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Re: ReTotal weight of a heavy truck -- freight car applications
Author: Dave Smith
Date: 05-27-2013 - 11:08
M. Harris Wrote:
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> Weight distribution in structural members subject
> to bending stresses, like bridges, is very
> important. A structure designed to resist bending
> will respond differently to a 100,000 lb load
> applied at one point than that same weight
> distributed evenly over the span of the structure.
> The location of the applied load with respect to
> the supports determines the bending stress in the
> structure at that point. Consider the example of
> a 2x4 stud 8' long supported at both ends. Stack
> bricks flat across the board until it bends just
> short of breaking. Then take the bricks off and
> stack them in the center of the board. The board
> will break before all the bricks are stacked. A
> bridge has to be built to handle dead load (the
> weight of the bridge itself), service load (the
> weight of the maximum expected number of heavy
> vehicles), and other loads such as wind and
> seismic motion. Each type of load has a different
> distribution of stress, and a different safety
> factor.
>
> M. Harris
> CE License #27924 CA
Not to sidetrack this thread, but since this is a railroad forum .....
There was a very heated discussion on the TRAINS forum awhile back regarding 2-axle vs 3-axle trucks for heavy haul freight cars and the impacts on rail wear. IIRC it was concluded the friction wear on rails from 3-axle freight trucks would outweigh the benefits of spreading that weight over more area. Not sure if we broached the idea of having more spread between the two axles of a 2-axle truck.
Obviously friction wear on a roadway has little to no effect on a bridge's load factor.
-------------------------------------------------------
> Weight distribution in structural members subject
> to bending stresses, like bridges, is very
> important. A structure designed to resist bending
> will respond differently to a 100,000 lb load
> applied at one point than that same weight
> distributed evenly over the span of the structure.
> The location of the applied load with respect to
> the supports determines the bending stress in the
> structure at that point. Consider the example of
> a 2x4 stud 8' long supported at both ends. Stack
> bricks flat across the board until it bends just
> short of breaking. Then take the bricks off and
> stack them in the center of the board. The board
> will break before all the bricks are stacked. A
> bridge has to be built to handle dead load (the
> weight of the bridge itself), service load (the
> weight of the maximum expected number of heavy
> vehicles), and other loads such as wind and
> seismic motion. Each type of load has a different
> distribution of stress, and a different safety
> factor.
>
> M. Harris
> CE License #27924 CA
Not to sidetrack this thread, but since this is a railroad forum .....
There was a very heated discussion on the TRAINS forum awhile back regarding 2-axle vs 3-axle trucks for heavy haul freight cars and the impacts on rail wear. IIRC it was concluded the friction wear on rails from 3-axle freight trucks would outweigh the benefits of spreading that weight over more area. Not sure if we broached the idea of having more spread between the two axles of a 2-axle truck.
Obviously friction wear on a roadway has little to no effect on a bridge's load factor.
