The Queen’s Tower at Imperial College London, a significant Victoria landmark, is undergoing extensive restoration. A primary challenge was providing safe access for skilled trades without compromising the integrity of this historic structure. The design required unobstructed access and working clearance around the 85-meter-high tower while avoiding physical contact with the tower itself. As a result, the temporary works solution had to be entirely free-standing and self-stabilising, presenting challenges such as managing lateral loads and minimising weight on the foundations.
Various structural approaches were explored. A structural steel frame with infill scaffolding was initially considered but rejected due to extended timelines and higher costs. Instead, a full scaffold solution was implemented, reducing carbon emissions by about 90%, accelerating project delivery, and lowering overall costs. System scaffolds were also assessed but lacked the flexibility needed, making tube and fitting scaffolding the best choice.
High-grade steel tubes and fittings were selected for their strength and stability. Aluminium, though lightweight, was excluded due to its greater flexibility and tendency to sway under wind loads, which would have required a larger gap between the scaffold and the tower. Additionally, aluminium’s lower load-bearing capacity would necessitate extra foundation support to counteract uplift forces, complicating the design further.
Scaffold structures are typically braced for rigidity, often using ledger bracing across working platforms. However, this approach would have obstructed the necessary clearance and workspace. To address this, an innovative fully braced exoskeleton was designed to support the loads of an inner access scaffold. The exoskeleton's shape played a vital role in managing wind loading, with a near-circular configuration identified as the most effective. As a result, a 10-sided decagon design was chosen and implemented for the project.
To minimise additional weight on the tower's foundation while ensuring the scaffold's stability, the exoskeleton featured a single-width scaffold with a wider buttress at the base (approximately 10 meters), reducing uplift values from external loading. While kentledge could further counteract uplift, it would impose considerable weight on the foundation. Instead, an innovative approach involved utilising guy ropes anchored to the foundation steps at strategic locations.
During the design phase, precise load paths were established to determine accurate leg loads under varying conditions. In some cases, leg loads were exceptionally high. A tripod leg arrangement allowed three uprights to work in unison, and heavy-duty splice arrangements were installed to prevent separation and provide uplift resistance.
