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Dear Bridge engs,

I am comparing the various methods used in the practice for calculation of live load distribution factor (LLDF) for various load effects. Please share your approach and the limitation if any that you faced.

Also, if someone has S-over equations, I'd be grateful to share it with me.

Thanks everyone for sharing their viewpoint.

Shoot for the Moon, even if U miss, U still land among Stars!


There may be many people who know what an S-over equation is, but I don't, and neither does Google.

Doug Jenkins
Interactive Design Services



Quote (IDS)

The wheel load distribution factor equations from the AASHTO Standard Specification (AASHTO 1996) are called “S-over” equations, which is only dependent upon the girder spacing.

Shoot for the Moon, even if U miss, U still land among Stars!


I don't understand, why wouldn't you use the LLDF equations from the AASHTO LRFD?



Quote (ernestog84)

I am doing parametric study and need to compare it with some other approaches used for LLDF.

Shoot for the Moon, even if U miss, U still land among Stars!


Dear all,

I have confusion wrt lever rule. In figure below, I want to find out LLDF using lever rule for exterior and interior girders on three-cell box girder.

  • for exterior girder one lane loaded, I found the fraction of truck loading multiplied to 1.2 for multi-presence factor. For two lane loading, shall I use the same fraction of load multiplied by 1 for two lane loading or I have to calculate again?
  • for interior girder one lane loaded, cay I say '(1-reaction at A obtained above) * 1.2 ' obtained above? Since for one lane loading only one wheel is going to first interior girder. In case of two-lane loading, two wheel loads are going to first interior girder, right? If so, then we take moment about point C to get reaction at point B multiplied by 1.0 (for multi-presence factor).

  • Please correct me if above procedure is inaccurate.

    Shoot for the Moon, even if U miss, U still land among Stars!

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