Monday, February 21, 2011

Salt Lake Temple Inverted Arches

I'll make this a quick post.  I work as a structural engineer and know a bit about the Salt Lake Temple from an engineering standpoint.  Back in 1993 President Boyd K. Packer gave a talk on the Salt Lake Temple and he said this:

They counted on the principle of the arch on each window distributing the immense weight of the stone above it. When the foundation was replaced with shaped granite stones, sixteen large inverted arches were built into it. There is no record as to why they decided to do that. That manner of construction was then unknown in this country.
If someday perchance there be a massive force wanting to lift the temple from beneath, the arches may well act to distribute the pressure.

That is a nice quote.  Unfortunately it is inaccurate.  I'm not saying that President Packer was trying to deceive us, only that he didn't understand exactly what he was talking about.  From an engineering standpoint an inverted arch will redistribute the forces that have been concentrated by arches above.  This allows for an even distribution of pressure to the foundation.  This is important.  Think about going outside and trying to push a bucket into the ground.  It doesn't work very well.  Do the same thing with a stake and it goes in fairly easily.  This is because the forces get distributed over a smaller area in with the stakes.  The same basic principle applies to buildings.  Even if the concentrated pressures are small enough to avoid catastrophic failure, they can still cause problems if uneven.  Major structural problems occur due to differential settlement, when one part of a building settles more than another.  Foundations crack, extra stresses get introduced to members, and everything goes out of plumb.  If foundation pressures can be kept uniform, then settlement will still occur, but because it is the same everywhere it will not be a problem.  This is precisely what has happened with the Salt Lake Temple.  The inverted arches have redistributed forces in the building keeping pressures near uniform leading to uniform settlement and a building in a good condition to this day settlement wise.  The building does not have to be lifted up for the inverted arches to be used and useful - they are serving a valuable purpose every day under normal gravity loads.
As for the comment about inverted arches being unknown at the time of the temple's construction, I don't think that is true.  Don't misunderstand, I think God's hand was still in the temple construction, but I think he brought people with an understanding of inverted arches to work on the temple rather than just mysteriously having the inverted arches added.

9 comments:

Tod Robbins said...

Word. I totally agree with the analysis.

Brian said...

I do get annoyed by the belief that temples are the way they are because each and everyone has had every detail dictated by heaven. Were this true, they would not have had to restart the construction of foundations on Salt Lake. Not many people realize that most of the exterior decoration on the Salt Lake Temple came from member suggestions.

Scott said...

Also if every detail was dictated they wouldn't have done numerous seismic upgrades to temples (and still are - Ogden for instance)

I read a story about a fire in either the Logan or Manti Temple. After the fire someone asked why the Lord let if break out and the answer was that they had discussed adding fire prevention measures but decided not to because the Lord would take care of it. Apparently the Lord didn't appreciate the apathy.

Karl said...

I do remember hearing Hugh Nibley talk about how a lightning bolt had struck one of the towers of the Manti temple, causing it to burn briskly.

In this particular Nibley discourse, he related that the installation of lightning rods had been discussed, but that the idea never became reality. I suppose everyone learned a costly lesson that day.

Scott said...

that was the story i was thinking of

Lane said...

The Oquirrh Mountain Temple's Angel Moroni statue being blackened by lightning comes to mind; especially since the Brigham City Utah Temple just got its Angel Moroni statue installed today with two lightning rods: one atop his head and the other at the end of the trumpet.

Cortney said...

Am I understanding this quote right that President Packer was suggesting that the temple could at some point be lifted to heaven?

Scott said...

That's the impression I got from the quote. I think it is bad speculation on his part. The arches help even out settlement.

Rhonda said...

That it's not at all the impression I had from the quote. We know there are numerous faultlines in the Salt Lake valley. The temple sits atop natural fill over the 'valley block'. Normally the mountain block does the rising during an earthquake, but is it possible for the reverse to happen? Considering
Isaiah's prophecy that every mountain will be made low and every valley exalted, I'd say yes.
That seems a much more likely scenario that President Packer may have had in mind.