ارزیابی پل راه آهن فلزی برای بارهای دینامیکی و لرزه ای

In this study, dynamic and seismic assessment of a railway bridge system with four discrete spans giving service on a double track railway line and located in an earthquake-prone region in Turkey is presented. A three-dimensional computer model of the bridge was generated using a commercial general finite element analysis software. Field measurements such as static and dynamic tests as well as material tests were conducted on the bridge system. Validation of the finite element model was performed based on the results of these tests. The calibrated 3D model of the bridge structure was then used for necessary calculations regarding structural assessment and evaluation according to train loads as well as seismic loads. Additional members were proposed to transmit seismic loads to supports. The fourth span, which had a permanent imperfection due to truck collision was studied in detail. Results have shown that due to excessive amount of capacity loss, the only choice was to write off the fourth span.

Most existing railway bridges giving service on current railway networks may not be capable of carrying the heavy vehicles of modern traffic, although no apparent signs of structural deficiencies are observed. However, studies demonstrate that there are large differences between the actual load carrying capacities of bridges and those predicted by conventional theory. To get the maximum use out of a bridge, its assessed load carrying capacity should be safely close to its actual resistance. For evaluating the safety of a bridge, safety index and rating factors are used. Actual reduced capacity of deteriorated members and the maximum loading due to the most critical composition and volume of heavy traffic that may be projected for the future affect these two safety parameters. Assessment of a railway steel truss bridge by using a validated computer model that was developed based on dynamic field measurements and laboratory tests was conducted by Ermopoulos and Spyrakos [1] under heavier train loads as well as seismic and wind loads with regard to current design codes. In another experimental and analytical study of a historic railway bridge by Spyrakos et al. [2], seismic and wind load carrying capacities of the bridge were evaluated based on the analytical model validated with static and dynamic field measurements and laboratory tests. Schlune et al. [3] proposed a methodology for finite element model updating for improved bridge evaluation and this methodology was applied to one of the world’s largest single-arch bridges. For numerous existing small and medium single span ballasted railway bridges in Austria, dynamic field measurements were performed by Rebelo et al. [4] and the calibration of the finite element models of these bridges was carried out using the measured modal parameters. Calcada et al. [5] conducted the experimental and numerical dynamic analyses of Luiz I Bridge, an old arch and double-deck iron bridge in Lisbon, to obtain an experimentally calibrated finite element model of the bridge structure. Full-scale ultimate load tests were carried out by Maragakis et al. [6] on a typical ballasted railway bridge, located in Los Angeles, to identify the contribution of bridge components during a seismic event. Chajes et al. [7] presented results of experimental load tests on a three-span, steel girder-and-slab bridge and generated a finite element model of the main span using the measured response of the bridge and using this calibrated model, various load ratings for the bridge were determined. Wang et al. [8] summarised a condition assessment procedure for bridges based on a complete system of field-testing, finite element modelling and load rating. A study was conducted by Akgul and Frangopol [9] on the rating and system reliability-based lifetime evaluation of a number of existing bridges within a bridge network, including pre-stressed concrete, reinforced concrete, hot-rolled steel and steel plate girder bridges. Itani et al. [10] discussed the behaviour of steel plate girder bridges during recent earthquakes and the experimental and analytical investigations that were conducted on steel plate girder bridges and their components. Results of these investigations show the importance of shear connectors in distributing and transferring the lateral forces to the end and intermediate cross frames. In this study, assessment of a railway steel bridge was conducted for train and seismic loads according to relevant specifications. A three-dimensional computer model of the bridge was generated and validated based on dynamic field measurements and laboratory tests. The calibrated 3D model of the bridge structure was then used for necessary calculations regarding structural assessment and evaluation.

In this study, assessment of a railway steel bridge was conducted for train-induced loads and seismic actions. A 3D computer model of the bridge was generated and validated based on dynamic field measurements and laboratory tests. The calibrated model of the bridge structure was then used for necessary calculations regarding structural assessment and evaluations according to train and seismic loads. For earthquake loading with respect to current national specification, it was concluded that existing supports were not able to transmit the earthquake forces to abutments and pier safely. In order to provide safe transmission of these support forces, additional supports and horizontal cross members were suggested. Also, the damaged cross bracing members were replaced accordingly. For the existing permanent deformation in upper and lower flanges, buckling analyses were performed. It was found that the imperfection of the flanges of the main girders of the fourth span causes 92% reduction in buckling load capacity. Replacing the bridge on fourth span was deemed necessary based on this value.