Papers by Author: Yong Sheng Ji

Abstract: The corrosion characteristics of steel bar in concrete are decided by the corrosion current distribution along the circumference of the steel bar. It is a general assumption that carbonation lead to a general corrosion on the rebar. However, the destruction of a large number of specimens indicated that before corrosion cracking, the carbonation-induced corrosion mainly distributes on the surface of the steel bar facing the concrete cover. This paper examined the corrosion mechanism from fundamental electrochemical principles and experimental verification. It was illustrated that the macrocell corrosion must co-exist with microcell corrosion, both macrocell and microcell corrosion mechanisms could play significant roles, and the total corrosion could be underestimated if each of two is overlooked.

Abstract: In order to study the influences of initial curing conditions on fly ash (FA) cement concrete durability, fly ash cement samples with 30% replacement ratio were fabricated and cured in water at 10°C, 20°C, 30°Cand 40°C for 3d, 7d, 14d and 28d respectively. Hydration degrees of fly ash at early age were measured using the selective dissolve method. Correspondingly the pore structure and morphology of FA-cement mortar and compared cement mortar were studied by using MIP and SEM methods. Then early age compressive strengths of FA-cement concrete and compared normal cement concrete were tested. Experimental results show that initial curing temperatures and ages are important factors to fly ash early age hydration degree, FA-cement system microstructure, morphology and early age compressive strength etc. High curing temperatures and longer curing time can lead higher fly ash hydration degree, and then higher compressive strength of FA-cement concrete, and make the micro-structures of fly ash-cement system denser.

Abstract: Setting up of an objective function, update parameters and use of robust optimization algorithm are three crucial steps in FE model updating. In order to calculate the gradient of the objective function, analytic optimization algorithm is not easy to be achieved, while the direct optimization algorithm may achieve the objective function optimization simply by comparing the size of the objective function to move the iteration point. In this paper, the eigenvalues and mode shapes are used as the optimization objective function, the direct optimization algorithm is adopted, an updated finite element model is achieved, and a numerical example is given.