Earthquake construction

[Hotzcatz]

Anyone wanna bet they add new restrictions to the building code for earthquake modifications now?

From what I've heard, folks on slab construction had much sharper jolts from yesterday's earthquake than folks on post and pier. On post and pier, the whole building sorta does the hula instead of the jitterbug. In Honokaa, reports are if it was made of concrete masonary units (CMU blocks) then it sustained damage, but I haven't gone to look yet.

Should cabinet doors have locking mechanisms so they won't shake open in an earthquake? Every door and drawer was shaken open, not only in our house but our neighbor's houses as well. Should shelves have a small lip on the front to keep stuff from shaking off? Should TVs and monitors be secured to their bases?

Should there be a length of flexible pipe on plumbing connections between the ground the the house? Should all supply lines going into a house be in a real easy to access spot so they can all be turned off at once in cases of emergency?

Some friends who are building up the hill have all their stuff on those stainless steel racks from Costco with rollers on them. She said nothing fell off the racks, but they could watch them roll back and forth. Her husband had been watching some large rocks in the yard. When the earth moved, the rocks didn't. Mass and inertia, just basic physics at work.

A lot of folks in Kona on concrete slab have their floors cracked in many places and their walls cracked as well. Concrete, concrete blocks and drywall have no flexibility to them while wood can bend for quite a bit before breaking. Steel is flexible to some extent, but how far can it bend before it stays that way?

Personally, I'm really glad we replaced the original foundation rocks with strapped concrete blocks several years ago. I don't think the house would have survived if the posts hadn't been attached to the blocks. Well, it might have survived, but it would have been quite crooked I'd think.

Anyone have any good ideas on how to build houses to survive earthquakes?

[Fishboy]

Cat,
I don't know much about building for seismic standards, but how a building withstands an earthquake is also related to whether it's built on bedrock versus soil. The physics has to do with the propagation of the wave through different media, but soil tends to move around in waves during earthquakes and bedrock just jolts. The difference is so obvious when you're in a building! A house built on bedrock will get shocked, but not roll around unless the earthquake is REALLY big.

Stay away from the big cracks in the ground ,
Brian

Edited by - fishboy on 10/16/2006 13:33:56

[nanasohana]

When we were building those shear walls and putting on all that strapping and anchors and ties etc., I admit I thought "this is such overkill" but as I was standing outside behind our house at the precise momment the quake hit and watching our house while keeping my balance, I was not thinking that...I was really glad.
I think any and all you can do to try to tie your house together from bottom to top is crucial. And anything to keep the house from that side to side movement or racking like with the shearwalls that run from bottom to top at each corner. I like the idea that if the house has to say dance a little on top of the ground, it would be able to, instead of being part of the ground and being at its mercy. I think l level homes would fair better. I think plywood sheathing on the roof instead of just purlins. And no ceramic or stone tile on the floor or stone or granite on the counters. And indeed securing bookshelves and tall furniture to the walls and securing large TVS somehow. Secure clasps of somekind on the cabinets to keep them from flying open. But if the really big one hits, I doubt if anything would keep from being damaged to a point.

[Rob Tucker]

Being firmly attached to the ground is better than having a building dance around.

There's only so much dancing a building can do and earthquake effect can be cumulative. That means that the effects of this quake may make the building less likely to handle the next one. Those wiggled and loosened nails usually stay wiggled.

The bad situation is like the one in the news where the chimney came down in Honolulu. Wood frame and masonry react differently to the seismic wave and end up beating each other to a pulp. When that stone chimney fell it only did so after whacking the heck out of the building frame.

I've been through enough earthquake recovery efforts to be fairly familiar with it all.

[HADave]

Is it not true that the Japanese Pagoda style structure remains quite quake-proof?
I believe they were built around a tall interior mast which hangs in the center supported by chains. As the pagoda oscillates in an earthquake the mast does not, acting as a damper to counteract drift. Sometimes the masts are fixed into the ground, helping to control excessive drift through their natural felexibility.

