Equivalent Shell Model of Elastic Gridshells Including the Effect of the Geometric Curvature

In this work, an equivalent continuum of a barrel gridshell is introduced. Constitutive identification procedures based on periodic homogenization are provided in the literature for this purpose, based on a flat Representative Element Volume (REV), notwithstanding that the geometry of the structures concerned is curved. Therefore, the novelty of the present study is the selection of a curved REV to obtain the equivalent elastic constants. The numerical validation of the identification procedure is made comparing gridshell response to that of the equivalent shell under homogeneous load conditions. Finally, in order to highlight the effect of the curved geometry on the constitutive law of the continuum, the response of the proposed model is also compared to that of a continuum obtained from a flat REV.

Relationship between the representative element volume and discontinuity parameters

We introduce an application of the discrete fracture network (DFN) model and 3D persistence to study the relationship between the representative element volume (REV) size and discontinuity information. To avoid the influence of heterogeneity on the distribution of discontinuities, the dam abutment rock mass of the Songta hydropower station is divided into eight statistically homogeneous domains based on the discontinuity orientation and trace length. An optimum DFN model is established for each homogeneous domain. Cubes of different sizes are extracted from the centre of the corresponding DFN model. Based on the discontinuity projection method, the 3D persistence values within the DFN model and each cube are calculated separately. The relative error of persistence for each cube and the DFN model are used to evaluate the size effect and to identify the REV size. Subsequently, the relationship between the determined REV size and the corresponding discontinuity information is systematically researched. Our results show that the discontinuity diameter, the volume density and the Fisher constant have separate linear relationships with the REV size. We present the empirical formulas for estimating the REV size according to the discontinuity diameter, the volume density and the Fisher constant.

A methodology of re-generating a representative element volume of fractured rock mass

In simulation of fractured rock mass such as mechanical calculation, hydraulic calculation or coupled hydro-mechanical calculation, the representative element volume of fractured rock mass in the simulating code is very important and give the success of simulation works. The difficulties of how to make a representative element volume are come from the numerous fractures distributed in different orientation, length, location of the actual fracture network. Based on study of fracture characteristics of some fractured sites in the world, the paper presented some main items concerning to the fracture properties. A methodology of re-generating a representative element volume of fractured rock mass by DEAL.II code was presented in this paper. Finally, some applications were introduced to highlight the performance as well as efficiency of this methodology.

Regularized lattice Bhatnagar–Gross–Krook model for the thermal flow in porous media

A regularized lattice Bhatnagar–Gross–Krook model for flow and heat transfer in porous media at the representative element volume scale is presented. In the model, the regularization process is extended to the existing Darcy–Forchheimer-based lattice Bhatnagar–Gross–Krook scheme. Numerical results show good agreement between the present model and the previous ones. Also, the present model shows better numerical stability than its lattice Bhatnagar–Gross–Krook counterpart.

Analysis Technique on Water Permeability in Concrete with Cold Joint considering Micro Pore Structure and Mineral Admixture

Cold joint in concrete due to delayed concrete placing may cause a reduced shear resistance and increased water permeation. This study presents an analytical model based on the concept of REV (Representative Element Volume) to assess the effect of water permeability in cold joint concrete. Here, OPC (Ordinary Portland Cement) concrete samples with cold joint are prepared and WPT (Water Permeability Test) is performed on the samples cured for 91 days. In order to account for the effect of GGBFS (Granulated Ground Blast Furnace Slag) on water permeability, concrete samples with the same W/B (Water to Binder) ratio and 40% replacement ratio of GGBFS are tested as well. Utilizing the previous models handling porosity and saturation, the analysis technique for equivalent water permeability with effective cold joint width is proposed. Water permeability in cold joint increases to 140.7% in control case but it decreases to 120.7% through GGBFS replacement. Simulation results agree reasonably well with experimental data gathered for sound and cold joint concrete.

Nonlinear Model for Viscoelastic Behavior of Achilles Tendon

Although the mechanical properties of ligament and tendon are well documented in research literature, very few unified mechanical formulations can describe a wide range of different loadings. The aim of this study was to propose a new model, which can describe tendon responses to various solicitations such as cycles of loading, unloading, and reloading or successive relaxations at different strain levels. In this work, experiments with cycles of loading and reloading at increasing strain level and sequences of relaxation were performed on white New Zealand rabbit Achilles tendons. We presented a local formulation of thermodynamic evolution outside equilibrium at a representative element volume scale to describe the tendon’s macroscopic behavior based on the notion of relaxed stress. It was shown that the model corresponds quite well to the experimental data. This work concludes with the complexity of tendons’ mechanical properties due to various microphysical mechanisms of deformation involved in loading such as the recruitment of collagen fibers, the rearrangement of the microstructure (i.e., collagens type I and III, proteoglycans, and water), and the evolution of relaxed stress linked to these mechanisms.