1 / 47

Alternative Designs for Anchorage to Concrete

Alternative Designs for Anchorage to Concrete. Dave K. Adams, S.E., M.ASCE. dadams@burkett-wong.com. Dave K. Adams. Education: B.S. “Structural Engineering” from University of California, San Diego (1990) Experience:

chet
Download Presentation

Alternative Designs for Anchorage to Concrete

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Alternative Designs for Anchorage to Concrete Dave K. Adams, S.E., M.ASCE dadams@burkett-wong.com

  2. Dave K. Adams • Education: • B.S. “Structural Engineering” from University of California, San Diego (1990) • Experience: • Present: Structural project manager at Burkett & Wong Engineers (San Diego, CA) • 1990 – 2012: Structural engineer at Lane Engineers, Inc. (Tulare, CA) • 1989 – 1990: Engineer-in-training at Coneer Engineering (San Diego, CA) • Affiliations/Registrations: • California-licensed civil and structural engineer • Seismic safety assessment program evaluator with the California Office of Emergency Services • Member of SEAOC and ASCE • Subject matter expert (structural) for California Board of Registration for Professional Engineers, Land Surveyors and Geologists

  3. Learning Outcomes • Learn the requirements for anchorage to concrete found in the 2012 International Building Code and ASCE 7-10 • When does the engineer have to use ACI 318-11, Appendix D? • Understand the basic requirements for anchorage in ACI 318-11, Appendix D • Discover relevant failure modes for anchorage systems and practical considerations for evaluating alternative anchorages • Study examples of how alternative anchorage systems can be calculated to meet the intent of the building codes • What is the intent behind code provisions? • What is the intent of ACI 318, Appendix D?

  4. Codes Referenced in This Presentation • ASCE 7-10, “Minimum Design Loads for Buildings and Other Structures” (ASCE 7) • 2012 International Building Code (I.B.C.) • ACI 318-11, “Building Code Requirements for Structural Concrete” (ACI 318) • Miscellaneous

  5. Presentation Outline • Anchorage requirements found in the 2012 I.B.C. and ASCE 7-10 • Basic intent of ACI 318-11, Appendix D • Ductile yield mechanisms • Examples • Concluding remarks

  6. Anchorage Requirements: 2012 I.B.C. • “Anchorage of … walls and columns to foundations shall be provided to resist the uplift and sliding forces that result from the application of the prescribed loads.” (1604.8.1) • Fairly general in scope • Tension & shear loads • Load combinations (1605) • “Concrete or grout in foundations shall have a specified compressive strength not less than the largest applicable value indicated in Table 1808.8.1.” (1808.8.1) • Seismic Design Category A – C: 2500 psi • SDC D – F: 2500 psi (Groups R & U) or 3000 psi (all other structures)

  7. Anchorage Requirements: 2012 I.B.C. • Sections 1905.1.9 and 1905.1.10 contain miscellaneous revisions to Appendix D • Exemption of anchors to resist wall out-of-plane anchorage forces from the “ductile steel element” requirement • Design shear strength need not be computed for common installations of light-frame sill or track anchorage • Allowable stress design (1908): • Tension & shear per Table 1908.2 • Load combinations w/o seismic • Normal-weight concrete with headed bolts • Not for post-installed anchors

  8. Anchorage Requirements: 2012 I.B.C. • “The protrusion of the threaded ends (of anchor bolts) through the connected material shall fully engage the threads of the nuts, but shall not be greater than the length of the threads on the bolts.” (2204.2.1) • Yes, but what if they do NOT fully engage the threads? • It simply means that any deviations to this condition require an engineered analysis to confirm that the carried loads are transferred to the system. • “Fastener Design Manual” (Richard T. Barrett, 1990)

