Key Engineering Materials Vols. 413-414

Abstract: The complexity of fatigue phenomenon results in the difficulty of fatigue life prediction. The fatigue phenomenon is treated as being in a grey system. By using of grey system theory, a new method for fatigue life prediction based on grey model GM(1,1) is proposed. Results of the example show that the prediction error can be reduced from 61.55% to 24.32%, and the prediction is on the safe side. Therefore, it is proved that the method is practical and useful for fatigue life prediction in engineering.

Abstract: The aim of this study is to investigate the creep-fatigue behavior of stainless steel materials. Based on the elevated-temperature tensile, creep and rupture test data, thermal creep-fatigue modelling was conducted to predict the failure life of stainless steels. In the low cycle thermal fatigue life model, Manson’s Universal Slopes equation was used as an empirical correlation which relates fatigue endurance to tensile properties. Fatigue test data were used in conjunction with different modes to establish the relationship between temperature and other parameters. Then creep models were created for stainless steel materials. In order to correlate the results of short-time elevated temperature tests with long-term service performance at more moderate temperatures, different creep prediction models, namely Basquin model, Sherby-Dorn model and Manson-Haferd model, were studied. Comparison between the different creep prediction models were carried out for a range of stresses and temperatures. A linear damage summation method was used to establish life prediction model of stainless steel materials under creep-fatigue.

Abstract: The aim of this study is to predict the dynamic behaviour of single lap-jointed cantilevered beams theoretically and to validate the predictions via experimental tests. The ABAQUS finite element analysis (FEA) software was used to predict the natural frequencies, mode shapes and frequency response functions (FRFs) of lap-jointed beams. The LMS (Leuven Measurement System) CADA-X dynamic test software and the LMS-DIFA Scadas II 48 channel data acquisition hardware were used in experimental measurement of the dynamic response of the lap-jointed beams. It is shown that the natural frequencies of the single lap-jointed cantilevered beams from experiment are lower than those predicted using FEA. It is also found that the measued FRFs are close to the predicted FRFs for the first two modes of vibration of the single lap-jointed cantilevered beam. Above the second mode of vibration, there is considerable discrepancy between the measured and predicted FRFs.

Abstract: Since the first application of steel orthotropic deck in bridges, engineers have shown great interest in the popularization of steel decks, based on their various advantages like light-weight, high capacity and so on. However, because of their complex configurations, repeated loading, and stress concentration, many details of steel orthotropic bridge decks are fatigue-sensitive. Recently, considerable increase in traffic volume and wheel loads has caused a number of fatigue cracks in steel orthotropic bridge decks in China. For example, bridge engineers have detected thousands of fatigue cracks in steel orthotropic deck on the main box girder of Humen Bridge only ten years after opening to traffic, which is the first modern suspension bridge with the main span of 888 meters in China. So the bridge owners pay more attention to evaluate the locations of fatigue damages. In current paper, the standard section of the real bridge deck was simulated and a kind of typical fatigue cracks was selected to analyze their fatigue life using S-N curve, the fatigue damage analysis was carried out on the longitudinal ribs to deck plate connections. The fatigue damage analysis results were consistent with the observations from real bridge decks.

Abstract: Generally, fatigue has not been considered as a key problem in the design of reinforced concrete bridges. Until the 1960s, reinforcement was mild steel and the stresses permitted in the steel bar and the concrete were such that fatigue and fracture failure was believed to be impossible. With the developments of reinforced concrete structures, higher working stresses were permitted and, in particular, high yield reinforcing bars were introduced. Design rules were issued to control cracking and to prohibit welding of reinforcement unless the risk of fatigue was negligible. In recent years, great deals of researches have been carried out, leading to a better understanding of the fatigue behaviors in concrete structures. Some studies showed that fatigue could occur in reinforced concrete structures in combination with other causes of deterioration. In the past eight years, considerable increases in traffic intensity and wheel loads have caused obviously fatigue damage in reinforced concrete structures in China. Some reinforced concrete bridges were damaged seriously, leading to the whole bridge collapse sometimes because of overloading and oversize trucks. So how to evaluate the fatigue safety of existing reinforced concrete bridges is an urgent problem in China. In the current paper, the assessment models of existing reinforced concrete bridges based on S-N curve and fracture mechanics approach were proposed considering the effect of overloading and oversize trucks. Finally the assessment method based on S-N curve and in-situ monitoring data was applied to a case study bridge.

