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.

Load testing and structural monitoring facilitated the passage of several super-heavy permit loads at the Burns Harbor access bridge near Portage, IN. Twenty super-heavy permit loads, with gross vehicle weights reaching 848 kips (3770 kN), were required to cross the bridge, which was the only feasible route out of the port. Preliminary load ratings were acceptable due to three factors; the specialized transport’s large footprint effectively distributed load, the bridge was designed for Michigan Truck Trains, and the bridge was assumed to be in good condition. The last condition came into question due to significant cracks throughout the prestressed concrete girders caused by delayed ettringite formation (DEF). While DEF cracks were a function of improper curing and not related to live-load effects, the Indiana Department of Transportation (INDOT) was concerned that repeated heavy loads would negatively influence cracks and the bridge’s overall long-term performance. Due to the cargo’s importance to the local community and lack of an alternate route, INDOT allowed use of the bridge after load tests proved that the transports would not cause damage or reduce the bridge’s service life. Structural monitoring performed during the entire transport period verified structural performance was not diminished during the numerous crossings.

This paper presents the current practice of bridge load testing in Germany. At first a brief summary of the historical value and meaning of load testing bridges at commissioning is given and also accidental over-load tests are described. While load testing of brides as part of the commissioning is common in many European countries today, in Germany load testing is only permitted in exceptional cases and to evaluate damage or questioned existing bridges. While proof loading is rare, short and long-time test under serviceability loads are a common engineering task in Germany. Especially the calibration and verification of numerical models by load testing shows a high potential for the future. As the infrastructure gets older and the traffic loads increase a high demand for experimental evaluation methods becomes more important and request further research work to answer open questions. The four given examples of load tests demonstrate possible applications and different tasks for load testing of concrete bridges.

The state of West Virginia is home to a substantial population of bridges that are in service well past their initial design lives. As these bridges have aged, and inevitably deteriorated, management has become a challenge. In 2006, The West Virginia Division of Highways (WVDOH) enlisted the help of Drexel University to develop an approach to managing these structures, with a particular focus on reinforced concrete bridges with little to no documentation. One such structure was the Barnett Bridge, located near Parkersburg, WV. This filled concrete arch bridge was built in 1929 with a 90 foot (27.4m) single span over a small creek. The bridge was posted due to challenges in accurately load rating the structure with only minimal historical documentation. Working side by side with WVDOH, and through a combination of load testing, repairs, and targeted long-term monitoring, the bridge was left in service. This paper presents the case study of the Barnett Bridge, from when it appeared in the local newspaper in 2008 as one of the bridges in the state with the lowest sufficiency rating, to present day where it still serves the surrounding area, with a focus on the proof load test that served as the cornerstone for the revitalization of this structure.

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.