Adhesive Anchors in Concrete Under Sustained Loading Conditions (2009)

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A-1 A P P E N D I X A Draft AASHTO Test Method—Standard Method of Test for Evaluation of Adhesive Anchors in Concrete Under Sustained Loading Conditions

A-3 OTHSAA1-XXXXT Standard Method of Test for Evaluation of Adhesive Anchors in Concrete Under Sustained Loading Conditions AASHTO Designation: T XXXX-XX ASTM Designation: XXXX-XX INTRODUCTION Adhesive anchor systems have widespread use in transportation structures such as bridge widening, concrete repair and rehabilitation, barrier retrofitting, utility installation on existing structures, and tunneling. These systems are used to anchor threaded rod and reinforcing bars in concrete. This test method determines an adhesive anchor’s ability to withstand sustained tensile loads under normal conditions. 1 SCOPE 1.1 This test method applies to structures used in AASHTO applications and is applicable to adhesive anchor systems with steel anchors in predrilled holes in concrete. 1.2 This test method determines the time to failure for adhesive anchors in concrete at various levels of sustained loading. 1.3 The static load test is developed from ASTM E 488 and the sustained load (creep) test is modified from ASTM E 1512 and ICC-ES AC308. 1.4 This test method only addresses the effect of sustained loads on adhesive anchors. There are numerous other factors that affect the load capacity of adhesive anchors and a complete battery of tests is essential to evaluate an adhesive anchor. Refer to ICC-ES AC308 for a listing of some of the many factors and related test methods that apply to adhesive anchors. 2 REFERENCED DOCUMENTS 2.1 ASTM Standards: A 193, Standard Specification for Alloy-Steel and Stainless Steel Bolting Materials for High Temperature or High Pressure Service and Other Special Purpose Applications C 31, Standard Practice for Making and Curing Concrete Test Specimens in the Field C 39, Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens C 42, Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete D 907, Standard Terminology of Adhesives

A-4 OTHSAA2-XXXXT D 2990, Standard Test Methods for Tensile, Compressive, and Flexural Creep and Creep-Rupture of Plastics E 488, Standard Test Methods for Strength of Anchors in Concrete and Masonry Elements E 1512, Standard Test Methods for Testing Bond Performance of Bonded Anchors 2.2 Other Standards: ICC-ES AC308, Acceptance Criteria for Post-Installed Adhesive Anchors in Concrete 3 TERMINOLOGY 3.1 Refer to ASTM D 907 for a complete listing of terminology related to adhesives. 3.2 Adhesive anchor – a post-installed anchor that transfers load to concrete through an adhesive compound embedded in a hole in hardened concrete. The adhesive materials used include epoxy, cementitious material, polyester resin, and others. 3.3 Creep – the deformation or displacement of an adhesive over time due to stress. 3.4 Embedment depth – distance from the surface of the structural member to the end of the installed anchor. 3.5 LVDT – Linear Variable Differential Transformer; an electronic instrumentation device used for measuring displacement. 3.6 Static load test – a test in which a load is slowly applied at a specified rate for one cycle until failure. 3.7 Sustained load (creep) test – a test in which a constant load is continuously applied until failure due to creep. 3.8 Symbols: d = nominal anchor diameter, in (mm) do = nominal diameter of drilled hole in concrete, in (mm) f’c = specified compressive strength of concrete, psi (MPa) hef = effective depth of embedment of an anchor, in (mm) 4 SIGNIFICANCE AND USE 4.1 Determination of mean static load of an adhesive anchor. 4.2 Determination of acceptable loads to apply to an adhesive anchor based on the lifetime of the structure. 4.3 Determination of an adhesive anchor’s ability to endure sustained loads. 4.4 The Stress versus Time-to-Failure graph is useful to the practicing engineer in selecting and designing adhesive anchors. 4.5 A Stress versus Time-to-Failure graph can give an indication of the reduction in capacity of an adhesive anchor due to sustained load at a given design lifetime.

