100+ year old residential timber analysis & reinforcement 2

[RattlinBog]

I'm hoping to get some advice and a sanity check on a few things. In my spare time, I've been starting to plan repairs for the first level framing of my own 100+ year old home. For background, I'm a licensed structural engineer (PE not SE) with about 5 years experience in heavy industry. I work with steel and concrete. My experience with timber design is limited to one undergrad class and sizing a handful of beams and crane mats--so very little practical experience. Virtually zero experience with residential. I'm trying to crunch some numbers so I have a better feel for what's going on in my house and planning to hire a local contractor for repairs.

See attached pdf for a drawing of my house, NDS calcs for a timber beam, and some photos. Below is what I hope to get a little help for:

1) At least one 2x8 floor joist is failing/splitting (photo 1). Joists are old-growth full length 19-20 ft, spanning over a 6x8 timber. No bridging or bracing. I still need to analyze joists per NDS, but I'm planning to sister the failed joist (and a few others) as full length as possible. Anyone see issues with sistering the old joist that is cracked per photo 1? I'll need to reroute electrical. I think I will also install bridging between joists where it's feasible. Some shoring/jacking will be required for this work. I'm assuming driving nails into old wood will be very difficult.

2) My 6x8 timber beam appears to be failing in bending at 350% utilization per NDS... Trying to be conservative, I assumed Douglas Fir-Larch No. 2 with Fb = 750 psi and Fv = 170 psi. Assumed DL = 20 psf and LL = 40 psf. I believe beam is picking up load from second floor as well. Beam is continuous over an S6 steel post at midspan. I assumed pinned-pinned at end connections. Perhaps that's wrong as beam is embedded in concrete wall. Could I call it fixed-fixed to reduce my moment to 7.6 kip-ft? Also, am I being too conservative with assuming No. 2 and Fb = 750 psi? I don't know what's reasonable for a 100+ year old timber.

3) The 6x8 beam has some other issues I want to address. It has a big, ugly notch (photo 2) from an old duct a few feet west of the steel post. I believe notch should be in compression, but it's not code-compliant and definitely not helping my flexure check. I'd like to sharpen my pencil on bullet point 2, and then I can design some reinforcement for that area, perhaps by building a U-shape from 2x lumber to nail from underneath. The beam also has some fairly significant checking (photo 3) on one face only for about 12 ft, starting at the steel post and running east. The other face of the beam has very minor checking. Checking is about 1/2" wide; I can stick my fingers in it. Could this checking be from a more serious issue than from regular drying/shrinkage?

I appreciate any help. Let me know if this type of post is not allowed. I repeat, this is not for work; it's a personal project on my own home.

 

[SWComposites]

Oh my. Were those beam notches present when you bought the house? And in the second photo it looks like there are 2 notches in the beam on either side of a joist (a relatively small one and a ~1/2 depth huge one!)?

The wood splitting looks very similar to that in the 1914 Seattle house that I used to own.

And depending on where this house is located, it is very likely that the wood properties are much higher than currently assumed by code.

 

[RattlinBog]

Yes, I'm a bit embarrassed to admit it, but I did buy the house with notches already present. I briefly saw the notch during the house showing with the realtor, but we didn't spend a lot of time in the basement, so I let it slip my mind in the rush. Looking back, I should have slowed down and looked more carefully, but we had a lot of houses to look at that day. Since then, I've been kicking the can down the road a bit too long. Need to address the issues. Also, the 1/2" checking on the east side of the beam was covered up by thin wood paneling. I recently removed that out of curiosity, which got me down this rabbit hole as alarm bells were ringing in my head.

In the second photo, you're right, there is a one smaller notch and a huge notch. Thankfully, the big notch is tapered upward at a 45, so the beam is full depth on the other side. I'm not saying it's good, though. There must have a been a larger, rectangular duct there at one point (replaced by round duct). It's ugly.

That's what I'm hoping for wood strength. I was browsing past threads on eng-tips, and some folks were saying Fb = 1000 psi for older wood. I'm in northern Minnesota.

 

[jayrod12]

1. Agree that joist at a minimum needs to be sistered. If I'm being honest, that one looks almost like it got crushed from the underside or something. You may want to jack it back up, but honestly I'd be putting the new joist as tight to the underside of sheathing as possible and just shimming it along the length as required to accommodate the existing deflection. It's quite likely that jacking the floor up will cause more damage than it's worth. Also, nails go into old wood far better than screws do. I've had many a screw head snap off. Just make sure you're buying real nails and not those thin garbage that shouldn't be used for anything but hanging pictures.

