Crane gantry girder design (BS5950) - How is the stiff bearing length calculated?

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British Standard

In this calculation the beam web bearing and buckling checks (cl 4.5.2.1 & 4.5.3.1) both refer to the stiff bearing length, b1. In BS5950 this refers to cl.4.5.1.3 which relates to Figure 13 and shows four methods of calculating b1 using various combinations of t, T, r, s and g. TEDDS simply takes b1 = hr.

The check being carried out here is the web bearing/buckling under the wheel load. The gantry girder bearing onto the support check is not within the scope of the calculation. The wheel load is taken to be applied as a point load to the top of the rail, which is probably slightly conservative.

To obtain the bearing length b1, dispersal through the crane rail is taken to occur at 45 degs, as suggested in the 3rd line of cl. 4.5.1.3.

  • Selecting 'End' from the calculation interface while using a plain beam will result in b1 = hr (the height of the rail), since the dispersal can only take place in one direction.
  • Selecting 'Internal' will result in b1 = 2hr
  • If there is a plate or channel attached to the top of the gantry girder then the web thickness of this is also added into the equation.

The sketches in Figure 13 are for instances where the load is applied through another beam bearing onto the beam being checked. For the check being carried out in the TEDDS calc. the beam bearing onto the beam being checked is in effect the crane rail.

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