  9. Anchorage Requirements: 2012 I.B.C. • “Fasteners, including nuts and washers, in contact with preservative-treated wood shall be of hot-dipped zinc-coated galvanized steel, stainless steel, silicon bronze, or copper.” (2304.9.5.1) • Fasteners, including nuts and washers, for fire-retardant-treated wood used in exterior applications or wet or damp locations shall be of hot-dipped zinc-coated galvanized steel, stainless steel, silicon bronze, or copper.” (2304.9.5.3) • “Foundation plates or sills shall be bolted or anchored to the foundation with not less than ½” diameter steel bolts or approved anchors … embedded at least 7 inches (bolts) into concrete … and spaced not more than 6 feet apart.” (2308.6) • However, this is for “conventional construction”

  10. Anchorage Requirements: ASCE 7-10 • “Foundation and other elements used to provide overturning resistance at the base of cantilever column elements shall be designed to resist the seismic load effects including overstrength factor, Ω0.” (12.2.5.2) • In structures assigned to SDC C – F, collector elements and their connections including connections to vertical elements shall be designed to resist the maximum of …” (12.10.2.1) • Diaphragm forces from Section 12.10.1.1 • Overstrength load combinations from Section 12.4.3 (except for structures entirely braced by light-frame shear walls), Em

  11. Anchorage Requirements: ASCE 7-10 • Anchorage of structural walls (12.11): • Fp = 0.4SDSkaIEWp (Equ. 12.11-1) • Ka = amplification factor for diaphragm flexibility (Equ. 12.11-2) • “Diaphragm to structural wall anchorage using embedded straps shall be attached to, or hooked around, the reinforcing steel or otherwise terminated so as to effectively transfer forces to the reinforcing steel.” (12.11.2.2.5) • Anchorage of steel pipe piles to the pile cap is identified for Seismic Design Category C in Section 12.13.5.3 • Anchorage of piles to the pile cap in SDC D – F is identified in Section 12.13.6.5

  12. Anchorage Requirements: ASCE 7-10 • Anchorage of non-structural components that are permanently attached to structures: • Fp = 0.4apSDSIpWp[1+2(z/h)]/Rp (Equ. 13.3-1) • Rp shall not be greater than 6 (13.4.1) • Concurrent vertical force = ±0.2SDSWp (13.3.1) • “Component attachments shall be bolted, welded, or otherwise positively fastened without consideration of frictional resistance produced by the effects of gravity.” (13.4) • “Determination of force distribution of multiple attachments at one location shall take into account the stiffness and ductility of the component, component supports, attachments, and structure and the ability to redistribute loads to other attachments in the group.” (13.4.4) • Design using ACI 318, Appendix D is deemed to comply with this requirement

  13. Basic Intent of ACI 318-11, Appendix D • Design requirements for anchors in concrete under in-service conditions, not short-term handling or construction (D.2.1) • Strength, safety, stability • Typically understood as applicable to a system of anchorages where stability of a portion of a structure is compromised by anchor failure, or for safety-related system attachments (sprinkler piping, guardrails, etc.) • However … the body of the code does not make simplifying categorizations, therefore the strength design of anchorages (regardless of loading source) requires use of ACI 318, Appendix D unless the system is excluded from the provisions or not specifically identified

  14. Basic Intent of ACI 318-11, Appendix D • Included: Headed studs or bolts, hooked bolts, post-installed expansion and undercut anchors, and adhesive anchors (D.2.3) • Excluded: Specialty inserts, through-bolts, multiple anchors connected to a single plate at the embedded end, grouted anchors, powder- or pneumatic-actuated nails or bolts, and reinforcement used as part of the embedment (D.2.2) • Excluded: High cycle fatigue loading or impact loading applications (D.2.4)

  15. Basic Intent of ACI 318-11, Appendix D • Excluded: Anchors in plastic hinge zones under seismic forces (D.3.3.2) • Excluded: Anchors installed within 8,000 psi concrete (drilled-in) or 10,000 psi concrete (cast-in-place) [D.3.7] • Excluded: Anchors where the spacing and/or edge distances are not achieved as described within Sections D.8.1 – D.8.7 • Section D.8.4 allows design calculations to be based on a smaller diameter bolt (yet still using the larger diameter bolt, subject to other requirements of the code) if that smaller diameter complies with distance restrictions • Typically, the minimum edge distance of anchor bolts must not be less than the typical concrete cover requirements for reinforcing bars from Section 7.7 (D.8.2).

