Post-Installed Mechanical Anchors

Expansion anchors transfer tension loads to the hase material via friction between the expansion elements of the anchor and the wall of the hole. The magnitude of the friction resistance is directly proportional to the degree of expansion force developed by the anchor. Expansion forces are produced in response to the relative movement of sloping surfaces within the anchor mechanism. The maimer in which this relative movement is produced is important for distinguishing the anchor function in response to tension loads. The two most common mechanisms for producing expansion forces are represented by displacement-controlled and torque-controlled anchors  

Undercut anchors transfer tension loads to the base material via bearing rather than fiiction, and as such offer a generally more rehable mechanism for resisting applied loads. This is achieved by producing a hole geometry (that is, an undercut) that permits the anchor to key into the base material. 

Undercut anchors represent a superior class of post-installed mechanical anchor. By relying on bearing to transfer tension loads, they offer several advantages over expansion anchors  

Many undercut anchors are developed around the concept of using a specialized tool to prepare the undercut in a previously drilled hole. These systems are capable of producing excellent anchorages at a variety of embedment depths. They are particularly suited to retrofit applications, although they may be costly and difficult to install because of the complexity of the undercutting tools and the time required to prepare the undercut and set the anchors properly. 

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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. 

ACI 355.2-00 and ACI 355.2R-00, Qualification of Post-Installed Mechanical Anchors in Concrete and Commentary, American Concrete Institute Farmington Hills, MI. 

ACI Provisional Standard, Qualification of Post-Installed Mechanical Anchors in... 

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. 

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. 

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