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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)

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 Reviewed, Postprint (published version)

Load testing of concrete bridges is a practice with a long history. Historically, and particularly before the unification of design and construction practices through codes, load testing was performed to show the travelling public that a newly built bridge was safe for use. Nowadays, with the aging infrastructure and increasing loads in developed countries, load testing is performed mostly for existing structures either as diagnostic or proof tests. For newly built bridges, diagnostic load testing may be required as a verification of design assumptions, particularly for atypical bridge materials, designs, or geometries. For existing bridges, diagnostic load testing may be used to improve analysis assumptions such as composite action between girders and deck, and contribution of parapets and other nonstructural members to stiffness. Proof load testing may be used to demonstrate that a structure can carry a given load when there are doubts with regard to the effect of material degradation, or when sufficient information about the structure is lacking to carry out an analytical assessment., Postprint (published version)

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 Reviewed, Postprint (author's final draft)

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)

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 Reviewed, Postprint (published version)