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| Shrewsbury with Atcham Borough Council | |||||||||||||||||||||||||||||||||||
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| Contract
Background: In order to effect the demolition safely and economically, Shrewsbury & ABC initiated a rigid pre-qualification and subsequent tendering regime, requiring substantial pre-qualification submissions and, for successful pre-qualified contractors, an exhaustive tender submission with detailed method statements to be submitted by all tenderers. Following comparison of tenders, Shrewsbury & ABC invoked an evaluation scoring system, which took into account all aspects of the submission from price, safety, method statements, quality of submission etc. before finally appointing Walter Forshaw to carry out the demolition despite not being the lowest tender. Building Construction: The contract was to demolish a ten-storey office building within the heart of the historical City of Shrewsbury; the structure being closely surrounded on all 4 sides. Available room around the site ranged from 8m to 14m to the nearest structure. Surrounding land use included a major city centre road, the central bus station, an office building, a multi-storey car park and shopping centre, between which the site had to be accessed. The building was constructed of an ‘Omnia’ pre-cast concrete floor system spanning from central reinforced concrete columns and beams which acted longitudinally into the reinforced concrete shear walls situated at either end of the building and centrally within the staircase and lift shaft core. The floors spanned from the central column and beam arrangement to pre-cast concrete wall panels. The unusual nature of this building construction had lead to considerable structural deterioration during its life span and had been historically linked to excessive sway during high winds. As a result, it was decided that demolition rather than refurbishment was the most suitable option. Demolition Method: Walter Forshaw evaluated all the options and decided that it would be necessary to fully scaffold the building and encapsulate the structure with Mona flex sheeting. The building was cleared of a small quantity of asbestos and soft stripped of the internal fixtures and fittings during scaffold erection. The lift shafts were cleared of the cars and guides to enable the shaft to be used as a debris chute during the soft strip and dismantling phase of the works. Prior to structural dismantling, the floors were back-propped in accordance with our engineer’s design to withstand the loads imposed by plant, equipment and debris, and the external wall panels were propped using push-pull props to maintain their structural integrity during the dismantling operation. The sequence of dismantling involved removing the lift houses and plant rooms, followed by the floor-by-floor deconstruction of the top 5 floors, prior to long reach demolition of the remaining structure. During the initial stages of the dismantling operation, it became apparent that due to the poor construction, pre-planned sequences had to be altered, as the inherent strength within the structure did not materialise as the design criteria indicated. Despite the challenges the early phases posed, the contract was completed on time and to budget and an unsolicited testimony received from the Planning Supervisor upon completion. Reference Details: Please contact WFL for reference contact details. See attached letter from John Pidgeon Partnership. |
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