Stress Evolution in Restrained Ggbfs Concrete Due to Autogenous Deformation: Bayesian Optimization of Aging Creep

Predicting early‐age stress evolution in restrained concrete by thermo‐chemo‐mechanical model and active ensemble learning

“…The mechanical field is formulated by a 13‐unit Kelvin chain rheological model and solved incrementally by the exponential algorithm (Bažant & Chern, 1985). The mechanical field adopted in this work has been discussed and validated based on the TSTM tests performed by the authors (see Liang, Li, et al., 2022). Taking the output of the material model and the TC field, the mechanical field can output the EAS evolution (i.e., a 672‐by‐1 vector), which is prepared for the further AEL process.…”

“…In this paper, a 13‐unit spring‐dashpot Kelvin chain is used. The Kelvin chain parameters (i.e., elastic modulus and viscosity in each unit) calculated here have an error range of 2% in the fitting process of the creep compliance and covers a wide range of time steps (Liang, Li, et al., 2022). Specific parameters of this Kelvin chain should be derived from the creep compliance surface J(t, t ’ ) obtained from the material model, which can be written as the following double‐power law: $$\begin{equation}J\left( {t,\ t{\rm{\rm{^{\prime}}}}} \right)\ = \frac{1}{{E\left( {t^{\prime}} \right)}} + {C}_0\ {C}_1\left( {t^{\prime}} \right){C}_2\left( \xi \right)\end{equation}$$where C 0 is a constant coefficient; C 1 is a power function to describe the aging of creep compliance; C 2 is a power function representing the non‐aging term, which mainly depends on the time of loading ξ ( ξ = t‐t′ ).…”

“…In this paper, the spectrum of third order ( k = 3) is used, which is sufficient for obtaining a Kelvin chain to mimic the code with a small error within 2% (Liang, Li, et al., 2022).…”

“…The geometry of the dog‐bone specimen in the TSTM test (Liang, Li, et al., 2022; Lokhorst, 2001) is used in the TCM model, which has a 100*150*850 mm 3 prism in the middle, and two clamping heads at the two ends. The dog‐bone specimen simplifies structural factors (geometry, boundary conditions), which can significantly vary from case to case and are difficult to parametrize in a single model.…”

“…Finer mesh is applied at the two ends of the middle prismatic part as shown in Figure 3. A study on the influence of mesh size on the modeling results was performed in the author's previous work (see Liang, Li, et al., 2022), by changing the number of elements from 270 to 6318. It was found that the EAS results remain constant after increasing the number of elements from 1150 to 6318.…”