INFLUENCE OF FIBER BRIDGING ON STRUCTURAL SIZE-EFFECT

The size-effect of structural element has been experimentally determin ed in concrete members under various load types. The importance of siz e-effect on safe structural design has been well recognized. Theoretic al models explaining and predicting size-effect based on fracture mech anics of brittle and quasi-brittle materials have made significant adv ances in the last decade. Structural size-effect can be reduced by mod ifying the crack bridging behavior of concrete. An effective means of controlling the crack bridging law is by fiber reinforcement. Since th e bridging law is fundamentally governed by fiber and interface proper ties, proper materials engineering can lead to effective means of redu cing structural size-effect. This paper studies analytically the effec tiveness of fiber bridging on the FRC beam structural size effect, by means of a flexural model which takes into account matrix crack extens ion and fiber bridging. The flexural strength (MOR) is shown to decrea se with beam height following Bazant's Size-Effect Law for ordinary co ncrete. When fiber bridging is introduced, the MOR is shown to be much less dependent on matrix properties. Instead fiber and interface para meters 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 sigma-delta bridging relation, the material charact eristics length, and the constituent fiber, matrix and interface prope rties are clarified. A generic size-effect law for FRC beams is obtain ed. Other related issues such as size-effects on R-curve behavior, cri tical crack length at MOR, etc., are also studied. (C) 1998 Elsevier S cience Ltd. All rights reserved.