I am geting ready to start pouring concrete for my roadbeds and I am curious if I should bank the curves or keep the surface level? If I should bank the curves, any thoughts on how much? Thanks in advance.
Absoluely do not bank the curves, especially if the curve is on a grade !
With short trains it probably wouldn't be a problem. If you use mid or longer trains, you very likely would encounter "stringlining" if you bank the curves. Been there, done that, before I put in concrete roadbed. The concrete and ladder roadbed were put in laterally level, and the stringlining stopped.
Stringlining: On mid to long consists, the weight of the trailing cars can try to straighten out the curve, pulling cars off the track on the inside of a curve.
Welcome to the new MLS. I have posted several threads asking about concrete roadbed, getting ready myself to pour, and I have learned that Marty is our resident expert. He wrote a great article that is still in the archive forum but here is the link for you, archive.mylargescale.com/articles/articles/concreteroadbed/roadbed01.asp, In the article he says about curves
" I always set the inside of a curve first so the outside form can be slightly elevated by one half bubble in the level. This will allow a little elevated curve."
More than likely Marty will log on and explain a little more for you, but please read his article it is very helpful.
I have tried to bank curves a half a bubble but it was more trouble than its worth it. Unless your using 20' dia or more.
heres an example photo. You welocme to go to my 1st class space and look for many photos.
I have 8' and 7.5' radius curves (16' dia and 15' dia) on my layout BANKED. I don't have any trouble with 40 and 50 car long trains. However, you don't NEED to bank the curves, they will work just fine flat but when a hot freight or passenger train hits those curves at speed it looks really cool! With the 7.5' Radius curve getting the track in place was pretty easy as I used flex track and had to pre-bend the rail with a rail bender. With the 8' Radius it was LGB sectional track and because it was one piece it didn't want to cooperate in setting it on the banked track correctly but since I glue my track down I just added more glue to more ties and weighted it down for a couple of days to hold it in place. It's been out there for about 3 years without any problems. The best advice I can give is use transition between the flat track and the banked track of at least 6 feet. The transition can start on a straight piece and end in the curve. If you are putting in "S" curves that are within about 10 feet of each other don't bank the curves or if you do don't bank them nearly as much. I will try to post some pictures later.
I know of an HO layout where they have a spiral tracks to get trains up and down to a different level. The "up" spiral has to be SUPRAelevated (outside rail LOWER than the inside rail, i.e.: cars lean out of the curve!) to keep the trains from falling into the spiral! You only need to bank curves if you expect to run at high speed. But then you need to compromise the bank for those trains that STOP on the curve so they don't fall over!
While in engineering school we studied this quite a bit, and although I don't remember most of it now I do remember that it was mostly for high speed trains. I found this on the web:
"Superelevation was not used in full-size practice when the maximum train speed was less than about 30
mph. Below 30 mph the lateral forces are low and don’t cause passenger discomfort or excessive wear on
rails or flanges. When train speeds started to exceed 30 mph, superelevation was introduced to address
both passenger comfort and track/wheel wear.
As soon as superelevation was introduced, the problem of how to go from flat track to banked track had to
be faced. Early attempts were approximate, but around 1880 the Cornu1 spiral (or an approximation to it)
was adopted. Although there are some issues with the “dynamics” of the Cornu, it remains the standard for
moderate-speed lines (less than 120 mph)."