Long-Term Performance of Epoxy Adhesive Anchor Systems (2013)

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Q-1 A P P E N D I X Q AASHTO Design Specification

Q-2 AASHTO 2010 LRFD BRIDGE DESIGN SPECIFICATIONS SECTION XXXX ADHESIVE ANCHORS X.Y-ADHESIVE ANCHORS X.Y.1-Definitions Adhesive - Chemical components formulated from organic polymers, or a combination of organic polymers and inorganic materials that cure when blended together. Adhesive anchor - A post-installed anchor, inserted into hardened concrete with an anchor hole diameter not greater than 1.5 times the anchor diameter, that transfers loads to the concrete by bond between the anchor and the adhesive, and bond between the adhesive and the concrete. Anchor - A steel element post-installed into a hardened concrete member and used to transmit applied loads to the concrete. Steel elements for adhesive anchors include threaded rods, deformed reinforcing bars, or internally threaded steel sleeves with external deformations. Anchor group - A number of similar anchors having approximately equal effective embedment depths with spacing s between adjacent anchors such that the protected areas overlap. Edge distance - The distance from the edge of the concrete surface to the center of the nearest anchor. Effective depth of embedment - The overall depth through which the anchor transfers force to or from the surrounding concrete. The effective embedment depth will normally be the depth of the concrete failure surface in tension applications. Manufacturer Printed Installation Instructions (MPII) - Published instructions for the correct installation of the anchor under all covered installation conditions as supplied in the product packaging. X.Y.2-Notations ANa = projected influence area of a single adhesive anchor or group of adhesive anchors based on actual edge distances and anchor spacing (in.2) (X.Y.5.1) ANao = projected influence area of a single adhesive anchor or group of adhesive anchors with an edge distance greater than or equal to cNa (in.2) (X.Y.5.1) ANc = projected influence area of a single adhesive anchor or group of adhesive anchors based on actual edge distances and anchor spacing (X.Y.6.1) ANaco = projected influence area of a single adhesive anchor or group of adhesive anchors with an edge distance greater than or equal to cNc (X.Y.6.1) c = edge distance from the center of the anchor to the nearest edge of concrete (X.Y.3) ca,max = largest of the edge distances that are less than 1.5hef (in.) (X.Y.6.2) cmin = distance from the center of an anchor to the closest edge of the concrete (in.) (X.Y.5.4) cNa = projected distance from the center of an anchor required to develop the full bond strength (in.) (X.Y.5.4) cNc = projected distance from the center of an anchor for a concrete failure prism with an assumed angle of 35° (X.Y.6.4)

Q-3 da = outside diameter of anchor (in.) (X.Y.5.2) hef = effective embedment depth of anchor (in.) (X.Y.5.2) Na = basic bond strength of a single adhesive anchor in tension in cracked concrete (X.Y.5.1) Nc = basic concrete breakout strength of a single adhesive anchor in tension in cracked concrete (X.Y.6.1) Nn = nominal resistance of an adhesive anchor bolt or group of anchors (X.Y.4) Nr = factored resistance of an adhesive anchor bolt or group of anchors (X.Y.4) smax = maximum spacing between anchors within a group (in.) (X.Y.6.2) cr = characteristic bond stress of adhesive anchor in cracked concrete (ksi) (X.Y.5.2) cr,min = minimum characteristic bond stress (ksi) (X.Y.5.2) = resistance factor for anchor bolts (X.Y.4) a = resistance factor for anchor bolts for adhesive bond and concrete breakout (X.Y.4) t = resistance factor for anchor bolts for tensile failure (X.Y.4) ed,Na = modification factor for edges effects beyond what is accounted for by the ratio (X.Y.5.1) ed,Nc = modification factor for edges effects beyond what is accounted for by the ratio (X.Y.6.1) sus = resistance factor for sustained load (X.Y.4) X.Y.3-General Conditions Adhesive anchors designed under this specification shall meet the following criteria: • Products shall be qualified for use in cracked concrete in accordance with ACI 355.4. • The effective depth of embedment, hef, must not be less than 4da, 1-5/8”, or the minimum stated in the Manufacturer’s Printed Installation Instructions (MPII). • The effective depth of embedment, hef, must be less than or equal to 20da or the maximum stated in the MPII, whichever is less. • Edge distance, c, from the center of the anchor to the nearest edge of concrete must not be less than the larger of 6da or the minimum stated in the MPII. • Anchors must be installed in holes drilled with a manufacturer’s approved rotary impact drill or rock drill unless otherwise permitted by MPII. • Concrete must be normal weight concrete as defined in Article 5.2. • The concrete member is considered cracked with normal temperature and shrinkage cracks and with minimum reinforcement. • The concrete at time of installation shall have a minimum temperature of 50°F or that stated in the CX.Y.3 ACI 355.4 contains the testing and evaluation requirements for adhesive anchor systems for use in concrete. ACI 355.4 was created from the product approval standards originally contained within ICC-ES AC58 and later in ICC-ES AC308. The limitation on the minimum and maximum effective embedment depth is included due to the limitation of the uniform bond stress model. Adhesive anchors gain their bond strength in part due to mechanical interlock with the sides of the hole. Rotary impact drills or rock drills create relatively rough sided holes as opposed to holes created with diamond core drills. NCHRP Project 04-37 report indicates that bond strengths of adhesive anchors installed in holes created by diamond cored drills can be 74% of anchors installed in holes created by rotary impact drills or rock drills. Several manufacturers prohibit the installation of adhesive anchors installed in diamond cored holes. Adhesive anchor systems can have reduced strengths in lightweight concrete which is not considered in this design provision. This design provision assumes that the concrete is cracked during the service life of the anchor system and that minimum reinforcement is present. If the designer can ensure that the concrete will remain uncracked during the service

