International Concrete Abstracts Portal

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.

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 motivation for full-scale testing of concrete bridges is significant, since it is deemed to solve some of the major challenges related to capacity evaluation of older concrete bridges combined with increasing load demands. A novel test rig was developed as a mean to evaluate the full-scale bridge response of concrete bridges spanning up to 12 m (39.4 feet). The test rig was fast to mount, applied the load accurately, and loaded the structures to a very high load magnitude. The bridges were loaded to maximum capacity of the test rig without cracking (approx. 100 tonne (220,000 lbs) axle loads). 3D scanning, LVDTs, distance lasers, and DIC cameras were applied to two of the bridges, as well as land surveying readings, in order to measure the structural behaviour during testing. The loading sequence worked well, and it was possible to measure deflections and strains. Using a wide-angle lens DIC-camera showed to be a promising method to measure strains, in-plane deformations and cracking during testing. Work regarding modelling in conjunction with monitoring is ongoing, to provide a more accurate way to evaluate the ultimate capacity of the bridges as well as stop criteria during full-scale testing.

Torsion due to superimposed loads is often ignored in prestressed concrete bridge girders because it is considered negligible compared to other forces that control the structural design. However, during load testing of prestressed concrete girder bridges, shear strains due to torsion can be on the same order of magnitude as shear strains due to the vertical shear force resultant for superimposed loads. The inability to differentiate between the two types of shear strains may lead to inaccuracy when determining the vertical shear force distribution in statically indeterminate bridge structures. Rosette strain gages need to be placed on both sides of the girder web to differentiate between torsion and vertical shear to characterize the shear distribution. The need for this instrumentation configuration likely applies to other studies in the literature that have calculated shear force through the use of rosette strain gages on only one side of prestressed concrete girder webs in bridges. This paper discusses best practices to quantify shear distribution data. The study included tests and finite element modeling of laboratory and field bridges.

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.