Situation: West Gate Tunnels Design Project, Australia

This project aimed to reduce congestion in Melbourne, Australia. One of its packages, Bridge 91, is a cable-stayed modular steel bridge designed for cyclists and pedestrians. I was the BIM Lead, responsible for delivering BIM models and shop drawings.

Task: Pre-camber is a critical concept in steel structures where an intentional upward curvature is introduced during fabrication to counteract downward deflections caused by dead loads, live loads, and other forces during the structure’s service life. In modular steel bridges like Bridge 91, pre-camber ensures that the bridge remains level after all components settle under load.

My task was to ensure the correct application of pre-camber values across the bridge span's sub-components. The design drawings provided a series of pre-camber values (0mm, 15mm, 25mm, to a maximum 110mm etc.) based on chainage stationing but lacked clarity on how to apply these values to different profiles such as the Deck, Kerb, and Soffit. The challenge was to develop a method to apply differential pre-camber values that accounted for varying profiles and elevations to maintain alignment and buildability.

Challenge: Bridge 91 had intermittent landing areas on the deck where cyclists and pedestrians could rest, avoiding a continuous ascend along the span. This variation possessed practical challenges in applying a uniform pre-camber value across the deck and other profiles, such as the kerb and soffit. Applying pre-camber values only to the deck would have led to differential deflections during erection, causing misalignment between adjacent spans and compromising structural integrity.

Action: To address this challenge, I raised a Request for Information (RFI) highlighting the need for differentiated pre-camber values. I proposed two solutions:

1. Interpolating and applying proportional pre-camber values: I calculated appropriate pre-camber values for each component using interpolation techniques and presented the results in a structured tabular format.
2. Applying pre-camber only to the deck: While simpler, this approach ignored variations in other profiles, risking misalignment.

The first option, involving interpolating and applying proportional pre-camber values, was accepted by the Project Engineer due to its technical effectiveness and alignment with design requirements. This approach ensured accurate modular buildability.

Potential Risks Avoided:

Had this issue not been identified and resolved:

• Fitment Issues: Prefabricated spans fabricated in China would not have aligned correctly during assembly in Australia.
• Structural Integrity Risks: Misalignment during erection could have introduced stress concentrations, compromising stability.
• Cost Overruns and Delays: Misalignment would have led to rework, increasing costs and delaying the project.
• Safety Concerns: Improperly aligned spans could have posed safety hazards for pedestrians and cyclists.

Conclusion of Example 1:

By identifying and addressing this challenge early, I applied scientific and engineering principles to analyze the problem and select an appropriate solution. I reviewed available techniques, applied interpolation methods to achieve accurate pre-camber values, and ensured proper constructability. Additionally, I identified potential risks and implemented a technically sound solution that safeguarded the structural integrity, safety, and timeline of Bridge 91.