Q-4 MPII, whichever is greater. • Concrete at time of installation shall have a minimum age of 21 days and a minimum compressive strength of 2500 psi. • The tensile loading on the group of anchors must be applied centrically to the anchor group. • Anchor group effects shall be considered wherever two or more anchors have spacing less than less than 3hef for evaluation of concrete breakout failure or 2cNa for evaluation of adhesive bond failure. Only those anchors susceptible to the particular failure mode under investigation shall be included in the group. • The tension loading on the anchor group must be applied concentrically to the anchor group. • Anchors must not be subjected to seismic loads. The contract documents shall also specify all parameters associated with the characteristic bond stress used for the design according to D.5.5 including minimum age of concrete; concrete temperature range; moisture condition of concrete at time of installation; type of lightweight concrete, if applicable; and requirements for hole drilling and preparation. life of the anchor, higher bond stress values can be used and the designer is referred to ACI 318-11 Appendix D for design in uncracked concrete. Adhesive anchor systems cannot fully cure at low temperatures. The MPII state the minimum permissible installation temperature which varies per product. The provision for installation in concrete that is at least 21 days old is due to lower bond strengths for adhesive anchor systems in early-age concrete. NCHRP Project 04-37 Report showed that adhesive anchor systems had reduced bond strengths in concrete specimens less than 14 days old. The provision for a minimum compressive strength of 2500 psi is due to adverse effects on adhesive anchor bond strength due to very low strength concrete. For adhesive anchor situations that fall outside of these limitations, the designer is encouraged to develop case- specific design criteria using other design resources such as those found within ACI 318-11 Appendix D. For adhesive anchors, the contract documents must also provide all parameters relevant to the characteristic bond stress used in the design. These parameters may include, but are not limited to: 1. Acceptable anchor installation environment (dry or saturated concrete; concrete temperature range); 2. Acceptable drilling methods; 3. Required hole cleaning procedures; and 4. Anchor type and size range (threaded rod or reinforcing bar). Hole cleaning is intended to ensure that drilling debris and dust do not impair bond. Depending on the on-site conditions, hole cleaning may involve operations to remove drilling debris from the hole with vacuum or compressed air, mechanical brushing of the hole wall to remove surface dust, and a final step to evacuate any remaining dust or debris, usually with compressed air. Where wet core drilling is used, holes may be flushed with water and then dried with compressed air. If anchors are installed in locations where the concrete is saturated (for example, outdoor locations exposed to rainfall), the resulting drilling mud must be removed by other means. In all cases, the procedures used should be clearly described by the manufacturer in printed installation instructions accompanying the product. These printed installation instructions, which also describe the limits on concrete temperature and the presence of water during installation as well as the procedures necessary for void-free adhesive injection and adhesive cure requirements, constitute an integral part of the adhesive anchor system and are part of the assessment performed in accordance with ACI 355.4. X.Y.4-Factored Resistance For adhesive anchors subjected to tensile loading, the factored resistance, Nr, of an adhesive anchor bolt or group of anchors at Service II Load Combinations shall be taken as: Nr = Nn (X.Y.4-1) CX.Y.3.2 This design specification only addresses tensile loading. For other loading applications (e.g., shear, combined tension and shear), the designer is encouraged to use other design resources such as those found within ACI 318-11 Appendix D. The ACI 355.4 product evaluation report classifies adhesive anchor systems into three categories based on their

