What expansion joint type to use for long bridge with transverse seismic movement?

[BridgeSmith]

We have a 980' long highway bridge to design in a high seismic region. We will be using seismic isolation bearings, so in addition to the regular longitudinal movements due to thermal expansion (nearly 7" total), the expansion joint will need to accommodate several inches of transverse displacement during an earthquake.

The joint does not have to survive undamaged, but the bridge will need to be passable by emergency vehicles immediately after an earthquake.

There are specialized modular (multiple strip seal) type joints available, they are very large (depth-wise) and very expensive, so we'd like to keep it simpler and more economical if we could.

Any suggestions?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[bridgebuster]

Rod - have you though about a finger joint. I know, they're a pain in the @$$ to maintain. A few years back, there was a viaduct rehab in NYS that replaced a modular joint with a finger. I was a bit surprised because NYSDOT tends to be very conservative. If I find the drawings I'll post them.

 

[wiktor]

Rod,
Try using finger joint (this will accommodate longitudinal movement) with trapezoidal or triangular elongated fingers, which could slide of top of each other in case of lateral movement.In case of earthquake, you may loose some fingers, but the bridge will remain derivable. Other option will be typical finger joint with the fingers attached by shearable bolts

 

[BridgeSmith]

We considered finger joints, but there was concern by my superiors that the earthquake movements could cause the fingers to end up sticking up and become a spike strip. Seems like a remote possibility to me, but they get the big bucks and call the shots...I just work here.

The trapezoidal fingers are an intriguing concept. Are there fabricators/suppliers of these as a packaged system?

I found a company in the UK, Trelleborg, that does a "Seismic Transflex" joint, but I haven't found a US supplier yet. I also haven't seen anything about the durability. Out here in Mountain West region of the US, we've not had good results with the older generations of transflex devices (almost all of the ones installed here 20-30 years ago had to be replaced after about 10 years).

Rod Smith, P.E., The artist formerly known as HotRod10

 

[wiktor]

Rod,
I'm unaware of any manufacturer of such joints, but will ask my Japanese friend. Anyway, it's easy manufacturing, some machining required.
Other option could be to attach one side of the finger joint assembly with bolts designed to shear off. I'm sure it will work - it worked just fine on the Manhattan Bridge, where wind tongue bearing plates were worn out, and the sideways movement of the bridge main span was shearing of joint's clamping bolts.

 

[BridgeSmith]

Watson Bowman Acme (WABO) has a modular finger joint device (Wabo Trident) where each set of 3 fingers can turn side to side to accommodate transverse movement. It looks very interesting.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[bridgebuster]

I remember Transflex, the miracle joint. We stopped using them in NY in the early 80's.

 

[BridgeSmith]

It was probably closer to 30 years (or more) ago than 20 for our department, as well. I keep forgetting how long I've here (almost 19 years now). Most were replaced before my time.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Guest090822]

I was going to suggest the multi-cell modular or finger joints as well. NYSDOT has been slowly implementing finger joints over the past few years for two reasons: 1) The modular joints aren't performing well, 2) the former head of bridge design that hated finger joints retired! I know Vermont never really stopped using finger joints, but this part of the country only has two seismic areas and they pale compared to the Western U.S. I've actually designed a bridge near Montreal that was considered a high seismic zone around here and seismic didn't control the design. I don't believe the Northeast ever goes past a Zone 2 for seismic, at least that I've experienced.

 

[BridgeSmith]

Thanks for info on the modular joints, Rick. I hadn't heard anything about issues with them, so knowing that helps in weighing things out.

