Prestressing strands

12.9 mm diameter 7-wire super strands (low relaxation) conforming to BS 5896: 1980 are used.

Standard Strand Pattern Positions 

Designers are recommended to choose from the 'standard' strand pattern positions shown for each beam type when finalising their combination of total prestressing force and eccentricity to meet their particular design requirements. Use of standard strand pattern positions allows a reduction in production costs, thus benefiting the client.

28-day concrete cube strengths 

Hume Prestressed bridge Beams are made with high strength concrete having a 28-day cube strengths of between 45 N/mm2 and 50 N/mm2. 

Cubes strength of concrete at transfer 

Although achievable, transfer cube strengths above 40 N/mm2 should be avoided where possible. A transfer cube strength of up to 38 N/mm2 should be adequate for most cases. It may be possible to avoid high transfer cube strengths by either a small increase in the construction depth or by the use of debonding.

Stacking 

Each beam should be stacked on timber bearers pierced at about 300 mm to 500 mm from each beam end. 

End slots for dowels at fixed end bearings 

Slots at beam ends can be formed in the bottom flange to accommodate dowel bars at fixed bearing positions where required.

Beam Lengths and Transportation

Subject to design considerations, Hume Prestressed Bridge Beams can be made to lengths (subject to end shortening upon transfer of prestress) required by the designer. Beam lengths should preferably be specified in increments of 50 mm. Maximum beam lengths of up to 27 metres have been successfully transported from Hume factories and launched. Where access to a: bridge site may be a problem, it is recommended that a check be made especially when using long (>22 m) beams for remote areas. For long beams, it is highly recommended that some top reinforcement (in the form of strands / bars) be placed near the top of the beam in order to facilitate transportation without cracking of the beams.