One Idea For Earthquake Foundation

Do some research on Cheyenne Mountain. That facility was built to stand a nuclear blast and used a concept not unlike yours.

thanks AH.. haven't much time for research... but following your advice turned up this. Is this what you are referring to?

Chris

You are on the trail. ;-)

One of the science networks showed buildings (California?) with a similar system in place now. The buildings rest on what are a bit like ball and socket joints that don't go all the way around to make a ball. There are concave shapes on the top of each of the foundation posts. Each of the building's mating posts has a convex shape pointing downward. Gravity keeps the building centered on the foundation depressions. When the ground shakes it is free to move under the building. Since any motion would put the building up the sides of the curved surface the force of gravity will return the building to the center of the foundation posts. I'm sure that someone with a lot of math skills can demonstrate why this is a mechanical low pass filter.

Bottom line, if I recall correctly it works well.

Bruce

I've seen that video of how that went together. It employed those sockets and some large mass dampers.

Thanks,

Chris

GA. Low pass filter is a good analogy.

Base Isolation is the name for the general concept in seismic design of "decoupling" the superstructure from the foundation by means of shifting the period of the superstructure away from the range of high ground accelerations expected at the building site (based on the approriate geotechnical evaluation). This can be done by various means: elastomeric pads, high density rubber bearings, or even springs as shown in the Norad link (among others). Methods such as those will produce a period for the superstructure based on the total mass above the isolation system and stiffness of the isolators themselves.

For the type of system Bruce mentioned however, known as a Friction Pendulum Sliding (FPS) Isolator, the engineer can dictate the desired period for the isolated structure independently of the mass above the isolation system. The radius of the curved sliding surface alone dictates this isolated period, just as the length a pendulum dictates its period of vibration. Friction between the large curved surface (typically stainless steel) and the small articulated slider (typically covered with a PTFE/teflon fabric) will dissipate some of the input energy.

The concave surface can face either up or down depending on the application. For example, in a project i'm working on, we have an old deck truss bridge that sits on unreinforced masonry piers. With the concave suface facing down, the vertical reaction on the articulated slider will not move relative to the pier, and therefore not introduce any eccentric load on the unreinforced masonry.

In some "high profile" applications, these types of bearings were used on the (new construction) San Francisco International Airport terminal and the (retrofit) San Francisco US Court of Appeals building.

With the company founder being the inventor of this system, I believe Earthquake Protection Systems is the only maker of this type of bearing. The various links on their website under "Products" will give you some more details.

Hope this helps.

-spak

Hiya Chris! Howzit going up here in the Great White North?

You're getting on the right track, but I see that some mods need to be made to your system to make it viable and earthquake resistant. This is more of a Structural Engineering problem dealing specifically with Seismic Design. I may be a Structural Engineer, but I'm not particularly well versed in Seismic Design like the guys out on the Left Coast. Perhaps some of our CA Structural Engineering members can help out more than I could?

From what little I know of Seismic Design requirements (here in NYS we don't have the large magnitude seismic events like CA, OR, WA or Missouri would experience), I offer the following:

1. Most structural failures of buildings etc. occur during seismic events due to loss of adequate soil bearing, where the underlying soil mass losses it's strength...this occurs in clayey soils, sandy soils and landfilled areas with a high water table and/or high soil moisture content. When the soil is vibrated by the earthquake (imparted horizontal velocities), the soil is "liquefied", and hence acts like quicksand and the building foundation losses adequate bearing capacity. The San Francisco Earthquake of 1906 (?) is a prime example of the liquidation of soil and structural failures during a high magnitude earthquake event. That's why is isn't a good idea to rely on individual spread footings like you've shown. Ideally, the better foundations to use are mat (raft) reinforced concrete foundations (the entire building with ride the oscillations and subside together when the soil becomes fluid-like), piles down to bedrock (such as steel H-piles, reinf. conc. end bearing piles, or steel tubular conc. filled end bearing piles), or reinforced concrete caissons down to bedrock. BTW, it's never a good idea to use friction bearing piles in an earthquake prone region....they must be end bearing to transfer the gravity loads to the rock surface below.

