Some thing I just thought of.

Nothing I'd concern myself with. You may have measurable imbalance on the wheel sets, but if it exists I sure haven't noticed it. How long of a bridge are we talking about?

 

Gilly 

Hammering (dynamic augment) is a problem on full-size steam locomotives but it decreases as models get smaller. I imagine that live steamers consider it when designing, building and running locomotives. It's negligible on "O" Gauge models, as Gilly posted.

Well its about 16 inchs long.Like I stated earlyer its just a thought.This is new and different for me.Well thanks for your reply.I just keep on building the bridge.

No need to worry in O scale.  Weight decreases by the cube of the scale, since we are dealing with 3 dimensional models.  Since Force=Mass x Acceleration, the force of the hammering is minimal in a 1:48 scale model whose mass is 1:110592 (48^3) of the real thing.  Also, our acceleration is typically 1:48 of the real thing, i.e. if the prototype operated at 60 miles per hour, the model should operate at 60 scale miles per hour, or 1/48 of 60 mph (1.25 actual miles per hour).  Again, since F=MA, and we have already established that M is 1:110592 of the prototype, and A is 1:48 of the prototype, F would be reduced by a factor of 110592 x 48 or 1:5308416... in other words, negligible.  I suspect that there will be those who will disagree with my math - such is the nature of the beast - but in my experience with live steam trains, the predicted model weight is usually very close to the prototype weight divided by the scale factor cubed, assuming prototype construction methods and materials.  At any rate, I think the math shows what the guys already said: don't worry about it. 

       
       


it'll be more than fine, but if you think you'll have an issue, re-enforce the bridge in some key places along the truss and mounting points. cut up an old wire hanger, make the little wires straight and use them between the mount points on the deck and the pylons to keep the bridge from "walking" if you think it will.

Thanks for the information.That the great thing about this forum.People are always willing to help each other out.Thats what I like about this forum.You guys are great.

Confidence builder:

I have been running an Imperial Railking Big Boy (12+ pounds) across a 2 track MTH Plastic 30" Arch Bridge and RealTrax with no supports other than leveling the ends for 5 years.

Even the Big Boy is No Problem as long as you have a straight entry to the bridge. The Boiler or Cab will hit the Arch if a curve leads into or out of the bridge.

I don't think you'll have any issue at all.   I've seen some MU'd articulateds going over some long bridges at clubs and never heard of any problems.

 

--Greg