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

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R-1 A P P E N D I X R AASHTO Design Guideline

R-2 AASHTO DESIGN GUIDELINES FOR ADHESIVE ANCHOR SYSTEMS This guideline addresses the design of adhesive anchor systems in transportation applications. ADHESIVE ANCHOR SYSTEMS Adhesive anchor systems are used to connect new construction to existing concrete using an adhesive and a threaded rod or reinforcing bar in holes with diameters no larger than 1.5 times the anchor diameter. Adhesives for adhesive anchor systems can be an epoxy, polyester, vinyl ester, acrylate, or hybrid mortar and consist of two parts (a resin and a hardener) and come in either cartridge or capsule format. The term “adhesive anchor system” includes all the materials and equipment necessary for proper installation. This includes not only the adhesive, but also the anchor, the mixing and delivery systems (dispenser gun, mixing nozzle), equipment for hole cleaning (air nozzles, air pumps, brushes), and the manufacturer’s printed installation instructions (MPII). The MPII provided with the adhesive anchor system includes the instructions for the correct installation procedure. The approval and acceptance of adhesive anchor systems is based on strict adherence to the MPII. This includes but is not limited to drilling procedures (drill type, drill bit type, and diameter), hole cleaning procedures (blowing, vacuuming, brushing), installation conditions (dry, moist, or submerged hole, adhesive temperature, and concrete temperature), adhesive dispensing procedure (discarding initial adhesive, maintaining nozzle tip submerged during dispensing), and adherence to gel/working and curing times. APPROVED ADHESIVE ANCHOR SYSTEMS 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. Products for use in AASHTO transportation structures must be ACI 355.4 approved. Individual DOTs might have additional testing requirements beyond what is required in ACI 355.4 for adhesive anchors. Consult your DOT’s QPL for approved adhesive anchor systems. In specifying an adhesive anchor system, attention must be taken to ensure that the adhesive anchor system is appropriate for the installation and in-service conditions (especially in-service temperature)

R-3 experienced by the anchor. If an anchor is exposed to service temperatures greater than or equal to 120°F for significant portions of its service life, the anchor should be evaluated for temperature category B (ACI 355.4 §8.5) at a temperature equal to or greater than the highest service temperature. DESIGN OF ADHESIVE ANCHOR SYSTEMS AASHTO Section X.Y. contains design provisions for single adhesive anchors and groups of adhesive anchors in tension. There are three tension failure modes (adhesive bond failure, concrete breakout failure, and steel rupture) as illustrated in Figure 1 that must be considered. Figure 1: Three adhesive anchor tension failure modes. Bond Strength The basic adhesive bond strength is based on a uniform bond stress model evaluated at the anchor diameter. Due to the thin bond line (~1/16”), this model works well for the stress at the anchor diameter and the hole diameter. The characteristic bond stress for each adhesive can be obtained from the Evaluation Service Report (ESR) created from the ACI355.4 testing program. If an adhesive anchor system is not chosen prior to design, AASHTO X.Y.3.2 contains minimum values for the characteristic bond stress that can be used in design. Separate values are given for sustained tension load applications, applications subject to earthquake loads, and for the combination of the two.

R-4 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 . Due to the creep deformation of polymers, adhesive anchor systems are particularly sensitive to sustained tension load. In cases of sustained tension load, the bond strength is adjusted by a sustained load resistance factor ( sus). The sustained load resistance factor is 0.55 for structures with a lifetime of 50 years and 0.50 for structures with a lifetime up to 100 years. Concrete Breakout Strength Concrete breakout strength assumes the creation of a 35° failure prism of concrete. As for adhesive bond strength, concrete breakout strength is susceptible to anchor spacing and distance to an edge. Two different modification factors for anchor spacing and edge distance are included, and . Steel Strength Adhesive anchors must also be designed for steel strength per the provisions provided in AASHTO LRFD Bridge Design Specifications Article 6.13.2.10. AASHTO Tension Design Provisions Limitations The AASHTO adhesive anchor tension design provisions place various limitations as listed in AASHTO LRFD Bridge Design Specifications Article X.Y.1 and discussed in the commentary. 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. Shear and Tension-Shear Interaction Adhesive anchors are susceptible to three shear failure modes (steel, concrete breakout, and concrete pryout). Refer to ACI 318-11 Appendix D for the design for these failure modes. Additionally, consult ACI 318-11 Appendix D in situations of combined tension and shear.

R-5 SAMPLE CALCULATIONS Included in this design guideline are two examples of sample calculations using the AASHTO design specifications for adhesive anchors found in AASHTO 2010 LFRD Bridge Design Specifications Section X.Y. The first example is for a single anchor in tension and the second example is for a group of anchors in tension.

R-6 Single Adhesive Anchor Sample Calculations Given: 5/8” ASTM A193 grade B7 threaded rod Effective embedment depth = 5” Anchor is located 7” from the nearest edge Conditions of X.Y.1 are satisfied Adhesive anchor system is not chosen Anchor is subjected to sustained load f'c = 4000 psi Find: Find the factored resistance Nr Calculation in accordance with the proposed AASHTO Design Specifications for Adhesive Anchors Code Reference DETERMINE RESISTANCE FACTORS Assume category 3 ASTM A193 B7 is considered a ductile steel element Assume a structure lifetime of 75 years X.Y.2 X.Y.2 X.Y.2

