Influence Line for Trucks 2

[dlawrence529]

I'm working on a work trestle for an upcoming bridge construction project. The contractor would like to back trucks with bridge beams onto the trestle for unloading. The truck/trailer/load will be +/- 140 kips on 6 axles. The trestle beams are simply supported spans. I'm trying to do this by hand, but it's quickly becoming a bookkeeping nightmare.

Is there a simple (preferably free or cheap) program that can create/analyze influence diagrams for beams?

Are there any assumptions that can be made to simplify the hand calculations? For example, is it common practice to create an influence lines at quarter points of the trestle beams rather than 1 ft increments across the beam?

 

[DETstru]

RISA does moving loads, you can look into that.

There's also this old publication from AISC. Not sure if it'll help you though.

https://www.aisc.org/globalassets/a...-reactions-for-continuous-highway-bridges.pdf

 

[RPMG]

The influence lines (shear and moment) are just triangles for simple spans, but I wouldn't use influence lines to solve this problem.

Place the wheel nearest the center of gravity at midspan and solve for moment.

 

[IDS]

See:

https://newtonexcelbach.com/2013/12/03/moving-load-spreadsheet-update-and-how-to-use/

Any questions, please ask.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[WARose]

For a simple span, you don't need influence lines. (That is for continuous spans.) AASHTO has a table that gives max. shear & moments for simple spans based on load spec (i.e. H20, etc). AISC also has a shear/moment max. equation for a multi-axial vehicle on a simple span beam.

 

[Lomarandil]

Yes, if your trucks are legal loads (e.g. HS-20) or can only put two axles on a span at any time (which is typical, it's uncommon to have long span trestles), I'd go with WARose's method.

If not, use a beam analysis software with some educated guess-and-check placement (or moving load analysis if available).

----
The name is a long story -- just call me Lo.

 

[IDS]

You don't need to do a moving load analysis for simply supported spans, but if you have a non-standard load with 6 axles (as stated in the OP) it makes life easier, and it allows you to see what is going on more clearly, so I'm not sure why people want to avoid doing it.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Lomarandil]

Sorry, I must have missed the truck information in the first post. I'm not opposed to moving load analysis if you have the tool. It sounds like OP might not have software capable of it right now.

(Also, some of my inherent bias against the "let the computer solve everything" trend is seeping in).

----
The name is a long story -- just call me Lo.

 

[IDS]

Sorry, I must have missed the truck information in the first post. I'm not opposed to moving load analysis if you have the tool. It sounds like OP might not have software capable of it right now.

He does if he followed the link in my first post in this thread.




Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[dlawrence529]

Thanks for all the responses. I looked into RISA 2D for the moving load analysis, but unfortunately RISA has moved to a yearly subscription license. I don't think I would use it enough to justify a yearly expense. The trend of moving toward yearly subscriptions for program licenses is becoming very frustrating.

I tried looking into AASHTO and AISC, but it seemed like the diagrams are geared toward specific loading or multispan beams. I don't deal with moving loads very much, so maybe I'm just having trouble applying them to my scenario.

Thanks IDS for the excel workbook. This looks like it is exactly what I need. Hopefully I will have some time to dive into it this morning