DHS
PURLINS

Steel Grade
 
  • G500
    G450
Yield Strength fy(MPa)
  • <1.5mm - 500
    >1.5mm - 450
Min. Zinc Weight (g/m2)
  • Z 275
Components
  • Fastbrace
    Bolted Brace Channel
DIMST DHS Purlin 1 Intro
Overview

Overview

The Dimond Structural DHS purlin range is available in 12 sizes from DHS 150/12 to DHS 400/20 to suit commercial applications from 5m to 18m spans. Speed of installation is assured as DHS purlins and girts are supplied complete with brace channels ready for site assembly.

Material Specification

Material Specification

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

Thickness
(BMT) (mm)
Steel Grade
Yield Strength
fy(MPa)
Zinc Weight
Z (g/m2)
DHS Purlins and Girts
Thickness
(BMT) (mm)
< 1.5
Steel Grade
G500
Yield Strength
fy(MPa)
500
Zinc Weight
Z (g/m2)
275
DHS Purlins and Girts
Thickness
(BMT) (mm)
> 1.5
Steel Grade
G450
Yield Strength
fy(MPa)
450
Zinc Weight
Z (g/m2)
275
Bracing channel
Thickness
(BMT) (mm)
1.15
Steel Grade
G250
Yield Strength
fy(MPa)
250
Zinc Weight
Z (g/m2)
450
End cleats
Thickness
(BMT) (mm)
2.00
Steel Grade
G250
Yield Strength
fy(MPa)
250
Zinc Weight
Z (g/m2)
450

BMT - Base Metal Thickness
Z450 zinc weight coil can be supplied with order lead times of up 12 weeks. Contact Dimond Structural on 0800 DIMOND (0800 346 663)

Tolerances

Length:

  • DHS Purlins ± 6mm
  • Bracing System ± 2mm

Depth/Width:

  • DHS Purlins ± 2mm
  • Bracing System ± 1mm

Holes Centres: ± 1.5mm

Web/Flange Angle: 89-93 degrees

Components

Components

Fastbrace

Fastbrace is a lock-in bracing system which runs in continuous lines between all purlins/girts and uses cleats with specially shaped lock-in tabs attached to each end of 89mm x 1.15mm (89/12) brace channel, suitable for use with DHS purlins from DHS 150/12 up to DHS 300/18. Fastbrace is fitted each side of the DHS purlin through pre-punched 18mm diameter round bracing holes, locking together to lower erection time. When a line of Fastbrace has been installed, the system provides resistance to restrict lateral movement of the DHS purlin system.

The end brace at the first and last bracing position is secured using the standard bolted connection on the outermost cleat end.

To ensure straight alignment of the bracing system, the bracing holes can be offset from the bracing line by 25mm over the last purlin spacing to accommodate the bolted cleat. If not, an angle of approximately two degrees from a straight alignment on the end braces is created.

Cranked Sag Rods are used in the lower bolt position to tie the bracing lines each side of the rafter together at the ridge (or at a step in the roof).

Where back to back DHS purlins are used, bolted end brace components are required each side, where the bolts can accommodate the extra purlin thickness.

For use, handling and maintenance guidelines, refer Environments 2.1.3, Handling And Storage 2.5.2 and Maintenance 2.1.6 of Purlin Design manual.

Fastbrace Components

Standard Brace

This is the standard Fastbrace component used almost everywhere in the system. It locks into other standard brace components, adjustable brace components, or end brace components.

End Brace

End brace is used at the end of a purlin bracing line, i.e. eaves or ridge, each side of a roof step, or at top and bottom girts on a wall. The end brace locks into either standard or adjustable brace at one end and is twisted between the purlin lips and bolted into position at the other end.

Adjustable Brace

This is the adjustable component in the Fastbrace system and is used where some level of adjustment on the purlin line is required. The purlin is adjusted into line and the 12mm diameter hex flange bolts on the brace tightened. The adjustable brace offers up to 20mm of adjustment.

Adjustable End Brace

Where the end purlin spacing is less than 800mm, an adjustable end brace with a bolted end cleat is available, as twisting of the end cleat is not practical. The adjustable cleat can be rotated up to 15 degrees from normal, to accommodate the change in angle from vertical portal to the roof slope of the rafter.

Bolted Brace Channel

Bolted Brace Channel is a bolted bracing system running continuously between all purlin/girt lines, which uses cleats clinched to each end of 89mm x 1.15mm (89/12) bracing channel, fastened with bolts through the DHS purlin (two bolts each end). Bolted Brace Channel is suitable for use on all DHS Purlin sizes.

At the ridge, cranked Sag Rods are used in the lower bolt position to tie the bracing lines each side of the rafter together.

For use, handling and maintenance guidelines, refer Environments 2.1.3, Handling And Storage 2.5.2 and Maintenance 2.1.6 of Purlin Design manual.