Q-5 where: Nn = nominal resistance of an adhesive anchor bolt or group of anchors as specified in Article X.Y.4. The factored resistance, Nr, of an adhesive anchor bolt or group of anchors at the strength limit state shall be taken as: Nr = sus Nn (X.Y.4-2) where: Nn = nominal resistance of an adhesive anchor bolt or group of anchors shall be taken as the smallest of: • Adhesive bond strength, Nn, as specified in Article X.Y.5.1. • Concrete breakout strength, Nn, as specified in Article X.Y.6.1. • Steel strength, Nn, as specified in Article 6.13.2.10. = resistance factor for anchor bolts shall be taken as: • a = 0.65 for adhesive bond and concrete breakout for category 1 • a = 0.55 for adhesive bond and concrete breakout for category 2 • a = 0.45 for adhesive bond and concrete breakout for category 3 • t = 0.75 for tensile steel failure sus = resistance factor for sustained load: • sus = 1.0 in the absence of sustained load or for concrete breakout failure or for steel failure • sus = 0.55 for the presence of sustained load for a lifetime of 50 years at 70°F and 10 years at 110°F • sus = 0.50 for the presence of sustained load for a lifetime of 100 years at 70°F and 20 years at 110°F sensitivity to installation procedures. ACI 318 then assigns different resistance factors based on anchor category. The three categories are described as follows: • Category 1 is for adhesive anchor systems with a low sensitivity to installation procedures and a high reliability • Category 2 is for adhesive anchor systems with a medium sensitivity to installation procedures and a medium reliability • Category 3 is for adhesive anchor systems with a high sensitivity to installation procedures and a low reliability ACI 318-11 uses a 0.55 factor for sustained load calculations which is in agreement with the ACI 355.4 sustained load testing program. The ACI 355.4 sustained testing program subjects an anchor to 55% of its mean short- term load strength at 70°F and 110°F for 1000 hours. Displacements from both tests are projected to 10 years at 110°F and 50 years at 70°F and anchors are qualified for sustained load if the projected displacements are less than a prescribed displacement limit. The factor for sustained load used by AASHTO has been correlated with the displacement limitations found in the ACI 355.4 testing program and provides reduction factors for structure lifetimes of 50 and 100 years at 70°F and 10 and 20 years at 110°F.

Q-6 X.Y.5-Adhesive Bond Failure X.Y.5.1-Nominal Resistance due to Adhesive Bond The nominal resistance of an adhesive anchor bolt or group of anchors due to adhesive bond failure shall be taken as: (X.Y.5.1-1) where: = basic bond strength of a single adhesive anchor in tension in cracked concrete as defined in Article X.Y.5.2. = projected influence area of a single adhesive anchor or group of adhesive anchors based on actual edge distances and anchor spacing as defined in Article X.Y.5.3 (in2). = projected influence area of a single adhesive anchor or group of adhesive anchors with an edge distance greater than or equal to cNa as defined in Article X.Y.5.3 (in2). = modification factor for edges effects beyond what is accounted for by the ratio as defined in Article X.Y.5.4. CX.Y.5.1 Adhesive anchors are susceptible to anchor spacing and distance to an edge. If located too close to each other or to an edge, adhesive anchors will not be able to fully develop their design strength. Two different modification factors for anchor spacing and edge distance are included, and . X.Y.5.2-Basic Bond Strength The basic bond strength of an adhesive anchor due to adhesive bond failure shall be taken as: (X.Y.5.2-1) where: = outside diameter of anchor (in.) = effective embedment depth of anchor (in.) = characteristic bond stress of adhesive anchor in cracked concrete (ksi). Shall be taken as the 5% fractile of tests performed in accordance with ACI 355.4. It shall be permitted to use the minimum characteristic bond stress, , as defined below. = minimum characteristic bond stress: • = 0.200 ksi • = 0.080 ksi for sustained tension load applications CX.Y.5.2 The equation for the nominal resistance of an adhesive anchor to adhesive bond is based on a uniform bond stress model developed by Cook et al. (1998) based on numerical studies and an international database of experimental tests. Due to the relatively thin bond line in adhesive anchors, the model is valid for the interface between the adhesive and the anchor as well as the adhesive and the concrete. The characteristic bond stress is determined from a battery of tests in ACI 355.4 for various combinations of installation and service conditions. In the absence of product- specific information, the minimum characteristic bond stress provided may be used. The minimum characteristic bond stress is the minimum allowed for qualification by ACI 355.4 for the given conditions. These are very conservative values and the designer is encouraged to specify approved product and use properties of these products in the design. ACI 318-11 Table D.5.5.2 classifies two installation and service conditions of “indoor” and “outdoor”. Indoor conditions are for anchors installed in dry concrete with a rotary impact drill or rock drill and subjected to minimal temperature variations over the service life. Outdoor conditions are for anchors installed in concrete exposed to weather and could be wet during installation or the service life. Outdoor conditions also provide for larger temperature variations during the service life. This standard assumes an “outdoor” installation and the values for the minimum characteristic bond stress, , are based on this

