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Earthquakes and wood

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Blog entry by daltxguy posted 02-23-2011 06:28 AM 3461 reads 0 times favorited 18 comments Add to Favorites Watch

The earthquake which occurred on Feb 22, 2011 in Christchurch, NZ is tragic with loss of lives, destruction of infrastructure and sad stories which will continue to unfold over time.

I don’t mean to take away from the human tragedy that this is and will continue to be for a long time and I hope I am not being insensitive by making a few observations about what buildings were damaged and which ones weren’t.

My own town of Murchison was the epicentre of a 7.8 magnitude earthquake in 1929 and lessons were learned then. In my town, all brick chimneys collapsed and were responsible for many injuries and since then, all buildings are all wood frame and all have wood siding with a very small minority with brick veneer ( which is, in my opinion, irresponsible ). This may strike people when they first arrive in town. To those who read too much “3 little pigs”, one might be forgiven for thinking that we live in a ‘poor’ town where there are no brick buildings.

However, I wanted to show a few photos from the recent quake in Christchurch which provides evidence that wood is a significantly important material in earthquake zones.

First a concrete and steel building which could not take the sideways impact of the 6.3 magnitude quake. Unfortunately there were casualties in this building.

Now look at another building whose brick facade crumbled but the frame stayed intact:

And another to show how a wooden framed window survived a fall from several stories to the street:

-- If you can't joint it, bead it!



18 comments so far

View Mark Shymanski's profile

Mark Shymanski

5115 posts in 2437 days


#1 posted 02-23-2011 06:35 AM

Interesting observations. I wonder if the ‘flexibility’ of wood and the fibrous nature of it better withstands the movements particular to earthquakes. Trees stand up to considerable wind loads over their lifespans, perhaps L waves et. al from the earthquakes are just another type of stress trees have endured if not adapted to.

I hope you and yours were safe in these most recent quakes, I’ve not been in reach of radio or TV lately so have missed much of the news.

-- "Checking for square? What madness is this! The cabinet is square because I will it to be so!" Jeremy Greiner LJ Topic#20953 2011 Feb 2

View daltxguy's profile

daltxguy

1373 posts in 2639 days


#2 posted 02-23-2011 06:45 AM

I guess I should add that this is not proof that wood is better or that steel and concrete cannot be engineered to survive a quake, just that wood naturally has properties making it very resilient to movement in many directions.

Mark, I think you are onto it. Trees do grow to respond to gravity and wind stress, ie; stresses in multiple directions. Wooden structures, if properly designed is a suitable material to meet earthquake stresses.

I am north of Christchurch 400km (240miles) and we rolled from the initial quake but it was very mild after traveling that distance. I am fine but Christchurch is a disaster area.

-- If you can't joint it, bead it!

View moshel's profile

moshel

864 posts in 2408 days


#3 posted 02-23-2011 07:15 AM

broadcasting live from the disaster area….
anyway, steve is basically right. over the last 70 (?) years free from earthquake, people imported here methods from other countries that are not suitable and managed to pass them by the engineering. you could see in the september earthquake that the method called “tilt slab” was a total disaster. the elements had no flexibility and the slabs break and fall nicely.
metal framing looks to be ok for single story houses but it remains to be seen if there will not be metal fatigue over years.

light cement blocks houses also fared pretty badly. not total mess like the tilt slab but lots of structural damage was apparent.

weatherboard houses had no damage unless liquication happened under them.

having said that, the buildings that collapsed were multi story buildings and I don’t think they would have fared better with timber framing (if possible at all).
as for the brick cladding – this was a 150 years old building. my house is cladded with natural stone and it didn’t even crack. the modern fixing (if done correctly) are much better than the old mortar.

anyways, i hope to forget the meaning of “aftershock” some day…

-- The woods are lovely, dark and deep, but I have promises to keep...

