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The fatigue behavior of RC beams subjected to moving loads is experimentally investigated. Analytical scrutiny is made on the shear fatigue behavior of RC beams subjected to moving loads based on strain path and time dependent fatigue constitutive models rooted in the multi-scale fixed four-way crack modeling of concrete. Moving load is found to cause dramatic reduction in fatigue life of RC beams as compared to that of the fixed pulsating load both in the experiment and analysis. The mechanism for the reduced fatigue life under moving loads in RC beams is discussed in contrast to that of RC slabs. A simplified relation for the prediction of fatigue life under moving load is proposed for practical use on the basis of standard shear fatigue design equation of JSCE code, used for fixed fatigue loading. The effect of randomness in the position of loading is examined and its implication for the reliability of current fatigue life assessment method of RC members is put forward. The applicability of the multi-scale computational platform is verified for the fatigue investigation of RC beams subjected to moving loads.

This paper investigates the causes of excessive long-term deflection of PC bridge viaducts by using 3D integrated material-structural analyses to take into account the coupled chemo-physics at various scales from the molecular size of water to the structural members. The excessive deflection observed at site is found to be rooted in the deformation of cement paste stemming from both externally applied loads and internal stresses driven by capillary surface tension and disjoining pressures in micro-pores. Not only the former but also the later effect is focused in the serviceability control of PC viaducts. It is found that the nonlinear, long-term deflection of the bridge viaduct can be approximately separated into the components of deflections provoked by external mechanistic and internal thermodynamic actions, even though each component is nonlinearly associated with the thermodynamic states of moisture in micro-pores of cement hydrates.

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The aim of this study is to clarify the mechanism of the progressive excessive deformation observed in real underground RC box culverts of about 30 years of age. It was found by the site-inspection, monitoring and the destructive testing that the excessive deflection of top slabs for the culverts, which is almost 10 times the design estimated value, accompanies the out-of-plane shear failure. It is also computationally investigated that the coupling of subsidence of the backfill soil and the combined creep and shrinkage of concrete after cracking is closely associated with the delayed shear failure found in the culvert in service. In order to prove the delayed shear failure under higher sustained loads, the timedependent shear crack propagation was reproduced in the laboratory test and the computational approach used in this study was examined.

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An experimental investigation on three shear-critical reinforced concrete beams was performed to investigate the mechanism of shear fatigue. The first beam was simply tested to failure under monotonic loading to determine the static capacity, whereas the other two were subjected to repetitive loading below its static capacity to failure. Of these two beams, one was subjected to a stationary pulsating load at midspan while the other was subjected to a step-wise moving load along the span. During each experiment, the crack pattern was monitored throughout using an automated crack mapping employing the digital image correlation technique. The results show that each beam exhibited a unique crack pattern which could be characterised as shear-flexure in nature. It is shown the nature of crack propagation under monotonic loading is dissimilar to that under repetitive loading, especially when the load is not stationary. Moving load is also shown to cause greater damage to the beam than the stationary pulsating load and result in a reduction in fatigue life by almost two orders of magnitude.