Practical considerations regarding results from static and dynamic load testing of bridges

Bridge tests are a helpful tool for bridge assessment and evaluation. Both in the case of a static and dynamic load testing, each element of the test: the load selection and application, the creation of a numerical model to follow the progress of the test or to check the validity of the test results, the measurement process itself and the comparative analysis of experimental results and calculations could be a source of errors in the bridge final evaluation if these errors and uncertainties are not properly considered. The article presents some of the most important factors that may bring errors in the interpretation of the test results and their comparison to targeted values or values derived from a numerical model. This, at the end, may result in the adoption of decisions that are not accurate and appropriate. The selected sources of feasible errors are presented with the division into static and dynamic loading tests. The presented examples of bridge load testing show how the use of improper test methods could lead to significant errors in bridge assessment and evaluation and, consequently, to wrong decisions.Peer ReviewedPostprint (published version

Badanie skutków oddziaływań bocznych na wiadukcie kolejowym leżącym na łuku

In the report some investigations of bridge structure, connected with the adaptation of the railway line to speeds up to 200 km/h for conventional trains and up to 250 km/h for tilting trains were presented. A railway track is the characteristic feature of tested viaduct, because the truck is curved over the whole length of span with radius of R = 2600 m. The tests of the viaduct required the verification of influence of the dynamic effects on the ultimate limit states which corresponded to the safety of structure, as well as the serviceability limit states, related to the safety of driving and the travellers’ comfort. In frames of investigations, a special train comprised of two locomotives and four passenger cars, was used with speeds in the range between 10 and 200 km/h. The report focuses on the problems addressing the influence of horizontal actions in the case of bridge with curved truck. The measurements of the horizontal and vertical displacements as well as the accelerations of span, and the speed of crossing test train were executed. The measured and theoretically calculated chosen courses of displacements and accelerations were introduced. The degree of divergence between measured and calculated values was analysed.W referacie przedstawiono badania konstrukcji mostowej związane z dostosowywaniem linii kolejowej do dużych prędkości: vmax ≤ 200 km/h dla taboru konwencjonalnego i vmax ≤ 250 km/h dla taboru z wychylnym pudłem. Charakterystyczną cechą badanego obiektu jest tor kolejowy leżący na łuku o promieniu R = 2 600 m. Zbadanie obiektów wymagało sprawdzenia wpływu efektów dynamicznych na stany graniczne nośności – bezpieczeństwo konstrukcji oraz stany użytkowności związane z bezpieczeństwem jazdy i komfortem podróżnych. W ramach badań wykonano jazdy taborem próbnym (dwie lokomotywy i cztery wagony pasażerskie) z prędkościami dochodzącymi do 200 km/h. W referacie skoncentrowano się na zagadnieniach związanych ze skutkami odziaływań bocznych, wywoływanych przez tabor kolejowy, wynikających z położenia obiektu na łuku. Prowadzono pomiary pionowych i poziomych przemieszczeń oraz przyspieszeń przęsła i prędkości przejeżdżającego taboru. Przedstawiono wybrane zmierzone i obliczone teoretycznie przebiegi przemieszczeń i przyspieszeń. Przeanalizowano stopień rozbieżności zmierzonych i obliczonych wartości przemieszczeń i przyspieszeń wynikający z występowania sił odśrodkowych

The Integration of Two Interferometric Radars for Measuring Dynamic Displacement of Bridges

Measurements of displacements of bridges under dynamic load are particularly difficult in the case of structures where access to the area under the tested structure is impossible. Then, remote measurement methods are preferred, such as interferometric radar. Interferometric radar has high accuracy when measuring displacement in the direction of its target axis. The problems appear when a bridge vibrates in two directions: horizontal (lateral or longitudinal) and vertical. The use of one radar to measure those vibrations may be impossible. This paper presents the application of a set of two interferometric radars to measure vertical vibration and horizontal longitudinal vibration with high accuracy. The method was positively verified by experimental tests on two railway bridges characterized by different levels of horizontal displacement. The accuracy of the radar measurements was tested by the direct measurement of vertical displacements using inductive gauges. In conclusion, in the case of vertical displacement measurements using one interferometric radar, the influence of horizontal displacements should be excluded. In the case of locating radars at the area of bridge supports, it is necessary to either use a set of two radars or first investigate the magnitude of possible horizontal displacements in relation to vertical displacements

Diagnostic load testing of bridges: background and examples of application

This chapter presents principles and justification of diagnostic load tests of bridges as normally performed. Normally, diagnostic tests serve to verify and adjust the predictions of an analytical model. However, as presented in the chapter, the results of a diagnostic load test in a bridge can also serve other objectives. Several examples of application are presented with the main objective not only to show how the tests are carried out, but chiefly to introduce which are the main issues to take into account to obtain accurate and reliable results that can be used in the assessment of the actual capacity of the bridge. In the case of static tests, conclusions regarding the measurement stabilization time are presented. For dynamic tests in railway bridges, the extrapolation to lower and higher speeds is also discussed.Postprint (published version

