I wonder how AREMA specifies the rocking effect exactly. Chapter 15-1.3.5 says all the impact effects should be applied on top of each rail. But the rocking effect is actually calculated for individual girders. For example, if I have four girders spaced at 2.5ft, the gage is 5ft, then RE is 24% for the two exterior girders and 8% for the two interior girders. Assume 30% due to vertical impact effect. When I calculate the impact, should I use
(a) the combination of girder REs under one rail
1+IM = 1+32%+30% = 1.62 for one rail (average 0.81 for one girder)
or (b) the largest RE
1+IM = 1+24%+30% = 1.54 for one rail (average 0.77 for one girder)
I read Part 9 Commentary but still could not figure out. I feel that (a) makes sense as eventually the moment/shear calculations are for one rail (or half track, or in this case involves two girders), but other folks in the office said (b) is usually the way how RE was handled. I wonder if anyone can help point to the right solution, or if there are any references on this subject that I can go look for the answer?
Thanks!
Yuan
(a) the combination of girder REs under one rail
1+IM = 1+32%+30% = 1.62 for one rail (average 0.81 for one girder)
or (b) the largest RE
1+IM = 1+24%+30% = 1.54 for one rail (average 0.77 for one girder)
I read Part 9 Commentary but still could not figure out. I feel that (a) makes sense as eventually the moment/shear calculations are for one rail (or half track, or in this case involves two girders), but other folks in the office said (b) is usually the way how RE was handled. I wonder if anyone can help point to the right solution, or if there are any references on this subject that I can go look for the answer?
Thanks!
Yuan
