Load Rating of Simple Made Continuous Steel Plate Girder Bridges

[saurav.str]

Can anyone enlighten me with the concept and process on modeling the 3 span - Simple Made Continuous steel plate girder bridges with concrete diaphragms? Apparently, AASHTOWare does not have option to choose multi span analysis for steel bridges of this kind.

Thank you.

 

[tatox]

Simple made continuous is using concrete link slab concrete, right?
So basically, it removes the expansion joint. the connecting plate should be designed for live load only or any transient load after dead load like nature: earthquake and temperature.
so you must calculate it in staged construction (birth and dead elements-loads fem).
the simple spans girder built and activated first.
If the whole slab and connecting slab poured together, than connecting slab will have negative moment due slab self weight in positive region. it active together.
if the connecting plate poured after the slab above girder hardened, then the connecting plate have small negative moment, rotation and tension due non dead load : transient load and nature load afterwards -> small moment than as designed as active in the same time.

 

[BridgeSmith]

The software doesn't analyze that type because that configuration is hardly ever used anymore. Nearly all multispan steel girders are designed to be continuous now.

Some older bridges with simple spans with steel girders have been made continuous for live load using what are commonly referred to as link slabs.

 

[saurav.str]

That is weird. Coz, I have studied recent AISC articles and people have started using SMC steel girders with Steel diaphragm. This bridge Im looking at is SMC plate girders with concrete diaphragms constructed in 2019. I was just wondering how it can be modeled in BrR just like we do for prestressed girders.

 

[BridgeSmith]

One way to model it would be as a continuous girder, but reduce the top flange and web at the piers to a size consistent with the tension restraint provided between the ends of the girder pieces.

 

[saurav.str]

Does that mean calculate the tension restraint provided by concrete diaphragm???

 

[BridgeSmith]

Use whatever tension restraint is there, whether that's reinforcing, a connection plate, or nothing. I wouldn't count on concrete in tension for load rating.

It seems the use of SMC steel girders has been kicking around for a couple decades, but it doesn't seem to be really catching on yet.

 

[bridgebuster]

@tsyox - a link slab does not provide any continuity. It only eliminates a deck joint.

@saurav.str - to me it sounds like your bridge has continuity for slab dead-load and not steel dead load. One way to analyze it would be calculate simple steel DL moments, run your model for slab and live load continuity, and combine the results manually. You would have to include longitudinal deck reinforcement in your model.

 

[saurav.str]

Thank you for the explanations. While playing with BrR, I did actually find a way to make the Girders Simple for DL and cont for LL. If you create a new member alternatives and link that to the girder, the member alternative box will give u an option for that.

 

[BridgeSmith]

@tsyox - a link slab does not provide any continuity. It only eliminates a deck joint.

Apparently, it depends on whose definition you use. In our venacular, replacing a section of a slab of a continuous girder to eliminate a deck joint (which we do regularly) is not considered a link slab.

A link slab, again in the terms we use, provides the tension flange to make simple span girders continuous over an interior support. Continuity of the compression flange is provided by a block of steel or concrete between the ends of the bottom girder flanges.

 

[OSUCivlEng]

BridgeSmith,

Who is we?

Simple made continuous or continuous for live load is used quite a bit in Kansas and Missouri. The concrete diaphragms that encase the beam ends over the pier are detailed with the beams to make the girders continuous for live loads.

Link slabs have been defined for decades as a reinforced slab over a pier in simple span bridge to eliminate a deck joint. If the spans are not too long, it actually speeds up construction and is cheaper than a continuous girder. Your definition of a link slab is more associated with a continuous for live load system.

 

[BridgeSmith]

I was speaking of my understanding of the terminology the bridge design section at the WYDOT uses.

I may have misunderstood the other engineers. You're saying a link slab makes the slab continuous, but the girders are not connected and free to rotate? So aside from the minor amount of bending capacity of the slab itself, the spans remain separate simple spans? Ok, that seems like a plausible way to define it and make that distinction.

We don't do either link slabs or SMC much at all. Mostly, we eliminate the existing deck joints on continuous steel girders. Not sure if there's an accepted term for that.