The flexural bond strength (FBS) of individual units (brick+adjoining underlying mortar bed) varies considerably between units, and might significantly affect the structural performance and reliability of unreinforced masonry (URM) walls in flexure. This paper describes an experimental program where full sized clay brick URM walls were constructed by masons with different levels of skills. The timing and placement of different batches of mortar were closely monitored. The FBS of each unit in each wall was obtained using the bond wrench test. This provided extensive data for a statistical analysis to assess the degree of correlation of unit flexural bond strengths between units within and between courses. The statistical analysis also included a comparison between the flexural strengths of units and prisms that were built for every new batch when building the walls. The prisms' characteristic FBS were assessed following the Australian Code AS3700, and compared to the characteristic values taken from the walls' units. The study recommended that FBS between units either within or between courses are statistically independent. Finally the paper showed that the differences between walls and prisms strengths may be relevant, highlighting the need of a more detailed study to analyse the meaningfulness the prisms' results.
8th International Seminar on Structural Masonry, 8th International Seminar on Structural Masonry: Proceedings (Istanbul, Turkey 05-07 November, 2008) p. 97-105