The minimum reinforcement of reinforced masonry under bending should according to DIN EN 1996-1-1:2013-02 [N 1], Section 8.2.3(1), be not less than &rgr;min = 0.05 % of the effective masonry cross-section for building elements, in which the reinforcement makes a contribution to the loadbearing capacity of the section, with the effective masonry cross-section being the product of the effective width (bef) and the usable height d of the building element. In order to limit cracking and increase the ductility of the element, the reinforcement area should according to [N 1], Section 8.2.3(3), be not less than 0.03 % of the gross cross-sectional area (of a wall). Other regulations ([1], [N 2], [N 3], [N 4], [N 5], [N 6], [N 7]) also prescribe minimum reinforcements in order to avoid brittle behaviour of the building element when the first crack forms or to limit cracking.
In this specialist article, the figures given in [N 1] for the minimum reinforcement of reinforced masonry beams, like flat lintels or prefabricated lintels, are checked. The work concentrates on avoiding brittle failure when the first crack forms.
In addition to geometrical requirements, the amount of minimum reinforcement depends on the tensile strength of the masonry ft, m. Values of &rgr;min vary considerably depending on the magnitude of the tensile strength of the masonry that can be assumed. For lintels over openings in facing brickwork facades, the height of any capping or soldier courses under the reinforcement layer also has an enlarging influence on the value of &rgr;min.
With regard to future regulations in standards or Allgemeine bauaufsichtliche Zulassungen (national technical approvals), it is recommended not to give lump sum values for &rgr;min but to undertake a calculation like for reinforced concrete, using the algorithms given in this article.