Gaston
I think you may have a hang up about 'level turning flight'. There is no structural or aerodynamic reason to be worried about level turning flight in particular.
Most issues associated with structural loading are related to g. For all formal flight tests where these are measured they are normally done during woigs level pull ups from either level flight or dives according to the amount of power or thrust available.
Rolling under g tests are another and quite separate subject as these involve not only wing bending but wing twisting at the same time.
I know this does not answer your original question as such but I want to get you away from this level flight turns issue into the more general case of applying load via g.