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Showing 7 results for Fatigue

T. Dahlberg,
Volume 8, Issue 1 (3-2010)
Abstract

The track stiffness experienced by a train will vary along the track. Sometimes the stiffness variation may be

very large within a short distance. One example is when an unsupported sleeper is hanging in the rail. Track stiffness

is then, locally at that sleeper, very low. At insulated joints the bending stiffness of the rail has a discontinuity implying

a discontinuity also of the track stiffness. A third example of an abrupt change of track stiffness is the transition from

an embankment to a bridge. At switches both mass and stiffness change rapidly. The variations of track stiffness will

induce variations in the wheel/rail contact force. This will intensify track degradation such as increased wear, fatigue,

track settlement due to permanent deformation of the ballast and the substructure, and so on. As soon as the track

geometry starts to deteriorate, the variations of the wheel/rail interaction forces will increase, and the track

deterioration rate increases. In the work reported here the possibility to smooth out track stiffness variations is

discussed. It is demonstrated that by modifying the stiffness variations along the track, for example by use of grouting

or under-sleeper pads, the variations of the wheel/rail contact force may be considerably reduced.


M. Z. Kabir, A. Hojatkashani,
Volume 10, Issue 4 (12-2012)
Abstract

The aim of current study is to investigate the effect of Carbon Fiber Reinforced Polymer (CFRP) composites on the fatigue

response of reinforced concrete beams. 6 reinforced concrete (RC) beams from which 3 were retrofitted with CFRP sheets, were

prepared and subjected to fatigue load cycles. To predict and trace the failure occurrence and its growth, a small notch was

induced at the middle span in bottom surface of all RC specimens. At the certain points, strains in concrete and CFRP were

measured in each cycle. The upper limit of applied load was considered at the level of design service load of bridges. In addition,

strain measurements facilitated to the calculation of interfacial shear stresses between concrete substrate and the CFRP layer.

The variation of such stresses through load cycles has been presented and discussed. Also, a discussion on possibility of the local

debonding phenomenon resulted from such interfacial stresses was presented. Load–deflection curves, strain responses and

propagation of tensile cracks provided an insight on the performance of the CFRP strengthened beams subjected to different

cycles of fatigue loading. Variation of load-deflection curves through fatigue load cycles depicted stiffness degradation which

was discussed in the research.


Z.y. Wang, Q.y. Wang,
Volume 13, Issue 4 (12-2015)
Abstract

This paper presents a finite element analysis and its related experimental test of corrugated steel web beams subjected to fatigue loading. A particular focus in this study was set on the fatigue failure arising from the web-to-flange welded joint of the corrugated steel web beam. A detailed three-dimensional finite element model which explicitly includes the geometry of the web-to-flange welds along the corrugated web was developed to simulate the test corrugated web beam. The finite element model is verified by comparing with related fatigue experimental test results. The effective notch stress approach was also applied to analyse the web-to-flange welded joint replicating the local critical region in the corrugated web beam. The fatigue strength of the web-to-flange welded joint was evaluated and compared numerically by considering the stress distribution at potential fatigue crack initiation location. The fatigue life of the corrugated web beam was assessed numerically by incorporating material S-N relation and employing fracture mechanics approach. The comparison with the fatigue test results show that it is possible to expect the fatigue crack failure arising at the weld root or weld toe corresponding to the sections with reference angle using the effective notch stress analysis. The range of these predictions was evaluated by comparing with fatigue test results with accuracy and can be considered between AASHTO fatigue categories B and B’. The parametric notch stress analysis incorporating the influences of corrugation angle was performed and demonstrates it is possible to expect the fatigue crack failure arising at the weld root or weld toe. Finally, a practical solution for possible fatigue life enhancement of such structure is proposed by decreasing the corrugation angle or smoothing the intersection geometry of the corrugated web is suggested together with a moderate increase of the flange thickness.


