Path-dependent fatigue constitutive models for concrete tension, compression and rough crack shear are proposed and directly integrated with respect to time and deformational paths actualized in structural concrete. This approach is experimentally verified to be consistent with the fatigue life of materials and structural members under high repetition of forces. The mechanistic background of the extended truss model for fatigue design is also investigated. The coupling of fatigue loads with initial defects is simulated and its applicability is discussed as a versatile tool of performance assessment.

A direct path-integral scheme with fatigue constitutive models for concrete tension, compression and rough crack shear is used to predict the life-cycle of RC slabs. The three-dimensional fatigue analysis successfully predicts the characteristic mode of failure under moving loads as well as in the case of fixed-point pulsation in shear. Importantly, drastically shortened fatigue life under traveling wheel-type loads is mechanically demonstrated by implementing a constitutive model of cracked concrete using a direct path-integral method of fatigue damage simulation. A sensitivity study is carried out to clarify the influence of shear transfer decay and compression fatigue on RC slab performance. The effect of boundary conditions on fatigue life is also investigated.

The initiation and subsequent propagation of corrosion-induced cracks is simulated by multi-phase mechanics where the coupled corrosion gel migration and crack-based fracture can be coherently taken into consideration. A key focus is given to the nature of corrosion products and their dependency on the corrosion rate and the anisotropic stiffness and permeability caused by cracking. Migration of corrosion gel to both micro-pores of cementitious composites and crack gaps are explicitly considered under the gradient of gel pressure, which is newly defined on the corrosion gel phase. The effects of cover depth, corrosion rate and the mix-proportion of concrete on the crack initiation and propagation are discussed with experimental facts. The broken symmetry of corrosion profile around reinforcing bars is successfully simulated as a nature even though the geometry of analysis domains would be in perfect symmetry. This scheme which allows kinematics of produced gel is indispensable for a versatile framework of durability mechanics.

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.

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