Beam penetrations

Service holes through beams may be necessary for cabling or plumbing. The positioning of these holes must be carefully considered as they could seriously affect the structural integrity of the beam.

Areas of high stress should be avoided close to the supports where the shear force is at a maximum and also at mid-span where the bending stress is at a maximum. This leaves the zones along the neutral axis and a point of compromise between the mid-span and supports.

Diagram for allowable zone for service holes. The service holes are on the neutral axis between a quarter and a third maximum span on either side of the beam. The prohibited zones for service holes is in the middle third of the beam.

Beam penetration

A two-storey house has a rumpus room above the garage. The waste pipe for upstairs must penetrate the floor beams. To ensure the holes are cut within safety limits, use the diagram to calculate the following distances.

The floor beams have a span of 6 m and are 300 mm deep.