  16. Basic Intent of ACI 318-11, Appendix D • How can we approach design of anchorages that are not specifically recognized within ACI 318, Appendix D? • Understand relevant anchor failure modes and whether those principles outlined in Appendix D apply to the alternate anchorage system • Table D.4.1.1 • Steel strength in tension (D.5.1) • Concrete break-out strength in tension (D.5.2) • Anchor pull-out strength in tension (D.5.3) • Concrete side face blow-out strength in tension (D.5.4) • Adhesive anchor bond strength in tension (D.5.5) • Steel strength in shear (D.6.1) • Concrete break-out strength in shear (D.6.2) • Concrete pry-out strength in shear (D.6.3)

  17. Basic Intent of ACI 318-11, Appendix D • How can we approach design of anchorages that are not specifically recognized within ACI 318, Appendix D? • Give consideration to the effect of cracked concrete on the alternative anchorage system • In SDC C – F, consideration of tensile capacity is required for cracked concrete unless it can be demonstrated through analysis that the concrete will remain uncracked (D.3.3.4.4) • Equations used for concrete break-out strength in tension and in shear are based on the assumption of cracked concrete (all types of applied loading), subject to modification for demonstrated uncracked concrete (D.5.2.6 & D.6.2.7)

  18. Basic Intent of ACI 318-11, Appendix D • How can we approach design of anchorages that are not specifically recognized within ACI 318, Appendix D? • Give consideration to the ductility of the anchorage system as a whole (anchors, attachment, element) • Brittle-type failures (shear, bond) do not redistribute anchor forces nearly as well as yielding of ductile steel elements • In SDC C – F, concrete failure mode strengths for tension loads are to be greater than the anchor steel strength [D.3.3.4.3(a)], which will result in a ductile governing failure mode • Steel anchors should satisfy the requirements as “ductile” steels, which have a tensile test elongation of at least 14% and a reduction in area of at least 30% (D.1)

  19. Basic Intent of ACI 318-11, Appendix D • How can we approach design of anchorages that are not specifically recognized within ACI 318, Appendix D? • Give consideration to the transmission of applied forces (tensile and shear) to a group of anchors based on their relative stiffness characteristics • ACI 318 takes this into account by delegating design equations to the most highly stressed anchor (Table D.4.1.1) • Consider eccentricity of the applied load • Consider torsional effects due to the applied load • Consider the shear force applied to a row of anchors located farthest from the edge (D.6.2.1)

  20. Basic Intent of ACI 318-11, Appendix D • How can we approach design of anchorages that are not specifically recognized within ACI 318, Appendix D? • Strength reduction factors can be determined from Section 9.3 and applied to the system according to the mechanism under consideration • Where applicable, the bearing strength of concrete can be evaluated using Section 10.14 • Shear strength of concrete and included reinforcement can be evaluated using the provisions of Chapter 11 • Modes of shear-friction can be studied using Section 11.6.4 • The effect of reinforcement or anchorages to resist eccentric loads similar to the geometrical arrangement of a corbel can be evaluated using the provisions of Section 11.8 • Developing the strength of reinforcing bars can be used as an effective tool in alternative anchorages, using the provisions of Chapter 12 and the basic stipulations of Sections D.5.2.9 and D.6.2.9

