Per ACI 318, two separate shear checks are required: One check recognizes that the footing may fail in shear as a wide beam along a critical section at a distance d from the column face in each direction. This is called “beam shear” or “one-way shear” as it resembles the shear check in a concrete beam.
1. The critical section for one way shear occurs at a distance 'd' from the face of the column. 1. The critical section for two way shear occurs at distance 'd/2' from face of the column along with periphery.
Two-way shear, or punching shear, is calculated for a section that is a distance of d/2 from the edge of the concrete column or modified base plate. The shear capacity is calculated using the smaller of the values calculated according to ACI 318-14 Table 22.6.5.2: Vc=4λ√f′c.
One-way slabs carry loads in one direction, supported by beams on two sides, suitable for long, narrow structures. Two-way slabs bend in two directions, supported by beams on all sides, ideal for heavier loads and larger spans. One-way slabs transfer load to two beams; two-way slabs transfer load to columns or walls.
Shear strength of the slab in the vicinity of columns/supports includes an evaluation of one-way shear (beam action) and two-way shear (punching) in accordance with ACI 318 Chapter 22.
Per ACI 318, two separate shear checks are required: One check recognizes that the footing may fail in shear as a wide beam along a critical section at a distance d from the column face in each direction. This is called “beam shear” or “one-way shear” as it resembles the shear check in a concrete beam.
One-way shear is experienced or resisted by a single plane of footings. It tends to shear off the member along that plane, in the direction of shear force. A two-way shear (or punching shear) is shear resisted along the periphery of a footing supporting a column.
The concrete shear strength in one-way action is defined by the expression φVc = φ2√f'c bd, where b is the footing dimension under consideration.
In case of one-way slab, if we increase the beams width to depth ratio, and increase the percentage of steel, perpendicular to the direction of bending, then one-way slab will be more economical and will be stronger than two way slab.
Shear or punching shear are among the most known sources of brittle failures in reinforced concrete structures. In concrete slabs, a major difference between shear and punching is the principal shear force direction with respect to the support [1].
Punching shear arises when a concentrated load is applied to a small area of a slab or, most commonly, the reaction of a column against a slab. The resulting stresses are verified along defined control perimeters around the loaded area.
Students should learn that the shear force required to shear the pin in double shear is twice the shear force required in single shear since there are two shear planes (the total shear area is doubled). However, while the shear force is doubled, the shear stress at failure is the same in both cases.
General shear failure is characterized by the existence of a well-defined failure pattern consist- ing of a continuous slip surface from one edge of the footing to the ground surface. Unless the structure prevents the footings from rotating, the failure is also accompanied by tilting of the footing.
The critical section for one-way shear in a reinforced concrete beam or slab is taken at a distance equal to the effective depth (d) from the face of the column or pedestal. This is based on standard design practices in reinforced concrete structures.
In summary, one-way slabs tend to bend in one way with support on both sides. Two-way slabs, however, tend to bend in both directions with support coming from all four sides.
Shearing forces act in one direction at the top, and the opposite direction at the bottom, causing shearing deformation. A crack or tear may develop in a body from parallel shearing forces acting in opposite directions at different points of the body.
In general, a one-way RCC (Reinforced Cement Concrete) slab, without the inclusion of beams, should not exceed a maximum span of 3.5 meters. This span limitation is an important consideration for ensuring structural integrity and safety.
Post-tensioned slabs incorporate high-strength steel cables that undergo tension after the concrete has cured. In turn, this provides additional strength and reduces cracking. Moreover, they are suitable for long spans and heavy loads, often used in parking garages and bridges.
One way slab- when the ratio of longer span(L) to shorter span(B) is greater than or equal to 2, the slab is known as one way slab. Two way slab- when the above said ratio is less than 2 the slab is called 2-way slab.
One way shear or beam shear is experienced or resisted by a single plane for example in beams and slabs. This normally is taken critical at a distance equal to depth of member from the support. It tends to shear off the member along that plane, in the direction of shearing force.
2. Maximum shear at a distance of d from the face of the column, where d is the effective depth of footing. N o m i n a l s h e a r s t r e s s = V B d < permissible one way shear in footing. Using the above equation we can calculate d.
Foundation shear strength is a key parameter that affects the stability, performance, and design of various structures, such as buildings, bridges, dams, and slopes. It measures the resistance of a soil or rock layer to sliding along a plane under an applied shear stress.
The Pile one-way shear check is in addition to this and is always performed. It checks each individual pile and the shear arising from load spanning between the pile directly to the column. Only the US ACI 318 code makes specific mention of a need for this sort of check, and only in relation to corner piles.
Punching shear is a phenomenon where a concentrated force on a slab causes a shear failure cone that "punches" through the slab. 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.