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The traditional first-order plastic hinge method (FPHM) utilizes the proportionality property to rapidly estimate the external load increment between any two adjacent plastic hinges, with superior computational efficiency. However, the FPHM cannot consider the influence of second-order effects and residual stresses. Although the refined plastic hinge method (RPHM) overcomes these problems, it must solve the nonlinear structural stiffness equation, resulting in low computational efficiency. In this paper, the second-order generalized plastic hinge method (sGPHM) is proposed to evaluate the ultimate bearing capacity of unbraced steel frames on the basis of using the proportionality property to estimate the external load increment. First, the element bearing ratio (EBR) that considers second-order effects and residual stresses is defined. Since the EBR and the external load are proportional, the plastic yield degree of the cross-section can be easily obtained. Then, the displacement increment and the load increment between any two adjacent plastic hinges can be rapidly estimated through the proportionality property between the EBR and the external load. Accumulating all load increments can determine the ultimate bearing capacity of frames. Finally, several benchmark frameworks in the literature are compared and analyzed with different methods to verify the superior calculation accuracy and efficiency of the proposed sGPHM. [ABSTRACT FROM AUTHOR]

In this paper, a resilience assessment framework for microencapsulated self-healing cementitious composites is proposed based on a micromechanical damage-healing model. A 3D micromechanical analytical model is constructed to analyze the performance evolution during the damage-healing process of self-healing concrete. The resilience assessment of microencapsulated self-healing concrete is defined by virtue of the residual stiffness, self-healing effect on stiffness and damage cumulative on stiffness, which corresponds to three main features of resilience; namely, the robustness, recoverability and adaptability. The assessment results indicate that the release of healing agents within microcapsules and healing process of extended microcracks allows the microencapsulated self-healing concrete to have higher resilience than conventional concrete. Moreover, a parameter sensitivity analysis is conducted to investigate the influence of the healing efficiency, the applied initial damage and the fracture toughness of the repaired microcrack on resilience of microencapsulated self-healing concrete. The results indicate that higher healing efficiency and applied initial damage leads to high resilience, and fracture toughness of the repaired microcrack makes less difference to the results. The findings of this paper lay a theoretical foundation for the resilience design of self-healing material layer of underground structures. [ABSTRACT FROM AUTHOR]

With the rapid development of high-speed railway construction around the world, the structural damage problem of tracks and bridges has attracted more and more attention. In this paper, considering the random structural damages of tracks and bridges, an efficient computational procedure is developed based on the probability density evolution method to systematically investigate the random characteristics of the dynamic responses varying with the damages in vehicle–track–bridge time-dependent systems. Firstly, a vehicle–track–bridge dynamic model with random structural damage parameters is established, and the random motion equations are derived based on the generalized energy principle. Then, the probability density evolution equation for each random response is established and the random feature is investigated by the proposed computational procedure. Finally, the representative numerical examples are applied and some conclusions for the effects of the random structural damages on the dynamic responses of the vehicle–track–bridge systems are presented. [ABSTRACT FROM AUTHOR]

Interfacial debonding between fibers and matrix is one of the dominant damage types in fibrous composites. This paper investigates weakening effect due to the interfacial debonding. For simplification, the fibers are assumed to be rigid since the modulii and strength of fibers are much greater than those of matrix, and the distribution of the radii of fibers is assumed to obey the logarithmic normal distribution. The matrix is assumed to be a viscoelastic material. The boundary of the composite is subjected to transverse loading condition, the direction of which is perpendicular to that of fibers. The interfacial debonding between fibers and matrix is analyzed by the energy criterion, and the evolution formula of nucleated porosity due to the debonding is derived by the statistical approach. A newly defined volume average method is proposed to establish the macroscopic constitutive relation of the composites. The effect of the material parameters of matrix, as well as the size of fibers on the critical stress for the interfacial debonding and damage evolution are discussed in detail. The results obtained in this paper indicate that the macroscopic strain rate, the dispersion degree of the fiber's radii, the adhesive energy at the interface, and loading condition play key roles in the overall mechanical properties of the composites. [ABSTRACT FROM AUTHOR]

A multi-scale micromechanical model is proposed to predict the damage degree of hybrid fiber-reinforced concrete under or after high temperatures. The thermal degradation of hybrid fiber-reinforced concrete is generally composed of the damage of the cement paste caused by thermal decomposition and thermal incompatibility, the deterioration of aggregates and fibers, and the interfacial damage between aggregates and the matrix. In this multi-scale model, four levels of hybrid fiber-reinforced concrete structures are considered when the thermal damage degree is derived; namely, the equivalent calcium silicate hydrate (C–S–H) product level, the cement paste level, the concrete level, and the hybrid fiber-reinforced concrete level. At the cement paste level, thermal decompositions of C–S–H product and calcium hydroxide are taken into account. In addition, a dimensionless parameter of the crack density is introduced to represent the thermal cracking of the matrix. At the concrete level, the interfacial damage of aggregates is simulated by a spring–interface model, in which the interfacial parameters are assumed to be functions of temperature. Moreover, at the cement paste level and the hybrid fiber-reinforced concrete level, a sub-stepping homogenization method is proposed to determine the effective properties. Comparisons between previously published experimental data and predictions and discussions illustrate the feasibility of the proposed multi-scale model in predicting thermal damage of concrete and hybrid fiber-reinforced concrete. [ABSTRACT FROM AUTHOR]

