Strength and behavior of L-shaped anchor bolts in tension

Material Information

Strength and behavior of L-shaped anchor bolts in tension
Arrighi, Barbara Anne McClure
Place of Publication:
Denver, CO
University of Colorado Denver
Publication Date:
Physical Description:
xi, 98 leaves : illustrations ; 29 cm


Subjects / Keywords:
Anchorage (Structural engineering) ( lcsh )
Strength of materials ( lcsh )
Anchorage (Structural engineering) ( fast )
Strength of materials ( fast )
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )


Includes bibliographical references (leaves 69-71).
Submitted in partial fulfillment of the requirements for the degree of Master of Science, Department of Civil Engineering 1987.
Statement of Responsibility:
by Barbara Anne McClure Arrighi.

Record Information

Source Institution:
University of Colorado Denver
Holding Location:
|Auraria Library
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
17800821 ( OCLC )
LD1190.E53 1987m .A77 ( lcc )


This item is only available as the following downloads:

Full Text


STRENGTH AND BEHAVIOR OF L-SHAPED ANCHOR BOLTS IN TENSION by Barbara Anne McClure Arrighi B.S.A., University of Georgia, 1974 A thesis submitted to the Faculty of the Graduate School of the University of Colorado at Denver in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering Department of Civil Engineering 1987 t"''"'1


This thesis for the Master of Science in Civil Engineering degree by Barbara Anne McClure Arrighi has been approved for the Department of Civil Engineering by I Er Harris John R. Mays Date 7kr 0<3 1987 ;;


Arrighi, Barbara Anne McClure (M.S.C.E., Civil Engineering) Strength and Behavior of L-shaped Anchor Bolts in Tension Thesis directed by Assistant Professor Judith J. Stalnaker The strength and behavior of smooth L-shaped anchor bolts in tension are reported. A review of the findings of earlier researchers with regard to bond and tensile strength of anchor bolts is discussed. Accepted procedures for the design of anchor bolts are reviewed. Pull-out tests were conducted and specimen configuration, experimental procedure, test equipment and materials used are described in detail. The results of these tests, as well as those of earlier researchers, show that strength of L-shaped anchor bolts is related to bolt diameter and embedment and hook lengths. Failure mode was pull-out by straightening of the hook. There were no concrete failures. Two additional, straight specimens with a nut and washer on the end were tested. They failed by steel fracture at the threaded portion at the top of the bolt. Behavioral and strength characteristics are discussed and evaluated against current design procedures. Load versus slip relationships provide insight as to the strength and behavior of L-shaped anchor bolts. This is compared to those same


iv characteristics of headed anchor bolts. A specific design procedure for L-shaped anchor bolts is presented. Further research is suggested. The form and content of this abstract are approved. I recommend its publication. Signed


To Bill When you can measure what you are speak-ing about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science. William Thomson (Lord Kelvin) v


ACKNOWLEDGMENTS I gratefully acknowledge the following for their assistance in the preparation of this thesis: Dr. Judith J. Stalnaker, thesis director, advisor and editor; Dr. Ernest c. Harris and Dr. John R. Mays, committee members; Mr. Hank King, Stanley Structures Steel Division, for fabrication and donation of the test frame; and Mr. James Crofter and Mr. Thomas Cummings, Electronic Maintenance and Calibration Laboratory, University of Colorado at Denver, for technical assistance. I also wish to acknowledge the receipt of a Junior Faculty Development Award presented to Dr. Stalnaker by the University of Colorado at Denver. This award funded the purchase of equipment and materials used to perform the pull-out tests. vi


CONTENTS ABSTRACT ... . . . . . . . . . . . . . . . . . . DEDICATION. . . . . . . . . . . . . . . . . . . ACKNOWLEDGMENTS. TABLES .. FIGURES. CHAPTER I. II. III. IV. v. . . . . . . . . . . . . . . . . . . . . INTRODUCTION ........... Purpose of the Study. Scope of the Study ... REVIEW OF THE LITERATURE. Findings of Earlier Researchers. Findings of Earlier Researchers of Similar Studies ....... Accepted Procedures for the Design of Anchor Bolts .... METHODOLOGY ...... Test Equipment. Materials ..... RESULTS AND OBSERVATIONS. Tests for Material Properties. Pull-out Test Results. Analysis of Results .. SUMMARY AND CONCLUSIONS. Summary ............. iii v vi ix X 1 3 4 5 5 9 12 19 35 37 45 45 47 61 64 64


viii Conclusions.......................... 65 BIBLIOGRAPHY. . . . . . . . . . . . . . . . 69 APPENDIX A. SELECTED RESULTS OF TESTS BY EARLIER RESEARCHERS . . . . . . . 7 2 B. DETAILS OF PULL-OUT TEST EQUIPMENT AND MATERIALS ............. 78 c. DESIGN COMPARISONS .................... 93


ix TABLES Table 1. Characteristics and Mark Numbers of Anchor Bolt Specimens ................... 39 2. Strength of Bolt Material ............... 46 3 Ultimate Compressive Strength of Concrete Cylinders ...................... 48 4. Ultimate Tensile Strength of Anchor Bolts. . . . . . . . . . . . . . . 56


FIGURES Figure 1. Shear Cone Failure Mechanism of 2. 3. 4. s. 6. 7. 8. 9. 10. 11. 12. 13. 14. 1S. 16. 17. Concrete . . . . . . . . . . . . . . . . 21 Bearing Stresses in Concrete ........... Placement of Headed Anchor Bolt in Wood Form. ...................... Placement of L-Shaped Anchor Bolt in Wood Form. ...................... Placement of Concrete .................. Vibration of Concrete .................. Trowelled Concrete Pads ................ Concrete Pads after Forms Stripped ..... Rod Placement through Test Frame ....... Ram/Load Cell Assembly ................. Strain Indicator ....................... Dial Gauges ............................ Strain Gage Conditioner and Amplifier ... Half-Bridge Configuration .............. Pull-out Test Assembly ................. Pull-out Test Assembly ................. Anchor Bolt Specifications ........ 21 2S 2S 27 27 28 28 30 30 31 31 33 33 34 34 38 18. Locations of Strain Gauges on Anchor Bolts. . . . . . . . . . . . . . 41 19. Spalling of Surface Concrete ........... so 20. Spalling of Surface Concrete ........... so


xi Figure 21. Position of Anchor Bolt Hook after Straightening. . . . . . . . . 52 22. Position of Tip of Anchor Bolt after Straightening .................... 52 23. Diagrammatic Straightening of Anchor Bolt Hook ....................... 53 24. Headed Anchor Bolt Failure ............. 54 25. Headed Anchor Bolt Fracture Planes ..... 54 26. Load/Slip Curves 3/8" Diameter Anchor Bolts. . . . . . . . . . . . . . 58 27. Load/Slip Curves 1/2" Diameter Anchor Bolts. . . . . . . . . . . . . . 59


CHAPTER I INTRODUCTION L-shaped anchor bolts are specified by structural engineers as connection devices to anchor building members to resist uplift and overturning forces. Common applications include the connection of steel column base plates to concrete foundations, wood sill plates to concrete stem walls, and steel bearing plates and angles to concrete masonry walls. L-shaped anchor bolts are less frequently specified for the connection of steel beams or other framing members to concrete walls and columns. Anchor bolts, whether L-shaped, headed, expansion-type or deformed, are used in construction of buildings, bridges and sign supports to resist the tensile and shearing forces caused by loadings of short duration. These lateral loadings are caused by seismic disturbances and/or high velocity winds. The ability of anchor bolts to resist these forces and securely hold structural members in place has been attributed to bolt diameter, embedment length, and bond to concrete. Because of interest in smooth reinforcing bars, bond strength between steel and concrete


received the attention of researchers in the late 1800's and early 1900's. To develop maximum tensile strength, the chemical and physical bond between steel and the surrounding concrete must be large enough to resist slip caused by tensile forces applied to a structure. End anchorages can also add additional resistance to slip. The researchers discovered that the diameter of a steel reinforcing bar and the length of embedment into the concrete had appreciable effects on resistance to external forces. The most important development during these years was the discovery that some sort of deformation at the end of the steel embedded in the concrete would greatly increase the anchorage's resistance to pull-out. Research today is centered around developing different types of anchorage bar deformations to resist pull-out. These include expansion anchorages, headed anchor studs and hooked, deformed reinforcing bars. Contemporary designers are content that previous studies on bond, embedment length and diameter of L-shaped anchor bolts have been conclusive. Designers seem to feel that minimum allowable limits published in design codes and handbooks are based on carefully controlled research and contain reasonable factors of safety. However, this is not actually the case. 2


Purpose of the study Design procedures for determining the diameter and embedment length of anchor bolts are published in ACI-349 (1), the PCI Design Handbook (2) and Uniform Building Code (3). The American Concrete Institute (4), the American Association of State Highway and Transportation Officials (5) and the American Institute of Steel Construction, Inc. (6) publish standards helpful in determining anchor bolt specifications. These procedures and standards suggest minimum allowable limits and their use is encouraged by city, county, state and federal agencies. The first two of these references, however, base the design considerations on pull-out tests performed on the headed anchor stud, a steel member that is circular in cross-section and has a large, disk-like deformation at the embedded end. Because L-shaped anchor bolts (steel members that are circular in cross-section and have a ninetydegree bent hook at the embedded end) are commonly specified by engineering practitioners, this study has been performed to analyze the applicability of the design procedures outlined in the various codes and standards as applied to L-shaped anchor bolts. Practicing engineers who depend on code specifications to design safe and economical structures need to be 3


assured that these guidelines apply to the materials that are routinely designated. Scope of the Study To be able to investigate the definitude of code requirements applying to L-shaped anchor bolts, experimental results were needed. Previous investigations of the characteristics of L-shaped anchor bolts in tension are sketchy and incomplete. Since experimental data is lacking, a test procedure, discussed in Chapter III, was set up, using a previously developed test procedure. This provides more accurate information as to the bond strength of the L-shaped anchor bolt in concrete, the bolt's resistance to pull-out when tensile forces are applied, the strain developed in the bolt as an increasing magnitude of load is applied, and the failure mode. Results obtained from the testing procedure can be analyzed and conclusions drawn as to the characteristics of L-shaped anchor bolts in tension. From these results, observations can be made about the applicability of code specifications to L-shaped anchorages. 4


