What minimum wood properties do you assume for existing buildings

[EcoGen]

When evaluating existing joists in typical residential buildings over 80 to 100 years old, what assumptions do you make about the material of the existing floor joists? I have a client who wants to install a 1,700 to 2,000 lbs aquarium in their living room up against a wall. There is a basement below and I haven't completed a site visit yet. But already I told her she has to remove a lot of drywall in the basement if she wants a structural engineer to determine if that sort of weight would be acceptable. And it may likely need reinforcing.

I'm thinking even if I was able to determine the depth, spacing, and span of the joists, what would you guys consider as minimum wood properties to check against? I was planning on going through NDS tables and picking the wood with the lowest Fb and conservatively assume that in the beam analysis.

My quick analysis assuming 16" OC and Eastern White Pine No.2 (Fb = 575 psi) with an assumed 10 ft span(to be verified): 2x8s don't work but 2x10s work comfortably.

 

[jayrod12]

Old lumber is significantly stronger than new.

Where I practice, if you have a building that age, you assume DFir select structural and that get's you pretty close to the bending stresses allowed in the codes from those days.

So I think if anything you're being over conservative.

Many homes in that era, where I am, are framed with 2x6 rough cut joists meaning truly 2"x6".

 

[Harbringer]

I'd assume whatever is your regions typical construction lumber (D.F, SYP, etc.) is still your regions typical construction lumber.

Then I'd look up the allowable value in the code from the period of construction. You have the internet and pdf's of codes up to at least 100 years old are available.

 

[EcoGen]

Thanks for your input guys! I did find some historical values from 1922 and 1944 (AWC archive link). The lowest Fb values there were higher (750 psi and 900 psi respectively). I think sticking to 900 psi assumption (which is like DFir No.2) for bending stress and use actual dimensions measured in the field vs nominal dimensions would be reasonable.

The building is in Washington DC but not sure how to figure out region specific historical info. Does anyone have any idea about old wood used in this area or how I would go about figuring that out?

 

[jayrod12]

Does using the lowest value get you where you need? Remember those were allowable values they published back in those days so Mr = Fb*S. If the 750 psi makes your design check work out, then I'd likely not really put much more though into it. If you were close at 575 psi, I'd like to think that a 40% increase in strength should get you there.

 

[dhengr]

Manaf_engineering:
How big is the tank, other than 32cu.ft.? What is the load path down to the foundation? There better be a bearing wall right below it down in the bsmt. That load, right up against the wall, doesn’t add real much to the bending in the joists, so bending might not be your worst problem, but, you better be sure to check reactions, shear and comp. perp. to the grain in those joists. A steel frame under the tank better distrib. the weight to all the joists, not just using four corner legs. Be sure to tie the whole tank and support frame back to the wall, so it can’t tip over. Put a sizable water catch pan under the whole thing and drain it to the bsmt. floor drain.

That’s a ton of water and tank. It might be interesting to look at the possibility on putting that tank and its support frame on a couple small pipe columns, which go right through the floor and down to small footings in the bsmt. Then, the tank would not be loading that 100 yr. old, unknown lumber. It would move vertically independent of the 1st fl. framing, but still be stabilized by some clips to the 1st fl. walls.

 

[EcoGen]

@jayrod12: Not sure what the exact spans are but based on photos of the finished basement below it may be 10 to 12 feet from exterior brick wall to middle beam line. so far 2x6 DFir No.2 (Fb = 900 psi) at 16" O.C. work for these spans but all these dimensions need to be verified in the field. I have a kick off meeting with the home owner on site and I want to know if it's worth having the homeowner remove potentially a loooot of ceiling drywall if I already know that it most likely won't work anyways.

@dhengr: These are good questions and concerns. At this point I'm trying to determine if and how much ceiling and wall drywall to remove. The Owner seems willing to do the removal and replacement all just to certify that the structure is OK withstand the new loads.
[ul]
[li]We haven't removed all the drywall yet, but I'm guessing the floor is made of joists spanning from exterior wall (brick most likely) to interior middle beam. This would be up against where the exterior brick wall end will be hopefully.[/li]
[li]You're right about bending not being much of a concern. Now as for load path, there's the whole concern of overloading the exterior wall and its footing that I haven't fully thought of yet. Hopefully I'm able to justify a less than 10% increase as a line load reaction on the exterior wall.[/li]
[li]If the joists are pocketed, I'll also check bearing stress on the exterior brick.[/li]
[li]Regarding the aquarium base, I can't tell how the load gets distributed to the base based on the sketches the contractor provided me. Their sketches don't show much about the base. It definitely has to be spread over a line and not 4 corner point loads.[/li]
[li]New steel framing, posts, and footings would put me at ease for sure. But of course the Owner is not going to like that.[/li]
[/ul]

I'll share some photos and diagrams as a separate post below so you have a better idea of what I'm talking about.

 

[EcoGen]

Living room wall where cabinets and aquarium will be installed:

Basement wall directly below the photo above:

Also, this is what the contractor has provided me for just the aquarium framing elevation and sections. I've highlighted the aquarium in blue hatched lines below.

Finished product EXAMPLE:

 

[EcoGen]

Surprising the owner actually had a full set of structural drawings for a renovation completed a couple years ago. It doesn't specifically state the existing framing at the aquarium location but in other areas it shows 2x8@16"O.C. framing pocketed into exterior brick wall on one side and supported by a steel beam on the other side (11.5' span). My calcs show those joists work even for conservative values. In my letter I'm still going to require that they verify the framing below that area by removing some finishes.