Steel Beam into Cavity Wall without pillar?

[GeorgeWBush]

Thanks Deanomy, that gives me some confidence in the design.

Several people have mentioned 2 beams and bolting together as opposed to one big one. I'll get my builders view tomorrow...

With regards to lateral stability the engineer mentioned the use of wind posts and I believe she will be including these in her final drawings (yet to be drawn).

 

[deanomy]

Two beams might need to be say 300 to 400mm deep, the 254UC might be better if headroom is critical, though don't take my word, I might just be a muppet, the builder would probably want to use a polystyrene beam (I'm joking) as it would be easier to lift. Builders don't like structural engineers as they believe most se's overdesign everything, but se's have to work to conservative design standards otherwise Building Control wont accept there calc's, structural engineers are timid folk!

 

[GeorgeWBush]

"...the 254UC might be better if headroom is critical..."

We did ask for the beam to be hidden within the ceiling so this all makes sense!

"...builder would probably want to use a polystyrene beam (I'm joking) as it would be easier to lift. Builders don't like structural engineers as they believe most se's overdesign everything..."

I'll bear this in mind when talking it over with him.

Thanks for the posts

 

[GeorgeWBush]

Had some more detail from the engineer on fixings and wind post:
View media item 31626
The wind post locations will be at the joint of the existing house (solid walls) and the new cavity walls leaving an 8m run of wall with no pillars/piers. 4m of this wall will be 2 storey, the rest single.

 

[RonnyRaygun]

Had some more detail from the engineer on fixings and wind post:
View media item 31626

I haven't seen the calcs so can't be sure of the thinking of your SE, but I still can't see where the lateral stability comes from in this design...does the SHS and the UC form a moment connection thus giving lateral stability? Very small bolts and thin plate if that's the case...

Oh, and there's no such thing as a FPFW (Full Penetration Fillet Weld).

 

[GeorgeWBush]

Oh, and there's no such thing as a FPFW (Full Penetration Fillet Weld).

What did she mean by this, or rather, what should the weld type be?

 

[RonnyRaygun]

Simply a Fillet Weld as far as I can tell. Any weld between two surfaces at 90 degrees to each other is a fillet weld.

You can have Full Penetration Butt Welds (FPBW), and similarly Deep Penetration Fillet Welds (DPFW), but you aren't going to use either on a connection such as the one shown.

 

[GeorgeWBush]

Apologies for the drip feeding of information, I'm posting as i get it...

Engineer has in fact specified a second set of wind posts, the second set being a pair of Ancon WP3 posts:
http://www.ancon.co.uk/products/windposts/channel-and-angle-section-posts
http://www.ancon.co.uk/downloads/s1/l1/windposts_brochure.pdf
View media item 31662
Does this design make more sense now?

Engineers calculations are available here (click the download link to open PDF, takes a while to open up):
http://www.mediafire.com/file/zo7zkb7plub0n91/se_calcs2.pdf

 

[geraint]

100x100x8 post....

slightly overkill i think...

but there again...

what do i know...

 

[RonnyRaygun]

Now I'm not a Chartered Engineer and I'm sure the person who did your calcs is...
But as far as I can see those windposts are not going to give any lateral stability to the building...they'll prevent the wall panel from blowing in, but not from falling over...

Maybe I'm missing something, or maybe your engineer simply isn't concerned about the lateral stability of your house...

I'f anyone else can shed some light on this please enlighten me!

 

[GeorgeWBush]

Now I'm worried...
Does this design make sense to anyone?

 

[deanomy]

Lateral stablilty might be OK if the wall between living room & kitchen and wall between kitchen and reception room act as butressing (shear) walls.

Structural masonry designers manual gives an example of how to calculate the overall stablility of a masonry structure, it assumes that the floor and roof act as diaphragms transferring the lateral load around the structure to shear walls.

Not really a big fan of putting posts in domestic properties, would only do so if absolutely had to, if masonry could not be justified to take lateral (wind) loads.

If the masonry panels need reinforcing (only if calc's say so), I would rather use bed joint reinforcement than windposts as it is generally cheaper - see BRC website.

I think possibly more details/calc's might be required to justify the overall stability, Building Controls checking Engineer should (hopefully) pick up on any potential problems.

 

[GeorgeWBush]

Lateral stablilty might be OK if the wall between living room & kitchen and wall between kitchen and reception room act as butressing (shear) walls.

Plan is to make the wall between living room and kitchen a stud wall. Would you advise making this a solid wall on foundations to act as a butress?

Wall between kitchen and reception is a masonry wall and so may be acting as a butress.

 

[jeds]

George, The problem is that you are altering the basic structural form of the rear of the house. As it currently stands the rear wall buttresses the side walls and keeps them stable. When you remove the rear wall you remove that stability. Imagine a house of cards built from squares instead of triangles. If you could get it to stand up at all it wouldn't take much of a breath to topple the whole thing over. In the majority of knock-through's some wall is left in place, so this isn't a problem. But when you remove the whole back wall you are left with only the thickness of the side walls which isn't a great deal.

Now, it's possible that there is restraint from elsewhere - like the diapragm floors etc. that have already been mentioned. But if not then some restraint needs to be introduced. This won't come from the wind posts in your drawing because the connections between the posts and beam are really just pin joints which offer no resistance at all to over toppling. As previously mentioned a common method is to produce a goalpost type frame with fixed connections at the supports. But as I said, this may or may not be necessary depending on your particular suituation. My advice is to ask your engineer to explain the lateral restraint and where it's coming from. I'm sure she will have taken it into account.

 

[GeorgeWBush]

Jeds - thank you very much for your post. I'll take this up with the engineer.

So what do the windposts do then?