A-5 OTHSAA3-XXXXT 4.6 Means for comparing adhesive anchor products for sustained loading applications. 4.7 The test methods in this standard should be followed in order to ensure reproducibility of test results. 5 TEST APPARATUS 5.1 Instrumentation and Data Collection: 5.1.1 All laboratory instrumentation (electronic load, displacement, temperature, and humidity sensors, etc.) must be calibrated with certified equipment. 5.1.2 A load cell or other load measuring device must be able to measure forces to within ±1% of the anticipated peak load. 5.1.3 As an alternative, a load cell is not required for monitoring the sustained load (creep) test if the test apparatus has a stiffness that is sufficiently low to ensure accuracy of 1% of the applied sustained load at the maximum anchor creep displacement and a stiffness- displacement relationship can be established to determine the load applied with reasonable confidence. 5.1.4 Displacements should be measured continuously by LVDTs, linear potentiometers, or an equivalent device with an accuracy of at least 0.001 in. (0.025 mm). 5.1.5 The instrumentation must be placed in a way so as not to interfere with the anchor or testing apparatus. The instrumentation should measure the vertical displacement and load on the anchor relative to the test specimen. The instrumentation should be placed in such a way that it will remain parallel to the axis of the anchor and will not be affected by the deflection and/or failure of the anchor or test specimen. 5.1.6 Two displacement measuring devices shall be placed equidistant from the anchor and their values averaged to obtain the actual displacement. One displacement measuring device may be used if it is placed centered on the anchor’s axis and can be shown to produce acceptable confidence. 5.1.7 Static Load Test: The measuring devices and the data collection system must be able to gather data points at least twice per second for the static load test. 5.1.8 Sustained Load (Creep) Test: The measuring devices and the data collection system must be able to gather data points according to a progressively reducing frequency as discussed in section 9.4.6.2 of this standard. 5.2 Test Apparatus: 5.2.1 Examples of suitable test apparatus for static and sustained load (creep) tests are shown in Figure 1 and Figure 2, respectively.

A-6 OTHSAA4-XXXXT Figure 1: Static Load Test Apparatus (Source: modified from Cook et al. [14.2]) Figure 2: Sustained Load (Creep) Test Apparatus (Source: modified from Cook et al. [14.2])

A-7 OTHSAA5-XXXXT 5.2.2 The test apparatus must be of sufficient capacity so as to not yield during testing. 5.2.3 Coupler: A coupler shall be used between the anchor and the test loading rod providing a non-rigid connection which does not transfer bending forces. 5.2.4 Confining Plate: 5.2.4.1 The thickness of the confining plate should be greater than or equal to the nominal anchor diameter ±1/16 in. (±1.5 mm). 5.2.4.2 In order to account for surface irregularities, a sheet of tetrafluoroethylene (TFE), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), or perfluoroalkoxy (PFA) of up to 0.06 in (0.15mm) of the same shape and dimensions of the confining plate shall be placed between the confining plate and the surface of the concrete. 5.2.4.3 The confining plate and the confining sheet shall be large enough that the pressure on the concrete underneath the plate does not exceed 0.40f’c. 5.2.4.4 The hole in the confining plate and the confining sheet shall be 1.5do to 2.0do. The initial shape of the hole shall match the anchor’s cross-section. The size and shape of the hole shall be maintained in all tests. 6 TEST SPECIMEN 6.1 Anchorage System - The anchorage system used in the tests should be representative of that used in the field. 6.2 Anchor Placement – Anchors shall be placed far enough apart so as to not interfere with the testing apparatus. 6.3 Structural Member: 6.3.1 The structural member used in the tests shall not have anchors located within 2hef of the edges and shall not cause early failure of the member or the anchor. 6.3.2 Reinforcing steel can be used but only what is necessary for handling and shall not interfere with the anchor. Reinforcing cannot be located within an imaginary cone projecting from the end of the embedded anchor to the loaded face of the structural member with an internal vertex angle of 120 degrees. 6.3.3 The depth of the structural member should be at least 1.5hef providing it is thick enough for installation and does not cause early failure of the member or the anchor. 6.3.4 The length and width of the structural member shall be large enough to ensure proper placement of the anchors in accordance with minimum spacing and edge distances. 6.3.5 The surface of the structural member shall be form-work or steel-trowel finish. 6.3.6 The concrete compressive strength at time of testing shall be from 2500 psi to 4000 psi (17 MPa to 28 MPa), unless otherwise specified. The aggregate should be of river gravel or crushed rock with a maximum aggregate size of ¾” or 1” (19mm or 24mm). The concrete mixture shall not include any materials such as blast furnace slag, fly ash, silica fume, limestone powder, or admixtures unless otherwise specified. 6.3.7 Cure the concrete for a minimum of 28 days ensuring proper moisture for hydration. 6.3.8 Concrete cylinders shall be made in accordance with ASTM C 31 and cured in similar conditions as the structural member. Cylinders shall be de-molded at the same time as form removal.

