Top Notch Purlins

Overview

Dimond’s range of Top Notch purlins are compact, lightweight and easy to install. They are ready for use in many smaller spanning applications from 2m to 7m. Top Notch purlins come in a full range of sizes from 60mm to 150mm depth, easily tek screwed to the supports without the need for purlin bracing and cleats.

Material Specification

Dimond Structural Top Notch Purlins are manufactured by roll forming galvanised steel coil produced to AS 1397.

Tolerances

Length: ±6mm

Depth/Width:

• 60 Top Notch purlin: ±1mm
• 100/120 Top Notch purlin: ±2mm
• 150 Top Notch purlin: ±3mm

Top Flange Width: ±1mm

Components

Support Strap

Additional hold-down straps are required in very high wind zones and above for Top Notch purlins in a continuous internal span configuration, as specified by the design engineer.

Manufactured from 0.75mm BMT x 30mm galvanised steel strip, which is tied over the Top Notch purlin and fastened each side into the support structure as detailed below.

Specific Design

Design Basis

Dimond Structural Top Notch Purlin Systems have been designed to comply with AS/NZS 4600:1996. Appropriate design limit state load combinations should be determined in accordance with AS/NZS 1170. It is recommended these be expressed as uniformly distributed bending loads (kN/m) for direct comparison with the tabulated data in the Purlin Systems Manual.

Self-weight of the Top Notch Purlin System is not included in any load tables and must be calculated as part of the total dead load of the building elements supported by the purlin.

Top Notch Purlin Systems are typically used as purlins and girts in lightweight building applications, for example, farm buildings
and light commercial sheds.

Design Considerations

Data presented in the Purlin Systems Manual is intended for use by structural engineers. Load situations other than uniformly distributed loads will require specific design.

Design capacities in the limit state format have been derived by the application of a capacity factor, ϕ_b = 0.90 for bending.

A design yield strength as outlined in Material Specification has been used for the Top Notch Purlin System.

These tables are intended for use where roofing or cladding provides full restraint to the top flange of the Top Notch purlin or girt. Loads are assumed to be applied about the major axis of symmetry (X-X).

The fixing type and size is critical to achieve the outward design loads. Refer Connection Design in section 2.4 Specific Design - Top Notch Purlin System in Purlin Systems Manual.

The Top Notch Purlin System does not require bracing to provide restraint. Therefore the loads are represented as inward and outward cases. However bracing battens can be fastened transversely along the underside of the purlins to enhance the performance of Top Notch purlins and are recommended where supports/restraints are further than 30 times the Top Notch purlin depth apart.

Gravity type loads can be assumed to act perpendicular to the roof plane for pitches up to 10 degrees. For pitches greater than 10 degrees, load components about the minor axis of symmetry (Y-Y) should also be considered.

When designing Top Notch purlins to be used as girts, it is assumed cladding and girt gravity loads are taken by a stiff eaves member such as a DHS Purlin.

Span Guide

As a guide, single spans are used most frequently for ease of installation. Deflections may govern on larger spans.

Double span configurations may be used where lower deflections are required.

Lapped end and lapped internal configurations are more economical on large purlin spans where better strength and lower deflections are required.

Deflection Guidelines

As a guide to acceptable deflection limits for serviceability of the Top Notch Purlin System, the following limits are recommended for wind load and dead load actions where there is no ceiling:

• Deflection for W_s ≯ Span/150
• Deflection for G ≯ Span/300

For further guidance on deflection limits, refer to AS/NZS 1170.

Specific Design

Specific design to AS/NZS 4600 is required where Top Notch purlins -

• are used as cantilever members.
• have suspended loads present (such as ducting and piping). Suspended loads must be connected to both Top Notch bottom flanges or with straps tied over the Top Notch top flange.
• have holes present.
• are subject to axial loading.
• are subject to combined loading.
• are subject to out of plane loading about the minor Y-Y axis.

For further specific design details refer to section 2.4 Specific Design - Top Notch Purlin System in Purlin Systems Manual

Load Span Tables

Download Top Notch Pulin Load Span Tables

Purlin Systems Durability

View Dimond Purlin Systems durability statement