How do you resist a punching shear in a flat slab?

How do you resist a punching shear in a flat slab?

Furthermore, it has been discovered that punching shear can be prevented by increasing the depth of the concrete floor slabs, or by increasing the diameter of the columns supporting the floor.

Do slabs have shear reinforcement?

The thickness of most long-span flat slabs, two-way slabs without beams, is controlled by the shear strength of the concrete slab surrounding the supporting column. This shear reinforcement consists of large-head studs welded to steel strips. …

How do you calculate punching shear in footing?

Punching shear is produced directly by the forces and moments acting on the column. For the simple case of a concentric footing with a downward load, the punching shear can easily be calculated as the volume of the bearing pressures on the critical area around the column.

How do you give shear reinforcement in slabs?

In flat-plate floors, slab-column connections are subjected to high shear stresses produced by the transfer of the internal forces between the columns and the slabs. Section 11.11. 3 of ACI 318-08 allows the use of shear reinforcement for slabs and footings in the form of bars, as in the vertical legs of stirrups.

What is punching shear capacity?

Punching shear is a phenomenon where a concentrated force on a slab causes a shear failure cone that “punches” through. Punching shear calculations require a demand value and a capacity value. Many hand calculations will consider a punching shear force against a punching shear capacity force.

What is General shear failure?

General Shear Failure Dense or stiff soil that undergoes low compressibility experiences this failure. Continuous bulging of shear mass adjacent to footing is visible. Failure is accompanied by tilting of footing. Failure is sudden and catastrophic with pronounced peak in curve.

Why is there no shear reinforcement in slabs?

For reinforced concrete (RC) slabs without shear reinforcement, shear and punching can be the governing failure mode at the ultimate limit state if subjected to large concentrated loads. Shear and punching of RC slabs without shear reinforcement has been a challenging problem in assessment based on current standards.

Why shear reinforcement is provided in slab?

Whenever the value of actual shear stress exceeds the permissible shear stress of the concrete used, the shear reinforcement must be provided. The purpose of shear reinforcement is to prevent failure in shear, and to increase beam ductility and subsequently the likelihood of sudden failure will be reduced.

What is punching shear failure in footing?

The punching shear failure is an undesirable failure mode, since it results in a brittle failure of the footing. In this study, a new method to increase the strength and ductility of the footing was proposed by inserting the punching shear preventers (PSPs) into the footing.

What are the types of shear failure?

Types of Shear Failure of Foundation on Soils

• General Shear Failure.
• Local Shear Failure.
• Punching Shear Failure of foundation soils.

What is punching shear?

Punching shear is a phenomenon where a concentrated force on a slab causes a shear failure cone that “punches” through. The applied shears and moments, along with the shape of the punching shear failure cone are used to calculate a maximum punching shear stress.

What is the formula of punching shear?

For an interior punching shear perimeter this will always be L1/2 or L2/2. For edge and corner cases this value is calculated as the moment of area of the shear perimeter/area of the sides.

What is punching shear in flat slabs and foundations?

Punching Shear Design Example Punching shear is a failure mechanism in flat slabs and foundations, due to concentrated loads causing shear stresses on a section around the load. This type of loading on a slab causes shear failure, which occurs suddenly without any prior warning.

What happens if you don’t use punching shear?

Due to this kind of failure, punching shear can cause catastrophic damage and harm to buildings and people. A common example is a column reaction in a slab, which cause punching shear failure in the slab if the shear stress is too high or no shear reinforcement is used in the slab.

Which is an example of a punching shear failure?

One possible method of failure is that the load punches through the slab. Some examples of the occurrence of concentrated loads on a slab are a column, particularly on a pad foundation, and wheel loads. This same type of failure could also happen in another way.

How is the shear perimeter of a punching shear calculated?

These give the distance from the shear perimeter edge to the centroid of the shear perimeter. For an interior punching shear perimeter this will always be L1/2 or L2/2. For edge and corner cases this value is calculated as the moment of area of the shear perimeter/area of the sides.