Parapet dead load deflection 1

[BridgeEI]

I have a fairly wide bridge with 10+ girders and I'm curious how others take care of the composite deflection for the traffic rail/parapet. For strength design, I distribute the rail weight to no more than 3 beams. But what about for the deflection?

I'm waffling back and forth whether to use the parapet deflection on all the interior girders..

 

[bridgebuster]

Typically the SDL is distributed equally. Is this the bridge staged construction because that changes things a bit.

 

[BridgeEI]

It is phased so that adds some complexity. I know AASHTO allows you to distribute it equally to all girders but it just doesn't seem intuitive to me, but it does clean up the deflections. Txdot only allows you to distribute it to 3 girders which seems more reasonable to me. I just don't know what they do about deflectionss.

Normally this isn't an issue, but I have some really long spans so it becomes exaggerated more than a typical bridge.

 

[bridgebuster]

With staged/phased construction the SDL deflection for each girder may not necessarily the same as it would if the deck was cast in one placement. A grid analysis would be very useful.

Download a copy of NSBA G13.1 Guidelines For Steel Girder Bridge Analysis. It's a very comprehensive publication. Also, In Chapter 5 of the NYSDOT Bridge Manual there is a discussion on computing SDL deflections for steel superstructures.

Link

 

[BridgeEI]

Thanks for the link, that's very helpful!

 

[bridgebuster]

You're welcome.

Remember when all else fails there's always a closure pour to set things right.

 

[BridgeEI]

I am calling for one on this project, however I've seen contractors completely omit it....

 

[Shz713]

I had similar issue before, you guys have well-defined guidelines in contrast to ours (AUS standards)!
As said by Bridgebuster, we almost do that in many cases since it is out of scope/not covered in states' practice

Shoot for the Moon, even if U miss, U still land among Stars!

 

[OSUCivlEng]

I'm curious about how other states handle closure pours and the locations of construction joints. Do other DOT's get worried if longitudinal construction joint falls in the wheel path? Closure pours have always seemed like a good way to handle phased construction when placing the deck. However, I'm not sure I've ever seen one used in OK.

 

[bridgebuster]

NYSDOT recommends the use of closure pours with staged (phased) construction. At lot of times on projects in NYC there's not enough room to have a closure pour and maintain traffic.

 

[3Fan]

Our DOT (Ohio) uses closure pours. There is guidance about: width, lap splices vs. mechanical connectors, no construction joints above the flanges, how to seal the construction joints (High Molecular Weight Methacrylate), a preference of the joint to be in the positive moment region of the slab, and the cross frames aren't to be attached in that bay until the concrete has been cast on both sides of the closure pour. If differential deflection is less than 1/4" between the two phases, then a closure pour is not required. But there is no guidance on not placing a construction joint at the wheel path. Depending on the State's reviewer though, they may make a comment. Therefore we do all that we can to not place a closure pour construction joint at a wheel path line.

 

[EQguys]

BridgeEI,

Unless there is a specific guideline from the state, I have always taken the barrier loads to be distributed as 60-40 between the exterior and the first interior girder. I have also found that the deflections due to the barrier loads beyond the first interior girder is almost negligible.

I would like to add another point to what 3Fan recommended. We recently did a wide bridge deck job with phasing for DDOT. At the bay where the closure pour was planned, we were not allowed to use SIP forms, even though the differential deflection between the two phases was less than 1/2 in. So we ended up using SIP forms at other bays and overhang bracket with timber forms at the closure pour bay during both phases. Something to consider for your project.