Column to base-plate - connection design 2

[Bridgegirl67]

I am new(er) in the design realm and am working on a column design. I have the column designed and the base plate established; my question is ...
How do I go about designing the angles, anchor bolts and welds I want to install at the top and bottom of my column to attach them to the plates? All of the information I have found is for beam to column connections and similar.
I very well could just be missing it... but please help.
My column is in compression with no excentric loading and it is for "temporary" purposes.
Thank you in advance!

 

[ToadJones]

why not just weld it to the base plate/Cap plate?

 

[Bridgegirl67]

I intend on calling for welding the angles to the base plate, however the purpose of this column it to act as a temporary support during staged construction. Therefore, it needs to be easily (comparitively speaking) assembled and dis-assembled.
A temporary support used on a previous project by the contractor (not designed by me) shows the angles attached to the flanges of the column. Obviously it worked, I just have to be able to show it and have hit a "stumbling block" of sorts.

 

[rscassar]

Is your column a wide flange section or a hollow section. If the bracing provided is for temporary purposes (say during the erection of steelwork), then the magnitude of forces wouldn't be as great as those of the lateral-force resisting system.

Welding the angle to the baseplate my not be easy to dis-assemble. I think it would be best to provided a cleat and a bolted connection for the angle. After the lateral-force resisting elements are installed the angle can be removed easily by unbolting. If possible, the cleats can remain depending whether they will be concealed within the wall cladding. Otherwise they can grind flush and reinstate whatever finish is on the steelwork.

Was the bracing for safety during steelwork erection?

 

[Bridgegirl67]

Kikflip - the column is a W14x90 and is for the partial demolition (staged construction) of a bridge. It is to be positioned under a cantilevered portion of a pier (I've attached a sketch). It isn't for erection as much as for mainaining traffic during demolition.

 

[DWHA]

I have done a lot of work with contractors for temporary support systems such as what you have shown. I would call out for a end plate welded to the W section. I would call the columnn length out to be +/- an inch short (and say field verify), then say shim +/- 1" as required for a tight fit. Shim plates to be the same geometry as the end plate. I would also have the end plate on top and bottom Hilti anchored to the concrete.

On something like this, I would call the weld to be 1/4" fillet all around (I have called out stitch welds but usually they will just weld all around anyway). Then I would use 4 - 3/4" Hilti anchors (Hilti Kwik Conn 3) top and bottom. State this in calcs and "say ok by examination" because the calculated load though the weld and Hilti anchors is really nothing.

 

[J2CUB612]

There are some good practical responses here already. If you also want to know about the design calcs, find AISC Design Guide 1 at

http://www.aisc.org.

It’s free to members.

If you, or someone in your office, aren’t a member you should really consider it if you design with steel. There are at least 23 design guides plus access to all kinds of aisc pubs as well as the steeltools web site with hundreds of tools like spreadsheets etc including some that do Design guide 1 calcs.

 

[Bridgegirl67]

While I stated it before, I would like to express again my gratitude for the assistance received here!
Thank you!!
Truly!

 

[Bridgegirl67]

One item however..
I know that I already thanked everyone for the input, which was extremely helpful...
DWHA, you stated you have done a lot of temporary supports for contractors such as this?... How do you establish/are there any guides to make this determination for those of us (me) who do not have the design experience to comfortably make a statement of "ok by examination" yet?! I am especiall looking for the design of the welds (or in my case angles and bolts *see attached*)at the base of the column! Thank You again.

 

[DWHA]

Bridgegirl67
There is not really any guidelines. You just have to think out side of textbook analysis and consider what exactly is going on from a pratical standpoint.

You have about 22" of weld for each angle. Which has a capacity phi Rn= 153 kips per angle. In you wildest imagination do you see a case where there would be a horizontal force greater than that? If no, then it is ok by examination.

Also, consider economics. For example, with welds; if you were to have called out a total of 6" of weld for that angle you would have saved the contractor 5 minutes, and it already took the contractor how to get the welder on, leather gloves & helmet on, pieces measured and clamped together at the proper location, etc. What is the cost of that extra weld. Not too much.

It takes time to get a "feel" for it. And if you are in doubt, it is your responsibility to properly calculate the capacity vs. the loads.

Also, ask those with more experience in you office and see what they would do. And remember the next time it you have a design that is the same.