Abstract:
The mechanical behavior of reinforced concrete crane girder bolted to rock wall of chamber is analyzed with nonlinear finite element method. The concrete and rock mass are modeled by Drucker-Prager elasto-perfectly plastic constitutive relation. The Drocker-Prager yield criterion has found wide practical application as a method of defining the stress conditions under which rock mass will deform inelastically and collapse. Combined with the extending project practice of underground powerhouse at hydropower stations,the fracturing mechanism and stability of crane girder are investigated numerically. Computational results show that the cohesion and friction angle between rock mass and concrete have a notable influence on the stability of crane girder bolted to rock wall of chamber. The safety factor of concrete crane girder will be reduced with the decrement of inner cohesion between the rock mass and concrete crane girder. The safety factor of concrete crane girder can exceed 3.7 while the failure of interface between the rock mass and concrete occures. The further excavation of underground powerhouse will affect the stress distribution of system bolts and rock mass near crane girder. It is very important for improving stress states and enhancing stability of concrete crane girder to control effectively rock damages induced by excavation blasting.

Abstract:
Rock-bolted crane girder is a widely used structure in underground powerhouse nowadays.In hydropower projects longitudinal crack between rock-bolted crane girder and surrounding rock masses can hardly be found.Aiming at the cracking phenomenon in an underground powerhouse,detailed analysis of the cracking mechanism is made based on geology,monitored data and construction process.It is concluded that the cracking initiates between late October and early November,2006;differential deformation caused by vein faults in the surrounding rock and excavation is the major cause leading to the cracking while the development of the differential deformation cannot be effectively controlled by support measures.So considering the discontinuous characteristics of rock masses,it is important to make detailed geological investigation and to forecast possible differential deformation on the sidewalls during construction period,so as to take effective support measures and assure the safety of the girder.

Abstract:
This study presents fatigue crack propagation experiments and the simulation used to estimate the life remaining in a crane that is currently in use at a port. The fatigue crack propagation experiments were performed by an Instron 8516 fatigue testing machine and the simulation was performed using the AFGROW software. The simulation results indicated that the critical size of the crack in the upper flange surface of the main jib was 107.4 mm and that it would take 818,000 cycles to reach that point. If the main jib of the crane undertakes 28,800 cycles per annum then its remaining lifespan should be 28.4 years.

Abstract:
Crack analysis is vital to explain behavior of concrete structures. In the present study, an interface element with softening spring is used to simulate cohesive zone model (CZM) in beam to accurately explain the propagation for mixed-mode crack. Modified crack closure integral method is implemented to model propagation of fracture process zone (FPZ) and stress-free region. An element stiffness matrix is used to derive forces in nodes due to normal and shear stress in the FPZ. Size effects such as depth of the beam, effective crack and initial notch are considered in calculation of the FPZ length and crack extension. By using this model, energy release rate is calculated directly by virtual crack closure technique (VCCT) by considering the variation of work done by external loads. The model decreases computational time and complexity for discrete cracks and provides accuracy as compared to other previous research.

Abstract:
Wedge-splitting tests of postfire concrete specimens were carried out in the present research to obtain the load-displacement curves. Ten temperatures varying from room temperature to 600°C were employed. In order to calculate the accurate fracture energy, the tails of load-displacement curves were best fitted using exponential and power functions. Three fracture energy quantities (fracture energy , stable fracture energy , and unstable fracture energy ) with their variation tendency and their mutual relationship were determined to predict energy consumption for the complete fracture propagation. Additionally, the stable fracture work was also calculated. All these fracture parameters sustain an increase-decrease tendency which means that the fracture property of postfire concrete shares the same tendency. 1. Introduction Since the application of fracture mechanics to concrete, the energy consumption for crack propagation in concrete has been a popular topic. For concrete, the specific fracture energy has been proven to be a useful parameter in the structure design and fracture behavior modeling. The specific fracture energy of concrete was defined based on a tensile test as the energy absorbed per unit crack area in widening the crack from zero to or beyond the critical value above which no stress can transmit [1]. Based on the work-of-fracture principle, three-point bending test [2], compact tension [3], and wedge-splitting method [4] were proposed as alternative methods to determine the specific fracture energy . It is computed as the area under the entire imposed load and load-line displacement curve divided by the projected area of uncracked ligament, so the fracture energy represents the average or nominal energy consumption of concrete for an entire crack propagation process. The existence of fracture process zone FPZ ahead of a crack is now well accepted. Since the 1970s, it has been known that the evolution of the FPZ undergoes two distinct periods—precritical stable crack growth and unstable fracture process [5]. There is no doubt that crack propagation is accompanied by energy dissipation, and the motive for crack propagation comes from either work provided by the imposed load or released strain energy. Fracture energy is one appropriate consideration to describe the amount of energy consumed during crack propagation process. It is worth noting that the fracture energy can only represent the amount of average energy dissipation for entire crack propagation from crack initiation to complete failure without characterizing crack stable

Abstract:
The article presents the design method of concrete elements, the property that defines this method is the inclusion in internal force the resultant voltage vector in crack-tip vicinity, where elastic stress exceeds concrete design stress to split. This method (if compared to traditional design methods) allows to determine construction stress strain behavior in all working stages. This method can be useful for experiments operation, assessment of residual structural load capacity during engineering survey, design of reinforced concrete constructions.