CHAPTER II REVIEW OF THE LITERATURE A literature search regarding L-shaped anchor bolts has shown previous research to be incomplete and to have procedural difficulties. Because L-shaped anchorages are often specified by structural engineers and because these engineers use the recommended design specifications for design, specified requirements need to adequately reflect the structural behavior of Lshaped anchor bolts. A review of the literature indicates that further examination of the characteristics of L-shaped anchor bolts must be made and incorporated into design specifications. For an in-depth review of previous studies, "The Development of Bond and Anchorage on L-Shaped Anchor Bolts in Tension" by William T. Fuller (7) should be perused. Findings of Earlier Researchers The earliest research on anchorages at the ends of smooth reinforcing bars concerned the bond and anchorage strength of steel reinforcing bars in


concrete beams. In 1876 and 1877, Thaddeus Hyatt used flat bars bent at right angles at the ends, each end having a knob similar to a bolt head. His investigations proved that concrete beams were less subject to failure if this type of reinforcing bar anchorage was embedded in the concrete. Hyatt's understanding of the concrete/steel interaction that caused this additional strength was vague. In the early 1900's, researchers began to study the bond formed between concrete and the steel reinforcing bar. They were interested in the magnitude of the bond stress which could be developed in order to predict strength of concrete beams. Duff A. Abrams, in his bulletin entitled "Tests of Bond Between Concrete and Steel," (8) studied various anchorages, including specimens with a ninety degree bend at the embedded end and with a two inch hook length. The L-shaped anchorages tested were threequarters and one inch in diameter. Embedment length was eight inches. Since Professor Abrams was concerned with the bond between concrete and steel, he reported that the average maximum bond resistance was 747 psi for the 3/4" diameter hooked bolt and 863 psi for the 1" diameter hooked bolt. *The works of Thaddeus Hyatt are described by Abrams and Mylrea in their publications referenced later in this section. 6


These bond resistance values are recorded in a table entitled "Effect of Anchoring Ends of Bars" of the research bulletin previously referenced and reproduced in Table A-1. This maximum bond resistance occurred at a slip of approximately .01 inch and about 19% of the compressive strength of the concrete cylinders in which the bolts were embedded. Although Professor Abrams' pull-out tests provided great advances in the field of bond resistance between concrete and steel, his results are outdated as to concrete strength and concrete specimen size. Concrete strengths today reach 3000 psi and higher while Abrams' tests were conducted on specimens with an average strength of 1720 psi. The size of concrete specimen used in Abrams tests was an 811 diameter cylinder. Compressive stresses may have been induced into the concrete, preventing tensile cracks from forming around the bolts and causing relatively high values in reported results. Professor Abrams' research suggested that bent anchorages indeed slowed bond failure. Secondarily, these bent anchorages also hindered failures due to slip. These findings should be correlated to the materials and applications used presently so that adequate design requirements can be developed. Since Abrams' significant tests on bond strength, almost no research has been specifically 7


performed on L-shaped anchorages until recently. This may be attributed to the introduction of deformed bars, headed anchor bolts, and expansion devices since the 1940's. In 1980, James M. Fisher (9) suggested a design procedure for determining the embedment and hook lengths for L-shaped anchorages. This procedure follows that recommended by the PCI. In 1981, in the article "Anchor Bolt Design for Shear and Tension" by Umesh J. Kharod (10), the author outlines a procedure for designing the size and embedment length of an Lshaped anchor bolt using the suggested allowable values in ACI 318-63 (11). In 1984, J. 0. Jirsa and his colleagues tested L-shaped anchorages for pull-out and published those results in the research report entitled "Strength and Behavior of Bolt Installations Anchored in Concrete Piers" (12). Jirsa et al. reported that embedment length of L-shaped anchorages has a negligble influence on the slip of the bolt when increasing loads are applied, although the quantity of their data is not sufficient to prove this. They also discovered that the anchor would fail by straightening of the hook. No classical cone of crushed concrete formed around the bolt, explaining the lack of surface cracking. An effective bearing area could not be defined because the deformation of the hook caused 8


complex stresses in the concrete around the hook. The L-shaped anchorages used were 1-3/4" in diameter with a 6" hook length. The embedment length was 35" or 42". The bolts were instrumented with strain gauges just below the concrete surface and again at the ninety degree bend. The authors illustrated the behavior of the L-shaped bolts under the action of tensile loads (Figure A-1). Unfortunately, the two specimens tested were manufactured from ASTM A36 steel for the 35" embedment and ASTM Al93 steel for the 42" embedment, therefore no comparisons can be made. This report seems to be the most conclusive evidence as to the anchorage mechanisms of L-shaped anchor bolts. It compares the effectiveness of L-shaped anchor bolts with headed anchor bolts plus straps and with L-shaped bolts plus straps. It suggests that the headed anchor bolt plus strap anchorage was the most effective in allowing the bolt to reach a higher level of stress. Since some code requirements are based on the strength of headed anchor bolts for design considerations, it is evident that those requirements should not be used as a basis for designing L-shaped anchor bolts. Findings of Earlier Researchers of Similar Studies The First Joint Committee on Concrete and Reinforced Concrete (13) recommended, in 1913, that a 9


10 bond strength equivalent to four percent of the 28-day compressive strength of concrete be used to determine anchorage sizes and types. This guidance was based on the findings of the research of Duff Abrams and did not include specific advice for L-shaped anchorages. In 1913, R. Salinger (14) reported research on the pull-out of anchorages with semi-circular hooks at the embedded end. Salinger's results were quite dissimilar to those of Abrams as to the maximum bond resistance of varying diameters of bolts. In 1928, T. D. Mylrea also discussed anchorages with semicircular hooks in his article entitled "The Carrying Capacity of Semicircular Hooks" (15). Mylrea designed tests to simulate the stresses produced in reinforcing bars with end anchorages embedded in concrete beams. Although both of these experiments produced conclusions as to tensile stresses in the steel and discussions on the relationship of steel to concrete bond, comparison of the characteristics of a semicircular hook to those of a right angle bend would be misleading. T. D. Mylrea offered a design procedure for the bond of plain bars in his article "Bond and Anchorage" (16) in 1948. In this method, he suggested that a decrease in average bond strength occurs with an increase in embedment length. He also stated that bond resistance in plain bars is attributed, in large


part, to friction between the steel anchorage and the concrete. These statements are in agreement with those of Professor Abrams, but may or may not be applied to L-shaped anchorages. The mechanics of the L-shaped anchorage was discussed in the article entitled "Behavior of Bent Bar Anchorages" (17) by John Minor and James Jirsa. This article defines the stress zones induced in the concrete and along the anchor bolt as the anchor bolt is pulled from the concrete. It also indicates the mode of failure of an L-shaped anchorage will be a straightening of the hook resulting in complete pullout of the bolt from the concrete. These anchorage mechanics are described for deformed bars, and although the induced stresses and failure mode may be similar for smooth bars, the maximum bond resistance for a deformed steel bar is much greater than that of a smooth steel anchor. Code requirements suggest that design based on deformed bars should not be considered adequate when designing smooth L-shaped anchorages. A paper presented by M. o. serbousek and s. P. Signer to the Fourth Conference on Ground Control in Mining entitled "Load Transfer Mechanics in FullyGrouted Roof Bolts" (18) records the ability of roof bolts to securely hold the rock mass of the roofs of mines and tunnels. The authors suggested that pull-11


out tests alone could not provide adequate data to evaluate the strength of these deformed roof bolts in tension. Strain gauges were installed on the roof bolts to monitor the rate of load transfer from the bolt to the rock mass when load was applied. This suggests that L-shaped anchorages might also be monitored with strain gauges when performing pull-out tests to fully define bolt behavior in tension. Accepted Procedures for the Design of Anchor Bolts Several national organizations, concerned with the safe design of structures, make recommendations for the design of anchor bolts. These suggested values are based on bond and anchorage research and are updated at intervals determined necessary by their governing bodies. ACI recommendations. The 1983 American Concrete Institute Building Code Requirements for Reinforced Concrete (ACI 318-83) (4) states in Section 15.8.1 that Forces and moments at base of column, wall, or pedestal shall be transferred to supporting pedestal or footing by bearing on concrete and by reinforcement, dowels, and mechanical connectors. 12


13 Further, Section holds that: Reinforcement, dowels or mechanical connectors between supported and supporting members shall be adequate to transfer: (a) all compressive force that exceeds concrete bearing strength of either member, (b) any computed tensile force across interface. Section states that anchor bolts and mechanical connectors must be designed so that the bolt will fail in tension, i.e. it must neck and break, before the surrounding concrete fails. The designer must choose the required diameter of the anchor bolt so that this requirement is met. Unfortunately, ACI 318-83 does not outline a procedure for accomplishing the anchor bolt design. In order to choose the proper embedment and hook lengths, the designer would need to know the allowable bond stresses of the bolt. The ACI 318-63 building code is the last of this series to publish bond values for plain (smooth) bars. Hook and embedment lengths could be determined from the current code requirements for reinforcement in tension; however, results would be misleading andjor unconservative because those guidelines apply to deformed bars. ACI Committee 349 recommendations. "Code Requirements for Nuclear Safety Related Concrete Structures" (ACI 349-76) (1) is often cited as a


source of guidance for the design of anchor bolts. This guide provides minimum requirements for the design of anchor bolts embedded into reinforced concrete and subject to tensile or shearing forces. R. W. Cannon, et. al in "Guide to the Design of Anchor Bolts and Other Steel Embedments" (19) discuss the purported meaning of the ACI 349-76 code as it pertains to anchor bolts. The authors reference the ACI 318-77 (20) building code requirements to establish requirements in this guideline. Drawings in the ACI 349-76 standard imply that it may be used for L-shaped anchors. However, since the criteria are based on the failure cone mechanism of concrete for headed anchors, it is not actually applicable for use in the design of L-shaped anchorages. Anchorage provided by a deformed head is not equivalent to anchorage provided by a hook. UBC recommendations. The 1985 Uniform Building Code (3) lists allowable shear and tension on bolts in Table No. 26-G and reproduced in Table A-2. Footnotes to this table state that: ... bolts [are] of at least A307 quality. Bolts shall have a standard bolt head or an equal deformity in the embedded portion. Some engineers might interpret this to mean that, if an L-shaped anchor bolt has a hook length area equal to that of a standard bolt head, these UBC allowable loads are applicable. Allowable tension, in pounds, 14