A-8 OTHSAA6-XXXXT 6.3.9 Test concrete compressive strength in accordance with ASTM C 39 for concrete cylinders or ASTM C 42 for concrete cores. Concrete strength at any point can be determined from a concrete strength-age relationship curve constructed from a sufficient number of compression tests conducted at regular intervals. It is also permitted, to linearly interpolate concrete strength from compression tests conducted at the beginning and end of a test series. 7 ADHESIVE AND ANCHOR INSTALLATION AND CURING 7.1 Prior to anchor installation, condition the test specimen to 75ºF ±10ºF (24ºC ±5ºC) and 50% ±10% relative humidity. 7.2 Hole: 7.2.1 Drill holes in accordance with the manufacturer’s specifications and document any deviations. Drilled holes must be perpendicular (±6º) to the face of the concrete test specimen. 7.2.2 In order to more easily compare data – the embedment depth hef should be 4.5in. ±0.1in. (115mm ±2.5mm) unless otherwise specified. A shallower embedment depth may be used if it is determined that a steel failure would occur prior to bond failure. 7.2.3 For anchors with a diameter d the minimum embedment depth hef shall conform to Table 1. Table 1: Minimum Embedment Depth d hef,min 1/2” 2 3/4” 5/8” 3 1/8” 3/4” 3 1/2” 1” 4d 7.2.4 Clean the holes in accordance with the manufacturer’s specifications and document any deviations. 7.3 Adhesive: 7.3.1 Prepare and install the adhesive in accordance with the manufacturer’s specifications and document any deviations. 7.3.2 Cure the adhesive according to the manufacturer’s specifications and document any deviations. 7.4 Anchor: 7.4.1 Install the anchor in accordance with the manufacturer’s specifications and document any deviations. 7.4.2 To ensure bond failure, use a high-strength steel (minimum strength equivalent to ASTM A 193 Grade B7). 7.4.3 In order to more easily compare data, anchors shall be 5/8” – 11 UNC (16mm) threaded rod unless otherwise specified. A larger anchor diameter may be used if it is determined that a steel failure would occur prior to bond failure. ≥

