Specifications

 

 

 

Concrete

 

The concrete shall consist of 13mm quartzitic stone, Swartkops River sand and Portland Cement, weigh-batched to produce a mix which has an average compressive strength of 50Mpa at 28 days for 150mm test cubes.

 

The mix shall be compacted by vibration in steel moulds, to produce dense concrete.

 

 

Prestressing Wire

 

Major posts are to be prestressed with four 5 mm dia. crimped prestressing wires, intermediates and stays with four 4,25mm crimped prestressing wires which are to be accurately positioned in the four corners of the moulds to give a concrete cover of 20mm. The prestressing wire shall comply with B.S. 2691 having a yield stress of approximately 1500MN and Young’s Modulus of approximately 200Gpa.

 

The prestressing wires shall be equally tensioned in the moulds by a force producing an initial stress of not more than 70% of the 0,2% proof stress. No prestressing wires shall be exposed when the posts are erected in concrete.

 

 

Fittings

 

The shear nuts, corner brackets and bolts shall be hot dipped galvanised. The studs shall be zinc plated or as specified.

 

 

Top Rail

 

The top rail shall be 125mm x 50mm steel channel. It shall have 12mm holes pre-drilled at 200mm intervals and end plates fitted.

The top rail shall be hot dipped galvanised.

 

 

 

Spacing of Posts

 

Major post spacing shall be a maximum of 3030mm centre to centre.

Intermediate post spacing shall be 200mm centre to centre. The gap between posts shall be 110mm.

 

Major posts shall have a 600mm deep x 450mm x 450mm footing. Intermediate posts shall have a 300mm deep x 250mm wide strip footing.

 

 

 

Bending Moments

 

The major posts and intermediate posts are designed to resist a minimum bending moment of 2.7kNm and 1.3kNm respectively, in any position before initial failure occurs.

 

(Note: The force required to break a post, so that it does not fully recover, is considerably greater than the above specification.)