Papers by Keyword: Crack

Abstract: The thermoelastic problem of a heat flux over a region with a crack near a rigid inclusion is studied. The inclusion is assumed fixed, which implies the translation and the rotation are restrained. The crack faces are assumed free of stress. Both of the inclusion and the crack are under thermal adiabatic condition. In the analysis, the original problem was reduced to a series of displacement boundary value problems by using the principle of superposition. The Green’s function method is used to obtain the solution of the prescribed problem in the forms of integral equations. The basic problems therefore become those for an edge dislocation, and for a heat source couple, as well as the problem of a plane containing the inclusion under a uniform heat flux. These problems are solved using the complex variable method along with the rational mapping function technique. The variations of the stress intensity factors at the crack tips with various crack lengths and heat flux angles are shown. The effects of the inclusion shape and size are also investigated.

Abstract: Early cracks of box girder are widespread during the construction stage of PC box girder bridges. The cracking resistance of a prestressed concrete continuous beam bridge was conducted from the point of construction technique. Experimental study on hydration heat and mechanical properties of box girder concrete at early age were carried out. The results shown that the casting temperature of the concrete, the peak temperature and the maximum temperature difference between inside and outside of the hydration heat were very low, which were 15.7°C, 8°C and 10.2°C, respectively. The strength development of the concrete was stable, and the mixture ratio was optimal. The concrete appearance quality was fairly good without visible cracks in the construction stage. The study reveals that the crack of girder bridges during the construction stage can be avoided by taking effective measures in the construction.

Abstract: On the basis of diffusion mechanism of crack and stress-strain of concrete, the mathematical differential formula and the pure theoretical model of stress-strain complete process of concrete are established. It is shown that stress-strain relationship of concrete is affected by Hooke’s law and diffusion mechanism of crack, and the law of which can be expressed by an exponential formula.

Abstract: The influence of superabsorbent polymers (SAP) as internal curing stuff on the restrained shrinkage and cracking of concrete was investigated. Results show that SAP in the mortar with slag and silica fume increases the compressive train of the steel ring, but postpones the initial cracking time of the mortar from 5 days to 6.5 days and reduces the crack width by 25% at age of 28 days.

Abstract: Internal force of a concrete member duo to temperature variation is related to stiffness. A reduction of stiffness occurs and the magnitude of the internal forces drops from the values existing before cracking when cracking occurred due to temperature variation. Internal force of axial tension member due to temperature variation developed in a jagged style with cracking. Calculation method of internal force and stiffness reduction coefficient of axial tension member due to temperature variation was presented accounting for cracking. Given example shows stiffness reduction coefficient has a close relationship with number of cracks and steel ratio. Member with high steel ratio subjected to the same temperature variation has more cracks and smaller crack width.

Abstract: Intermediate crack debonding is a common failure mode of reinforced concrete (RC) beam flexurally strengthened with externally bonded prestressed fiber reinforced polymer (FRP). This study analyzes the effects of flexural cracks and interface softening behavior on the interface shear stress of RC beam strengthened with prestressed FRP under three-point bending loads, and presents an analytical solution for the FRP axial force at the flexural crack section of the strengthened beam. By regarding the interface fracture energy as the debonding criterion, a new theoretical model to predict the debonding load-carrying capacity of RC beam strengthened with prestressed FRP is proposed.

Abstract: This paper discusses that the causes and the corresponding control measures of mass concrete crack in the construction stage. And through the analysis of engineering example, it describes the application of the control measures of mass concrete crack in the basement foundation slab of high-rise building in construction process, and analyses the construction effect of its.

Abstract: This study is the first part of investigation into the interfacial mechanics performances of cracked reinforced concrete (RC) beam strengthened with prestressed hybrid fiber reinforced polymer (HFRP). Finite element (FE) analysis models were established for such beams with different concrete crack height in this paper. The analysis results indicate that the existing of the flexural cracks obviously affect the stress distribution in the interface between concrete and HFRP, and a sudden change of the stress would arise at the cracks. For cracked RC beams strengthened with prestressed HFRP, both the shearing stress and normal stress of the adhesive layer and fiber sheet are much larger than those without cracks, and the growth rate increases with the crack height.

Abstract: Application of orthotropic steel bridge decks has become increasingly widespread, but with the growing traffic, the bridge decks frequently get fatigue damage, even forming cracks. This paper makes an overall analysis on the orthotropic steel bridge decks cracks of a certain bridge in Southern China, and experimentally studies on both in-situ and new strengthening materials, including low temperature impact toughness, conventional mechanical properties and fatigue performance. Test conclusions indicate that the two materials have good performance, which means the cracks have no business of in-situ materials, and the strengthening materials can be put into use.

Abstract: Based on experiments on two beam specimens (one is a concrete beam with a formwork without demoulding, another is a normal concrete beam), the basic mechanical properties of the flexural beam with a formwork without demoulding, in the condition of monotonic loads were studied, including failure patterns, normal section bearing capacities, change rules of deflections, concrete strain of midspan, strain of strengthened reinforcing steer and so on. The comparison of bearing capacity is also made between a concrete beam with a formwork without demoulding and an ordinary concrete beam. The results indicate that by calculating bend-bearing capacity in current code, a beam with a formwork without demoulding is as safe as an ordinary concrete beam, a concrete beam with a formwork without demoulding meets the requirements of deflection limit value. Its bend-bearing capacity is approximate to an ordinary concrete beam.