Main Cause Of Cracks Research Articles

Reliability Analysis of Super 13Cr Tubing in Ultra-Deep Gas Well

Abnormal oil casing pressure appeared in the process of test production of multiple Ultra-Deep Gas Wells in Tarim Basin. The super 13Cr oil pipe string was used to analyze the causes of pipe string failure in view of the oil casing channeling well during the test and blowout period. The construction process of the well was analyzed in detail. Combined with the review of the operation flow and the detection of fracture string material and fracture morphology, the causes of pipe string fracture were analyzed and calculated in detail. Through field investigation, analysis and calculation, it was found that the main cause of cracking of super 13Cr tubing in this well is the decrease of vibration natural frequency caused by excessive fluid velocity in pipe and too long span of pipe string. At the same time, the mixed failure of stress corrosion cracking and stress load interaction occurred in Cl−1 environment and other corrosion environments.

Refined Finite Element Analysis of Crack Causes in SRC Arch Rib Bridges considering Multiple Factors

The SRC (steel-frame reinforced concrete) arch bridge is an important part of the development of arch bridges. Scholars worldwide have studied it from various aspects because of its stronger stiffness and stability than other types of bridges especially when crossing the canyon. The steel frame is a stress bracket during construction. Concrete becomes the main axial-pressure bearing structure when it fills the inner pipe and the encased frame. This article mainly focuses on the crack problems of SRC arch bridging during the postconstruction operation, local model of the midspan arch rib, and the equivalent relationship between the coefficient of expansion and the temperature of concrete. This study uses a cooling method to simulate the shrinkage process with detailed analysis of three properties including concrete shrinkage, temperature gradients, and concentrated hanger rod force. It is concluded that the SRC arch bridge will have large tensile stress on both inner and outer surfaces of slab and web when the temperature changes, and it is the main cause of cracks. The results agree well with measured data. At last, we come up with some reference suggestions in the design and construction of similar bridges in the future.

A new accelerated-replacement method and full-scale test of a new superstructure for existing OSPG railway bridges

Existing open-steel-plate-girder (OSPG) railway bridges in Korea are so old that they can no longer provide the desired ride quality when trains pass over them due to loss of integrity. In addition, existing bridges do not have ballast, thus impacts from passing trains are delivered directly to piers and abutments. The damage that accumulated is one of the main causes of cracks in pier concrete. To cure this problem, replacement of the existing bridges is required. However, since they are still in service, conventional construction methods cannot be used for their replacement. A new method is necessary to quickly replace the existing bridges in a way that does not disturb the existing train schedule. In this study, a new accelerated-replacement method is proposed using a newly developed crane-vehicle which possesses cranes able to lift a replacement bridge, and which is able to travel on existing train tracks. This study also addresses the design and manufacture of a new bridge deck appropriate for accelerated-replacement construction. Finite element analyses and experimental tests were conducted to estimate the performance of the new bridge deck. The analyses included a static load case and dynamic analysis at various train speeds. The experimental tests included static loading and modal tests to capture the fundamental natural frequency and damping ratio of the bridge deck, and a dynamic amplification test. The results of this study can be used for practical replacement of aged existing open-steel-plate-girder bridges and to improve the integrity and ride quality of railway bridges in Korea.

Crack Mechanism, Temperature Control, and Anti-Cracking Measures of Sluice

To address the problem of sluice concrete easily cracking during construction, this study introduces the crack mechanism of concrete structures. Temperature differences and constraints are the main causes of cracks. Anti-cracking measures should focus on optimizing concrete mixing ratio and improving construction technology. Using simulation calculation to model the actual construction process and temperature control measures, this study analyzes the causes of crack and selects timely and reasonable temperature control measures, which are necessary links in engineering construction. A three-dimensional finite element analysis was conducted for a huge concrete sluice structure. The causes of cracks are discussed, and timely and feasible anti-cracking measures are proposed to provide technical support for project construction.

The Cause of Cracks in the Cement Concrete Pavement of County-Highway and Precautionary Measures

This article has analyzed the main cause of cracks in the cement concrete pavement of county-highway and proposed some precautionary measures and disposition measures.The measures of cracks in cement concrete pavement mainly have pressure injection and grouting,expansion seam grouting,directly grouting,striped overlay and nozzle grouting.

Causes of Cracks of External Wall Insulation

With construction of the growing amounts of energy saving buildings, there are defects cracks in external wall insulation because of lack of construction and management experience. The purpose of this study is to find out main causes of cracks of external wall insulation covered by ceramic tile, to conduct construction industry to control engineering quality by paying attention on them. On basis of document study, field investigation to construction workers, supervisors, project managers, both material and construction causes of cracks are studied by investigation and designed questionnaires, including 32 detailed reasons and their harmful levels. Meanwhile, the base data from them is analyzed, and Pareto charts of causes of crack are drawn accordingly. The result shows that grid cloth and plaster mortar are the main material reasons, and that plaster mortar construction, grid cloth laid, detail treatment, configuration of plaster mortar are the main construction reasons.

