Bridges and track structure are designed based upon axle loadings. Overloading a car would be over-stressing both the track structure and the bridges. There is a safety factor in the calculation (for loading errors and also to consider cumulative fatigue loadings) but the weights actually matter. You can only exceed the load limit so many times before something is going to give, whether the subgrade becomes mush or something breaks.
In highway engineering, we are required to account for the cumulative effects of 18,000 pound axles on the bridges (the rated individual axle loading that all truck traffic is mathematically converted to). Every bridge currently has an estimated remaining fatigue life that is mathematically equivalent to multiples of 18,000 pound axles. Once that life is exceeded, theoretically the bridge should be removed from active truck traffic usage. Cars are not considered in the analysis.
For pavement design, cars are statistically insignificant. One truck, on average, does the pavement damage of 5,000 automobiles.
Traffic counts and vehicle classification counts are completed every year to aid in the cumulative truck traffic calculations.
All state owned or federally funded bridges are subject to inspection every two years by federal law. Major bridges including the river bridges are required to be inspected every single year. I'm not sure if freight rail requirements differ slightly, but their bridges are likely on the same inspection schedules.
John Mock
I looked into this a bit, and I think I found something that makes sense.
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In the trucking industry, maximum GVW is specified for safety. At 80,000 pounds a class 8 truck can drive and stop safely. These vehicles need to share the public roadways with other drivers, and safety is the primary concern.
With railroads, maximum weights are there to protect the equipment, not so much people. That is why the maximum capacities are specified differently.
I think this explanation might have a bit of truth to it.
-Kevin
Living the dream.
SeeYou190Why not just put the full allowed gross weight of the car?
Because it rains and snows in real life.
On a nice sunny day you load a car of coal to full gross weight. Then it rains. The water soaks the coal load. Now the car weighs MORE than its max allowed weight.
Dave H. Painted side goes up. My website : wnbranch.com
Is there any penatly for running a freight car overweight?
The car can be stopped enroute and the car returned for the shipper to reload the car, the car can be stopped enroute, the shipper could remove part of the load where the car is, the railroad could reduce the load and bill the customer. If its a chronic problem the railroad could refuse to supply the industry with cars untill they figure out how to properly load the cars.
SeeYou190 So, if you weighed a car and it was 176,000 pounds, you then had to do math to see if the car was overweight. Adding the LD LMT and the LT WT together and subrtracting the actual weight and making sure you have a positive number. . Why not just put the full allowed gross weight of the car? . This whole system seems very silly to me.
So, if you weighed a car and it was 176,000 pounds, you then had to do math to see if the car was overweight. Adding the LD LMT and the LT WT together and subrtracting the actual weight and making sure you have a positive number.
Why not just put the full allowed gross weight of the car?
This whole system seems very silly to me.
That's probably why they changed it to what you suggest.
Reading the last sentence of my above quote, I would think there was.
Ed
So back to the OP's question, It looks like a 70 ton car could carry 106 rails instead of 90 and still be "legal" to operate.
Here's a comment lifted from the Steam Freight Car group:
"The capacity is a nominal rating which allows car clerks and shippers to quickly ascertain whether a given car is suitable for the order of magnitude of their intended shipment.
The load limit is the absolute limit and is used after loading the car to compare the car's total weight on the scale to the allowable weight. Now, not that many cars were actually weighed, but a shipper could get into hot water if they released an overloaded car."
dehusman CAPY - is the intended capacity of the car. In this case 140,000 lbs or 70 tons. LD LMT - is the maximum capacity of the car based on bearing size and car design. LT WT - is the tare weight of the car. Lt Wt + Ld Lmt = the maximum safe weight of the car. If you exceed that you will damage the bearings or the car. The actual weight of the car minus the Lt Wt can't exceed the Ld Lmt.
CAPY - is the intended capacity of the car. In this case 140,000 lbs or 70 tons.
LD LMT - is the maximum capacity of the car based on bearing size and car design.
LT WT - is the tare weight of the car.
