# Excess Camber Slope Calculation for Bearing Recess Geometry

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Nate
Excess Camber Slope Calculation for Bearing Recess Geometry

I have a 126.33 foot WF66G girder that will be placed on a ~5% slope. The girder will have a sole plate mounted on it to ensure it seats level on the bearing pad. I am trying to calculate the correct slope of the sole plate. I have my calculation broken down into slope due to the longitudinal profile of the girder and slope due to excess camber in the girder. My slope due to longitudinal profile of the girder matches what PGSuper calculates in the 'Bearing Recess Geometry' Table in the 'Details Report'. However, I'm having a hard time matching the Excess Camber Slope, and I'm curious how PGSuper is calculating this.

1. When calculating the excess camber using D-C, what value does PGSuper use for D? If I work backwards to calculate the D value PGSuper is using, it appears to be using ~63% of D.40 (actual 40 day camber, not what is reported in girder schedule) or ~53% of D.120. In my calculations I took D40 and D120 from the 'Camber Details' section of the 'Details Report', as the girder schedule would have round off error. I'm assuming this is also what PGSuper does?

2. What geometric assumptions does PGSuper use when determining the camber slope? Does it assume a straight line between the start of the girder at bearing seat and the girder quarter point, with the camber at the quarter point taken as 3/4C? Or does it use calculus to actually determine the slope at the bearing seat assuming the camber follows a circular arc? Both of these methods come out fairly close, but I'm curious if there is an accepted standard of practice for this sort of calculation.

I can post my PGSuper file and calculation if this would be helpful.

Thanks,
Nate Bloss

Rick Brice
Excess Camber Slope Calculation for Bearing Recess Geometry

The excess camber slope is computing at the CL Bearing using the same loads as computing the excess camber. Excess camber is computed as D-C with D based on maximum timing which is typically set to 120 days.

For uniform loads such as the girder, slab, barriers, etc, slope is wL^3/(24EI). The equation for concentrated loads for harped strand prestress and diaphragms is different, I don't have the closed form equation handy, but its easy enough to look up.

The D slope is due to girder, diaphragm, prestress, and creep. The C slope is due to deck, haunch, and traffic barrier. Depending on your model, there may be additional loads included.