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AREMA Rocking Effect(RE)

AREMA Rocking Effect(RE)

AREMA Rocking Effect(RE)

(OP)
I am at a complete lost as to how the AREMA rocking effect is calculated. Some texts suggest that RE is calculated as the Total Bridge System while others suggest it is calculated for each Girder.

My method for understanding RE is taken from the text "Design of Modern Steel Railway Bridges". For example I have 4 Girders Spaced at 2.5'. The vertical LL is distributed evenly to all 4 beams, then the applied rocking effect is resisted by a force couple with an arm equal to the distance between the centers of resisting members each side of the track center line.

Therefore RE = (0.2*5ft)/(2*(1.25+1.25)) = 0.20

However, I took an excel sheet from my coworkers that calculates the RE for each girder. Using the same example the sheet calculates the following:

Exterior Girder RE = 0.12
Interior Girder RE = 0.04

This gives an average RE = 0.08. This is a huge reduction from the 0.2 I calculated!!

Can anyone explain what this sheet is doing? Is the vertical LL not distributing to each girder equally? Any help would be really great!

-Marc

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