Yuya Takahashi 교수

A coupling model reflecting the interaction between freeze–thaw cycles (FTCs) and alkali–silica reactions (ASRs) is established from the microscale to the macroscale under the consideration of non-uniform environmental and mechanical conditions. At both material and structural levels with/without reinforcement, the deformation and damage patterns of specimens under single and coupled FTCs and ASRs were simulated by multiscale finite element analysis and partially verified by experiments. Further

This study set out to investigate the effect of gel migration through micro-pores and cracks on concrete expansion caused by alkali–silica reaction (ASR). First, sensitivity analyses with permeation of produced silica gel were conducted by using a computational scheme of multi-scale poro-mechanics. Then, silica gel movements were found to substantially affect the ASR expansion of concrete with the possibility of its scale effect being rooted in the drugging force when the silica gel is in motion

This paper empirically studies firm's strategic exit decisions in an environment where demand is declining. Specifically, I quantify the extent to which the exit process generated by firms' strategic interactions deviates from the outcome that maximizes industry profits. I develop and estimate a dynamic exit game using data from the US movie theater industry in the 1950s, when the industry faced demand declines. Using the estimated model, I quantify the magnitude of strategic delays and find tha

This paper proposes several statistical tests for finite state Markov games to examine whether data from distinct markets can be pooled. We formulate homogeneity tests of (i) the conditional choice and state transition probabilities, (ii) the steady-state distribution, and (iii) the conditional state distribution given an initial state. The null hypotheses of these homogeneity tests are necessary conditions (or maintained assumptions) for poolability of the data. Thus rejections of these null im

To estimate the remaining life of existing RC bridge decks damaged by alkali silica reaction (ASR), multi-scale numeri-cal analysis with chemo-hygral model is integrated with visual inspection data at site. First, the applicability of the poro-mechanical models for ASR expansion in the multi-scale frame are examined with the experiments of the real scale RC slabs and the model is validated to bring about fair prediction of the 3D anisotropic expansion and the fatigue life of the slabs. Second, v

For evaluating damages of structural concrete by ASR, an analytical platform to rationally deal with the complex interaction of multi-scale chemo-physics events is being developed. For experimental verification of the predictive model proposed, ASR expansion tests under several magnitudes of confinement are conducted and the results are compared with the multi-scale simulation. It is experimentally found that the highly deviatoric compression may bring about isotropically confined ASR expansion.

This paper reviews numerical studies on the effect of expansion and damage due to alkali-silica reaction (ASR) on the mechanical performance of concrete and reinforced concrete at the structural scale level. Previous research on model development that has focused on the performance of RC members or structures is collected and summarized based on how they operationalize expansion progress. The models can be divided into three categories: models that receive the target expansion amount as an input

This study proposes reasonable models to evaluate chloride ion ingress in cementitious materials with dense micropore structures. Salt water immersion tests with mortar specimens, including low water-to-cement (W/C) ratio materials, were conducted. The results show that chloride ion ingress is so slow in specimens with low W/C ratios that existing models cannot follow experimental trends, and pores in the nanometer range may have significant effects on the total extent of chloride ion transport.

The extraction behavior of uranyl species from HNO 3 aqueous solutions using CH 2 Cl 2 containing pyrrolidone derivatives as extractants has been studied to find an alternative to tributyl phosphate as an extractant.In this study, we used N-cyclohexyl-2-pyrrolidone (NCP), N-octyl-2-pyrrolidone (NOP), and N-dodecyl-2-pyrrolidone (NDP) as the extractants.As a result, it was found that NCP, NOP, and NDP (abbreviated as NRP) extract U(VI) as UO 2 (NO 3 ) 2 (NRP) 2 , that a part of NCP in CH 2 Cl 2 p