Science Project - Q for engineers?

[jussi]

So my nephew asked me for help with his science project. It has to do with earthquakes and it's affects on buildings. I've only gotten a brief description so far but he has to make a model, shake it somehow, and report on his observations. He wants to make several models that are engineered in different ways. Perhaps using different types of joinery. I already have an idea on a device that will shake the buildings. That way we can limit that cause of the destruction to the building's construction without the magnitude of the earthquake being part of the equation.

Any suggestions on the different types of construction we could use? I planned looking up earthquake related building materials. Should I just glue everything?

[LCHIEN]

just a suggestion. among the range of construction types used you want to have one so weak which you know will fail... sort of a control to make sure that some damage is occurring from your tests.

[cabinetman]

It's an interesting project. For construction there aren't that many real time methods...steel/glass, block, stone/brick, wood framing, etc. You don't want to be "builder of the year", because it has to fail. I'm thinking a finishing sander or better yet, a ROS, could be used to create the "vibration".

.

[TB Roye]

Have him contact the University of California Berkley, I know they have big Earthquake/seismology Department there or nearby. He may have to drill down through the Uniersities website to find it. The or CalTech might have one or maybe even CAl Poly San Luis Obispo

Tom

[eccentrictinkerer]

Google "MTS Systems". They are located here in the Twin Cities. LINK
They build everything from lab shake tables to platforms big enough to test large buildings.

Years ago, as a process control sales rep, I helped design an electrically heated reservoir to keep 10's of thousands of gallons of oil from gelling in cold weather. The project was the largest shake platform in the world, and was located in Japan.

[jackellis]

Perhaps this will help give you some ideas:

Homes out here have to have metal hangars at framing joints to keep critical joints from separating. Our decks are also built this way because nailed connections aren't strong enough when things start shaking. So depending on the scale, you might build one model with nails or brads or pins in the joints, and another with gussets.

Homes also have to have a certain amount of what we call shear wall area. Sheathing is nailed to the outside of the house on a very specific schedule so if the building shakes, the sheathing helps keep joists from collapsing on themselves. You might try two thicknesses of shear wall - one of very thin cardboard or very thick paper, and another of thicker cardboard or thin wood. Or maybe do one that's nailed around the perimeter and another that's nailed more solidly.

The third idea is for tall buildings. They are going to sway quite a bit but these days they're being on shock absorbers to help damp the movement.

A fourth is to use unreinforced masonry. Plaster of paris might do the trick or perhaps even paper mache. You could do one with just plaster and another with plaster reinforced with chicken wire.

A fifth idea is to make one structure that's bolted to the "foundation" and another that isn't. One of the major causes of structural damage in older homes arises when the house is shaken off the foundation. Bolting the sill to the foundation is a very cheap and very effective way of preventing structural damage in low rise structures under even strong earthquakes. In this instance, I speak from experience.

In all cases, the idea is to keep the structure from collapsing on the occupants. Limiting or preventing major structural damage short of collapse is a distant secondary concern. You want people to be able to survive the event. If the building ends up being unsafe, well that's too bad.

Our home in the mountains is built to the same seismic standards as homes much closer to SF, because there are two faults that lie under Lake Tahoe. The house is engineered to shake with a 240 psf snow load on the roof - which is equivalent to an M-1 tank - without collapsing. It's bolted to the very substantial steel reinforced foundation and there are lots of galvanized steel hangars buried underneath the wallboard. It'll twist and flex a bit like it's supposed to, but only a monster quake with 20 feet of snow on the roof is going to cause significant damage.

[TB Roye]

I house is built on a concrete slab but the sills are bolted to the footings and slab. Don't know what will happen if the big one hits. I imagine we will either slide into the newly made Sacramento bay (SF being gone) or have beach front property. Living here most of my life and have only felt maybe 6 quakes. I probably have more to fear with one of the 3 major dams collapsing or one of the Leevies failing and a wall of water wiping out the Sacramento Valley than the Actual Earthquake. Jack Ellis gave you some good information and he does know from experience. Good luck post pictures

Tom

[leehljp]

I don't what idea you have for a shaker but here are three more possible ones if yours doesn't pan out:

I don't remember if it was Tesla or Edison, (I lean towards Tesla) but one of them created an "earthquake" of sorts by attaching a small variable speed motor with an offset weight on a main vertical beam of a building (New York or Philadelphia) in the 1880s-90s and gradually inceased the speed until it hit the harmonic of the building, almost causing it to collapse and causing panic in a block radius. It doesn't take much.

Another and simple "vibration" unit can be a VS 1/4 or 1/3 sheet sander firmly attached to a support beam. It should shake enough in a few minutes to see if something is going to happen, or to see if one joint is stronger than another.

Also, pneumatic paint shaker from HF! That will do it!

What ever you do, please post the results here! This sounds interesting!

[jackellis]

Tom, your house is unlikely to slide off the slap unless the bolts are defective or the sill rots pretty badly. If the earthquake is big enough, the structure might twist enough to make the house uninhabitable, but I don't think it will collapse. If you have a brick chimney, it could collapse and come through the roof, but if your home was built in the last 20 or 30 years, even that's unlikely.

As I've probably pointed out before, we used to live about 11 miles as the crow flies from the San Andreas Fault. In the '89 earthquake, we had one filing cabinet tip and a drawer front fall off, and our neighbor's pool sloshed over, weakening the footings of an old fence and retaining wall, which collapsed. Maybe a few hairline cracks along wallboard joints. In San Francisco, the tall office tower that's PG&E's headquarters swayed a lot and I'm sure furniture on the upper floors got thrown around, but the building was inhabitable the next day.

This isn't the third world. Newer stuff is built to resist damage in strong quakes, and to not collapse on inhabitants in really strong quakes. Tough building codes are better (and probably cheaper) than earthquake insurance.

[TB Roye]

I don't worry about it. Quake insurance is too expensive, I do have flood insurance. I figure if it is bad enough SF won't be there and I will have beach front property. I felt the 89 quake pretty good was home watch the series and 10 minuets late was on my way back to work to open up the CHP vehicle facility and start getting cars ready to head for SF. Within 15 5 other employees showed up and by the time the official word came out we had 20 cars checked out and ready to go and Officers started showing up buy midnight we had 100 used and new CHP cars and Officer on the way to the Bay Area. My wife who worked for the State Dept oh Housing spent a few weeks down there helping the suddenly homeless. Thank God they don't happen as often as Tornado's or Hurricanes. Not good to mess with mother nature. Our evacuation plans would be to head up HWY 88 to Silver Lake and the Family cabin. It is stocked with the necessary supplies to last a few weeks in not longer and can sleep 15 if necessary.

Tom

[jussi]

Thanks for all the suggestions guys and I'll pass them along to my nephew.

[mpc]

Another thing to "help" dramatize the differences in the various structural materials & techniques is to have masses representing furniture and whatnot on the floors. Something that'll put some inertia into the models. They'll also lower the resonant frequency of the structure so it'll likely be easier to excite.

Depending on the intent of the demos, it might even be worthwhile to make a couple building models with identical structures but differently spaced internal masses. Make one with the "big heavy air conditioner" stuff on the top floor and another with that mass on a low floor. And perhaps a third with a top-floor mass on rollers and springs to center the mass in the structure. Some buildings today have such a system to absorb some of the energy.

mpc

[LinuxRandal]

Is there a particular form of construction he should be looking at according to the instructions?
I am trying to figure out if they are after him learning more about things like skyscrappers and how they react, then early 20th century home construction (think San Fran 1907) verses current home construction, verses alternative methods (monolithic dome).