Q-7 “outdoor” condition. X.Y.5.3-Projected Influence Areas The projected influence are of a single adhesive anchor without the influence of edge or spacing effects used to determine bond strength, , shall be computed as: (X.Y.5.3-1) where: (X.Y.5.3-2) The parameter ANa is the projected influence area of a single adhesive anchor or group of anchors. For a single adhesive anchor, ANa is the projected rectangular area that projects outward from the center of the anchor in all four principle directions a distance cNa but shall not exceed the distance, c, to the edge. For a group of anchors, ANa is the projected rectangular area that projects outward from the outer rows of a group of adhesive anchors in all four principle directions a distance cNa but shall not exceed the distance, c, to the edge. The value of ANa shall not exceed nANa0 where n is the number of anchors in the group. CX.Y.5.3 The parameter ANao is the projected influence area of a single anchor without any influence of edge effects as illustrated in Figure 1. Figure 1: Projected influence area ANa0 The parameter, cNa, is the critical radial distance from the centerline of an anchor to where stresses in the concrete due to the adhesive bond stress are negligible. This is a function of anchor diameter and bond strength. This parameter has been calibrated from ACI 318-11 equation (D- 21) by inserting the value of τuncr slightly larger than the maximum characteristic bond stress in uncracked concrete from a sampling of seventeen ICC-ES AC308 approved adhesive anchor products. The parameter ANa is the projected influence area of a single adhesive anchor or group of anchors as illustrated in Figure 2 for a single anchor and Figure 3 for a group of anchors. Figure 2: Projected influence area ANa for a single anchor

Q-8 Figure 3: Projected influence area ANa for a group of anchors X.Y.5.4-Modification Factor for Edge Effects The modification factor, , for anchors located close to an edge beyond what is accounted for in Article X.Y.5.3, shall be computed as: If cmin ≥ cNa then (X.Y.5.4-1) If cmin < cNa then (X.Y.5.4-2) where: = distance from the center of an anchor to the closest edge of the concrete (in.) = projected distance from the center of an anchor required to develop the full bond strength as defined in Article X.Y.5.3 (in.).

Q-9 X.Y.6-Concrete Breakout Failure X.Y.6.1-Nominal Resistance due to Concrete Breakout Failure The nominal resistance of an adhesive anchor bolt or group of anchors due to concrete breakout failure shall be taken as: (X.Y.6.1-1) where: = basic concrete breakout strength of a single adhesive anchor in tension in cracked concrete as defined in Article X.Y.6.2. = projected influence area of a single adhesive anchor or group of adhesive anchors based on actual edge distances and anchor spacing as defined in Article X.Y.6.3 (in2). = projected influence area of a single adhesive anchor or group of adhesive anchors with an edge distance greater than or equal to cNc as defined in Article X.Y.6.3 (in2). = modification factor for edges effects beyond what is accounted for by the ratio as defined in Article X.Y.6.4. CX.Y.6.1 Adhesive anchors are susceptible to anchor spacing and distance to an edge. If located too close to each other or to an edge, adhesive anchors will not be able to fully develop their design strength. Two different modification factors for anchor spacing and edge distance are included, and . X.Y.6.2-Basic Concrete Breakout Strength The basic concrete breakout strength of an adhesive anchor shall be taken as: (X.Y.6.2-1) where: = specified compressive strength of concrete for use in design (ksi) = effective embedment depth of anchor (in.) If an anchor is located closer than 1.5hef to three or more edges, hef used in the calculation of equations X.Y.6.2- 1 and X.Y.6.3-2 shall be taken as: (X.Y.6.2-2) where: = largest of the edge distances that are less than 1.5hef (in.) = maximum spacing between anchors within a group (in.) CX.Y.6.2 The equation for the nominal resistance of an adhesive anchor due to concrete breakout failure assumes a 35° concrete failure prism based on fracture mechanics (Fuchs et al. (1995), Eligehausen and Balogh (1995), Eligehausen & Fuchs (1988), CEB (1994)). Note that equation (X.Y.6.2-1) has been calibrated from ACI 31-11 equation (D-6) by a factor of 0.0316 ( ) for the conversion of f’c from psi in ACI to ksi in AASHTO. The 0.54 coefficient incorporates both the conversion factor described above and the kc value from ACI 318 determined from a database of tests in uncracked concrete evaluated at the 5% fractile (Fuchs et al. (1995) and adjusted for cracked concrete (Eligehausen and Balogh (1995), Goto (1971)). The adjustment on hef in cases where anchors are located very close to three or more edges is correct the approximation of the factor which produces overly conservative results.

