Hello I'm tasked to evaluate the roof of a small power station situated beneath a rather high tower in an alpine landscape, by means of FEA. One requirement is that the roof shall endure chunks of ice falling on it. Problem is, I am stumped as how to find the loads. The Eurocode norms I am expected to use just shrugs at impact loads and suggests that it be left to "experts". Well, I am the ordained resident "expert" here... Had it been a ball of steel or some such and strictly elastic behaviours, it would not have been that hard - preservation of energy, the kinetic energy should equal the stored energy of the elastically deflected roof. Then I get the theoretical deflection and if I put it into the FE analysis I get the stresses on the roof components. Unfortunately, it's not that simple. Primarily because the ice will fracture, secondarily because the forces involved do seem at a first glance to be unreasonable in all aspects. I mean, a 3 kg ball of ice that falls 60 m has a kinetic energy of about 1800 joule. Slightly less because of drag, but let's ignore that for now. The roof bends about 45 mm for a 1 kN load, so its "spring factor" is about k = 22 kN/m. The required spring force for absorbing a certain energy is F = √2kE → F = 8.9 kN. That is a 900 kg force right there. And the elastic deflection required is ca 400 mm. So far I am inclined to believe the numbers - problem is that I think the ice will shatter. The chunk will be smashed into snow. That will probably dissipate a bit of the energy. Or will it? See - according to a laboratory study I found on the web, they found that a puck of ice hammered with a pressure sensor at 100 ft/s (incidentally more or less identically to the impact speed I expect) will shatter into snow. At some 10-14 MPa pressure, or about 15 kN. And that was a small ø38 mm specimen. Other sources also list the crush strength of ice at some 5-10 MPa or so depending on temperature and deformation rate. Am I to suppose that "my" 3 kg ice chunk, estimated to ø100 mm diameter, will need a whopping 100 kN or so to get pulverized? That is ten tons! And if the roof only deflects 400 mm @ 8.9 kN, the ice chunk will not shatter but just bounce off ? I have a hard time interpreting these numbers. Anyone has any idea what to make of them?