Abstract: Based on fatigue test results of corroded wires obtained from dissection of actual parallel wire cables which were used on a certain domestic cable-stayed bridge, the fatigue properties of corroded parallel wire cable are investigated by the method of Monte Carlo simulation in this paper. The results of fatigue life and corrosion degree of corroded wire are presented. Comparisons between the original design information and fatigue test results, it can be seen that corrosions make the fatigue lives of wires decreasing sharply. The fatigue life of individual wire is described by Weibull distribution considered some useful parameters such as, stress range, mean stress, mean static strength and length effects. The effects of percentage of broken wire, cable S-N curve parameter on cable fatigue life are discussed. It can be seen that the cable fatigue lives are controlled by a small fraction of the cable wires with the shortest fatigue lives. Finally, the S-N curves of cable are calculated by Monte Carlo simulations based on the results of individual wire fatigue test, and compared with the results of cable fatigue test.

Abstract: With increasing application of adhesive bonding structures, the quality assessment of adhesive bonding became critical. Ultrasonic approach was an acknowledged promising method in many Nondestructive testing (NDT) techniques. The research object was to use analytical models to develop a quantitative understanding of the affections in different situations on the dispersion properties. An improved global matrix method was introduced to compute the dispersive curves, which can effectively eliminate the instability for thicker layers and higher frequencies. In order to evaluate the disbond defect, the cohesive strength degradation mode and the spring mode were then adopted to describe the cohesive failure and the interface failure, respectively. In the paper, cohesive failure, interface failure and mixed failure were analyzed for the steel/adhesive layer/insulation layered structure. Interface failure induced the modes of multilayer structure to regress to the modes of single layers, while the cohesive failure made the dispersive curves move to the lower frequency direction, and changing the relative position of spring layer led the dispersive curves shift to the higher frequency direction. Among all the factors, the interface failure was dominant. Finally, the variety of the dispersive modes in a special frequency band (1~1.5MHz) was found that can be regarded as parameters of the adhesive bonding quality.

Abstract: This paper presents the analysis of strain time histories measured by structural health monitoring system. The main objective of this study is to prepare data for reliability estimation of main components as well as the entire structural system. The strain and corresponding temperature data is collected at the following stages: closure segment reconstruction stage and operating stage. The strain monitoring of the closure segment during the reconstruction stage provided valuable information on early-life strain development and reference characteristics for events such as post tensioning and temperature change. These lessons learnt from the reconstruction monitoring can be used for understanding subsequent bridge behavior, including damage detection and reference points of subsequent monitoring. Specially, the loading test results reveal the effectiveness and correctness of the strain acquiring system and provide evidence for reliable long-tem monitoring. Strain and temperature data have been recorded at sampling frequency of 62.5Hz since loading test, which would provide information linear stress-strain relationships. The long-term creep and shrinkage model were provided by Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridge and Culverts (JTG D62-2004). Through the statistical analysis of the online strain response, the probability model of long-term performance under environmental and random traffic loading are obtained which gives the potential of its application of reliability based assessment on cable stayed bridges where they evaluated the reliability of elements such as cables and stiffening girder.

Abstract: Finite element model updating aims at reconciling the analytical model with the test one, to acquire a refined model with high-fidelity in structural dynamic properties. However, testing data are inevitable polluted by noises. In this study, the mode parameters and design variables are modeled as fuzzy variables, and a fuzzy model updating method is developed. Instead of a single optimal model, a set of satisfactory models is obtained. The most physically compatible solution is sorted by insights to the structures. The proposed method is applied to a real concrete bridge, for which a physically meaningful model is identified.

Abstract: When a metal or composite structure begins to fail, for example due to high cycle fatigue, acoustic emissions caused by the propagation of cracks give rise to bursts of ultrasonic waves travelling through the structure. The health of a structure can be monitored by means of sensors which detect these waves. Acoustic emissions are often generated in experiments by breaking a pencil lead against the surface of the structure in a standardised way but the forces that this imparts are not well understood at present. A Local Interaction Simulation Approach (LISA) algorithm has been implemented to simulate the propagation of ultrasonic waves. This code has been validated against experiments in previous work and has been shown to accurately reproduce the propagation of Lamb waves (including reflections and dispersion etc.) within thin-plate like structures. This paper deals with the use of the LISA code to characterise the forces associated with standard pencil lead breaks. The displacement due to waves emanating from a break is measured and a Differential Evolution (DE) optimisation scheme is used to find the optimal profile of forcing to match the simulation with experiment.