This paper presents the development of a probabilistic model for the cross-sectional area of corroded reinforcing steel bars (rebars), in order to assess the time-dependent reliability of corroded reinforced concrete (RC) structures. The indicator R, which is the ratio of the average to the minimum cross-sectional areas of corroded rebars, was adopted to quantify the longitudinal variation of the cross-sectional area. By using a three-dimensional laser scanning technique, the areas of the discrete cross-sections were evaluated along the length of a rebar at intervals of 1 mm. The statistical results showed that R could be characterized by the Gumbel distribution. Both the location parameter and the scale parameter for the probability distribution of R increased linearly with increases in the corrosion degree and were dependent on the element length and the diameter of the corroded rebar. The results of a time-dependent reliability analysis of corroded RC beams demonstrated that an element length o...

This paper presents the results of a study on the mechanical behavior of concrete columns strengthened with fiber-reinforced polymer (FRP) and subjected to concentric and eccentric compression loading. A numerical analysis model was developed based on the effectively confined concrete area and the stress-strain relationship of the confined concrete established based on compression tests of circular plain concrete columns. The model was verified against the test results of square concentrically loaded plain concrete columns and square eccentrically loaded reinforced concrete columns. An analytical formula of the maximum compression load of square or rectangular fiber reinforced polymer strengthened concrete columns, with respect to the same but nonstrengthened columns, was developed based on the parametric study results by using the verified model. The analytical formula was further verified with the test results of 23 square and rectangular fiber reinforced polymer strengthened columns reported in...

The purpose of this paper is to investigate the diffusivity of the interfacial transition zone (ITZ) experimentally using cementitious composite materials made of rod-shaped aggregates and cement mortar. Two types of tests were conducted: the porosity distribution of the ITZ at different distances from aggregate surface was measured by backscattered electron images, and the water vapor diffusivity of the composites was measured by the penetration rate of water vapor through thin slides of specimens. The surface roughness of rod-shaped aggregates was considered as a testing parameter. The diffusivity of ITZ was calculated based on the measured diffusivities of the composite and it was also modeled according to the measured porosity distribution within the ITZ. The results showed that the porosity of ITZ decreases with increasing distance from the aggregate surface, a rougher aggregate surface decreases the porosity of ITZ in the first 10 μm from the aggregate surface, and the ratio of averaged wate...

This paper presents a three-dimensional combined elastic-plastic and damage model for nonlinear analysis of wood members and connections. A strain-driven implicit algorithm was developed based on plastic theory and continuum damage mechanics, and it was incorporated in the model. The model considers both ductile and brittle wood failures, as well as irreversible deformation and softening behavior of wood. A mesh independence strategy and viscous regularization technique were employed to improve the computation efficiency. The model was tested and validated based on test data. It was found that the irreversible deformation and the softening behavior of wood under compression can be traced by the model with acceptable accuracy. The modeling results of mortise-and-tenon wood connections implied that the proposed model can reasonably predict the strength softening, stiffness degradation, and pinching effect of such connections under reversed cyclic loading. Comparison with elastic-plastic models also indicated that the proposed model was superior regarding the prediction of the connection moment resistance (less than 14.8% error).

This paper presents the results of a study on the compressive behavior of timber columns with longitudinal cracks. Material property tests and full-scale compression tests were conducted to investigate the failure modes and the recovery in the load-carrying capacity of cracked timber columns with the use of fiber-reinforced polymer (FRP) sheet wrapping. Different combinations of column geometries, crack dimensions, and types and spacing of FRP sheets were considered. A finite-element method (FEM)-based model was developed and verified on the basis of the test results. A parametric study was also conducted by using the verified model to further quantify the influences of crack dimensions and types and spacing of the FRP sheets. It was found that wrapping FRP sheets around cracked timber columns can recover their load-carrying capacity by up to 20%.