Journal of Engineering Mechanics

This paper compares three approaches for predicting the bridge response under moving vehicles. The first approach represents the vehicle as a concentrated moving load, while the second and third approaches simulate the vehicle using single (1-dof) and two (2-dof) degrees of freedom models, respectively. The vehicle–bridge models have been implemented following a finite-difference formulation. These models have been validated against the experimental displacement response of a mid-span prestressed reinforced concrete bridge. Parametric analyses have been conducted to investigate the impact of road roughness on the discrepancies between the models’ predictions. An increasing level of road roughness, modeled according to ISO-8608, tends to conceal the mutual differences between the models’ outcomes. Furthermore, a Monte Carlo simulation has been employed to fit the probability distributions of two indicators, comparing the bridge displacement responses in three roughness scenarios and considering variable velocity and vehicle characteristics. The primary objective is to assess whether there are scenarios where vehicle–bridge interaction modeling becomes indispensable for accurately estimating the vehicle’s effect on the bridge response. The paper presents expressions for four probability density functions of the chosen metric, facilitating the comparison between the 1-dof and 2-dof models with the concentrated load approach.

In this paper, for the first time, isogeometric analysis (IGA) and nonlocal theory are used to investigate the free vibration and transient response of bidirectional functionally graded porous (BFGP) curved nanobeams with elastic boundary conditions (BCs) and variable nonlocal parameters. Different from traditional boundary conditions, where a curved beam’s beginning and end positions are connected by an elastic system of straight and torsion springs, this allows for greater flexibility in controlling the stiffness of the springs to obtain arbitrary boundaries. One thing that sets this research apart from others is the hypothesis that the mechanical characteristics of the materials, including nonlocal parameters, are supposed to change according to Voigt schemes in the direction of thickness, length, and porosities of the beam. On the basis of higher-order shear curved beam theory, Hamilton’s principle is used to develop the curved nanobeam’s equations of motion. The accuracy of the proposed model is established by juxtaposing the current study’s findings with those of credible papers. A comprehensive examination has been conducted to analyze the impact of input parameters on the free vibration and transient response of BFGP curved nanobeams. Furthermore, the benchmark solutions elucidated in this work might serve as a valuable reference for analyzing the free vibration and transient response of BFGP curved nanobeams in other investigations.

Abstract

This paper presents a time-dependent analytical solution for undrained elastoplastic response of a porous, fluid-saturated medium to fluid source at the center of an embedded spherical, porous, fluid-saturated inhomogeneity inclusion. The solution considers poroelastic coupling in the inclusion while solving for the surrounding matrix stress using a Lagrangian formulation of the incurring elastoplastic deformations. The solution for plastic deformation of the matrix is obtained using the large deformation theory of plasticity with associated flow rule of either the strain-hardening Drucker-Prager model or smoothed strain-hardening Mohr-Coulomb model. The obtained solution is used as a proxy model to study caprock stress evolution upon fluid injection in subsurface rocks to mimic applications such as ${\mathrm{CO}}_2$ geo-sequestration. Findings indicate that the (poro)elastic models that are predominantly utilized in the existing studies of the subject could substantially underestimate the caprock shear failure threshold. Results obtained from a presented case study show that 0.8% allowance for elastoplastic strain in the caprock could yield up to 100% increase in fluid injectivity of the embedded reservoir. The presented solution may further serve as a rigorous benchmarking tool for verification of related numerical solution schemes.

Practical Applications

Caprock integrity concerns arise when injecting fluid into an embedded rock formation, e.g., during ${\mathrm{CO}}_2$ geo-sequestration or when withdrawing fluid from a reservoir, e.g., during oil and gas production. This work assesses possible enhancement in the estimated caprock integrity threshold because of plastic deformation beyond elastic limit, yet prior to rock failure. A time-dependent analytical solution for a geometrically idealized model of porous and fluid-saturated reservoir and surrounding caprock is developed for this purpose. Findings indicate that 0.8% allowance in the caprock total elastoplastic strain beyond elastic limit of the rock results in more than a twofold increase in the injectivity of the embedded reservoir. Higher values of plastic strain-hardening parameter or total strain allowance would allow for higher injectivity thresholds. These results underline the necessity for consideration of plastic deformation and stress analysis in studies on caprock integrity analysis.

Despite alkali–silica reaction (ASR) being a major durability problem in concrete, structural features and properties of ASR gels remain poorly understood. Inspired by the success of coarse-grained (CG) simulations in unveiling key features of calcium-silicate-hydrate (C-S-H) gels, we deploy these simulations to model ASR gels. Our goals are (1) to test the suitability of these simulations to capture ASR gels structural features and mechanical properties; and (2) to quantify any alkali-dependency in the response. Effective interactions obtained at the molecular scale for Na-ASR and K-ASR (sodium-ASR and potassium-ASR) products are adopted. Simulation results are consistent with the available data on the structure, elastic, and viscous behavior of ASR gels. The ASR gel mesotexture development and mechanical properties are ion-specific, with Na-ASR showing a more rigid/less viscous behavior overall. Our results demonstrate the suitability of CG simulations to investigate ASR.