how to convert moving axle load of vehicles into equivalent uniformly distributed load ?

[shaz2015]

i want to know how to convert moving axle loads of vehicles into equivalent uniformly distributed load ? i want those to check the stability of existing bridges.

 

[CELinOttawa]

You really should not do that... You need to apply the design loading as a series of axles, or at most as a resolved set of point loads. That's why the codes and standards don't just simply use a UDL, but rather a combination of UDL and point loads.

 

[cooperDBM]

For each point along the span, each load effect at that point will be maximized by the vehicle being at a different position along the bridge. A UDL can't simulate that variation. Bridge codes will use a UDL to simulate dispersed lighter traffic (i.e. cars) in conjunction with a moving heavier truck load. That case usually governs for long spans where whole alternating spans are loaded. The UDL is determined by statistical analysis for a certain level of traffic.

 

[KootK]

It depend on which member you're checking the stability of. Piers/bents? Girders? Through trusses?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[JStephen]

For you bridge guys- sort of a curiosity question relating to the above- are dynamic effects taken into account with the vehicle loading?
The reason I ask, I have noticed on occasion, riding a bicycle over pedestrian bridges, that you seem to get noticeably more bounce in the bridge at certain speeds, and didn't know if this was ever an issue on "real" bridges?

 

[MikeHalloran]

Dynamic effects do occur on real bridges; it's why soldiers are trained to _not_ march in step on bridges. Marching in step can excite resonances.

Resonances were not quite ignored in bridge design until 'Galloping Gertie' fell.

Mike Halloran
Pembroke Pines, FL, USA

 

[IDS]

The Australian bridge code has a dynamic load allowance, which varies depending on the type of load. Some other codes incorporate the dynamic allowance in the specified load.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[CELinOttawa]

Bridge codes always address dynamic loading, but the exact method differs...

 

[shaz2015]

In AREMA code (fig-8.2.1) live load provisions, E-80 axle load diagram shows a trailing load (train load) of 8000 lb/linear ft after the locomotive. i was wondering how the train load of passenger/freight coaches or wagons have been converted into a UDL.

Thank you All for the responses!

 

[CELinOttawa]

Okay, well that is much more specific... The reality is that a railroad bridge will face a highly variable, highly symmetrical, loading following the engine. This is also of an unknown length. The weight of those cars typically is also not as significant as the locomotive...

The exact method of conversion I can't comment on, but I would guess it is point loads divided by typical length of car.

 

[mike20793]

AASHTO uses a 33% increase in the live load to account for vehicles bouncing caused by uneven roadways. Back to the original question, you need to use the influence lines to examine the critical axle locations for shear, positive moment, and negative moment (if applicable). This is a bit different than joist design, for example, where you can find an equivalent load based on max shear/moment caused by special loading. It's not applicable here because the load is moving.

 

[jreit]

There is a very useful program Quick Bridge by Professor Turkann that draws the influence lines for you for moving axle loads. It is free.
If you want to account for dynamic load, just increase the axle loads accordingly.

 

[shaz2015]

i checked the web page of prof. yelda Turkann but couldnt find that software. can u guide me how to get it?

thanks!

 

[shaz2015]

@ CELinOttawa:

in case of longer spans, more than the length of locomotive(s), the trailing loads may become significant.

 

[CELinOttawa]

Agreed...

 

[jreit]

It is Professor Noyan Turkann.

http://www.engineeringcivil.com/wp-content/uploads/2498/2498.

XLS

Just remove the space between the . and the xls.

Hope this helps.