Tao Ma,
Volume 14, Issue 5 (7-2016)
Abstract

This study focused on the design of heat-resistant asphalt mixture for permafrost regions. Vermiculite powder with low thermal conductivity was used to replace some of the fine aggregates in asphalt mixture to lower the thermal conductivity of asphalt mixture. Asphalt mixtures with different mass ratios (0, 3, 6, 9 and 12%) of vermiculite powder were prepared for performance and thermal property evaluation. Wheel tracking test, low-temperature bending beam test, freeze-thaw splitting test and fatigue test were conducted to evaluate the influences of vermiculite powder on the high-temperature rutting resistance, low-temperature cracking resistance, moisture stability and anti-fatigue performance of asphalt mixture. Mathis TCI analyzer was used to analyze the influences of vermiculite powder on the thermal conductivity of asphalt mixture. Temperature monitor system was used to figure out the influences of vermiculite powder on the inside temperature of asphalt mixture. It is proved that vermiculite powder has no significant influences on the performances of asphalt mixture while it obviously affects the thermal property of asphalt mixture. By addition of 9% to 12% vermiculite powder in asphalt mixture, the performances of asphalt mixture can still well meet the performance requirements for permafrost regions the thermal conductivity can be reduced by 40% to 55% and the inside temperature of asphalt mixture can be lowered by 1 to 2°C. It proves the feasibility by using vermiculite powder to produce heat-resistant asphalt mixture for permafrost regions.


Mohammad Reza Saberi, Alireza Rahai, Masoud Sanayei ,
Volume 15, Issue 1 (1-2017)
Abstract

Steel bridges play a very important role in every country’s transportation system. To ensure that bridges perform reliably, engineers monitor their performance which is referred to as Structural Health Monitoring (SHM). An important element of SHM includes the prediction of service life. There is ample historical evidence that bridge damage is pervasive and their life time is decreasing. To manage costs and safety, service life prediction of bridges is necessary. We present a statistical method to predict service life for steel bridges. A nonparametric statistical model based on the bootstrap method for stress analysis for fatigue life prediction of steel girder bridges is proposed. The bootstrap provides a simple approach for reproduction of the probability distribution of measured strain data. The bootstrap is sensitive to the number of events in the verification sample (data), thus we introduce a stable survival distribution function (SDF). An index is presented in this paper for inferring the service life of steel bridges, which can be known as the Life Index (µ). The life index function shows variation of the age of steel bridges under daily traffic loads. A regression model is developed which relates the service life of steel bridges using a bridge life index based on measured operational strain time histories. The predicted remaining service life derived from the model can contribute to effective management of steel bridges. The proposed method assists bridge engineers, bridge owners, and state officials in objective assessment of deteriorated bridges for retrofit or replacement of deteriorated bridges. Timely repair and retrofit increase the safety levels in bridges and decrease costs.


Artur Duchaczek, Zbigniew Mańko,
Volume 15, Issue 4 (6-2017)
Abstract

The paper is presented an attempt to assess service life of steel girders in military bridges (or by-pass temporary bridges) when fatigue cracks are detected in them. A function describing the geometry of fatigue cracks, the so-called crack shape factor Y, for two different, assumed calculated models, was presented. The function was used to plot sample graphs allowing assessing the remaining service life of such structural elements or engineering structures in a simple way. This method of analyzing can be used not only for the military bridges but also for other steel structures with existing cracks. The work is also presented assessments of possible applications of two FEM calculated models using shell elements to test stress and deformation at the top part of a fatigue crack located in a web of a steel girder used in the military bridges. The results of the conducted numerical analyses were compared with the results obtained in experimental research conducted in laboratory conditions using extensometers.


Dr. Kabir Sadeghi, Dr. Fatemeh Nouban,
Volume 15, Issue 5 (7-2017)
Abstract

This paper describes both global and local versions of an energetic analytical model to quantify the damage caused to reinforced concrete (RC) structures under monotonic, cyclic or fatigue loading. The proposed model closely represents the damage to structures and yields a damage index (DI) for the RC members. The model is cumulative and is based on the energy absorbed. The energy under the monotonic envelope curve at the failure of the member is taken as a reference capacity. The data required to apply the model in any given situation or member can be obtained either by numerical simulation or from experimental tests. An analytical computer program was developed to simulate numerically the response of RC members taking into account the nonlinear behavior of the materials and structures involved. The proposed model was verified by comparison with practical tests undertaken by other researchers on over 20 RC columns. The comparison demonstrates that the model provides a realistic estimation of the damage of the RC structural members. The comparison between values of the proposed DI calculated based on experimental test data and numerical simulation results for a cyclic loading case shows that to calculate DI, it is not necessary to perform expensive experimental tests and that using a nonlinear structural analytical simulation is sufficient. The results are also compared to a damage model proposed by Meyer (1988).



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