For the sort of general tat the people tend to put in their lofts, there is no need to strengthen the floor. Boarding the floor and fixing the boards down to the joists will enable a measure of loadspread, although it could still result in deflection sufficient to crack the ceiling finishes, depending on what is actually bunged up there.
Collapse is unlikely - you'd have to be going some to get that to happen - something like paper storage with the void filled to the gills, or heavy individual pieces, such as engine blocks (and not just the odd one).
There is not much logic in the live load allowances that we have to design for: many people actually put far more weight on their attic joists than they do on the floors. Dynmaic loading is not a design requirement for domestic floors, so jumping up and down doesn't come into it.
Collapse is unlikely - you'd have to be going some to get that to happen - something like paper storage with the void filled to the gills, or heavy individual pieces, such as engine blocks (and not just the odd one).
There is not much logic in the live load allowances that we have to design for: many people actually put far more weight on their attic joists than they do on the floors. Dynmaic loading is not a design requirement for domestic floors, so jumping up and down doesn't come into it.
