Here is a defect that is frequently referred to as a tension beam. This occurs with long, overextended limbs that extend out from the canopy at an open angle. This structure creates a lever in the tree which applies tension and compression to the affected limb.
With gravity, wind, ice and snow load, tension occurs on the top side of the limb and compression on the underside of the limb. When this pressure becomes too great the limb will actually split apart in the middle under the opposing forces. In some cases the limb will fail completely, in other cases the limb will split but remain attached to the tree in a hazardous manner.
Limb reduction and support cables can prevent this occurrence. We also put rods through the crack and at the ends of the crack to prevent it from opening any further. A split limb may go unnoticed by property owners and a qualified arborist should perform a careful inspection of the tree canopy.