The BNR Overhead structure is a 350-foot-long, five-span steel bridge that carries Highway 99 over the Burlington Northern Railway which connects Vancouver to the US Interstate network. To alleviate traffic congestion and encourage sustainable commuting, the Governments of BC and Canada provided stimulus funding for the addition of dedicated bus lane on this major artery. MMM was retained by the BC Ministry of Transportation and Infrastructure (BC MoT) to lead the widening design of this bridge. Due to seismic deficiency of the existing bridge, an options analysis was added to the scope to compare short- and long-term solutions for accommodating the dedicated bus lane and the seismic upgrading of the bridge. Challenges in this project included poor soils in the footprint of the bridge and its approaches, the lightweight construction of the original structure, the compressed design and construction schedule to meet stimulus funding deadlines, and the requirements for uninterrupted movement of the highway and the railway traffic. The final design entailed widening of the existing bridge on both sides and utilizing helical minipiles to allow piling to occur beneath the bridge deck. To accommodate the anticipated excessive earthquake displacements and to prevent potential collapse due to soil liquefaction, a “catcher” system was used. This structurally independent system, in addition to the use of seismic ties at deck joints, provides the required supports to the superstructure in the event of design earthquakes. The project was completed on time and received the 2011 Deputy Minister’s Award of Merit from BC MoT.
