Shangtong Yang

Prediction of concrete crack width under combined reinforcement corrosion and applied load

As a global problem for reinforced concrete structures located in a chloride and/or carbon dioxide–laden environment, reinforcing steel corrosion in concrete costs approximately

Numerical Simulation of Behavior of Reinforced Concrete Structures considering Corrosion Effects on Bonding

100 billion per annum worldwide for maintenance and repairs. The continual demands for greater load for infrastructure exacerbate the problem. This paper attempts to examine the whole process of longitudinal cracking in concrete structures under the combined effect of reinforcement corrosion and applied load. A model for residual stiffness of cracked concrete is derived using the concept of fracture energy. It is found that the corrosion rate is the most important single factor that affects both the time-to-surface cracking and crack width growth. The paper concludes that the developed model is one of very few theoretical models that can predict with reasonable accuracy the crack width on the surface of reinforced concrete structures under such a combined effect. The developed model can be used as a tool to assess the serviceability of corrosion-affected concrete infrastructure. Timely repairs have the potential to prolong the service life of reinforced concrete structures.

A symplectic analytical singular element for steady-state thermal conduction with singularities in composite structures

Corrosion of reinforcing steel in concrete can alter the interface between the steel and concrete and thus affects the bond mechanism. This subsequently influences the behavior of reinforced concrete structures in terms of their safety and serviceability. The present paper attempts to develop a numerical method that can simulate the behavior of reinforced concrete walls subjected to steel corrosion in concrete as measured by their load-deflection relationship. The method accounts for the effects of corrosion on the stiffness, maximum strength, residual strength, and failure mode of the bond between the steel and concrete. In the numerical method, the corrosion-affected stiffness and maximum strength of the bond are explicitly expressed as a function of the corrosion rate. It is found in this paper that the increase in the bond strength due to minor corrosion can increase the load-bearing capacity of the wall and the corrosion-affected reinforced concrete walls exhibit less ductile behavior compared with the uncorroded walls. The paper concludes that the developed numerical method can predict the behavior of corrosion-affected reinforced concrete seawalls with reasonable accuracy.

Elastic fracture toughness for ductile metal pipes with circumferential surface cracks

ABSTRACT In modern design of composite structures, multiple materials with different properties are bound together. Accurate prediction of the strength of the interface between different materials, especially with the existence of cracks under thermal loading, is demanded in engineering. To this end, detailed knowledge on the distribution of temperature and heat flux is required. This study conducts a systematical investigation on the cracks terminated at material interface under steady-state thermal conduction. A new symplectic analytical singular element is constructed for the numerical modeling. Combining the proposed element with conventional finite elements, the generalized flux intensity factors can be solved accurately.

Accurate cover crack modelling of reinforced concrete structures subjected to non-uniform corrosion

Surface cracks have long been recognized as a major cause for potential failures of metal pipes. In fracture analysis, the widely used method is based on linear elastic fracture mechanics. However, for ductile metal pipes, it has been known that the existence of plasticity results in easing of stress concentration at the crack front. This will ultimately increase the total fracture toughness. Therefore, when using linear elastic fracture mechanics to predict fracture failure of ductile metal pipes, the plastic portion of fracture toughness should be excluded. Otherwise, the value of fracture toughness will be overestimated, resulting in an under-estimated probability of failure. This paper intends to derive a model of elastic fracture toughness for steel pipes with a circumferential crack. The derived elastic fracture toughness is a function of crack geometry and material properties of the cracked pipe. The significance of the derived model is that the well-established linear elastic fracture mechanics can be used for ductile materials in predicting the fracture failure.

