AARoads Forum

National Boards => Bridges => Topic started by: Mike2357 on August 14, 2021, 01:19:31 PM

Title: Will Continental Drift Ever Affect Bridges?
Post by: Mike2357 on August 14, 2021, 01:19:31 PM
Given that the continents are shifting an inch or two every year, could this ever end up straining the structural supports until they collapse? If for example, Long Island started drifting east away from Manhattan, would the Brooklyn Bridge ever snap?
Title: Re: Will Continental Drift Ever Affect Bridges?
Post by: NE2 on August 14, 2021, 02:54:29 PM
(http://upload.wikimedia.org/wikipedia/commons/thumb/8/8a/Plates_tect2_en.svg/1280px-Plates_tect2_en.svg.png)
Not in the U.S. except on the west coast, but maybe it would be an issue for a Gibraltar bridge.


http://www.atlasobscura.com/places/midlina-bridge-between-continents
Title: Re: Will Continental Drift Ever Affect Bridges?
Post by: Evan_Th on August 14, 2021, 02:58:07 PM
Not in the U.S., but maybe it would be an issue for a Gibraltar bridge.

The San Andreas Fault is already causing minor damage (http://geologycafe.com/fieldtrips/anzar_road.html) to California roads.
Title: Re: Will Continental Drift Ever Affect Bridges?
Post by: kalvado on August 14, 2021, 03:13:40 PM
Plates boundaries are seismic regions, and construction has to account for that.
An example which comes to mind is Akashi-Kaikyo bridge in Japan. An earthquake occured during bridge construction, things moved,  and final geometry of the bridge was a few feet longer than originally planned.

Quote
Of particular interest was the performance of the bridge in the January 17, 1995, Hyogo-ken Nanbu Earthquake, which provided a full-scale test of tower response. The earthquake caused a permanent lateral and vertical offset of the Awaji tower and anchorage. This resulted in a 0.8-m increase in span length between the main towers and a 0.3-m increase in the southern side span length. The increased distance between towers was accommodated by the redesign of the two center stiffening panels, which are 0.4 m longer than originally designed. The earthquake caused a one-month delay in the construction schedule during which the bridge was carefully inspected. The lost time was made up during the remaining 3-year construction period, and the bridge was opened on schedule.
Title: Re: Will Continental Drift Ever Affect Bridges?
Post by: Max Rockatansky on August 14, 2021, 07:53:00 PM
Not in the U.S., but maybe it would be an issue for a Gibraltar bridge.

The San Andreas Fault is already causing minor damage (http://geologycafe.com/fieldtrips/anzar_road.html) to California roads.

There is a bridge in Parkfield which has a noticeable bend in from the San Andreas Fault moving.
Title: Re: Will Continental Drift Ever Affect Bridges?
Post by: Mike2357 on August 14, 2021, 08:02:01 PM
Wait is there actually a real San Andreas city??
Title: Re: Will Continental Drift Ever Affect Bridges?
Post by: 1 on August 14, 2021, 08:05:54 PM
Wait is there actually a real San Andreas city??

It exists, but it's pretty small. The San Andreas Fault, a fault line, is much more well known.
Title: Re: Will Continental Drift Ever Affect Bridges?
Post by: NE2 on August 14, 2021, 10:50:29 PM
Not in the U.S., but maybe it would be an issue for a Gibraltar bridge.

The San Andreas Fault is already causing minor damage (http://geologycafe.com/fieldtrips/anzar_road.html) to California roads.

There is a bridge in Parkfield which has a noticeable bend in from the San Andreas Fault moving.

https://www.schweich.com/imagehtml/IMG10475sm.html
Title: Re: Will Continental Drift Ever Affect Bridges?
Post by: Max Rockatansky on August 14, 2021, 10:54:22 PM
Not in the U.S., but maybe it would be an issue for a Gibraltar bridge.

The San Andreas Fault is already causing minor damage (http://geologycafe.com/fieldtrips/anzar_road.html) to California roads.

There is a bridge in Parkfield which has a noticeable bend in from the San Andreas Fault moving.

https://www.schweich.com/imagehtml/IMG10475sm.html

A couple of mine from over the last half decade for comparison.

https://flic.kr/p/S4ptrk

https://flic.kr/p/2iBRaKp
Title: Re: Will Continental Drift Ever Affect Bridges?
Post by: jp the roadgeek on August 15, 2021, 01:40:37 AM
Given that the continents are shifting an inch or two every year, could this ever end up straining the structural supports until they collapse? If for example, Long Island started drifting east away from Manhattan, would the Brooklyn Bridge ever snap?
Long Island was formed as the result of a glacier, which is totally independent of plate tectonics.  Id imagine a few roads in Iceland might have issues. 
Title: Re: Will Continental Drift Ever Affect Bridges?
Post by: SectorZ on August 15, 2021, 07:46:16 PM
They can affect all sorts of things, even fault lines that aren't the official borders of the plates.

https://arizonasports.com/story/1201199/cals-new-football-field-features-the-fault-line-its-stadium-sits-upon/

In this case, California Memorial Stadium was built on top of the then-unknown Hayward Fault at Cal-Berkley. They've been making repairs constantly since 1923 as the stadium slowly pulls itself apart.
Title: Re: Will Continental Drift Ever Affect Bridges?
Post by: triplemultiplex on August 16, 2021, 04:51:33 PM
Given that the continents are shifting an inch or two every year could this ever end up straining the structural supports until they collapse? If for example, Long Island started drifting east away from Manhattan, would the Brooklyn Bridge ever snap?

Heh, about 180 million years too late to worry about plate tectonics messing with greater NYC. ;)

The Palisades over in New Jersey are flood basalts from when North America and Eurasia parted ways during the break-up of Pangea.  Once that was over, things have been pretty stable geologically.


The plates move at about the same rate one's fingernails grow, which is about 2 cm/year.  So if one did have a bridge spanning a plate boundary, it would be possible to design it so that it could accommodate that type of change over a ~100 year life span.
If you spanned, say, Gibraltar the ends of your bridge would be inching toward each other, but given that the bridge is gonna last a max of 2 or 3 centuries, you're only accommodating ~6 feet per century of movement.

Worth noting, though, that the tectonic plates are thick; many miles.  The little bit on the surface we might be punching foundations into can behave differently than the larger plate.  In practice, you're getting less movement from the layers on the surface because their forward movement, in the case of Gibraltar, is resisted by the surface layers on each side of the plate boundary.  This means a lot of the surface movement is actually vertical instead of horizontal.

Bottom line, I think this only a minor problem on the time scale of a bridge's lifespan.  By the time tectonic movement would become a problem, you've already exceeded the bridge's lifespan and it will need replacement anyway.