The parametric study using FEM and the experiment of T-beams prestressed with external tendons have been performed to investigate the factors thought to influence on the shear mechanism of externally prestressed concrete beams. The effects of prestressing force and stirrup can be observed as important factors to the failure mechanism. The simplified truss model, having a small number of degrees of freedom, has been modified and proposed by adapting the formulation to predict the angle of concentrated stress flow and the thickness of diagonal compression members for evaluating the shear carrying capacity of externally prestressed concrete beams. The predicted results show the good agreement with experimental results.
The present study is aimed at investigating the shear behavior of reinforced concrete beams with doubly reinforced rectangular cross-section, with and without steel fibers, affected by distributed cracks. The influence of the distributed cracks was mathematically quantified with the help of a crack density parameter. Monotonic loading tests were conducted on the RC beams and their failure indicated a mixed mode between both diagonal tension and diagonal compression failures. Due to the reinforcement layout, the effect of the longitudinal compression reinforcement on the shear carrying capacity should be taken into account. The distributed cracks were shown to have less influence on the peak load of doubly reinforced concrete beams.
Crack-induced debonding failures are observed to be very dominant and sometimes unpreventable in concrete members strengthened with externally bonded FRP composites. Many research efforts have been concentrated on developing the debonding predictive models and different models have already appeared in some design guides and codes. However, most models are either lacking of comprehensive under-standing of failure mechanisms (empirical models) or too complex for use in practice. As a complement to our preliminary proposal which has been adopted and included in the current JSCE guideline, this pa-per presents a theoretically reasonable and analytically feasible methodology on how to predict the debonding failure induced from intermediate flexural cracks in FRP strengthened R/C beams. The predictions based on the present analytical model are compared to 180 experimental data collected from existing literature and a close agreement has been obtained.
This paper presents the results of the laboratory investigations on the corrosion of paint-coated steel plates with defects under laboratory conditions of simulated marine environment and in the field. First, experimental qualitative evidence showing significant similarity of the polarization behavior between divided, which were used for measurement of each potential and macrocell current, and undivided steel plates was established. Macrocell and microcell corrosion were then monitored in paint-coated steel plates with defects under different exposure situations and temperatures. Lastly, corrosion rates in an existing paint coated steel structure in the field were estimated. Results show that values of electrochemical measurements in divided steel plates are almost the same and showed the same trend as the undivided steel plate. Macrocell corrosion occurred between the painted part and the defect part of the steel plates. The exposure condition where high oxygen supply and high temperature exist, provided the most severe environment for corrosion of paint coated steel with defect. Moreover, corrosion rates in an existing steel structure in the field were successfully estimated.