Modal experiments are present to study dynamic behaviors of an external prestressed steel beam. The impact testing is introduced, when the input is fixed and FRFs are measured for multiple outs. Modal results indicate that the modal shape will increase when external prestressed load exists; the first order frequency of external prestressed load on the beam is higher than that of no load, but the amount of loads have little influence on the value of damping coefficients and the first order frequency; and there are denser frequencies with lager external prestressed load.
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.
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 variable section influence on the vibration of a simple supported beam under the action of a moving constant concentrated force is investigated in this work. The technique is based on analytical approach with the assumed model method and the numerical approach of Newmark method. Comparisons with the results between vary-section beam and constant-section one indicate that it is a wise approach to economizing materials and lightening the load of gravity by applying vary-section beam on the condition that the maximum stress cannot change dramatically.
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