LRFD Lever Rule

[bridgeengineer2007]

Since AASHTO LRFD's design load is a combination of the HL-93 Truck and Lane, do you use both the truck and lane when computing the lever rule, or do you only consider the Truck Wheel Loads?

 

[CivStruck]

I compute a separate LLDF (live load distribution factor) for the truck wheels and the lane load. I draw a triangle with the peak of the traingle at 1 at the suspect girder and going to 0 at adjacent girders (or remaining at 1 if an overhang is adjacent). I then compute the ordinate on this 'influence tringle' for each wheel load and add them then divide by 2 to get it in terms of per truck. I also compute the area under the 'influence triangle' where the lane load is and divide this by 10 ft lane width to get it in terms of per lane. Then I can use my truck and lane moment/shear effect (from a single truck or lane analysis: lane load being 0.64 k/ft) along with these LLDF which are already in terms of per lane. Just multiply them together along with multipresence (and impact for the truck only) to get moments and shears.

 

[CivStruck]

If you have unique dead load such as a sidewalk or pedestrian loading on that sidewalk you may also choose to use this approach of the area under the influence triangle to distribute that load transversely. This is even sometimes done for barrier, but they are typically divided equally between all beams.

 

[tre5205]

Is there a example hand calculation of how to compute the lever rule distribution factors?