Multi-physical analysis of saturation-dependent creep behavior for RC beam under sustained load and wet-dry cycles

Abstract

A multi-physical and multi-scale analytical method based on thermo-hydro-mechanical models is adopted to evaluate the long-term deflection of RC beams with cracking under sustained loads and cyclic wet-dry conditions. The major physical-mechanical coupling mechanisms considered in this study includes: 1) water transport and phase equilibrium in the microstructure of gel and capillary pores; 2) accelerated moisture transport affected by cracking in concrete; 3) saturation-dependent creep coefficient considering gel and capillary pores; 4) combination of creep deformation and non-uniform shrinkage. The numerical approach is firstly verified by experiments where the thermo-hydro-mechanical interactions are found to be well analyzed. Then, parametric cases of cyclic wet-dry conditions are investigated to achieve deeper and wider conclusions. It has been found that under the cyclic wet-dry ambient conditions, there is an extreme drying state for concrete members depending on the drying humidity and its period. For the long-term mid-span deflection of beams, generally it will grow faster if the drying humidity is lower, which owes to the saturation-dependent creep coefficient, which has been called as Pickett effect. Meanwhile, beam's bottom-side cracking caused by sustained loads may also accelerate the moisture transport, which leads to an uneven drying state between upper and lower part of beams and viaducts, and eventually causes up-warping of them. For some cases, this up-warping can be significant enough to alter the macroscale structural creep deformation. At last, the difference between wet-dry cycle and dry-wet one has also been discussed. It can be proved that for the long-term deformation under wet-dry cycles, the moisture state will greatly affect the time-dependency from many aspects, for which the thermo-hydro-mechanical numerical approach is beneficial and needed in practice.