RSJ - which one

[Matt the sign]

Hi,

I'm building an extension on my existing shed and the design i've come up with will require the roof rafters on one side to rest on an RSJ that is supported at each end.

I thought I'd use 8" x 8" timber posts at either end to support the RSJ (which will be 6m long).

My question is how do I work out what size RSJ to use?

The roof will be a mixture of 18mm ply sheets with felt tiles and polycarb type panel as used on conservatories

Hope this makes sense

 

[gordon stephenson]

from past experience I would say an RSJ 8" deep would do the job of supporting your roof timbers etc. not taking into account any extra load you might want to hang on the beam also. I have 2 6"x5" heavy duty rsj's(thicker webs) spanning the width of my garage that I do use as lifting beams and they are 18' long

 

[Matt the sign]

Cheers Gordon, how much weight can you lift on your set up ?

 

[Matt the sign]

http://cgi.ebay.co.uk/RSJ-Steel-Bea...emQQptZLH_DefaultDomain_3?hash=item33536a74c6

I assume this would be plenty big enough then ?

 

[gordon stephenson]

Hello Matt,
Don't know any figures but I'v hoisted the front end of my 4.2Ltr Land-Cruiser up to place big choc's underneath prior to working on the bottom side, If you hang on a little while I'm sure you will ge a few, more technical answers.( I have read on one American forum that the "rule of thumb" that some use is 1" of depth for each foot of span, this seams to me as a Gross over estimation I.E A 20" deep beam in your case.

 

[Matt the sign]

Thanks Gordon,

I'll see what else is said.

As its at the bottom of my garden I can't get a vehicle anywhere near so I wont be tempted to lift that kind of weight (I've got an 80 series too)

I think you're right though, 6" should be fine, we'll see who agrees

 

[KTMMICK]

Do you have a friend who is an architect? They would be able to calculate it for you, it is important you get the right one.........not sure wooden posts either end is the way forward. But as someone mentioned wait and someone will no doubt have the answer you are looking for.

 

[Paul.]

If you give me an idea of the imposed loading, allow a bit for wind and snow weight, I'll do a calc for you, steel on wooden columns though not something I would do

 

[Welderpaul]

Go for steel columns (Universal Columns) rather than timber. The work to fabricate a 'shoe' to adequatley transfer the load into the timber would be more work than sticking two plates on either end of the columns.

 

[Matt the sign]

If you give me an idea of the imposed loading, allow a bit for wind and snow weight, I'll do a calc for you, steel on wooden columns though not something I would do

Thanks Paul, although I dont know how to calculate the imposed loading (infact I dont really know what that means ) The roof will be 6m wide, 6m deep and 2m high at the centre, so roughly i'll use 18 sheets of 8' x 4' x 18mm ply, and if I put rafters every metre then I'll use 120 odd metres of 4" x 2" ..... They'll be a back wall and a left hand wall, the right hand side is to be supported by the rsj and the front will be a set of doors. I'm happy to use steel uprights although I would be pleased to be shown (with a link perhaps) what it is im after.

Thanks for your help Paul and Paul and everyone else

 

[Hitch]

Putting the beam ontop of 2 box section posts is a very common method. Something like that, 100x100x5,possibly 120x120, base plate 300x300x12mm plate.

Steel box is probably cheaper than 8x8 timber anyway

 

[Matt the sign]

http://www.parkersteel.co.uk/macros...ID=280ZX3H3JZH&Status=guest&Product_No=213144

Is this the stuff Hitch ? £176.00 + VAT for a 7.5 m length .... are you sure I cant use 8" x 8" timber !

 

[Hitch]

Probably the 100x100. bit cheaper, seems fairly steep though...

Give someone some numbers, theyll tell you what you need, instead of guesswork.

 

[Welderpaul]

Imposed loading is just a posh way of saying the amount of load you are going to put on the beam.

The loading consists of a few things - dead weight: (Weight of the structure on top of it), live loads: snow, wind, you when your on the roof etc.

 

[Matt the sign]

Thanks Hitch but I dont have any numbers

I'm not in a rush to do this, If know one knows then i'll over engineer it and keep a look out for bargains on Ebay

 

[Matt the sign]

Imposed loading is just a posh way of saying the amount of load you are going to put on the beam.

The loading consists of a few things - dead weight: (Weight of the structure on top of it), live loads: snow, wind, you when your on the roof etc.

Thanks Paul, given the stuff i've mentioned before is it possible to estimate the load ?

 

[brightspark]

Imposed loading is just a posh way of saying the amount of load you are going to put on the beam.

The loading consists of a few things - dead weight: (Weight of the structure on top of it), live loads: snow, wind, you when your on the roof etc.

theres allso fixed load and moveable load to consider fixed is for walls. and moveable is floors which can store things on top

 

[Matt the sign]

theres allso fixed load and moveable load to consider fixed is for walls. and moveable is floors which can store things on top

Alright, alright, enough already

Tell me what I need to know !

 

[snowcat]

Alright, alright, enough already

Tell me what I need to know !

Lucky no ones mentioned Finite Analysis yet...

seriously work on the max load then put a safety factor of x1.6>2.0 standard engineering practice to make allowances for the for mentioned loads.

 

[morph]

203x133x30 job done