Olympic Park Footbridge: £19M Steel Span Opens in London

A single-span bridge is, structurally, one of the most straightforward concepts in civil engineering: a beam supported at two ends, carrying loads across a gap. But conceptual simplicity does not mean simplicity in execution, particularly at 44 metres.

The span length matters because it determines the bending moment the bridge must resist. For a uniformly distributed load on a supported beam, the maximum bending moment occurs at midspan and is calculated as M = wL²/8, where w is the load per unit length, and L is the span. Double the spa,n and you quadruple the bending. Sufficiently deep 44 metres, the sections must be deep enough and strong enough to resist significant bending without excessive deflection.

Steel was the obvious material choice here. Its high strength-to-weight ratio means the bridge could be fabricated off-site and transported as a single unit. A concrete bridge of the same span would have been far heavier, making pontoon transport impractical. It would likely have required in-situ construction with temporary supports (falsework) in the river.

The pontoon installation method introduces its own engineering challenges. The bridge had to be designed not just for its permanent load case (pedestrians, cyclists, wind, thermal expansion) but also for the temporary load case during installation. A pontoon is different from a bridge in that it is supported at different points than its final bearings. The bending moment diagram changes entirely. Engineers must check that no section of the bridge is overstressed during the float-in, and that the pontoon itself has sufficient buoyancy and stability to carry the load without listing.

Hydraulic jacking is the final step. The bridge arrives on the pontoon slightly below its final elevation. Hydraulic jacks, positioned at the abutments, lift the structure off the pontoon deck and onto the permanent bearings. This requires precise control: both ends must rise at the same rate to prevent twisting or uneven loading. The bearings themselves are engineered to accommodate thermal movement (steel expands roughly 12 micrometres per metre per degree Celsius) and rotational flexibility.

For A-level students, this project illustrates several key concepts. The bending moment equation (M = wL²/8) is fundamental to mechanics. The idea of a supported beam, with reactions at each end, appears in every structural analysis course. Material selection, weighing strength, weight, cost, and fabrication method, is core to Design and Technology. And the temporary works planning, how you build the thing before it becomes the thing, is the kind of real-world engineering problem that textbooks rarely cover but working engineers face daily.

The constrained site adds another layer. In an open field, you would crane a 44-metre bridge into place in an afternoon. In East London, surrounded by live railways and waterways, you spend months planning the logistics, securing possessions (periods when the railway is shut down for engineering access), coordinating with the Canal and River Trust for waterway access, and designing bespoke temporary works. The engineering of the bridge itself might be the simpler half of the project.