| Light-rail viaduct, as one of the main forms of urban rail transit engineering, with merits such as less investment, shorter construction period, and less impact on ground transportation, has been widely used. This paper focuses on deformation monitoring (including pier settlement and girder deflection/camber) of simply supported beam bridge (SSBB) and continuous girder bridge (CGB), two most widely used types of light-rail bridge, and studies the resulting effect of profile changes on train-bridge interaction systems. It is not only inevitable to make the scientific alert threshold but also significant to ensure the safe operation of light-rail trains on the viaducts. By applying theoretical, experimental and numerical analysis methods, the author launched his scientific work in strain-based deformation monitoring, vehicle-bridge coupling dynamics and girder deformation denaturation as follows:1. Strain-Based Deformation Monitoring Method and Experimental Study of Light-Rail Girder Bridge(1) Based on the overall model of track-girder (simply supported)-pier under the symmetry corner pattern, this paper has verified the consistency of vertical deformation between track and girder by numerical analysis, thus establishing the theoretical basis for monitoring pier differential settlement of SSBB with measurable strain of rail bottom. Then, in accordance with theoretical deduction, it has established the analytical expression between rail strain caused by settlement and pier differential settlement of SSBB featuring significance in physics and simplicity.(2) This paper, based on the fixed bearing model and variable stiffness model with piers-supported, has studied pier differential settlement denaturation of light rail CGB, and launched comparative analyses from pier settlement, support reaction and beam moment etc. Taking 3-span CGB as a research object, it has established the identification theory of CGB’s pier differential settlement by using strain, and verified the analytical expression with experimental results of applying two types of strain sensors on it. The results are in good agreement with theories under different working conditions. Additionally, the paper has presented an identification strategy on CGB’s pier differential settlement by taking the strain, that is, scheme design→settlement discrimination→settlement position→settlement quantify.(3) Based on the basic theory of mechanics, the paper, with the sectional curvature obtained by using strain and the curvature function by the least squares method, has established a basic approach to gain the deflection equation based on strain when taking the quadratic integration of curvature function. When launching another fielded loading test of prestressed concrete box beam, this approach has been verified with high accuracy with an easy solution, which can be used in light-rail girders, bridges or beams with no direct measurement deflection.2. Coupling Model and Dynamic Assessment of Light-Rail Train-Track-Bridge Interaction Systems with Girder Deformation(1) In this paper, dynamic physical models of each subsystem are introduced in detail, including light-rail train, track and bridge. With employing Hertz elastic contact theory and spring-damper elements, wheel-track and bridge-track interact with each other. By applying the inverse Fourier transformation, we have generated random irregularities (time domain) of the track. We have achieved the quantitative control of the initial state of pier settlement and girder deflection/camber before dynamic solution by the forced displacement method and uniformly distributed load adjustment, respectively. From the angle of system dynamic, this paper has proposed a modeling approach of light-rail train-track-bridge interaction systems with girder deformation. The light-rail model can be simplified as a damped mass-spring system, and analytic solution of the model on a damped mass-spring system over simply supported beams can be obtained by derivation. At the same time, the numerical solution based on ANSYS platform can also be obtained by wheel-track contact algorithm. In accordance with the comparison between the numerical solutions and the analytic solutions, the reliability of the second method and its results can be proved. Therefore, the result of dynamic analysis of light-rail train-track-bridge interaction systems based on ANSYS can be indirectly demonstrated, which provides the foundation for the study of dynamic performance assessment of vehicle-bridge interaction systems and girder deformation denaturation.(2) Based on the verified modeling theory and the method of light-rail train-track-bridge interaction systems, SSBB and CGB of a city light-rail viaduct are chosen as research objects. Based on finite element software ANSYS and multi-body dynamics theory, matches among two different bridge types (SSBB and CGB) and two different running forms (single-lane and opposite running) produced four 3-D visual finite element models of light-rail train-track-bridge interaction systems, and the vehicle-bridge dynamic analysis and assessment have been carried out. This paper studies the effect of light-rail train speed on dynamic performances of interaction systems in a systematic way. The results show that speed has no significant impact on the vertical deflection of girder. However, as speed increases, the offload factor increases and the running stability worsens.3. The Effect of Girder Bridge’s Deformation on Running Performance of Light-Rail Train and the Determination of Alert ThresholdBy applying real time coupling simulation model of light-rail train-track-bridge interaction systems with girder deformation, this paper studies how the safety and stability of running light-rail trains on bridges will be influenced by factors such as pier settlement, girder deflection/camber, speed and running forms. The results show that:(a) Light-rail trains run over the multi-span SSBB: running forms have insignificant effect on the safety of light-rail train at the same speed and girder deformation; when the train at a low speed (40km/h and 60km/h), running forms has no effect on the maximum vertical acceleration of the body (av), while the effect will be evident when it is over or at 80km/h; the influence of the Sperling index on running forms can be easily differentiated, greater to the opposite running than the single-lane. When taking all factors into consideration, we can conclude that speed best influences running safety and stability of light-rail train, and girder deformation the second, running forms the least, (b) Light-rail train running over the CGB:running forms have no effect on the offload factor, av, Sperling index at the same speed and girder deformation; speed also appears to be the biggest factor having influences on running safety and stability, girder deformation the next, and running forms the least.In one word, taking the targeted light-rail bridge project including SSBB and CGB as an example, the light-rail trains meet the requirements of safety and stability under the operating speeds (V<80km/h) with pier settlement ≤30mm or girder deflection/camber ≤20mm. With speed increases, girder deformation is becoming the controlling factor. The light-rail train can meet running requirements at 100km/h when deformation monitoring of viaduct and maintenance of track are enhanced.The main contributions made in the thesis:(1) Based on the overall model of track-girder (simply supported)-pier under the symmetry corner pattern, this paper has established a monitoring approach of pier differential settlement of light-rail SSBB. Based on strain of girder beam, it has also established a monitoring approach of pier differential settlement by using stress redistribution mechanism of CGB.(2) From the angle of system dynamic, this paper has established real time coupling dynamic analysis models of light-rail train-track-bridge interaction systems with girder deformation (including pier settlement and girder deflection/camber).(3) This paper has revealed how factors such as pier settlement, girder deflection/camber, speed and running forms influence the performance of the train when passing viaduct so as to determine the alert threshold in a scientific way. |
