RDG was contracted to design a scheme to enable the deconstruction of two link bridges connecting two office buildings. The site was bound by high security requiring full hoarding protection to ensure that the site was not visible from the outside. The link bridges, spanning 16 meters, were located at both the north and south ends of the buildings, extending from ground level to the roof. The land was situated on a heritage site with part of the London Wall beneath it, which imposed loading constraints with a maximum reaction force of 10kN point load or 10kN per square meter. Site access for materials was limited due to a highly controlled service road on the north side and a pedestrian shopping area on the south side. As a result, materials had to be manoeuvred piece small.
The deconstruction required craneage facilities above each link bridge with a capacity of 10 ton safe working load, split between two 5 ton hoists. The steel column within the building was used as a strong point to transfer the crane loads into the foundations, avoiding contact with the building fabric, as per the client's request. Conventional crane facilities usually run on steel. However, this option was not feasible due to the 16-meter span between the two buildings and site access constraints. The solution was to design a series of aluminium lattice beams to form a lattice girder, with a tubular tracking system placed on top of the beams. Each crane section had a maximum length of 2.7 meters, requiring a splice joint at the midpoint.
An access scaffold was erected on the exterior of both link bridges to facilitate the removal of the link bridge windows. The scaffold could not be freestanding due to the 10kN point load constraints and could not be tied to the building fabric. To address this, a birdcage scaffold was designed to fill the void between the two link bridges to transfer the loading from the external access scaffold into a support frame. The birdcage allowed all horizontal and lateral loads to dissipate, ensuring that the 10kN point load limit was not exceeded.
Skips were positioned on the north side of the site, while materials from the south side were transferred via a tracking system. As the materials being maneuvered exceeded the permissible load, a transfer trolley system was designed to distribute the weight safely to the ground, ensuring the 10kN constraints were adhered to.
