2-story extension of exist. steel building
2-story extension of exist. steel building
(OP)
Hello, I have a question to you guys. I work on a project in NYC, extension of 9-story steel building. We are adding 2 additional floors, it's a commercial space so LL has to be at least 100 psf. The building was built 100 years ago. It's got dimensions in plan 45'x100'.Since it's a commercial space, the owner cannot get rid of people during the construction time. We had a meeting today, my boss who is a PE was there with me, and he told them to check only a few columns every two stories and we will be ready to evaluate the building to establish if columns have to be reinforced or not..I know that some of the columns are simply not accessible but most of them can be checked. Furthermore, it looks like the 9th floor was added later on because the columns are different ( they did one probe already). We could find a two double angles (6x4) for the internal column at the 9th floor.
First I am wondering if columns like that would have enough capacity to carry additional two floors, but that can be easily checked. Second, what would be your approach in case like that, what would you start from, would you check all columns one by one or would you check 2-3 columns at each floor and assume that all of them are the same..? What about the beam to column connection ? Should be checked to I guess. I am not sure if we should include the column schedule on our drawings and show what load we are adding to the existing footings or not necessarily..? I would appreciate any thoughts on this subject. Thanks!
First I am wondering if columns like that would have enough capacity to carry additional two floors, but that can be easily checked. Second, what would be your approach in case like that, what would you start from, would you check all columns one by one or would you check 2-3 columns at each floor and assume that all of them are the same..? What about the beam to column connection ? Should be checked to I guess. I am not sure if we should include the column schedule on our drawings and show what load we are adding to the existing footings or not necessarily..? I would appreciate any thoughts on this subject. Thanks!






RE: 2-story extension of exist. steel building
I would want to check the taller building for wind and seismic loads if applicable. Hopefully, there are some existing drawings available to make the work a little easier.
BA
RE: 2-story extension of exist. steel building
RE: 2-story extension of exist. steel building
This is a tough problem. If your boss is overly confident, you have very little wiggle room. If you quit, someone else will do it.
RE: 2-story extension of exist. steel building
Like BA said, we should check the columns and footings and its capacity. In order to check wind and seismic loads we would have to know the beams and connections too - basically we should get familiar with a framing as a whole right?It sounds reasonable.
RE: 2-story extension of exist. steel building
The phrase ‘get intimate with the existing structure and details’ may be quite a bit more appropriate the your phrase “get familiar with a framing as a whole.” It seems to me that the owner should be willing to devote a fair amount of time and money to start to understand the two story addition potential of his bldg. If they just want the whole thing blessed for a few bucks, they should probably get in touch with their favorite church/minister, they are in the business of blessing things for a small donation. And, their obligations and liability are slightly different too, for that small donation.
RE: 2-story extension of exist. steel building
RE: 2-story extension of exist. steel building
What you are probably being expected to do is:
---Check some gravity sizing.
---Not think about lateral.
---Get a building permit.
You should NOT go this route.
You are hired to assess the structural ramifications of the proposed renovation. All of it.
8 stories original up to 11 doubles your overturning lateral moment.
The 45' weak dimension is pretty skinny. You may be introducing uplift where there was none previously.
This early in the project, your job is to educate. Educate the owner by emphasizing the information you have to somehow obtain. This is a tough conversation to have because owners are generally better at negotiating and controlling meetings than we engineers are. But it's very important.
If he is willing to play ball and listen to your needs, keep pursuing. If not, I'd just reiterate that information to him and let him decide if he wants to re-shop.
You need, as a start:
---As XR implied, to mention EARLY ON that his expansion plan may require a new lateral system for the whole structure. Bring some numbers or sketches to help. This is an unknown. It's not a yes, not a no.
---To walk each floor of a building and sketch out some column layouts, unless the renovation drawings show them well enough.
---As BA said, to determine what the foundations are (corbeled brick? Concrete? Deep?)
---To determine what the lateral system is (it could just be the limestone/masonry skin). Also check the elevator core and stair walls, which too may have been added as a renovation.
---To determine floor construction/weight. Find an electrical room without a ceiling and start there.
---Spot-checking the columns may be OK for starters, but if you are getting say 0.99 stress ratio you may want to do more than spot-check.
---This is without getting into any of the potential corrosion/water issues that may have transpired in 100 years with multiple renovations.
RE: 2-story extension of exist. steel building
Dik
RE: 2-story extension of exist. steel building
RE: 2-story extension of exist. steel building
You also can get some help from the building code. Chapter 34 gives some guidance regarding which members need to be checked and/or upgraded.
RE: 2-story extension of exist. steel building
Dik
RE: 2-story extension of exist. steel building
- NYC is unique in that the code allows quite a bit of leeway in terms of not upgrading lateral. The 2 on 9 would be nothing out of the ordinary. There is a little flowchart that determines if you need to upgrade but generally speaking I wouldn't be surprised if you aren't required to. Not saying it's right - but that's the code in nyc and it's common.
- Top column might be original, I've seen them switch at top floor if columns don't stack or I guess savings in steel... not sure but I just worked on one that had single angle columns at top floor and everything below was built up shapes.
RE: 2-story extension of exist. steel building
Best,
Jacek
RE: 2-story extension of exist. steel building
Dik
RE: 2-story extension of exist. steel building
RE: 2-story extension of exist. steel building
RE: 2-story extension of exist. steel building
RE: 2-story extension of exist. steel building
and I am trying to get as much info as I can from it. I agree with you that thorough investigation should be carried out - undoubtedly. But it seems like we are going to make some assumptions based on how they used to build at that time. I am not PE yet so basically I do what I am asked to do but I am trying to do my best to assess the building properly.
It looks like the gravity loads will not be an issue. Columns can withstand an extra load from two additional stories. When it comes to lateral stability - I want the client to open a few column - to - beam connections to make sure there are moment connections frames. Plus there are 3 core shafts - 2 staircases plus elevator.
Thank you for your answers. I really appreciate that.
Best
RE: 2-story extension of exist. steel building
As for the structure, I'd approach the problem assuming that everything needs to be supplemented to support the additional loads (and they probably built the thing wrong), prove me wrong. As Bookowski noted, NYC's code is unique (and a PITA) and may not require an upgrade to the lateral system. If that's the case, this sounds like a great project for your competition to put its name on. This causes my estimator to hate me, but, all early assumptions should add cost to this project. Only with assurances should those costs be removed. Optimism should be beaten down at every meeting with the owner. Save your optimism until the end.
So you checked the corner columns and they're good (you've already checked overturning)? OK, remove 4 columns from the "supplement columns on the ground floor" cost item.