Q-10 X.Y.6.3-Projected Influence Areas The projected influence area of a single adhesive anchor without the influence of edge or spacing effects used to determine concrete breakout strength, , shall be computed as: (X.Y.6.3-1) where: (X.Y.6.3-2) The parameter ANc is the projected influence area of a single adhesive anchor or group of anchors. For a single adhesive anchor, ANc is the projected rectangular area that projects outward from the center of the anchor in all four principle directions a distance cNc but shall not exceed the distance, c, to the edge. For a group of anchors, ANc is the projected rectangular area that projects outward from the outer rows of a group of adhesive anchors in all four principle directions a distance cNc but shall not exceed the distance, c, to the edge. The value of ANc shall not exceed nANco where n is the number of anchors in the group. CX.Y.6.3 The parameter ANc0 is the projected influence area of a single anchor without any influence of edge effects as illustrated in Figure 4. Figure 4: Projected influence area ANc0 The value cNc is the distance from the center to the edge of the assumed failure prism with a 35 angle. This is simplified from a 35° angle as illustrated in Figure 5. Figure 5: Assumed failure prism The parameter ANc is the projected influence area of a single adhesive anchor or group of anchors as illustrated in Figure 6 for a single anchor and Figure 7 for a group of anchors. Figure 6: Projected influence area ANa for a single anchor

Q-11 Figure 7: Projected influence area ANa for a group of anchors X.Y.6.4-Modification Factor for Edge Effects The modification factor anchors located close to an edge beyond what is accounted for in Article X.Y.6.3, shall be computed as: If cmin ≥ cNc then (X.Y.6.4-1) If cmin < cNc then (X.Y.6.4-2) where: = distance from the center of an anchor to the closest edge of the concrete (in.) = projected distance from the center of an anchor for a concrete failure prism with an assumed angle of 35° as defined in Article X.Y.6.3 (in.). X.Y.5-References ACI 2011. Building Code Requirements for Structural Concrete, ACI 318-11, American Concrete Institute, Farmington Hills, MI. ACI 2011. Qualification of Post-Installed Adhesive Anchors in Concrete, ACI 355.4-11, American Concrete Institute, Farmington Hills, MI. Cook, R.A., Kunz, J., Fuchs, W., and Konz, R.C. (1998), “Behavior and Design of Single Adhesive Anchors Under Tensile Load in Uncracked Concrete,” ACI Structural Journal, Vol. 95, No. 1, pp. 9-26. Eligehausen, R. and Balogh, T. (1995), “Behavior of Fasteners Loaded in Tension in Cracked Reinforced Concrete,” ACI Structural Journal, Vol. 92, No. 3, pp. 365-379. Eligehausen, R., and Fuchs, W., “Load Bearing Behavior of Anchor Fastenings under Shear, Combined Tension and Shear or Flexural Loadings,” Betonwerk + Fertigteiltechnik, 2/1988, pp. 48-56.

Q-12 “Fastenings to Concrete and Masonry Structures, State of the Art Report,” Comité Euro-International du Béton (CEB), Bulletin No. 216, Thomas Telford Services Ltd., London, 1994. Fuchs, W., Eligehausen, R., and Breen, J.E. (1995), “Concrete Capacity Design (CCD) Approach for Fastening to Concrete,” ACI Structural Journal, Vol. 92, No. 1, pp. 73-94. Goto, Y., “Cracked Formed in Concrete around Deformed Tension Bars in Concrete,” ACI JOURNAL, Proceedings V. 68, No. 4, Apr. 1971, pp. 244-251. ICC-ES AC58 (2005), Acceptance Criteria for Adhesive Anchors in Concrete and Masonry Elements, ICC Evaluation Services, Inc., Whittier, CA. ICC-ES AC308 (2008), Acceptance Criteria for Post Installed Adhesive Anchors in Concrete, ICC Evaluation Services, Inc., Whittier, CA.