Evaluation of crack width in FRC structures and application to tunnel linings

摘要

When steel bars are placed in a concrete structure, the evaluation of crack width and crack spacing is generally required in the serviceability stage. According to more or less aggressive conditions, crack width shall be limited in order to avoid, for instance, the corrosion of steel reinforcement. The presence of fibers in the concrete cast may help to achieve this goal, since fibers remarkably increase the bridging actions across a crack. However, new mechanical models are needed to evaluate these effects, which are generally neglected by classical approaches. Code requirements are based on semi-empirical formulae, in which the average structural performances are analyzed by referring to a single cross-section, instead of a wide portion of an R/FRC or RC element in bending. To evaluate crack patterns more accurately, a suitable block model is therefore introduced in this paper. With the new approach, the bridging effects of fibers, as well as the bond-slip mechanism between steel bars and FRC in tension, arerntaken into account. By means of such model, it is possible to predict at one time the values of crack width, crack spacing, and crack depth, and compare them to data obtained by bending tests on concrete beams. Moreover, to evaluate the possible crack patterns in R/FRC tunnel linings, the proposed block model has been extended to the serviceability stage of massive structures subjected to combined compressive and bending actions. This paper follows a previous work by the same authors (Chiaia et al. Mater Struct 40(6):593-694, 2007) and completes the design procedures for FRC cast-in-place tunnel linings.