Design and construction New lease of life Graeme Middleton, business development director at Cemplas, gives an overview of the demanding partrefurbishment of Hunters Bridge multi-storey car park in Welwyn Garden City, which was a finalist at this years British Parking Awards he part-refurbishment of this complex British lift slab* (BLS) structure will be of interest to most if not all car park owners and operators for one key reason: Pipers Row car park in Wolverhampton. This was also a lift-slab structure, which catastrophically partially collapsed early one Sunday morning in March 1997. Structural repairs and deck re-waterproofing are commonplace within the upgrading of most reinforced concrete car parks, but few come with as many warnings to proceed with caution as that of a lift-slab structure. The Hunters Bridge 673-space car park was built in 1973. The clients project brief given that the site of the car park is earmarked for re-development by 2029 was for the project team to appraise the condition of the structure and undertake repairs to extend its safe working life by a further 10 years, within strict budgetary constraints. But it was far from just re-waterproofing the top deck and carrying out a few localised concrete repairs T the engineers responsible for the design of the structural steel strengthening collars, which were installed as part of a previous major repair contract in 2003. Given the structure type and consideration of maximum permissible weight loadings, this presented production planning issues from the start. Surface preparation plant and machinery had to be a minimum of 20m apart at all times, so removing the existing top deck waterproofing was not a simple exercise. Storage of plant and materials would normally be adjacent to work areas, but because of the weight-restriction reason, materials had to be kept within a secure area on the ground level. This meant continuous contractor traffic throughout the car park, which had to remain in use at all times. Traffic management was required to protect both users and workforce. Challenging conditions As part of the team, Conisbee consulting engineers undertook an engineering assessment, combining investigative works and studies of the archive survey data. It also had discussions with 28 britishparking.co.uk PN May20 pp28-29 Design and construction Cemplas.indd 28 23/04/2020 15:04