Deflections and AREMA Design
Deflections and AREMA Design
(OP)
I'm stepping into the world of Rail Bridge Design and the daunting AREMA manual.
The Cooper E-80 loads that we design the bridges for are irregular. AREMA has done us designers a favor and tabulated the maximum moment that your primary members would see for most simple spans:
HOWEVER, most design in the rail world is deflection controlled instead of strength.
While envisioning the moving Cooper E-80 load, my brain comes to a screeching halt:
1. Does maximum deflection and maximum moment occur at the same engine position on the bridge?
AND
2. Without using STAAD is there a less than rigorous way of calculating the deflection?
I ask because my superiors are questioning whether I know what I'm doing in STAAD and want to see some hand calculations. Not only that, some here are asserting there is a simple way to do it using the maximum moment given in AREMA and I just don't believe them.
The Cooper E-80 loads that we design the bridges for are irregular. AREMA has done us designers a favor and tabulated the maximum moment that your primary members would see for most simple spans:
HOWEVER, most design in the rail world is deflection controlled instead of strength.
While envisioning the moving Cooper E-80 load, my brain comes to a screeching halt:
1. Does maximum deflection and maximum moment occur at the same engine position on the bridge?
AND
2. Without using STAAD is there a less than rigorous way of calculating the deflection?
I ask because my superiors are questioning whether I know what I'm doing in STAAD and want to see some hand calculations. Not only that, some here are asserting there is a simple way to do it using the maximum moment given in AREMA and I just don't believe them.






RE: Deflections and AREMA Design
Think about the following:
If AREMA shows where wheel loads are for maximum span moment, then that wheel load configuration is likely to give you max live load deflection.
I would treat that load as if it is uniformly distributed and use statics to determine deflection. If you have negative moments too, then treat the span as simple, find deflection delta1, then treat the span as loaded only by the negative moment, find delta2. Algebraic differences should give you a close estimate.
Dont know what load factors are used in Arema for deflection. Have a look at that.
respects
ijr
RE: Deflections and AREMA Design
RE: Deflections and AREMA Design
RE: Deflections and AREMA Design
IJR:
AREMA does not show the location of the Axle Loads, only gives Maximum Moment.
Stillerz:
It's was a great problem for that :) however I'm working with a few senior employees for the first time... and they're lacking confidence in STAAD and myself (I'm the new kid on the block).
cntw1953:
Plan B.
Thanks everyone
RE: Deflections and AREMA Design
RE: Deflections and AREMA Design
STAADS moving load facility works very nice for this...I use it for crane runway analysis quite often.
RE: Deflections and AREMA Design
This might be an over-simplification of what you are doing; I dont know.
For me, it helps to sketch out the loads ...helps in understanding what the text is saying.
RE: Deflections and AREMA Design
RE: Deflections and AREMA Design
RE: Deflections and AREMA Design
For a uniform load, Δ = ML2/9.6EI
For a concentrated load at midspan, Δ = ML2/10EI
For constant moment across the entire span, Δ = ML2/8EI (it can't be more than that).
My best guess would be half way between uniform and point load, i.e. Δ = ML2/9.8EI
BA
RE: Deflections and AREMA Design
Look at page 53 of this link it might help:-
http:/
desertfox
RE: Deflections and AREMA Design
- Use the wheel loads on each side of the RF to position the wheel load pattern that will yield max M:
2. Position the wheels so centerline of the simple span fall in the MIDDLE of one of the wheel load and the RF, calculate moment under this wheel.
3. Repeat step 2 for another wheel (ie: re-position the wheel, and get moment under that wheel), and compare the two results.
Now you got the max moment and location of the wheels (pattern) that produce it.
Hope this is clear. Best reviewed in elementary "Structural Analysis" textbook with graphical expressions.
RE: Deflections and AREMA Design
Try this link its better than the last one I posted:-
http:
desertfox
RE: Deflections and AREMA Design
If you have two wheel loads a fixed distance apart, workout the resultant load of the two and the position it would take up between the wheels.
Position this resultant line of action of the two loads at the centre of your beam, this will give you the position of the train for the maximum bending moment, then revert back to taking moments on the beam using the individual wheel loads this will yield the maximum bending moment on the beam.
Then use superposition or Macaulay's method to obtain deflection.
desertfox