Lever Rule DF Calc Truck Placement

[jrw501]

Hey guys, I had a question about laying out design trucks for DF calculations using the lever rule. The attached picture comes from Barker and Puckett's Design of Highway Bridges, an LRFD Approach. I just wanted to verify that what they are showing violates AASHTO's 2' minimum from the design lane (based on 12' design lanes) and that the wheel line from the 2nd truck would need to be 6' rather than 4' away.

I'm looking at a similar problem where I'm trying to maximize the load going to the adjacent truss, but wanted to make sure I'm not being unconservative.

Thanks!

 

[bridgebuster]

The illustration is correct. Lever rule only applies to a fascia. The first wheel is 2' from the barrier. At first glance the sketch can be deceiving because it shows two wheels at each end of the axle. Ordinarily, when we sketch it out in calculations we just show a vector.

 

[jrw501]

Can you overlap design lanes though? I'd think it would be okay we considered the design lanes as just the loaded part (10' wide) since the 2nd truck would be 2' away from the edge of the design lane, but since the AASHTO design lanes are 12' wide (even though only 10' is loaded) isn't it too close?

 

[bridgebuster]

12' is the standard lane width for an interstate highway. This is the number we use for laying out the spacing of trucks across the bridge. 10' is the lane width for applying the uniform load. You can't overlap the lane loads. Hope this helps.

 

[jrw501]

Yep, thanks.

 

[bridgebuster]

you're welcome