Portal Frame Column Base Connection Design
Portal Frame Column Base Connection Design
(OP)
Hi,
I am designing a 30m span portal frame, 11m high. The frame has been analysed as a pinned frame. When designing the baseplate I found that due to horizontal forces I need to provide 30mm dim holding bolts. We also intend to cast the baseplates with concrete stubs.
My issue is that the plate cast in concrete will be very stiff and this will attract moments from the frame. I am concerned that due to these moments I will get a pull out failure (concrete cone failure) before steel yielding. As I have provided a large dim bolts for resiting shear they wont yield before concrete failure.
One option is to drop down the steel grade from 8.8 to 4.6 (195 N/mm2) to initiate a steel failure before concrete ,but I have always specified 8.8 grade to date so I am a bit slow to change our standard details.
Will appreciate all your advise.
Thank you
Karol






RE: Portal Frame Column Base Connection Design
Second,based on what you said, you concrete stub is able to take the load. It's just because the concrete stub failure will happen before steel yielding. I am not sure if that is really something you need to worry about since you have already have enough capacity to take your design loads. But that is a good point though.
Bottom line is you can always reinforcing your concrete stub(if you don't want to resize the concrete stub) to prevent the pull out failure. That is what ACI Appendix D allows.
Moment curvature analysis,reinforced concrete column design and prestressed concrete pile design at www.structurexpress.com
RE: Portal Frame Column Base Connection Design
I just want to be sure that wont get concrete pull out. The frame even designed as pin jointed it will still need to resist some nominal uplift forces due to wind etc. So if I will get a concrete pull put failure due to additional moments from the frame I assume this would effect my holding bolts and frame stability?
Maybe these local failure issues can be ignored as long as the frame and pad foundations are designed for pin bases??
RE: Portal Frame Column Base Connection Design
I just want to be sure that wont get concrete pull out. The frame even designed as pin jointed it will still need to resist some nominal uplift forces due to wind etc. So if I will get a concrete pull put failure due to additional moments from the frame I assume this would effect my holding bolts and frame stability?
Maybe these local failure issues can be ignored as long as the frame and pad foundations are designed for pin bases??
RE: Portal Frame Column Base Connection Design
Moment curvature analysis,reinforced concrete column design and prestressed concrete pile design at www.structurexpress.com
RE: Portal Frame Column Base Connection Design
RE: Portal Frame Column Base Connection Design
near the end I posted a paper that talks about using pedestal reinforcement to preclude concrete breakout failure. I would also recommend, as a check, to use the hilti profis program - I have verified its results against my own hand calcs many times and have never found an error for a rigid plate assumption. The nice thing is, you can tell it you are using anchor reinforcing, and then it will tell you the stress ratio, neglecting the failure modes the reinforcing takes care of.
RE: Portal Frame Column Base Connection Design
Would you be able to give me some indication on baseplates/holding bolts sizes for 30m span portal frame and 10 meter high? Maybe a baseplate detail with a typical pedestal edge distances /rebar?
My columns are 686UBs. I assumed that the horizontal forces due to wind are taken by the holding bolts thus got 30mm dim bolts. I was going to provide 600mm embedment in concrete pedestals and keep 6xdim from the centre of the bolts to the edge of the stub.
Following structSU10 posted paper I understand that will need to provide sufficient rebar to avoid concrete failure in case my theoretical pinned bases will attract some high moments.