Retrofit Bolting of Houses without Cripple Walls is Simple, Affordable, and Effective
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- Опубліковано 6 вер 2024
- www.bayarearetr... Houses on level lots without cripple walls still need a seismic retrofit, even if they are bolted to the foundation. If your house was built after 1950 or so, and you know it is bolted according to earthquake provisions of the building code with a half inch bolt every six feet, (which was and still is the code) then go to • Retrofit bolted homes?... to see how these bolted homes can benefit from a seismic retrofit.
However, many houses on flat lots do not have any foundation bolts; bolting did not become California State Law until the late 1950s. Up to then, some cities required house bolting, and some didn't. The way you find out is to crawl under your house, put your hand on top of the mudsill and see if you find any bolts. If they are spaced 6 feet apart then your house is bolted according to the current California Building Code. If not, you need a seismic retrofit that targets bolting the house to the foundation.
Houses on level lots without bolts are attached to the foundation with a type of retrofit bolting hardware peculiar to homes where the floor sits directly on top of the foundation. These homes usually only have 18 inches of crawl space under the floor so normal foundation bolts cannot be installed. This hardware has undergone rigorous testing and is certain to be effective in an earthquake and is the only retrofit hardware used by Bay Area Retrofit. Use of tested retrofit hardware is essential to a good retrofit. Another very important seismic retrofit components are called shear transfer ties, which are also thoroughly tested.
Some companies such as Quakebusters, EarthquakeSafety, and many others use a retrofit strategy called angle irons in lieu of the tested systems shown here. Angle irons are an untested system and are discussed in Video 13 • Angle Irons and Untest...
Extremely helpful! I am about to call an earthquake retrofit company, now I know exactly what to ask for! Thank you!!!!!
Nicely explained so that most any homeowner can understand it. When the ground starts to move, it's easy to remember how Newton's First Law applies; a house at rest wants to stay at rest (in other words, in the same spot, even though the ground is moving below it).
It really is as simple as "How do I keep a box from sliding off the table when I shake the table"
Interesting video and informative, but your basic premise referenced throughout the video regarding the source of the energy in earthquakes is backwards. You present earthquake scenarios as the earthquake acting on the house, then the various bolting strategies transfer that energy and movement into the foundation and finally into the earth. This is of course reversed. Forces in an earthquake come from the earth, into the foundation, then finally into the house. The house is last, not first. For example, 4:40, you say, "...when the earthquake force tries to slide the house to the right...". That premise is incorrect, the earthquake force tries to move the foundation to the left as the house sits still due to inertia.
All of the bolting schemes attempt to keep the house from getting shaken off of a moving foundation. Inertia tries to keep the house still as the earthquake moves the foundation back and forth. Bolting ties the house to the foundation so the house moves with the foundation and does not fall off of it. A properly bolted house will move more violently in an earthquake, but will hopefully still be sitting on the foundation when the shaking stops. More of your belongings in the house break, but hopefully you still have a house.
If you were talking about keeping a house attached to the foundation in a severe wind storm where the force acts on the house, not on the foundation, you'd be correct.
Good info otherwise though.
You are correct and if you read the text on called "How to retrofit a home built before 1940" this is clearly explained with an illustration. No matter how you explain it the net result is the same. The force of inertia must be resisted when the ground accelerates and then stop is the same if you describe it as force attacking the house. Engineers and contractors describe it as pushing against the house because this is so much easier to conceptualize.
From a conceptual and design point of view the way ground movement and inertia work it is exactly the same as if the house were being struck by the force. It is a semantic difference and nothing more. Go back to the website and look at the page on retrofit engineering. I explain all this at the beginning because I keep hearing this comment over and over again.
This guy does not know a foundation sill plate from a mudsill. This type of wrong information stays in the trades for some time. ALSO this type of property more than likely already has enough existing original bolts. Get at least three bids before you hire someone like this.
