Modelling a Bridge Construction
Geometry & Trigonometry
Model the changing shape of an arch bridge as it is built out in stages from both banks, using curve fitting rather than full structural analysis.
Introduction
Arch bridges such as the Sydney Harbour Bridge and the Hoover Dam Bypass Bridge were built as two independent halves growing out from each bank, supported by cables, until they met in the middle. At each stage of construction the growing arch had a different shape, and engineers had to check the two halves would align before joining them. This exploration asks you to model the shape of a growing arch at different construction stages using curve fitting, working from photographs of a real construction sequence.
Guiding Questions
- Watch a bridge being built in stages. What curve does the partly built cable or arch follow at each stage?
- Fit a curve to the partly built arch or cable at two different construction stages. How does its shape change as more sections are added?
- Cantilever arches are built out from both sides before they meet in the middle. Model the curve of each half and check how closely they line up at the point where they are due to join.
- Compare your staged model with photos of a real construction sequence.