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Adding a 5th Floor

Adding a 5th Floor

Adding a 5th Floor

(OP)
I've got an owner who wants to put a 5th floor on a 115 year old 4 storey masonry load-bearing wall (4 wythes of brick) building.  It has wood-framed floors & flat roof.  He has a prospective tenant who wants to run a rooftop restaurant, mostly glass-enclosed.  The building is only 28' wide, but 150' long.  I think I can drop a steel structure on top of the walls consisting of basically a pre-eng frame with floor beam/tie at the column base that will carry joists between the frames.  If the frames are close together (15-16') & the baseplates big enough, the brick can carry the gravity loads and there is minimal lateral load on the masonry.  The brick walls extend 2' above the wood roof joists so the roof can remain in place.  I have not done any calcs yet, it has all come up very quickly. Am I crazy?

RE: Adding a 5th Floor

The entire structure may have to be brought up to current code.  Are you prepared for that scenario?

Also have to consider wind, which 115 years ago, was not per our specs today.  Snow?   

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: Adding a 5th Floor

(OP)
Yes snow is an issue but I hope to mitigate it wih sloped glazing & a metal roof, making it actually less than current snow loading, & wind is not a major concern because every building around it is many stories higher.  I have been working on other structural issues with the rest of the building because the owner has just purchased it, kicked out all of the tenants, and is doing a complete revamp of the whole thing in & out.  I could get into major structural work down to grade to carry the new floor, but naturally the owner doesn't want to spend money on that & I'm wondering if anyone has seen this sort of thing done elsewhere.

RE: Adding a 5th Floor

Regardless of what is around you, by code, you still have to apply the required wind forces to the structure.  

The adjacent buildings can always be demolished, exposing the structure to wind.  Remember that you cannot control the land that you do not own.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: Adding a 5th Floor

As M^2 the structure needs to be constructed in accordance with the building code.  If you are in the US you probably need to follow the IBC or the IEBC depending on your jurisdiction.  If I remember correctly, you can not change the demand/capacity ration of any LFRS element by more that 10% if you do you need to make sure the existing structure is up to snuff with the current code requirements.  This can be found in Chapter 34 of the IBC.

Thinking really simply for a moment, if you are adding a story to a 4 story building you are going to be increasing the demand/capacity ratio of the existing building by at least 25%.  This doesn't mean that the existing building in inadequate, it just means that a more complex/detailed analysis may need to be run.

Good Luck.
 

RE: Adding a 5th Floor

(OP)
Any idea where to find the capacity of round and rectangular cast iron columns?  The interior columns are round & the columns in the grade level storefronts are rectangular.   

RE: Adding a 5th Floor

I do not see too many old URM buildings that ever figure for wind or seismic.  As M^2 said, the Code (US anyway) specifically prevents you from assuming shielding form existing buildings.  You can use the lower Exposure factor, but must account for the wind.  Seismic doesn't care if there is a building next door and with URM that low R factor could hurt you.  ASCE31 had methods to analyze existing buildings for seismic.

RE: Adding a 5th Floor

(OP)
It's in Ontario; NBC provisions for wind & seismic govern.  NBC also has guidelines for analyzing existing buildings however they don't apply to any additions or alterations, which is likely going to kill the project because an alteration on the roof affects the whole building. Credit is given for satisfactory performance if a building is more than 30 years old regardless of what the analysis shows, however that doesn't apply when you change something.

RE: Adding a 5th Floor

@shobroco - I Googled "Capacity of round and square cast iron columns" . There is a company that publishes "The Building Trades Pocketbook". It has info and a solved example on design of C.I. columns. You can access it online. (www.chestofbooks.com/architecture/Building-Trades.../index.html)
The link may not work from here.  

RE: Adding a 5th Floor

(OP)
DST148- Thanks, the link didn't work but it didn't take any time to find it.  The book looks pretty helpful for a lot of things; I am frequently involved with old buildings.  This building is 1897 so the 1905 book is from the right era.

