×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

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

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

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

(OP)
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.

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

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.

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

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.

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

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.

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

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?

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

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

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

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/

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

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

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

(OP)
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!

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

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.

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

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.

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

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.

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

(OP)

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

thanks!

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

(OP)
@ CELinOttawa:

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

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

Agreed...

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources