Designing Structural Anchorage to Concrete By J. Bret Turley, PE n the last issue of Construction Canada, this author explored the various designs of structural anchors intended for masonry assemblies.1 Given how the methodology for designing these structural anchorages changed significantly in 2004, a closer look at similar products for use with concrete is warranted. Annex D of Canadian Standards Association (CSA) A23.3-04, Design of Concrete Structures, introduces a new and comprehensive limit states design (LSD) procedure for determining factored tension and shear resistance of both cast-in-place (CIP) anchors and prequalified post-installed mechanical anchors installed in cracked and uncracked concrete. It now also specifies the test standard by which post-installed mechanical anchors are to be pre-qualified for use under LSD methodology. Annex D is an informative, rather than mandatory, part of the standard. However, as it represents the state of the art relative to the design of structural anchorage to concrete, it is written in ‘mandatory’ language to facilitate its formal adoption by design professionals or regulatory authorities. CSA A23.3-04 is referenced by the 2005 National Building Code of Canada (NBC), which forms the basis of most provincial building codes. Apart from Annex D, there are no other standards referenced by NBC or provincial codes that address the design of structural anchorage to concrete. CSA A23.3-04 was amended in August 2009 to include revisions to Annex D pertinent to the seismic design of anchors. While the annex I does not currently address post-installed adhesive anchors, there is a CSA subcommittee working to develop the design and test provisions necessary to incorporate these product types. New design methodology The design of anchors under Annex D’s limit states design method is either based on: • calculation using design models that result in the prediction of resistance in substantial agreement with the results of comprehensive tests; or • test evaluation using the five per cent fractile values (or characteristic values) of the test results to determine the factored resistance for seven possible failure modes. The latter approach is predominately used. There are four possible failure modes for tension: • steel fracture; • concrete breakout; • anchor pullout or pull-through; and • concrete side-face blowout (this is applicable for CIP headed anchors only). Similarly, there are three possible failure modes for shear: • steel fracture; • concrete breakout; and • concrete pry-out. 16 January 2010 Construction Canada CC_JanFeb10.indd 16 12/22/09 11:55:30 AM Photo © Dreamstime.com Feature