Papers by Keyword: Crack Opening

Abstract: In order to effectively predict the opening of crack, the variation law of the crack is studied, and the indicator variable principal component neural network model is established by combining indicator variable model and principal component analysis with neural network theory. This new model can solve the problems of nonlinearity between the effect variable and the affecting factors and the colinearity between the affecting factors effectively and improved the prediction accuracy. By a case study, it showed that the prediction results are close to the actual values.

Abstract: During the long-term operation of concrete dam, the cracks in concrete dam might have propagated. Aiming at this situation, based on the comprehensively consideration of the evolution and abnormality situation of concrete dam crack, a method to determine the warning value of the opening of concrete dam crack was proposed. First, the time-effect of crack opening was extracted and its variation law was analyzed, according to this, the occurring time of the unstable propagation of crack was determined. Then, the warning value of crack opening after the last propagation of crack was determined by use of the low probability method. Apply this method to analyze the measured data of a concrete dam crack; the warning value of crack opening was determined successfully; this shows that this method has certain application value.

Abstract: In the present work, an experimental campaign on reinforced concrete elements subjected to simultaneous loading and degradation due to corrosion is presented. The specimens are loaded in tension and the cycling action is designed in order to simulate in terms of stress peak and stress variation, the effect of the passage of vehicles under fatigue design situations. The environmental action is simulated by means of corrosion induced with an electrochemical process; the corrosion rate is chosen in order to obtain about 27 years of equivalent carbonation attack within 25 days of test. In the mean time, 6.5·106 loading cycles are achieved. In addition to those standard tests, also other static tests were conducted in order to have a comprehensive analysis of the deterioration processes. Evolution of transversal crack due to loading and of longitudinal cracks due to corrosion is monitored. They can be related to the internal bond condition between steel and concrete. Results highlight the differences in terms of corroded and uncorroded specimens, static and cycling test and also different loading amplitude. Finally it can be observed as the growing of the damage is significantly different when a cycling action, combined with a chemical attack, is present.

Abstract: Corrosion modifies the steel-concrete interface in reinforced concrete structures. Moreover in structures subjected to cyclic load, a simultaneous mechanical deterioration due to the load is present. Both phenomena can lead to an evolution of cracks width during the service life. In order to evaluate the crack openings increase, an experimental campaign on reinforced concrete ties subjected to simultaneous loading and corrosion have been realized. Transversal crack opening, initially due to loading and longitudinal corrosion cracks evolution is monitored. Results highlight the differences in terms of corroded and uncorroded specimens, static and cycling test and also different loading amplitude. Finally it can be observed as the growing of the damage is significantly different when a cycling action, combined with a chemical attack is present.

Abstract: Bond between steel and concrete in reinforced concrete structures plays a fundamental role. The stress transfer mechanism depends on the condition of the contact surface between the two materials, the mechanical characteristics of concrete near the rebar and on the available level of confinement. Corrosion of reinforcing bars in concrete structures modifies those three factors. Because of corrosion, on the rebar surface a granular oxide layer is present and with its expansion it generates a significant radial pressure; consequently tensile stresses grow till cracking of the concrete cover with a subsequent reduction of the confinement effect. Moreover the presence of a mechanical action modifies the resisting mechanism producing an increasing damage. In this study, a model is presented for the numerical simulation of experimental tests on r.c. ties subjected to mechanical action; furthermore some considerations on reinforced concrete ties subjected also to corrosion effect are reported. From those analyses it is possible to estimate a modified bond-slip law between the reinforcing bars and the concrete, in order to take into account the level of damage.

Abstract: Corrosion modifies the steel-concrete interface in reinforced concrete structures. The efficiency of the connection between the two materials is reduced and the structural behavior both in service and in ultimate condition is affected. Moreover in structures subjected to cyclic load, a simultaneous mechanical deterioration due to the load is present. In this work an experimental analysis on reinforced concrete structures under both cyclic load and corrosion of reinforcing bars is presented. Three couples of reinforced concrete ties are connected in series and subjected to the same stress variation in order to produce the cracking conditions and to activate the bond mechanism. However, while one of the two reinforced concrete ties is only subjected to cyclic load, the second one is also corroded using an accelerated electrochemical corrosion process. The simultaneous effect of the cyclic load and corrosion is evaluated monitoring the crack opening on the structures during the test and by means of visual inspection of the sample. The test results show the correlation between the mechanism of bond and the average level of stresses for an amplified stress range.

Abstract: The cyclic crack tip opening displacement is well related to fatigue crack opening behavior. In this paper, we investigate the effect of the maximum stress intensity factor, Kmax, when predicting fatigue crack opening behavior using the cyclic crack tip opening displacement obtained from FEA. The commercial finite element code, ANSYS, for fatigue crack closure analysis in this study is used. We derive the prediction formula of crack opening behavior when using the cyclic crack tip displacement obtained from the FEA. The numerical prediction shows the good results regardless of stress ratios. It is confirmed that the crack opening behavior depends upon the maximum stress intensity factor Kmax.

Abstract: An elastic-plastic finite element analysis (FEA) is performed to examine the opening behavior of fatigue crack, where the contact elements are used in the mesh of the crack tip area. The relationship between fatigue crack opening behavior and cyclic crack tip opening displacement was studied in the previous study. In this paper, we investigate the effect of the element size when predict fatigue crack opening behavior using the cyclic crack tip opening displacement obtained from FEA. The cyclic crack tip opening displacement is well related to fatigue crack opening behavior.