Development of a Flatjack for Testing High Strength Masonry

Ogden, G., Schuller, M., & Woodham, D., Development of a Flatjack for Testing High Strength Masonry, Proceedings of 17th International Brick and Block Masonry Conference, Kraków, Poland, July 2020.


Flatjack methods are commonly used for in situ evaluation of masonry compression behavior, compressive stress within masonry assemblages, and for loading units during tests to evaluate mortar bed joint shear strength. The original flatjack methods considered applications for evaluating historic masonry construction with typical compressive strength in the range of 2.1 to 6.9 MPa (300 to 1000 psi). Some stone masonry construction and most modern masonry have compressive strengths greater than 6.9 MPa (1000 psi). In these cases, masonry compressive strength is estimated based on relationships between compression modulus and compressive strength. A new flatjack design has been developed for evaluating high strength solid-unit masonry with the ability to directly capture nonlinear response and determine peak compressive strength. Laboratory calibration and proof testing shows the new flatjack design can apply stresses of 31 MPa (4400 psi) or greater and has been used in the field for compression and shear testing with good results.