  21. Ductile Yield Mechanisms • ACI 318 requires consideration of the ductility of anchorage systems in SDC C – F, where the governing failure mode for tension loading is to be ductile yielding of the steel [D.3.3.4.3(a)] • However, ACI 318 allows consideration of the maximum tension or shear loading that can be transferred to the anchors through a ductile yielding mechanism in the attachment in flexure, shear, bearing, or a combination [D.3.3.4.3(b) & D.3.3.5.3(a)] • Considering material overstrength • Considering strain hardening • Considering the expected yield strength

  22. Ductile Yield Mechanisms • Strain hardening (also called work-hardening or cold-working) is the process of making a metal harder and stronger through plastic deformation. When a metal is plastically deformed, dislocations move and additional dislocations are generated. The more dislocations within a material, the more they will interact and become pinned or tangled. This will result in a decrease in the mobility of the dislocations and a strengthening of the material. • These mechanisms can be achieved by designing for the plastic moment capacity, Mp, based on the expected yield strength of a material

  23. Ductile Yield Mechanisms • Expected yield strength: • Section RD.3.3 of ACI 318 recommends a factor of 1.5 be applied to the specified yield strength of a material to arrive at the expected yield strength • Table A3.1 of AISC 341-10 (“Seismic Provisions for Structural Steel Buildings”) identifies the coefficient Ry for a variety of steels as a multiplier to change the specified Fy of a material to the expected Fy

  24. Example: Drag Connection • Design the anchorage of a steel drag roof beam to the side of a special reinforced concrete shear wall (the beam aligns parallel to the long axis of the wall) • We will develop the tension force into wall drag bars (called “anchor reinforcement” in Section D.5.2.9 of ACI 318) • This is also a bit different than the specifics of Appendix D because Section 12.10.2.1 of ASCE 7 requires an overstrength factor to be applied to the connection in Seismic Design Category C – F • There is also a vertical (shear) force applied to the system from the beam’s reaction • Assume the tension force and shear force are equally distributed to each bolt Plan View of a Section Through the Wall, Looking Down on the Drag Beam Connection

  25. Example: Drag Connection • Load Combination 5 (ASCE 7, Section 12.4.3.2): • (1.2 + 0.2SDS)D + Ω0QE + L + 0.2S • Say SDS = 0.45 (Seismic Design Cat. C) • Say QE = 20 kips, L = 0 (this is a roof beam), S = 0 (no snow load) • Say D = 6 kips • Ω0 = 2.5 (Table 12.2-1) • Applied strength-level seismic tension force, Nua = 2.5(20) = 50 kips • Applied strength-level vertical shear force, Vua = (1.2 + 0.09)(6) = 7.74 kips • Materials: • f’c = 3000 psi (Normal-weight) • Futa (ASTM A307, Grade A) = 60 ksi [“Ductile” per definitions in ACI 318, Appendix D, for use with φ in Section D.4.3(a)] • Fy = 60 ksi (ASTM A615 reinforcing bars)

  26. Example: Drag Connection • Steel strength in tension (D.5.1): • Nsa = Ase,Nfuta • Ase,N = 0.462 in2 for a single 7/8” diameter anchor bolt (effective tensile or shear area) • 4(0.462)(60 ksi) = 110.9 kips • φT = 0.75 [D.4.3(a)] • The anchor’s tensile strength is used in the equation because most anchor material does not exhibit a well-defined yield point

  27. Example: Drag Connection • Concrete breakout strength in tension(D.5.2): • Section D.5.2.9 explains that the design strength for “anchor reinforcement” as determined from Chapter 12 may be used in lieu of the breaking strength equations here • By fully developing the anchor tension force into the “anchor reinforcement”, we are setting up ductility for this failure mode (nominal capacity of this mode will be based on the strength of the bars in tension) • The ACI 318 committee recommends that the reinforcing bars to be used should be located not more than 0.5 times the effective depth of embedment of the anchor bolts from the bolt pattern centerline (RD.5.2.9)

