AREMA code questions

[Knarf1Man]

We recently purchased the 2009 AREMA manual. My questions relate to the use of Table 15-1-15 (Max. Moments, Shears and Pier/Floorbeam Reactions for E80 Live-Load) on page 15-1-77.

To simplify, let's assume that I have a single track that bridges over an unloading pit. There are multiple 12-foot simple-spans that frame into floorbeams, which bear directly on the pit-walls.

My two questions are as follows:

1) For the floorbeams, do I use the listed "Max.Pier Reaction" for a 12-ft span, or do I use the value for a 24-ft span, or do I multiply the 12-ft span value by two (2)?

2) I also see that this table states "All Values are for one-rail (one-half track load)". Does this mean I should size my rail support-members/beams for 100% of the listed values? I know in the past, we have always assumed the tabulated values were NET moments/reactions from an E80 loading that were based off axle-loadings, and thus we always divided the values by two-rails (i.e., 50% of the listed values). Our resulting member sizes were very close/similar to those listed in AREMA Figure 15-8-6 on page 15-8-21.

Any help or clarification on this subject will be greatly appreciated. TIA (Thanks In Advance)

 

[jdonville]

Suggest you post in one of the structural forums...

J

 

[Knarf1Man]

Ok .... for those who may be interested, here's the official response directly from AREMA

Answers:

1) For the floorbeam reactions, use the 12-ft span pier reaction listed. The pier reaction is based on a 12-foot span on either side of the pier, or a total influence on the pier of 24 feet. Keep in mind that the pier reaction listed is only the vertical force, and does not take into account the eccentricity of the reactions between the two sides that will create an overturning moment on top of the pier that needs to be accounted for in the pier design, if you are using two separate supports for the beams. If it is a single floorbeam, the overturning moment would not be generated.

2) The forces and moments listed in Table 15-1-15 are for one rail, so whatever superstructure support you have for each individual rail needs to be designed to 100% of the force or moment listed in that table plus the applicable impact. Impact is not included in Table 15-1-15.