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.

Self-consolidating concrete (SCC) has emerged as an alternative to build stronger structures with longer service life. Despite the advantages of using SCC, there are some concerns related to its service performance. The effect of a smaller coarse aggregate size and larger paste content is of special interest. It is fundamental to monitor the response to service loads of infrastructure employing SCC in prestressed concrete members. Bridge A7957 was built employing normal-strength and high-strength self-consolidating concrete in its main supporting members. The diagnostic test protocol implemented in this research included static and dynamic tests and the calibration of refined finite element models simulating the static loads acting on the structure during the first series of diagnostic tests. The main objective of this study centered on (a) presenting a diagnostic test protocol using robust and reliable measurement devices (including noncontact laser technology) to record the bridge’s initial service response; and (b) obtaining the initial spans’ performance to evaluate and compare the SCC versus conventional concrete girders’ response when subjected to service loads. The initial response of the end spans (similar geometry and target compressive strength, but with girders fabricated using concrete of different rheology) was compared, and no significant difference was observed.

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.