  28. Example: Drag Connection • Concrete breakout strength in tension(D.5.2): • Bar tensile capacity = AbarsFyφ= 4(0.6013)(60 ksi)(0.90) = 129.9 kips • φT = 0.75 [RD.5.2.9] • Lap length of bars = “L” – 2” – [(24”-9”)(1/2) – 3”] = “L” – 6.5” • “L” is equivalent to hef of the anchor bolts as used in other equations in ACI 318 • Required anchor bolt embedment to develop full strength of bars = (FyΨtΨedb)/[20√(f’c)] per ACI 318, Section 12.2.2 • Ψt = 1.3 [12.2.4(a)], Ψe= 1.0 [12.2.4(b)] • Embed “L” = (60,000)(1.3)(1.0)(7/8”)/(20)(54.77) = 62.3” + 6.5” = 68.8” (less if the rebar is hooked near the end of the wall)

  29. Example: Drag Connection • Concrete pull-out strength in tension (D.5.3): • Npn = Ψc,PNp • Ψc,P = 1.0 (D.5.3.6, cracking may occur) • Np = 8Abrgf’c, Abrg is bearing area of a heavy hex head bolt against concrete in uplift (D.5.3.4) • Npn = (1.0)(8)(1.8496 – 0.6013)(4-bolts)(3 ksi) = 119.8 kips • φT = 0.70 [D.4.3(c)] • Concrete side-face blowout in tension (D.5.4): • Ca1 = closest edge distance = 7.5” • Tension is carried through by the rebar • This mode will not govern the design

  30. Example: Drag Connection • Steel strength in shear (D.6.1): • Vsa = Ase,Vfuta = 110.9 kips (same as Nsa) • φV = 0.65 [D.4.3(a)] • Concrete break-out strength in shear (D.6.2): • Vcbg = (Avc/Avco)(Ψec,VΨed,VΨc,VΨh,VVb) • Where the shear load is applied parallel to the concrete edge, Section D.6.2.1(c) requires use of the above equation (which is used for loads applied perpendicular to the edge), but allows the formula to be increased by 2 and Ψed,Vtaken to be 1.0 • Ψc,V= 1.2 (D.6.2.7, rebar near edge) • Ψec,V= 1.0 (D.6.2.5, no eccentricity)

  31. Example: Drag Connection • Concrete break-out strength in shear (D.6.2): • Vcbg = (Avc/Avco)(Ψec,VΨed,VΨc,VΨh,VVb) • The load-bearing length of an anchor for shear, le, is determined using Section D.6.2.2 • For anchors with a constant stiffness over the full embedded length, le = “L” = heff • However, le ≤ 8da = 8(7/8”) = 7”. • The member “thickness”, ha, in our case is the length of the wall, but there must be a practical limitation ACI 318, Fig. RD.6.2.1(b) ACI 318, Fig. RD.6.2.4

  32. Example: Drag Connection • Concrete break-out strength in shear (D.6.2): • Vcbg = (Avc/Avco)(Ψec,VΨed,VΨc,VΨh,VVb) • Using the principles outlined in Figures RD.6.2.1(b) and RD.6.2.4, it is reasonable to suggest that we can use ha = 1.5Ca1 = 1.5(7.5”) = 11.25” • Ψh,V= √(1.5Ca1/ha) = 1.0 (D.6.2.8) • Vb will be the smaller of Equation D-33 or D-34 • Vb = 7(le/da)0.2√(da)√(f’c)Ca11.5 = 11.17 kips (Equ. D-33) • Vb = 9√(f’c)Ca11.5 = 10.13 kips (Equ. D-34) • Equation D-34 governs! ACI 318, Fig. RD.6.2.1(b) ACI 318, Fig. RD.6.2.4