Of course, I'll probably have to drill small holes in the columns to get thicknesses.

RE: Adding a 5th Floor

In Ontario, it may be able to accommodate revisions under Part 11 of the OBC... but, the addition of another floor may be another issue as well as significant change in use and occupancy.

The addition of a restaurant may require a 100 psf LL and may be difficult to accommodate.

In addition, any change in the loading regime that the building has been exposed to for the last decades? may have other effects, differential settlement, etc.  Also old buildings derived their longevity by natural ventilation, air leakage, etc.  Change in use may increase humidity substantially... and the addition of an added vapour barrier may have adverse effects on the old 4 wythe walls...

Dik

RE: Adding a 5th Floor

(OP)
The owner has just stripped all of the interior back to the structure, including removing the lath & plaster from the brick walls.  He wants to clean them & leave them exposed in the new offices, so there won't be any vapour barrier or insulation.  Not the best for energy efficiency, but it's the look he is selling.  The good thing is that I can see all of the structure now:  walls, floors, and roof, and there are 2 interior brick cross walls that add substantially to the rigidity.  The 100psf for the restaurant won't be a problem for the floor because the floor stucture would be new, above the roof structure, but it's a pretty substantial increase in load on the walls & foundations.  There is a lot to review before i can even tell him if it's feasible.

RE: Adding a 5th Floor

Humidity issues can cause deterioration of the existing brick... Building can be cold, even though you have 4 wythes... You may require that an Architect be involved... have him sort out the building envelope issues... The main reason the old brick buildings withstood the 'test of time' was that they were leaky... change the environment at your (or better, Arcitects) peril...

Dik

RE: Adding a 5th Floor

(OP)
There are 2 architects involved; one for the interior space and one for the building exterior; it is a designated heritage property.  The owner deals with the same architect for all of his interior fit-ups but he isn't experienced in heritage restoration; the exterior architect & I are the ones getting him through the heritage permit process & the exterior restoration, but we've been drawn into more things because of the proposed 5th floor addition.  There will also be another architect involved if the addition goes ahead because the restaurant company has their own guy.  I have enough nightmares with one architect on a project; I'm not sure if I can deal with 3.  One is already complaining about being at the bottom of the food chain; he's used to being top dog.

RE: Adding a 5th Floor

One of the retrofits you may have to do is tie the floor joists to the brick walls.  Usually there are some embedded straps, but these may not be adequate.  To reinforce the connection, thru bolts are usually used with rosettes on the outside of the wall.  With adjacent buildings, this may not be possibie, leaving little alternative but expansion or chemical anchors that cannot be used with vibratory loads.

How close are the adjacent buildings?

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: Adding a 5th Floor

What part of the building is designated?  Facade only? If not, then removal of lath and plaster may be an issue...

Dik

RE: Adding a 5th Floor

(OP)
MM:  I looked at the joists yesterday, there is a bit of a mixed bag.  The building had an addition within a few years of original construction & that end is tied together, but the original building just has the joists sitting in pockets.  The building is on a corner, with both narrow ends (28') exposed.  One long wall is the street front but the other is built against another brick building of similar age, so tie rods won't work unless the neighbour doesn't mind some iron decorations on their office walls.  Any thoughts on epoxy or polyurethane adhesive on each joist at the pockets?  Lots of contact points so each one doesn't have to carry much, and it brings the floors into play as diaphragms (diagonal subfloor sheathing on all of them).

RE: Adding a 5th Floor

(OP)
Dik:
Designation includes the exterior facade on 2 street fronts, not including the grade level storefronts which were changed in the 1960s.  Specifically the masonry walls (brick with sandstone trims & embellishments), windows, and sheet metal ornamentation.  The owner is a little tough to keep a leash on but we have got heritage approval for the facade restoration as of last week (he had already scaffolded & cleaned it without permission) and the interior is not listed in the designation.  The Heritage Board is reviewing the proposed 5th floor addition, & the owner assumes he'll get their blessing & wants to be ready to go when it comes.

