Here on the South Oregon coast, we are in, according to the IRC codebook, siesmic category D2….same as LA area and due to a subduction fault zone with a geologic history of catastrophic earthquakes.
So to build here, foundations are typically engineered for the seismic forces, not to metion 110 mph wind loads.
The custom home I am currently building, a two story which includes a daylight basement with living space on both floors and a 10/12 roof (and a lot of vacant attic space), is a warren of shear walls and seismic hold-downs.
My dilemma is as follows: In this structure, there are 40 (forty) Simpson PHD holddowns specified (PHD 2’s thru 8’s) on both the exterior walls AND on some of the interior walls.
PHD hold downs are secured to double-stud framing after being bolted to, typically, SSTB28 or SSTB34 7/8″ hold down bolts which are imbeddend in the foundation to a specified imbedment line (scored on the bolt). Their initial placement has to be quite precise to meet the vertical loadpath specified by the engineering. This is often at corners, at windows or at door frames.
Along comes the homeowner and decides that a different window would be better, or the location of a door would create beTter “flow.”
Aside jack-hammering out a LOT of concrete, does anyone have a solution for an effective and, structurally effective way of relocating these anchors.
Replies
I think you should talk to your engineer. What we've done in the past is to drill and expoxy all thread. Sometimes you can't, but your engineer will know if and where you can.
That's what I've typically done in the past, but, intuitively, the finished strength of the epoxied all-thread seems somehow lacking when measured against one of those long hold down bolts, which are hooked around the footing rebar.
Yet, to be honest, in a reasonably modest residential structure, is there a lot of major overkill here?
The basement foundation on this housae (3300 sq. ft.) has a 10' X 10" concrete backfilled foundation wall, with #6 vertical rebar on 7 1/2" centers and #6 horizontals on 12" centers.....all this atop a footing that is 6 feet wide, 14" deep, with a 10" keyway underneath the footing where it bears the high wall.
This project is near the top of a ridge, with no higher elevation earthmass to effect the forces of immediate backfill.
I don't mean to sound like I'm whining; it's a nice project with great clients who are a pleasure to deal with and, for the most part, stay out of my hair....kind of like that rare waitress or waiter who you never see until you want something.
And I'm starting to wonder what my question is here. (maybe an age thing).
But I've built about 4 houses dealing with this issue. On the first one, I just wasn't careful about placement of the holddown bolts. It led to some time-consuming extra framing.
But on subsequent projects, HO changes, often practical ones, created misalignment of the bolts with the finished loadpath. Of course I bill extra for the changes, but dragging an engineer into numerous change orders just feels like a lot of money is being spent for A$$ coverage.....
Here's a photo of one, properly done.
I agree with you that it is hard to beat the strength of embedded anchors. The epoxies that Simpson sells and Hilti sells are very strong. I know that they use them in commercial applications. It may not be as strong as the anchor, but it may be strong enough in your case.
I do love those PHD holddowns though. They are much faster and easier to install than many of the other holddowns.
If the seismic sections of your plans have a PE stamp on them, neither you or the homeowner get to change things without the engineer signing off on the change(s). Only the engineer can evaluate the effect of a change on the seismic integrity of the structure.
This is too true especially in my little backyard of Sunny SoCal. We move a lot of openings, and add and subtract them, but always with a letter from the engineer of record. Usually on the large customs that we do, I overkill to the tenth power the number of anchor bolts and upgrade the shear panels and the nailing schedules. We usually get a little extra credit for this. We have used a lot of epoxy and retrofit bolts per engineering requirements, so don't discount their strength. You understand of course. that in today's business environment, construction is less about building things and more about avoiding liability. And all these ultra cool engineering theories and computer models that produce them will mean squat when that 9 point fiver rolls through here on the next go around.
If you get a 9.5'er down there you'll have way more problems than some structural damage. If memory serves me correctly, not even the San Onofre and Diablo Canyon nuke plants are designed for 9.5. You could certainly build a two bedroom ranch to survive a 9.5 but only Bill Gates could afford it. - lol
As someone with both PE and GC licenses, I get a kick out of these Engineer v.s. Builder debates. Unfortunately, it's pretty rare when either "side" has a good understanding of what the other one does - or how and why they do it that way.
Early in my engineering career (mid 70's), I was lucky enough to spend most of my time in the field working directly with the construction crews. Seeing how things actually got built gave me a very different perspective than my office dwelling contemporaries - and I think it made me a much better engineer. On the flip side, I was often able to explain why something was engineered like it was and how it really did make sense. I also like to think that some of the construction guys became a little less inclined to start cussing the "damn fool" engineer.
It's all about communication, so give the engineer a call and talk about the changes. It can't hurt and it may result in a better job.