2) Old growth lumber like this is closer to DFir Select Structural grade. FB closer to 1300-1400 PSI is what I would expect at a minimum. I've had luck analyzing it as continuous over the support to keep the moment down a bit, however in my locale these usually have multiple interior supports, not a single mid-span. I can't see a scenario where the beam wouldn't support the second floor in an old house like this. It appears as though at some point someone would've framed the second floor framing such that it doesn't load up the beam as much, or the wall of the bathroom and beside the stair is loadbearing and then the main floor joists move it back to the beam. Kind of depends how that from entry addition was framed and how they accommodated the second floor framing support.

3)The checking does not concern me in the slightest. But that giant notch does. I think once you address the notch you should be in much better shape overall.

 

[RattlinBog]

jayrod12, thank you. Do you think it would be reasonable to change my 6x8 beam from being pinned-pinned to fixed-fixed (continuous)? See attached FBD. That would drop my moment from 11.3 to 7.6 kip-ft. Beam ends are embedded in concrete wall. Might be a dumb question, I just don't have residential / wood experience to feel confident.

 

[XR250]

1) No, you cannot count on any fixity at the embedded end
2) The crushing of the joist that Jayrod mentioned looks like termite damage to me. I would poke them with a phillips head screwdriver.
3) I would sister the notched girder span with an LVL on each face ripped to the same depth if you want to keep the ceiling height the same.

 

[RattlinBog]

XR250, thanks for the advice. If I keep pinned-pinned but use Fb = 1400 psi, I'm still getting 188% bending utilization (assuming full section, no notch). Attached updated calcs, as well as calcs for 2x8 joist (OK in flexure and shear).

Spit-balling a bit: I could sandwich both sides of beam with LVLs, possibly deeper than beam and nail a 2x6 to bottom to fill gap. I don't care about losing a bit of headroom if it means I can sleep peacefully at night. Perhaps I can sister 2 LVLs on either side of midspan post. The post and chimney will interfere with a full length reinforcement. I could also strategically place a couple more posts to reduce moment.

I'll speak with a contractor to get the ball rolling. It'll take some time to move elec and mech for the work, too.

Edit: Trying to get attachment to work. Doesn't seem to like "&" symbol

 

[RattlinBog]

Sorry for double post. My attachment didn't work with the "&" symbol. Tried to edit last post, but it's not working. Here's the working attachment for updated NDS calcs.

 

[DoubleStud]

Where exactly the big notch on the 6X8?

 

[DoubleStud]

Really too bad, you could really ask for some deduction of the agreed price to fix all of this. This is really bad. Your floor is probably sagging and make a lot of creaking sound.

 

[RattlinBog]

DoubleStud, see attached updated section. Notch is +/- 6 ft from midspan steel post. Your question reminded me that I forgot about a wood post supporting the beam that's located in a little utility / breaker box room in my basement! The wood post is a little scary looking too; it's split down the middle...

I'm definitely long past any kind of negotiation. I've been living here a while. Like I said, it's a bit embarrassing to even talk about. I just need to get my head of the sand and get it fixed. There are a few (3-4) spots that creak, but I wouldn't say it's widespread. Regardless, I'm planning to reinforce the beam, several joists, and add bridging to help this floor.

 

[jayrod12]

The checking in the wood post also isn't as concerning.

I agree, no to the fixed-fixed. Where is the additional post? As I alluded to in my previous post, it's possible that the long span section of your beam (the 12.5 foot span) is only supporting main floor load, and not second floor load, based on the layout of the walls on the main floor supporting the second floor, but that would need some investigation to confirm.

I'd also expect that where there's the additional post, the beam calculates out just fine.

Have you reviewed the underside of the beam closely at the mid-span of the 12.5 long segment? It's possible there used to be a post there as well that was removed at some point, and since nothing fell down, no one cared. It wouldn't be the first time I've seen that.

 

[DoubleStud]

If this was my house, I would finish the basement and design it so that I have many walls right below the timber beam. I would first jack up the joists so that main floor is level. Once it is level, I would build "load bearing" wall below the beam especially by the notch. I put quotations on the load bearing because it is only bearing on the slab on grade. While this is not ideal, it is still much better than before.


