FRANCIS DRAN Chief Engineer of the Building Section, CERIC, France

The formula in EC6 for the characteristic strength of masonry calculated from the unit and mortar strengths does not agree with the results of tests already carried out in France on solid and hollow dense aggregate concrete units. For a hollow unit 100 mm wide with a compressive strength of 2.5 N/mm2 the formula gives wall strengths higher than the unit strength and further there is a discontinuity at a mortar strength of 10 N/mm2, For solid units 150 mm wide the EC6 curve is conservative. 60 wallettes were tested made from hollow units from four different factories. The widths of the units were 100. 150 or 200 mm, the heights 200 or 250 mm and the mortar strengths M5, M15 or M30. The units were tested wet and dry. Many of the results for the wallettes were lower than would have been calculated by the EC6 formula. A new formula is proposed for the characteristic compressive strength of masonry.