We don't need no stinkin' bridge shoes...

[DKS]

With a ton of new highway bridge work going on in my area, I happened to notice a new (to me, at least) construction method, whereby deck girders are bolted directly to the abutments at both ends of the bridge, and concrete is poured around the ends of the girders. Ed's Law: no bridge shoes.



Not sure if this has migrated--or will migrate--to railroad bridge construction, but I thought it was rather novel. Evidently expansion/contraction is handled differently. Brute force?

[C855B]

Oo. That's ugly. Keep an eye on it, this has got to be thermal expansion Hell. I'll ask my ex-DOT engineer buddy if there's something new we don't know about since there's a whole bunch of voodoo science going on with concrete admixtures.

[Scottl]

It kind of looks like the concrete the beams are mounted to is an isolated block, so perhaps it can move a bit.

[Frisco Larry]

I am a retired bridge engineer with the Kansas Dept. of Transportation.  We have been building bridges with no moveable bearings since the late '70's.  It eliminates the high maintenance problems inherent with expansion joints.  It was observed that the joints tended to rust and lock up with no particular harm, so it was decided to just build the bridge locked up in the first place. It is limited to bridges of a total of about 300'-400'.  Not sure if anyone knows where the temperature movement actually goes, it is assumed that the bridge accommodates expansion by simply arching up between the supports. 

[peteski]

I am a retired bridge engineer with the Kansas Dept. of Transportation.  We have been building bridges with no moveable bearings since the late '70's.  It eliminates the high maintenance problems inherent with expansion joints.  It was observed that the joints tended to rust and lock up with no particular harm, so it was decided to just build the bridge locked up in the first place. It is limited to bridges of a total of about 300'-400'.  Not sure if anyone knows where the temperature movement actually goes, it is assumed that the bridge accommodates expansion by simply arching up between the supports.

So bridge engineers simply decided to stop utilizing expansion joints?  Without any research or experimentation before implementing the new technique on real bridges?  Nobody knows what happens to the bridge under extreme temperatures?! If this is the way new construction methods are implemented on bridges, it doesn't give me a "warm and fuzzy" feeling about using those bridges. 

[Ian MacMillan]

Several of the new NH Route 16 (Spaulding Turnpike) expansion bridges use this method as well.

[DKS]

I am a retired bridge engineer with the Kansas Dept. of Transportation.  We have been building bridges with no moveable bearings since the late '70's.

Interesting. As someone with a fascination for bridges, and who pays fairly close attention to their design, I can say I have never seen this particular construction method until now. I guess I'm not in Kansas any more...

[Philip H]

So bridge engineers simply decided to stop utilizing expansion joints?  Without any research or experimentation before implementing the new technique on real bridges?  Nobody knows what happens to the bridge under extreme temperatures?! If this is the way new construction methods are implemented on bridges, it doesn't give me a "warm and fuzzy" feeling about using those bridges. 

Peteski,
Studies of new techniques take time, and data, and science, none of which seem to be politically palatable these days.  Ditto maintaining bridges once they are built.  Neither of those gives me a warm and fuzzy feeling either.

[DKS]

It kind of looks like the concrete the beams are mounted to is an isolated block, so perhaps it can move a bit.

Nope, they are bolted tight into the tops of the main abutments. There are other portions added around them that make them look isolated.

[dmidkiff]

We build integral abutments here in Colorado.  The bridge girders rest on a concrete beam (abutment cap) that is supported on steel H piles; then the girders are cast in a concrete diaphragm.  Generally, the girders rest on neoprene pads and are not bolted to anything, the cast diaphragm locks everything in.  The abutment cap can move with temperature change, deflecting the H piles.  The expansion joint is moved off the bridge to the end of an approach span, which is a slab of concrete 20'-40' long than rests on the fill and moves as one big unit with the bridge.  There are restrictions in total bridge length to ensure the movements are not overly excessive.



Not sure about Kansas, but letting the girders arch would make sense too as long as the bridge length was controlled.  With 300'-400' bridges, they would need to be multiple spans, is there any movement allowed at the interior piers?  Or are they integral as well?

Doug

[Frisco Larry]

I did not want to get too technical in previous post.  I mentioned that it had been observed that expansion joints tended to freeze up and no harm appeared once that happened.  Expansion joints are a major headache and have been studied to death for years.  It was decided to build a bridge without any expansion joints about 1978.  It was monitored and sure enough no problems. So that is now commonly done.  Our bridges are very similar to the drawing in Doug's post.  Cast-in-place concrete  and precast concrete bridges have been built without expansion joints for even more years.  The stresses from temperature changes, on paper, are not insignificant, but the bridges dissipate these stresses harmlessly.  There are many theories as to how bridges do this but as far as I know no one knows for sure.  Sorry to burst any bubbles, but bridge design is frequently as much art as science (and sometimes smoke and mirrors).  And even with all the computers we have now, trial and error is still used to come up with new solutions.

[peteski]

I guess I just don't like the fact they my life depends on trial-and-error construction methods (especially in this day and age).  But it is what it is, I guess.

I wonder if this type of construction works equally well in climates where there are wide temperature swings as it does in more temperate climates. 

[nsbob]

With the girders not bolted to anything, just make sure it's not over a waterway where a barge can run into it.   The investigation of the Sunset Limited Amtrak crash determined that the bridge girders were not bolted to the pilings because the bridge was designed to be a swinging bridge, which it never was.  Worst train accident in Amtrak history.

[pnolan48]

I guess I just don't like the fact they my life depends on trial-and-error construction methods (especially in this day and age).  But it is what it is, I guess.

Pete,

Most of engineering was trial and error. In the day and age of the Romans, there wasn't much more than trial and error--oh, and yes, experience. Perhaps experience counts for something?

I'm pretty sure all the expansion forces are internalized, eventually. A reinforced concrete slab may not expand as predicted by math; the internal concrete might just be pressurized a bit.

[peteski]

Pete,

Most of engineering was trial and error. In the day and age of the Romans, there wasn't much more than trial and error--oh, and yes, experience. Perhaps experience counts for something?

I'm pretty sure all the expansion forces are internalized, eventually. A reinforced concrete slab may not expand as predicted by math; the internal concrete might just be pressurized a bit.

I guess that I expected that some sort of math was involved, especially since we are in the 21 Century, where computer simulations seem to be done for lots of applications. Even in the 2nd half of the 20th Century, I would have expected some sort of scientific (read mathematical) approach, rather than just experimenting. After all, we don't live in the age of the Romans. 

I do know that things like load limits of a bridge are calculated - why not expansion?  Or, are bridges and skyscrapers just built haphazardly, by trial and error?  If they crumble - no big deal?    Was Geo. Washington, or Brooklyn Bridge (in NYC) built using trial and error?!