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AREMA DPG Bridge Cross Frame Design for Derailment Load

AREMA DPG Bridge Cross Frame Design for Derailment Load

AREMA DPG Bridge Cross Frame Design for Derailment Load

I'm designing a new 64' DPG bridge for Cooper E80 load and sizing the "X" configuration cross frame diagonals (at 60 degrees with the vertical) with top and bottom horizontal braces (cross frames at 8' spacing with 8' c/c girders) and the derailment loads (AREMA MRE Article 15-1.3.10) I'm getting are in the order 200 kips, which still allows me to use 2-L6x4x1/2 for the top horizontal brace (with the 150% allowable overstress), but when checking the end connections and gusset plates, I required approximately 9 bolts in double shear when using the 17 ksi allowable shear stress for bolts (slip-critical). This seems quite high...when most sample bridges I've seen only have 3 or 4 bolts at each end.

This requiring appears to have been added to the manual in 2005 and I'm wondering if designers are actually designing the cross frames for the derailment load? If so, do these loads appear to make sense and does anyone have any guidance on designing the cross frames for this load. Is using the slip-critical allowable stress the correct approach given that this is an "exceptional" load case?

Thanks in advance for any assistance!


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