Cracking of welded joints at elevated temperatures
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In order to select the optimal treatment strategy for cracked pavements, the cracking conditions should be accurately investigated and evaluated. In this study, the effects of longitudinal cracking on falling weight deflectometer (FWD) deflections were investigated, and a rapid and non-destructive approach was accordingly proposed to evaluate the longitudinal cracking severity using FWD data for semi-rigid pavements. 3D finite element models were developed to simulate various intact and cracked pavements to compute the surface deflections under FWD loading. Two cracking types, namely, cracking in asphalt concrete layer (AC cracking) and cracking in both AC and cement-treated base layers (AC + CTB cracking), were considered. In most cases analyzed, the deflections of cracked pavements are greater than those of intact pavements, and they are only slightly smaller than those of intact pavements in other cases. The effects of longitudinal cracking on deflections increase with increasing crack width and decreasing distance between the crack and the loading center, and longitudinal cracking generally has greater influences on the pavement with a thicker AC layer and weaker subgrade. The effects of AC + CTB cracking on deflections are significantly greater than AC cracking, especially for the cracks near the loading center, and the influences of both AC cracking and AC + CTB cracking are negligible when the deflections are measured more than 1.8 m away from the crack. Accordingly, a rapid and non-destructive approach was proposed to distinguish the AC cracking and AC + CTB cracking using FWD data for semi-rigid pavements.
Asphalt concrete
Falling weight deflectometer
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This chapter contains sections titled: Introduction Types of Cracking Causes of Cracking and Splitting Reducing Fruit Cracking Summary and Conclusions Literature Cited
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ABSTRACT Severe mechanical damage such as cracks can occur in foods during cryogenic freezing. Ten physical properties of 22 different materials were correlated with freeze‐cracking incidence. Statistical analyses revealed that several properties correlated significantly with freeze‐cracking. This implies that freeze‐cracking depends not only on moisture content but on combinations of several properties. A set of equations based on densities and porosities was developed to predict freeze‐cracking incidence with an accuracy of 98% in noncracking products and 70% in cracking products during cryogenic freezing. In addition, susceptibility of various food commodities to freeze‐cracking was determined.
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This paper analyzed the reasons of early age cracking of reinforced concrete floor, and proposed the calculation model of early age cracking of reinforced concrete floor. Solution process of early age cracking of reinforced concrete floor was described in detail through a calculation example. Comparison between the method provided in this paper and the finite element analysis method was conducted. Measures were discussed when the early cracking appeared. The further research contents needed were indicated in this paper.
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Abstract Excessive cracking due to restraint of thermal and shrinkage strains is a widespread problem in the concrete construction industry. In design, restraint induced cracking is managed by the provision of reinforcement intended to distribute internal strains in such a way as to control the cracking pattern and limit crack widths. The area of secondary (horizontal) reinforcement required in members such as retaining walls and water tanks is often governed by the need to control early age thermal cracking. This paper presents results from four edge restrained walls tested at Imperial College London and the University of Leeds as part of an Engineering and Physical Sciences Research Council funded project into restraint induced cracking. The paper describes the development of volumetric strain and cracking in the tested walls. The cracking performance is assessed by comparing the restrained strain with the tensile strain capacity of concrete.
Shrinkage
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Following phenomena were experienced on the welding with plate thickness 100 mm to 200 mm.(1) The weld cracking increases with an increases of the plate thickness (number of welded layer).(2) Weld cracking occurs several days after welding.In order to assure above phenomena and study the preventive method of the weld cracking, the weld cracking test was carried out and the weld cracking phenomena were observed.The main results obtained are as follows.(1) It is clarified that weld cracking increases with an in crease of the thickness of welded plate, and the initiating position of weld cracking lies just under the surface bead.(2) Incubation period of weld cracking is 4 days after welding.(3) Weld cracking is prevented with lower temperature postheating for 0.5 hr at 300°C in case of local gas heating for a 2 1/4 Cr-lMo steel.(4) It is clarified that above phenomena are based on the distribution of hydrogen in thick weldment which is reported by authors in the previous reportt.
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The traditional fracture energy cracking criterion in a smeared cracking model,with the limitation of poor convergence and misjudgement of micro-cracks,is not applicable in the meso-level simulation of drying shrinkage micro-cracking in concrete.A modified smeared cracking model with an equivalent fracture energy cracking criterion is proposed and employed in the simulation of drying shrinkage micro-cracking in concrete specimens using an explicit method available in the commercial software ABAQUS.The micro-crack patterns from simulations of single-aggregate and random-aggregate-structure specimens agree well with the experimental results,showing the applicability of the modified smeared cracking model in modeling the meso-level drying shrinkage micro-cracking in concrete.
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The cracking behavior of lightweight aggregate concrete(LWAC) was investigated by mechanical analysis, SEM and cracking-resistant test where a shrinkage-restrained ring with a clapboard was used. The relationship between the ceramsite type and the cracking resistance of LWAC was built up and compared with that of normal-weight coarse aggregate concrete(NWAC). A new method was proposed to evaluate the cracking resistance of concrete, where the concepts of cracking coefficient ζt(t) and the evaluation index Acr(t) were proposed, and the development of micro-cracks and damage accumulation were recognized. For the concrete with an ascending cracking coefficient curve, the larger Acr(t) is, the lower cracking resistance of concrete is. For the concrete with a descending cracking coefficient curve, the larger Acr(t) is, the stronger the cracking resistance of concrete is. The evaluation results show that in the case of that all the three types of coarse aggregates in concrete are pre-soaked for 24 h, NWAC has the lowest cracking resistance, followed by the LWAC with lower water absorption capacity ceramsite and the LWAC with higher water absorption capacity ceramsite has the strongest cracking resistance. The proposed method has obvious advantages over the cracking age method, because it can evaluate the cracking behavior of concrete even if the concrete has not an observable crack.
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