Uncertainties of unidirectional composite strength under tensile loading and variation of environmental condition

Analytical model to predict the lifetime of concrete members externally reinforced with FRP

“…In brittle materials there are three regimes of crack growth as K II varies from 0 to its critical value K IIC . Consequently, the relationship between da/dt and K II /K IIC exhibits three different trends [22,23,25,31,36,[44][45][46][47].…”

“…The literature [2,3,5,13,[21][22][23]26,28,43,47,49] also reveals that v c and N depend on humidity and temperature as well, but these dependences are not strong. Ultimately, for concrete members with a carbonation depth greater than the cover, K IIC is close to 1.0 MPa m 0.5 [31,36,[44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61], v c to 0.0015 m/s [22][23][24]31,36,41,[43][44][45][46], and N to 16 [18,24,41,43,59]. It is to note that N is the exponent and thus it is important to provide the model with a reliable value; however, N = 16 is simultaneously an accurate and preservative assumption.…”

“…[2,3,5,13,[21][22][23]26,28,43,47,49], brings out the fact that, in a carbonated concrete, the ranges of variation of K IIC , v c , and N are reasonably narrow. In fact, these parameters depend mainly on the depth of carbonation and the strength of concrete.…”

“…In order to plug into the model the actual values that K IIC , v c , and N assume in a specific concrete, instead of a priori values, tests have to be accomplished, either on-site or in laboratory [18,[22][23][24]29,31,36,39,41,[43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58]. On the contrary to K IIC , however, v c and N are not simple to be measured; thus, it is more convenient to use the aforementioned values borrowed from literature.…”

“…Unfortunately, practice often extends this property from the separate and standalone FRP-composite material to the entire FRP-strengthened system. However, durability of a RC member externally reinforced with FRP depends not only on durability of the individual materials, but also on the capacity of the concrete cover to sustain the bond stresses s b [22][23][24][25]. In fact, on one hand, the FRP-composite material keeps its original strength, elasticity, and toughness [5,13,15,16,[26][27][28]; on the other hand, however, the combination of s b and initial cracks (flaws) in the concrete cover may give rise to slow crack growth up to the critical length, and eventually to debonding of the external reinforcement [29][30][31][32][33][34][35][36].…”