For prestressed concrete girders, a lot of cases of applying the external cable strengthening method for the fracture of internal cable, have been reported. But it is difficult that external cable are set up at the anchorage in girder end because of the restriction in construction. Therefore, there is concern that the strengthening effect for the shear capacity is not secured when the internal cable fractures in girder end. On the other hand, the shear capacity when the internal cable fractures near anchorage, was not clarified. In this study, the static loading test with the large specimen which simulated actual bridges, were conducted and it was found that the shear capacity exceeded the design capacity, sufficiently, even if internal cables fractured near anchorage. In addition, because the shear capacity at the testing was higher than it of the previous assumption, the shear capacity was inspected by FEM analysis and the shear capacity evaluations in foreign countries were investigated, too.

View full abstract

 There are a lot of parts damaged with the corrosion which induced by chloride ions in the antifreeze agent, mainly at the bridge-girder end of the expressway in Hokuriku region. Firstly in this paper, the progress of this corrosion mechanism at the double reinforcing bars was clarified experimentally. Next, based on the result, "Combined Corrosion Control Method" was proposed as an effective repair method. The feature of this method was the combination of an advantage of the electrolytic anticorrosion using the sacrificial anode (zinc) and an advantage of the patch repair using mortar with the corrosion inhibitor of high concentration. That is, the actual situation of the chloride induced corrosion by the antifreeze agent at the RC bridge was understood. Also, for the double reinforcing bar whose damages were most, the mechanism of the deterioration progress was cleared. Additionally, the effect of a new repair method was estimated, and a cost for the practical use was calculated. As a result, it could be confirmed that "Combined Corrosion Control Method" has efficiency as a repair method for chloride inducing corrosion by the antifreeze agent.

View full abstract

 In order to maintain or manage concrete structures properly, it is very important to evaluate its deterioration grade accurately. And sometimes cracks are used as an index of deterioration grade. For this reason, crack opening weight loss or relationship between crack width and weight loss have been studied by many researchers. Recently, however, it is reported that not only cover thickness or reinforcement diameter which have been thought to be main factor for crack opening but also corrosion products may have large influence. This is because each corrosion products have its own crystal structure, density and volumetric expansion ratio. More than 20 kinds of corrosion products were observed so far, and its formation process has been made clear. However, formation process of corrosion products in concrete is still unclear and it is difficult to predict corrosion products formed in concrete constructed in various environment.
 Then in this study, in order to arrange formation process of steel corrosion products in concrete, XRD analysis of steel corrosion products formed under various corrosion environment was carried out. Additionally, in order to investigate electrochemical property of corrosion products, polarization test was carried out for steel corroded under different environment.

View full abstract

 The majority of steel-concrete sandwich members are monolithic with shear connectors or other anti-displacement stops. However, considering there are only few cases of research available about steel-concrete sandwich members which have no slippage stops, but feature shear reinforcing steel plates in the direction perpendicular to the member's axis, and that furthermore, there is not a study case on the member which is composed of steel elements connected with bitten joints, we conducted a bending test on an actual size structure of this type to confirm its bending behavior. Through our test, we clarifies a typical deformation behavior due to the slippage working between the steel plate and concrete, producing fractural cracks that, without being dispersed are concentrated around the shear reinforcing steel plate. We attempted to establish a model of this relationship in terms of equilibrium of forces between the depth of a crack produced around the shear reinforcing steel plate and the rotational angle. The model was verified to be effective in quantitatively evaluating the bending deformation.

View full abstract

 To improve the precision of simulation on drying shrinkage induced cracking, in this paper a cracking model is proposed based on an existing multi-scale analytical system.
 First, three models related to water status in micro-pores are proposed; firstly, an effective driving force model via micro-cracks near the concrete surface; secondly, a local tensile strength model in which the strength is increased by the progression of drying; and finally, a water diffusion speed model via cracking.
 Furthermore, two models related to shrinkage of aggregate are also discussed; firstly, an apparent aggregate shrinkage model in which aggregate shrinkage is decreased by the influence of micro-cracks around an aggregate; and secondly, an apparent tensile strength model in which tensile strength is increased by shrinkage of aggregate. With the proposed models, the beam specimen which is exposed to drying conditions can be reasonably simulated.

View full abstract

 On the post-tensioning PC bridges, fracture of PC cable by not filling PC grout has been reported in the world. However, there is no report which clarified the quality about safety when PC cable fracture.
 In this study, we investigated the characteristics of concrete, rebar, PC cable, PC grout and filling situation of PC grout. Moreover, we carried out the loading test and nonlinear analysis using PC bridge, which constructed after more than 40 years.
 According to the experiment results, it is clear that materials did not deteriorate and the ultimate load was higher than the design ultimate load by approximately 20 percent. Even though 1/5 of the PC cable was fractured, ultimate load of the PC bridge was almost same as the design load. But, when 3/5 PC cable was fractured, the ultimate load was comparatively greater than the design load.

View full abstract

 This paper corrects the estimated values of alkalinity of pore solution published in the previous study and shows the effect on the conclusion in the published study. Although it is required to correct the absolute value, the corrections do not affect the conclusions described in the published study. By comparing to previous studies relating alkalinity estimation, the absolute values of alkalinity of pore solution after correction are re-considered.

View full abstract