The other option is to design it so that you have perpendicular walls roughly at quarter point (between fdtn and steel post). Put stud pack there and pour isolated pad. This will break up the timber beam span to half. You will also support the area where it is notched.

The damaged joists, this isnt as critical to fix. Maybe with additional walls you add, it will break the span of that joist.

 

[phamENG]

I agree with everything jayrod said except for the nails/screws. As long as you use quality screws and pre-drill (sometimes needed even for self drilling), it'll go easier than most nails. The nail may go in fine, but I've seen contractors crack old timbers as they drive the nail. Wood gets more brittle as it ages.

I don't have any experience with DF lumber - we're all Southern Pine and SPF around here - but I've found that the lumber values aren't going to be that much higher for old stuff. (I can hear the gasps and curses already!) Wood hasn't really changed much in the last few millennia. Sure, new growth stuff in some species can be a little less dense and that can impact the design values, but I haven't heard of that happening with Douglas Fir, only Southern Pine. Straight grain lumber is straight grain lumber, and a knot is a knot. I actually de-grade old stuff a bit because of the age and increased potential for creep-rupture in heavily loaded members.

The reason it's okay is because wood strength data has an absurdly high coefficient of variability. In order to ensure new structures are sufficiently reliable, wood design values are based on the 5th percentile of average tested strength of clear specimens. Then, they get grouped into grades based on direction of grain, spacing of grain, size and location and spacing of knots, etc. So there's a real possibility that a modern No.2 DF beam with an allowable flexural stress of 750psi has an actual maximum rupture stress of close to 2000psi. But it may also be 752psi, so we stick to 750. US codes don't have a great way to deal with this, unfortunately. It's left up to the engineer, which leaves the space open to a lot of folks to come in and say it's good because it's been here forever rather than develop a sound engineering basis for such an appraisal. At least one jurisdiction in Canada has a really good means of assessing existing structures by adjusting the statistics for the age of the structure. It's pretty neat. I think jayrod might know what I'm talking about.

I say all that to say that your beam is stronger than the code basis because the code is written for the design of randomly selected graded lumber. That's not what you have. Your beam is painted, which makes it hard to try to judge what 'grade' it should fit into. I'd say, once you verify loading, follow XR's advice and sister a pair of LVLs on either side of the beam, preferably full length. Make sure your existing beam can carry the dead load and at least 5psf of live load (whatever is reasonable for what you have in the house - you could be a minimalist or a hoarder, I have no idea) and design the LVLs to carry all of the design live load.

You may also want to consider finding an engineer locally that you can work with on this. Just like you wouldn't want a guy who's just done houses for 10 years to design a steel mill, a steel mill engineer may not be the most efficient at designing a house.

 

[phamENG]

Yes, I'm a bit embarrassed to admit it, but I did buy the house with notches already present.

Also, don't worry about it. Unless you have enough money in the bank for the house purchase to be comparable to one of us plebes buying a cup of coffee, it was an emotional time. It's the same reasons lawyers don't represent themselves and doctors don't diagnose themselves. These should be external, objective reviews and inspections.

Now, if you failed to get a home inspector, then you should hide your face in shame for all of time.

 

[ryaneng]

Now, if you failed to get a home inspector, then you should hide your face in shame for all of time.

Not to get off topic, but why do you think this is such a mistake? I bought my house without a home inspection, and have no regrets. Most of the home inspection reports I have read haven't provided much more context to the condition of a house than a thorough walk-through would provide.

 

[RattlinBog]

Attached is a clearer photo of the notch. Notch is 5" deep x 13" wide and tapers at an angle, so remaining wood depth is 2.5-3" at the thinnest and full depth at the end of the notch. It's an ugly, rough cut too.

Where is the additional post?

About 8'-6" west of steel post, which is an S8 (not S6 like I said previously).

Have you reviewed the underside of the beam closely at the mid-span of the 12.5 long segment? It's possible there used to be a post there as well that was removed at some point, and since nothing fell down, no one cared.

Yes, just looked again--no sign of an old post in that area. However, about 6-12" east of the S8 post is a circular indentation from an old round post/pipe. I'm guessing it was replaced with the S8.

I would finish the basement and design it so that I have many walls right below the timber beam.