A-9 OTHSAA7-XXXXT 8 SPECIMEN CONDITIONING 8.1 Begin conditioning of the test slabs to their final environmental condition upon completion of the manufacturer’s specified curing time, and within 7 ±5 days. 8.2 Do not begin tests until the temperature and humidity of the test specimens have stabilized for at least 24 hours. Note 1 – Depending on the size of the structural member it might take several days to raise and stabilize the concrete temperature to the final elevated temperature. 9 TEST PROCEDURE 9.1 The test procedure consists of two types of tests (Static Load Test and Sustained Load (Creep) Test). Static load tests are conducted initially to determine the mean static load. Subsequently, several sustained load (creep) tests are conducted at various percentages of the mean static load. 9.2 General Requirements: 9.2.1 All tests will be confined tests. 9.2.2 The tests will be conducted at specified temperature and humidity. The temperature shall be monitored via thermocouples or temperature sensors placed in the concrete test specimen. The thermocouples or temperature sensors can be either cast-in-place or installed in a maximum ½ in. (12mm) diameter hole and sealed to ensure accurate concrete temperature readings. The thermocouples or temperature sensors should ideally be placed at the mid-depth of the anchor but not deeper than 4.5 in. (114mm). 9.2.3 Alternatively, the temperature can be monitored daily by a temperature sensor located in the test chamber if a confident correlation can be shown between test chamber temperature and test specimen concrete temperature. 9.3 Static Load Test: 9.3.1 Environmental Conditions – Conduct the static load tests at a minimum temperature of 110ºF +10ºF/-0ºF (43ºC +5ºC/-0ºC) and below 40% relative humidity. Following the required adhesive curing time, raise the temperature to the minimum elevated temperature of 110ºF (43ºC). Do not begin testing until the temperature and humidity of the test specimen have stabilized for at least 24 hours. 9.3.2 Number of Test Specimens – A minimum of five (5) anchors shall be tested and their results averaged. 9.3.3 Test Setup: 9.3.3.1 Ensure that the test apparatus and instrumentation complies with the requirements of section 5 of this test method. 9.3.3.2 Ensure that the test apparatus is centered over the anchor and that the force applied is acting through the center of the anchor and perpendicular to the structural member. 9.3.3.3 Place the confining sheet around the anchor as discussed in section 5.2.4.2 of this standard. 9.3.3.4 Place the confining plate over the confining sheet assuring that there is full bearing with the structural member around the anchor. 9.3.3.5 Connect the loading rod to the anchor by means of a non-rigid connecting coupler and ensure that it is acting in-line with the anchor.

A-10 OTHSAA8-XXXXT 9.3.3.6 The amount of pre-tensioning to the apparatus during test setup shall be uniform for all samples. 9.3.4 Loading: 9.3.4.1 Initial Load – Apply an initial load not exceeding 5% of the estimated ultimate load capacity of the anchor system in order to bring all members of the test apparatus into bearing. Zero the displacement readings. 9.3.4.2 Rate of Loading – Two loading rates are allowed by ASTM E 488, the Continuous Load Rate and the Incremental Load Rate. The continuous load rate is the only load rate allowed in this test method for the calculation of mean static load and for inclusion in the Stress versus Time-to-Failure graph. Note 2 - The incremental load rate can be used in optional additional tests as a method to (1) provide an indication of an adhesive’s displacement sensitivity to load at the higher stress levels and (2) determine appropriate stress levels to test at for the sustained load (creep) tests. This method is discussed in further detail in Appendix X1. 9.3.4.2.1 Continuous Load Rate - Apply a uniform load rate such that failure will ideally occur at 2- min. Failure shall not occur in less than 1-min or greater than 3-min. 9.3.4.2.2 Incremental Load Rate - Apply the load in steps with the first increment not greater than 50% and each increment thereafter not exceeding 15% of the total expected load. Maintain each load increment within a tolerance of ±2% for 2 minutes. 9.3.5 Data Collection – Collect load and displacement readings according to section 5.1.7 of this standard. 9.3.6 Determination of Failure – See Appendix X2 for a description of the various failure modes and methods to determine static load strength. 9.3.7 Calculations: Determine and record the mean static load by averaging the individual static load strengths from each test series. 9.4 Sustained Load (Creep) Test: 9.4.1 Environmental Conditions – Conduct the sustained load (creep) tests at a minimum elevated temperature of 110ºF +10ºF/-0ºF (43ºC +5ºC/-0ºC) and below 40% relative humidity. Following the required curing time, raise the temperature to the minimum elevated temperature of 110ºF (43ºC). Do not begin the test until the temperature and humidity of the test specimen has stabilized for at least 24 hours. 9.4.2 Test Series – Conduct a minimum of two series of sustained load (creep) tests within two load ranges (PL1 and PL2) based on the mean static load from the static load test: 9.4.2.1 Percent load level range 1 (PL1) is suggested to be between 70% and 80% of mean static load. 9.4.2.2 Percent load level range 2 (PL2) is suggested to be between 60% and 70% of mean static load. 9.4.2.3 It is not necessary that all test specimens be tested at the same percent load level, but that they lie within the ranges and the averages of the two test series should vary by at lest 10%. 9.4.3 Number of Test Specimens – A minimum of five (5) anchors per series shall be tested. 9.4.4 Test Setup:

