Simple pinned connection or moment resisting?

[Vennegoor]

Hi everyone, sorry for the second post in one day.

I am currently looking to install an RSJ and steel column in my house in place of a load bearing wall.

My question is in regards to how structural engineers normally model the connections.

See diagram below:

Screenshot 2021-03-25 At 14.42.00

• Vennegoor
• 25 Mar 2021

I have assumed that the connection between the column and beam can be treated as a pinned connection and therefore there is only a negligible transfer of moment from the beam to the column. That way the base connection of the column only needs to resist the small moment developed due to lateral loading at the top of the column (essentially modelling it as a cantilever with an axial force [from the beam] and a small horizontal load).

Is this assumption reasonable? I only ask because I've seen lots of people embedding their columns in relatively large foundations which suggests to me they're trying to resist larger moments. I understand that with a goal post setup that it's essentially a portal frame and moments must be transferred to the foundations, but I don't see the requirement to transfer the loads like this if a pinned connection is assumed?

Any advice or structural analysis re-education would be appreciated.

 

[tony1851]

It would normally be a pinned joint - the 4 x 16mm 8.8 bolts would be fine.

What would be of more concern is building a cavity wall off a 100mm slab?

 

[Vennegoor]

It would normally be a pinned joint - the 4 x 16mm 8.8 bolts would be fine.

Thanks Tony, and so modelling the column as a cantilever with only an applied horizontal and vertical force a the top would be fine - without modelling for any significant applied moment at the top? If this is the case them I expect the 400x400x10 base plate on the slab should do the trick as the moments and shear are minimal (thus I don't expect the slab depth and lack of structural rebar should be a problem).

What would be of more concern is building a cavity wall off a 100mm slab?

Regarding this, yes, sorry. The floor slab is between 100-150mm deep but I expect that the cavity wall is sat on a deeper strip foundation although I haven't checked yet. The house was constructed in the 1950s so I expect the cavity wall will be sat on a strip foundation.

 

[^woody^]

... or punching shear from the column

 

[Vennegoor]

Punching shear from the column is fine.

 

[tony1851]

Having seen the view of the house on the other thread, do you really need such big sections?? For domestics, some of the smaller UBs are usually fine for those spans, and surely the column could be something like a 100 x100 box section?

 

[Vennegoor]

Having seen the view of the house on the other thread, do you really need such big sections?? For domestics, some of the smaller UBs are usually fine for those spans, and surely the column could be something like a 100 x100 box section?

I tried a 152x152x30 UC as the beam initially and whilst ULS was fine, deflection under serviceability was greater than 1/360 of the span with a utilisation of about 1.6. I suppose a UB could be a better option so that it can be deeper and narrower, I'll check later.

I then just selected the same section size for the column for ease but will look at a 152 column or perhaps even a 100x100 SHS as you say.

Thanks again!

 

[tony1851]

What loads (live and dead) is the beam carrying?

 

[Vennegoor]

What loads (live and dead) is the beam carrying?

Hi Tony,

I'm working off these loads below.

Screenshot 2021-03-25 At 22.22.26

• Vennegoor
• 25 Mar 2021

From these I've listed the breakdown of permanent and imposed loads (Eurocode, I'm showing my youth!). You'll notice that whilst there are no walls directly above the beam (B3) that I'll install, it is still picking up loads from wall 1 and wall 2 from the floor above (the joists run from top to bottom). See below:

Screenshot 2021-03-25 At 22.22.41

• Vennegoor
• 25 Mar 2021

I've modelled wall 1 as a UDL along a part of the length of the beam, and wall 2 as a point load. See below:

Screenshot 2021-03-25 At 22.27.56

• Vennegoor
• 25 Mar 2021

Max BM is 34kN and SF is about 38kN. I may have been a bit conservative with these figures but I'd rather be safe than sorry.

Screenshot 2021-03-25 At 22.31.57

• Vennegoor
• 25 Mar 2021

Thanks again

 

[tony1851]

We really need to see a first floor plan, with walls and joists spans, and general pic showing the roof.

 

[jeds]

Go with Tony's advice. That section is way too big, and the column way, way too big.