RC frame - large beam on small columns?

[greznik91]

Im dealing with a RC frame building. There is a RC slab above - 200 mm thick.

RC slab:

Columns supports are pinned.
All connections between column - beam are modeled as a moment connection.
That mean that bending moment is transfered from end of the beam to a column.
Based on spans I think my yellow columns are pretty small in cross section dimensions (300/1000 mm)
I have made some calculations and its barely OK but my gut feeling is not good at all.

Your opinion?

Also - since columns/walls are pretty close together, I think the best way to go is to make continuous footings instead of spread footings connected with foundation beams.

 

[dik]

Your column seems to be robust enough... is it marginal because you are transferring a high moment? Can you use a transfer moment equal to DL + maybe 30% of LL? Done lots of parkades where I've used a LL = 15psf for alternating loading and moment transfers at columns.

Dik

 

[KootK]

I'd be inclined to design the beam as though it were pinned at each end. Moment transfer into the narrow columns might be questionable.

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.

 

[WARose]

It all starts with a good estimate on the cracked stiffness of the members in question. But even that can vary so I usually take a couple of passes based on the range(s) of possible stiffness. Checking the joint wouldn't hurt either.

 

[BAretired]

The beam is 600x500 and the columns are 300x1000. Increase the beam width to 1000 to match the column. Design the beam as per KootK's recommendation, i.e. wL[sup]2[/sup]/8 at midspan, but supply top steel for wL[sup]2[/sup]/24 each end.

BA

 

[Tommy385]

Do you need RC-frames for horizontal loads? Since there is a stair opening im guessing that its not 1-floor structure.
That beam with 9 m span and 50 cm height doesn't look convincing...

(Are you working with Eurocodes? your software looks like Radimpex)

 

[greznik91]

thanks for help

Yes, I need RC frame for horiz. loads (earthquake).
The beam is 60/60 cm.

Yes im working with Eurocodes and software Tower.

 

[Tommy385]

If you are taking horizontal loads you are not allowed to redistribute bending moments.(EC2 5.5 (6))

I would:
- assume all connections with beams/columns/walls as pinned (and still add upper rebar for the fixing moments), so no frames.
- use longer walls as cantilevers for horizontal loads. hopefully there is a basements, if not than I would "insert" this moments into strip footings

I hope it helps..

 

[greznik91]

Thanks for answer Tommy385

EC2 5.5 (6) states: 'For the design of columns the elastic moments from frame action should be used without any redistribution.'

I have been thinking to design columns based on a moment from envelope ( moment I got from modal analysis and from ULS(so I dont know what kind of redistribution you were thinking about).

There is no basement, so yes, I agree, I have been planning to do strip footings anyway.

 

[Tommy385]

I meant this..
dik (Structural)20 Aug 18 13:28
Your column seems to be robust enough... is it marginal because you are transferring a high moment? Can you use a transfer moment equal to DL + maybe 30% of LL? Done lots of parkades where I've used a LL = 15psf for alternating loading and moment transfers at columns.

 

[greznik91]

makes sense.

tnx again!