Earthquake Retrofit an Old House, by Greg E.

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2011 was a year of deadly and devastating tornados, and an earthquake that shook the east coast.  One of the largest tornados hit a suburb in my county in the Birmingham Alabama area. We are also only one state over from the New Madrid earthquake zone that starts in the Memphis area.  After taking several closer looks at the foundation and basement of our 50 year old house, I realized we were living with a false sense of security.

After researching online, I learned that in certain large events, mainly earthquake, but also from high winds, if the house gets shaken, the metal [pier] poles holding up the center of the house in the basement may or may not move in unison with the rest of the house above them that they are supporting.   Our house [has a conventional perimeter foundation and aside from the perimeter it] is simply sitting on those poles, and that is it. In large earthquakes, houses with basements can simply fall into the basement below them, if the support poles [or posts and piers] do not stay intact. I set out looking for an easy fix, and discovered nothing readily available on the market for this situation.   Maybe in frequent earthquake territory like California, there might be something on the market, but I did not find anything at the big box hardware stores or online. 

It appeared it was time to get creative. I am not in the construction business, but I’m guessing I do have a few more tools than the average household. My small shop has a miter-saw, table saw, drill press, chop-saw, and a small, bottom of line wire-welder. There are lots of people with way more tools than this, but this is a modest amount and I’m comfortable using them.   I spent a much of my time staring at the rafters and those metal poles, knowing there had to be way to tie them together.
The goal is not to keep the house from swaying, but rather, if the house is swaying, the poles sway in unison with the house. This way, when the house stops swaying, the metal poles are still in position as there were intended, holding up the center of the house.   The metal poles of our old house are 4-1/2 inches in diameter.  A double row of 2”x10” rafters run lengthways of the house, with 2”x10” rafters attached perpendicular to them.   These perpendicular rafters run from the center of the house out to the foundation. I would like to have been able to tell you that all of the rafters are evenly spaced, but they are not. Wiring and plumbing run along the bottom of the rafters, and it appears that plumbing had a major say-so in what rafters went where.   Sure, there are a few rafters that are evenly spaced, but quite a few that were placed very close to another rafter to accommodate the plumbing.

So, in staring at the poles and rafters, I obviously needed something to attach to the pole, and something that could be attached to the rafters, and each of these had to be able to be attached to each other.   Oh, and in my case, cost was an issue. To explain: most of those tools were bought before we had kids. Now my paycheck is spent before it gets home. And in this economy, it’s not getting any better either. I wanted to make the house a little bit safer than it was before I started, and yet still not break the bank. Besides being on a tight budget, time is precious these days too, and I can only work on this project on the occasional, rare, weekend free from other events begging for priority on the calendar.   

I knew I could drill holes in the wood, even if I have to use a right-angle attachment to do so, to mount some type of brace. As is ‘just my luck’, some of the closest together rafters were the ones near the poles I was going to be working on. But, what kind of bracing to use?   Flat aluminum or steel [stock] is readily available at the hardware stores, but in an earthquake, you never know for sure what direction the house is going to be shaking in. Nature has a tendency to keep that thing called the ‘epicenter’ to herself and let the scientist figure that one out later. Angle iron has support both vertically and horizontally. Luckily, and beloved neighbor, ‘Joe’ had given me some scrap angle iron before he passed away a couple of years ago. I still had the rusty angle iron in the shop, and I would need to clean it up with a portable electric grinder and a wire wheel attachment on a drill, but it was free, and I had plenty of it to do the job. I love to recycle, and re-using this free angle iron for my project is better than it getting sold for scrap.  I wanted to clean up the surface rust and paint it to roughly match the gray color of the poles. The drill press would eventually come in handy for the angle iron too. 
I did some research on eBay, and found that the do make U-Bolts in the needed size, but due to the size and weight, the shipping and handling were going to cost more than the U-Bolt. I discovered that one of the auto parts chain stores carried the 4-1/2” U-Bolt on their web site. The highway nearby has just about a half dozen auto parts stores within a 15 minute drive.  The auto part store that had the U-Bolts had them at a very attractive price, and they would ship them to your local store for free.  Bingo. This way I could get the U-Bolts at basically the same price as I’d seen on ebay, but without the shipping and handling costs.   The auto parts store only needed a couple of days to get them to the store.  This worked out great for me, because I ordered them early in the week, and wouldn’t be using them until the weekend anyway.  

The large 4-1/2” U-Bolts are made out of steel that is 3/8” diameter. I could drill 3/8” inch holes in the angle iron, to attach it to the U-Bolt, and additional holes to attach it to the rafters.  I wanted angle iron on each side of the pole, where-ever possible, for the push-pull effect that an earthquake might cause.   I also wanted to put two holes in each piece of angle iron where it attached to rafters, so that it would be rigid enough to move the poles with the house.   If I were to only put one hole in each piece of angle iron where it attaches to the rafter, it would like just be a pivot point and the angle iron could easily let the pole shift away from the center of the house.  

I wanted to paint the U-Bolt, and angle iron pieces, because they would be in contact not only with each other, but also with the metal pole. Although in this particular instance they are all steel, I’m not sure what kinds of steel they are.   I’ve learned that dissimilar metals that are in contact with each other can vastly increase the oxidation (rust) rate of the metal. As a side note, always be aware if you are using aluminum, steel, and any alloys, that are touching or are bolted to each other, as this can oxidation can become a real issue.   Don’t think that aluminum oxidizes?  Next time you are in a salvage yard, look at the chalky white powder on some of the aluminum parts you see is oxidation. It just doesn’t turn dark like steel does when it rusts (oxidizes).  

I made a dry fit of the U-bolt to near the top of the pole, about 3-4 inches from the top. I wanted to keep it near the top for leveraged strength, but not so near the top that if it did attempt to sway in an earthquake that it would try to jump over the top of the pole. Measured the lengths I needed for the angle iron to have a piece on each side, and cut them with the chop saw.  Drilled them on the drill press, then painted all of the pieces and let them dry completely. In keeping with the recycling theme, I was able to use up some old cans of [rust preventive] ‘primer gray’ color that matched the existing gray color of the metal poles well.   

The U-Bolts come with a bracket that fills in the gap of the opening at the open end of the ‘U’, and with the two nuts needed to hold it all together.   When measuring for bolts to use on the rafter, take into account not only the thickness of the rafter, but the thickness of your angle iron, the nut, and washers.   I recommend using washers on sides of the rafter, where the bolt head is and on the other side where the nut meets the angle iron. I even painted the washers, in case they are a different metal from the angle iron.   Who knows, a few seconds of extra painting could add years to the project and protect the old house for the next generation.  

Are there better ways to do this project?  Sure.  Are there more expensive ways to do this project?  Sure.   This just happened to be the best fit for my situation, of wanting to build a little more safety into a 50 year-old house, without having to take out a loan to do it. Maybe you can adapt some of these ideas into your next project.

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This page contains a single entry by Jim Rawles published on October 26, 2011 5:52 PM.

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