Causes of Cracks on Structures in Ngara-Tanzania

Development of macro and micro cracks on plastered walls and floors have been studied at different sites under site investigation whereby building inspections, construction history, engineering properties of soil and building surroundings assessment were conducted. We did revision of structural calculations and laboratory experiment to find out the source of cracks. Micro and macro cracks have no structural problems on the structure so long as the developed cracks are within the serviceability limit state [1]. There are two main causes of cracks in the structure that are structural and nonstructural sources [2]. The first task was to identify whether the source of cracks are structural or non structural. During site investigation the modes of crack formation, depth and length of crack, crack patterns and direction were studied at different sites in Ngara. Theoretical calculations of crack width and particles size distribution of sand from three main sources were analyzed after performing both sieve analysis and decantation tests. In depth site investigation, literature review and laboratory tests result showed that the causes of cracks are nonstructural and all three reliable sources of sand in Ngara contain more quantities of fines than that specified in BS 882. This paper is looking for the causes of cracks on structures and recommending further research on new idea of using simple technology and low cost methods that is affordable by both the government of Tanzania and local community of Ngara to overcome the problem of structures that develop micro and macro cracks.

Deterioration of concrete in a hydroelectric concrete gravity dam and its characterisation

A hydroelectric concrete gravity dam in the Snowy Hydro network had shown signs of concrete distress in the form of cracking in some sections of the dam wall, and vertical movements in the wall, measured in routine surveys on the crest of the dam wall. Concrete elements of the associated power station had also shown some degree of distress in the form of cracking. Alkali-aggregate reaction (AAR) was considered among other mechanisms as a likely cause of cracking. In order to investigate the main causes of cracking of the various elements of the power station and the dam wall, core samples ranging in length from 0.3 m to 10 m were extracted and investigated for the presence of AAR, its extent, likelihood of continuing reaction, residual expansion potential, and effect on the strength of concrete. Results of the investigation showed that mild AAR was present in some sections of the wall of the power station but not in the floor, where drying shrinkage could have caused the cracking. Mild AAR was also present in sections of the dam wall with minor visible cracking, but it was stronger and more widespread in the badly cracked area. It was suggested that the walls of power station could be treated by appropriate surface coating to mitigate the progress of AAR, and the badly cracked portion of the dam wall be anchored to stabilise the vertical movement. Other portions of the dam wall did not appear to need treatment.

A heuristic approach to microcracking and fracture for ceramics with statistical consideration

Microcracking damage and toughening are examined for ceramics. These effects have been found to depend on the material microstructure and macrocrack growth. Isotropic damage, attributed to random distribution of microcrack location, length and orientation can be associated with a disordered microstructure and a non-uniform residual stress field. When the applied stress is the main cause of cracking, the microcrack distribution is no longer random such as a system of quasi-parallel cracks. To highlight the effect of crack interaction, discrete models are advanced where damage is simulated by a distribution of microcracks. The dilute concentration assumption is invoked to simplify the analysis. The two-dimensional discrete model is based on a phenomenological approach that is statistical in character. Interactions of microcracks and with a macrocrack are considered by means of a boundary element technique (A. Brencich, A. Carpinteri, Int. J. Fracture 76 (1996) 373–389; A. Brencich, A. Carpinteri, Eng. Fract. Mech. 59 (1998) 797–814) where both isotropic and anisotropic damage could be treated. Comparisons with other results are made to show that the model can be applied to analyse the fracture behaviour of different materials.

Experience in operating the yalta hydraulic tunnel

1. The long-term continuous operation of the tunnel shows that the main technical and economic decisions and organizational measures made during its design and construction were well-founded. The 7.3-km-long tunnel was constructed from two portal faces within 4 short years under complex geological and hydrogeological conditions with a considerable savings of the then scarce construction materials — reinforcement steel and cement. 2. Damages in the tunnel occurred and increased gradually. Cracking in the concrete lining that formed in stretches isolated from one another reached during operation 9% of the length of the entire tunnel. Noncorrespondence of the work of the lining to the calculated scheme caused by rock pressure that developed on stretches of the tunnel driven in argillites and siltstones of the Taurian series disturbed by tectonic processes should be considered the main cause of cracking. Damages that formed as a result of technological origin also occurred: poor quality of the concrete, poor placement and care of the concrete mix [1], insufficient cleaning of the rock surface before applying the shotcrete, etc. 3. The extent of the damages and labor expenditures on their elimination could have been reduced to a considerable degree by timely and systematic engineering intervention during operation of the tunnel. The absence of standards regulating the equipping of hydraulic tunnels with monitoring and measuring apparatus and procedure of observations of the condition of the structures is a significant cause of the unsatisfactory operation of the tunnel.