Masonry Magazine September 2011 Page. 38
CODES AND STANDARDS
Post-installed anchors loaded in tension, especially adhesive anchors and screw anchors, demonstrate a capacity to resist loads, even when placed in adjacent cells.
Small diameter screw anchors have been used for many years for attachments to masonry walls and, in recent years, large diameter (up to 3/4-inch diameter) anchors have become available and are used effectively in many applications.
Grout-filled masonry walls consist of three components: concrete masonry units (CMU), mortar and grout. Unlike with concrete, whereby the components are mixed together, in masonry construction the three components are kept separate. Installation of the anchor location in these three different components or at the interface of the components can influence its performance of the anchor.
For example, a review of anchor manufacturers' literature and independent assessments, such as International Code Council Evaluation Service Reports, show that, often, the vertical (end) mortar joint is either excluded from proper location of an anchor, or the performance is significantly reduced. Often, installation in the horizontal mortar joint does not reduce the capacity of the anchor. Designers and installers should verify that the installation complies with the parameters required by an Evaluation Service Report or the manufacturer's published instructions.
Post-installed anchors loaded in tension, especially adhesive anchors and screw anchors, demonstrate a capacity to resist loads, even when placed in adjacent cells. There is little influence of spacing when anchors are placed in different grouted cells, even when embedments are deep. The masonry failure is localized, allowing anchors to sometimes be placed closer together than would be allowed in concrete. In one test performed by a manufacturer, three 3/4-inch diameter adhesive anchors were installed in the center of three consecutive grouted cells at an embedment of almost seven inches. The two outer anchors were then loaded to 75 percent of capacity.