St Botolphs Bridge
Early in 2013 Britcon were awarded a design and build contract for Lincolnshire County Council to replace the existing St Botolph's Footbridge located in the heart of Boston town centre. The existing structure, built in the 1970's and crossing the River Witham, has been replaced by an iconic 65m long bowstring arch bridge complete with decorative lighting providing a bright, welcoming gateway into the town.
The new structure is wider than the existing bridge and has an elliptical deck allowing people to admire the nearby Boston Stump without obstructing the crossing. The features of bridge include a non-slip surface and improved access for pedestrians, wheelchair users, dismounted cyclists, pushchairs and mobility scooters. The bridge colour matches the yellow lighting of the octagonal lantern in the church tower, where it is believed to have been used as a marker to guide travellers on land and sea. There is also a tri floral motif installed into the parapet which will replicate the nearby Town Bridge.
A Key aspect of the project involved an intense development phase to design this contemporary bowstring arch bridge, which was the preferred structure following extensive consultations between the Council and public. Working with client Lincolnshire County Council, lead designer HBPW a series of workshops was arranged by Britcon to finalise the detailed design, and resolve the many issues of building a bridge on such a confined site. Additional specialist subcontractors and designers were also appointed early in the contract and invited to provide valuable input into the design development phase. Also to satisfy the technical approvals required for complex bridge structures the design was subject to a Category 3 check, which involves employing an independent consultant to review and either approve or amend the lead design calculations.
Our pre-construction works comprised a major trenching exercise to reveal utility locations some of which were diverted prior to the main works. A major dilapidation survey was undertaken of the surrounding area and surrounding buildings and a mini anchor piling system was also developed to avoid vibration adjacent to nearby properties. An additional site investigation consisting of two cable percussion boreholes and laboratory testing was undertaken to provide ground information to aid the foundation design.
The bridge components have been fabricated and painted off site in three elements comprising the central span and two end ramps. Where feasible early foundation and ducting works have been undertaking while keeping the old bridge operational and minimising the duration where there is no crossing in place. However, there came a point, based on health and safety grounds, where the surrounding area was closed off from the public. This allowed Britcon to remove the old bridge, which was undertaken using a 500 tonne crane to lift out the central span followed by the two end sections. Following the departure of the old structure the new steel assembly for the central span was delivered to site, and assembled in a rented car park adjacent to the river in preparation for lifting into its permanent position. The lighting installation has also been undertaken during this phase with LED lights running through the handrails of the bespoke parapets and up-lighters attached to the main structure. The parapets themselves are fabricated in stainless steel with sabre fin shape posts with tensioned cables running between them.
The illuminated handrail is also cast in stainless steel with a hardwood top rail.
A 1000 tonne crane was required to lift in the bridge which will took place over the weekend between Saturday 22 and Sunday 23 February 2014. The crane was mobilised and assembled during Saturday with the central section lifted into position early by early evening. The two ramp sections arrived Sunday morning with a police escort and were lifted into position during the same day.
The final phase of the works involves upgrading the pubic realm areas on both sides of the bridge. High quality block paving will be laid to replace the existing and new bollards, ornate street lighting and seating areas will be provided to enhance the area.