View mafe's profile

mafe

9622 posts in 1814 days


#4 posted 02-23-2011 12:25 PM

What a story.
Happy you are with us!
Beeing a Architect MAA. and Constructing architect from BTH, I will say that you can build in any material at any place. But the normal ways of building with brig, to make a free standing wall and rest the load of the roof on this is not enough for a earthquake. You can put the brigs into frames, and then it will be no problem. Also to say that concrete is not good there, that is not right at all, I would at any day prefere to be in a well constructed concrete house under a earthquake that any other building. But!!! It have to be made for the loads and movements. The wood frame house have a tendency to stay better, due to it’s flexibilitie yes, but more because of the lightness, not so much load stress when shaken, and usually it’s the more cheap way to build in small size buildings. Stell frames are quite stiff yes, so they also needs the right dimension, but then they can be exelent too. Look at all the highrise buildings in earthquake zones build in middeleast.
So it’s the price and the right dimensions. All materials are not good when not dimensioned right.
Facianting photos, glad I was in Copenhagen.
Best thoughts my friend,
Mads

-- Mad F, the fanatical rhykenologist and vintage architect. Democraticwoodworking.

View stefang's profile

stefang

13530 posts in 2059 days


#5 posted 02-23-2011 05:30 PM

Hi Steve, I have been following with this tragedy on the net. I grew up mostly in the Los Angeles region of California where earthquakes are pretty common. I have read about the efforts made in California and Japan regarding earthquake resistant structures. I do think that there are two major types of construction to be considered, Residential/small commercial and large multiple-story buildings. I’ll give you my own experience with residential.

In 1971 we lived in a small valley (Simi Valley) which was very close to the epicenter of a major (7.3 scale) earthquake. We lived in a sub division with larger (2 story) and smaller homes. Many of our more well off neighbors had swimming pools, cement block walls and chimneys. We had a chain link fence around our back garden and no chimney (young and poor). All of these houses were wood framed with stucco outside surfaces which was plastered (probably sprayed) over chicken wire fastened to tar paper attached to the wood frame. Basements aren’t allowed there so all of the houses are constructed on top of a simple reinforced concrete pad that simply ‘floats’ on the dirt below it. I’m not sure how the plumbing was completed underground.

The Earthquake severely damaged every single wall, chimney and swimming pool in the area. Huge 6 lane highway overpasses collapsed along with a good deal of elevated roads, etc. A Catholic mission from around 1740 I think (San Fernando Valley Mission) was also severely damaged if not entirely destroyed. Just about every building made of concrete bricks for miles around were damaged to one degree or another.

In spite of all this damage, the wood framed houses themselves pulled through the ordeal almost without any significant damage (as far as I know). Our house and property suffered no damages whatsoever, in spite of a very sever shaking. The irony was that we had sold our house two weeks before the earthquake and we were due to leave California for Norway in another two weeks time. Lucky for us, no problems popped up and the transfer went without a hitch. I thought it was the end of the world while the quake was shaking our house at 4:30 A.M.!

When it comes to larger buildings in California, most are steel framed with various types of external covering. The newer, taller buildings in the L.A. area are designed to withstand earthquakes. I bet that an earthquake in the 7 scale in L.A. would do a lot of damage to the older buildings, but I doubt any of the modern skyscrapers built in the 1970s and onwards would be badly affected, Also, I assume the builders and insurers would be focused on the inevitability of future earthquakes. I do think the key is anticipating earthquakes and building for the eventuality. The big problem is having people working and living in older buildings or where earthquakes haven’t been taken into consideration.

My family and I arrived in Noway on 19th February. Earth quakes are experienced in Norway, but they are almost unnoticeable. I mentioned to my wife on our first night here that it was reassuring that most of the country was under-layered with rock, so no danger of quakes. At about 3 A.M. that first night we felt a shaking, and the next day there was a news story about it having been a 4,6 scale quake off the coast. Not so long afterward I got a job at a new oil supply base supporting oil exploration activities off the coast of Norway. The office block where I worked was part of the workshop building which housed an overhead traverse crane to move heavy oil field equipment being worked on around the shop. Every time they moved something the whole building shuddered a lot like the beginning of a quake. It took me a long time to get used to that after my experience in California!

I’m very sorry about what happened in NZ, with so many killed and injured and a lot of people still not accounted for, not to mention the destruction of so much essential infrastructure. I hope the international community will be quick to assist your country in recovering from this disaster.

