steel sizes and weight.

Matt · Apr 10, 2024

I originally thought that rsj steel was priced per ton, but after playing on parkers steel website it it size dependant.

So anyone tell me which is the strongest.

quote 1
457 x 191 x 74kg/m columns
305x 165 x 40kg/m rafters

quote 2
406x 178 x 54kg/m columns
406x 146x 46kg/m rafters

there is approx 1tonne difference in steel for columns and rafters but on the online pricing there is next to no difference in value.

I guess there would be a higher galvanising cost on quote 1 as slightly more surface area.

David. · Apr 10, 2024

Quote 1 looks stronger to me, the fact that they have gone heavy on the legs suggests that they are not "budget". What span?
For comparison a Dale 60ft span here has 10"x 5¾" rafters and that was Industrial spec at the time, for silage bunkers.
I thought galvanising was per ton?

Matt · Apr 10, 2024

David. said:
Quote 1 looks stronger to me, the fact that they have gone heavy on the legs suggests that they are not "budget". What span?
For comparison a Dale 60ft span here has 10"x 5¾" rafters and that was Industrial spec at the time, for silage bunkers.
I thought galvanising was per ton?

65ft span.
Galv Is per ton. But belive its the weight of galv applied.

So weighed in and then weighed out.

Matt · Apr 10, 2024

David. said:
Quote 1 looks stronger to me, the fact that they have gone heavy on the legs suggests that they are not "budget". What span?
For comparison a Dale 60ft span here has 10"x 5¾" rafters and that was Industrial spec at the time, for silage bunkers.
I thought galvanising was per ton?

It slightly puzzles me as we seem to be going bigger and bigger steels. Yours is 250mm x 150mm in round numbers

15ft bays?

Like said in original post, how come 2 diff steel sizes, 1 with more weight be the same money. Must be some more expensive sizes than others

B R C · Apr 10, 2024

My grain store is 65ft span and has 457 columns for 3m grain loading and that was 20 years ago. I’m surprised that there is much difference in price per tonne, to get the best prices you have to go through one of their sales team. Galvanising is per tonne of steel after its been galvanised, they do weigh it before though as well.

HatsOff · Apr 10, 2024

Matt said:
I originally thought that rsj steel was priced per ton, but after playing on parkers steel website it it size dependant.

So anyone tell me which is the strongest.

quote 1
457 x 191 x 74kg/m columns
305x 165 x 40kg/m rafters

quote 2
406x 178 x 54kg/m columns
406x 146x 46kg/m rafters

there is approx 1tonne difference in steel for columns and rafters but on the online pricing there is next to no difference in value.

I guess there would be a higher galvanising cost on quote 1 as slightly more surface area.

If I had to choose it'd be quote 1. All things being equal, stronger columns are better. Also, rafters that are a bit squatter shouldn't suffer from twisting if there's a lot of wind uplift.

But don't you have a design or schematic you need to work to? Even for ag buildings it's shouldn't be plucking numbers.

designanddetail · Apr 11, 2024

Change your rafters on quote 1 to 406x140x39UB, then that will be the best option. A deep slim rafter is better that a shallow wide one due to the bending, both options should have rafters stays, probably in 2 locations up each rafter.

All buildings should have site specific calculations, even agri sheds, but most firms don't, even the biggest firms out there. If they were designed then you could still end up with different steel sizes from different companies/engineers.

HatsOff · Apr 11, 2024

designanddetail said:
Change your rafters on quote 1 to 406x140x39UB, then that will be the best option. A deep slim rafter is better that a shallow wide one due to the bending, both options should have rafters stays, probably in 2 locations up each rafter.

All buildings should have site specific calculations, even agri sheds, but most firms don't, even the biggest firms out there. If they were designed then you could still end up with different steel sizes from different companies/engineers.

Not sure I've ever seen a agricultural shed where they've bothered with stays!

The 305x165x40 option will maintain stability and bending resistance (which is lost due to LTB in uplift conditions) better than a 406x140x39.

goldeneagle · Apr 11, 2024

The steel sizes will in some cases will be what the manufacturers engineer is comfortable with as it is their licence to practise at risk if it fails where a certificate is required.

You can use different weights and sections of steel to achieve the same end goal with varying factors of safety. A quote for a column size doesn't show the additional detail that can be added to steel to add restraint and maintain its serviceability in different loading conditions. However adding detail costs labour and materials so sometimes more efficient to use heavier/larger steel section to accomplish.

If you know what you want size wise not overly expensive to get a structural engineer to spec a shed for yourself and then get quotes from your chosen vendors

HatsOff · Apr 11, 2024

goldeneagle said:
adding detail costs labour and materials so sometimes more efficient to use heavier/larger steel section to accomplish

This is absolutely right and it's almost impossible for the designer to know what will work out cheaper for the fabricator. They might have a newly qualified welder they're quite happy to task welding stiffeners or they've got the MD working on shop floor due to short staffing and they'd rather just go up a steel weight or two to save time.

(My background is a engineer and I've done a lot of industrial shed designs over the years. Basically you can't win and just have to go with what you know is safe and reasonably efficient for both fabrication and weight.)

mx110 · Apr 11, 2024

last shed I put up here 2018? I had 3 quotes all used different sizes of steel, wasnt much between them all and I went with the most local guy and the middle price. I actually gave him a copy of the other quotes after and he said that's interesting one of the firms actually used the same structural engineer as himself yet they quoted on different size steel.

steel sizes and weight.

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