Influence of fiber bridging on structural size-effect

size-effect of structural element has been experimentally determined in concrete members under various load types. The importance of size-effect on safe structural design has been well recognized. Theoretical models explaining and predicting size-effect based on fracture mechanics of brittle and quasi-brittle materials have made significant advances in the last decade. Structural size-effect can be reduced by modifying the crack bridging behavior of concrete. An effective means of controlling the crack bridging law is by fiber reinforcement. Since the bridging law is fundamentally governed by fiber and interface properties, proper materials engineering can lead to effective means of reducing structural size-effect. This paper studies analytically the effectiveness of fiber bridging on the FRC beam structural size effect, by means of a flexural model which takes into account matrix crack extension and fiber bridging. The flexural strength (MOR) is shown to decrease with beam height following Bazant’s Size-Effect Law for ordinary concrete. When fiber bridging is introduced, the MOR is shown to be much less dependent on matrix properties. Instead fiber and interface parameters dominate the MOR of the FRC beam. At the same time, beam height-size-effect on MOR is shown to diminish within the practical range of real structural sizes. The relationships between structural strength MOR, the composite a-6 bridging relation, the material characteristics length, and the constituent fiber, matrix and interface properties are clarified. A generic size-effect law for FRC beams is obtained. Other related issues such as size-effects on R-curve behavior, critical crack length at MOR. etc., are also studied. c; 1998 Elsevier Science Ltd. All rights reserved.