RE: Adding a 5th Floor

"There are 2 architects involved; one for the interior space and one for the building exterior"

Has either architect addressed the vapour barrier issues? Do either have experience with historic masonry?

RE: Adding a 5th Floor

shobroco:

Had a job like this in Everett once where we had only about a foot between the buildings.  We found a special insert that had a folding section that would spring out when it cleared the wall.  

How much distance is there between the buildings?

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: Adding a 5th Floor

(OP)
Dik:The exterior architect has lots of experience with historic masonry & he's working on several aspects of the envelope; I've dealt with it a fair bit as well.  There has never been a vapour barrier in this building & there won't be now, however we are looking at interior surface treatments.  We are working with a masonry restoration company that has been a leader in this field for several decades.
 
MM: There is 0 distance between the buildings; in fact they have a common wall in one area.  There is a sign painted on the former exterior of the neighbouring building that was uncovered when the plaster was removed.

RE: Adding a 5th Floor

Just a caution... new buildings due to their use have a lot more vapour... that should be addressed...

Dik

RE: Adding a 5th Floor

I have never done epoxy in the beam pockets but that is an interesting thought. I wouldn't be surprised if it hasn't been tested. Although unrelated I know when installing a wood Shearwall to an existing wood diaphragm I think there have been some installations that use wood glue to establish the diaphragm connection rather than trying to use an -a34 clip or similar with small screws to the underside of the diaphragm. Not really similar but kinda on the same line.

Also for some ideas I'd recommend checking out FEMA 547 it's a good reference for retrofitting existing buildings.  

RE: Adding a 5th Floor

I think a lot of this will depend on your local code.

I am in NYC and we do this type of thing all the time. The code here is extremely forgiving with alterations to existing buildings including adding stories and increasing load while not forcing you to upgrade. Whether or not that is good practice is a separate issue but it is done very frequently.

As for cast iron columns - you can find a lot of literature that will give you the original design strength equations (look at a book called 'Historical Building Construction', it has a lot of good references). I would not trust those at all though. If you follow the history of those equations you will find that the design capacity was successively reduced as we learned more about cast iron columns until eventually we stopped using them. One of the biggest problems is the connections. They are truly close to a pin, they basically just stack the columns and add some very wimpy connection plates. I would not increase the load at all on existing cast iron, it is unpredictable. You should span outer brick wall to wall, and add posts/reinforce as required at those areas.

RE: Adding a 5th Floor

all i can say is good luck.
whenever an alteration is done to a building here, we have to bring it up to code requirements (seismic).

RE: Adding a 5th Floor

The last one that I did like this had a listed exterior and high ceilings. It was also completely empty. We found that by progressively gutting and replacing the interior structure on a different grid, we could squeeze an extra floor in the same height with just a slightly raised glass mansard (almost hidden behind the existing parapet from a ground view), the mansard being only two or three feet high at the top of the wall. We would have needed major strengthening of the existing structure to make code.

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Adding a 5th Floor

(OP)
Thanks to everyone for the input.  I just spent 2 days with a metal building systems company at their annual meeting & one of their guys did this 25 years ago on an 11 storey building of the same age (not a full 12th floor addition, just a section).  I have told the owner that we might be able to do it but I have a lot of issues to work through.  I have the MBS company doing a design for the full structural package of the addition, floor included. I am specifying where they can load the walls; they will give me reactions, & I have to go from there.  I'll post a thread in a while when I know where it's going.

RE: Adding a 5th Floor

This may not fly with a dedicated building, specially the facade... Depending on the building and the approvals required this could take months/years...

Dik

RE: Adding a 5th Floor

(OP)
Dik:  The pretty pictures are currntly under review by the heritage board; they are not opposed to the first impressions, but it's a long way from approved.  They issued a permit & gave the owner some slack on the facades and the work he had already started only because they know the team presenting the proposal (myself, the architect, & the masonry company) but that's only going to go so far with the rest of it.  The bigger issue will likely be the building itself & whether or not it can handle it.

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