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Bridge Deck – The Basics

Hanson Concrete Products has been the leading exponent of the development of pre-cast permanent formwork for many years and the company has supplied OMNIA Bridge Deck for numerous projects to most civil engineering contractors.

omnia precast concrete permanent formwork systems from hanson concrete products
OMNIA Bridge Decking is a practical and economical means of providing permanent formwork to deck slabs of bridges, especially where these span over live roads, rail tracks and rivers.

omnia precast concrete permanent formwork systems from hanson concrete products
Within the definition contained in BS 5400 Part 5, OMNIA Bridge Decking can be considered as participating formwork, and the concrete and reinforcement in the pre-cast plank taken as part of the deck with corresponding cost savings compared to traditional methods of construction.

omnia precast concrete permanent formwork systems from hanson concrete products
The planks are primarily designed to cope with temporary condition loads only, however it is very often the case that Structural Engineers use the reinforcement provided to carry out this function as part of the working condition design, and furthermore very often ask us to increase the amount of reinforcement in the plank thereby saving reinforcement in the in-situ portion.

Design

The type of OMNIA lattice girder and plank reinforcement are normally designed by Hanson Concrete Products, restricting deflection, as a proportion of span, to 400 in the temporary condition. Additional tensile reinforcement may be included, if required by the deck designer to reduce the amount of in-situ reinforcement placed by the contractor.

omnia precast concrete permanent formwork systems from hanson concrete products
The lattice girder can be selected to provide, wherever possible, a chair for the top mat reinforcement and is aligned during manufacture to ensure ease of fixing longitudinal reinforcement over the OMNIA planks.

Dimensions

OMNIA Bridge Decking can be manufactured in lengths up to 3.75m and depending on the overall slab depth can be used for clear spans of 3.65m with a preferred bearing of 50mm at each end.

click to enlarge

A typical cross section of a Bridge Deck plank shows the arrangement of the lattice girder and the reinforcement with the precast concrete.

Manufacture

OMNIA Bridge Deck is manufactured to all relevant British Standards and the “Specification for Highway Works”, using C50 concrete in planks 300mm wide x 60mm deep, although special widths can be manufactured up to 600mm wide for use as infill panels at transverse beams or abutments.

omnia precast concrete permanent formwork systems from hanson concrete products
The upper surface of the OMNIA planks is water washed during manufacture to expose the aggregate, which, together with the projecting lattice, accommodates horizontal shear stresses at the pre-cast / in-situ interface.

omnia precast concrete permanent formwork systems from hanson concrete products
The manufacturing tolerances and soffit finish (Type F2), are as specified / defined in BS 5400 and the DoT “Specification for Highway Works” Works’ and the production process is controlled by the procedures set out in our model specification.

Transportation, Handling & Erection

OMNIA planks are normally supplied on pallets with 24 planks each, and can be offloaded directly on to the deck using a suitable lifting frame.

omnia precast concrete permanent formwork systems from hanson concrete products
Prior to placement of the planks, flanges of support beams should be painted and a bearing material (e.g.a bitumenised compressible strip) applied. This can be obtained from a number of companies including:

Compriband Washington 0191 417 8700
Fosroc Milton Keynes 01908 261220
Schlegel Henlow Camp 01462815500
Servicised Slough 01753 692929

Planks generally require a nominal bearing of 55mm, however to reduce the potential for movement, the maximum amount of bearing will be designed by our draughtsman. We would normally expect there to be a set-off dimension of h+5mm (usually 25mm) from the face of any shear studs to the face of the Omnia plank.

omnia precast concrete permanent formwork systems from hanson concrete products
Once laid, to prevent grout leakage, joints between planks should be sealed using a fillet of mortar along the joint, adhesive tape, or a proprietary sealant.