding moment-curvature relationship. The results differ appreciably from those from conventional assumptions. The new approach shows a better agreement with test results than the conventional approach. Further test comparisons are, however, recommended. The new approach may form the basis of changed design assumptions, particularly for high-strength concrete.

Reviews the tensile failure of concrete structures subjected to a variety of practical loading. Attention is focused on the propensity of fracture failure of concrete structures and the fracture properties of cementitious materials. The relevance of fracture mechanics to modern concrete design code is highlighted.

Fracture behavior of epoxy and polyester polymer concrete (PC) systems are investigated in Mode I fracture using single-edge notched beams with varying notch depths. The beams were loaded in four-point bending. Influence of polymer content on the fracture behavior of epoxy PC andpolyester PC at room temperature was studied using uniform Ottawa 20-30 sand. The polymer content was varied between 10 and 18 percent of the total weight of the composite. The flexural strength of the polymer concrete systems increase with increase in polymer content while the flexural modulus goes through a maximum. The critical stress intensity factor KIC was determined by two methods, including a method based on crack mouth opening displacement. At the same polymer content, the epoxy PC has a higher fracture toughness than polyester PC. The KIC for epoxy PC and polyester PC increases with increase in polymer content and PC flexural strength. The critical stress intensity factor of PC is represented in terms of polymer content and polymer strength. Numerical tests based on random sampling and stratified sampling procedures were performed to substantiate the experimentally observed fracture toughness values of polymer concrete.

Conventional concrete and mortar are both major construction materials because of their advantages in durability, economy, and comparably good mechanical properties. However, brittleness and low tensile strength are weak constitutions of these materials. Therefore, they provide less resistance to the propagation of cracks. Fibers can resist against the propagation of cracks due to the contribution of traction, resulting from the fibers-matrix bond mechanism, on the crack face. Some exact mathematical formulations to express thestress intensity factor and the crack opening displacement are proposed in this research to interpret the fracture behavior of fiber reinforced cementitious composites. Using these formulations, two fracture criteria can be performed to evaluate the tendency of crack propagation of this composite material. These two criteria are stress intensity factor and crack tip opening displacement. To achieve a more reasonable solution, the couple effect between the crack opening displacement and the fiber bridging traction is also considered. From the numerical results shown in this study, it is concluded that the fiber reinforced concrete provides higher resistance against the propagation of cracks than ordinary plain concrete, and one can clearly understand the resistance ability of fibers for the fracture behavior of concrete.