Bolted Brace Channel Components

Bolted Channel Brace

This is the standard component used in the bolted channel bracing system and is used almost everywhere.

Adjustable Bolted Channel Brace

This is the adjustable component in the bolted channel bracing system and is used where some level of adjustment on the purlin line is required. The purlin is adjusted into line and the 12mm diameter hex flange bolts on the brace tightened. The adjustable brace offers up to 20mm of adjustment.

Brace Channel Section Properties

Tabulated properties are based on full unreduced sections.

Code
D x B
(mm)
t
(mm)
Mass
(kg/m)
Weight
(kN/m)
Area
(mm2)
l
(mm)
a
(mm)
lx
(106mm4)
ly
(106mm4)
Zx
(103mm3)
Column
J(mm4)
Column
Iw(109mm6)
DB 89/12
D x B
(mm)
89 x 34
t
(mm)
1.15
Mass
(kg/m)
1.52
Weight
(kN/m)
0.015
Area
(mm2)
186.3
l
(mm)
6
a
(mm)
9.17
lx
(106mm4)
0.223
ly
(106mm4)
0.024
Zx
(103mm3)
5.00
Column
J(mm4)
84.13
Column
Iw(109mm6)
0.040

Note: Mass assumes a total coated weight for the zinc coating of 450 g/m2

C100/19 Purlin

Dimond Structural can supply a C100/19 Cee section (100mm x 50mm x 1.85mm BMT) for economy as a small section purlin or girt. Any limitation placed on the design and use of the Dimond Structural Purlin Systems as detailed in the Purlin Design manual also apply to the C100/19 Purlin. C100/19 purlins are typically braced with Sag Rods.

Design information for the C100/19 purlin can be provided by contacting Dimond Structural on 0800 Roofspec (0800 766 377).

Portal Cleats

Portal Cleats are supplied by the fabricator or installer and welded on to the portal frame. Cleat thicknesses generally range from 6mm to 12mm thickness. The hole centres are laid out to suit hole punchings in the DHS purlin, refer CAD Details. The cleat height may need to be increased where an expansion step in the roof is detailed.

General Purpose Bracket

General Purpose Brackets are supplied by Dimond Structural and are typically used to connect trimmer purlins etc. General-purpose brackets are not load rated and are suitable for application only in non-structural elements. Holes and cleat dimensions are set-out to suit use with the DHS Purlin System only, refer CAD Details

Sag Rods

At the ridge, cranked Sag Rods are used in the lower bolt position to tie the bracing lines each side of the rafter together.

Supplied by steel erectors and fabricators in 12mm diameter engineering round bar grade 250 MPa, galvanised or electroplated finishes, with double nuts and washers each end. Where loads require, 16mm diameter engineering round bar can be used.

Note, alternating brace channel and sag rods have been superseded by the use of Fastbrace and the Bolted Brace Channel systems which run continuously between all purlin/girt lines.

Timber Battens

Where Timber Battens are to be fastened to the DHS Purlin System, Dimond Structural recommend using an ex 50mm x 50mm timber batten or a depth of batten to account for insulation and ventilation requirements, gauged two sides and treated to H3.1 timber preservation such as boric or LOSP (low organic solvent preservative). CCA treated timber should be avoided, as chemicals used in the CCA treatment (e.g. copper and chromium) could contact the galvanised purlin surface and the fasteners, causing dissimilar metal corrosion.

The batten is fixed onto the top flange of the DHS Purlins, once the netting or safety mesh has been laid on the structure. For example 50mm x 50mm battens, fixings to be 10g – 16 x 75mm. Countersunk rib head – wingtek. The coating finish is a zinc-plated AS 3566 class 2 finish. Longer, other types of fixings may need to be considered when the timber depth is greater.

The spacing of the wingteks is dependent on the DHS material thickness it is being fixed into. Refer to the following table.

DHS Purlin BMT
(mm)
Maximum Fastener Centres
(mm)
1.15
Maximum Fastener Centres
(mm)
250
1.25 to 2.0
Maximum Fastener Centres
(mm)
300

BMT - Base Metal Thickness

Design

Specific Design

Design Basis

Dimond Structural DHS Purlin Systems have been designed to comply with AS/NZS 4600:1996, based on physical testing and analysis carried out by the University of Sydney, who are recognised for their expertise in the area of cold form design. The structural analysis consisted of several modules including cross-sectional analysis, an AS/NZS 4600:1996 design module, inplane structural analysis, and finite element lateral buckling analysis.

Methods in AS/NZS 4600:1996 for determining pure shear, combined bending/shear, lateral buckling and distortional buckling have, in some cases, resulted in lower purlin capacities than previously published. These are included in the design tables in the Purlin Design manual.