  33. Example: Drag Connection • Concrete break-out strength in shear (D.6.2): • Vcbg = (Avc/Avco)(Ψec,VΨed,VΨc,VΨh,VVb) • Avco is the maximum projected area for a single anchor that approximates the surface area of the full break-out cone or an anchor that is unaffected by the edge distance, spacing, or depth of the member • Avc approximates the full surface area of the break-out cone for a particular arrangement of anchors. This being the case, the number of anchors in a group is not included within the equation. • Avco = 4.5(Ca1)2 = 4.5(7.5)2 = 253.1 in2 • Avc = [2(1.5Ca1) + S]ha = [2(1.5)(7.5) + 9](1.5)(7.5) = 354.4 in2 • Vcbg = (354.4/253.1)(1.0)(1.0)(1.2)(1.0)(10.13)(2) = 34.0 kips • φV = 0.70

  34. Example: Drag Connection • Concrete pry-out strength in shear (D.6.3): • This mechanism will also be controlled by the tension capacity of the reinforcing bars used to anchor the system, therefore no additional calculations are necessary • Combined forces (D.7): • In Seismic Design Categories C – F, Section D.3.3.4.3 requires some form of ductility in the connection system (recall previous slides) • For our example, we are applying Em tensile forces, and thus comply with the option outlined in paragraph (d) • In Seismic Design Categories C – F, Section D.3.3.4.4 requires design tensile strengths for concrete failure modes to be multiplied by an additional factor of 0.75

  35. Example: Drag Connection • Combined forces (D.7): • Governing Nua/φNn = 50 kips / (0.75)(0.70)(119.8 kips) = 0.79 • 0.75(0.70)(119.8 kips) = 62.9 kips as a concrete failure mode strength governs over the steel failure mode strength of (0.75)(110.9 kips) = 83.2 kips • Governing Vua/φVn = 7.74 kips / (0.70)(34 kips) = 0.32 • Since both of these values are greater than 0.20, Equation D-42 applies: • Combined forces = 0.79 + 0.32 = 1.11 < 1.2 … O.K.!

  36. Example: Grout Bonded Concrete Anchor • Grout bonded concrete anchors are not addressed in Appendix D (D.2.2) • Polymer or cementitious grout is commonly used • Anchor bolts used may be threaded rods (with or without a nut and washer at the embedded end), headed bolts, or deformed reinforcing bars (with or without an end anchor) • Installed in a pre-drilled hole with a diameter 150-300% larger than the diameter of the fastener

  37. Example: Grout Bonded Concrete Anchor • Tensile failure mechanisms include (1) tensile failure of the bolt, (2) full depth concrete cone break-out, (3) bond failure at the grout-concrete interface with a shallow concrete cone failure, and (4) bond failure at the steel-grout interface with a shallow concrete cone failure for unheaded fasteners • Current industry practice is to define the bond failure strength using the uniform bond stress model, which requires consideration of the grout-steel and grout-concrete bond strength of a particular product

  38. Example: Grout Bonded Concrete Anchor • Example parameters: • Determine the capacity of a ¾” diameter ASTM A36 anchor rod with 12” effective embedment • Concrete 28-day compressive strength = f’c = 3000 psi • Say edge distance is not a concern • Check 1: Steel tensile strength • Nsteel = φAsFu, where As is effective cross-sectional area of the anchor and Fu is the tensile strength • φcan be defined using ACI 318-11, Section D.4.3 (0.75 for “ductile” steels and 0.65 for “brittle” steels) • As = 0.334 in2 (AISC “Manual of Steel Construction”, Table 7-17 (14th Ed.) • Fu = 58 ksi • Nsteel= 0.75(0.334)(58 ksi) = 14.5 kips

  39. Example: Grout Bonded Concrete Anchor • Check 2: Uniform bond strength • Nbond = φ(τ)(π)(di)heff • φcan be defined based on the understanding that bond failure is similar to shear-friction, as it involves slippage along an interface. For such a failure mode, Section 9.3.2.3 of ACI 318 calls for a value of 0.75. • A recommended value may also come from the manufacturer • direpresents either the diameter of the anchor or the diameter of the hole, in. • The bond strength needs to be checked between the steel-grout interface (using the anchor diameter) and the grout-concrete interface (using the hole diameter)

