Structural Design of Earth Masonry in Accordance with Eurocode 6 – Considering Moisture Content and E/fk Ratio

Abstract

The load-bearing behaviour of earth masonry is similar to conventional masonry, with two key differences: compressive strength and Young's modulus are dependent on moisture content, and the ratio between Young's modulus and characteristic compressive strength (E/fk) is significantly lower. The current design concept according to the Lehmbau Regeln does not explicitly address these factors, relying instead on a general safety margin, leading to an underestimation of the load-bearing capacity of modern earth masonry.

Compression tests on small-scale masonry specimens and storey-high walls revealed that compressive strength and Young's modulus decrease inversely proportional to the increase in relative humidity. Additionally, it was found that conventional masonry design guidelines overestimate the buckling resistance of earth masonry due to its low E/fk ratio of ∼440. However, this ratio remains independent of moisture content, simplifying structural design, as the load-bearing capacity is only influenced by wall slenderness.

The study's findings form the foundation for the newly published German design standard DIN 18940, which explicitly considers moisture content through service classes with moisture factors and addresses the low E/fk ratio with a bilinear adaptation of the reduction factor considering the slenderness. Along with the introduction of the semi-probabilistic design concept and rigid-plastic determination of cross-sectional load-bearing capacity, modern earth masonry can now be applied in buildings up to four storeys.