Reinforced bending load-stressed masonry - Suggestions for future designs / Bewehrtes biegedruckbeanspruchtes Mauerwerk - Vorschläge für zukünftige Bemessungen

European standardization bodies are currently working on the amendment to EN 1996-1-1, which will also affect the evaluation of reinforced masonry in Germany. For that reason, discussion suggestions are being made here for revisions to lay the groundwork for building materials evaluations and especially, evaluations of bending load-stressed masonry walls or beams at their serviceability limit state (SLS) for load-bearing capacities. Information already presented in E DIN 1053-3:2008-03 [N3] is being incorporated as well.
Characteristic values for the compressive strength of the masonry parallel to the bed joints fk,∥ are essential for the design of reinforced masonry, although they are currently not included in national application documents for Germany. For the time being, they can be mathematically calculated using conversion factors for the characteristic compressive strength values vertical to the bed joints fk or by using the declared axial compressive strengths of the masonry units.
The ultimate strains for masonry in general should be set consistently at &egr;mu = ∣-0.002∣ as several masonry types do not exhibit higher compressive strain values. The use of steel strains higher than &egr;su = 0.005 does not change any measurement results. Varying stress-strain curves of the constitutive equations on masonry under compressive strain (parabolic, parabolic-rectangular, tension block) lead to differing values of recordable bending moments despite having the same mechanical reinforcement percentage at higher normal forces. Therefore, clear guidelines should be made for the type of applicable constitutive equation for masonry walls under compressive strain. With the introduction of a tension block, the number values of the reduction factors λ for the compression zone height x, which is dependent on limit strains, and where applicable, reduced compressive strength, need to be determined, as with reinforced concrete construction.
A modification of the bending moment based on the second order theory according to [N4] is presented for the calculation of reinforced masonry walls in danger of buckling. The use of reduction factors for the load capacity of the masonry cross section, such as for unreinforced masonry, does not appear to be appropriate as buckling safety evidence because here, the design task is the determination of a required reinforcement cross section.