Strengthening Fabricated Columns of Premanufactured Steel Buidling
Strengthening Fabricated Columns of Premanufactured Steel Buidling
(OP)
I am trying to strengthen the building columns of a metal fabrication shop. There is a 10 ton overhead crane, and I am adding two more 15 ton overhead cranes. The runway beams are good if I keep hook centers 15' apart with bumpers. I just need to reinforce the columns.
The building is a prefabricated metal building. The bailing columns are steel plate stitched welded into a W colum. The web is about 36" and the flange is about 10" with a 3/8" thickness. The crane runway rest on beam seats welded to the side of the column. It seems like to much to get into the total engineering of the column because I would have to analyze the whole building loads. The columns were designed for the 10 ton crane, so I really only need 15kips of additional strength. I was thinking I could do it a few different ways:
1) Cap the front of the column with a C-channel.
2) Box the front of the column with a MC-channel. (Weld flanges of MC to front flange of column). I would think this would give a lot more strength since it creates box column
3) Weld flat steel bar to the front of the column - increasing the flange thickness.
I'm a mechanical engineer, but it's been a long time since I have done this detailed of a structural calculation. I figure I can be conservative on the steel and be assured I have a good safety factor.
Does anyone have experience strengthening fabricated metal building columns like this?
Thanks!
The building is a prefabricated metal building. The bailing columns are steel plate stitched welded into a W colum. The web is about 36" and the flange is about 10" with a 3/8" thickness. The crane runway rest on beam seats welded to the side of the column. It seems like to much to get into the total engineering of the column because I would have to analyze the whole building loads. The columns were designed for the 10 ton crane, so I really only need 15kips of additional strength. I was thinking I could do it a few different ways:
1) Cap the front of the column with a C-channel.
2) Box the front of the column with a MC-channel. (Weld flanges of MC to front flange of column). I would think this would give a lot more strength since it creates box column
3) Weld flat steel bar to the front of the column - increasing the flange thickness.
I'm a mechanical engineer, but it's been a long time since I have done this detailed of a structural calculation. I figure I can be conservative on the steel and be assured I have a good safety factor.
Does anyone have experience strengthening fabricated metal building columns like this?
Thanks!






RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
That sounds like a hope and a prayer method by a non-structural engineer. This does not sound like good engineering to me.
The interplay between the axial loads and the flexural loads in the columns are not easily understood and just adding steel without, as haynewp suggests, doing the proper building analysis is not defensible.
The required steps, in my view, would involve full measurements of the steel columns, girders, etc., a current-code wind/seismic analysis along with the gravity/crane combinations, possibly sampling the steel to determine the Fy/Fu, etc. If you don't know how to do this I'd recommend you get some help.
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
It is good feedback to understand there is not good understanding on column strengthening techniques in the community. I will just add a column under the beam seats that I can select based on strength from my structural reference book. Probably go with a W8x24 with a 12x12x3/4" base plate. At 25' that should be more than enough strength for the additional 12kips or so for the crane. Would it be worth while to stitch weld the sister column to the building column for added strength? Also, I assume having the orientation of the sister column opposite of the building column would add the most strength to the structure?
Am I off base on any of this?
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
As previously suggested, use separate crane columns with separate footings. That approach will be the simplest and most cost-effective approach.
If you were going to rry to modify the columns, you would just get a progression of problems to solve - a ripple effect in the structure. Just keep it simple, and above all, hire a local structural engineer to do this.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
Right now I am looking at using a W8x24 with a large base plate to spread the load. It will be mounted on the floor with 4 anchor bolts and be welded to the underside of the beam seat.
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling
Installing a new load this size would generally require reanalyzing the structure and ensuring that it meets current code. Do you know when it was built? What does this do to the seismic requirements for the lateral force resisting system? Is it a moment frame system? If so, how does this affect the spanning beams, the beam connections, the column anchorage and the foundation? Even if it's not a moment frame, the foundation is a big deal. You might end up with deflection concerns as well. From the most basic standpoint, it's something that deserves a great deal of consideration because you're adding a load that's likely a large percentage of the existing structure capacity. Supporting a small platform or something at the top of a column, yeah maybe just throw reinforcement on your column that equals the applied moment and compression loads and take a quick look at the beams. Add something an order of magnitude bigger and you're starting to be in a situation where you have to look more in depth.
Personally, I'd be terrified of installing crane systems where the operators have the ability to run it in such a way that the structure is overloaded when the cranes aren't. What happens five years down the line when it gets sold to someone else and the only reason the thing works is that you keep the hooks fifteen feet apart? The crane capacities are written in giant letters on the actual equipment and need to be certified regularly, so you can be pretty comfortable that people know to keep the cranes at or below capacity. I wouldn't be comfortable in a situation where you could overstress the beam by a factor of two due to operator error.
Also, just because the load is between two columns doesn't mean it only affects that bay's structure. A crane rail is likely a continuous beam and depending on the stiffness of the system could pass load to a number of bays. Any thrust loads will also get pulled down the structure based on the brace or column stiffnesses.
This doesn't even get into the issues of connections, specific code requirements for crane structures, or all the fun dynamic stuff.
Yeah, reinforcing the column might be the right solution, but there's a lot more involved in deciding that it is. The reason people are suggesting that you install an independent support system that doesn't tie into the building is that it's likely that you'll have problems making a pre-engineered building with this much additional load pass code without significant additions, so it's better to go with a simple system that you can fully control.
RE: Strengthening Fabricated Columns of Premanufactured Steel Buidling