This paper addresses application of an energy-based plastic-damage model for concrete to the modeling of hysteretic responses of reinforced concrete (RC) shear walls. Both damage evolution and plastic flows are accounted for within the framework of thermodynamics, resulting in consistent energy-based damage evolution laws. The model is implemented in the commercial software package ABAQUS via the user-defined material subroutine and applied to two representative benchmark tests of RC shear walls under cyclic loading. It is shown that with the steel reinforcement properly accounted for, the energy-based plastic-damage model can capture realistically the failure modes, load capacities, and overall load–deformation responses of RC shear walls. [ABSTRACT FROM AUTHOR]

For spatial design freedom, steel castings are widely used in bridges, airport terminals, and offshore platforms. However, different from hot-rolling technology, casting process variables, such as the casting temperature and those related to graphite spheroidization and post-heat treatment, may cause casting defects. To improve the safety and effectiveness of steel castings, a study consisting of experiments and numerical calculations is performed to investigate the effect of pores on the damage and fracture of cast steel. The chemical composition, metallography, and tomographic imaging of cast and hot-rolled steels were compared, providing a clear understanding of cast steel at the microstructure level. In addition, a complete Gurson–Tvergaard–Needleman damage model is used to predict the ductile fracture of cast steel containing pores. Good agreement is obtained between the measured and predicted tensile curves as well as between the measured and predicted void volume fraction evolution. [ABSTRACT FROM AUTHOR]

Water changes natural seepage in the surrounding geological environment and weaken rock mass of valley during reservoir impounding, which result in large time-dependent deformation of foundation of dam. A nonlinear creep damage model considering water effect is proposed by taking into account the influence of pore pressure on the spherical stress tensor and yield surface. The elastic-viscoelastic model is consisted of a spring and several cascaded Kelvin models. The model is implemented in the ABAQUS user material subroutine. The accuracy of the model is verified by the triaxial creep test of saturated sandstone and dry sandstone. Then it is applied in the valley contraction analysis during impounding of Xiluodu high arch dam. [ABSTRACT FROM AUTHOR]

In order to simulate the specific load-carrying behavior of masonry arch bridges, nonlinear finite element analyses may be carried out. To that end, an associated analysis concept is proposed in this paper. The applied smeared crack model allows one to realistically reproduce characteristic damage patterns observed at existing bridge structures of this type. By using the proposed analysis concept, load-bearing reserves may be revealed and possible causes for existing damage may be identified. The concept includes appropriate failure criteria and corresponding safety margins. The latter approximately conform to valid design codes, but also account for the specifics of nonlinear analyses. In parametric studies, the objectivity of the analysis results and influences of different material parameters on the load-bearing behavior were investigated. Furthermore, two examples of the safety evaluation of existing masonry arch bridges are presented. In both cases, observed damage patterns could be reproduced in the numerical simulations. Destructive load tests at a disused bridge provided an additional opportunity to validate the proposed analysis concept. [ABSTRACT FROM AUTHOR]

Three distinct length scales are involved in the deformation evolution and catastrophic rupture of heterogeneous rocks in general: two essential ones are the specimen size macroscopically and the grain size at micro-scale respectively, the other is the emerging localized band of deformation and damage. The band initiates almost nearby the peak load, and the rupture eventually occurs afterwards within the localized band. In this paper, we report that with the evolution of concentrated high strain and damage in the localized band, a power-law singularity emerges within the localized band preceding the eventual rupture. The localization of deformation imposes a spatial non-uniqueness on the power-law singularity, and then leads to a trans-scale characteristic of the power-law singularity. Based on this characteristic, it is demonstrated that the singularity presented by the global response of a whole specimen comes from the singularity of local response in the localized band. The localization and the power-law singularity are associated precursory events, spatially and temporally, respectively, before macroscopic rupture. In particular, based on the power-law singularity exhibited in the zonal areas near or across the rupture surface, a prediction of the occurrence time of catastrophic rupture can be made accordingly. This provides a practically helpful approach to the prediction of rupture, merely by means of monitoring the zonal areas adjacent to the localized band. [ABSTRACT FROM AUTHOR]

A computational homogenization model using microstructures obtained from X-ray micro-CT is developed to estimate the porosity-based elastic properties of ultra-high performance concrete under freeze–thaw action. The model is transformed directly from micro-CT which is capable of reflecting realistic distribution of porosity and heterogeneities inside the ultra-high performance concrete. Factors are taken into consideration, including the determination of representative volume element, the position and numbers of representative volume element cubes, fiber orientation, image resolution, applied filter, and pore distribution. The relationship between the material internal structure and freeze–thaw resistance is studied at micro-scale. The volume-averaged homogenization approach is applied to calculate the effective properties of the ultra-high performance concrete which are compared with experimental data. It is demonstrated that the proposed model provides an effective tool to evaluate the elastic properties of the ultra-high performance concrete based on microstructural characterization data. [ABSTRACT FROM AUTHOR]

The torsional fatigue behavior of a high-strength spring steel, SWOSC-V, was investigated. Of particular interest were the influences of small scratches and superimposed static shear stress in the very high cycle fatigue regime. To achieve the research objectives, an ultrasonic torsional fatigue testing machine was developed. S-N curves showed the fatigue limit for the tested material condition (i.e. with no residual stresses at specimen surface). This study revealed that a notable influence of the stress ratio, R, on the torsional fatigue behavior was not explicitly recognized. Concerning the influence of small scratches, it was found that the area -parameter model can predict the lower bound of the torsional fatigue limit, irrespective of the value of R. [ABSTRACT FROM AUTHOR]