This report considers the strength of filler beam bridge decks without transverse reinforcement. It describes the testing and analysis of three such bridge decks and refers to previous work on a half-scale model. It discusses how the additional, uncodified strengths found in this type of structure can be invoked in the assessment of existing bridges. The testing involved one load test to collapse on a bridge in Herefordshire (Wormbridge) and non-destructive vehicle load tests on two bridges in Lancashire (Pepper Hills and Lancliff Cross). In each case the structures proved to be far stronger than could be predicted using the conventional assessment rules. Assessments were obtained from the bridge owners and, in the case of the collapse test, independent conventional and non-linear assessments by a consultant. A back analysis of the test results was done by TRL and a model for the behaviour of these decks at the ultimate limit state has been developed. It is concluded that despite having no apparent transverse bending capacity the decks were able to distribute both working and ultimate loads well. The good distribution characteristics indicate that it is appropriate to assess this type of deck using the standard assessment loading with full width lanes rather than the concentrated wheel path loading used for trough decks. The favourable distribution characteristics indicate that it is safe to design or assess filler beam decks using an elastic load distribution based on a shear key deck model with uncracked section properties. The authors recommend this form of distribution for assessments under standard highway loading. Sample assessment calculations based on this report have been prepared for Lancashire County Council by Parkman Consultants and are available from The County Surveyor and Bridgemaster, PO Box 9, Guild House, Cross Street, Preston PR1 8RD.

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