Abstract:
A quantitative description for the spatial distribution and the evolution of a crack network in mining rock stratum is one of the most difficult and fundamental problem in the subject of surface subsidence. In this paper, the physical models are employed to simulate the spatial distribution of a crack network. By using the fractal geometry, the self-similarity of spatial distribution of crack network is discovered. As a result, the conception of fractal crack network is proposed. Furthermore, the evolution of a crack network with the increasing of mining width is investigated. It is shown that (1) the spatial distribution of a crack network displays the fractal behavior, so, the fractal dimension can be used to describe quantitatively the evolution of the crack network, (2) the fractal dimension of the crack network increases with increasing of mining width, (3) the surface subsidence increases with the increasing of fractal dimension of crack network.

The object of this research effort was, upon request for
evidence from a building contractor, to compare the influence of various
amounts and types of fibers on crack widths, using a steel ring mold.
Comparisons were made between synthetic fibers (polyolefin) of 48 mm length, hooked-end steel fibers of
diameters 0.6 mm and 1.05 mm, both of 50 mm length. 10-liter samples were extracted from
concrete ready-mix truck batches at delivery sites, whereupon fibers were mixed
into the samples, layer by layer, by applying a drill-mounted mortar mixing
device. For each amount of fiber content, 4 rings were cast, and of the plain
concrete control samples, 5 rings were cast. After removing the outer steel
casting, strain gages were installed on the exposed outer concrete surface.
Strain values were continuously logged, and crack developments and crack widths
were measured daily. Sufficient data with statistically high significance were
obtained to indicate that: A
synthetic fiber content of 3 kg/m^{3} did not decrease crack-widths as compared to the non-fiber concrete samples.
Synthetic fiber contents of 5 kg/m^{3} and higher, did reduce crack widths on par with hooked-end steel fibers in the
amounts of 25 kg/m^{3} and above. Hooked-end steel fibers of aspect ratio 80 are more efficient with
regards to crack width reduction, yielding 33% narrower cracks, than hooked-end
steel fibers, at equal weight-contents, with aspect ratio 45.

Abstract:
The purpose of this study was to develop an analytical model to predict the time required for cracking of concrete due to corrosion of the iron reinforcement. The concrete and cement specimens used for this study were batched with cover material ranging from 0.75 to 1.3 in (1.91 to 3.30 cm). The extent of cover material was not formulated into the model under the assumption that crack initiation would tend to produce visible cracking within a relatively short time period. The model was derived using both Hooke’s Law and the volume expansion induced by the corrosion oxides. Correlation achieved with specimen cracking data from the literature was relatively good with a 95% level of confidence. This model presents a key benefit to facility and infrastructure managers by enabling them to plan the time when corrosion mitigating actions are required. It also provides a significant convenience as the condition of the concrete structure or its environment changes over time. The only parameter that needs to be updated over time is the corrosion rate measurement. This single parameter captures the most influential impact that stems from several other parameters which tend to be required in models that are more mechanistically definitive.

Abstract:
This paper presents a single-domain boundary element method (SDBEM) for linear elastic fracture mechanics analysis in the 2D anisotropic bimaterial. In this formulation, the displacement integral equation is collocated on the uncracked boundary only, and the traction integral equation is collocated on one side of the crack surface only. The complete fundamental solution (Green's function) for anisotropic bi-materials was also derived and implemented into the boundary integral formulation so the discretization along the interface can be avoided except for the interfacial crack part. A special crack-tip element was introduced to capture exactly the crack-tip behavior. A computer program with the FORTRAN code has been developed to effectively calculate the stress intensity factors, crack initiation angle, and propagation path of an anisotropic bi-material. This SDBEM program has been verified having a good accuracy with the previous researches. In addition, a rock of type (1)/(2) disk specimen with a central crack was made to conduct the Brazilian test under diametrical loading. The result shows that the numerical analysis can predict relatively well the direction of crack initiation and the path of crack propagation. 1. Introduction In rock masses, the interbed construction suffers from cracking which is caused by various factors. Of greater concern are those cracks that develop as a result of initiation and propagation path, leading to significant change in the failure resistance of the structure. Many relative researches and discussions are started like wildfire and never stopped. Because of the discontinuities of weak interbed on laccoliths (rock mass), there are many damages that occurred which are due to earth stress efforts or under geotechnical engineering, such as slope slip, tunnel collapse, deep excavation collapse, and crack openings which are due to deep well drilling. Crack is one of the fracture models to cause those damages because the crack openings and propagation on the field affect the rock mass structure stability. This paper will discuss the behavior of crack propagation on the basis of the theory of fracture mechanics. We defined the rock sample on interbed as “Bimaterial rock”. Theoretically, interfacial crack problems in isotropic Bimaterials were studied [1–3] where the authors showed that the stresses possess the singularity of . Rice [4] re-examined the elastic fracture mechanics concepts for the isotropic interfacial crack and introduced an intrinsic material length scale so that the definition of the stress intensity factor