Probability and structural reliability assessment of mortar joint thickness in load-bearing masonry walls

• We studied the influence of joint thickness on the reliability of masonry walls.
• Statistical and spatial analysis of the filed data on joint thickness is presented.
• Data exhibited large scatter due to high variability of the quality of workmanship.
• A structural reliability analysis of the masonry under compression was performed.
• Probabilistic modelling of joint thickness results in higher reliability indices.

Mortar joint thickness has a significant effect on capacity of structural masonry. Data on mortar joint thickness (bed and head joints) were collected from twelve typical storey-high walls at three different building sites and from four walls built in a research laboratory in Switzerland. The data obtained allowed an analysis of the spatial distribution of the joint thickness in each wall and the characterization of the probability distribution of joint thickness. The data has been statistically analysed and the results discussed: the central and dispersion measures were calculated and several probability distributions have been fitted to the sample data and subsequently tested using standard methods of statistical theory. Further, the results obtained from all four building sites have been compared, thus providing quantitative information about the quality of the work on different sites. The presented probabilistic information is then used to define reliability-based limit state specifications where the joint thickness acts as an important random variable. The reliability of the structural masonry subjected to a concentric normal force found that probabilistic modelling of bed joint thickness results in higher reliability indices.