@@jamesgillett2255 1950's houses definitely do not have original bolts. My house has zero bolts, is a very common style from the 40's through the 50's. This video is not for a modern house - meaning 70's on up. I am far from a expert and it would sound like you may also be in a different trade?
THANK YOU HOWARD, VERY HELPFUL TO UNDERSTAND EARTHQUAKES AND RETROFITTING .
Do you know of any sheering hardware that works for houses without mudsills?
What about 100 years old 2 story house will those mud sill get rotten?
I understand the value of adding foundation anchors. Do you also add the transfer ties?
Which brand or type of sheer transfer tie should we use?
Also on the horizontal portion of this sheer transfer tie, that is, the part being nailed into the mud sill, what do we do if there’s not enough headroom to nail it in?
Those retrofit foundation plates that homedepot sells are very very overpriced! They're 16 gauge galvanized, and they want almost $30 each. They're light and flimsy. It's cheaper to get yourself a piece of stainless plate and drill a few holes in it on your drill press, and use that as a foundation plate. At least it won't rust away after 20 years like 16 gauge metal will. Anyone with a plasma cutter can cut 20 or 30 plates for you in probably less than 20 minutes. And you can probably find a partial sheet of some 1/8" or 1/4" stainless plate used for less than a couple hundred dollars. Compare that to 30 simpson foundation plates at a cost of $900. Total ripoff
...except, few people know anyone with a stinking plasma cutter ;) The simpson plates are at least tested and easy to get through local building inspectors. If not dealing with a inspector, you are on track
At 6:56, the video identifies that a two story building weight is about 80lbs per square foot. Your diagram shows 1000 square feet, which should mean that (assuming it's also a 2-story building), 80,000 pounds of earthquake force, not 16,000 pounds. Even if this was halved for a 1 story building (improbable due to the roof weight), the the force would be 40,000 pounds, not 14,000 pounds. Something here is not adding up.
No, look again. You need to multiply 80,000 by 0.2 G-Force factor. Which gives 16,000 pounds. Each side resists half of that, or 8000 pounds per side.
You did not look at the part of the video that explains the engineering. If a house weighs 80,000 pounds and this IS MULTIPLIED BY THE 0.2 Gs ground acceleration you end up with 16,000# of force. Please watch the video one more time. It is very clear.
It is 80 pounds for the foundation footprint. It is correct. Actually, this number is off as there are many variables that have an impact of weight. Go to www.bayarearetrofit.com/earthquake-retrofit-engineering/ if you want to see how it really works.
It is 80 pounds per square foot of the second story foot print. It is 80,000# of WEIGHT, not force. The 80,000# is multiplied by the anticipate ground acceleration of 0.2Gs. I thought I made it clear. Please read it one more time.
Nice but what if you have a slab foundation with those hollow concrete blocks on top
Geeeez, sounds tricky. I would not know what to do.
Sounds scary. Never saw one of those.
Standard type of construction in many areas of the country also. Experienced builders have the answers for you. So shop around for people who actually do the work them selfs not these college pukes posing as builders. /// You can rent or find a meter for under $100 at Home Depot to measure the placement of bar in the grouted blocks. Do your own survey and sketch work unless you have a few thousand dollars for an engineer to do that work for you. It is easy work overall.
Thanks, this is a very well made video, very informative.
A few thoughts: 1. a little puzzling to think of the force going from the house down to the foundations, as commented below by elephantcup I expected the opposite [on reflection, however, you probably had in mind the effect of gravity]; 2. where I grew up houses are made of bricks and/or concrete from the ground up, so it's surprising to see houses made of wood and without proper nailing of the different parts! 3. after you've properly attached your house to the foundations, don't you need to check whether the foundations are strong and/or do something about the forces that will be applied to it? In some of the footage, the foundations looked weak, wouldn't a proper retrofitting involve recasting that in modern concrete with steel reinforcement bars?
