Live Load Distribution Factor 1

[SebasR0310]

Hi, I'm just a beginner in bridges and I have what I think is a very basic question, but I have to ask.

When the live load distribution factor "g" is calculated by AASHTO, the longitudinal stiffness parameter "kg" is involved, which depends on the area of ​​the beam and the moment of inertia. So, if I have a bridge with different beam geometries (for whatever reason), will each beam have its own "kg" parameter?

My question is because I have seen that sometimes the internal and external beams have a different geometry.

Another question is:

Is it equivalent to make the lever rule in any case to use the formulas of the code in the tables or is it different?

 

[BridgeSmith]

To answer your question, theoretically you should use the average kg for the girder of interest and the adjacent girders on either side.

Generally, only older bridges have different exterior girders. The requirement that exterior girders have at least the same capacity as interior girders (to account for possible future widening of the bridge) has been a requirement of the AASHTO spec for several decades. Because of that requirement, new designs usually have all the same girders.

The lever rule is the conservative default when the bridge configuration is not within the applicable limits shown in the righthand column of the table.