Abstract: Swelling deformation in a concrete structure in direct contact with water inevitably causes changes in its performance. In this study, we develop a humidity diffusion model based on Fick's second law, conduct physical tests to determine saturated humidity diffusion coefficient, and verify the model against the test data of one-dimensional water absorption in concrete. The mechanism of humidity influencing the deformation of a simply supported concrete beam is studied through experimental tests and numerical simulations. And we analyze the simulations to examine humidity effect on elastic modulus, swelling effect on the deflection and strain distribution of the beam, and the combined effects of humidity and swelling on beam stress response. Results show that the model and its parameters adopted in this study are applicable to simulating nonlinear humidity distribution in a beam. The deflection and strain distribution are less affected by humidity change and its effect on elastic modulus, but they are greatly changed by the swelling caused by water absorption. The combined effect of their changes has a greater influence on beam stress response. Thus, we suggest that in designing concrete structures in direct contact with water, the effects of humidity should be considered.

Key words: humidity, diffusion coefficient, elastic modulus, swelling, deformation