Abstract
Time-dependent responses of cracked concrete structures are complex, due to the intertwined effects between creep, shrinkage, and cracking. There still lacks an effective numerical model to accurately predict their nonlinear long-term deflections. To this end, a computational framework is constructed, of which the aforementioned intertwined effects are properly treated. The model inherits merits of gradient-enhanced damage (GED) model and microprestress-solidification (MPS) theory. By incorporating higher order deformation gradient, the proposed GED-MPS model circumvents damage localization and mesh-sensitive problems encountered in classical continuum damage theory. Moreover, the model reflects creep and shrinkage of concrete with respect to underlying moisture transport and heat transfer. Residing on the Kelvin chain model, rate-type creep formulation works fully compatible with the gradient nonlocal damage model. 1-D illustration of the model reveals that the model could regularize mesh-sensitivity of nonlinear concrete creep affected by cracking. Furthermore, the model depicts long-term deflections and cracking evolutions of simply-supported reinforced concrete beams in an agreed manner. It is noteworthy that the gradient nonlocal enhanced microprestress-solidification theory is implemented in the general finite element software Abaqus/Standard with the implicit solver, which renders the model suitable for large-scale creep-sensitive structures.
Highlights
Concrete creep is the deformation phenomenon developing over time under the load action (Bažant and Li 2008)
The current mechanical models are suitable for describing serviceability limit states (Schlappal et al, 2020)
The model successfully regularizes the mesh-sensitivity problem, which is already concerned with mechanical analyses of materials exhibiting softening, but less with the nonlinear creep intertwined with cracking
Summary
Concrete creep is the deformation phenomenon developing over time under the load action (Bažant and Li 2008). The key parameter in implementing the GED-MPS model is to obtain the local equivalent strain field ε(ε′), which is a function of the strain tensor ε′ To this end, we turn our attention to the numerical treatments of increments of creep strain tensors, namely the aging viscoelasticity Δεv and the viscous flow Δεf. Meshsensitivity solution is a concern, as the creep depends on the stress tensor and the damage state at each material point To this end, the proposed GED-MPS model is applied to the same bar. Conventional linear viscoelastic analysis considering only creep and shrinkage deformations, without intertwined effect with concrete damage and cracking (termed as MPS in Figure 10), is compared to the GED-MPS model in Figure 10A for specimens B2-a and Figure 10B for specimen B2b. It is noteworthy that h 1.0 illustrates the effect of creep on the long-term deflection only, without shrinkage effect
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