Papers by Author: Isam A. Mahmoud

Abstract: Rapid moisture loss in concrete and the coupled shrinkage strain in concrete elements cause distress in structural members at early ages. The shrinkage stresses and the associated cracks can be reduced by controlling the rate of the moisture loss. However, under some circumstances, controlling the rate of the moisture rate is not practically possible which may add additional cost to the concrete construction. A finite element based technique is suggested in this paper to predict the shrinkage stresses and consequently predict the possibility of having shrinkage cracks. The technique utilizes the analog between the heat transfer and moisture diffusion, thermal stresses and shrinkage stresses. The analysis was performed using thermal and structural modules in the commercial finite element software ANSYS. The process described in this work makes the determination of restrained shrinkage stresses in problems of concrete structures readily accessible to design, repair and construction engineers.

Abstract: Precast concrete construction with prestressed precast hollow core slab as floor and roofing is being extensively used in the Gulf region. These one way slabs are sometimes subjected to unforeseen loads with a partition wall in shear zone or as a cantilever. A detailed experimental program involving full-scale load testing of hollow core slabs has been conducted involving testing of virgin and CFRP strengthened slabs in flexure and shear. This paper presents the results of the experimental and numerical evaluation of flexural and shear behavior of the hollow core slabs. The hollow-core slabs were modeled using the nonlinear finite element software DIANA and the load deflection behavior and ultimate capacity were evaluated numerically. For the FE model, concrete was modeled using Drucker-Prager with tension cut-off failure criterion, and Von-Mises plasticity with multilinear isotropic hardening was used to model the prestressing strands. Comparison between the experimental and the numerical results indicated that the finite element model predicted experimentally determined results successfully.