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Load Testing and Ratings of Salvaged Precast Prestressed Concrete Channel Bridge Girders


Six representative precast prestressed concrete channel bridge girders, salvaged from the previous CN Rail overpass on the Portage La Prairie By-Pass, section of the Trans-Canada Highway, were tested to failure. Three girders were tested under single point loading at midspan (flexural tests) and the other three girders were tested under single point loading at quarter point (shear-flexural tests). The conditions of girders were assessed prior to the tests. In addition, core samples were taken from the girders to determine their compressive strengths, chloride ion contents and air void contents. All six girders exhibited higher load carrying capacities than initially predicted using sectional analyses. After examining all the test measurements including strains and deflections, we concluded that the observed higher load carrying capacities were a result of load spreading and the ability of sections adjacent to the loaded sections to develop plastic deformation prior to the collapse of the loaded girders. However, we do not expect the same higher loading capacity, observed under the monotonic single point loading, to be realized under the real bridge loadings which are multiple point and repetitive. All the girders were load rated in accordance with the AASHTO Allowable Stress Rating (ASR), Load Factor Rating (LFR) and the Load Resistance Factor Rating (LRFR) methods. All six girders failed the ASR and the LRFR service limit ratings under the standard AASHTO vehicles. All six girders failed the ratings at inventory level under HL-93 loading, HSS 30 and CL-625 design trucks, several RTAC vehicles and CS-1 to CS-3 rating vehicles at the strength limit states. All girders with poor condition also failed at the operating rating level. Based on our review of the methods and comparisons with the observed test results, we recommend the LRFR method to be used for future girder load ratings.

Conference Paper Details

Session title:
Mike Lau
Asnee Pochanart
Ruth Eden