is given by the UBC for various diameters of bolts for 2000 to 5000 psi concrete. A minimum embedment length is also recorded for each bolt diameter. Another section in the UBC references anchor bolts. Section 2719 declares that: Anchor bolts shall be designed to provide resistance to all conditions of tension and shear at the bases of columns, including the net tensile components of any bending moments which may result from fixation or partial fixation of columns. This section then refers the user to an AISC specification. These guidelines tell the designer that anchor bolts must be designed, but do not suggest a procedure for that design. AISC recommendations. The American Institute of Steel Construction (AISC) Manual of Steel Construction (6) devotes Part 4 to steel connections. Table I-c, reproduced as Table A-3, tabulates the minimum allowable tensile strength for anchor bolts based on the grade of the steel. The suggested details in the same chapter indicate that a hook length of three to four inches be specified and the embedment length should be based on the design requirements for uplift. Part 1 of the "Specification for the the Design, Fabrication and Erection of Structural Steel for Buildings" (21) addresses anchor 15


bolts in general in Section 1.22 by stating that Anchor bolts shall be designed to provide resistance to all conditions of tension and shear at the bases of columns, including the tensile components of any bending moments which may result from fixation or partial fixation of columns. The Commentary (22) for this specification expands on this statement to suggest that the largest tensile force on the anchor bolt is produced by bending moment at the column base and at times amplified by uplift forces which are in turn caused by lateral loads that induce an overturning tendency. This code provides minimal information for the engineer to design an Lshaped anchorage and does not address the issue of bond deemed so important by previous research. PCI recommendations. The Prestressed Concrete Institute (PCI) Design Handbook (2) includes a design procedure for headed studs under tensile loads, using the shear cone failure mechanism. Drawings suggest that L-shaped anchors may be used for column base plate connections and that the same procedure as for headed studs is adequate for L-shaped anchor design. One paragraph states that The strength of the concrete when the bolt is in tension may be critical and can be determined by assuming a shear cone pull-out failure as described for headed studs (Sect. 6.5.2). In addition to design procedures for headed anchor studs, the PCI Handbook gives suggestions for a 16


nominal bond stress on smooth anchor bolts and a nominal combined bearing stress on the hook. AASHTO recommendations. The American Association of State Highway and Transportation Officials (5) publishes standard specifications for use in highway bridge design. Specific references to anchor bolts state that they shall be designed to resist uplift forces. Section 3.17.1 asserts that: Provision shall be made for adequate attachment of the superstructure to the substructure by ensuring that the calculated uplift at any support is resisted by tension members engaging a mass of masonry equal to the largest force obtained under one of the following conditions: (a) 100 percent of the calculated uplift caused by any loading or combination of loadings in which the live load plus impact loading is increased by 100 percent. (b) 150 percent of the calculated uplift at working load level. And, in section 3.17.2, that Anchor bolts subject to tension or other elements of the structure stressed under the above conditions shall be designed at 150 percent of the allowable basic stress. Section 10.29 addresses anchor bolts used to secure trusses, girders and rolled beams to the substructure. This section provides minimum requirements for these bearing locations including number of bolts, bolt diameter and embedment length. These minimum allowable requirements are based on span length. This standard indicates that the anchor bolt should be provided with positive anchorage. Design 17


18 practitioners rarely, if ever, specify L-shaped anchor bolts for superstructure to substructure connections. Other recommendations. Many handbooks of engineering calculations are published to aid the design engineer. One such handbook, Standard Handbook for Civil Engineers (23) mentions anchor bolt applications. The section on plate girder bridges in this manual presents a table entitled "Requirements for Anchorage of Base Plates" which lists diameter of bolt required, number of bolts required and embedment length of bolts for anchorage according to span length. This manual refers the user to the AASHTO specifications for further information.


CHAPTER III METHODOLOGY The procedure used to conduct pull-out tests of L-shaped anchor bolts conformed to ASTM Standard E 488 "Strength of Anchors in Concrete and Masonry Elements" (24). This standard was also used to determine the necessary size of concrete pad specimens and the testing frame so that compressive forces would not be induced in the concrete. Three possible failure modes of L-shaped anchor bolts subject to the pull-out test are: 1) a shear cone failure of the concrete; 2) straightening of the anchor bolt hook and eventual pullout; and 3) fracture of the anchor bolt itself. Background. The pull-out test measures the force required to pull out an L-shaped anchor bolt whose hooked end is embedded in concrete. The pullout test is a function of concrete and anchor bolt tensile strength. Three modes of failure are possible. For very short bolts, a shear cone failure of the concrete may occur. The cone diameter is, conservatively, two times the embedment length plus one bolt diameter. The vertex of the cone is located


at the bend of the anchor bolt hook and radiates to the concrete surface at a 45 degree angle (Figure 1) A second failure mode may be straightening of the anchor bolt hook and and eventual pull-out. This mode induces bearing stresses in the concrete at the tip and at the inside bend of the hook (Figure 2). Some surface cracking of the concrete may occur as the bolt starts to slip upon pull-out. The third failure mode occurs if the anchor bolt itself fails. This mode suggests that the concrete, the hook of the bolt and the bond between concrete and steel are of sufficient strength to prevent the bolt from pulling out. It also indicates that the cone is large enough so that the concrete does not fail. The bolt will neck at a point along its exposed length, then snap. Specimen Configuration. A total of twenty specimens were tested. Test specimens were chosen for varying embedment lengths with constant hook length. Diameters of 3/8" and 1/2" were specified because of maximum load limits of the test equipment. The four embedment lengths were 4", 6", 8" and 10", each with a 3" hook. Tests on these four embedment lengths were replicated twice for the two diameters of bolts. One L-shaped anchor with 6" hook and embedded at 6" was tested to determine if hook length increases resistance to pull-out. Headed anchor bolts, one for 20


21 Concrete Surfoce Figure 1. Shear Cone Failure Mechanism of Concrete p v ---llo. .....Jo. .....Jo. ---llo. t r iT Stresses Figure 2. Bearing Stresses in Concrete


each of the two diameters selected, were fabricated as control specimens. The 1/2" diameter bolts were instrumented with strain-resistance gauges to measure elongation of these bolts. These gauges were secured along the length of the bolt embedment area and along the hook. Monitoring these areas gives additional information as to the magnitude of stresses developed at the various locations along the anchor bolt. The strain gauges were attached to the bolts before embedment into the concrete. Small, fine wires were soldered to the strain gauges to send the straingauge signal to the signal amplifier and indicator. In many cases, these wires may have grounded to the anchor bolt inciting a connection, through the anchor bolt, to other strain gauges on the same bolt. This condition made many of the strain gauges unusable. After the bolts were embedded and the concrete had cured, pressure from the concrete onto the silicone covering the strain gauges introduced some initial strain into the strain gauges. This initial strain changed the resistance of the gauges, causing some difficulty in matching the gauge to a temperature compensating strain gauge. The active strain gauges that were monitored because they could produce reliable results were bounded by an upper limitation. As the anchor bolts 22


were loaded and began to slip out of the concrete pad, the gauges were scraped off the anchor bolts and remained embedded in the concrete. The instant of detachment was apparent and further strain readings obviously could not be taken after that point. All specimens must be subjected to the same environmental factors to ensure reliabilty of results. L-shaped anchor bolts were embedded in concrete pads of sufficient size to simulate field conditions and to keep the test frame from inducing stresses into the concrete. A maximum of twenty concrete pads could be placed in the laboratory used, therefore limiting the number of specimens that could be tested. Concrete pad sizes were determined using ASTM Standard E 488. With the L-shaped anchor bolt embedded in the middle of the pad, the diameter of the calculated shear cone for each bolt diameter and embedment length controlled the width of the pad. Concrete pad length was calculated using the shear cone diameter plus the bearing area required for the test frame. An additional 311 of clearance was added to all dimensions. Depth of the concrete pad included the embedment length of the anchor bolt specimen plus J" of bottom clearance. These sizes were checked for bending failure and it was determined that reinforcing would be required. Pad width was increased by 611 to accomodate the addition of top, longitudinal 23


reinforcing bars. As these bars were well away from the anchor bolt, they should not affect test results. Appendix B includes these calculations. The hydraulic jack and pump used to load the test specimens has a maximum loading capacity of twenty tons. This restricted the size of anchor bolts that could be tested. L-shaped anchorages specified for connections are rarely smaller than three-quarters of an inch in diameter, except in light-frame wood structures. The hydraulic assembly used in this test procedure has the capacity to load up to a one-half inch diameter bolt to failure, possibly a larger diameter. Experimental procedure. Twenty wood forms were constructed to encase the concrete while wet, these concrete pads meeting the size requirements for each L-shaped anchor bolt specimen. The forms were arranged on the floor of the testing laboratory in a manner to allow ease of concrete placement. Because each pad would weigh up to 2000 pounds, movement would be difficult after concrete placement. Top, longitudinal reinforcing steel was wired to chairs anchored to the form base. Anchor bolt test specimens were located in the center of the appropriate forms and secured at the required embedment by bolting to a 2x4 wood cross brace (Figures 3 and 4). With the anchor bolt specimens in place, a local concrete 24


Figure 3. Placement of Headed Anchor Bolt in Wood Form Figure 4. Placement of L-Shaped Anchor Bolt in Wood Form


supply company was contracted to supply 3000 psi concrete and a pumping service supplied equipment and manpower to pump the concrete into the forms (Figure 5). After each form was filled, the concrete was vibrated (Figure 6) and the surface trowelled smooth (Figure 7). After two weeks, the side of the forms were stripped (Figure 8). The concrete was allowed to cure for 28 days to reach maximum compressive strength before pull-out tests were performed. During the concrete pour, four concrete cylinders were poured, one at the onset of the pour, two during mid-pour, and one at the end of the pour. These were loaded to failure with an hydraulic testing machine after 28 days to determine the actual compressive strength of the concrete used. In addition, 3/8" and 1/2" diameter straight anchor bolt specimens were loaded to failure in tension in a universal testing machine to determine actual ultimate and yield strengths of the steel. Pull-out tests were performed over a time span of one month. A test frame (Figures B-1, B-2 and B-3) was positioned on the concrete pad and centered over the threaded projection of the embedded L-shaped anchor bolt. Grout pads were formed using plaster of Paris under each vertical support of the test frame to insure uniform load distribution and stability of the frame. Whitewash was brushed on the longitudinal 26


