Design ID were appointed by the Contractor to act as Principal Designer and Lead Footbridge Designer on this 63m Single Span Bowstring Truss Footbridge over the Pennyburn Inlet adjacent to the River Foyle in Derry City. The scheme comprised of 650m of shared pedestrian and cyclist greenway running along the banks of the River Foyle, forming a key connection with the existing path network within Bay Road Park. We led the design of the footbridge superstructure and substructure, connecting greenway paths, pedestrian guardrails, drainage and scour protection within the sensitive enviroment of the River Foyle.
One of the key challenges of this project lay in the design of the bridge superstructure. As the Client anticipated that the greenway could form part of a new Derry City Marathon route, it was of critical importance that the footbridge could sustain comfort levels for users during such an event. We worked collaboratively with the Client to agree bridge geometry that satisified planning conditions and prepared a comprehensive dynamic analysis of the structure to demonstrate its suitability. As the bridge geometry and slenderness set at planning stage had effectively set the natural frequency, and therefore its propensity to resonate and vibrate under dynamic loading, we proposed a monitoring and mitigation strategy to allow for the post installation of a Tuned Mass Damper, should the bridge require it following its use in reality. This approach saved the Client unnecessary cost for what could have been additional weight and structural elements, making the bridge unfeasible to be lifted in, or potentially conflicting with its planning approval.
Throughout the construction process we also provided construction logisitics and temporary works design services, to include but not limited to: working platform designs in support of access plant / craneage and lifting design.
The greenway design included specifications, alignment and geometry, line marking, signage, drainage and embankment stability. These designs were carried out in accordance with the DMRB. We produced Works and Site Information documentation in line with CDM Regulations and the MCHW such as Bill of Quantities, specifications, utility layouts, and pre-construction inspection reports.
As this project involved design along the edge of the brownfield industrial site on the banks of the estuary, the creation of new drainage infrastructure, whilst aiming to utilise and tie into the existing networks, was one of the most challenging aspects. Historic foundations, concrete slabs and old drainage runs had the potential to cause problems on the surface for our proposed design. We surveyed existing drainage, completed drainage assessments, to ensure positive drainage from all areas of the new road and lorry park areas. The merits of different construction options were considered based upon ease of construction, projected cost, health and safety and the ongoing operations.
Client: FP McCann
Structural Detailer: Stuctural Design & Detailing
