Bridges

Constructed in 1968, the Hay Street Bridge complied with bridge height clearance standards at that time. However, data indicated that the bridge was hit 20 times by over-sized vehicles, nine of those during the past five years to 2020. BG&E was engaged by Main Roads Western Australia to undertake optioneering work and concept designs that led to detailed design and documentation for the modifications to Bridge No. 0923 on Hay Street over the north and southbound carriageways of the Mitchell Freeway and the southbound entry ramp onto the Freeway. BG&E's innovative design provided additional clearance to reduce the likelihood of collision. The superstructure of Bridge No. 0923 consists of 11-cell reinforced concrete box girders. The bridge is nominally 58 m long with three continuous spans. The superstructure is supported on four reinforced concrete pier columns and walled abutments.

Our highly-experienced team designed an out-of-the box solution to raise the height of the bridge by removing three-cells of a 21 m middle span of the continuous bridge and adding a bridge protection beam. BG&E designed the removal of the section of the middle span of the continuous bridge to work with the grade of the Freeway below and achieve an increased vertical clearance with minimal impact to the Freeway below and road above. The removal of the three northern cells from Span 2 of the existing bridge resulted in compatibility effects within the other spans from changing a continuous bridge to simply-supported for this section of the superstructure. These issues were addressed with detailed design of post-tensioned strengthening inside the cells. The detailed design of a bridge protection beam at the northern edge of Span 2 made use of the existing pier columns and pier diaphragms, with reuse of the stone feature edge parapet also incorporated.