Figure 5. Placement of Concrete Figure 6. Vibration of Concrete


28 Figure 7. Trowelled Concrete Pads Figure 8. Concrete Pads after Forms Stripped


sides of the concrete pads to help identify cracks if they should form during the pull-out tests. An ASTM A36 all-thread rod, 1/2" in diameter for the 3/8" diameter bolt specimens and 5/8" in diameter for the 1/2" diameter bolt specimens, was attached to the top of the anchor bolt with a threaded reducing coupler nut. The rod is larger in diameter than the test specimen to insure that it would not fail in tension before the bolt specimen. The rod was passed between the beam channel members of the test frame and through the hole in the hydraulic ram (jack) support plate (Figure 9). The hydraulic ram, used to apply the pull-out loads, was slipped over the pullout rod and rested on the test frame support plate. The ram was attached to an hydraulic pump by means of a coupling tube. The load cell was placed on top of the ram and around the pull-out rod. The ramjload cell assembly was secured to the pull-out rod with two nuts and a washer (Figure 10). The load cell was wired to a strain indicator (Figure 11) to provide load output readings. Dial gauges, gradated in 0.00111 increments and having a range from 0.00011 to 1.000", were attached by means of connecting straps to the top of the anchor bolt projection and were positioned at 0.000011 on the surface of the concrete pad (Figure 12). These gauges 29


Figure 9. Rod Placement through Test Frame Figure 10. Ram/Load Cell Assembly


Figure 11. Strain Indicator Figure 12. Dial Gauges


measure anchor bolt slip as the bolt is pulled from the concrete. The lead wires from the strain gauges on the 1/2" diameter bolts were plugged into a multi-channel strain gage conditioner and amplifier system by means of solderless connectors (Figure 13). A half-bridge configuration was used with temperature compensating strain gauges (Figure 14). The digital readout of the conditioner/amplifier system displayed bridge voltage. This completes the pullout test assembly (Figures 15 and 16). Loads were applied to the anchor bolt test specimen by hand using the hydraulic pump. The load was transmitted through the pull-out rod to the test specimen. At each load increment reading, measured in strain on the strain indicator, dial gauge readings were taken to monitor anchor bolt slip from the concrete. Voltage readings for wired strain gauges were also taken at these load readings. Test specimens were either loaded to failure of the bolt or concrete, until the dial gauges had recorded their maximum slip of one (1) inch. The experimental data obtained from each pullout test provided load/slip information and the failure mode for all specimens. Internal strain data, measured by the embedded strain gauges, provided additional information about the 1/2" diameter L-32


L-shoped Anchot" Bolt L: --Figure 13. Strain Gage Conditioner and Amplifier Strom Gouge T empet"otut"e Compensotmg Strom Gouge Bolt Motet"lol Figure 14. Half-Bridge Configuration 0 33


Figure 15. Pull-out Test Assembly Figure 16. Pull-out Test Assembly


shaped anchor bolts. These results are discussed in Chapter IV. Equipment and material specifications are given in the next section of this chapter. Test Equipment Much of the equipment and many of the materials required to perform the pull-out tests of Lshaped anchor bolts were purchased with funding from a Junior Faculty Development Award from the University of Colorado at Denver. Other equipment was borrowed from engineering departments at the University or was donated by local suppliers in the Denver area. Purchased and donated equipment is available for further research studies by the Department of Civil Engineering at the University of Colorado at Denver. Test equipment used to perform the experimental tests described in the previous section include the test frame assembly, the load cell, the hydraulic jack and pump assembly and strain and volt indicators. Equipment to measure actual concrete and steel strengths include hydraulic and universal testing machines. Test frame. The test frame is comprised of ASTM A36 structural steel W shapes, channels and plates. It is adjustable to fit on varying sizes of concrete pads from 2'-0" to 4'-0" in width. The frame is collapsible for ease of movement and sections are 35


connected by A307 5/8" diameter bolts. Figures B-1, B-2 and B-3 show the test frame configuration and specifications. The frame was designed as a simple span beam connected to a column support at each end and with an assumed concentrated load at midspan of the beam of 14 kips. The height of the web is sufficient to provide at least 9" of clearance from the top of the concrete pad to the bottom of the beam channel. The flange of the column member acts as a base plate. Since no lateral loads are applied during testing, anchorage connections are not required at the column to concrete pad juncture. One inch thick spacer plates are provided to give sufficient clearance between beam channel members for the threaded pullout rod. One half inch plates support the load cell and jack at midspan of the beam. This test frame set up was partially modified from the original design (Figure B3) for ease of fabrication. The test frame is set on the concrete pads in which the anchor bolt specimens are embedded. The column members of the frame are far enough apart so as not to induce compressive stresses in the calculated failure cone zone of the concrete. Strain Gage Conditioner/Amplifier. This system was used to generate high-level signals from strain gauge inputs to a digital readout display. The 36


output was displayed in volts. Voltage readouts were converted to strain during calibration of anchor bolt material using the universal testing machine. Materials The following paragraphs describe the properties of materials used to perform the pull-out tests on L-shaped anchor bolts. Anchor bolts. Anchor bolts were fabricated from ASTM A36 grade rolled steel with a minimum bend radius for the 90 degree hook of 3/4" for 3/B" diameter bolts and 1" for 1/2" diameter bolts. 2" of 10 UNC 2A screw threads were provided at the top of each bolt to provide connection to the threaded pullout rod. A 3" hook length was detailed according to AISC specifications discussed previously. Extra-long hook lengths were detailed at 6". Headed anchor bolts were straight members with a 2" thread at the top and a 1" thread at the bottom. A nut and washer assembly was secured on the bottom threads to simulate a headed member. Figure 17 illustrates anchor bolt specifications. Anchor bolts were assigned mark numbers to designate diameter, embedment length, replication, and special characteristics. Table 1 shows these mark number assignments and tabulates the mark numbers for each test specimen and the characteristics of each. 37


91-3/81 Rod 1111111111111111 1'-P 10Tl. 10T2 1P BTl. 8T2 91 6Tl. 6T2. 6TX 71 4Tl. 4T2 :111111111111111 T --&-Coc.o-o 'M 0 M

Table 1 Characteristics and Mark Numbers of Anchor Bolt Specimens ============================================================================ MARK BOLT NOMINAL ACTUAL HOOK CONCRETE PAD DIMENSIONS NUMBER DIAMETER EMBEDMENT EMBEDMENT LENGTH -----------------------LENGTH WIDTH HEIGHT (in) (in) (in) (in) (in) (in) (in) ============================================================================ 4T1 3/8 4 3.88 3 36 24 7 4T2 3/8 4 3.81 3 36 24 7 6T1 3/8 6 5.75 3 36 24 9 6T2 3/8 6 5.88 3 36 24 9 8T1 3/8 8 7.88 3 40 28 11 8T2 3/8 8 8.00 3 40 28 11 10T1 3/8 10 9.63 3 44 32 13 10T2 3/8 10 10.00 3 44 32 13 6TX 3/8 6 5.94 6 36 24 9 6TK 3/8 6 5.88 ---36 24 9 4H1 1/2 4 4.19 3 36 24 7 4H2 1/2 4 4.19 3 36 24 7 6H1 1/2 6 6.00 3 36 24 9 6H2 1/2 6 5.69 3 36 24 9 8H1 1/2 8 8.44 3 40 28 11 8H2 1/2 8 8.25 3 40 28 11 10Hl 1/2 10 10.25 3 44 32 13 10H2 1/2 10 9.94 3 44 32 13 6HX 1/2 6 6.34 6 36 24 9 6HK 1/2 6 5.84 ---36 24 9


Concrete pads. Concrete pad sizes were calculated according to the procedure described in the design considerations of the methodology section of this chapter. Figure B-4 illustrates concrete pad sizes used for this project. Table 1 tabulates the pad dimensions for each anchor bolt mark. Concrete strength specified was 3000 psi at 28 days, although actual strength was higher. Top, longitudinal reinforcing bars were placed, one on each side and 3" clear of the edge. These bars were designated as #6 deformed ASTM Grade 60 reinforcing bars. Chairs to support the reinforcing bars in the correct position were of standard 16 ga. steel. Chairs were attached to the bottom of the concrete forms with 1/2" galvanized staples. Reinforcing bars were tied to the chair supports with standard tie wire. Strain gauges and wiring. One-half inch diameter anchor bolts were filed with emery cloth and cleaned with mineral spirits to remove mill coating and dirt from locations of strain gauge attachment. These locations are illustrated in Figure 18. Strain gauges, specified at a resistance of 120.0 ohms and a gage factor of 2.03 at 76 degrees F, were attached to the anchor bolts with an epoxy cement and allowed to set up. Thirty-four-gage monofilament wires, 2011 in length were soldered to the two soldering tabs of the 40


6T 0 6T J L 68 -----5T -5T 58 5T 5T J L 58 0 ----0 ----TID r 4T 0 4T 48 4T 0 4T L 48 ----------3T I 0 "': 3T 38 3T 0 3T 38 3T 0 38 -----1 T & 2T I I 1:': .!.!_ 2T 1T & 2T 1T 2T lT & 2T I !"> 1T 2T -18 & 28 I llB 128 I 18 & 28 18 & 28 4Hl 6Hl 8Hl 6T 0 6T J L 68 ------5TI 0 .... 5T 58 5T 5T J L 58 ----0 ------4T I 0 --48 4T 0 4T 48 4T 0 L 48 ------------3T I 0 __ ___ 38 3T 0 3T 38 3T 0 ----38 -------1T & 2Tlj __ t __ 1T 2T 1T & 2T 1T 2T 1T & 2T I 1T 2T -18 & 28 18 & 28 18 & 28 .3' .2' 4H2 6Hl 8H2 Figure 18. Locations of Strain Gauges on Anchor Bolts I-'


----------------N 5T isl 5TI 0 58 6T 0 6T. 68 --------------4T I 0 4T 48 5T 0 5T. ---------------JT I 0 3T 38 4T 0 --4T. 48 -------------lT & 2T I_ I lT 2T 1T,2T & 3T I 1!\) lT 2T 3T --18 & 28 us I2B I 18,28 & 38 .2' 10Hl 6HX 5TI 0 58 0 ,_ --Jll,! 3H 38 3T 4T I 0 48 2T 01----j'": 2T. 28 3T I 0 38 lT 0 ---n 18 1T & 2T lT 2T --------18 & 28 .25' 10H2 6HK Figure 18 (continued) I\.)


strain gauges. Wires were secured intermittently along the anchor bolt length with thin strips of electrical tape to prevent tangling and disconnection from the soldering tabs. Wires were labelled with mark numbers (Figure 18) to indicate the location of the strain gauge on the bolt. After the anchor bolts were embedded in concrete, 26 gage wire, 3 feet in length, was attached to each monofilament wire to provide adequate length to reach the input jacks of the signal amplifier and indicator. All wires were of the same length and size so that equal resistance in all wires was encountered. Temperature compensating device. A temperature compensating device was required to complete the half-bridge circuit. This "dummy" was created to cancel the effects of change in electrical resistance due to temperature change. The dummy consisted of a portion of anchor bolt material instrumented with eight strain gauges and associated wiring as described above. This instrumented bolt was fastened inside a brick mass to simulate the same conditions as if it were embedded in concrete. This approach was taken so that the dummy could easily be carried to each anchor bolt/concrete pad specimen. 43


