Trellis and Trestles – Innovative Busway Bridge Design

An innovative design and construction of a bridge in Edmonton to carry bus traffic from a Light Rail Transit Station is described. The overpass crosses a high volume road at a very high skew and traverses a highly sensitive ground slope. The 455 m long bridge consists of 70 m long “Trellis” structure over the roadway and two “Trestles” type structures, 63 m and 322 m long. The “Trellis” structure consists of twelve 30 m long simple spam precast prestressed concrete NU girders at approximately 6 m spacing, placed perpendicular to the roadway below, over which are placed partial depth precast concrete panels and cast-in-place concrete deck slab. This arrangement avoided the traffic disruption on the roadway and is more economical than a conventional bridge. The “Trestles” consists of 1.5 m diameter cast-in-place concrete piles at 7 m spacing along the length of the bridge, extended up to carry a cast-in-place concrete deck slab, 7.7 m wide and 0.4 m average thickness. The cast-in-place concrete piles act as “shear keys” to provide stability to the soil slopes. The entire structure is designed and constructed as a contractor proposed value engineering alternative to the original tendered design consisting of a conventional two span bridge over the roadway and tangent pile retaining walls at the ground slope, resulting in over $ 0.5 M savings to the Owner.