Also if memory serves me right they also pointed out that heavy roof systems were not the answer for safe building in eathquake territory, so will the 06 IBC, with it requirement for heavily sheathed roof framing, as required for hurricane protection, really be such a smart idea in an area where earthquakes are more prevelant than hurricanes? just my lame opinion but I looked at the new 06 codes as a backdoor approach to impact fees...through taxes

Aloha! HADave

[Kapohocat]

HADave, you hit the nail on the head so to speak!

Hurricanes and earthquakes act on totally different components of the structure. As we know, an earthqauke works from the ground up, a hurricane typically tears roofing off first. More damage is caused when the quakes get to the harmonic moment (a roller) than a jolt (a shaker)...

I disagree that post and pier is better in a quake.... but then again it is MHO. I do think once those nails start to pull loose, it eventually reaches a point where the tie will fail. And at the moment, the termite treatment (borate) causes the galvinized hanger nails to react with the metal ties and fail. (buy Zinc coated ties where ever possible)....


-Cat

Edited by - kapohocat on 10/16/2006 17:15:49

[Carey]

Dave, from all of the references I read, when we thought about building, you are right about the roof, EVERY seimic book I read (most printed 2002-2004) stated that for earthquakes, the lighter the roof the better, but we do also have to consider the widespread potential for high wind events....(kind of a no win, eeny meeny miney moe)
Many of the references repeatedly stated things like the more symetrical a structure the better (offset levels and L's or T's in a building layout make for easier fracture zones). Some biggies that were evident on the Kona side, take care when tieing a structure together ie. addition to an older house should be integratal in the connections, brick, block & stone masonery must be reinforced, and any masonary alongside a structure must be tied in. any land build up with retention walls was a good failure point potential (as was seen frequently in the pics from yesterday).
The info I used were all seismic handbooks that industrial architechs use (our old neighbor was one, so I was able to raid his bookshelves before we moved... earthquakes were/are our biggest trepidation, so I spent time researching the buggers)
Aloha, Carey

[Hotzcatz]

I'll chime in for Dave's "light roof" construction. If anything is going to fall on me, I don't want it to be heavy. Also the more weight at the top of the swing has got to put more stress on the walls holding it up. Our roof is very light with just tin on 2" x 4" rafters at 4' on center with 2" x 3" purlins at 4' on center and that's about it. Doesn't weigh all that much and should it fall, I think we would be able to crawl out from underneath. Bruised and battered no doubt, but still crawling, one would hope. The eaves are only about a foot and a half wide which is odd, but the house was built about 100 years ago and getting supplies up the coast was a lot harder so maybe they built to match the tin they had available? Anyway, the eaves are narrow enough that the roof may survive a hurricane, too, I dunno. Wish they were wider for day to day sun on the side of the house protection, though.

Puna and Kona have almost no soil, so if the house is directly attached to the ground, then the house would get the earthquake shocks directly. I would think some sort of gravel base or something which could shift sideways would lessen the shocks going to the house. Maybe double the 6" gravel base to 12". That should help the house structure shift - if it is slab construction - and lessen the impacts but it would stress the inground plumbing connections.

We have two houses here built side by side both where the bagasse pile was from the old sugar mill. One house was built on a standard 4" thick concrete slab/6" gravel base and it has had extensive cracking from the lack of ground support under it. The other house is on a "floating" concrete slab, with enough concrete and rebar in it to make it self supporting without much soil support. I'm thinking the house on the "floating" slab will have had less damage than the "standard" slab, but I haven't gone to look yet.

I personally don't trust Simpson ties and nails to be the only thing holding the joists up. It isn't any harder to set the joists on top of the beams than to face nail them with Simpson fittings, so unless the homeowner absolutely demands the joists be face hung, I always put them directly on top of the beams. I think people are beginning to rely too much on these metal ties and straps. IMHO a house should be built so it is structurally sound without the clips, ties and straps. You can add them, you are required by code to add them, but I still don't trust them. Maybe fifty or a hundred years from now, then I will consider them a "proven" building system, not that I'm going to be around then anyway.

I dunno, with post and pier foundations, you can go look at the foundations and if nails were coming loose, they can be nailed back in or a larger nail put back in. When building houses for myself, the nails are galvanized and nailed in with hammers instead of with nail guns. And the nails are set in different directions so they can't all pull out in one direction. If a board is properly nailed on, it almost has to be destroyed to remove it. I would think folks would assess their own houses after an earthquake or hurricane and nail back in popped nails and check foundations and other structural items.