Other materials. Design of the formwork constructed to encase the concrete pads is illustrated in Figure B-5. 44


CHAPTER IV RESULTS AND OBSERVATIONS Tests for Material Properties Steel. Straight pieces of steel from the same stock as the L-shaped anchor bolts were tested to failure in tension using the universal testing machine. Two specimens each of 3/8" diameter and 1/2" diameter material were tested. There was not a definite yield point, so the yield strength was determined by the 0.2% offset method, with results shown in Table 2. Ultimate tensile strength of each specimen was determined and the two results for each diameter were averaged. The 3/8" diameter material had an ultimate tensile strength of 70.06 ksi while the 1/2" diameter material exhibited an ultimate strength of 65.95 ksi, as shown in Table 2. Anchor bolts were fabricated from ASTM A36 steel, having a minimum specified ultimate tensile strength of 58 ksi. Anchor bolt material used in the pull-out tests had an average ultimate tensile strength in the middle of the 58 to 80 ksi range that has been previously recorded for A36 material. Concrete. Four concrete cylinders, poured during the placement of the concrete in the forms,


Table 2 Strength of Bolt Material ============================================= Mark Number Yield Strength from Tests of Bolt Material* (ksi) Minimum Specified Tensile Strength** (ksi) Ultimate Tensile Strength from Tests of Bolt Material*** (ksi) ============================================= 4Tl 4T2 6Tl 6T2 8Tl 8T2 lOTl 10T2 6TX 6TK 4Hl 4H2 6Hl 6H2 8Hl 8H2 lOHl 10H2 6HX 6HK 56.48 45.33 *0.2% Offset Method **AISC p. 1-5 58 58 ***Maximum load (kips) from averaged material tests divided by crosssectional area of bolt material 70.06 65.95 46


were tested in the hydraulic testing machine to determine compressive strength of the concrete used. The concrete ordered was specified to have an ultimate compressive strength of 3000 psi at 28 days, with a water-to-cement ratio of 0.3 and with no fly-ash. The 28-day-strength of the concrete delivered was much higher than that specified. Ultimate compressive strength of each cylinder is shown in Table 3, along with the average strength of the four cylinders. For subsequent design calculations, the average strength of the first three cylinders was used (4306.0 psi) rather than the average of all four. The fourth cylinder was placed after the pumping equipment operator had to add water to the concrete remaining in the pipeline to flush it out. Pull-out Test Results The 3/8" diameter L-shaped anchor bolts were tested first because they were not instrumented with strain gauges. Data was recorded for load/slip relationships. Data logged for the 1/2" diameter anchor bolts included slip and strain at given loads. General Observations. General displacement behavior for the L-shaped configuration was essentially the same for the 3/8" diameter and 1/2" diameter at all embedment lengths. Displacement of bolts from the concrete increased rapidly with each 47


Cylinder Number Ultimate Strength (psi) ---------------------------------------1 4244 .1 2 4323.7 3 4350.2 4** 4102.7 ========= 4306.0* 45.1 55.2 <---Average strength (1-3) <---standard deviation for average of strengths <---standard deviation of cylinders (1-3) *This value is used for f'c in pull-out test calculations. **Test cylinder 4 was omitted from average due to addition of water to concrete near end of concrete placement. 00


increased load application after an initial resistance. The 3/8" diameter L-shaped bolts started to slip at applications of 500 to 1500 pounds of load, while 1/2" diameter bolts did not start to slip until load applications of 1500 to 2500 pounds. L-shaped anchorages with extra-long (6") hooks began to slip in these same ranges. Headed anchor bolts displayed different, although expected, behavior. The two headed anchor specimens also commenced slip in the above mentioned load ranges, but were much more resistant to continued displacement at augmented load applications. L-shaped anchor bolts failed by straightening of the hook and the bolt pulling from the concrete. Headed anchor bolts reached ultimate when the bolt material yielded and snapped. During pull-out of the 3/8" diameter and 1/2" diameter L-shaped anchor bolts, minor spalling of the surface concrete around the bolt was observed (Figures 19 and 20). This spall is attributed to superficial breakage of the bond between the anchor bolt and the concrete. As load was applied, the 3/8" diameter bolts emitted characteristic steel sounds, much like that of a spring being stretched. These noises occurred frequently as load was applied until yield of the hook was reached and the bolt began to slip freely. As the 49


Figure 19. Spalling of Surface Concrete ... "": .. Figure 20. Spalling of Surface Concrete


applied load was increased, the bolt hook straightened in short bursts, causing the steel to screech as it yielded. The 1/2" diameter bolts, on the other hand, were relatively quiet. An occasional snapping sound would be transmitted through the test frame. Several 3/811 diameter and 1/2" diameter bolts were extracted completely from the concrete. Upon examination of these straightened bolts, a slight bend at the location of the original bend for the hook can be detected (Figure 21). A more apparent bend, approximately one (1) inch from the end of the bolt (Figure 22), indicates that some concrete failure in bearing at the hook radius occurred. As the bolt pulled free, the bend at the tip of the hook was allowed to slip through the zone of crushed concrete without resistance (Figure 23). The specimens with extra-long hooks behaved in much the same manner as those with 311 hooks. Both tested diameters of headed anchor bolts failed by steel fracture. As load was applied, these bolts resisted pull out and eventually necked then snapped (Figures 24 and 25). This yielding and failure developed at the threaded portion of the bolt, indicating that the weakest section of the bolt is at the cross-sectional area of least diameter. Failure mode. None of the pull-out tests resulted in failure of the concrete rather than the 51


Figure 21. Position of Anchor Bolt Hook after Straightening Figure 22. Position of Tip of Anchor Bolt after Straightening 52


Concrete surfoce Surfoce concrete spoll Pos1 t1on of bolt ot ul t1mote lood Zone of crushed concrete ----Areo of poss1ble crushed concrete /"'-,/-.., : \ ./ I -o: ft Figure 23. Diagrammatic StraighteJ Anchor Bolt Hook


Figure 24. Headed Anchor Bolt Failure Figure 25. Headed Anchor Bolt Fracture Planes


steel. There are two reasons for this. First, the concrete compressive strength was much greater than anticipated and specified. Secondly, the shortest embedment length (.4")" was only marginally likely to result in concrete failure, even if the ultimate compressive strength (f'c) was 3000 psi. Appendix c shows the calculations to determine the required embedment length such that concrete failure does not control. As these calculations illustrate, with "perfect" materials (0=1), the 1/211 diameter bolt embedded at 4" would result in a concrete failure if the ultimate tensile strength of the steel (Fu) is 65.95 ksi and the ultimate compressive strength of the concrete is 3000 psi. Surface crack development. Since the pull-out tests of the specimens embedded at 411 were designed for the shear cone failure mechanism of concrete, some cracking of the concrete was expected. Because all specimens failed due to yielding of the anchor bolts, no surface cracking was detected at any time during the tests. No conical failure surface formed at the anchorages. Ultimate tensile strength. Table 4 shows the tensile strength of all tested specimens, along with steel material properties. L-shaped anchor bolts did not meet the minimum specified tensile strength nor 55


Table 4 Ultimate Tensile Strength of Anchor Bolts ======================================================== Mark Number Ultimate Load from Pull-out Tests (kips) Ultimate Tensile Strength from Pull-out Tests* (ksi) Minimum Specified Tensile Strength** (ksi) Ultimate Tensile Strength from Tests of Bolt Material*** (ksi) ======================================================== 4Tl 4.301 55.15 4T2 3.474 44.54 6Tl 3.633 46.58 6T2 4.562 58.49 BTl 4.048 51.89 8T2 4.301 55.15 58 lOTl 4.367 55.98 10T2 3.761 48.22 6TX 4.986 63.92 6TK 4.953 63.50 4Hl 5.866 41.31 4H2 6.061 42.68 6Hl 6.094 42.91 6H2 7.202 50.72 8Hl 7.821 55.08 8H2 7.365 51.86 58 lOHl 7.104 50.03 10H2 7.560 53.24 6HX 7.723 54.39 6HK 8.903 62.70 *Maximum load (kips) from pull-out test divided by tensile stress area (AISC Threaded Fasteners p. 4-141) **AISC p. 1-5 ***Maximum load (kips) from averaged material tests divided by crosssectional area of bolt material 70.06 65.95 56


57 the ultimate tensile strength determined from tests of bolt material. This implies that straightening of the hook is the most important factor in the design of Lshaped anchorages and not yield of the bolt material at the location of least cross-sectional area. Load/slip relationships. Bolt tension versus bolt slip curves are illustrated in Figures 26 and 27. The 3/8" diameter bolts consistently straightened at a lesser applied load than did the 1/2" diameter bolts. All L-shaped anchor bolts started to straighten between 0.05 and 0.1 inches of slip. Most of these test specimens required a small additional applied load to displace the bolt 0.4 inches. The 3/8" diameter bolts show no effect of embedment length up to the 1011 embedments. Bolts with 4", 6" and 8" embedments straightened completely between 3 and 4 kips. The two 10" embedded specimens straightened at 3 kips of applied load, implying that an embedment length greater than 8" decreases the pull-out resistance of this diameter of L-shaped anchor. The 1/2" diameter bolts do show some relationship to embedment length. The 4", 6" and 8" embedments straightened at approximately 5, 6 and 7 kips respectively. This indicates that increased resistance to pull-out can be achieved by greater embedments with this diameter of bolt. Note, again,