A-11 OTHSAA9-XXXXT 9.4.4.1 Ensure that the test apparatus and instrumentation complies with the requirements of section 5 of this test method. 9.4.4.2 Ensure that the test apparatus is centered over the anchor and that the force applied is acting through the center of the anchor and perpendicular to the structural member. 9.4.4.3 Place the confining sheet around the anchor as discussed in section 5.2.4.2 of this standard. 9.4.4.4 Place the confining plate over the confining sheet assuring that there is full bearing with the structural member around the anchor. 9.4.4.5 Connect the loading rod to the anchor by means of a non-rigid connecting coupler and ensure that it is acting in-line with the anchor. 9.4.4.6 The amount of pre-tensioning to the apparatus during test setup shall be uniform for all samples. 9.4.5 Loading – Apply an initial load not exceeding 5% of mean static load in order to bring all members of the test apparatus into bearing. Zero the displacement readings. Apply the remainder of the sustained load within 2-min ±1-min in as smooth a manner as possible. Note 3 – A suggested modification to the sustained load (creep) test apparatus shown in Figure 2 is presented in Appendix X4 to provide for smooth load transfer. 9.4.6 Data Collection: 9.4.6.1 Temperature - Record the concrete specimen temperature at a maximum 1-hour interval. Alternatively, the concrete specimen temperature can be recorded at 24-hour intervals if the test chamber temperature is recorded at 1-hour intervals. 9.4.6.2 Displacement – The frequency of displacement readings can be reduced over time. Note 4 - The following schedule is a suggestion: every three seconds during loading, every minute for the first hour following loading, every ten minutes for the next nine hours, and every hour thereafter. 9.4.7 Determination of Failure: Failure for the sustained load (creep) test will be determined as the onset of tertiary creep. A discussion of tertiary creep and a method to determine its onset can be found in Appendix X3. 9.4.8 Calculations - Determine and record the time to failure and load level at failure for each specimen. 10 CALCULATIONS AND INTERPRETATION OF RESULTS 10.1 Determine the five individual static load strengths from each static load test. Methods to determine the static load strength can be found in Appendix X2. 10.2 Determine the mean static load by averaging the individual values from the static load tests. 10.3 Determine the time to failure for each sustained load (creep) test series as the initiation of tertiary creep. A procedure to locate the onset of tertiary creep can be found in the Appendix X3. 10.4 Determine the failure load level for each sustained load (creep) test series at the initiation of tertiary creep.

A-12 OTHSAA01-XXXXT 10.5 Normalize the load levels for the sustained load (creep) test to a percent of the mean static load from the static load tests. 10.6 Plot the normalized values from the static load test and the sustained load (creep) test on a Stress versus log of Time-to-Failure graph. 10.7 Extend a linear trendline through the fifteen points plotted. 10.8 A Stress versus Time-to-Failure graph can give an indication of the reduction in capacity of an adhesive anchor due to sustained load at a given design lifetime. 11 REPORT 11.1 Data Collection: Report the type of test (static load or sustained load) and the following applicable information: 11.1.1 Date of test and date of report. 11.1.2 Test sponsor and test agency. 11.1.3 Anchor information: manufacturer, model, type, material, finish, shape, dimensions, and other relevant information. 11.1.4 Adhesive information: manufacturer, model, type, lot, material, application method, and other relevant information. 11.1.5 Structural member information: description, dimensions, reinforcing, mix design of concrete, aggregate type, curing method, strength at time of test, age of concrete at time of test. 11.1.6 Installation information: description of the procedure, tools, and methods used to install the adhesive anchor. Include the drilling and cleaning of the holes as well as the installation of the adhesive and anchor. Document any deviations from the manufacturer’s specifications. 11.1.7 Adhesive curing information: temperature and humidity conditions, length of cure, time when conditioning of test specimen began. 11.1.8 Temperature and humidity conditions at time of installation, and during adhesive cure, conditioning, and final testing. 11.1.9 Embedment depth and diameter of hole of installed anchors. 11.1.10 Test information: description of test method, amount of initial load, and actual rate of loading. 11.1.11 Number of samples tested per series. 11.1.12 Static Load Test Data: 11.1.12.1 Individual and average load values per anchor and COV. 11.1.12.2 Individual and average displacement values at maximum load 11.1.12.3 Load versus displacement curves per anchor. 11.1.12.4 Load versus time curves per anchor. 11.1.13 Sustained Load (Creep) Test Data: 11.1.13.1 Individual time-to-failure values per anchor.

