Determining Categories for Post-Installed Mechanical Anchors

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					 Determining Categories for Post-
   Installed Mechanical Anchors
Q.     In Appendix D of ACI 318-08,1 the strength reduction
       factor (φ) for tensile strength of mechanical anchors
when the anchor is governed by concrete breakout, side-
                                                                                            bits, respectively, are used to drill the holes the anchors
                                                                                            are installed in. ACI 355.2-072 also prescribes whether the
                                                                                            tests for each of these scenarios are performed using low-
face blowout, or pullout strength varies depending on the                                   strength (2500 to 4000 psi [17 to 28 MPa]) or high-strength
anchor category. How do I determine what category the                                       (6500 to 8500 psi [46 to 60 MPa]) concrete. In the third
anchor I’m using falls into?                                                                scenario, a reduced amount of installation effort, such as
                                                                                            an installation torque only half of that recommended by

A.     Anchor categories are determined based on post-
       installed mechanical anchor tests described in ACI
355.2-07, “Qualification of Post-Installed Mechanical
                                                                                            the manufacturer, is used to install the anchor. The fourth
                                                                                            scenario assesses the tension capacity of the anchor after
                                                                                            being subjected to 100,000 cycles of a prescribed tensile
Anchors in Concrete (ACI 355.2-07) and Commentary.”2                                        load. In all reference and reliability test scenarios, each
This document is like an ASTM Standard in that it covers                                    test must be repeated a minimum of five times.
the tests to be conducted and the requirements for                                              Reliability tests of post-installed mechanical anchors
determining whether a mechanical anchor is acceptable                                       for use in cracked concrete use the same test scenarios
for use in uncracked concrete only, or both cracked and                                     as those for uncracked concrete, but criteria are also
uncracked concrete. The tests for determining the anchor                                    given for performance when a crack with a minimum
category are performed by an independent testing and                                        width intercepts the anchor. A key qualification criterion
evaluation agency. Anchor manufacturers that have                                           is that the coefficient of variation of the test results must
performed the tests report the category in their technical                                  be less than 20%. If this criterion cannot be achieved, the
literature. It’s important to remember that a post-                                         anchor is considered unqualified.
installed mechanical anchor category is determined for                                          The reliability test results are used to calculate a charac-
each anchor diameter. Therefore, the anchor category for                                    teristic tensile capacity Nb,r for each reliability scen
				
DOCUMENT INFO
Description: Q. In Appendix D of ACI 318-08,1 the strength reduction factor ([straight phi]) for tensile strength of mechanical anchors when the anchor is governed by concrete breakout, sideface blowout, or pullout strength varies depending on the anchor category. Reliability tests of post-installed mechanical anchors for use in cracked concrete use the same test scenarios as those for uncracked concrete, but criteria are also given for performance when a crack with a minimum width intercepts the anchor.
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