Post-Installed Anchor Design

The tenn post-installed anchor is used to descrihe devices installed in holes drilled in hardened concrete for the purpose of transferring loads. Post-installed anchor types include expansion, undercut, screw, grouted, and adhesive anchors. 

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Traditionally, post-installed anchor design has been based on mean ultimate test data divided by a global safety factor of four (4). This approach has been replaced by a system involving more rigorous qualification testing and strength design concepts. 

The objective of this committee was to update the previous report, summarizing the State-of-the-Practice for the design of cast-in-place anchor rods, welded anchors, and post-installed anchors as used in petrochemical facilities. 

The following factors should be considered when designing connections using post-installed anchors ... 

Post-installed anchor connections may be deserving of special attention if they a) transfer loads as part of the structural load path of a building or other structure, b) are used in a building or structure that has been assigned a high importance classification (for example, emergency response facilities), or c) should be designed with post-installed anchor systems that are more robust. Post-installed anchor bolts that tend to be more robust include most undercut anchor systems, some heavy-duty expansion anchors, and many adhesive anchor systems. 

The design of proprietary post-installed anchors generally depends on information developed via prequalification testing. ACI 355.2 is a prequalification standard for post-installed mechanical anchors that provides data for design in accordance with ACI 318 Appendix D. It has been incorporated into ICC-ES acceptance criterion AC 193 for the purpose of issuing evaluation reports for these products. 

Note For specific anchor category designation consult the post-installed anchor manufacturer or associated evaluation report from ICC-ES or other evaluation service. 

Post-installed anchors must satisfy certain qualification requirements in order to be used to resist seismic loads in a structure assigned to Seismic Design Categories C, D, E, or F. These involve the performance of specific tests and application of acceptance criteria for qualification and determination of relevant design parameters. ACl 318 Appendix D references ACl 355.2, Qualification of Post-installed Mechanical Anchors in Concrete, for the quahfication of expansion and undercut anchors. This document has been incorporated into acceptance criteria used by the ICC Evaluation Service for issuance of Evaluation Service Reports on anchors to demonstrate conformance with IBC Section 104.11, Alternative materials, design and methods of construction and equipment. AC 193 provides acceptance criteria for mechanical anchors. AC308 provides acceptance criteria as well as supplementary design provisions for adhesive anchors. 

This chapter provides basic information regarding installation of anchors, with the initial focus being on key factors and practices affecting post-installed anchor installations. Anchor constructability considerations which address and detail quality control, inspection, design, and construction practices that will help ensure constructible and structurally effective anchor installations are then outlined. Finally, anchor repair procedures are provided - with specific recommendations made for the repair of common anchor installation problems such as misalignment and erroneous projections. 

Post-installed bolts will be required at times for attachment of equipment which may be subjected to large accelerations during a blast. Expansion anchors should be avoided for most blast design applications unless the load levels are low. Typically "wedge" type anchors are qualified for dynamic loads although most of these ratings are for vibratory loads and are based on cyclic tests at low stress levels. These should only be used where ultimate loads are less than the rated capacity with a margin of safely. Epoxy anchors have shown excellent dynamic capacity and may be considered for critical applications. 

ACI Committee 355 published the State-of-the-Art Report on Anchorage to Concrete in 1991. This was the first of a two-volume set whieh emphasized behavior and did not include design methods and procedures. In 2000, ACI Committee 355 published the ACI Provisional Standard, Qualification of Post-Installed Mechanical Anchors in Concrete (ACI 355.2-00) and Commentary (ACI 355.2R-00). This document prescribed testing programs and evaluation requirements for post-installed mechanical anchors intended for use in concrete rmder the design provisions of ACI 318/318R-02. It was designated an ACI Standard in 2001 and has since been updated twice, most recently in 2007. 

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