6. ..-. rn a. ... .::f. D

9. 8. 7. (/) Cl. ... .:i. ....... 0 0 _J 8. 7. 6. (/1 Cl. ... .:i. ....... 0 0 _J 9. 8. 7. 6. (/) Cl. ... .:i. 0 0 _J 0.1 0.2 0.3 0.4 SLIP (mchesl 8. 7. 6. (/) Cl. ... .:i. 0 0 _J 0.1 0.2 0.3 0.4 SLIP (mchesl Figure 27. Load/Slip Curves 1/2" Diameter Anchor Bolts


that the 1011 embedments did not attain outstanding resistanc:;:e to pull-out over the 6" and 8" embedment lengths. The extra-long hooks for both the 3/8" diameter and 1/2" diameter L-shaped anchorages had greater resistance to pull-out than their 311 hook counterparts. The 3/8" diameter, 6" embedded length, extra-long hook had increased slip with almost no additional load at 5 kips, about one kip of applied load after the 611 embedded length, standard hook. Similarly, the 1/211 diameter, 6" embedded length, extra-long hook had increased slip with little additional load at 6.75 kips of applied load. This is, again, about one kip of applied load after its equivalent 3" hook complement. The 1/2" diameter, extra-long hook with 6" embedment bolt also exhibits a resistance capacity almost equal to that of the 8" embedment length, standard hook. This demonstrates that a 6" hook for 3/8" and 1/2" diameter L-shaped anchor bolts can give some additional capacity for resistance to pull-out. The headed anchor bolts for both diameters show a maximum slip of 0.2 inches. The 3/8" diameter headed bolt exhibits a slightly higher capacity than all embedments of the standard hook by yielding at 4.75 kips. Its resistance to pull-out, however, is 60


not as great as that of the L-shaped anchor with extra-long hook. The 1/2" diameter headed anchor bolt was the most resistant to pull-out, yielding at 8.25 kips. This implies that headed anchor bolts, of sufficient diameter, are superior to L-shaped anchorages when large axial loads are applied. Load/strain relationships. Because of grounding of the strain gauges, the strain data was not used in this analysis. Analysis of Results Anchorage type. The 1/2" diameter headed anchor bolt displayed the largest capacity for resistance to displacement when load was applied during the pull-out tests. When connection devices are required to anchor structural members in buildings and bridges to resist large uplift and overturning forces, headed anchor bolts are more efficient if diameter must be kept to a minimum. This may be the case when considering an economical solution. If the uplift and overturning forces on a structure are minimal, as in light-frame wood, residential construction, the L-shaped anchor may be the reasonable, economical solution, as exhibited by the pull-out tests performed on the 3/8" diameter and 1/2" diameter anchor bolts. 61


Embedment length. Smaller diameter bolts do not acquire additional strength if embedment length is increased. If factored, calculated uplift and overturning forces on a structure do not exceed 3 kips, a 3/8" diameter L-shaped anchor bolt in 4000 psi concrete is sufficient to resist these loads. An embedment length of 4" will carry the load as well as an embedment length of 8". Economically, the 4" embedment length is adequate. Factored uplift and overturning forces applied to a structure in excess of 3 kips would require a 1/2" diameter bolt or larger. For the 1/2" diameter bolts, increased embedment did result in some increased load-carrying capacity. Hook length. Increasing the length of the hook of an L-shaped anchor bolt can supply some resistance to pull-out of the bolt. This may be advantageous if embedment length is limited due to restricted concrete depth. Bolt diameter. The diameter of the bolt is an important requirement in resisting pull-out. Larger diameter bolts have higher ultimate strengths because they have more cross-sectional area. The 1/2" diameter bolts resisted displacement at applied loads almost twice those applied to the 3/8" diameter bolts at an equivalent slip. 62


Bond to concrete. The steel to concrete bond for smooth anchor bolts is minimal. For all pull-out tests on L-shaped and headed anchors, the bond (at least near the concrete surface) was broken at the onset of load applications. As soon as the bolt commenced to slip, the concrete around the bolt spalled. Tensile strength versus straightening. The Lshaped anchor bolt specimens did not fail by fracture so they did not reach the ultimate tensile strength of the bolt material. Straightening by yielding at the bend is the important feature. Calculations should be included in the design procedure to determine the applied load at which the anchorage begins to straighten. This parameter would control the diameter and embedment length specified for the anchorage used in a specific structure. 63


CHAPTER V SUMMARY AND CONCLUSIONS Summary In this study, the strength and behavior of Lshaped anchor bolts embedded in reinforced concrete pads were investigated. Twenty pull-out tests were conducted: eight each on 3/8" diameter and 1/2" diameter L-shaped bolts with 311 hook lengths embedded at various lengths into the concrete; one each on 3/8" diameter and 1/2" diameter L-shaped bolts with 611 hooks and 611 embedment lengths; and one each on 3/8" diameter and 1/2" diameter headed anchor bolts embedded at 611 Bolt material used was ASTM A36 steel. Concrete strength was 4306 psi at 28 days. The main objective of the pull-out tests was to determine the strength and behavior of smooth, Lshaped anchor bolts under tension loads. Tests indicated that, in all cases, these bolts pulled out by straightening of the hook. Headed anchor bolt specimens yielded by fracture but did not pull out of the concrete. The strength of embedded L-shaped anchor bolts was greater for larger diameter bolts. The 1/2" diameter bolts resisted slip at about twice the


applied load as that of the 3/8" diameter bolts for all embedment lengths in both cases. Increasing the embedment length of the 3/8" diameter L-shaped bolts did not provide any appreciable resistance to pull out. Increasing the embedment length of the 1/2" diameter bolts up to 8", however, showed improved resistance to pull-out. Increasing the hook length of both specimen diameters provided some additional resistance. Conclusions The strength and behavior of L-shaped anchor bolts differs from that of headed anchor bolts. The failure mode of an L-shaped anchorage is pull-out due to straightening of the hook. The headed anchor bolt, with embedment as tested, on the other hand, fails by fracture of the bolt. Design practitioners have specified L-shaped anchor bolts as connection devices to resist tensile forces caused by lateral loadings. These engineers have depended on published specifications and minimal allowable standards to design these connections. However, the published standards are often based on pull-out tests performed on headed anchor bolts. Because failure mode and strength of L-shaped anchors differ dramatically from those of headed anchors, the specifications and standards currently 65


available should not be applied to L-shaped anchorages. current design procedures. ACI 318-83 states that anchor bolts must fail in tension before the surrounding concrete fails. From the pull-out tests conducted, headed anchor bolts can meet this requirement. L-shaped anchor bolts of the diameters tested pull out by straightening. They do not reach their ultimate tensile capacity. Therefore, the ultimate tensile strength of the bolt material cannot be used to determine the required diameter that will cause the bolt to fail in tension before the surrounding concrete fails. Since bond of smooth steel anchorages to concrete is minimal, the ACI 318-83 recommendations for hook and embedment lengths of deformed bars should not apply to smooth anchor bolts. Deformed bars in tension gain most of their strength from mechanical bond (interlock of deformations with concrete), affecting required hook and embedment lengths. Because no additional resistance to pull-out is realized from bond of smooth anchorages, longer hook and embedment lengths andjor bolt diameters would be required to achieve the same resistive strength as that of deformed bars. The ACI 349-76 code bases design requirements on the failure cone mechanism of concrete for headed 66


anchor bolts. However, the pull-out tests reported here demonstrate that the failure mechanism for Lshaped anchor bolts differs dramatically. Anchorage provided by a deformed head is not equivalent to that provided by a hook, therefore, design requirements are not interchangeable. The PCI Handbook suggests that their design procedure for headed anchor bolts can be used for Lshaped anchor bolt design. The strength of 3000 psi concrete when the bolt is in tension may be critical for embedment lengths less than 4". Shear cone pullout failure for headed studs, however, should not be assumed to apply to L-shaped anchor bolts. Instead, the designer should consider L-shaped bolt tensile force at onset of straightening and choose diameter, embedment length and hook length based on this tensile load. A bolt diameter must be assumed initially, then verified. Design comparison. Appendix c compares pullout test results of L-shaped anchor bolts to UBC allowable loads and to ACI 318-63 ultimate capacity requirements. Table C-1 contrasts the results of these two codes when they are used to design L-shaped anchor bolts. Additional required studies. Further research needs to be conducted to analyze the design procedure, 67


suggested above, for accuracy. Diameters of 5/8", 3/4", 7/8" and 1" should be subjected to pull-out tests to determine if strength and behavior are similar to those tested herein. Monitoring the behavior of these L-shaped bolts and hook lengths with strain gauges along the embedment can provide valuable insight. Rather than place the strain gauges on the surface of the bolts, a thin channel should be grooved along the top and bottom sides of the bolts. This would prevent the gauges from being abraded off the bolt, but it might create some unlikely bond between concrete and steel. Smaller concrete pads can be used so that more tests and replications can be performed at one time. The shortest embedment length required to insure bolt over concrete failure can be determined using similar methods to those calculations outlined in Appendix c. Concrete pads can then be sized according to anchor bolt embedment and hook lengths. The additional concrete required to provide for a shear cone failure is not necessary. 68


REFERENCES 1. ACI Committee 349, Code Requirements for Nuclear Safety Related Concrete Structures CACI 349-76), Detroit: American Concrete Institute, 1976. 2. PCI Design Handbook -Precast and Prestressed Concrete, Jrd ed. Chicago: Prestressed Concrete Institute, 1985. 3. Uniform Building Code, 1985 Edition, Whittier, Calif.: International Conference of Building Officials, 1985. 4. ACI Committee 318, Building Code Requirements for Reinforced Concrete CACI 318-83), Detroit: American Concrete Institute, 1983. 5. Standard Specifications for Highway Bridges, 13th ed. Interim 1985, The American Association of State Highway and Transportation Officials, 1983. 6. Manual of Steel Construction, 8th ed. Chicago: American Institute of Steel Construction, Inc., 1980. 7. Fuller, William T., "The Development of Bond and Anchorage on L-Shaped Anchor Bolts in Tension," Master's Report, University of Colorado at Denver, 1987. 8. Abrams, Duff A., "Tests of Bond Between Concrete and Steel," Bulletin No. 71, University of Illinois Engineering Experiment Station, 1913. 9. Fisher, James M., "Structural Details in Industrial Buildings," Engineering Journal, Vol. 18, No. 3, Chicago: American Institute of Steel Construction, 1981. 10. Kharod, Umesh J., "Anchor Bolt Design for Shear and Tension," Engineering Journal, Vol. 17, No. 1, Chicago: American Institute of Steel Construction, 1980.


