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PROCEEDINGS OF THE NINTH INTERNATIONAL CONFERENCE ON CIVIL AND STRUCTURAL ENGINEERING COMPUTING
Edited by: B.H.V. Topping
Dynamic Diagnosis of Bridges
Department of Structural Mechanics, University of Zilina, Slovak Republic
J. Bencat, "Dynamic Diagnosis of Bridges", in B.H.V. Topping, (Editor), "Proceedings of the Ninth International Conference on Civil and Structural Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 84, 2003. doi:10.4203/ccp.77.84
Keywords: dynamic analysis of structures and bridges, experimental analysis, bridges dynamic diagnosis.
This paper provides an overview of current trends in the field of structures and bridges testing. It examines what is driving the continuing expansion of structure and bridge testing and their role in the management of the building industry and bridge infrastructure.
Realistic modeling of the bridges behavior for dynamic analysis and determining relevant parameters for evolution existing bridges via dynamic diagnosis of bridges is considered. Also dynamic loading test of bridges phenomena (test procedure, data acquisition and recording, data processing) analytical and experimental findings and the future study are discussed.
Testing of the structures is only way of assessing the reliability of assumptions made in mathematical modeling and is the most satisfactory means of determining relevant parameters for evaluation existing structures (e.g. parameters for evaluation of the service or remaining life of structures, deterioration, reliability, fatigue etc.). Nowdays the important role in the diagnosis of the structures plays monitoring of the structural parameters (relative change of eigenfrequencies, damping parameters fatigue parameters ). A comparison of the values of certain quantities obtained by experiment and by theoretical analysis and computation is the necessary prerequisite for both static and dynamic loading tests, respectively. The same situation is valid for the diagnostics of the structures. The criteria expressing the reliability of the structure are determined by the permissible differences between the experimentally ascertained and theoretical values of the quantities concerned. No criteria of the correctness of the solution are given for comparison of experimental and theoretical values; there is only the permissible difference in the monitored values of stresses, strains, vibration frequencies and modes obtained by experiments and theoretically.
There are several objectives of dynamic testing of bridge in full-scale ambient and forced tests. The report on this topics was presented in . The main reason for performance of the dynamic loading test (DLT) is to evaluate dynamic properties of the bridge. These properties are used for dynamic model calibration or as a reference to monitor changes in structural performance. Monitoring of the bridges performed in the same bridge during the several years show that frequency measurements carried out at the same temperature conditions have a small coefficient of variation (1%) because of ambient conditions (temperature, humidity, etc.). Experimental analysis and results are detailed in Reference [2,3]. Therefore greater changes in dynamic parameters obtained in dynamic tests made in the same conditions are related with structural modifications and not with ambient changes. There are also the so-called proof-loading tests for checking if the construction of the bridge has been performed according with the design. This dynamic loading tests (DLT) comprise in many countries evaluation of the dynamic implication factor (DAF) or impact factor (IF), or dynamic allowance factor (DLA) greater than 1: the amount by which the static effects are increased by bridge-vehicle interaction. Several countries have standards to obtain this coefficient in a normalized way (Switzerland, Canada, USA, U.K., Spain, France, Germany, India, Czech Republic, Slovak Republic).
Nowdays, there is an another group of dynamic test focused to the analysis of the effects of traffic in the fatigue behavior (experimental stress-spectra in main structural elements) or related to the weigh-in-motion (WIM) techniques where the dynamic response of the bridge is use to obtain the characteristic (gross weight, axle weight and spacing, distance between vehicles, etc.) of the traffic itself via calibration of the system.
There has been a considerable amount of research conducted in the fields of bridge dynamic. A review of the analytical and experimental findings has suggested the following conclusions full-scale testing under traffic loading is the only economical and practical way to evaluate the DAF with reasonable confidence. It is also a reliable method for determining structural dynamic properties and can be useful for inspection purposes.
The assessment of one road and one railway bridge is included to explain some typical problems associated with bridge testing technology.
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