Crane Wheel Loads (Impact etc)

[Samwise Gamgee]

I am designing framing/foundations to support bridge crane and have a couple of questions. The crane operates as shown in both directions. I have a question in regards to impact load.
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[li]Design guide-11 has an example which says the impact load is 20% of the load equally distributed between the 4 wheels. Does that mean crane will have 4 wheels on one side of crane beam has 2 wheels on one of the crane beam and the other 2 are on opposite side of the crane beam.
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[li]Design guide example also shows the maximum wheel load is 38.1kips for a 20T crane. What does that mean ? Does it mean its wheel load per wheel ? If there are 2 wheels on one side, does that mean they have capacity of 38.1*2 = 76k and if there are 4 wheels on one side, does that mean total capacity = 4*38.1 = 152k. Something isn't making sense to me.[/li]
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[straub46]

Review the loads. Crane design assumes that the hoist, trolley, and crane load goes to one side (the hook is all the way on one side of the crane), and the bridge weight is evenly distributed. So for the example, the load per side is 57.2/2 + 40 + 10.6 = 79.2 kip. 79.2 kip/2 = 39.6 k/wheel. The wheel load usually comes from the crane supplier, so it will be slightly less than the number provided since the hook can't be under the beam. So for the beam design, you would use (2) 38.1 kip loads 12' apart. You would apply the impact load factor to the 38.1 kips, so 38.1 kip*(1.2) = 45.72 kip.

Obviously both crane beams can't be fully loaded simultaneously as the hook can't be on both sides of the crane at the same time.

Go Bucks!