How big can I have my rsj?

[Robertspaw]

Hi
I am planning a side return extension to my Victorian terrace house. The side wall is 7m long so we'll need a rsj this long to open up the whole side of the house. Our structural engineer hasn't done the detailed calculations yet but says it would probably need to be approximately 450mm deep and 500kg total weight. He's queried whether the project is possible on this basis as he says it's too heavy for builders to lift. Does anyone have any experience of dealing with similar projects and how you did it there? Or any suggestions of how you can get round this?
Many thanks
Peter

 

[John D v2.0]

Given enough cranes and hosts, ie money, it would be possible, but the downstand would be quite big also on a 18 inch beam. Have you considered demolishing what's above and rebuilding the whole thing? Might still be prohibitive, but worth a thought.

 

[^woody^]

Or any suggestions of how you can get round this?

Use a different engineer. One that has a clue.

 

[endecotp]

When he says "not possible", is he really saying "not possible with your budget"?

 

[tony1851]

A 450 deep beam on that span is ridiculous and - as above - your SE is either trying to put you off or is clueless.
One of the 203 x 203 beams would almost certainly do.
If a beam is too long or too heavy, it can be supplied in two (or even three) lengths, with pre-drilled holes and plates for bolting together insitu.
Change your SE.

 

[Doggit]

Whilst it might ruin the aesthetics of the room, but a central pier would overcome a lot of problems, and it could be in steel to reduce it's size to a minimum.

I suspect a pair of 305x102 might do the job, and at 250Kg each, would be easier to lift/jack into place. Can your SE think outside the box, or is he very fixed in his thinking.

 

[John D v2.0]

Oh yes that's a good point, our SE for the knock through specified two PFC bolted together back to back to make it safer to install. He also specified a central column to split the span as one option.
The SE should do a bit more than calculations, he should input into the design and hopefully save you more than he costs!
Although ours saved us cost by waiting until the builders stated and then telling them they had to dig a new hole 1m deep for the Brick pier. Originally they said use the existing.

 

[tony1851]

Whilst it might ruin the aesthetics of the room, but a central pier would overcome a lot of problems, and it could be in steel to reduce it's size to a minimum.

I suspect a pair of 305x102 might do the job, and at 250Kg each, would be easier to lift/jack into place. Can your SE think outside the box, or is he very fixed in his thinking.

I always think that putting a central pier in the room is a failure aesthetically. In OP's case, agree it would result in shallower beams, but only down to 152mm, which is only 50mm less than a 203mm. Also, the central pier will add a lot to the cost if it is in steel, and would look clunky if done in brickwork.
OP's SE can't even think inside the box, let alone outside.

 

[Doggit]

I suspect you skip read the OP Tony, his SE is suggesting a 450mm beam, so using a central post would then save on the depth from that point. If he can get away a 152mm, then he'd be saving 300mm on the size of the beam.

 

[Robertspaw]

Thanks for your messages. I haven't had the structural engineers full report yet - this is just what he said was likely to be required. I really don't want a central pillar but I guess I just want to know what's a feisible way round his original concerns and how can I push the structural engineer to give the right solution? Should I be asking him to look at 2 beams side by side or is splicing the beams the best option? Any other thoughts would be very welcome. Thanks!

 

[John D v2.0]

I think the number one thing is interview a few se's and find out their approach. If it's just bash out a calculation for whatever you ask, then they'll be cheap but you'll spend more and have a naff result.
If they mutter something about proposing a few options for the general arrangement and working with the architect on the design, then you're home and dry.
They're like accountants, they save more than they cost if they're good.
Just a tip I got from our SE - generally the deflection is the limiting factor on beams, not the strength. And the deflection is controlled by adjusting the depth in proportion with the span.

 

[tony1851]

I suspect you skip read the OP Tony, his SE is suggesting a 450mm beam, so using a central post would then save on the depth from that point. If he can get away a 152mm, then he'd be saving 300mm on the size of the beam.

I didn't skip read it - I was referring to my previous suggestion of having a 203 deep beam; the idea of a 450 deep beam is just too ridiculous to take seriously.

 

[tony1851]

I think the number one thing is interview a few se's and find out their approach. If it's just bash out a calculation for whatever you ask, then they'll be cheap but you'll spend more and have a naff result.
If they mutter something about proposing a few options for the general arrangement and working with the architect on the design, then you're home and dry.
They're like accountants, they save more than they cost if they're good.
Just a tip I got from our SE - generally the deflection is the limiting factor on beams, not the strength. And the deflection is controlled by adjusting the depth in proportion with the span.

Yes, deflection is one of the main concerns with steel beams, but also lateral buckling, particularly when using long, narrow-flange beams that are not adequately restrained along their length.