Multi-scale modeling of structural concrete performance is presented as a systematic knowledge base of coupled cementitious composites and structural mechanics. An integrated computational scheme is proposed for lifespan simulation of reinforced concrete. Conservation of moisture, carbon dioxide, oxygen, chloride, calcium and momentum is solved with hydration, carbonation, corrosion, ion dissolution, damage evolution and their thermodynamic/mechanical equilibrium. The holistic system is verified by the reality.

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Finite element analysis using fiber technique was carried out to study the post-yield buckling mechanism of reinforcing bars. It was found that the softening of compressive stress takes place due to the geometrical nonlinearity associated with the lateral deformation of the compressed bars, especially after the absolute strain exceeds the yielding strain. It was clarified that the post-buckling average stress-strain relationship over the analysis domain can be specified in terms of the product of square root of yield strength and slenderness ratio of the reinforcing bar. Moreover, a unique relationship between the average stress and average strain of reinforcing bars including the effect of buckling is established through various parametric analyses. The comparison of analytical results and proposed model with experimental data showed good agreement.

ABSTRACT:The main aim of this study is to propose simple and reliable method to predict the buckling length of longitudinal reinforcing bars and also to predict the spalling of cover concrete in reinforced concrete members. Stability analysis is conducted giving due consideration to both geometrical and mechanical properties of the longitudinal reinforcing bars and lateral ties. The tie stiffness required to hold longitudinal reinforcing bars in different buckling modes is derived from energy principles, and it is compared with actual tie stiffness to determine the stable buckling mode. The buckling length is computed as the product of the stable buckling mode and the tie spacing. The proposed buckling length determination method is experimentally verified for various cases. A design method for lateral ties to avoid buckling induced strength degradation is also recommended. The effect of lateral deformation of longitudinal bars is quantitatively evaluated and incorporated in the simulation of cover concrete spalling. Analytical prediction considering spalling and buckling according to the proposed methods showed better agreement with the experimental result.Key words: buckling length, cover concrete, lateral deformation, lateral ties, reinforcing bar, spalling, stable buckling mode, stiffness INTRODUCTIONDuring earthquakes, reinforced concrete members may experience significant lateral deformation of the longitudinal reinforcing bars accompanied by spalling of cover concrete due to large compressive strain. Analytical models neglecting these inelastic material mechanisms cannot capture the post-peak softening behavior accurately, and will consequently overestimate the response ductility (Suda et al. 1996). Hence, average stress-strain relationships of concrete and reinforcing bar including spalling and buckling mechanisms are needed.It is commonly assumed that the behaviors of reinforcing bar in tension and in compression are similar. In reality, average behavior in compression is different from that in tension. This difference is mainly attributed to the geometrical nonlinearity associated with large lateral deformation of buckled reinforcing bars. Various average compressive stress-strain relationships including buckling (Monti and Nuti 1992; Gomes and Appleton 1997; Rodriguez et al. 1999) have been proposed based on experimental and/or analytical studies of bare bar under axial compression. All of these relationships implicitly or explicitly suggest that the average compressive response of bare bar is a function of length to diameter ratio. For practical application in reinforced concrete members with a system of lateral ties, the bar length used in such bare bar constitutive relations should be replaced with the buckling length of longitudinal reinforcing bar. Hence, the potential buckling length should be pre-determined considering geometrical and mechanical properties of reinforcing bars and cover concrete spalling that may also affect the reinforcement stability.Longitudinal reinforcing bars inside RC mem...

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.