In this research, we conducted loading tests of pre-tension prestressed concrete (PC) girder which had been deteriorated due to chloride attack. Because distribution of corrosion of PC strands was different in each girder, failure mode and structural performance were also different. As next step, we conducted the evaluation of the residual strength of girder with Finite Element (FE) analysis. If the weight loss of PC strands were carefully considered based on the measurement results, numerical results succeeded to simulate loading test by using adequate constitutive model for corroded PC strands. In contrast, it was found that the accuracy of evaluation reduces if the degree of corrosion of PC strands were estimated from external cracks of girder.
This study is intended to establish a method of evaluating fatigue damage for RC bridge deck slabs (hereinafter referred to as “RC slabs”) , using the wave shapes of average strains which are measured by long basis optical strand sensors on the undersurface of RC slabs with traffic load on bridges. First of all, the wheel load tests were conducted with three different conditions of RC slab specimens. As a result, it was found that the following indicators could be the ones for evaluating fatigue damage of RC slabs. (1) Average strain amplitude in transverse direction measured by sensors. (2) Average strain amplitude ratio obtained by dividing longitudinal average strain amplitude by transverse average strain amplitude. (3) Change point of the average strain amplitude ratio in time-shift. Furthermore, to validate the reasonability and the applicability of the method, same sensors were applied on the undersurface of the RC slab of a practical bridge whose fatigue damage was carefully examined. The result showed the consistency with the actual fatigue damage.
The result of air permeability test devised by R. Torrent is supposed to be affected by moisture content in surface layer of concrete. In this study, air permeability test, crack observation, and measurement of surface humidity were carried out under various humidity condition and drying shrinkage stress analysis were carried out. And the following knowledge have been obtained : moisture content in a surface layer of concrete influences the air permeability of concrete, occurrence grade of microcrack in concrete depending on the behavior of moisture content is related to air permeability of concrete, when density of microcrack becomes than a constant value, a change occurs in the relationship and so on.
Concentrating on the structure with 40% stirrups fractured caused by ASR, the mechanism for stirrup damages is evaluated based on the investigation data that is obtained during the replacement. From observations of the alignment order for damaged stirrups, the distribution trend of damage is analyzed. Moreover, crack depths in 44 stirrups from the same corner section of the structure are observed in detail. Rather than caused by the shape and partial area of structure, it is considered that there are causal factors to induce the different damages in stirrup itself. One influential factor is speculated as the different initial crack depths in stirrups owing to the crush of ribs during the bending operations. Besides, in order to evaluate the effect on stirrups, the distribution and the directionality of cracks are discussed in the cross section cut along the perpendicular to the bridge beam axis. Therefore, from the estimation of deformation behavior in the cross section, the expansion feature influencing the region inner the stirrup is learned. As a consequence, it is considered that the bent part of stirrup has the opening deformation owing to the effect of ASR expansion, which further yields the results that stirrups with initial crack or defect are fractured randomly.
In the conventional repair method of honeycombing of RC structures, the repair boundary with sound concrete may cause delamination. In this study, we proposed a new repair method which injects the epoxy resin without removing the honeycombing and then performed cyclic loading tests of RC beam specimens repaired by the proposed and conventional methods, in order to investigate delamination behaviors. The experimental results showed that the specimen repaired by the proposed method increased cracking bending capacity and decreased crack width, compared to the sound concrete specimen. In addition, delamination at boundary was not observed. On the other hand, the specimen repaired by the conventional repair method showed delamination because of shrinkage before loading and the delamination width was increased by loading. It was also found that the cyclic loading accelerated delamination in the specimen repaired by the conventional method.
The occurrence of bleeding water at the interface between formwork and concrete is one cause of deterioration of the concrete surface layer. However, the bleeding water mechanism has not been fully examined. This study was carried out to better understand the bleeding water mechanism as affected by experimental factors such as powder type, powder concentration, the height of placing and mix proportions. It was found that that at least three locations had areas with different volumes of bleeding water present. In addition, the amount of bleeding water was the least in the area 0.5 cm from the mold surface, and the greatest in the area from 0.5 to 4.0 cm from the surface. It was understood that the change in bleeding amount in each region may be due to the convection phenomenon caused by the hydration reaction as well as changes in powder concentration, that the increasing rate of the bleeding amount is different with an increase in the placement height, and that the areas of bleeding water are different depending on the presence of aggregates.