Is there any general discussion or public input about the building codes before they are adopted? If we can request the County to amend the heavy roof covering requirement because earthquakes are historically more prevelant than hurricanes, I would think that would be a good thing.

Brian, you may have something about "stay away from big cracks in the ground". While discussing the earthquake with a neighbor, when I mentioned going outside during the quake he was alarmed and said the earth could eat you up if you did that and it is safer inside the house since it would require a bigger hole to eat the whole house. He's been through five or six big earthquakes and that's his opinion.

[Rob Tucker]

Attaching a home foundation to bedrock is the preferred seismic connection. Softer soils can, and will, actually amplify the seismic effect. In some soils the movement is similar to Jello wiggling and liquefaction can result. Liquefaction is more likely if there is a lot of bound water or saturated soil conditions. Simply put it is better to take the jolt once than to have it amplify multiple times. One whack is better than ten whacks. Duration of the event matters a lot for this reason. A simple earthquake jolt is one thing. 30 seconds of jolts is another.

Kona may have benefited by the general lack of soil. Lots of raw stone.

Anchorage, in 1960, got, I believe, a 9.5 event that lasted seven minutes. Very bad.

The increase in requirement for "Simpson" steel fasteners is the result of engineering analysis of earthquake related building failures. Simpson does extensive testing and owns one of two earthquake simulators on the west coast. (The other is at U.C. Irvine). Simple nailed wood connections failed regularly. In addition the type of failure matters too. Most un-reinforced failures were of a "catastrophic" type. That means the structure resisted the seismic force to a point of complete failure. Collapse. A "gradual" type failure is preferred. Simpson ties can, alone, change the nature of a failure from catastrophic to gradual. Care to guess which one is more survivable?

I have seen test results of shear walled wood frame where the catastrophic failure occurred at 9 kps. (Think of kps as thousand/pound/second). Interestingly, reinforced concrete systems (ICF) tested to a gradual failure point of 89 kps.

My home is reinforced concrete. I built it myself for less than $100 psf.

I do try to remember though that nothing made by man cannot be defeated by nature. We do have the ability to do better. Simpson is cheap compared to a destroyed home.

One big thing affecting upcoming codes came from FEMA. Prior to the Northridge Earthquake the basic engineering standard was for people to survive earthquake events of “X” magnitude. That standard was very, very successful. Compare L.A. to Mexico City.

Following Northridge FEMA put the word out to the engineering community that from now on the buildings were expected to survive. Liability was the leverage applied. And now the safety factors in residential design are reaching the point in some locales (SoCal) where “affordable housing” is but a memory.

Just some facts. I did a lot of recovery work and building post mortums in L.A. after Northridge. I also noticed that for about one year after the event people were very earthquake aware. After that it was back to what's cheap and expedient.

[HADave]

i believe also that IBC's speak of moisture content requirements being near 18-19 percent b-4 closing in of the frame is allowed,( sheetrocking) seems to me this would be problematic for Puna builders.

Am I wrong thinking that Hi-Bor was a noncorrosive treatment or at least much less-so that other decay/insect treatments. So is the requirement for high zinc coatings, on fasteners, that important. Here was a couple of links that lead to be believe it was not...and I am by no means trying to argue a point, just looking for clarification
http://strongtie.com/productuse/coatings.html

http://strongtie.com/ftp/fliers/F-PTZMAXBI06.pdf

After reading the article yesterday about recorded quakes since 1868 and remembering the maps of high wind events for the islands it is deffinately apparent that quakes seem to be the bigger concern. I sure hope any modification they force one to make is truly in the best interest of the habitant. I just don't see 5/8 plywood over 16"/24" spacing as anything more than overkill, of course at $30 plus per sheet it is quite abit of tax revenue generated by the State. Were snow loads are an issue yes but not Hawaii. Perhaps 'sips' would be a better step up from sheet metal covered purlins. It would certainly be more rigid and provide greater protection during wind events than sheet metal, not to mention the energy coefficient results....jmho

Aloha HADave