RHS Side Wall Capacity Check
RHS Side Wall Capacity Check
(OP)
Hi all,
Currently going through the design of the glazed roof system, as shown below.
In particular, I'm having a good look at the connection of the cantilevered/tapered "T" member (multi-coloured 380BT) coming into the main beam(grey 400x300x8.0 RHS).
I would like to check the capacity of the RHS side wall if I were to directly weld the "T" member. Note I've used the plastic section modulus for the RHS side wall.
My design philosophy so far: Would be great if anybody could provide some feedback on my philosophy and/or ideas about this connection.


Currently going through the design of the glazed roof system, as shown below.
In particular, I'm having a good look at the connection of the cantilevered/tapered "T" member (multi-coloured 380BT) coming into the main beam(grey 400x300x8.0 RHS).
I would like to check the capacity of the RHS side wall if I were to directly weld the "T" member. Note I've used the plastic section modulus for the RHS side wall.
My design philosophy so far: Would be great if anybody could provide some feedback on my philosophy and/or ideas about this connection.








RE: RHS Side Wall Capacity Check
Most of the compression force will be concentrated close to the tip of the WT stem because the side wall will be stiffest there. As such, you're going to get a tension force very high on the RHS side wall and a compression force very low on the RHS sidewall. That should greatly reduce the flexural demand on the RHS side wall and simultaneously increase the local demands on your welds (unless you're claiming compression bearing at the stem tip).
There are a few documents that would be relevant here:
1) AISC design guide on HSS connections by Packer.
2) The CIDECT design guies.
To my knowledge, neither document covers exactly this case. However, they both cover similar cases and a review of the documents might generate some good ideas. This is a very common scenario. I imagine that everyone has their own take on it. Hopefully we see some of that show up in this thread.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: RHS Side Wall Capacity Check
I understand where you are coming from regarding the tens/comp forces will tend towards the RHS return sidewalls.
If the sidewalls are pinned however, it also increases the flexural demand on the plate element in question...
Would a reasonable solution be to weld the T section to say a 16mm plate, which is then welded onto the side of the RHS?
Would be good to hear from anyone who has done a similar connection.
EDIT: Do you just register on the CIDECT website to download the PDF's which are "free of charge?"
RE: RHS Side Wall Capacity Check
I wouldn't do this. The CHS wall shouldn't be the limiting factor here. It should definitely be possible to make this work with a direct weld.
It's been a while but I believe so.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: RHS Side Wall Capacity Check
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: RHS Side Wall Capacity Check
All along I've assumed the bending stresses can 'follow' the flange around the cutout, as the section actually gets deeper than 400mm... How would one check this though?
RE: RHS Side Wall Capacity Check
RE: RHS Side Wall Capacity Check
That's why I'm going with a large and somewhat thick hollow section.
RE: RHS Side Wall Capacity Check
Without introducing web stiffeners, it would be very difficult. You get cross flange bending and concentrated web loads at the flange knuckles. I would try to make it work using just the web section strength at the flange knuckle locations.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: RHS Side Wall Capacity Check
Some sort of check for the transverse and longitudinal stresses in the RHS is also warranted at the connection. At the top and bottom flanges the flange forces result in a tension/compression across the RHS flange that must be combined with the normal longitudinal bending stresses.