Dalton Park
Client:
Ballast Construction North East
Year of Completion:
2002
Architect/Designer: Napper Architects
Architect/Designer: Napper Architects
Design of membrane connections only, fabrication and installation. 7 no. Non-weldable PVC canopies totalling 5028m² The Dalton Park Development consists of a series of single-storey retail buildings separated by a continuous street that runs the length of the site. The fabric canopies are located above these units, and span the width of the open street, providing partial coverage to the shoppers below. The fabric canopy structures consist of stressed PVC-coated polyester fabric membranes, together with supporting cables, rods and a grade 50 steelwork frame. This statement should be read in conjunction with the Engineer’s drawings and Project Specification, which provide layouts, details and specification information for the structure and materials adopted.
Description of the Canopy Structures
The works consist of the following membrane structures:
• Tent Type 1 – Narrow Street Canopy (2 no;)
• Tent Type 2 – Wide Street Canopy (2 no;)
• Tent Type 3 – Knuckle Space Canopy (2 no;)
• Tent Type 6 – Entrance Canopy (1 no;)
There were originally planned to be 2 other tent types, covering the fast food outlet and the playground, but these were omitted post-tender. Arup drawing S.28.L.400 indicates the locations of all of the above canopies.
The canopies were erected approximately 4 to 6 metres above finished ground level, and are fixed to the roof structure of the surrounding single storey developments.
There are 2 number Tent Type 1 Street Canopies, each comprising approximately 1000m² of stressed membrane. Each canopy is rectangular on plan – approximately 14 metres by 60 metres - and forms a series of conical shapes along its length. Four vertical flying masts and perimeter edge cables support the canopies. The membranes are restrained at their ends by inclined arches, which are stabilised by cables anchored to foundations, and by stiff connections back to the longitudinal steelwork. The fabric surrounding each flying mast also has a fail-safe support system, comprising nominally taut (e.g. non-active ridge) PVC belts in pockets running from each of the four lower support corners to corresponding quarter points around the circumference of the head ring. Double layer fabric reinforcement is included in the top 1 metres of the membrane. A steel framework attached to brackets located on the main building roof structure supports the canopies. The steel canopy frame will equilibrate all internal horizontal forces, and will rely on the main building structure for vertical load support and overall stability only.
The 2 number Tent Type 2 Street Canopies are similar to the Tent Type 1 Canopies, and each comprises approximately 1000m² of stressed membrane. The overall dimensions are approximately 18 metres by 20 metres, with the 4 no; flying masts inclined at 15° to the vertical in alternating parallel directions. The structural concept of the canopies is similar to those for Tent Type 1.
The 2 number Tent Type 3 Knuckle Space Canopies represent shallow conical geometries, and each comprises approximately 500m² of stressed membrane. The overall dimensions are approximately 20 metres by 25 metres. As with the street canopies, the support system comprises a horizontally self-equilibrating steel frame and edge cables. The central portion of the canopy is attached to an elliptical steel ring that is supported by a cable suspension system that is supported on A-frame and V-frame masts springing from and tied back to the main building superstructure.
The Tent Type 6 Entrance Canopy is similar to a single bay of the street canopies, and comprises approximately 250m² of stressed membrane. The overall dimensions are approximately 20 metres by 15 metres, and the form represents a single rectangular conic bay, with boundary edge cables on 3 sides, and an inclined arch on the fourth side. A single flying mast supports the membrane, with failsafe belts and double layer reinforcement from the ring at the top of the mast as with the street canopies. The inclined arch is restrained by 2 vertical CHS columns fixed to the foundations. As with the street canopies, the support system comprises a horizontally self-equilibrating steel frame.
Design Criteria
All of the membranes consist of anticlastic surfaces that were designed, analysed and defined by the Structural Engineer.
The membrane and supporting structure were designed to support appropriate wind and imposed loads derived from BS 6399.
Design wind speed = 46.8 m/s
Imposed snow load = 0.6kPa (Projected)
The designs were developed using non-linear analysis software, and for the membrane field the following Factors of Safety were applied:
• Permanent long term (self weight + prestress) >10
• Medium term (self weight, prestress and snow) >6
• Transient short term (self weight, prestress and wind) >5
(based upon unfactored characteristic loads and ultimate uniaxial strip tensile values)
The design was assessed against the above criteria, together with that specified by the relevant UK Codes including:
• BS 6399 in respect of imposed loads
• BS 5950 in respect of steelwork
• BS EN 10088 in respect of stainless steel
• ASCE Standard Guidelines for the Structural Applications of Steel Cables for Buildings
