This paper discusses the path dependency of high cycle fatigue behaviors of RC bridge slabs under various loading histories in use of laboratory experiments and numerical behavioral simulation. A prototype standard RC slab and another two specimens, which were initially loaded statically in advance, were prepared for the subsequent wheel-type loading. All three of them were tested under a moving load of 160kN. Observed is the independency of the progressive mid-span deflection on the loading histories. Furthermore, the same trend is rather observed at a level of 220kN as well with another set of specimens of exactly the same shape and dimension. The observed phenomenon in the experiments was successfully simulated by direct path-integral 3D nonlinear FE analysis considering the varying boundary conditions from the preliminary loading state to the main one to introduce the high cycle fatigue damages.
As moving load testing of RC slabs of highway bridges takes several months, drying shrinkage of concrete progresses concurrently with fatigue-induced damage during this time. Further, as actual bridges are placed in service after drying shrinkage has progressed to some extent, RC slab fatigue life test results do not correspond with the actual life of RC slabs in service. This study investigated the effect of the combined action of drying shrinkage and fatigue-induced damage by using multi-scale analysis based on thermodynamics. The increase in deflection under fatigue load was found to be the result of the combined action of shrinkage and load-induced fatigue damage, and the process by which damage progresses through their interaction was elucidated.
By replacing the blast furnace slag fine aggregate with natural fine aggregate, hardening properties improving effect, such as long-term strength enhancement, drying shrinkage reduction, and carbonation inhibition of concrete is known to be obtained. In this study, for the purpose of revealing the mechanism of hardening properties improvement of blast-furnace slag fine aggregate, we focused on the difference in particle size of the blast-furnace slag fine aggregate, and investigated the influence of each particle diameter on properties of hardened mortar. As a result, it was found that blast-furnace slag fine aggregate is effective in strength enhancement and drying shrinkage reduction as particle size is small, and particle size smaller than about 0.045 mm is more effective. Next, we confirmed the influence that content of the particle size smaller than about 0.045 mm gave to properties of hardened concrete. As a result, it was found that the compressive strength is remarkably enhanced, and effect on drying shrinkage and carbonation was small by adding about 5% of blast furnace slag powder as the particle size smaller than about 0.045mm.
Triaxial compressive tests were carried out at different confining pressure and water content to understand the deformation mechanism of hardened cement paste. Results showed that stress did not decrease up to 10% strain, and macroscopic damage was not observed when tested under a certain confining pressure. This confining pressure differed depending on moisture content. Stepwise creep tests were conducted, and the slopes of the obtained differential stress-strain rate curves in a double logarithmic chart were around three, indicating that deformation was caused by dislocation creep. A sample saturated with sucrose solution exhibited more brittle behavior after the peak stress as compared to the behavior of the sample saturated with tap water. The results indicated that the deformation of cement paste was probably affected by dislocation, mechanical twinning, and pressure solution. Those mechanisms can affect cement paste and concrete deformation under low confining pressures.
In the maintenance of concrete structures whose degradation is produced by abrasion, it is necessary to predict an amount of abrasion quantitatively. Currently, however, the prediction method is not established. In this study, we examined effects of external force and factors of concrete quality (e.g. weight, speed, the number of blow, compressive strength) on the amount of abrasion using the shock abrasion examination device with the steel boll falling on a concrete surface. Based on the regression analysis of huge amount of experimental data, we developed the prediction method of abrasion depth development of concrete. The method was validated by applying the method to the abrasion of actual concrete structures.
Geopolymer using fine powder of melt-solidified slag made from municipal waste as an active filler occasionally loses rapidly fluidity after mixing. The possibility of improving the fluidity were investigated for two methods, one is to use the stored fine powder of the slag and the other is to use fine powder of the stored slag. Influence of storage method and storage period on chemical ingredients was investigated using several chemical analyses. Influence of storage method and storage period on fluidity and compressive strength of the geopolymer were also investigated. It is revealed from the chemical analyses that hydrate and calcium carbonate are generated during storage when the slag is stored after grinding and that hydrate is generated during storage when the slag is stored before grinding. The experiments showed that the fluidity of the geopolymer mortar which use the slag powder as an active filler was improved. Compressive strength of air cured geopolymer mortar is decreased with the increase of storage period as generation amount of hydrate or calcium carbonate increases in the slag. It is confirmed that improvement of fluidity and reduction of compressive strength are caused to the change in the slag by storage. Meanwhile compressive strength of steam cured geopolymer mortar is not influenced by the change in the slag by storage. It is conceivable that this is caused to the restraint of reaction based on latent hydraulicity as condensation polymerization dominates under high temperature.
A new seismic retrofitting method reinforcing the termination zone of the longitudinal bars of RC bridge pier in which reinforcing members were placed only two-sides of the pier and enables to retrofit without removing machine room under viaduct was developed, and its flexural reinforcing effect was clarified. Beam tests were carried out using RC beam specimens in which two-sides of the existing beam were retrofitted by fixing RC reinforcing beams with anchor bars. From the beam test results, it was clarified that the ratio of the load carried by reinforcing beams to the load carried by existing beam was proportional to the products of the ratio of the rigidity of reinforcing beams to the rigidity of existing beam and the ratio of reinforced length within shear span to the effective depth of existing beam. Cyclic loading tests were also carried out using model pier specimens of the actual pier structures of the Touhoku-Shinkansen, in which the new seismic retrofitting method was expected to applicate. From the test results, it was clarified that the damage at the bar cut-off sections of the pier, in which failure mode factors S before retrofitting were under 1.0, could be avoided by reinforcing two-sides of the pier with RC reinforcing members such that the failure mode factors S' after retrofitting were about 1.3.
Effect of chloride in liquid water on drying and wetting behavior of concrete was experimentally investigated. Experimental result showed that equilibrated water content increases and moisture transfer rate in concrete decreases with increasing of chloride content in concrete. Consequently, concrete tends to wet by the existence of chloride. Analytical method for coupled transport of water and chloride in concrete which effect of chloride on moisture transport is taken into account was proposed. Increasing of equilibrated water content due to chloride can be expressed by considering decreasing of saturated vapor pressure and change in physical property of liquid water. Decreasing of moisture transfer rate in concrete due to chloride can be expressed by considering decreasing in transfer rate of liquid water in accordance with chloride concentration.
The experimental equations under the simply supported condition has been used as the shear capacity of steel reinforced concrete (SRC) beams in Standard Specifications for Hybrid Structures. On the other hands, the support condition of members of the rigid frame viaduct is different from the simply supported because both ends are fixed. The study has evaluated the shear mechanism and shear capacity of SRC short beams under fixed both ends based on results of experiment and finite element analysis. The results indicated that the shear capacity was affected by support condition and increased with the decrease of the flange width of steel-frame. In addition, the effect of stirrup on the shear capacity was limited. Finally, the paper proposed calculation equation of shear capacity for SRC short beams under fixed both ends.