Engineering advice needed for steel floor supports

[[1ponders]]

I want to span 3 meters with steel joist and I'm not sure what sizes to use. Basically I'll have 4/100x100x3 steel posts in each corner for a suspended 3meter x 3 meter floor.

what size bearers and joists will I need. I'm considering either 100/12 or 115/15 C Purlins or 100X50X2 RHS for bearers and 75X50X2 RHS for joists. I'd much rather use the C Purlins as they are considerably cheaper but will they support the 3 meter span.

What about if I were to place a third bearer across the middle with a post at each end? (It would also help take some of the "flex" out of the floor) It's a fine line between paying for extra posts and bearer to going slightly larger and thicker with the joists.

[Terry B]

Know idea:shrug:
Maybe ask here
http://www.woodworkforums.ubeaut.com.au/index.php

[[1ponders]]

do they do steel stuff Terry?;)

I'm trying to avoid timber as much as possible. We've noticed a few little white crawly buggers around the place lately, 'specially when there is a bit of celulose lying on the ground :scared:

[sheeny]

Sorry, Paul, I can't answer you right now... all my safe load tables, etc are at work:rolleyes:.

A bit more info is required also...

I assume this is for an obs (what else????:shrug::D)...

Is your pier independent of the floor? (So we don't need to account for the weight of the scope, etc Silly question, I know!;)).

How much is the weight of the obs building/shed you plan to put on it? I assume the walls are around the perimeter only?

If you know your terrain category and design wind speed, that will help, but if not I'm sure assumed figures for Oberon will be conservative!:lol::P

Hopefully someone else will jump in with a "my obs has xyz sections under it" and save me some work next week...;):P:whistle:

Al.

[Terry B]

Fair enough. There is a metalwork forum in the woodwork forum as well (go figure :shrug: )
Generally helpful people but maybe someone with more engineering skill than me is needed.

Is there a building and roof to supprt as well or just a floor?
How far above the ground will it be?
If it is a decent distance then wood is cheaper and termites are very easy to see climbing your metal posts.

[[1ponders]]

Thanks for the reply guys.

Basically there will be a 3x3 meter ply or chip board floor and then a Titan (to keep with the Astronomy theme :) )steel frame garden shed the same as this one (http://www.titangarages.com.au/Sheds2.php). So as far as weight being carried, very little.

Al, the pier will be completely independent of the floor so no weight there.

About the only other weight will be the weight of a desk and computer....oh and fridge, lounge chair, foot stool....:D

[acropolite]

http://www.litesteelbeam.com.au/documents/publications/icf/ICF_7StorageFloor5.pdf
I think this will answer your question. If not you may find more useful info at this location. http://www.bluescopesteel.com.au/go/product/lysaght-zed-and-cee-purlins-and-girts . If that doesn't work google "c section joist span tables"

[[1ponders]]

Thanks Phil. I'll have a look and see how I go.

[Shawn]

Did you see the way I did mine, spans 4.5 meters, deliberately springy to minimise vibration transfer through to the pier, a matrix of C section Purlin...
Theres some pics here in the archives Im sure...;)

Shawn

[Shawn]

Stressed diaphragm type...need not be heavy...

[snowyskiesau]

Have a look at the Onesteel site, there should be details of the products and pointers to relevant building standards.

http://www.onesteel.com (http://www.onesteerl.com.au/)

[[1ponders]]

Thanks Geoff, unfortunately the link isn't working.

[sheeny]

Try dropping the "r" out, Paul.

Al.

[[1ponders]]

I did a guggle search and found it. Dropping out the r didn't work. Turns out its www.onesteel.com not .au

There are a couple of handy tables there that my nonengineeringtechnicaljargonbrain can understand :P

[snowyskiesau]

Sorry about that - I'll proof read my next post ...

I did have a look over the woodwork forum mentioned earlier (my second favourite site)
but there was not a lot of information on steel deck construction.

[Lee]

Paul - overengineer the bad-boy.... much more fun! :D

[[1ponders]]

:lol: true Lee, but much more expensive. Thanks go to Al. He ran some figures through his machine at work and emailed me a list of options. I now know how much I'm under engineering it when I buy the steel I can afford and not the steel I need.:lol:

Actually Al it should be sweet. I just won't be getting that paramount ME and 12.5" RC as quickly as I'd like ;)

[sheeny]

Cool! Glad to help! Is it going to be that expensive , Paul?;):P Actually, you are saving money since you won't have the termite problem:D:D:D!!!!:whistle:

BTW the "machine" at work was just a couple of books of safe load tables and design capacity tables - cellulose rather than silicon technology:P.

Al.

[sheeny]

Paul,

I had a thought the other night... if you bring the piers in to a lesser span, you will reduce the bending moments in the joists and bearers. I dismissed this initially because the cost of steel is based on the weight and the saving by going down a size isn't going to be a lot. But if you are scratching for money, it might be worth another run through the calcs with say 2.4m span and 300mm cantilever (over hang) all round? Maybe even a 450mm cantilever?

If you've already bought your steel it still might be worth doing this just to make your structure a bit stiffer and stronger... just a thought.;)

Al.

[Bassnut]

Sheesh Paul, I dont thing you have to worry about the math that hard. I just eyeballed it, a bit of good 'ol ozzie common sense and rip into it.

This shed is 3600 by 2400mm and solid as.

http://fredsastro.googlepages.com/observatory

The floor frame was made with 2 by 4s, (treated pine) and tougn and groove for the floor.

[[1ponders]]

I had a look at yours Fred and being an ex-builder (of sorts :P ) I was surprised at the spans and joist sizes you were using. I considered timber to start with, but unfortunately over the past few weeks I found a "few" of the little white timber munching buggers around the place when I pick up any pieces of timber that have been lying for a while. So I decided to go for steel. That way only the floor itself will be timber and it is treated so I should be sweet.

Al, I thought of the cantilever myself and while it may be possible on one side it wont be on the other side (internal staircase ;) ). I'll have to take my plans to work and scan them (A3) so I can post what I'm doing.

[[1ponders]]

Just checked yours again Fred. I didn't see the middle supports for the bearers along the long side the first time. Do you find you get much movement with such small support piers?

[Bassnut]

Paul, I did worry about them to start, but they were sooo convienient. Its all been OK for a year or so now, been through a couple of storms, seems OK. I dont feel any movement as such stomping on the floor, solid as. It dose look a bit dodgy I guess though. I dont think the timber munching buggers can reach the timber due to the steel piers, can they?.

[Lee]

They certainly can - keep an eye out for little mud tracks up the piers.....

[[1ponders]]

Definately!!! One of the advantages of using steel posts. :thumbsup: