04-10-2012, 04:24 PM
Plain concrete structural elements
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Scope of application
Plain concrete structural elements are considered as being both those built of concrete
without any reinforcement and those which have reinforcement only to reduce the effects of
cracking, generally in the form of fabrics close to their faces.
This chapter is applicable in a purely subsidiary manner to those plain concrete
structural elements which have their own specific standards.
COMMENTS
Examples of structural elements that may be constructed using plain concrete are, among others, the
following: building walls, on basement floors or on other floors, generally with steel fabrics on both faces, foundation
footings for brick or concrete walls, footings and foundation piles consisting of reinforced concrete or rolled steel
pillars and containing walls in situations of little height etc.
The employment of other types of reinforcement in certain concrete elements, such as steel fibres,
may have effects similar to those of the previously mentioned fabrics, such as those designed to reduce
cracking and improve ductility.
COMMENTS
When the effective section is geometrically difficult to determine, it may be replaced by an
approximate effective section, consisting of the total section, with the centroid coinciding with point G1 (figure
52.4.b). Any potential error is always on the side of safety, since the effective section has maximum area. If a
suitable choice is made, any error committed will be small.
Consideration of slenderness
In a plain concrete element that is subject to compression, with or without shear stress,
the first order effects produced by Nd are increased by second order effects because of its
slenderness (52.6.3). In order to take these second order effects into account, Nd should be
considered as acting at point G2, which results from displacing G1 (52.4) by an imaginary
eccentricity as defined in 52.6.4.
Beams
Beams that are subject to bending should be designed in accordance with Article 42 or
the simplified formulae of Appendix 8, based on the design values for the strengths of the
materials (Article 15) and the increased values of combined actions (Article 13). In the event
that bending is combined with shear force, the member should be designed for shear in
accordance with Article 44, and in accordance with Article 45 if torsion is also present. For
composite members the Limit State for longitudinal shear (Article 47) should be verified.
Where necessary, the Cracking, Deformation and Vibration Limit States should also be
verified, in accordance with Articles 49, 50 and 51, respectively.