Roadway plate design 1

[jjalex1]

What is the deflection criteria for a temporary roadway plate?

 

[oldestguy]

I'd check with the jurisdiction that "owns' the road. They may have a spec.

 

[WARose]

I generally just use AASTO's deflection criteria......which is L/800 (for live load + Impact).

 

[bridgebuster]

I agree with OG; different jurisdictions have different rules. I've seen some places that have a minimum thickness based on trench width and others, like NYC, that have deflection limitations (3/4" in NYC). Also, it's good to check with the AHJ because they may have specific anchoring details.

 

[jjalex1]

Thanks I'm in NYC. I was told yesterday by a coworker that NYSDOT doesn't want plates down because there was a really bad motorcycle accident and the cyclist sued.

 

[bridgebuster]

@jjalex1 - is it just in Region 11 or statewide? I've seen bridge plans for several projects in Regions 8 & 10 that had roadway plates. I also did a bridge project in Region 11 that had a roadway plate detail - just in case.

 

[oldestguy]

Looks like there might be some legal issues. I'd be very careful and maybe even let my attorney know what the situation is.

 

[jjalex1]

It's Region 11. Bridgebuster, what is the limiting criteria for deflection? I found the NYC DOT Highway rules August 2016 edition and it says for plating and decking if the deflection is more than 3/4", heavier sections or plates or decking or intermediate supports shall be used.

 

[dik]

WARose: Do you have a formula for the deflection? Is it based on a single wheel load or maybe tandem or a UDL over the entire plate?

Dik

 

[WARose]

WARose: Do you have a formula for the deflection?

Of the plate? I've used Roark's before......but a FEA solution is a bit easier for me. The most common mistake I see people make is putting the load in as a point load.....when a pressure load cuts back on the deflection/stress.

Is it based on a single wheel load or maybe tandem or a UDL over the entire plate?

Just the applicable AASHTO service live load (plus impact). (Typically the HS20-44 load.) Most of the time, the geometry of a plate dictates a single wheel.

 

[bridgebuster]

@jjalex1 - on NYSDOT projects that I've seen with plates, the thickness is specified. Meanwhile, they also have a policy for utility work in State ROW's, which says plates are permitted but nothing more. The NYCDOT Highway Rules only specify the maximum deflection. Attached is a plate "spec" that was used a few years ago on the Belt Parkway in Brooklyn, when the City was doing the Fresh Creek Bridge.

 

[dik]

WARose: I'd treat it as a tire inflation pressure over an area...

Dik

 

[WARose]

WARose: I'd treat it as a tire inflation pressure over an area...

Yep, I've seen that done myself. AASHTO (16th edition, Sect. 3.30) calls out the tire contact area as: "...a rectangle with an area in square inches of 0.01P, and a Length in Direction of Traffic/Width of Tire ratio of 1/2.5, in which P= wheel load in pounds."

You work that out and it comes to a tire pressure of 100 psi...which is about what it typically is.