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.

A large subset of the Dutch bridge stock consists of reinforced concrete slab bridges, for which assessment often results in low ratings. To prioritize the efforts of the bridge owner, more suitable assessment methods for slab bridges are necessary. Research efforts over the past years resulted in the development of several methods, at levels requiring increasing costs, time, and effort for increasing accuracy. The last option, when an analytical assessment is not possible due to uncertainties, is to use proof load testing to evaluate the bridge directly. To develop recommendations for the proof load testing of reinforced concrete slab bridges for the Netherlands, different methods are combined: pilot proof load tests on bridges with and without material damage, a collapse test, tests on beams taken from an existing bridge and new beams with similar dimensions cast in the laboratory, and an extensive literature review. The result of this study is a set of recommendations that describe how to prepare and execute a proof load test, and how to analyze the results. This paper summarizes the research program about proof load testing from the Netherlands and gives an overview of the currently developed recommendations and topics for further research.

Nowadays, finite element analyses provide information about the performance of a structure, but they are more or less simplified. Therefore, load tests are the only way to find the “real” behavior of an existing bridge subjected to the rating process. In this paper, the state-of-the-art concerning load tests of concrete road bridges is presented, and the problems of the execution of such tests are specified. It is pointed out that only load tests accompanied with current finite element analyses may result in a proper assessment of the level of safety of the bridge. The authors’ procedure of complex assessment of such bridges combines in-situ examination of the structure, load testing, and finite element modeling. The paper discusses the following topics: aims and fundamentals of static diagnostic and proof load tests; the load application method according to different codes and specifications; the basis for proper assessment of the target load: reliability index, partial factors approach, global rating factor approach; establishing the load allowable on the bridge, based on the applied proof load; and the proposed procedure of assessment of existing concrete road bridges by load testing.

The paper presents principles of diagnostic load tests of concrete bridges performed in Europe and one example of application from Poland. The common basis of the load testing techniques and methods were developed within the European Research Project ARCHES (Assessment and Rehabilitation of Central European Highway Infrastructure) and the main objectives and results of the project will be presented herein. Based on that, an example of application will follow. The presented example of load tests is an evaluation of newly built reinforced concrete slab bridge. The bridge is a seven-span continuous structure with spans length of 14.05+18.03+15.31+15.63+18.97+18.60+14.34 m [553+710+603+615+747+732+567 in]. After construction, during cleaning the bottom surface of the structure many cracks were noticed in the tension zone. The process of bridge load testing was concentrated on the analysis of the cause of cracks appearing and estimation of the load carrying capacity of the bridge. The investigation range contained the following: tests of material properties, analytical calculations, visual examination of the bottom surface of the structure before, during and after load testing; measurements under test loading: deflection, selected cracks width and supports displacement. The final conclusions included the causes of crack appearing and recommendations for the future bridge service.

Off-system concrete bridges with no design plans are currently a concern in New Mexico as many exist throughout the State. Load rating these bridges is problematic since the design documentation is limited or missing, thus creating uncertainties regarding the safe load limits. Two prestressed concrete bridges, a double T-beam and box beam bridge, were evaluated using advanced analyses and experimental methods (including load testing and rebar scanning). Both bridges have damaged and/or missing shear keys between the adjacent beams and thus, the load distribution path was uncertain. The bridges were evaluated based on the following procedures: estimating the material properties from past specifications and amount of prestressing steel via Magnel diagrams; verifying the steel estimate with a rebar scanner; load testing based on strain measurements; and rating the bridges using the load test results. Rating factors were determined for legal loads based on serviceability (i.e., concrete cracking) and strength (i.e., shear or flexural capacity). The serviceability ratings from load testing and strength ratings from analytical software were compared to determine the final load ratings and need for posting the bridges.