Abstract Due to the limited drilling accuracy of the drilling jumbo, the unavoidable outward inclination of perimeter blastholes is a key factor causing overbreak and damage to the remaining rock mass. However, effective methods to control this issue remain limited. In this study, a combined approach of laboratory blasting experiments and numerical simulations was adopted to investigate the crack propagation characteristics, stress response, and damage evolution of the surrounding rock under equal-length blastholes and long–short hole combined arrangements. The results indicate that the long–short hole configuration effectively guides interhole crack propagation along the designed contour. This approach can significantly reduce overbreak and decrease both the peak strain and damage level on the remaining rock mass side. Further analysis reveals that the short-to-long hole ratio (SLR) has a significant influence on blasting performance, and an SLR of 0.5 produces the lowest overbreak and retained-rock damage volumes among the investigated cases under the present model conditions. These findings demonstrate that a properly designed long–short hole combination can effectively control overbreak and surrounding rock damage while maintaining excavation efficiency, providing a practical approach to mitigate overbreak induced by outward inclination in engineering practice.
Abstract The mechanical properties of structural concrete are greatly influenced by both lateral confinement and elevated temperature. Nevertheless, it remains challenging to establish a constitutive formulation that can simultaneously capture thermal strain development, irreversible deformation, and stiffness deterioration in concrete subjected to multiaxial loading during fire exposure. Hence, this paper proposes a three-dimensional nonisothermal plastic damage model for concrete. Specifically, a capped yield surface that evolves with temperature is used to define the plastic behavior, and a nonassociated flow rule is adopted to govern the plastic strain increment. The evolution of plasticity and stiffness degradation is further governed by hardening and damage formulations that depend on both temperature and confinement, with regularization introduced to reduce mesh sensitivity during strain-softening. Moreover, a stress triaxiality measure is embedded in the load-induced strain formulation to capture the contribution of lateral confinement during heating. For numerical implementation, the model is implemented in Abaqus version 2021 through a UMAT subroutine, and the stress update is carried out by an explicit scheme that couples adaptive Runge-Kutta-Dormand-Prince sub-stepping with stress correction to maintain the accuracy of the updated stress state. Its predictive capability is assessed against 26 material-level tests and five concrete-filled steel composite column tests under ambient-temperature and fire conditions. The comparisons indicated that the model captures key experimental features, including confinement-induced strength enhancement, thermal deterioration, thermal strain evolution, and stiffness degradation, thereby supporting its application to nonlinear analysis of structural concrete under ambient and fire scenarios.
Abstract Evaluating time-variant structural system reliability is vital for the life-cycle design and health monitoring of trusses. However, the numerous failure modes inherent in highly redundant trusses make calculating their system reliability extremely challenging. In this work, a constructed structural pseudostiffness matrix is employed to characterize the possible system failure of trusses induced by member failures. Its advantage lies in avoiding the search for failure modes and enabling the minimum eigenvalue of the matrix to serve as an explicit performance function for identifying truss failure. Considering the time-dependent nature of the structural parameters, a generalized density evolution equation for this minimum eigenvalue is established. To improve the efficiency of solving the equation, an analytical expression for the time derivative of the minimum eigenvalue is derived based on sensitivity analysis of the eigenvalues with respect to time-dependent structural parameters. Neumann expansion is also employed to efficiently approximate the inverse of the time-dependent tangent stiffness matrix. Additionally, a numerical strategy for calculating the time-variant system reliability of trusses is proposed, and three numerical examples are employed to validate the accuracy and efficiency of the proposed method by comparing the results with those of Monte Carlo simulation, the single-loop kriging surrogate model method, and the time-dependent adaptive support vector machine method.
Abstract A corotational finite-element formulation is developed for piezoelectric plane frames subject to small strains but large deformations. In the corotating (local) system, the element is linear and superconvergent, with no electrical degrees of freedom. The formulation is derived from a piezoelectric beam theory that incorporates the Timoshenko displacement assumption and assumes a quadratic variation of the electric potential through the thickness of each piezoelectric patch. All linearizations required by the Newton–Raphson solution procedure, including those related to certain induced follower loadings, are explicitly and consistently derived. The proposed formulation (a) avoids membrane, transverse shear, and piezoelectric lockings; (b) yields assembled stiffness matrices that are not affected by the high condition numbers, typically found in piezoelectric finite-element models; (c) requires no special corotational algorithm; and (d) effectively handles large deformations, as demonstrated through numerical examples, including shape control applications.
Abstract Exposure to high temperatures severely deteriorates concrete mechanical performance and aggravates the intrinsic stochasticity of its deformation response, creating critical obstacles to the reliability evaluation of fire-damaged concrete structures. Distinct from concrete at ambient temperature, specimens heated to elevated temperatures display prominent stress–strain dispersion from the very start of uniaxial compression, and this scatter becomes more significant with rising temperatures. Traditional stochastic damage models that merely treat fracture strain as a random variable cannot reproduce this early-stage random fluctuation accurately. Within the mesoscopic stochastic fracture framework, this paper develops a novel constitutive model by introducing two statistically independent random fields for elastic modulus and fracture strain, and derives closed-form analytical formulas for the mean and variance of full-range stress–strain curves. The model is fully calibrated and verified against systematic uniaxial compression test data covering four concrete strength grades and multiple thermal levels with abundant replicate specimens. Validation outcomes revealed that high temperatures generate additional elastic-stage randomness driven by spatially uneven thermally induced microstructural deterioration. The scattered ascending segment of stress–strain curves is governed by the randomness of elastic modulus, whereas peak bearing capacity and postpeak softening evolution are controlled by the variability of fracture strain. Comparative analyses demonstrated that the dual-random-field model outperforms classic single-random-field formulations in capturing both average mechanical behavior and probabilistic dispersion, particularly for the ascending branch under medium and high temperatures. The established model delivers a solid constitutive foundation for probabilistic analysis and fire safety assessment of concrete structures under thermal exposure.