-- Mike, an American living in Norway.

View daltxguy's profile

daltxguy

1373 posts in 2639 days


#6 posted 02-23-2011 08:02 PM

Thanks Moshe, Mads and Mike (3M?) for the comments, experience and stories. All fascinating and all excellent points!

As I said, the pictures ( which I admit are highly selective) is not proof of anything, it was just my immediate observation that all things being equal – assuming that all these buildings were designed to the same standards ( even though those standards may have been inadequate), wooden framed structures seem to hold reasonably well.

As an engineer explained on a news report, the original brick buildings were designed to withstand the force of gravity but not a sideways impact or ground acceleration in the vertical direction. These buildings were not designed to be thrown into the air and then subject to a free fall.

Some work is being done now on using wood even for high rises ( using engineered wooden spans). I have seen a few examples. Here in NZ there is active research into making this possible since New Zealand is a timber producing nation. As energy prices increases and concern about CO2 emissions increases ( let’s hope it does), steel and concrete may become prohibitively expensive or just prohibited period.

The NZ parliament is a big granite building built in Wellington near a known fault line. It actually sits on giant ball bearings ( I mean really big) on a track which allow the building to roll independently of the earth movement. It has not yet been put to the test to my knowledge but I have some confidence in that design.

-- If you can't joint it, bead it!

View Steven Davis's profile

Steven Davis

112 posts in 1639 days


#7 posted 02-23-2011 08:05 PM

The grim quote for earthquakes is “Earthquakes don’t kill people, buildings kill people”.

As a native Californian, I’ve lived with earthquakes my whole life. What is so sad is that it is relatively easy to build so that earthquakes will not hurt much. The way we build with wood is naturally earthquake tolerant. It can be done with steel and concrete… brick is pretty much always a disaster (each brick winds up moving separately with predictable, devastating results).

Best wishes in this difficult time.

-- Steven Davis - see me at http://www.playnoevil.com/ and http://www.stelgames.com/

View lilredweldingrod's profile

lilredweldingrod

2495 posts in 1831 days


#8 posted 02-23-2011 08:06 PM

Mike, How well I remember the Northridge quake! And I was only 4miles for the epicenter of the Whittier Narrows quakes right after that. Those two felt like the house was knocked off the foundation. When it got daylight, I checked the house for damage. Not even a crack in the stucco.
Now I live in a wood frame and stucco house on top of the San Andreas Fault. This house was built in 1987. We have experienced some good shakers here with no damage. But then, California has worked out some very sinceable building codes that have saved countless lives over the years.
It is always a sad thing to hear about the toll these natural disasters bring. My heart goes out to all. How I wish I could do more.

View moshel's profile

moshel

864 posts in 2408 days


#9 posted 02-23-2011 09:02 PM

During the construction of my new house it looked like lots of stuff that used to be made of metal is now made of plywood/timber I beams. incredibly strong things and very easy to work with. only place matal beams were used was to hold the backbone of the roof (we have “open space” with one support) and places that had no “anchoring” point and were load bearing. 2 or 3 places overall. the metal I beams were re-enforced in most cases with LVLs or timber structurally bolted to them, i assume to give more dampening to sideway movement.

basically the roof beam could be made from timber but it would have to be 15-20” thick beam and these are very expensive and also heavier than the metal I beam.

The sideway movement we had during this earthquake was at least 5cm at the bottom of the building. I assume this would translate to 20-30 cm up near the roof. no calculations or facts, just a feeling. no wonder less flexible buildings collapsed.

-- The woods are lovely, dark and deep, but I have promises to keep...

View grimt's profile

grimt

24 posts in 2285 days


#10 posted 02-23-2011 09:45 PM

Steve, Just to let you know that I have heard from both Mark and Dave and we are all ok. All of our buildings have been hit harder this time though nothing in comparison with our friends in the CBD and out in Lyttleton and Sumner. All of our immediate family and friends are safe and well though, as you know, Christchurch is not a big city so we are all bound to know someone who was not so lucky.

Stay safe…

gt

View daltxguy's profile

daltxguy

1373 posts in 2639 days


#11 posted 02-23-2011 10:00 PM

Graeme – thanks for the update. Glad to hear. Did your beech workbench move at all? :)

-- If you can't joint it, bead it!