Diagnostic load testing of bridges: background and examples of application

This chapter presents principles and justification of diagnostic load tests of bridges as normally performed. Normally, diagnostic tests serve to verify and adjust the predictions of an analytical model. However, as presented in the chapter, the results of a diagnostic load test in a bridge can also serve other objectives. Several examples of application are presented with the main objective not only to show how the tests are carried out, but chiefly to introduce which are the main issues to take into account to obtain accurate and reliable results that can be used in the assessment of the actual capacity of the bridge. In the case of static tests, conclusions regarding the measurement stabilization time are presented. For dynamic tests in railway bridges, the extrapolation to lower and higher speeds is also discussed

Practical considerations regarding results from static and dynamic load testing of bridges

Bridge tests are a helpful tool for bridge assessment and evaluation. Both in the case of a static and dynamic load testing, each element of the test: the load selection and application, the creation of a numerical model to follow the progress of the test or to check the validity of the test results, the measurement process itself and the comparative analysis of experimental results and calculations could be a source of errors in the bridge final evaluation if these errors and uncertainties are not properly considered. The article presents some of the most important factors that may bring errors in the interpretation of the test results and their comparison to targeted values or values derived from a numerical model. This, at the end, may result in the adoption of decisions that are not accurate and appropriate. The selected sources of feasible errors are presented with the division into static and dynamic loading tests. The presented examples of bridge load testing show how the use of improper test methods could lead to significant errors in bridge assessment and evaluation and, consequently, to wrong decisions.Peer Reviewe

On-site assessment of bridges supported by acoustic emission

Load testing has considerable possibilities in bridges as regards their safety assessment. This paper presents a comparison study on the diagnostic and the proof load test supported by acoustic emission. Diagnostic load testing is based on the comparison of real bridge behaviour with analytical calculation. Proof load testing is based on incremental loading until the bridge materials approach their elastic limit, but never going beyond this point, to prevent the bridge from being damaged. Tests are compared in the case of a three-span concrete bridge, made of prestressed precast beams. In a diagnostic load, reaching accurate diagnosis was made possible by the calibration of the calculation model based on deflection measurements and by the definition of concrete (performance) parameters, mainly concrete tensile strength. In proof load testing, accurate assessment of the actual capacity was possible, thanks to the support of acoustic emission measurements.Peer ReviewedPostprint (author's final draft

Proof load testing supported by acoustic emission: an example of application

The load testing method has considerable possibilities in bridges with the objective of their safety assessment. One type of load tests is proof load. Proof load testing is a full-scale and non-destructive examination of load-carrying capacity. Proof-load testing has been applied to various types of structure in many parts of the world. Originally, it provided a way to check the design assumptions and quality of construction. Later, it became an effective approach to assessing load-carrying capacity of existing structures. The aim of the proof load test is to discover hidden mechanisms of response that can not appear under “normal” levels of load, but that develop at higher ratios of load and may increase the bridge load capacity. For this reason, in such test, the load introduced in the bridge is relatively high and due to the risks of damaging the structure, this type of tests is restricted to bridges that have failed to pass the most advanced theoretical assessment or when such theoretical assessment is not possible due to the lack of bridge documentation. The objective of this test is to directly obtain the maximum allowable load in the bridge with a required safety level. Acoustic emission has been identified as a useful technique in the follow up of the loading process in proof load tests in order to stop the load increase before any damage can be inflicted to the bridge. In the paper the results of field-test of Barcza bridge, a three span concrete bridge made of pre-stressed pre-casted beams, are presented. Thanks to the AE signals it was possible to evaluate the cracking limits without introducing any significant damage to the girders.Peer ReviewedPostprint (published version

Some relevant experiences from proof load testing of concrete bridges

The paper presents the results and experiences derived from a series of proof load test on concrete bridge structures. There are three main parts of the paper. The first part is a theoretical part related to the assessment of the target values of the proof load tests. The load level in the test necessary to guarantee a predefined safety level under real traffic conditions can be obtained in a reliability-based methodology with two different approaches depending on if data is available or not for the bridge under evaluation. The second part is an evaluation of the measurements results during static loading. The important element is the correct and accurate estimation of the elastic and permanent values of measured quantities taking into account their speed of stabilization. The third part is connected with an incremental loading and is about estimation of the time when the bridge materials approach their elastic limit during incremental loading and therefore, the test should stop.Postprint (published version

On-site assessment of bridges supported by acoustic emission

Load testing has considerable possibilities in bridges as regards their safety assessment. This paper presents a comparison study on the diagnostic and the proof load test supported by acoustic emission. Diagnostic load testing is based on the comparison of real bridge behaviour with analytical calculation. Proof load testing is based on incremental loading until the bridge materials approach their elastic limit, but never going beyond this point, to prevent the bridge from being damaged. Tests are compared in the case of a three-span concrete bridge, made of prestressed precast beams. In a diagnostic load, reaching accurate diagnosis was made possible by the calibration of the calculation model based on deflection measurements and by the definition of concrete (performance) parameters, mainly concrete tensile strength. In proof load testing, accurate assessment of the actual capacity was possible, thanks to the support of acoustic emission measurements.Peer Reviewe