Flexural Tensile Strength of Concrete Block Masonry

This paper reports the results of 172 flexural tests of 790 mm by 1,590 mm 31in.×62in. concrete block masonry walls. In addition to evaluating tensile strength both normal and parallel to the bed joint, the parameters included in the study are three sizes of block; three percentages of solid; four block strengths; two types of mortar; hollow blocks and ones grouted with three strengths of grout; and special conditions such as stack pattern, partial grouting, and empty head joints. The results confirm the orthotropic nature of masonry where for hollow blockwork, tensile strength parallel to the bed joint is two to four times higher than tensile strength normal to the bed joint. Grouting of the blockwork resulted in a greater increase of strength for tension normal to the bed joint so that these ratios are between 1 and 1.5. While the percent solid of the block has a marked influence, the tensile strength is not found to be significantly influenced by block size or block strength for the range tested. Grout strength is found to have little influence, particularly for tension normal to the bed joint. Comparison of the test values with allowable stresses recently adopted in North American building codes tends to raise questions regarding the justification for the allowable stresses for tension normal to the bed joints. Conversely, the practice of equating groutfilled hollow masonry to solid masonry tends to ignore the very large benefits derived from the continuity provided by the continuous columns of grout. A general discussion of behavior and design concludes this paper.