Existing foundations are almost always stronger than the wood bolted to the foundation. Either the bolt will fail, the wood will fail, or the concrete will fail. Even intuition will tell you concrete and steel are stronger than wood. Go to the website and type in SEAOSC and read the full report on this published by the Structural Engineer's Association of Southern California.
Foundations are almost never a failure point. Do a search on "Old Foundations" on the website.
@@BayAreaRetrofitTV SAEs often have engineers with little or no experience in residential wood frame retrofit work these days. Most of our SEA members here in Northern California try to crib that super expensive over built city of San Leandro planning department mess that became the Berkeley Plan Set A disaster for anyone willing to pay for a structural engineer. In fact SEAoNC got that mess codified for gods sake. It costs home owners many thousands of dollars more than or in place of standard retrofit practices. Much of the most recent or Latest Developments such as some mess titled a Napa Advisory are poorly put together. It is easy to see where little or no actual hands on experience working in crawl spaces composed or helped guide some of this crap going down as gospel now a days. The days of S.E.s actually having some experience doing this work, keeping design costs down are long gone. Go to Civil engineers to find people with actual experience doing this work. Chances are that you can ask 20 wood working group members of the local SEAs in your area if they have ever done one of these jobs or even been in a crawl space one time to find an answer of "uh no" from every last one of them. It is not the old days of working with great engineers any more. Most of the S.E.s around the bay area are sadly lacking in experience. They are the ones to call for tall commercial buildings just not residential or older structures.
This was a good, informative video. I would encourage you to edit it so it doesn't seem like you're using a walkie talkie to narrate. The content was top-notch.
Great video! I have a one story home with basement and have added Simpson strong tie 7x9 retro plates since my sill sits on my foundation wall. My question is - What is the correct spacing for those strong tie a35 transfer ties/angle brackets? Directly above the flat plate? On either side? 2 ties for every plate? Have seen different configurations in different videos. Any help would be appreciated. Thanks!
32 inches on center for a one-story house according to the LA Standard Plan Set #1 Chapter A3.
Read the section on the base shear formula
A-35s with a palm nailer install at the very edge or boundary of lumber framing. The palm nailers drive the Simpson N-8 nail in at a toe angle nail. This can split the joists blocks or top plates easily. Some buildings types built with post WWII lumber will split faster than full dimension older old growth heart douglas fir on the West Coast. Use an L bracket such as the L-70 or the L-90 with the N-10 nail to keep from ruining the blocks to top plate connection instead. And you can use much less of them also. The A-35s are a mark of inexperienced builders or those careless to any splitting or destruction of framing lumber. You can refer to the KCSM Video that went coast to coast on PBS stations in the early 1990s. It is the video copied by many of these new age You tube experts. The title of it was Earthquake Home Safe Home.
Yes that plan set has problems too. A-35s have no place in retrofit work except for being dirt cheap each.
@@jamesgillett2255 Simpson Strong Tie recommends the A-35s in there retrofit guide: embed.widencdn.net/pdf/plus/ssttoolbox/daokkfyn2v/F-SEISRETRGD12R.pdf .I have old growth redwood and plan to screw them in. I will test to verify your observation.
Very nice video! Thanks for providing it.
I've been looking into doing a seismic retrofit of my 60 year old ranch house located in the bay area. Your advice in confirmed by others. Actually, some other sites reference you!
I notice that some of the pipes under my house are not supported very well. Specifically, I have a long run of copper pipe that has very few hangers. Is this a problem if there is an earthquake, or is the copper flexible enough to move around assuming the rest of the house stays affixed to the foundation?
Thanks again, and great job with the videos!
Don't worry about the pipes, we see this all the time. Cheap and easy to fix but I see no pressing need.
Notice the lack of safety gear in that area such as a basic barrier between the dirt and the work people. Then again when you employ day laborers there may be little need to keep them safe with barriers, good ventilation, enough lighting etc... Look for builders who actually know what they are doing, the men who do their own work. These college pukes posing as builders are a plague on most trades in the area and the country in general.