Appropriate design load combinations for each Limit State should be determined in accordance with AS/NZS 1170. It is recommended these be expressed as uniformly distributed bending loads (kN/m) assumed to be acting in-plane applied about the major axis of symmetry (X-X) and uniform axial compression loads (kN) applied about the rotational axis (Z-Z) for direct comparison with the tabulated data in this manual.

Self-weight of the DHS Purlin Systems 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.

DHS Purlin System Design Considerations

Data presented in this manual is intended for use by structural engineers. Load situations other than uniformly distributed and axial loads will require specific design.

The design capacity of the DHS Purlin System is largely dependent on the amount of restraint provided to the purlin section. Data presented in DHS Purlin System Load Span Tables 2.3.4 of Purlin Design manual assumes that bracing prevents both lateral movement and rotation of the section at that point.

Design Capacities in the Limit State format have been derived by the application of a capacity factor, 𝜙:

Bending 𝜙b = 0.90

Compression 𝜙c = 0.85

A design yield strength of 500 MPa has been used for DHS purlins and girts. This is in line with the minimum specified yield for G500 material and is less than the consistent minimum yield stress in the G450 material used in manufacture.

Tables in the Purlin Design manual are intended for use where roofing or cladding is attached to one DHS purlin or girt flange, where it is assumed that the screw-fastened cladding significantly prevents lateral movement of the flange to which it is attached. Where this assumption does not hold, it is recommended that the number of braces required is specified such that the purlin load capacity, 𝜙bWbx is not less than the capacity for the Fully Restrained (FR) case.

Gravity type loads can be assumed to act perpendicular to the roof plane for roof pitches up to 10 degrees provided the DHS purlins are placed with their flanges facing up the slope. For roof pitches greater than 10 degrees, load components about the minor axis of symmetry (Y-Y) should also be considered.

Span Guide

As a guide, single spans are used most frequently, particularly where purlins/girts are set down between the rafters/columns.
Deflections may govern on larger spans.

End and internal continuous 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 DHS Purlin System used as purlins or girts, the following limits are recommended for wind load and dead load actions,

  • Where there is no ceiling:
    • Deflection for Ws ≯ Span/150
    • Deflection for G ≯ Span/300
  • Where there is a ceiling:
    • Deflection for Ws ≯ Span/200
    • Deflection for G ≯ Span/360.

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

Bracing Guidelines

For roofs, the out of plane component of the dead load of the roofing and purlins is assumed to be carried in tension by Fastbrace or Bolted Brace Channels tied across the ridge or into the ridge beam for monoslope roofs. In order to minimise lateral deflections to purlin members, we recommend a maximum spacing between bracing lines and/or support framing of 3.5 metres.

For walls, the following table gives the maximum allowable wall heights for Dimond Structural bracing systems, where the dead load of cladding and girts is assumed to be carried in tension to an eaves beam by Fastbrace or Bolted Brace Channels.

In order to minimise deflections in the girt member, we recommend a maximum spacing between bracing lines and/or support framing of 3.5 metres.

Specific design of the bracing system and connections is required for wall heights greater than the limits shown or where the bracing is designed to carry compression loads.

Maximum Wall Height
Purlin Thickness BMT
(mm)
Fast Brace
Bolted Channel Bracing
1.15, 1.25
Fast Brace
5.0m
Bolted Channel Bracing
15.0m
1.45
Fast Brace
6.5m
Bolted Channel Bracing
15.0m
1.75
Fast Brace
8.0m
Bolted Channel Bracing
15.0m
1.95
Fast Brace
-
Bolted Channel Bracing
15.0m

BMT - Base Metal Thickness
Basis to table: 1) Maximum spacing of bracing lines/portal frames 3.5m and 2) Maximum cladding weight 6.7kg/m2

Specific Design

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

  • have suspended loads present (such as ducting and piping). Hangers must be connected to the web of the purlin or to the bottom flange within 25mm of the web. Under no circumstances should loads be hung off the purlin lips.
  • are used as cantilever members.
  • are used as truss or portal members.
  • have holes present.
  • are subject to out of plane loading about the minor Y-Y axis.


For further specific design details refer to section 2.3 Specific Design - DHS Purlin System in Purlin Design manual

Load Span Tables

Load Span Tables

Download DHS Pulin Load Span Tables

Click to downloadUpdated May 2020
Durability

Purlin Systems Durability

View Dimond Purlin Systems durability statement

CAD Details

Relevant Product CAD Details

Below you will find all of the relevant product CAD technical details in .dwg, .pdf & .rvt format.


If you have any questions regarding the details below please contact one of our technical team on 0800 550 660

Download all .dwg filesLast updated March 2020
Download all .pdf filesLast updated March 2020
Purlin Design Manual
Material Specification
Section Properties
Installation