A-13 OTHSAA11-XXXXT 11.1.13.2 Individual load values and percent mean static load values at failure per anchor. 11.1.13.3 Individual displacement values at failure per anchor. 11.1.13.4 Load versus displacement curves per anchor. 11.1.13.5 Displacement versus time curves per anchor. 11.1.13.6 Load versus time curves per anchor. 11.1.13.7 Stress versus Time-to-Failure curve. 11.1.14 Photographs, sketches and descriptions of failure modes observed. 11.1.15 Summary of findings 11.1.16 Listing of observers of tests and signatures of responsible persons. 12 PRECISION AND BIAS 12.1 Precision – No precision has been established for this test method. 12.2 Bias – No bias can be established because no reference material is available for this test. 13 KEYWORDS 13.1 adhesive anchors: anchors: bonded anchors: creep test: concrete: post-installed anchors: static load test: sustained load test: test methods: time to failure test 14 REFERENCES 14.1 Cook, R. A., and R. C. Konz. Factors Influencing Bond Strength of Adhesive Anchors. ACI Structural Journal, Vol. 98, No. 1, 2001, pp. 76-86. 14.2 Cook, R. A., R. C. Konz, and D. S. Richardson. Specifications for Adhesive-Bonded Anchors and Dowels. Report No. 96-3, University of Florida, Gainesville, FL, 1996. APPENDIXES (Non-mandatory Information) X1 INCREMENTAL LOAD RATE X1.1 As discussed in 9.3.4.2.2 the incremental load rate is a method that applies the load in several load steps and holds the load for two minutes and then increases to the next load level. X1.2 This method can provide an indication of an adhesive’s sensitivity to sustained loading at higher load levels. X1.3 Figure 3 shows a load versus displacement curve and a time versus displacement curve for an anchor under incremental loading.

A-14 OTHSAA21-XXXXT - 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000 0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080 0.090 0.100 DISPLACEMENT (in) LO A D (lb f) 0 100 200 300 400 500 600 700 800 900 1000 TI M E (se c) Load Time Figure 3: Load-Displacement and Time-Displacement Curves with Incremental Loading X1.4 As shown in Figure 3, as the load is held constant, the anchor in this graph displays more displacement at the higher load steps. X1.5 Figure 3 also shows that at the lower load levels, the displacement will tend to stabilize. Additionally, at the higher load levels, the anchor will continue to displace. This is indicated by the slope of the time-displacement curve. X2 DETERMINING STATIC LOAD STRENGTH X2.1 Cook and Konz [14.1] classify three types of load-displacement response (strength- controlled, stiffness-controlled, and displacement-controlled) for adhesive anchor systems. These three types of responses and methods of their analysis are summarized below: X2.2 Strength-controlled. This failure mode is defined by a very sharp peak in the load- displacement curve. There is a drastic reduction in the stiffness of the adhesive anchor beyond the peak. The static load strength is determined to be at the peak on the load- displacement graph. Figure 4 shows a typical curve of a strength-controlled failure.