2. At your bearing pad (node), the wooden beams (or even steel Wide Flange or reinf.. conc. beams) should extend to one another (butted together w/o space between them) and be tied-together with framing angles with structural through-bolts, bolted end straps or side plates, and the like. The reason for this is to provide continuity and allow for the building framing above to slide back and forth all tied together due to the imposed horizontal oscillations, without separations occurring. The key here is to keep the floor framing acting as a integral member, not separate members. Remember, it's the mass of the building above the foundation that is accelerating back and forth...the heavier the gravity load, and hence greater mass, produces the greater horizontal forces acting on bolts, columns, beams, and ultimately imparting those horizontal forces (as wells as the gravity loads) the foundation. Imagine a good sized solid chunk of Jello (which for our purposes is our imitation of a soft soil mass) in your large spaghetti bowl....first place a single ice cube atop it (making sure it sticks well) and shake the bowl violently side to side...the result is not much will happen! Add a few more ice cubes to the Jello "soil" and shake it like before....the additional mass of the ice cubes will case either the top of the Jello to shear or the ice cubes will shear off. That's as close of an analogy I can think of off the top of my head at this juncture! :-)

3. You need to provide some sort of structural steel lip attached to the underside of each floor beam in close proximity to the edge of the bearing pad, but too close as to limit it's side-to-side travel and hence promoting the "binding things up" scenario, which will result in the framing being sheared off it's foundation below. This limiting device is needed to prevent the beams from slipping off the bearing pad. The bearing pad needs to be a Fluorocarbon coated steel bearing pad or dome (like you've shown) to facilitate horizontal movements....it's very slippery stuff, and yes, there are manufacturers that do make these types of pads (not just for seismically designed building either). Maybe even provide a upside down Fluorocarbon coated concave dome pad that's attached to the underside of the beams that'll ride atop the central bearing convex-shaped dome....fit like a big glove over a smaller glove sort of.....allowing horizontal as well as rocking movements. Just athought........

4. The bearing pads (nodes) need to be bolted down to reinforced concrete pier with a entire ring of steel anchor bolts, washers and hex nuts below in order to have the entire system secured.

5. I dare say that you can get rid of the four independent rockers and their piers and spread footings because they're not needed and it's a very costly construction. You can rely on a single reinforced concrete pier and centralized bearing plate or dome, where the bottom of the pier is tied directly into the reinforced concrete mat foundation or a reinforced concrete pile cap.

Again, I'm not an expert in seismic design and I may be off-base in some of my observations....possibly a SE Forum member with earthquake deign experience may have some better or novel approaches than I

Not bad for starters Chris! Have a great day and I look forward to seeing an revisions to your system!

Hi Mark,

that is a lot to take in... and likely quite valid.. and of course, invalidates most of my idea..

I won't say that feels good.. but I am also one to acknowledge truth and reality when it comes my way.

So thank you. I will definitely ponder everything you said.. and if I can come up with some mods.. I'll show them.

Cheers,

Chris

I didn't find much either... so other than the typical antiquake ideas... with the mass dampers.. I haven't found much.

it does seem to be an interesting structure.

but I do recommend not flying directly across the runway because doesn't that lead to some airspace sharing problems? (screenshots from google earth)

not usually - but a miss is as good as a mile

Awesome drawings. Only problem I see is it is still too rigid of a system. I do love the intricate drawings. Very nice!!

Very good idea, and innovative method, of how to build a man-made island on muck, especially the "sand columns".

Unfortunately, it has been reported that the compacted fill for that airport is subsiding much more (and faster) than what had been predicted by the design engineers, and that they may now have to increase the height of the sea wall substantially to hold back the sea. The same problem is currently happening at the new opened airport in Hong Kong Harbor. I believe that I had read the report about this problem in Engineering News Report (ENR) somewheres around 2 years ago, if I'm not mistaken.

I light of what happened on the northern Pacific coastline of Japan 3 weeks ago with the height of the Tsunami breaching the major sea walls there, it probably would be a wise decision to construct higher sea walls around the airport anyhow.

Hi Chris,

Interesting design, are you structural? Do you have an idea of the additional cost /SF this might add to the structure Vs. the cost saved e.g. insurance from lost of property and or people within the structure?

Regards, Gary

Gary L. Josey

groundStar, LLC