Not a bad idea, but I'll try to stick with reinforcement and possibly adding posts. My basement is small and kind of a concrete dungeon. I don't have intentions to finish it, and I feel like a wall will make it feel tiny. I'll keep it in the back of my mind, though.

The nail may go in fine, but I've seen contractors crack old timbers as they drive the nail.

I'm a little nervous about that. I'll look into a few different options and see what the contractor thinks too.

don't have any experience with DF lumber - we're all Southern Pine and SPF around here - but I've found that the lumber values aren't going to be that much higher for old stuff.

I'm not confident about Douglas Fir...it was a bit of guess. Whatever wood it is, though, I'm not going to get the numbers to work out. I need to reinforce regardless. Thank you for the background info on the stress values.

follow XR's advice and sister a pair of LVLs on either side of the beam, preferably full length. Make sure your existing beam can carry the dead load and at least 5psf of live load (whatever is reasonable for what you have in the house - you could be a minimalist or a hoarder, I have no idea) and design the LVLs to carry all of the design live load.

I like this approach. I'm a bit ignorant about LVL specs and where to find them. I did a bit of digging tonight. I'm seeing Boise Cascade, Weyehauser, Louisiana-Pacific, etc. Is one of those more engineer-friendly (nice specs) than others?

You may also want to consider finding an engineer locally that you can work with on this.

I may reach out to a friend from the consulting firm I used to work at. I live in a small town, and most firms/engineers are doing heavy industry work. I don't know a "go-to" residential engineer in the area.

Now, if you failed to get a home inspector, then you should hide your face in shame for all of time.

I detect a bit of tongue in cheek--haha--or maybe I'm wrong. We did hire a home inspector, but he didn't catch any structural issues. He caught some nice electrical problems that previous owner fixed, though. I think this notch was just kind of a case of bad luck / lesson learned / should've been paying better attention scenario. The basement used to be poorly lit before I put up some LEDs. The beam where the notch is located is unpainted and dark/dirty. It seems ridiculous now, but it was easy to just walk by it.

Thanks for the help everyone. I'll do some studying on LVLs, come up with a couple reinforcement options, and start reaching out to contractors.

 

[Goatenstein]

Most LVL manufacturers do a good job being "engineer-friendly". Almost all LVLs are manufactured to a 2.0E specification with only slight variations in fb values from company to company. If you want to be conservative, design the LVL assuming it is made by Weyerhaeuser. Their LVLs have an fb of 2,600 psi, which is about the lowest in the industry.

 

[RattlinBog]

Thanks Goatenstein--makes sense to go with a conservative Fb.

I have another question for those with more experience on this. See attached calcs for section properties and strength at my 6x8 beam notch location. Note that I doubled loads acting on beam to include 2nd floor loads. Using software for structural analysis, I updated my FBD to include the wood post that's 4 ft from west end. My notch is 6.5 ft from west end, and I'm getting M = +1.84 k-ft and V = 0.2 k at notch. Section properties at notch are Ix = 84.8 in4, Sxtop = 17.7 in3, Sxbot = 31.4 in3, Q = 20.3 in3.

Assuming Douglas Fir-Larch Dense No. 1:
fb = M/Sxbot = 703.2 psi and Fb' = 1400 psi, so bending utilization = 50% at notch
fv = VQ/It = 9.4 psi and Fv' = 170 psi, so shear utilization = 5.5% at notch

However, should I be reducing my Fb and Fv to account for the notch / reduction? My Ix went from 193.4 in4 to 84.8 in4, which is 43.8% of original. Should I take 0.438*Fb and 0.438*Fv? I'm not trying to go crazy sharpening my pencil here, but a reduction in Fb would make a big difference. This shouldn't change how I reinforce this beam too much, but I'm still curious.

 

[ChorasDen]

My Ix went from 193.4 in4 to 84.8 in4, which is 43.8% of original. Should I take 0.438*Fb and 0.438*Fv? I'm not trying to go crazy sharpening my pencil here, but a reduction in Fb would make a big difference.

Check 3.4.3.2 of the NDS for stress concentration reductions at notches. I believe NDS applies these specifically for shear design, but I would consider the same approach for fiber bending as well. Keep in mind those approaches listed in NDS aren't intended for such severe notching, so care should be considered.

I disagree about the lack of concern about the rupture in photo 8 of the original attachment. Appears from here that it is tension perp failure, and if it's across a large portion of the section, it will dramatically affect the performance of member for design.