Numerical modelling of non-uniform corrosion induced concrete crack width

Abstract Concrete cover cracking caused by reinforcement corrosion is a significant durability problem of reinforced concrete (RC) structures. Extensive research has been carried out in the last few decades while most were focused on corrosion of a single reinforcing bar. Very little research has examined the whole cover cracking of RC structures due to multiple reinforcement corrosion. This article develops a numerical model to predict the structural failure of the whole cover of concrete induced by corrosion of multiple reinforcing bars. Moreover, a non-uniform corrosion model is established based on experimental results, in contrast to conventional uniform assumption. Two typical cover failure modes under the non-uniform corrosion of multiple reinforcing bars are identified and discussed. The effects of cover thickness, reinforcement spacing, fracture energy of concrete, etc., on cover cracking patterns and crack width are also investigated. The derived numerical model is verified by comparing the results with those from experiments in literature. Accurate prediction of concrete cover cracking can allow timely maintenance of existing structures and rational design for new buildings which prolongs the service life of the RC structures.

A symplectic analytical singular element for steady-state thermal conduction with singularities in anisotropic material

AbstractCorrosion of reinforced concrete is one of the major deterioration mechanisms that results in premature failure of the reinforced concrete structures. In practice, concrete crack width is o...

J-Integral solution for elastic fracture toughness for plates with inclined cracks under biaxial loading

Modelling of steady-state thermal conduction for crack and v-notch in anisotropic material remains challenging. Conventional numerical methods could bring significant error and the analytical solution should be used to improve the accuracy. In this study, crack and v-notch in anisotropic material are studied. The analytical symplectic eigen solutions are obtained for the first time and used to construct a new symplectic analytical singular element (SASE). The shape functions of the SASE are defined by the obtained eigen solutions (including higher order terms), hence the temperature as well as heat flux fields around the crack/notch tip can be described accurately. The formulation of the stiffness matrix of the SASE is then derived based on a variational principle with two kinds of variables. The nodal variable is transformed into temperature such that the proposed SASE can be connected with conventional finite elements directly without transition element. Structures of complex geometries and complicated boundary conditions can be analyzed numerically. The generalized flux intensity factors (GFIFs) can be calculated directly without any post-processing. A few numerical examples are worked out and it is proven that the proposed method is effective for the discussed problem, and the structure can be analyzed accurately and efficiently.

Experimental test and analytical modeling of mechanical properties of graphene-oxide cement composites

Surface cracks with different orientations have been recognized as a major cause of potential failures of thin metal structures, which are often under biaxial loading. It has been known that, for cracked ductile metals, plasticity results in an easing of stress intensity at the crack front and ultimately increases the total fracture toughness of the metal. To enable the use of linear elastic fracture mechanics for ductile material failure prediction, the plastic portion of fracture toughness must be excluded. This paper aims to develop a J-integral based method for determining the elastic fracture toughness of ductile metal plates with inclined cracks under biaxial loading. The derived elastic fracture toughness is a function of the plate and crack geometry, strain-hardening coefficient, yield strength, fracture toughness, biaxiality ratio, and inclination angle. It is found that an increase in yield strength or relative crack depth, or a decrease in Mode-I fracture toughness, leads to a larger ratio of elastic fracture toughness to total fracture toughness. It is also found that the effect of biaxiality ratio and inclination angle on elastic fracture toughness is highly dependent on total fracture toughness. It can be concluded that the developed model can accurately predict the fracture failure of ductile thin metal structures with inclined cracks under biaxial loading.

Stress Intensity Factors and Weight Function for Internal Surface Faults in Cylindrical Vessels

Graphene oxide has recently been considered as an ideal candidate for enhancing the mechanical properties of the cement due to its good dispersion property and high surface area. Much of work has been done on experimentally investigating the mechanical properties of graphene oxide-cementitious composites; but there are currently no models for accurate estimation of their mechanical properties, making proper analysis and design of graphene oxide-cement-based materials a major challenge. This paper attempts to develop a novel multi-scale analytical model for predicting the elastic modulus of graphene oxide-cement taking into account the graphene oxide/cement ratio, porosity and mechanical properties of different phases. This model employs Eshelby tensor and Mori-Tanaka solution in the process of upscaling the elastic properties of graphene oxide-cement through different length scales. In-situ micro-bending tests were conducted to elucidate the behaviour of the graphene oxide-cement composites and verify the proposed model. The obtained results showed that the addition of graphene oxide can change the morphology and enhance the mechanical properties of the cement. The developed model can be used as a tool to determine the elastic properties of graphene oxide-cement through different length scales.