11. ACI Committee 318, Building Code Requirements for Reinforced Concrete CACI 318-63), Detroit: American Concrete Institute, 1963. 12. Jirsa, J.O., N.T. Cichy, M.R. Calzadilla, W.H. Smart, M.P. Pavluvcik, and J.E. Breen, "Strength and Behavior of Bolt Installations Anchored in Concrete Piers," Research Report 305-1F, Project 3-5-81-305, Austin, Texas: Center for Transportation Research, Bureau of Engineering Research, The University of Texas at Austin, 1984, pp. 109-140. 13. Report by the First Joint Committee on Concrete and Reinforced Concrete. New York: Proceedings of the American Society of Civil Engineers, 1916. 14. Saliger, R., "Schubwiderstand und Verbund in Eisenbetonbalken" ( Connection-rod Resistance and Bond in Reinforced Concrete Beams), 1913. 15. Mylrea, T.D., "The Carrying Capacity of Semicircular Hooks," ACI Journal Proceedings, Vol. 24, Detroit: American Concrete Institute, 1928. 16. Mylrea, T.D., "Bond and Anchorage," ACI Journal Proceedings, Vol. 44, Detroit: American Concrete Institute, 1948. 17. Minor, John and James 0. Jirsa, "Behavior of Bent Bar Anchorages," ACI Journal Proceedings, Detroit: American Concrete Institute, April 1975. 18. Serbousek, M.O. and S.P. Signer, "Load Transfer Mechanics in Fully-Grouted Roof Bolts," Conference Proceedings, Morgantown, West Virginia: Fourth Conference on Ground Control in Mining, 1985. 19. Cannon, R.W., D.A. Godfrey, and F.L. Moreadith, "Guide to the Design of Anchor Bolts and Other Steel Embedments," Concrete International Design and Construction, Vol. 3, No. 7. Detroit: American Concrete Institute, 1981. 20. ACI Committee 318, Building Code Requirements for Reinforced Concrete CACI 318-77), Detroit: American Concrete Institute, 1977. 70


21. "Specification for the Design, Fabrication and Erection of Structural Steel for Buildings," Manual of Steel Construction, 8th ed. Chicago: American Institute of Steel Construction, 1980, p. 5-57 0 22. "Commentary on the Specification for the Design, Fabrication and Erection of Structural Steel for Buildings," Manual of Steel Construction, 8th ed. Chicago: American Institute of Steel Construction, 1980, p. 5-149. 23. Merritt, Fredericks., ed. Standard Handbook for civil Engineers, 2nd ed. New York: McGraw-Hill Book Company, 1976. 24. ASTM Standard E 488, "Strength of Anchors in Concrete and Masonry Elements," Annual Book of ASTM Standards, Section 1, Vol. 01.05, Philadelphia: American Society for Testing and Materials, 1985. 71




73 CONTENTS TABLES Table A-1. Effect of Anchoring Ends of Bars ..... 74 A-2. Allowable Shear and Tension on Bolts................................. 75 A-3. Material for Anchor Bolts and Tie Rods. : .............................. 76 FIGURES A-1. Behavior of L-Shaped Anchor Bolts Under the Action of Tensile Loads ...... 77


Size of Round Bar and Manner of Anchoring 3/4-in, no anchorage l-in, no anchorage 1/4-in,anchored with nut only 3/4-in, anchored with nuts and 2-1/2-in cut washer 3/4-in, 1/4 circum. 3/4-in, 1/2 circum 3/4-in, 45 deg bend, 2" long 3/4-in, 90 deg bend, 2" long 3/4-in, 135 deg bend, 2" 3/4-in, 180 deg bend, 2" l-in, 1/4 circum. l-in, 1/2 circum. l-in, 45 deg bend, 2 in long l-in, 90 deg bend, 2 in long l-in, 135 deg bend, 2 in long l-in, 180 deg bend, 2 in long Number of Tests 15 11 5 6 5 5 5 5 5 5 5 5 5 5 5 5 Age at Test days 78 66 62 75 69 71 70 69 69 69 62 62 62 62 62 62 Embedment 8 in. Stresses are given in psi. Avg Bond Stress at End Slip of 0.0005 in. 0.001 in. 290 367 324 370 292 339 320 373 The average compressive strength of 6-in cubes was 2040 psi. Maximum Bond Resistance (psi) 454 478 925 1020 736 607 829 747 672 894 858 653 776 863 866 1005 Adapted from Duff A. Abrams, "Tests of Bond Between Concrete and Steel" (University of Illinois Engineering Experiment Station, 1913, p.96) -...I


75 Table A-2 Allowable Shear and Tension on Bolts (lbs)* # ======================================================== Diameter (inches) 1/4 3/8 1/2 5/8 3/4 7/8 1 1-1/8 1-1/4 Minimum** Embedment (inches) 2-1/2 3 4 4 5 6 7 8 9 Minimum Concrete Strength (psi) Tension*** 2000 3000 2000 to 5000 500 500 200 1100 1100 500 2000 2000 950 2750 3000 1500 2940 3560 2250 3580 4150 3200 3580 4150 3200 3580 4500 3200 3580 5300 3200 *Values are for natural stone aggregate concrete and bolts of at least A307 quality. Bolts shall have a standard bolt head or an equal deformity in the embedded portion. #Values are based upon a bolt spacing of 12 diameters with a minimum edge distance of 6 diamet6rs. **An additional 2 inches of embedment shall be provided for anchor bolts located in the top of columns for buildings in Seismic Zones Nos. 2,3 and 4. ##Values shown are for work with or without special inspection. ***Values shown are for work without special inspection. Adapted from Uniform Building Code, Edition (Whittier, Calif.: International Conference of Building Officials, 1985), p. 456.


Strength (ksi) ASTM Specification Proof Load Yield (Min) Tensile (Min) Maximum Diameter (in) Type of Material Headed or Unheaded -------------------------------------------------------------------------------A36 -36 58 8 c u A572 Gr 50 50 65 2 HSLA u A572 Gr 42 -42 60 6 HSLA u A588 50 70 To 4 incl HSLA u 46 67 4 to 5 ACR 42 63 5 to 8 C = Carbon HSLA = High Strength Low Alloy Notes: ASTM specified material for anchor bolts ... can be obtained from either specifications for threaded bolts and studs normally used as connectors or for structural material available in round stock that may then be threaded. Anchor bolt material that is quenched or tempered should not be welded or heated to facilitate erection. Adapted from Manual of Steel Construction (Chicago: AISC, 1980, p. 4-4.) m


fN TN .iTN M 1 k Cn t1col Pos1t1on of bolt ot ul t1mote lood Zone of cr-ushed concr-ete ----Ar-eo of poss1ble cr-ushed concr-ete sect1on Vo1d or-eo Figure A-1. Behavior of L-Shaped Anchor Bolts Under the Action of Tensile Loads 77




CONTENTS TEST FRAME CALCULATIONS. . . . . . . . . . . . 80 CONCRETE PAD CALCULATIONS....................... 82 FORMWORK CALCULATIONS. . . . . . . . . . . . . . 84 Figure B-1. B-2. B-3. B-4. B-5. FIGURES Test Frame Elevation ........... Test Frame Sections and Details ........ Test Frame Sections and Details ........ Size of Concrete Specimens ......... Formwork Details ....................... 86 87 88 89 90 79


TEST FRAME CALCULATIONS Source: William T. Fuller, "The Development of Bond and Anchorage on L-Shaped Anchor Bolts in Tension" (Denver: University of Colorado at Denver, 1987), pp. B3-B4. I o !'e ,. :?oi. w/ 4-!0/e." d> AL.J... -.. I ; 1 0 ............... \ 1 = 1'o'' .=,I II ... 1 X. '5 LCNG,rH "' ru?.. WI X It M = s .4" = lo.::!"" et ?y41 HEAVY HE:JC. t-JUTS {TYI" lo.5tCI'Z.) '!. ( .;L ) 2.1.Gr :-.o"!. 1"-'. 2.92 (MIN. Fote. 2. 1t.J veer. Pt.ANe) = IZooc(1) ,..,= 3G,('=t,l') ::. Z,.l.c:., o.!'. r!>uPP>...'E.o a 2 X = '2 !N:" II (I.. '"" = z.c.2 = .OIB /' .-. 0 1'. A .. =. 'Z. (c..-'2.(e,lz.=.J] X "Z : 1.1:. f.= /1.,:;. 4.0 C '/, 14 1<. /8 -= 1.7S. S;:t._1"'.!::? Ll5E cp A ::Or f3oi_TS j =-C.... I c. 80


95'-= OOOJ...'Zf'5"'l.'?' s = a / "S'Z..,. S = L 'i -i :. '?1'0 .-I "'C I -J..--:; l'i:>l <:;gi7 :. .... :l 'iL I & S"I'Z." -1 s I \,. Z 1) I 'Z. =Gi z >1 51712.' :. -= .J. SOL' og = s'%: :;: '? = Cf 0-1)1( '? X +.-)...<'.l. I II II r"C t;'iC,./ ::J,.-..:"-:d I 18


CONCRETE PAD CALCULATIONS Source: William T. Fuller, "The Development of Bond and Anchorage on L-Shaped Anchor Bolts in Tension" (Denver: University of Colorado at Denver, 1987), pp. B5-B6. I I FAILUR-E: I Jl ,. : 4 :., i = 14 x 1.1 = n.e," I L =2.'-o" PL .... MoJ = 4 .,_ .= 11.9 I foa. : I 2.11 ee:. !-JcGLEC:. reo .,! M.,"' = ]ftsc12ooo) = 1.111-l<-<<: foiZ ... o-14 d = 1 I. 5 -. 5. .: 5' b +" F; t1 A.,:: .sc. :. u::.e: '2 -II: G. ToP L.CN61TUON.:O..L WI QTrj 3Y c_;' =.;.: 8:..:-' 'S : 21 u -0 '23.0 vu = T =II.. I = .a=l.ooz.) 5 = II. 2 r. 11.9;o:. l11hl. \J,.d/Hu: .417 ae p ..... =-.oo1=. "'-1r / """ lk.' / vv ?,I IT CoUS.TFUL IHAI THE: 4'' EI"1!!>EO S.P!:C..I f'1 E.r-1 1-JIL..L.. A t...oAO OF 141r 1T CoE-!1, THe FAC.To!e oF s.AFE.T'"( L-JIL..L e,E, NO 5H F'!.. RE:INF. 16 g;:-oUifZE'Q oV" = + 2Soo(oou)(.411J] = 11.4\C. 11.9" DE'SI(:J'J t1ETt1oo-B [ '1f. 1.1 J : C..o. 2 l'lSIJ '> [ 1r::. = 58.!. PSI] :. -as-82


