steel box section v timber

[jimbo1962]

Hi all
if I wanted to boast about the strength of a steel frame versus a timber one
how would I find out the dimensions of a timber beam or post for example, that had
the same strength as a 50x50x3mm steel hollow section, for example.
say it was a better pine like Larch
would it be 3 x 3 inch or 4 x 4 inch ?
are there comparative strength tables anywhere on line ?

 

[Munkul]

Structural timber has a standard rating, usually C16

https://www.hitchcockandking.co.uk/h-k-news/c16-or-c24-timber-for-your-construction-project/

You'd have to work it out. Depends what size timber section vs what size steel section, I beam or box, etc.

 

[atomant48]

It also depends what you mean by strength (and I am NOT trying to be clever here). When you spec wood you accept a certain amount of deflection - I was walking on some wooden bridges in a park last weekend that had a lot more than I would ever want!! - and wood can go along way before it reaches maximum “strength”. So I guess the easiest way to do a like for like comparison would be to work out the loading and deflection on your steel frame and then use that to spec the wooden if that makes sense. What kind of load are you applying?

edit. Just ran some numbers to give an idea. Putting your 50x50 box as a 3m length and standing in the middle it looks to have about 15mm deflection. To achieve the same with wood you’d be about 180x50 type size. Quite a big difference.

 

[sako243]

It also depends massively on the span you are trying to bridge. My parents rebuilt a barn a few years back and the spans they needed in a single joist were 8m. Steel over that distance became a law of diminishing returns as in order to stop it sagging you needed more steel, in order to stop that steel from sagging, well you see the problem.

Apart from sourcing straight enough trees then timber didn't have the same problem of deflecting as much under it's own weight.

 

[eLuSiVeMiTe]

It also depends massively on the span you are trying to bridge. My parents rebuilt a barn a few years back and the spans they needed in a single joist were 8m. Steel over that distance became a law of diminishing returns as in order to stop it sagging you needed more steel, in order to stop that steel from sagging, well you see the problem.

Apart from sourcing straight enough trees then timber didn't have the same problem of deflecting as much under it's own weight.

Flitch beams serve a purpose too.

Usually 10mm plate sandwiched between the two joists and bolted through.

Amazing material when you look at it's properties

 

[frank horton]

out of interest...
here wood is so expensive I compare it like for like with steel.....
and it cost about the same.....so why bother with wood for structural.....
wifey wants a roof over the Bar B Q and Pizza oven...to keep the sun off.....area 5mx5m......
would look great with post and beam, aint gonna happen....
will use cut limestone for the pillars and steel for the roof frame......
easy.....

 

[sako243]

Flitch beams serve a purpose too.

Usually 10mm plate sandwiched between the two joists and bolted through.

Amazing material when you look at it's properties

Wasn't aware of that construction method - filed away for use later perhaps...

 

[Mark 2]

Flitch beams serve a purpose too.

Usually 10mm plate sandwiched between the two joists and bolted through.

Amazing material when you look at it's properties

Ooh I like those. Similar principle to the stair stringer.

 

[mike os]

strength or stiffness?

 

[mtt.tr]

Flitch beams serve a purpose too.

Usually 10mm plate sandwiched between the two joists and bolted through.

Amazing material when you look at it's properties

Or gluelam

 

[eLuSiVeMiTe]

Ooh I like those. Similar principle to the stair stringer.

Holes have got to be a tight fit to the bolt
Usually one high then next one low. Max 600c
Used them a lot on extensions with big skylights. Takes the flex out of the timber

 

[eLuSiVeMiTe]

Or gluelam

Aye but require a lot more effort to build unless it's on display.

Used a few for ridges in the past

 

[mtt.tr]

Aye but require a lot more effort to build unless it's on display.

Used a few for ridges in the past

Just buy them fully speced joints cut lovely.