ABSTRACT
The nonlinear behavior of žber reinforced concrete (FRC) is best characterized by tension or ²exure tests. Analysis of the results however points out to different behaviors and conclusions. Figure 14.1a presents tensile stress-strain response as compared with equivalently elastic ²exural stress versus de²ection of alkali-resistant (AR) glass textile reinforced composite material [1]. It is imperative to note that the general shapes of these curves are similar as they represent initial linear portions followed by a range with a reduced stiffness that is due to distributed cracking. There is however a fundamental difference in the magnitudes of nominal elastically equivalent stress from the tests and the associated deformations. The two main parameters characterizing the tensile response are the žrst cracking tensile strength or the bend over point (BOP) and the ultimate tensile strength (UTS). In the ²exural loading case, the žrst cracking is referred to as the limit of proportionality (LOP) and ultimate strength as the modulus of rupture (MOR). The fact that the MOR value may be several times higher than the UTS can be attributed to several parameters, including the nature of equations used, the size effect, and also the nature of the loading. This discrepancy has been well known in the želd [2] and is best shown by comparing the cumulative probability distribution functions for the four strength parameters. The distribution of BOP and UTS in tension followed by LOP and MOR in ²exure is shown in Figure 14.1b using the results from thin section textile cement composites [1]. Fundamental overpredictions of žrst cracking and ultimate strength in ²exure as compared with the tension are by as much as 300%. Therefore, use of ²exural data as fundamental material properties in the design of cement composites may be misleading and nonconservative.
