ACCIDENTAL CRANE ACTIONS

ACCIDENTAL CRANE ACTIONS

3D and Calculation Crane – Three accidental actions are provided for in EN 1991-3, which are buffer forces related to crane movement, buffer forces related to crab movement and tilting of a crane equipped with a mast. The buffer forces relate to the situation where the crane or crab runs into the end stops at the extreme
of their travel on the gantry or crane bridge respectively. This is an accidental situation because most cranes are equipped with limit switches which automatically slow and stop the crane or crab before the end of their travel and an impact would thus only occur in the event of failure of the limit switches.

1. Buffer forces related to crane movement

The principle that is given in EN 1991-3 for the determination of the end stop buffer forces related to crane movement is that the forces should be calculated considering “the kinetic energy of all relevant parts of the crane moving at 0,7 – 1,0 times the nominal speed.” An application of this principle is given in an equation for the calculation of the buffer force on each end stop as:

Where:
-7 is the dynamic amplification factor for the end stop forces
v1 is the initial speed of the crane, taken as 70% of the long travel speed [m/s]
mc is the total mass of the crane and hoistload [kg]
SB is the spring constant of the buffer [N/m], determined from the energy-deformation and force-deformation buffer curves.

2. Buffer forces related to crab movement

EN 1991-3 specifies that if the hoistload is free to swing, the total buffer force resulting from collision of the crab with the end stops may be calculated as 10% of the combined weight of the crab and the hoistload. In the case where the hoistload is not free to swing, the crab buffer forces should be calculated in a similar manner to the crane buffer forces.
The distribution of the buffer forces between the wheels of the crane depends on the wheel configuration and whether the wheels are fixed or free to move laterally.