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Re: INSP - Special Inspection Epoxy Anchors[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)seaoc.org
- Subject: Re: INSP - Special Inspection Epoxy Anchors
- From: "Sandy Pringle" <sandyp(--nospam--at)sic-inc.com>
- Date: Thu, 15 Jan 1998 20:27:50 -0700
At 10:28 AM 1/15/98 -0800, you wrote: >Pringle ... Silva ... anybody? > >For wedge anchors and the like, I have seen >special inspection criteria which use torque on >the nut to test the anchor. I understand that >this is generally justified because in these types >of anchors, the ability of the anchor to resist >forces is intimately connected to the amount of >torque applied during installation. > >What about torque testing of epoxy anchor systems, >Like Hilti's HY150 (we are trying to anchor stuff >in Zone 4). Stan, You may download Guideline 3, "TORQUE TESTING & INSTALLATION INSPECTION OF DRILLED-IN ANCHORS", a City of Los Angeles document, from the Inspection Practices Committee section of the SEAOC web page, which is pretty thorough, but the following is more specific: Wedge anchors are installed with the anchor capacity developed through an amount of pressure to the sides of the hole. Critical to this operation is the psi of the concrete, the diameter, depth and cleanliness of the hole once the issue of edge or interval spacing is addressed. Wedge anchors require that the hole depth be greater than the embedment requirement to accommodate the withdrawal of the anchor as it is tightened and simultaneously expanded. Just how tight the nut is directly relates to the amount of pressure of the actual wedge part of the anchor to the sides of the hole. This is determined by a specific torque that is part of the installation process. This is generally a one time operation and is performed by at the time of installation. Once the anchor is installed and properly torqued, the nut can be removed and whatever is required may be fastened since the anchor is already well and properly set. The fastening of hardware or whatever has its own tightness requirements and is not part of the anchoring capacity. For anchors installed through existing framing, care must be taken not to unduly compress the member. This can be accomplished by the use of large steel plates and must be considered as some torque values for standard sizes (7/8 Hilti Kwikbolt, for example) with 300# torque would surely damage unprotected framing. Other friction type anchors may also require torque as part of their installation, but generally the wedge anchor has higher values and is most frequently used for structural applications. This torque is part of the installation process and any subsequent torquing is not required; in fact, were you to torque an anchor, say 5 days after the initial installation torque, you would find the anchor would require more turns of the nut to re-achieve the torque. This is due to some degree of elongation or relaxation within the body of the anchor and to a concrete compression aspect within the hole at the point of contact with the wedge portion of the anchor. These issues are considered by the manufacturers and the accreditors (ICBOES for example). The bottom line is that wedge anchors are generally supposed to be installed with continuous inspection by a qualified Special Inspector present. Testing or torquing after the fact for wedge anchors is redundant if the installation included a torque requirement. Testing of these anchor systems is part of their Research Report approval, but if, for whatever reason, specific anchor testing is desired, a Tension Test per ASTM Standard using a tripod and a gauge to determine load capacity is the preferred method. There does exist a un quantifiable although relatively accurate formula for the translation of torque to tension values that can be used, but the coefficient of friction is the variable in this formula and generally this system is used for brand new, clean anchors. Hkd/12 = torque ft# where H is the load capacity, k is the coefficient of friction (use .4 for conservative values) and d is the diameter of the anchor, but for truly accurate requirements, the tripod test is needed. Epoxy anchors have no torque requirements, only installation monitoring by a Special Inspector since once all the installation criteria requirements have been met you will have the same anchor that has been tested and re-tested before the approval was ever issued. But once again, you may feel a specific project warrants the extra margin of verification (perhaps the psi of the concrete is not clear). The tripod system is preferred, but if the expense becomes and issue and you opt to use the torque/tension translation, the tension should be backed off once the test is complete. Epoxy anchors are not supposed to be left under tension loads due some element of creep. Whew!! I wonder how many of you will read this whole thing? R. Sandy Pringle, Chair STRUCTURAL INSPECTION CONSULTANTS Inc. SEAOSC (800)598-1970 Fax (310)376-5294 Inspection Practices Committee Hermosa Beach & Redondo Beach, CA sandyp(--nospam--at)sic-inc.com http://www.sic-inc.com It's not a matter of where you stand, but in what direction you're headed.
- Re: INSP - Special Inspection Epoxy Anchors
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- Re: INSP - Special Inspection Epoxy Anchors
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