Sliding Shear and Punching Shear

Sliding Shear

The failure by sliding shear is a possibility in structures subjected to earthquakes. Construction joints across members, particularly when poorly prepared, present special hazards. Flexural cracks, interconnected during reversed cyclic loading, may also become potential sliding planes

  1. Sliding shear in walls and diaphragms:

Shear transfer across potential sliding planes across walls and diaphragms, where construction joints occur or where wide flexural cracks originating from each of the two edges.

  1. Sliding shear in beams:

Sliding displacements along interconnected flexural and diagonal cracks in regions of plastic hinges can significantly reduce energy dissipation in beams. With reversed cyclic high-intensity shear load, eventually a sliding shear failure may develop.

  1. Sliding shear in columns:

For purposes of verifying sliding shear, particularly in potential plastic hinge regions, it is advisable to consider columns as beams. However, when the vertical reinforcement is evenly distributed around the periphery of the column section as is typical, more reliance may be placed on the dowel resistance against sliding of the vertical bars. Any axial compression on the column that may be present will greatly increase resistance against sliding shear. Therefore, no consideration need be given to sliding shear in columns constructed with a relatively even distribution of vertical reinforcement.

Punching Shear

Punching shear occurs where a two-way concrete flat slab or plate is connected to a column without beams. It is the tendency of the slab to drop as a unit around the column. The column appears to “punch” through the slab, hence the term “punching shear.” The cracking due to the overstress which may lead to this type of collapse, is most visible on the top surface of the slab.

 

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