View jynx's profile

jynx

3 posts in 1226 days


#12 posted 07-22-2011 01:20 AM

Steel performs much better than timber in an earthquake because its light weight

Steel has a significantly higher strength-to-weight ratio than wood. A steel frame is typically one-third the weight of a wood frame. Consequently, damage through “inertia” will be significantly reduced since there is less weight to move during an earthquake, and less weight that must stop.

Vanson Frame & Truss Steel technology allows for frames to pass all load requirements without additional bracing there is No requirement for plywood or GIB bracing and it comes with a 50 year warranty from NZ Steel it is the only framing material for which any kind of Structural Durability warranty is offered.

It worked out way cheaper than timber framing as well as being safer A basic 2-3 Bedroom Home will take approx 3 days to erect & erecting steel is not weather dependent like timber it causes less maintenance problems so builders report less downtime from call-backs so you save money on labour, gib bracing and the trusses include eaves soffit
Unlike timber Steel frames are straight and true, which means walls, ceilings and roofs do not have ripples or bumps or gib wont crack!
I have been to see a show home they are building it looks fantastic!!

It is backed by the asthma foundation and recyclable

check out thier website http://www.vanson.co.nz/ I am re building in steel for sure!!

View daltxguy's profile

daltxguy

1373 posts in 2639 days


#13 posted 07-22-2011 02:24 AM

The above post is complete bollocks. I’m flagging it, so if it disappears, just know that someone just posted a giant ad for steel framed buildings being so much better than wood with a shameless plug for a specific NZ company who will be happy to take your money and build you a house out of steel.

Apparently the steel industry is threatened by good old, reliable, strong and earthquake proof timber and are resorting to guerilla tactics in user forums for wood. Nice!
Do your homework. Check the facts. Make an informed choice.

For my money, however, it’s timber all the way for earthquake zones and many other reasons.

-- If you can't joint it, bead it!

View jynx's profile

jynx

3 posts in 1226 days


#14 posted 07-22-2011 02:37 AM

I wasn’t posting a giant ad, I have done heaps of homework to re build and everything I read said good stuff about steel in earthquakes if wood is a better option in an earthquake can you tell me why, I have not signed anything yet so may change my mind. I just want a safe home this time around!

View daltxguy's profile

daltxguy

1373 posts in 2639 days


#15 posted 07-22-2011 03:24 AM

Some non-scientific but hard to ignore evidence is right there in the pictures which I posted. Top building – steel and concrete; church – timber frame.

Most of the facts which you’ve quoted come straight out of the ads which the steel industry is producing and is misleading.

Is steel stronger than wood pound for pound? Not necessarily. Wood like Douglas Fir is actually considered extremely strong and perhaps in certain measures better than steel – but strength is not what keeps a house together in an earthquake, it’s good design.
Steel is stiff, wood flexes, that’s much better in an earthquake. The stiffness is part of the reason why brick facades collapsed. None of the energy is absorbed.

Wood framed buildings have a long history. There are buildings in Japan which have stood for 100’s of years. Japan is clearly a seismic region.

Buildings in Murchison were rebuilt entirely with wood frames ( and wood cladding ) after the huge 7.8 experienced there in 1929. ( Well, steel wasn’t even an option – it hasn’t been around long enough)

Steel framed buildings haven’t even been around that long, so there is no data to compare with.

Have you ever held a steel stud in your hand? It’s stiff if the load is along it’s length. Put a load to its side and it collapses like a drinking straw. All earthquakes are not just up and down but sideways too.

Now, never mind your wifi reception in a steel framed house, short circuited wires – look out. Fires, better hope the fire is not so hot that it melts the studs and the roof falls on you ( remember WTC?)
If the house leaks, well, you better hope the quality of the galvanisation is good. Metal rusts same as wood rots.

As for the claim of straight and true – well wood comes straight and true as well, if properly milled and dried. I’ve seen plenty of timber framed walls which are flat and smooth, haven’t you? So there is no advantage there, they just want you to think that.

-- If you can't joint it, bead it!

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