Adding a 5th Floor

[shobroco]

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?

 

[msquared48]

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

 

[shobroco]

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.

 

[msquared48]

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

 

[SteelPE]

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.

 

[shobroco]

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.

 

[dcarr82775]

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.

 

[shobroco]

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.

 

[DST148]

@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. (

http://www.chestofbooks.com/architecture/Building-Trades.../index.html)

The link may not work from here.

 

[shobroco]

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.

 

[dik]

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

 

[shobroco]

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.

 

[dik]

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

 

[shobroco]

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.

 

[msquared48]

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

 

[dik]

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

Dik

 

[shobroco]

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).

 

[shobroco]

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.

 

[dik]

"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?

 

[msquared48]

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