Rigid frame bridges, where the abutments are structurally connected to a continuous deck to form an integral structure, have the advantage of reduced maintenance costs because of the absence of bridge bearings. However seasonal expansion and contraction of the bridge deck causes cyclic movements of the abutments which lead to variations in the earth pressures acting on the abutment walls in service. In turn, these lead to considerable uncertainties in design. In this study the behaviour of two existing portal frame bridges spanning the M1 was studied over periods of up to 14 months. These bridges were instrumented to monitor the longitudinal thermal movements of the deck and the associated change in vertical level at various points along the deck. (A)

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