How much will this Bridge Move?

Not to be mean, but I think I will go to bed now with this question plagueing my sleep...and OH WELL why not answer the question!!! Not as much as the next earthquake you get Jeff. AND are you really taking pictures under there???

> Not to be mean, but I think I will go to bed now with this question plagueing my sleep...and OH WELL why not answer the question!!! Not as much as the next earthquake you get Jeff. AND are you really taking pictures under there???

It was a serious question. I'm trying to draw on the experience of the people here who have measured movement in similar concrete bridges. I'm just curious what the ballpark movement might be over the course of a day or a week.

No, I didn't take the picture. It was from the street view feature of google maps.

Thanks,
Jeff

Jeff,

I would move forward with your experiment, and verify the results your self. I would saturate the area with control, before construction starts. The more control the better.

I wish I had an answer to your question regarding the bridge movement, but I don't. The only thing I can offer you is that I worked for a company one time that did alot of highway work, and they did some design survey work on a MAJOR highway interchange reconstruction, and they had numerous control points on bridge overpasses. I never heard of any issues, but I did not do very much work on that job at all, as I came in on the very tail end of the survey portion of that project.

Please post your results, as I would be interested in seeing what you come up with.

Good luck!

>I'll set some control on it, with good ties beyond the bridge

That's the ticket that will keep you on an even keel.

Control points to use for resections would be fine. I wouldn't want to set an instrument on it, unless all traffic is stopped. If it's not a robot and somebody is running the instrument and can check the backsight, probably be OK. Depends on what you are trying to lay out.

Two things to watch for,

Movement vertically will be much less over the bent caps

Look for expansion joints in the bridge deck to get an idea where the most horizontal movement will be. Temperature will be the major factor so time of day is important.

James

It will move and as James said, temperature will be a big factor. As always, the key is, how tight must your work be. I've used control similar to this but with good, tight control points off the structure to use with a least squares program for adjustment. You don't really need to occupy the off-structure points but you do need to be able to tie into them from the structure.

Bridges by nature are designed to move. I would not put anything on the deck or approach slab. There should be someplace on the end of the abutments that would accomodate.

I'm with "roadhand", bridges are designed to flex and articulate. You want solid, use the abutments. We usually drill and set disks in the top of the abutments. Works great for PERMANENT control points.

It is designed to move, if it had been constructed to be rigid it would have a solid foundation to bedrock the whole length of the thing and then it would still move. The expansion joints say movement, they are there to allow movement without placing more stress on the structure caused by movement caused by loading, wind and temperature changes. Control for your grid belongs elsewhere as others have stated. Standing on long spans and having loaded trucks going by at speed, you can feel some of those bridges move a lot.
jud

I can't respond to how much is too much movement for your purpose but maybe this will be helpfull. I was once working on a raised wooden platform that was tied to a building that had a big compressor or something in it. When that compressor kicked on I swore that platform was shifting an inch or more horizontally. I decided to find a stable point to monitor the actual movement from, and found that it was relativley miniscule and that the platform returned to it's pre-shift location. I decided a human's built-in motion detection system must be quite sensitive.
Chris

I had my gun set up next to the Sammamish river, during the 2001 Nisqually Quake. When the shaking stopped, I turned to 0 and checked my back site and it was dead on. I was still level and still over the point and so was my back site.

I watched big Cottonwood trees whip back and forth and the water in the river slosh up the banks. I was about 35 miles from the epicenter, 6.8 is pretty big though.

Radar

It will move, but I also think unless something drastic happens, it returns to the same place each time. I wouldn't count on that for extreme precision, but for earthwork, should be fine. No way I'd set up on it tho.

All bridges expand and contract. Usually one end of the span is pinned to the abutment seat. The other is allowed to slip. Around here on our bridges we see 3/4" to 1 1/2" movement in length between the morning and the peak of the heat. Really depends on the span length and the temp. It would get less the closer you get to the pinned abutment. You could calculate it fairly easy. The rate is approx the same for conc as it is for steel. Jrl

Thanks for all of your replies. As an experiment,I set a few points on the bridge that I will check from ground control periodically throughout the project. I'll keep you updated.

This doesn't have much relevance to the bridge that I was asking about, but did you know that the Golden Gate Bridge can move as much as 16 feet vertically?

Golden Gate Bridge Youtube Video

The coefficient of expansion for concrete is approximately 0.00001 m/m per degree Celsius. If your bridge is 100m long then it should lengthen about 1mm per degree.

http://www.supercivilcd.com/THERMAL.htm

mm, Celsius. What are you talking about?!

OK then...

A change of 0.00001 varas, per vara of original length, per 0.8 degrees of change on the Réaumur scale.

How much is that in Smoots?