In 2000, the Centre Street Bridge in Calgary underwent a major rehabilitation to remove deteriorated concrete and upgrade the structure, originally built in 1903, to modern design standards. Beneath the main arches, the old deck structure was removed and a new reinforced concrete deck constructed. The design of this deck incorporated a hybrid reinforcement design concept that will produce more durable deck slabs.
It has been shown that top reinforcement does not contribute significantly to the strength of a concrete slab on girder bridge deck and that it can be removed entirely from the deck. The current isotropic steel reinforcement approach has two major drawbacks. Non-essential reinforcement is responsible for most of the costly maintenance deterioration problems and the protection of this same reinforcement leads to higher initial construction costs.
Although this top layer may not be essential for strength, it is desirable for reasons of serviceability and continuity to have secondary reinforcement in the upper portion of a deck slab. The Centre Street Bridge lower deck utilizes a hybrid design concept with GFRP reinforcement for the top layer and steel reinforcement for the bottom layer. Based on an improved understanding of
concrete bridge deck slab behaviour, the bottom layer of steel reinforcement is designed for strength based on arching principles and the top layer of non- corrodible fibre-reinforced polymer (FRP) reinforcement is provided as secondary reinforcement.
The lower deck is constructed with a 200-mm-thick reinforced concrete deck slab supported by four steel stringers at a spacing of 1870 mm across the width of the deck. Steel transverse floor beams support the deck and stringers at 4510 mm intervals. The floor beams are suspended from hanger rods that are attached to the heavy concrete arches forming the main support system for the entire structure. The bottom reinforcement is 15M steel bars at 300 mm in both directions, satisfying the 0.3 percent reinforcement criteria of the empirical design method. The top layer was a GFRP grid made from 10 x 13 mm grid element at 250 mm in the transverse direction and 10 x 10 mm elements in the longitudinal direction. The properties of the grid are an ultimate strength of 600 MPa and a modulus of 30 MPa. As required by CHBDC provisions, this amount of GFRP provides the equivalent strength to the steel layer it replaces.
© «Reinforcing Concrete Structures with Fiber Reinforced Polymers» by ISIS Canada