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Purlin Design Software (Australia + New Zealand)

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tally25

Structural
Sep 11, 2017
9
Hi guys,

I'd thought I'd do a little survey here to see how others in the industry go about their purlin/girt design. Over the years I've seen many different 'approaches' to purlin design when reviewing other peoples comps. In general, I tend to think designers don't put much energy into designing these elements, which are quite important (especially when used for lateral support of precast/tilt-up panels). I myself am guilty of questioning my approach to the design of purlins in the past, especially when AS1170.2 was updated a few years ago.

Personally I have traditionally performed purlin/girt design using hand calcs, but then eventually I made a spreadsheet that would (mostly) take care of the wind local pressure calcs for you - which to me is the tedious bit if you want to do it properly. The spreadsheet would ultimately require the user to input the capacity read from the manufacturers span tables, and would have certain limitations in terms of different span arrangements, point loads and axial loads etc. As is always the case in the engineering world, there is a level of engineering judgement and rationalization that must be exercised when using the spreadsheet outside of these limitations.

I've had a look for purlin design software packages available in Australia and found a few packages; COLDSTEEL (University of Sydney), SUPAPURLIN (Lysaght/Univeristy of Sydney) and EX-FACTA (Stramit).

I'm interested to learn how my fellow engineers out in the industry go about their routine purlin/girt design. Specifically,
[ol 1]
[li]How do you currently design your purlins? Hand-calcs, spreadsheet, design software package, other?[/li]
[li]Is this your preferred approach, or are you looking for a better solution?[/li]
[li]If you use a design program, which one do you use and why?[/li]
[li]What are your thoughts on the package you use i.e. what are the pros/cons?[/li]
[li]What features would your ideal purlin software design package have?[/li]
[li]Do you think there would be sufficient value added to the business to warrant paying for a software package over your current purlin design approach, provided it met all your purlin design needs? [/li]
[/ol]

Cheers
 
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I'll start off with my thoughts.
[ol 1]
[li]At the moment, a spreadsheet. I may supplement that with additional checks using Stramit EX-FACTA for difficult span/load arrangements[/li]
[li]Ideally I'd prefer a decent purlin design software package. I find that my spreadsheet is not flexible enough.[/li]
[li]I use EX-FACTA because its free and EXACTA purlins are a commonly used product on the jobs I work on. Haven't used any others however I understand that SUPAPURLIN is limited to Lysaght SUPAPURLIN sections only and is not free. I also understand COLDSTEEL is expensive.[/li]
[li]EX-FACTA
Pros: handles any span arrangement, can input axial loads, can model any load arrangement, design results show an envelope of action vs capacity which is handy, its free!
Cons: Limited to Stramit sections only, clunky UI, output reports are terrible to the point of illegible, manual input of loads (you still have to calculate your own wind loads etc), limit on how many load cases you can design, you have to create a new model for every purlin you want to design rather than have them all in a single 'project file'[/li]
[li]Ideally I'd like the package to have: Automated local pressures, clear report output, clean UI, all purlins in one 'project' file, easily model different spans, no limitations on number of load cases etc, a program that investigates all local pressure configurations on a per-load-case basis rather than a rationalized enveloped approach to get the most economical design possible, handle custom sections (e.g. historical sections), section libraries for all major manufacturers as standard, handles UDL, variable distributed loads, concentrated load, axial load, direct moment input[/li]
[li]If the business performs purlin design on a regular basis, and it offers more than the currently available packages then yes. The package would have to handle purlin sections from any manufacturer though as an absolute must. Support for custom section libraries would be a real selling point as well.[/li]
[/ol]
 
For anything non standard we have a licence to PURLIN by University of Sydney.

I used to work for a company that helped produce manufacturers tables for one of the local NZ suppliers. Generally if you're within the limitations of the suppliers tables, I'd recommend that you just use the tables (they cover the design adequately). But you can sometimes get a more efficient design using the right software because the tables usually have some limitations like differences in span lengths being the critical documented case. Usually there was zero fat in the tables as they try to beat out the competitors. Also with point loads there is no cheating by using manufacturers tables, concentrated loads simply are not covered in NZ at least, and with cold formed section design the combined shear and bending is usually critical.

Difficulties like the effective moment of inertia being dependant on the loading do make it hard to setup spreadsheets correctly. Even PURLIN just takes some average stiffmess as far as I remember rather than calculating effective stiffnesses strictly in accordance with the code.

For checking non-standard configurations the software is very handy, but the cost can be prohibitive unless you're making a lot of use of it. If you're doing stuff that's almost always within the scope of the suppliers tables, then you're likely wasting effort in doing the design in specialist software.
 
I have always used the tables, and where there is a gray area, I just tend to the conservative side. The tables were originally prepared using a combination of calculation and full scale testing, so I trust them. As to axial compression loading, I try to steer clear of using purlins for that.
 
Thanks for your feedback Agent666 and hokie66.

Full disclosure - I am currently developing a purlin design program (Windows based) for in-house use at this stage, but I am interested to learn if this would be a product the wider industry is interested in using as well.

Would a purlin design software package with the following key features be something you would consider adding to your set of design tools for your everyday engineering work?
[ol 1]
[li]Intuitive and easy to use UI similar to common existing structural software such as Space Gass/Microstran, Structural Toolkit etc.[/li]
[li]Support for any load arrangement, with helper tools for the easy generation of local pressure wind load arrangements[/li]
[li]Section libraries provided as standard with most manufacturers purlin products to choose from (Australia and New Zealand)[/li]
[li]Ability to create and analysis custom purlin sections and libraries (e.g. historical sections)[/li]
[li]Clean report output (to PDF or printer) with options to choose what goes on the report[/li]
[li]All purlins in one project file, instead of separate files[/li]
[/ol]

Your thoughts on this would be very helpful and much appreciated.
 
There a lot of people entering this space, here is a company that is slowly joining the group.

Recommend you take a good look around before jumping in if your wanting a return on investment.
 
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