 |
|
|
|
|
|
|
| |
Home >
BlueScope Steel >
Galvaspan® Purlins & Girts
GALVASPAN® PURLINS & GIRTS
Appraisals, Tests :
Index |
|
Standards
At present, there are no Australian Standards relating specifically to purlins; several are relevant entirely or in part.
The most important of these is AS/NZS4600, the SAA Cold formed steel structures code. AS/NZS4600 is referred to in the Building Code of Australia and the various State building regulations. Compliance with AS/NZS4600 is a requirement of these building codes.
AS/NZS4600 cites three materials standards, namely:
- AS1397, steel sheet and strip - Hot-dipped zinc-coated or aluminium alloy zinc coated
- AS1594, Hot-rolled steel flat products
- AS1595, Cold-rolled unalloyed low carbon steel sheet and strip.
Purlins are normally rolled from steel manufactured in accordance with one of these standards. Other steels are not excluded but their properties and suitability must be established by the purlin manufacturer by analysis, test or other means. The design engineer should independently satisfy himself that such steel is suitable.
Other relevant standards include:
- AS1170, the SAA Loading code.
- Part 1 Dead and live loads and load combinations.
- Part 2 Wind forces.
- AS4100, the SAA Steel structures code.
Supply Conditions
AS/NZS4600 requires that cold formed sections must be adequately protected from corrosion. The type of coating should be specified by the engineer, after proper account has been taken of the use of the structure, climatic or other local conditions, maintenance provision and, for coatings applied before forming, and the forming process used.
The corrosion protection available for light gauge cold formed purlins ranges from elementary paint systems to heavy galvanized coatings.
Two finishes are commonly available, they are:
- Galvanized steel with a zinc coating weight of 350g/m2
- Galvanized steel with a zinc coating weight of 450g/m2
300mm and 350mm sizes are usually produced with 450g/m2 zinc coating.
The zinc coating on galvanized purlins is fully compatible with the zinc and zinc/aluminium coatings used on modern roof and wall sheeting. If minor damage occurs to the coating on the purlins, the base steel is protected by its own surrounding coating. The protective coating on the sheeting is not corroded by an unprotected base steel nearby.
The use of purlins with an increased coating mass (Z450) and/or additional post paint systems should be specified for those environments requiring additional corrosion proteciton. It is recommended you contact BlueScope for assistance in detailing purlin specifications for severe exposure environments.
Tolerances
Properly controlled, the roll-forming process is able to produce to quite close dimensional tolerances and the following may be regarded as typical of the tolerances used by purlin manufacturers.
| Depth |
1mm |
| Hole Centres |
>± 2mm |
| Flange Width |
± 2mm |
| Camber |
1 in 500 |
| Overall length |
>± 5mm |
| Bow |
1 in 250 |
Note: Tolerances for material thickness are nominated in AS1365, Tolerances for hot-rolled and cold-rolled unalloyed low carbon steels (coils and cut lengths).
Section Properties
Two basic cold formed shapes, C and Z, are used for purlins in Australia. While each has individual characteristics, both perform effectively and in many instances the choice of one section over the other can come down to the personal preference of the designer.
Generally, C Sections are used for simple span constructions with the purlins butted at internal supports. In cases where deflection is a design limitation and the building is of a suitable size, single C Sections can be used over two or more bays.
Z Sections with one broad and one narrow flange are designed to nest neatly and are intended for lapping at internal supports. Lapping over internal supports produces structurally continuous lines of purlins for the length of the building. Structural continuity results in improved rigidity but lapping also doubles the thickness of purlin over supports where the bending moments are greatest. This results in a saving of up to 50%, but typically 30% to 40%, of the steel in the purlins compared with simple span C sections. Where additional strength is required from the purlins, for example in end bays or where additional loads are applied locally, Z sections of the same depth but greater thickness can be lapped as required.
|
All products contained herein © BlueScope Steel. Page layout © 1996-2008 Architecture Media (Selector) Pty Ltd.
All rights reserved.
|
|
|
|
Photographs