After 28 years of beating nails into lumber, you can believe that I have talked to plenty of engineers. I agree that the ones who have spent some time out in the field with the framing crews are far easier to get along with. Almost all of what I know about seismic forces and how they react with a building envelope come from those enlightened ones. However, on any one project I have to deal with the engineer of record and what drives me crazy is the lack of any kind of consistency among the ranks of those who engineer these buildings. Last year I did two homes for the same builder. I did them 8 months apart and the plans were identical in every detail that matters. They were within a mile of each other on the same street. The only thing that was different was the engineer. When I got the engineering specs for the second house, it was like a whole new house. At least double the hardware and much of it industrial. I went in for a meeting/screaming match with the architect and two weeks later we had a revised packet that was identical to the first house, signed and stamped by the same engineer.
What I have noticed, is that when I have a major complaint about something that just will not work in the 3 dimensional world that I inhabit, suddenly it disappears and we are provided with an alternative that should have been there all along. Say what you will, it stills smacks of smoke and mirrors. And then there are the building inspectors, but hey, look at the time.
> not even the San Onofre and Diablo Canyon nuke plants are designed for 9.5.
Nor has there been a 9.5 anywhere on earth in recorded history. The largest ever earthquake, IIRC, was a 9.0 in South America.
While the Richter scale theoretically is open-ended, the amount of energy available for an earthquake ultimately is limited by the size of the earth. One of many mistakes in that made for TV movie about a 10.5 earthquake is that a quake that large could only happen on a much bigger planet, like Jupiter or Saturn.
-- J.S.
Adhesive anchors are the answer. Attached is a link to ITW Ramset/Red Head's A7 Acrylic Adhesive. Use this with standard threaded rod.
http://www.ramset-redhead.com/a7prod01.asp
Kind of a closing-the-barn-door thing, but I wonder if a partial solution (in the future) wouldn't be to overengineer things to start with, so you can tolerate the removal of a few anchors.
Notchman,
I don't think that you are seeing to right dilemma here.
I think you need to look back to the contract and implace a section dealing with change orders. IMHO, it should require that all CO's be signed off by an engineer and since engineers get paid all proposed CO's must have a fee paid before they get sent to the enginneer. You don't even start to estimate a CO until it comes back.
Even something as seemingly minor as adding 2" to the width of a door or window can be a nightmare in your area.
When the location of almost every stud must be detailed to the 1/8" before the foundation is poured, it means there are no minor CO's.
SamT
I worked a long time in CA, where seismic retrofits of older homes are common. The typical method is to drill and epoxy bolts. There's no doubt that the stab anchors are stronger, but the epoxied bolts are incredibly strong too. If they move an opening and interfere with a load path, that's basically what you have to do. It's not a bad idea to orient the owners to this issue in a preconstruction meeting. Show them the structural pages and explain the fact that the load paths are created starting with the formwork, and that changes later are either expensive or impossible.
Did you say the footer is 6 feet wide??
Hi, I am in the same siesmic zone that you are in. I deal with the same hold down headaches all the time. The house I'am just finishing the home owner wanted to move two windows closer to the corner to eliminate parts of a exterior shear wall and two phd 5 hold downs. My standard reply Is yes of course we can do that .But lets get the engineer to sign off changes. I have a good working relationship with my building insector and plan on keeping it that way. Call the engineer It might seem like a pain but I'd rather cya. Pat
Simpson has all the information you need to retro-fit holdowns. The size of holddown will have an uplift and tension values. They also have values for threaded rod epoxied into concrete. Your biggest problem is if you already have the sub-floor on is spending some big bucks on bits. You might need to embed the bolts up to 12" deep. (30"-36" bit length.) I just started working on a project on San Juan Island in WA that has a s**t load of HD15s. 1 1/4 anchor bolt with 5 1" diameter machine bolts. The engineer spec out a-35s @ 3" o.c. and a a-35 is 4 1/2" long? Shear nailing on that wall was 3" nails @ 2" o.c. I'm going to take some pics next week and post them for all to see, some crazy stuff.
Welcome to the island. Where are you working?
Roche Harbor, Fairbanks Construction who are from Bainbridge are building these two bedroom cottages, 1400 sq. ft, 3 stories. Working 40 hrs in four days but we only get in eight the first day because of travel, So not any time to enjoy the Island, would like to go back in the summer time for some fun instead of work.
I've been working at White Point for quite a while and go by Roche occasionally for coffee or lunch... I've seen those units going up above the DeHaro. Let me know if they're looking for help with the trimout there.
I just started helping them out with some frameing, but there are at least two supers on the job, I would just stop by and talk to one of them. I'll be there in the AM. I'm working on the first house right on the road, stop by. Jeff