With more and more precise calculation and analysis to the bridge, and its carrying capacity assessment and repair reinforcement universal attention, it is necessary to acquire the influence line of bridge responses corresponding with moving-load position. A method is presented to obtain the influence line by experiment. A laser rangefinder with large range is added to original test instruments. The moving load position parameter can be looked on as displacement after the signal conversion, which can be synchronously collected together with the response signal. The inverse function principle is introduced to process the data. The examples indicate that the present approach can accurately measure the influence line.
The system of a simply continuous beam was looked on as one span beam with several internal elastic supports of inexhaustible stiffness. There were two types of models such as the dynamic models by a moving concentrated force and by a moving mass. A three-span beam was introduced as example solved with the present model by a moving concentrated force and FEM, which verified that the present model was correct. Two cases of the example bridge by a moving concentrated force and by a moving mass were considered. The results indicate that mass of the moving load has little influence over the dynamic responses of the simply continuous beam bridge.
The external post-tensioning technique has been commonly used in the construction field because it facilitates the analysis of structures and is widely applicable for many types of structures. In this research, 12 steel H-beams were built and tested in terms of the amount of tendon or prestressing force. The results show that the externally prestressing method can increase ultimate bearing capacity of the beams. The prestressing force is the significant factor that influence the strengthening of steel H-beams. However, the amount of deviators cannot significantly influence the bearing capacity.
The effect of bridge vibrationinduced bylive loads such as vehicles and pedestrians is an important factor of bridge fatigue damage. It takes much labor and material resource to perform vibration experiments on bridges subjected by real moving loads in field. In order to carry out laboratory experiments on bridges subjected by moving loads, a fixed load with harmonic vibration simulates a moving load on bridge in the beam theory. A simply supported bridge is considered in the present study. The dynamic responses of bridge under different loads are established by the analytic method. Amplitude and frequency of the simulated load are generated on the principle of equal displacements due to both a moving load and a fixed harmonic load impacting on a simply supported beam. Comparisons of numerical results of two types of load on the same beam indicate that the harmonic load can simulate a moving load effectively. It is possible that the field test on bridge can be carried out indoors.
The optimal placement of actuators is studied with the combination of numerical calculation and modal test methods. The results indicate that the optimal excitation position is close to the maximum displacement of a cantilever beam, but the conclusion is not the same as a simply supported beam. The calculation results are consistent with the experimental results, which show that the approach in the present study is correct, and can be popularized.
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