Foe SE:.I'JCI'-J(a FAILVItE I 5 EM5EQI"1l:.Nr Pu =2 3.e/" L ; 2'-4'' 2'!..&:'2.!.:!>) 9'-1(. Hu:: 't =" PLA.I N ; f. I t/'t."\ _/ I ... J:. H,.,,.. ,1\. r J = .(.:x... :...; :.OCO J/'4r::.Crzooo) = 4.4-" 1!..9 foFZ. ::<.E1NFo12C.E0 :. r.!c:tr-JF. Mu "' i 3> ."l I 1'. d-= II-1.:.-.!::::l 9" b-= 2'2-;-c.. : 2e'' A..,.= .4S :I'J1 II IO E1-12>!:0Me.'\JT Pu-= 1.3.f:;,,.._ L -= -z.'-o" ..A '2..3.8("2.k 1)!'-,-,..,-4 1"=>.9 Pol?. PLAt N :. v-II OTH ;;;.,-c.; Ll-:.t: ToP LCN61n.JOI NA '&rC.E.L. _/ r::--\r:zCQCtl"lll 1._ "d:Jr1,, ,(Qa,.S,J ";ooo JL tZ. .J/]: 7.5 "15.4 .: iC?aNF. Fol2. N F.::lec=o c.oi'..IC.e.E:TE: : Mu = c .,. II" 'a = u.. +-(. :. ; ?.." A) r, 4.2, g..'"( LisE: z.-;:::C# ToP t...oNC:oiTUOor-JAL 83


FORMWORK CALCULATIONS Source: William T. Fuller, "The Development of Bond and Anchorage on L-Shaped Anchor Bolts in Tension" (Denver: University of Colorado at Denver, 1987), pp. B7-B8. JJ (j r 2. I Go(., "'-= Hf M = 2c..:, 1/ 3 II:, wr ,A.PA 1 < 7 DUIZATIOIJ f,,. 14-3o(I.ZS.)-: = 44 i785 = ,111 t --cao = +r t,C..I w : fz.(ISoJ ... :. = 141 p,_,. r-1 =-z.o.e"' v e,e.s."" '2o.eCIZJ i 11B5 ".14 IIJ. 'o 4+ .., z..o1 t'' .... t.l) = 0::: IIC.. F'!.F ,_,. M,. zo.1S. v =-a:. I" LJ5E '2 APA R....,ic:Q SHEATH!f\JG. eXT. 3!./IC,. $C. PA12.At..'-Et.. To rACe G.i<.AI N. 84


710 : S8 "?10 : (."1>'"0\)(00::0.LQ/ -= ""' Iii 2. L ' (L"J''C)(.l"!;S ./c:i ? 1St:! b :: S'l ... ".1 c_got) .J l<;d I b'5 ? 1'1. ... Cd L''i :. "'j-( 't '.79"Sb .._Qol = =" :!1-lg-gb -=H :d L'9S.: = ri : S .,)(1 .1.09 ':!?;JTi: "3 +i..L 0 N 'v' N"2l3tiUl OS -zjO ........ f ;;-;,n;!:loc;. ),. s:a 1 :tad c;. ;;+u. z:j 0.::1 <;;t 01'1"1 c;.t ON c;J '?I f-\.L Nl """''-'.l'f"=3 : ;.lOf'l


....t q->( 3 .} -.;t $ -$ c;:) $ _, ,. :J: w ::r

Ft 111.-I WI 'l 1 /1"' 41 k: i I 11 ,_ __ e ______ e_ __J. t O:,ECiiON C C. Figure B-2. Test Frame Sections and Details 87


1'-o'' D-D Z'' '2.'' zw T T ..;. .... ---vv E-E 88 V;'' G?'' __ _;:__ __ '2'' '2'' 'l. I"'"""' '<.\ ..---1---1-----. +0 TYPICAL.. ?1-tl ( 4 i'OTAL..) l-OO?E: t-1AT:=a.IA!,_ I, 4 1?/e,'' Q AU.. e,ol ."TO:, -1.-J I t !:NO '2. 4. l( "'1;4-u A. 30'1 i? H/ !!:7 d;' x A?01 NUi? a Figure B-3. Test Frame Sections and Details

PAGE 100

41 ( 4-SPEC! .13<:> s '2. 5 L e!.AS:' = [2(3) +z(z.o)] s 83 Sf" G EM (c IC..1 C.Y. C.i5 3ASC 3'-o'' x2'-o -= c;,,o '5:F SIDE:S rzLZ(3) U?..:))]= l.SOSF 2L.A-Y. I oro 3ASE 3'-4-,. A 11-411 = 7 .S SF ia.4 12" NEEDED) c.Y. 22'30 aa.::.e: d' X ?;,1 0' = I 'Z .o s;: fz(z)[4-+;.o}t7,5 SF f'----(d9' :J-o" 4'-otl Figure B-4. Size of Concrete Specimens Source: William T. Fuller, "The Development of Bond and Anchorage on L-Shaped Anchor Bolts in Tension" (Denver: University of Colorado at Denver, 1987), p. B2. 89

PAGE 101

.i1 e r_; Fr--1SeOMeiJT;S (lz ToTAL J .. >< X .A I;( 1 :>< 1}. 0 I -N r '1. >< ToP VI f:\..l 11-dl Figure B-5. Formwork Details Source: William T. Fuller, "The Development of Bond and Anchorage on L-Shaped Anchor Bolts in Tension" (Denver: University of Colorado at Denver, 1987), pp. B9-Bll. 90

PAGE 102

>< lA r.J ,-ry >.:: 16 >c: .., v >< ,00 .... -.. = (<;nt-U ... 9.J.N3Hct3
PAGE 103

92 IOd e..x "' .... 6) 2 f'\-"1'\oolccO e.,... :.a II IO /' !,. ;-,4-U!:. e e.<.. ?:x 4-. j.S b)@ '2d Z)(4 1 10 2:c.ot I, :) c)cu.-Jct+i:'Q l Fore! I :c C..'=o 1 ;:.A.. I! NO I x 4::. 1 2 I!A. et.JO ----...... AL.SO, Ft Q ToP oF c.::ut!NERS. I I ( I II PL., 0 4-0l"& 4-o !.JOOO ;>< I I ,.. I I I :"-. I I I I I I I I I I I I I I I I I I I '' I I I I 3-5 I I I I I I i 11t, u A... YWoc I I I I I Bo-nbM I I I I I I I I I I I I I I I I I _I I I I N I I I I I I I I I I I I I I I I I I I I I >< I ;::o-c:;: ToP VI 1?\.J 2,;w..4 A. BoL-T' TE:t1PtAro( t-Jor Aeove.) [ _I I I T-(1"-CAL.. '510e. V'l Figure B-5 (continued)

PAGE 104


PAGE 105

CONTENTS CALCULATION OF EMBEDMENT LENGTH REQUIRED TO INSURE THAT CONCRETE FAILURE DOES NOT CONTROL........................ 95 DESIGN COMPARISON............................... 96 TABLES Table C-1. Comparison of Pull-out Test Results to Selected Code Requirements .......... 98 94

PAGE 106

CALCULATION OF EMBEDMENT LENGTH REQUIRED TO INSURE THAT CONCRETE FAILURE DOES NOT CONTROL Upper bound steel strength: Ps, upper bound = (Ab) (Fult> Design tensile strength of concrete: (Q)c)(Pn) = (Q)c)(Pc) = = (Q)c) (IT) (le)2(4) To insure non-concrete failure: (Q)c) (le)2(4) (Fult> Req'd le = (Fult)/[(Q)c) (IT) (4) For 1/2" diameter bolts with Q)c = 1, Fult = 58 ksi and f'c = 3000 psi: Req'd le = 4.07" For 1/2" diameter bolts with Q)c = 1, Fult = 65.95 ksi and f'c = 4306 psi: Req'd le = 3.96" For 1/2" diameter bolts with Q)c = 1, Fult = 65.95 ksi and f'c = 3000 psi: Req'd le = 4.34" 95

PAGE 107

DESIGN COMPARISONS The Uniform Building Code (3) gives an allowable load of 0.5 kips for 3/8" diameter bolts and 0.95 kips for 1/2" diameter bolts. These allowable loads are conservative and do not account for embedment length of the bolt. In ACI 318-63 (11), ultimate bond stress is given as uu = 1/2(9.5) and where f'c is given in kips per square inch (ksi) and the diameter, d, is given in inches. For 3/8" diameter and 1/2" diameter bolts, this equation gives 0.831 ksi and 0.623 ksi respectively for an f'c of 4.306 ksi. However, ACI 318-63 allows an upper limit of 0.250 ksi for the ultimate bond stress. If no strength is attributed to the hook (similar to the calculations of Kharod (10)), then the ultimate capacity of the anchor bolt is given by Pu = uu(TI) (d) (le) = 0.250(TI) (d) (le) where d (diameter) and le (embedment length) are given in inches. These provisions attribute all anchor bolt strength to embedment length, ignoring any strength contributed by the hook. This is in direct contrast to the loads allowed by the UBC. 96

PAGE 108

Table C-1 shows a comparison between L-shaped anchor bolt pull-out test results and the UBC allowables. It also compares pull-out test results and the ultimate capacity as predicted by ACI 318-63 provisions for bond stress. 97

PAGE 109

Table C-1 Comparison of Pull-out Test Results to Selected Code Requirements 98 ============================================================ Mark Pull-out UBC Ratio of Ultimate Ratio of Number Test Allowable Pull-out Capacity Pull-out Ultimate Load Test by Test Load* Ultimate ACI Ultimate Load 318-63# Load to to UBC ACI 318-63 Allowable Ultimate (kips) (kips) Load** (kips) Capacity## ============================================================ 4Tl 4.301 8.6 1.178 3.7 4T2 3.474 6.9 1.178 2.9 6Tl 3.633 7.3 1. 767 2.1 6T2 4.562 9.1 1. 767 2.6 BTl 4.047 8.1 2.356 1.7 8T2 4.301 0.50 8.6 2.356 1.8 lOTl 4.367 8.7 2.945 1.5 10T2 3.761 7.5 2.945 1.3 6TX 4.986 10.0 6TK 4.953 9.9 4Hl 5.866 6.2 1. 571 3.7 4H2 6.061 6.4 1. 571 3.9 6Hl 6.094 6.4 2.356 2.6 6H2 7.202 7.6 2.356 3.1 8Hl 7.821 8.2 3.142 2.5 8H2 7.365 0.95 7.8 3.142 2. 3 lOHl 7.104 7.5 3.927 1.8 10H2 7.560 8.0 3.927 1.9 6HX 7.723 8.1 6HK 8.903 9.4 ============================================================ *From Table 4 ** Ultimate Pull-out Test LoadjUBC Allowable Load # From Calculations, p. 95 ## Ultimate Pull-out Test Load/ACI 318-63 Ultimate Capacity