Bolting of Stramit Exacta^® C&Z Purlins or Girts to cleats and at lapped joints should be by standard M12 grade 4.6 bolts unless the shear capacity of the bolt is exceeded as indicated in the design Capacity Tables. If so, bolts will need to be upgraded to grade 8.8 bolts.

For 300 series purlins use M16 or M16 grade 8.8 as indicated in the tables. Always use the correct size and grade of bolts, ensuring all bolts are securely tightened.

Bridging used with girts may be subjected to compressive (or tensile) loading due to gravity during installation. These loads become cumulative with increasing wall height, unless a separation joint is included.

The capacity of Stramit^® Boltless Bridging, Stramit^® Bolted Bridging and Stramit^® Large Series Bridging to resist these loads is given in the Stramit Exacta^® Purlins and Girts Product Technical Manual. These capacities are based on the mass of the girts plus a 1.1kN load to allow for riggers.

Bridging provides resistance to purlin rotation during the installation of roof and wall sheeting. For this reason a maximum bridging (or bridging to cleat) spacing of 20 x purlin depth, but no greater than 4000, is recommended. Failure to do so can lead to misaligned fastenings, causing additional stresses on the fasteners and roof sheeting. Excessive purlin rotation can be a safety hazard during construction.

Stramit therefore recommends that at least one row of bridging be used in each purlin span. Stramit^® Bridging is only designed to allow purlins and girts to resist wind loads once the sheeting has been attached. Purlins, girts and bridging should not be subjected to loading from stacked materials, even when sheeting is attached, or from lifting assemblies of framing.

The Stramit^® Exacta C&Z Purlins Product Technical Manual incorporates both design capacity tables (load tables) and design member moment capacities. The latter enables engineers to input properties and capacities into their preferred structural analysis software. 

With this capability, it is practical to select purlin (and girt) configurations that are outside those listed in the design capacity tables. In particular it allows the analysis of irregular purlin configurations and complex loading patterns.

The design capacity load tables incorporate different span types, up to 3 rows of bridging, inward or outward loadings and deflection criteria all based on UDL loading.

All Stramit C or Z Purlins and Girts may be available with downturn lips for special projects. Purlins of this shape cannot normally be lapped and are usually used in single or short double span construction.

Stramit can supply lappable Zs, subject to inquiry, providing a unique section that offers strength and economy as well as a downturned lip.

Please contact your local Stramit office for details on availability, minimum order quantity and delivery lead times. Remember to allow additional cleat length for clearance between the downturn lips and the support beam.

Stramit EX-Facta™ Design Software allows designers to use the properties of Stramit Exacta^® purlins under actual site conditions rather than using the simple UDL load tables in a traditional load table.

The interactive software offers:

• fully variable span dimensions
• variable lap lengths
• visual display of span efficiencies
• up to 10 span continuous systems
• multiple combined load cases
• variable UDL within spans
• concentrated/point loads+D53
• variable bridging positions
• mixed bridging numbers
• cantilevers, or
• any combinations of the above.

Fascia purlins (either specifically designed or Stramit Exacta^® C purlin) are normally subjected to lower loads and are usually restrained by sheeting attached to the top flange and lower lip.

However should the fascia purlin support the wall girts via the fascia bridging system, ensure sufficient allowance is made to carry this extra load.

Stramit Exacta^® C&Z Purlins and Girts are custom punched to project requirements. Standard hole size is 18x22mm. Recommended web hole centres are:

• C/Z 100 40mm
• C/Z 150 60mm
• C/Z 150 70mm (Vic & Tas)
• C/Z 200 110mm
• C/Z 250 160mm
• C/Z 300 210mm
• C/Z 350 210mm.

Stramit generally recommends a lap length of 15% of the span. Lapped Span Design Capacity tables (including continuous) are based on a 15% lap. Where span lengths are unequal (eg reduced end spans) each purlin should have 7.5% of each adjacent span added as the lap length on that spans side of the support.

The lap length however, can be varied, and the design verified using Stramit Purlin design software. This allows unsymmetrical laps, or longer laps that improve the purlin capacity.

Stramit Exacta^® C&Z Purlins & Girts are manufactured from Z350 galvanised coating (350g/m²) or ZAM^® coated steel conforming to AS1397. Other coatings, grades and materials may be available, subject to inquiry.

The mass and steel grade for each Stramit Exacta^® purlin is detailed in the Sizes section.

Please refer to the Stramit Exacta Purlin and Girts Technical Manual for the full and effective section properties. Any designs carried out using the printed section properties should be calculated using AS/NZS 4600.

The standard size and thickness range is in accordance with the table below.

Exacta^® C-Sections are mono-symmetric and their freestanding, stable shape allows easy handling and storage. They are adaptable to 'I' and 'Box' configurations.

The Exacta^® Z section range is asymmetric. The uneven flanges allow the sections to be lapped to permit structural continuity, a factor that contributes significantly to building economy. The savings achieved by lapping Z sections, with the increase in strength and rigidity, more than compensates for the extra purlin material in the lap itself.

Purlin spacing is influenced by both member and roof sheeting capacity. On large and medium sized buildings it is generally more economical to reduce the purlin or girt spacing at the building edge and ends to account for the higher wind pressures.

Additional intermediate runs of purlins can be positioned in the highest loaded areas. Also remember to close purlin spacing (or add additional purlins) around roof penetrations and in areas of increased loading (eg air conditioning plant).

For special or large projects, Stramit can produce purlins outside the standard size range. These include:

• any web between 100mm and 400mm
• any flange size between 30mm and 130mm
• any lip size between 9mm and 35mm (plus no lips )
• thicknesses between 1.0mm and 3.0mm
• material strength between 300MPa and 550MPa
• a maximum strip width of 640mm.

We can also calculate the performance of these special sections to suit project specifications.

Loads to be suspended from roof purlins must be accounted for in design. No allowance is made for this in the Capacity Tables. Any such loadings must be connected to the purlin web by using hangers and/or screws.

Attachments to the purlin bottom flange must be within 25mm to the web. Connection design should follow the rules within AS/NZS 4600, including a check on bearing of the purlin. Loads should not be suspended from wall girts.

If the lower web hole in a lap is used for attaching fly bracing ensure that an additional bolt is used.

Purlin laps must be bolted in the top web hole and the lower flange holes at both ends of the lap as shown below. Bolting only in the web of lapped purlins does not provide full structural continuity and excessive loads could be placed on to roofing screws that penetrate both purlins within a lapped region.

Consideration should be given to handling and installation issues as part of site induction safety procedures. Specific consideration should be given to pack handling, and avoidance of cuts, trips, slips and falls, long section handling, particularly in windy conditions, and surface temperature on sunny days.

Wear safety glasses with side shields when cutting or trimming product. Cut resistant or leather gloves should be worn when handling product. Foot protection should be warn when handling and transporting product.

Stramit recommends that good trade practice be followed when using these products, as outlined in AISC/Australian Standards HB62 part 1 and HB39.

Stramit Exacta^®C&Z Purlins and Girts are not designed to be walked on. Residual oil may be present on these components from manufacturing. Do not walk on purlins or bridging.

Stramit does not recommend the welding or hot cutting of purlins, girts or bridging. The heat produced in welding will affect the material properties of the high-yield strength cold-formed steel used by Stramit in its purlins.

In many instances considerable stress concentrations are likely to arise, even with good quality welding. In addition, welding will locally remove the protective coating, leading to a potential reduction in durability.