查看更多>>摘要：The Baling River Bridge is a single-span simply-supported suspension bridge with a main span of 1088 m. The steel stiffening truss is employed as its main girder and comprises the integral joints connecting the chord members. The integral joint is a key structure and determines the safety of the bridge, but it is very complex in detail and has an undefined fatigue resistance. In order to investigate its mechanical behavior and fatigue reliability, a fatigue test was performed on a 1:1.4 scale model of the integral joint of the main truss of the Bridge. With an assumption of the load spectra represented by the standard fatigue vehicle in BS 5400, the test fatigue load was derived accounting for the multiple vehicle effect and the model scale. The test result shows that no cracks were detected in the model when subjected to two million stress range cycles, and the structure has an reliable fatigue resistance satisfying the design requirement. This type of integral joint is an alternative for long-span truss bridges.
查看更多>>摘要：How to judge the rockburst proneness of rocks is one of the key works to predict rockburst. A preliminary approach is made to the relationship between the rockburst proneness and the spectrum characteristic of the rocks by means of experiments in the present paper. The following conclusions are obtained. Firstly, under the condition without loading, there is not any regular relation between the rockburst proneness and the spectrum characteristic of the tested rocks. And secondly, under the condition of uniaxial loading, the spectrum curves of the tested rocks with different rockburst proneness all change with the increase of stress. These curves possess similar tendencies, but different shapes, inflexions and developing rates.
查看更多>>摘要：Ceramic - metal interfaces are often present in composite materials. The presence of cracks has a major impact on the reliability of advanced materials, like fiber or particle reinforced ceramic composites, ceramic interfaces, laminated ceramics. The understanding of the failure mechanisms is very important, as much as the estimation of fracture parameters at a tip of the crack approaching an interface and crack propagation path. The asymptotic solution of the stress field at the tip of a crack normal to a bi-material interface is presented. A cracked sandwich plate loaded by uniform normal stress was numerically investigated using Finite Element Analysis. The numerical results of the circumferential stress distribution were compared with the analytical solutions. The results for the non-dimensional stress intensity factors show that at lower crack lengths the influence of material mismatch is lower but this influence increases with increasing the crack length.
查看更多>>摘要：The objective of this investigation was to develop a test methodology to assess the fatigue performance of cold patch asphalt mixtures, potentially usable in the field as a quality control method.The methodology was developed by identifying the relationships between the parameters from a Laboratory Fatigue Test (IDT,according to ASTM D4123 ), and the penetration rate (NPR) from a lighter version of the Dynamic Cone Penetrometer (DCP) at various densification levels. Multiple linear regression analysis (MLRA) was used to develop equations to estimate number of load cycles to fatigue, and critical tensile strain. The fatigue equations were satisfactorily validated after comparing the measure stability parameters from two mixtures not used in the regression analysis. Cross-validation using SPSS procedure was also implemented.
查看更多>>摘要：The use of gneiss as aggregates might help meet the pavement constructing demands. However, the study of the pavement performances of gneiss asphalt mixture is few. In this paper, the microstructure of gneiss aggregate was studied by Scanning Electron Microscopy (SEM). And the pavement performances of gneiss asphalt mixture with different improving measure were characterized by means of Indirect Tensile Strength Test and Four-Point Bending Fatigue Test. Gneiss is flaky, surface texture rougher and imporosity characteristic in microstructure, resulting to its adhesion and processing property are poor. Experiment results indicate that the use of hydrated lime replacing limestone power partly in filler can improve pavement properties of the gneiss asphalt mixtures distinctly.
查看更多>>摘要：This paper presents a computational framework for simulation of delamination that combines the features of the discontinuous Galerkin methods with the versatility of the cohesive zone models. Within the finite element formulation of the discontinuous Galerkin methods, displacement discontinuities (jumps) are allowed across the element boundaries. Thus, the cracks are naturally included in the model without modifying the initial mesh. The displacement discontinuities across the element boundaries are used to compute the separations in the cohesive fracture law. The delamination initiation occurs when the traction across the element boundaries reaches its maximum; when the separation exceeds a critical value, total decohesion occurs. Numerical example is presented to illustrate the validity and effectiveness of the present methodology.
查看更多>>摘要：Adhesively bonded connections involving pultruded FRP typically fail in a brittle manner, making their analysis a case study for the application of statistical size effects. For brittle materials, in which failure is often caused by a single critical defect, statistically based size effects on strength are adequately explained by probabilistic theories such as the Weibull strength theory. A previously implemented probabilistic dimensioning method for adhesively bonded balanced joints is extended to a complex joint involving a tube and a lamella, both made of pultruded FRP. Instead of the previously used 2d approach the extension requires a 3d formulation. The entire joint is idealized as being constituted by n elements; its survival depends on the simultaneous survival of all elements. By the means of a 3d FEA, failure triggering stress components in all n elements were determined; a probability of failure is associated to each element using the corresponding combination stresses combined into an appropriate failure criterion, hence defining a theoretical joint strength.
查看更多>>摘要：High-performance concrete will undergo severe damage under fire conditions. It is well known that vapor pressure induced by high temperatures plays an important role in the damaging process. This paper presents a method of vapor pressure modeling, called equivalent expansion method, which can be implemented in FEM analysis. The modeling procedure consists of two parts, i.e. vapor pressure determination and vapor pressure modeling incorporated in FEM analysis. In order to make analysis more accurate, steam table is'employed instead of ideal gas equation.
查看更多>>摘要：Interactions between adjacent, insufficiently separated buildings have been repeatedly observed during major earthquakes. This phenomenon, known as the earthquake-induced structural pounding, may be the reason of local damage at the contact points as well as may lead to the extensive damage at the base of the colliding structure or even initiate its total collapse. In this paper, we examine the importance of inelastic modelling of structural behaviour as the result of damage due to earthquake excitation and structural pounding. The study concerns two adjacent four-storey buildings with different dynamic properties. In the numerical simulations, the nonlinear viscoelastic model is used to model the pounding force during collisions at different storey levels of the structures. The model allows us to take into consideration the dissipation of energy due to damage taking place at the time of collision. Three different ground motion records with different peak ground acceleration levels are used in the study. The comparison between elastic and inelastic damage-involved structural behaviour is investigated. The results of the study show significant changes in the dynamic responses of the inelastic systems as compared to those of elastic ones. The results clearly indicate that modelling the colliding buildings to behave inelastically is really essential in order to obtain accurate damage-involved structural response under earthquake excitation.
查看更多>>摘要：High speed MODE I crack growth in elastic-plastic materials, involving large scale plasticity and dynamic effects connected to rapid propagation, is faced through a cohesive model to tune force nodal release. The stress resisting to the opening of the edges in the cohesive zone should account of effective stress field ahead crack tip. In this paper a reference value is accounted: it represents the maximum closing stress measured at the crack tip, where the cohesive effects begin. A bi-parametric analytical formulation of stress distribution ahead the crack tip is suggested. The bi-parametric formulation is able to extrapolate the stress at the tip whatever is the T-stress (i.e. the stress acting in the direction of fracture propagation), thus completely defining the cohesive loads.
NETL
NSTL