A-15 OTHSAA31-XXXXT Figure 4: Typical Strength-controlled Failure (Source: Cook and Konz [14.1]) X2.3 Stiffness-controlled. This failure mode is defined by a large initial stiffness and a drastic change in stiffness, which does not decrease but rather continues to increase at a lower slope. Due to the lack of “peak” in the curve, the static load strength is determined by finding the point at a tangent stiffness of 30 kip/in (5 kN/mm). The tangent stiffness (slope) at a given data point can be approximated by calculating the slope between a point five data points after and five data points before. Figure 5 shows a typical curve of a stiffness-controlled failure. Figure 5: Typical Stiffness-controlled Failure (Source: Cook and Konz [14.1]) X2.4 Displacement-controlled. This failure mode has a load-displacement curve with a relatively constant stiffness above the stiffness-controlled threshold of 30 kips/in. The maximum load occurs at very high, and impractical, displacements. In this case, the static load strength is set at a point with a displacement of 0.1 in (2.5mm). Figure 6 shows a typical curve of a displacement-controlled failure.

A-16 OTHSAA41-XXXXT Figure 6: Typical Displacement-controlled Failure (Source: Cook and Konz [14.1]) X3 DETERMINING ONSET OF TERTIARY CREEP X3.1 As discussed in the appendix of ASTM D2990, the displacement versus time curve will display three regions. Region 1 is the primary creep region and is characterized by an initial rapid decrease in the creep rate. Region 2 is the secondary creep region and is characterized by a relatively steady slope. Region 3 is the tertiary creep region and is characterized by a rapid increase in creep ending in rupture. Figure 7 shows these three regions for a hypothetical sample. Figure 7: Regions on the Creep Curve (Source: ASTM D 2990-01) X3.2 The onset of tertiary creep is found by analyzing the change in the slope of the creep curve: X3.2.1 This method calculates the slope at a given point as the slope between itself and the prior data point.

A-17 OTHSAA51-XXXXT X3.2.2 The change in slopes between the given point and the following data point is plotted and examined over the region just prior to rupture. It is suggested that this examination be conducted on a normal graph (not log time). The rupture point is easily identified on the displacement vs. time graph. A suggested range for examining the change in slope is from 80% to 100% of time to rupture. Due to minor fluctuations in the displacement readings, the slope might change from positive to negative several times over this range. X3.2.3 Tertiary creep is defined as the time the change in slope becomes positive for the last time prior to rupture. Figure 8 shows a sample graph for determining the initiation of tertiary creep. 8.15 -0.050 0.000 0.050 0.100 0.150 0.200 0.250 6.0 6.5 7.0 7.5 8.0 8.5 9.0 TIME (hr) D IS PL AC EM EN T (in ) SL O PE (in /h r) -0.040 0.000 0.040 0.080 0.120 0.160 0.200 CH A N G E IN SL O PE (in /h r2 ) Displacement Tertiary Point Slope Change in Slope FIRST POSITIVE CHANGE IN SLOPE JUST PRIOR TO RUPTURE INITIATION OF TERTIARY CREEP Figure 8: Sample Graph Showing Initiation of Tertiary Creep X3.3 Failure for the sustained load is defined as the initiation of tertiary creep. The failure point for each sustained load test is plotted on the Stress versus Time-to-Failure graph. Figure 9 shows a sample Stress versus Time-to-Failure graph. X3.4 A Stress versus Time-to-Failure graph can give an indication of the reduction in capacity of an adhesive anchor due to sustained load at a given design lifetime.

A-18 OTHSAA61-XXXXT 0% 20% 40% 60% 80% 100% 120% 0.01 0.1 1 10 100 1000 10000 100000 1000000 10000000 TIME (hr) PE RC EN T ST RE SS (% ) Figure 9: Sample Stress vs. Time-to-Failure Graph X4 SUGGESTED SUSTAINED LOAD (CREEP) TEST APPARATUS FOR SMOOTH LOAD TRANSFER X4.1 It is important that the load to the anchor be applied in a smooth manner. This can be accomplished with a hydraulic ram. X4.2 Figure 10 shows a modified test apparatus for the sustained load (creep) test incorporating a hydraulic ram that reacts against a plate connected to the existing test apparatus by means of four threaded couplers. The ram and the upper plate can be removed following tightening of the loading rod nut.

A-19 OTHSAA71-XXXXT Figure 10: Suggested Load Transfer for Sustained Load (Creep) Tests (Source: modified from Cook et al. [14.2])