Design Information: BS EN 1992 (Eurocode 2)
The design of punching shear reinforcement is typically carried out in accordance with the recommendations contained in BS EN 1992 (Eurocode 2). Shearfix designed to BS EN 1992 can also be applied to structures designed to BS 8110.
The shear stress in the concrete is calculated at the column face and at the basic control perimeter u1 (2d from the column face) to determine whether punching shear reinforcement is required.
If reinforcement is required, the position of the outer control perimeter at which shear reinforcement is no longer needed (uout) is then calculated. Studs are arranged to start at 0.3d or 0.5d from the column face to within 1.5d of the outer control perimeter (uout); intermediate studs are positioned at 0.75d centres. The Ancon software defaults to a stud start point of 0.5d, although 0.3d is available as an option.
A radial layout will normally provide the most cost-effective solution and rails can be arranged with either 30º or 45º between them. The tangential spacing between studs is kept to within 1.5d for studs within the basic control perimeter (u1) and 2d for studs outside the basic control perimeter; additional secondary rails are added as necessary to comply with this requirement.
For internal, edge and corner columns where lateral stability does not depend on frame action between slabs and columns, and where adjacent spans differ by less than 25%, the recommended β values from BS EN 1992 can be applied to the design shear load VEd.
However, β values are most accurately determined on a case-by-case basis, taking the column location, geometry and loading conditions into account. By applying the moments, these β values can be calculated automatically. Alternatively, the β values can be calculated manually and applied directly.
Openings in the slab
Where there are openings in the slab within 6d of the column face a section of the slab will be ineffective and the perimeter lengths will be reduced. A series of rectangular or circular openings can be added around each column using the Ancon design program which then calculates the required punching shear reinforcement.
Large and Elongated Columns
Research1 suggests that punching shear stresses are greater at column corners than along column
edges. This effect is more pronounced for larger or elongated columns. The current Eurocode does
not explicitly recognise this effect, although the latest Model Code 20102 and other publications do.
The only limit in the current Eurocode is the aspect ratio which differentiates a column from a wall,
i.e. 1:4 (BS EN 1992-1-1, 9.5.1).
Ancon’s design program allows the designer to select between two options for dealing with large and elongated columns: “EC2” and “Best Practice”. Ancon recommends “Best Practice” which reflects latest research findings and the rules in the widely-accepted Model Code 2010, as we believe this to produce a more accurate design. Both options provide valid solutions, however there may be differences to the length and number of rails.
There is no limit to the perimeter length effective in resisting punching shear of a circular column as a circular column has no ends or corners at which the shear stresses could focus.
1 Einpaul, J., Bujnak, J., Fernandez Ruiz, M. and Muttoni, A. (2016). “Study on Influence of Column Size and Slab Slenderness on Punching Strength” ACI Structural Journal, V. 113, No. 1, pp. 135-146
2 fib (2013). 7.3.5 Punching, Model Code for Concrete Structures 2010, pp.227-234
An Ancon Shearfix manual to EC2 is available. Contact Ancon for a copy.
In addition to the Shearfix design program, a design sheet is available to download below, which allows engineers to summarise the critical details of their project and request technical assistance with a Shearfix design.
Shearfix Design Sheet to Eurocode 2 (PDF, 109 KB)
Ancon will be exhibiting at Futurebuild 2019 from 5th - 7th March at ExCeL, London. Ancon will be on stand C82.
Ancon is pleased to announce the appointment of Peter McDermott as Group Managing Director, effective 1st January 2019 following the retirement of Stuart Maxwell.