Description of the works
The project involved the partial demolition, structural modifications, and stabilization of the B & M unit due to extensive fire damage. Temporary supports were installed to secure the building, enabling subsequent structural and forensic investigations to be conducted safely.
Sequence of demolition:
- Site Establishment
- Phase 1 – Relocation of stock and temporary works
- Phase 2 – Removal of stock from site, forensic testing and structural integrity surveying.
- Phase 3 – Demolition and site finish.
The store suffered a fire which was contained to the stockroom. The intense heat caused damage to the roof and the main steel portal frame members to buckle in the affected area, this in turn created movement across the portal framed structure.
Propping was undertaken in two stages. The initial stage involved the area adjacent to the fire-damaged section, enabling the fire investigation teams to conduct their assessments and for the store to be cleared of stock in preparation for rebuilding works. The second stage of propping provided support to the retained portal frame, allowing the removal of the compromised steel sections and the re-alignment of the apex in preparation for the installation of the replacement structure.
The installation of the stage one towers was executed under constrained conditions due to the presence of stock within the store. Consequently, the equipment had to be manually transported into the work area and assembled using a scissor lift. The floor was identified as ground bearing, with limited additional information regarding its construction. IBC containers filled with water were strategically placed at the centre of each tower and connected at a low level to provide kentledge, ensuring resistance to horizontal loads. When the first stage propping works were in place, the forensics team were allowed access and following completion of their investigations, B & M staff removed all stock from the shop floor.
Once the fire investigation and store clearance were complete, the towers were released and moved to the centre of the frame of the structure to allow the demolition of the damaged section to commence while protecting and stabilising the section of the structure which was to remain in situ. A high reach excavator fitted with specialist attachment (rotating grapple) removed the roofing sheets up to the apex of the building in a careful and controlled manner to minimise any unwanted stain on the superstructure. All cold formed purlins and rails were removed by utilising the high reach excavator fitted with a shear attachment. The plant operator and the site supervisor had to remain vigilant throughout the operation ensuring that the superstructure was not subjected to strain.
Once the superstructure had been exposed, the rafters/ stanchions were lifted out. Prior to removal, the rafters / stanchions were held in place with certified chains attached to the excavator arm which held them securely in place while the operatives carried out the dismantling work. Operatives accessed the rafters using a MEWP (scissor lift). The rafters were unbolted at the middle section using hand tools. If the bolts proved stubborn, they were cut through using oxy-cutting equipment. The stanchions were cut through 1m above slab level and the rafter and stanchion could then be hoisted up and lowered steadily down to ground level in a careful and controlled manner. This method was repeated for bays 4-10.
The successful execution of this project required the combination of engineering, temporary works and demolition expertise to design and deliver a timely, flexible solution to allow clearance and re building following the fire.
