Bridges

The limits of the incremental launching technique were recently tested on the Majura Parkway project in the ACT.

The final design of the Molonglo River Bridges comprised curved twin 205m long incrementally launched box girders, with main spans of 54m and skewed supports at 30 degrees. Rigorous modeling and analysis of the 3.3m deep post tensioned box girders was essential in deriving and understanding the inherent indeterminate behavior of skewed post tensioned box girders. Calibrated FEA and space frame models allowed the effective torsional stiffness to be calculated and models to be tuned to achieve the desired behavior. Top and bottom flange concentric tendons were used to resist launching actions. Draped web tendons were stressed from both ends after launching with no internal blisters or couplers. While this gave rise to a very effective and economic design, large hyper-static actions from the second stage stressing resulted from the skewed supports. The ends of the box girders were also skewed to 30 degree to minimize the end spans. This complicated the launch nose connection, post tension anchorage zones and an already congested reinforcement layout.

BG&E used BIM to create 3D Revit models of the congested areas to ensure these zones were buildable. The 3D models became part of the deliverables and were used in interactive workshops to assist the contractor with the construction of the bridge.