R-7 CALCULATE THE FACTORED RESISTANCE DUE TO ADHESIVE BOND FAILURE Calculate Projected Influence Areas Figure 2: Schematic of ANao. Figure 3: Schematic of ANa. Determine the critical radial distance from the centerline of the anchor to where the stresses in the concrete are negligible Determine the projected influence area without the influence of edge effects Determine the projected influence area of a single anchor (X.Y.3.3-2) (X.Y.3.3-1) X.Y.3.3 Calculate the Modification Factor for Edge Effects Determine cmin Since (X.Y.3.4-2)

R-8 Calculate the Basic Bond Strength Determine characteristic bond stress Since product is not chosen, use the minimum values specified in X.Y.3.2 for sustained load applications Calculate the basic bond strength X.Y.3.2 (X.Y.3.2-1) Calculate the Nominal Resistance Due to Adhesive Bond (X.Y.3.1-1) Calculate the Factored Resistance Due to Adhesive Bond (X.Y.2-2) CALCULATE THE FACTORED RESISTANCE DUE TO CONCRETE BREAKOUT FAILURE Determine if a reduced embedment depth is necessary Anchor is not located closer than 1.5hef to three or more edges, therefore no reduction in hef is necessary Calculate Projected Influence Areas X.Y.2.4 Figure 4: Schematic of ANco. Figure 5: Schematic of ANc.

R-9 Determine the center to the edge of an assumed failure prism with a 35° angle Determine the projected influence area without the influence of edge effects Determine the projected influence area of a single anchor (X.Y.4.3-2) (X.Y.4.3-1) X.Y.4.3 Calculate the Modification Factor for Edge Effects Determine cmin Since (X.Y.4.4-2) Calculate the Basic Concrete Breakout Strength Calculate the basic concrete breakout strength (X.Y.4.2-1) Calculate the Nominal Resistance Due to Concrete Breakout Failure (X.Y.4.1-1) Calculate the Factored Resistance Due to Concrete Breakout Failure (X.Y.2-2)

R-10 CALCULATE THE FACTORED RESISTANCE DUE TO STEEL FAILURE Calculate the Nominal Resistance Due to Steel Failure (6.13.2.10.2-1) Calculate the Factored Resistance Due to Steel Failure (X.Y.2-2) DETERMINE THE LIMITING RESISTANCE Summary of Factored Resistances Bond Failure Concrete Breakout Failure Steel Failure Limiting Resistance Note: If an ACI 355.4 approved product was chosen prior to design a higher characteristic bond stress could have been used. For example: (X.Y.3.2-1) (X.Y.3.1-1) (X.Y.2-2)

R-11 Adhesive Anchor Group Sample Calculations Given: 4 5/8” ASTM A193 grade B7 threaded rod Effective embedment depth = 5” Centerlines of anchor group are located 6” from the one edge and 7” from another edge Anchors are spaced 8” apart Conditions of X.Y.1 are satisfied Adhesive anchor system is chosen Category 1 Temperature range A (maximum short term = 110°F) (maximum long-term = 80°F) Anchors are subjected to sustained load f c = 4000 psi Find: Find the factored resistance Nr Calculation in accordance with the proposed AASHTO Design Specifications for Adhesive Anchors Code Reference DETERMINE RESISTANCE FACTORS Given category 1 ASTM A193 B7 is considered a ductile steel element Assume a structure lifetime of 75 years X.Y.2 X.Y.2 X.Y.2

R-12 CALCULATE THE FACTORED RESISTANCE DUE TO ADHESIVE BOND FAILURE Calculate Projected Influence Areas Determine the critical radial distance from the centerline of the anchor to where the stresses in the concrete are negligible (X.Y.3.3-2) Figure 6: Schematic of ANao. Figure 7: Schematic of ANa. Determine the projected influence area without the influence of edge effects Determine the projected influence area of a single anchor Check maximum limit of ANa (X.Y.3.3-1) X.Y.3.3 X.Y.3.3

R-13 Calculate the Modification Factor for Edge Effects Determine cmin Since (X.Y.3.4-2) Calculate the Basic Bond Strength Obtain characteristic bond stress from ICC-ES AC308 ESR Calculate the basic bond strength ICC-ES AC308 ESR (X.Y.3.2-1) Calculate the Nominal Resistance Due to Adhesive Bond (X.Y.3.1-1) Calculate the Factored Resistance Due to Adhesive Bond (X.Y.2-2) CALCULATE THE FACTORED RESISTANCE DUE TO CONCRETE BREAKOUT FAILURE Determine if a reduced embedment depth is necessary Anchor is not located closer than 1.5hef to three or more edges, therefore no reduction in hef is necessary X.Y.2.4

R-14 Calculate Projected Influence Areas Determine the center to the edge of an assumed failure prism with a 35° angle (X.Y.4.3-2) Figure 8: Schematic of ANco. Figure 9: Schematic of ANc. Determine the projected influence area without the influence of edge effects Determine the projected influence area of a single anchor Check maximum limit of ANc (X.Y.4.3-1) X.Y.4.3 X.Y.4.3 Calculate the Modification Factor for Edge Effects Determine cmin

R-15 Since (X.Y.4.4-2) Calculate the Basic Concrete Breakout Strength Calculate the basic concrete breakout strength (X.Y.4.2-1) Calculate the Nominal Resistance Due to Concrete Breakout Failure (X.Y.4.1-1) Calculate the Factored Resistance Due to Concrete Breakout Failure (X.Y.2-2) CALCULATE THE FACTORED RESISTANCE DUE TO STEEL FAILURE Calculate the Nominal Resistance Due to Steel Failure (6.13.2.10.2-1) Calculate the Factored Resistance Due to Steel Failure (X.Y.2-2) DETERMINE THE LIMITING RESISTANCE Summary of Factored Resistances Bond Failure Concrete Breakout Failure Steel Failure Limiting Resistance