Lt Wt + Ld Lmt = the maximum safe weight of the car. If you exceed that you will damage the bearings or the car.
The actual weight of the car minus the Lt Wt can't exceed the Ld Lmt.
In answer to your question about separators between layers of rail as a freight car load, AAR loading rules for open top cars required 1x4s as minimum diminsion separators for rail loaded on flatcars. Using 2x4s would be OK, especially in gons.
As an aside, the discussion abut capacities left out an important item: track capacity to bear weight. This is usually defined by the bridges with the lightest limit but, other engineering factors may also play a role. For a long time 263,000 pounds was the universal limit but new, higher tonnage cars caused it to be raised to 286,000 pounds per four axle car, nationwide. On some lines that see very heavy loads, the limit is 315,000 pounds.
7j43kThe question then may be: Why have CAPY at all?
Because different cars are designed to haul different things. For example a Boxcar. It may be designed to carry 50 tons. If you fill it to full cubic footage capacity with grain you will exceed that. Same with a hopper or gon. It may be designed to carry 50 tons of coal. If you fill it to the same "fullness" with rock or iron ore you will exceed the capacity of the car.
They have a capacity because loading stuff in a rail car is not an exact science and people tend to overload freuently. Shooting for a "capacity" helps keep them from overloading and damaging the car.
On modern cars they eliminated one of them.
SeeYou190 The terms are like this: CAPY (Capacity) 140000 G LD LMT (Load Limit) 159000 LT WT (Light Weight) 44000
The terms are like this:
CAPY (Capacity) 140000 G
LD LMT (Load Limit) 159000
LT WT (Light Weight) 44000
CAPY is a nominal load capacity
LD LMT is the true load capacity (do not exceed)
LT WT is the weight of the car empty
(LD LMT) + (LT WT) = Total maximum weight of car (do not exceed) (GVW)
The question then may be: Why have CAPY at all?
dehusmanAt 1500 lbs/rail a 70 ton gon could hold about 90 rails from a tonnage capacity.
The "70 Tons" is not the car capacity, but the total weight.
Car capacity is very confusing to me, I come from the trucking industry.
Or something similar.
I have been told that actual maximum load weight is LD LMT minus LT WT, which on this car would be 115,000 pounds, this would be about 75 rails by your calculation.
Hopefully someone with better understanding of this nonsense can give a better explanation.
An 18 wheel truck can have a GVW (Gross Vehicle Weight) of 40 tons. That is so simple. If you weigh 79,750 pounds you are OK, 80,150 and you are not.
Structural steel, like I-beams, would be common too. The rail line that ran past my old house lead to a steel company that sold to the construction industry. I don't recall ever seeing the beams or girders stacked above the sides of the gondolas.
Thanks, Dave. Very helpful info.
Paul
Modeling HO with a transition era UP bent
I searched for "stacks of rail" images and it looks like 4x4's are used to separate the layers of rail.
At 1500 lbs/rail a 70 ton gon could hold about 90 rails from a tonnage capacity. Assuming the gon had an interior width of 9 ft and the base of the rail is 6" wide, that would allow 18 rails in each level, which makes 5 stacks. That makes 5 stacks with 4x4 spacers about 48" tall which is a common height of a gon side. The rail would not be stacked above the sides of the gon because its liable to shift.
If you make a load of rail, I would suggest only making the sides and top layer solid, because it will weigh too much if you don't. Also if you use old brass code 100 track for your rail, plan to only make it about 4 layers high, because the brass track is taller than real rail. Real 115 lb rail (a common size up until the 1960's) would be about 6.5 inches tall. Code 100 rails are closer to 7.5-8 inches tall.
I have 2 Tichy 52' war mill gondolas that I am about to assemble. I wonder if rail lengths might have been shipped in these cars.
I have found that 39' was a common length for rail, but have not found a photo on how arranged in a gondola. Would each level of rail have a wood (or steel strip) separator for stacking layers? More than 2x4 I would presume.
https://en.wikipedia.org/wiki/Track_(rail_transport)
Any insight would be appreciated.