A sectional approach for the bending creep of FRC based on uniaxial tension creep tests

摘要

The creep behavior of FRC elements remains an important obstacle to use FRC in structural applications. Owing to the residual post-cracking strength properties of FRC, creep deformations play an important role in the cracked sections and influence durability and SLS requirements of structural elements. Therefore, it is of high importance to take creep deformations into account in the design phase. In this paper, the results of an experimental campaign involving both bending tests and uniaxial tensile creep tests on polymeric FRC are presented. In the bending tests, a notched FRC beam is subjected to loading-unloading cycles while the deformations over the cracked section were recorded. The uniaxial tensile creep tests were performed on precracked FRC samples to quantify time-dependent crack growth. The bending behavior of FRC can be accurately predicted by the uniaxial constitutive model of Model Code 2010 in the loading phase assuming a plane section approach. For the unloading phases, a bilinear deformation distribution is assumed and a scalar damage evolution function is fitted by an inverse analysis algorithm. The results of the sectional analysis compared favorably with the experimentally observed data. Finally, a sectional analysis approach is developed and presented in which bending creep deformations are calculated using the uniaxial creep compliances. The initial stress and deformation distribution in the cracked section is predicted by the inverse analysis. The results show that the bending creep deformations of FRC can be quite large, and creep coefficients as high at 7 are observed within 120 days. However, it should be noted that the creep algorithm does not (yet) take into account additional cracking in time, and as such, the predicted creep deformations are a lower limit of what can be expected in reality. More research is needed to upgrade the algorithm to allow predictions including the time-dependent cracking behavior.