SLOTTED BLOCK TIE (TYPE II) DESIGN PHILOSOPHY
Robert G. Drysdale, Ph. D., P.Eng., President of Drysdale Engineering and Associates Limited examined masonry tie usage in a brief report entitled "Structural Requirements for Non-Loadbearing Masonry Backup Walls and Potential for Composite Action" and dated September 4,1991. In the report Drysdale stated " . . . theoretically (composite action) is a very attractive engineering idea." Drysdale further stated that " . . . Literature, calculations, and tests used to develop design information for such systems must clearly show not only the benefits of the coupling of the two wythes, but also the detrimental effects of restrained differential movements."* Drysdale concluded by noting "At this point in time practice and 'conventional' wisdom has been to allow the two wythes to move independently in the plane of the wall and ties have specifically been designed to accommodate such movements."
The design of the Slotted Block Tie (Type II) not only satisfies this "conventional" wisdom, but eliminates numerous traditional masonry tie potential pitfalls such as welded connections, fasteners into concrete blockwork, multi-part ties that do not possess positive restraint between tie components, multi-part ties that allow excessive free play, and multipart ties that undergo excessive deformation under load. Above all this, the Slotted Block Tie (Type II) has been engineered.
* The effects of restrained differential movement associated with Shear Connected walls has been addressed in Prairie Masonry Research Institute technical booklet entitled "Differential Movement In Cavity Walls And Veneer Walls Due To Material and Environmental Effects", authored by Ajay Goyal, Dr. Michael A. Hatzinikolas and Prof. Joseph Warwaruk and dated August 1992. Although the effects of restrained differential movements are real, their magnitudes were found to be relatively small and could easily be incorporated into composite wall designs.and could easily be incorporated into composite wall designs.