We only have a small area of the state where seismic is a big deal (around Yellowstone NP), and it's hard to get too concerned about it even there. Of course, we have to follow the specs, but the reality is that if the seismic event of the magnitude we design for ever occurred, it would be accompanied by a volcanic eruption that would make the condition of the bridges irrelevant. That said, the last bridge I designed for that area should survive a quake well beyond the magnitude of the design event, and likely the MCE (2500 year event). Those lead-rubber seismic isolator bearings are incredible pieces of technology. Those combined with some fairly easy and cheap capacity protection, creates a very robust system.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Guest090822]

BridgeSmith - I will clarify that it's the rubber seals that don't perform. The manufacturer's claim a 25-year life, but in the Northeast with all the salt we put on the roads, we are lucky to get 10 years. The old finger joints were good, but maintenance crews didn't keep up with cleaning the troughs which eventually wore out and then the salts from winter leaked right onto the bearing and girder ends. I've spend half my career fixing so many bearings and repairing girder ends it's enough to drive you crazy. I had a group of 300 engineers bust out laughing at a conference a few years back when some guy that was presenting on the design of joints asked "What do all joint have in common", my reply was "They all leak!"

I went skiing in Jackson Hole back in 2004 - what a place!

 

[BridgeSmith]

We fight basically the same fight with joint seals and rusty girder ends here. Your reply would get the same response in a group of our engineers.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[bridgebuster]

Rod,

If the powers that be are all for a modular joint, why not put it in the approach slab? This way no leakage to worry about. In NY, the trend is to go jointless wherever possible.

I've inspected a fair amount of bridges with fingers, rarely have I found a problem with the assembly. It's everything around it that goes bad from lack of maintenance.

 

[BridgeSmith]

I've already made my pitch for a semi-integral abutment, bridgebuster, but was unsuccessful. They want a traditional sill type because of the large thermal movement required. I did a 485' one with the semi-integral abutment last year. We inserted a layer of elasticized geofoam (Terraflex) behind the abutments to accommodate the thermal and potential seismic movements.

Putting the expansion joint at the end of the approach slab, as in the detail you posted on a sleeper slab has become our preferred configuration for our medium to large bridges (150' to 500'). For short bridges, we typically use compression seals between the fully integral abutments and the approach slabs.

I'm curious as to what type of bearing supports the end of the superstructure in the detail you've shown. Is it a slab bridge on a stub abutment, or is that the concrete end diaphragm I'm seeing there, with a bearing below, that's not shown?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[bridgebuster]

Rod - most likely elastomeric bearing with a masonry and sole plates. I’ll check when I get home.

They are elastomeric.

 

[crossframe]

When considering the cost of a modular joint compared to a finger joint on a 980-ft bridge, will there really be that much of a difference to the overall construction cost? I'm all for stretching the money as much as possible, but you might want to consider the overall impact. Sometimes it matters, sometimes it doesn't.

 

[BridgeSmith]

You're right crossframe, the cost difference wouldn't be that significant. Our main hesitation with the modular joints, particularly for this application, is our lack of familiarity with the systems, the limited number of successful installations (of the modular joints that accommodate transverse movement), and the major departure from our typical bridge end configurations, due to the depth of the blockout required. I know coping the ends of beams is common in the building industry, but it's rare for bridge girders, and in the bridge world we rely heavily on successful past practice. It's probably due to most major bridges being one-of-a-kind that discourages 'experimentation'. Maybe we rely on past practice too much, but that's another discussion.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Guest090822]

Have you considered just using shear blocks for any transverse movements? In a seismic event, any joint can only go so far, worst case it buckles up or the opening gets bigger. Nothing a road plate can’t handle after the emergency along with some torches if any metal sticks up. It’s the transverse movement that that could cause issues. Back in the 1990’s and early 2000’ shear blocks were common for seismic reasons. I’m assuming you know what I’m talking about. If not I can post a sketch.

 

[BridgeSmith]

We're not concerned about maintaining the seal after a seismic event. However, the access requirements are that emergency vehicles cannot be delayed waiting on a road plate or torch. Emergency vehicles must be able to cross the bridge immediately following the event.

We will most likely employ a shear block of some kind to limit the movement, but the foundation material may not provide enough lateral resistance to be able to limit the movement to a value less than 4".

Rod Smith, P.E., The artist formerly known as HotRod10