  40. Example: Grout Bonded Concrete Anchor • Check 2: Uniform bond strength • Nbond = φ(τ)(π)(di)heff • Τ is the characteristic bond stress of a particular product, typically with different values for the steel-grout interface and the grout-concrete interface • There may be a different set of values provided by the product manufacturer for indoor and outdoor installations, and adjustments may also be necessary due to temperature of service • Laboratory testing has shown that, for the most part, there is less variation in expected product results with polymer-based grouts than cementitious grouts • Characteristic values for the steel-grout interface: 1200 psi – 2400 psi • Characteristic values for the grout-concrete interface: 600 psi – 1200 psi • Numerous conditions will dictate a grout’s strength to be used in design, therefore it is critical to understand the basis of recommended values

  41. Example: Grout Bonded Concrete Anchor • Check 2: Uniform bond strength • Nbond = φ(τ)(π)(di)heff • For this example, let’s assume the grout-steel bond strength does not control. • di = diameter of the hole (use 2da) • Use a value of τ= 600 psi (grout-concrete surface, indoor, ambient temperature service) … this will be dictated by the product manufacturer • Nbond = 0.75(600 psi)(3.142)[2(3/4”)](12”) = 25.4 kips

  42. Example: Grout Bonded Concrete Anchor • Check 3: Concrete break-out strength • Nconcrete = φ(4)(Ac)√(f’c) • The characteristic value of φ in regions of potential cracking has been defined in earlier codes with a value of 0.65. It would be reasonable (and consistent) to also consider a value of 0.75 when supplementary reinforcement is present across the plane of the potential pull-out cone. • Ac = projected pull-out cone of concrete = π(heff)2 = 3.141(12”)2 = 452 in2 • Nconcrete = 0.65(4)(452)(54.77) = 64.4 kips • Steel governs the capacity (strength) at 14.5 kips

  43. Example: Partially-Threaded Nut on Anchor Bolt • Remember Section 2204.2.1 of the 2012 I.B.C.: • “The protrusion of the threaded ends (of anchor bolts) through the connected material shall fully engage the threads of the nuts, but shall not be greater than the length of the threads on the bolts.” (2204.2.1) • Pull-out load, P = (1/3)πdmFsL (“strength”) • “Fastener Design Manual”, Richard T. Barrett • The 1/3 value is somewhat empirical and allows for a mismatch between threads • dm = mean diameter of the threaded hole, in. (approximately equal to the pitch diameter)

  44. Example: Partially-Threaded Nut on Anchor Bolt • Pull-out load, P = (1/3)πdmFsL (“strength”) • Fs = Tensile strength of the weaker material (bolt or the tapped hole) • L = actual length of thread engagement, in. • For this example: • 5/8” diameter, ASTM A307 bolt • L = ½ the total height of the installed heavy hex nut = 5/16” (AISC “Manual of Steel Construction”, 14th Ed., Table 7-19) • dm = 0.576” (AISC “Manual”, Table 7-17) • Fs = 60 ksi • P = (1/3)(3.142)(0.576”)(60 ksi)(0.313”) = 11.3 kips (“strength”)

  45. Summary & Closing Remarks • ACI 318, Appendix D identifies design requirements for anchorages to concrete, but some types of anchorage are specifically excluded from the provisions (for various reasons) • The provisions within Appendix D may also be deemed overly-restrictive for certain types of structures or attachments • For example, perhaps the anchorage of simple non-building structures can be evaluated from a more simplistic point of view • The 2012 I.B.C. and ASCE 7-10 allow for different solutions that can be deemed to comply with the requirements of the code when justified by analysis and/or testing • From an engineering perspective, it is important to evaluate a broad range of design solutions to a given problem

  46. Final Questions?

  47. THANK YOU!!

More Related