Luis Alfonso Orta

Concrete overlays are widely used to strengthen or rehabilitate deteriorated concrete structures. Shrinkage of the new concrete will be restrained by the substrate, producing tensile stresses that may crack the overlay. In this study the free shrinkage profiles are computed using Fick's Second Law accounting for the non-linearity of the differential equation that expresses diffusivity as a function of relative humidity. The numerical analysis is validated using closed-form analytical expressions and experimental data. The results overcome the flaws of using shrinkage models (e.g. ACI-209 1 , CEB-FIP-1990 2 , Bazant and Baweja B3 Model 3) to predict the shrinkage profiles. The results show large concentration of strains at the interface and top drying face of the overlay. They also show a slow growth of shrinkage strains at the mid-depth of the overlay. The magnitude of the fictitious holding force and its location necessary for the computation of restrained shrinkage stresses ar...

Bridge deck rehabilitation typically involves removal of unsound concrete and placement of an overlay to restore the original geometry of the deck. A water-proofing membrane is typically applied after three to four days of drying to extend the life of the overlay by preventing the ingress of de-icing chemicals. Shrinkage of the overlay is restrained at the interface with the substrate producing tensile stresses in the overlay that may cause cracking. This paper investigates the effect of the water–proofing membrane on the restrained shrinkage of the overlay. The migration of internal humidity is modeled using Fick's Second Law of Diffusion. Tensile creep strains that develop simultaneously with shrinkage strains are considered. A stress analysis based on fundamental equilibrium, compatibility and constitutive equations is developed and calibrated using ancillary tests reported in the literature. Sensitivity and reliability analyses are performed using simulation with stratified ...

The stresses, strains, and curvatures due to the shrinkage restraint of new concrete bridge deck overlays by the underlying older substrate are investigated. A time history analysis method is derived that, for each time increment, computes free-shrinkage and creep strains, enforces compatibility and equilibrium using a time-dependent stiffness matrix, and determines incremental mechanical and total strains. A new model for tensile creep strains has test-predicted ratios for experimental results reported by others that average 1.00, with a coefficient of variation of 11%. The resulting stresses and mechanical strains are nonlinear across the depth of the member, with large stress gradients in the top and bottom faces of the overlay at early ages of drying. Simplified analytical methods proposed by others are often not accurate: neglecting swelling of the substrate underestimates the mechanical strains, neglecting tensile creep markedly overestimates the mechanical strains, and assuming uniform free shrinkage through the overlay thickness initially overestimates the mechanical strains but subsequently underestimates them at older ages. The studies also found that application of a waterproofing membrane at the top of the overlay 3 days after the end of curing has very little effect on the maximum tensile stresses in the overlay. The age-adjusted equivalent modulus method accurately estimates the overlay tensile stress at early ages, but fails to predict the time of cracking.

Bridges are subjected not only to service loads but to severe environmental conditions. Every day traffic load increases and structural resistance decreases due to aging. This study presents the reliability assessment of a reinforced concrete T-beam with exposed reinforcement. It is based on test results conducted by others, Monte Carlo simulation and structural analyses using commercial software. The obtained results show that the probability of failure increases from (10)-3 to 3(10)-3 and the corresponding reliability index decreases from 3.0 to 2.8.