Anchoring To Concrete - PDHonline
PDHonline Course S293 (6 PDH)Anchoring To ConcreteInstructor: Marvin Liebler, P.E.2016PDH Online PDH Center5272 Meadow Estates DriveFairfax, VA 22030-6658Phone & Fax: 703-988-0088www.PDHonline.orgwww.PDHcenter.comAn Approved Continuing Education Provider
www.PDHcenter.comPDHonline Course S293www.PDHonline.orgINTRODUCTION-----------A concrete anchor is a steel shaft either cast intoconcrete at placement or post-installed after the concretehas hardened.Cast-in anchors are threaded shafts with a buried endtermination of a hex head, threaded nut, or 90 (L-) or 180 (J-) hook, or headed (non-threaded) studswelded to a surface plate.Post-installed anchors include adhesive and expansiontypes. Two of the expansion types are torque-controlled,where expansion is controlled by torque on the bolt, ordisplacement-controlled, where a plug or sleeve is impactedand the expansion is controlled by the length of travel ofthe plug or sleeve.The anchors are designed to transfer the design loads fromthe superstructure to the foundation. In many cases, thistransfer is, either from steel column base plates to thefoundation, or from precast concrete members to thefoundation.An example of the connection of cast-in anchor to precastis shown in the following photograph, in the constructionof a salt storage building in Western New York. The largecast-in bolts transfer the tensile force caused by themoment generated by the horizontal force of the soilagainst the precast walls to the foundation.Shear is not transferred by the bolts, but by bearingbetween the buttress and foundation, due to the socketingof the buttress into the foundation.The footings, anchors, buttresses, wall panels, and lintelscomprising the complete foundation system for the saltstorage building with arch roof under construction weredesigned, fabricated, and erected by the precast firm“New Eagle Silo” of Arcade, New York. 2016 Marvin LieblerPage 2 of 72
www.PDHcenter.comThis PDHonline Course S293www.PDHonline.orgpaper describes:Anchor MaterialsConcrete CrackingGeneral RequirementsBolt BendingAnchor Tension ReinforcementAnchor Shear ReinforcementDescription of Failure ModesBase Plates and Anchor BoltsExamplesAppendix 1 – Definitions of TermsAppendix 2 – Citations ListAppendix 3 – Anc programThe basic reference is “Building Code Requirements forStructural Concrete (ACI 318-11) and Commentary,Appendix D”, Reference 1. Citations not noted with a sourcerefer to this specification. 2016 Marvin LieblerPage 3 of 72
www.PDHcenter.comPDHonline Course S293www.PDHonline.orgANCHOR MATERIALS--------------------The most common steel material for cast-in anchors is ASTMF1554, Grade 36. This is generally less expensive and morereadily available than other types. It is also desirablewhere a ductile failure rather than a concrete failure isrequired, and the least concrete distance restrictions arepresent with its low yield and ultimate strengths.Cast-in anchors are of three (3) types, headed bolts,headed studs, and hooked bolts, installed in place prior toconcrete placement. Cast-in gives greater control, butless flexibilityHeaded bolts are cylindrical threaded steel barsterminated in the concrete either by an integral head ornut, either of which may include a washer or plate. Careshould be taken in the selection of a washer or plate, ifused, because the stresses may exceed those allowable onconventional washers.Headed studs are cylindrical steel bars (normallyunthreaded) with an embedded head and welded to a steelplate at the surface. They are usually used to transfershear loads between steel and concrete, typically incomposite beams.Hooked bolts refer to cylindrical steel bars with threadedconnections at the ends, and possibly throughout. They aredefined by the embedded end, either “L” (90 ) or“J” (180 ). Allowable bend diameters are not specified byACI 318-11, only bent rebars. Appendix D does specifydistance from the inner surface to the end of the hook.In projects requiring ductility, i.e., the lowest failureload is tension in the steel anchor, the concrete pulloutstrength must be greater than or equal to the tensilecapacity of the steel anchor. This is, in general, notpossible with hooked bolts as shown in the discussion ofpullout strength in the pullout capacity discussion below. 2016 Marvin LieblerPage 4 of 72
www.PDHcenter.comPDHonline Course S293www.PDHonline.orgPost-installed anchors material and design properties areobtained from ICC-ES Evaluation Reports such as Reference 2for expansion anchors and Reference 3 for adhesive anchors.Cast-in headed anchors refer to headed steel bars welded toa base plate. They are usually used to transfer shear loadsbetween steel and concrete, typically in composite beams.See also the discussion on pullout strength for furtherdescription.Post-installed gives greater flexibility, but less control.CONCRETE CRACKING----------------Anchor design for the concrete breakout, pullout, bondstrength, and pryout failure modes depend upon judgment ofcracked versus uncracked concrete in computations.Courses and control of cracking are discussed in Ref. 4as follows : Plastic Shrinkage CrackingThis is due to the evaporation of water near thesurface, shrinking the surface layer but restrained byinner concrete, developing tensile stresses in the warsurface layer. This results in a differential volumechange. To slow down the evaporation, fog nozzles,plastic sheeting, windbreaks, and sun shades may beused. Plastic Shrinkage Settlement CrackingDuring the consolidation phase, the plastic concretemay be restrained by rebars, (cracking increases withrebar size), slump (increasing slump equals increasingcracking), and cover (increases with decreasingcover). Hardened Concrete Drying ShrinkageThis is caused by volume change as the concreteshrinks, but is restrained. This may be reduced bycontraction joints, proper detailing (especially nore-entrant corners), or shrinkage-compensatingconcrete. See Reference 5 for further details. 2016 Marvin LieblerPage 5 of 72
www.PDHcenter.comPDHonline Course S293www.PDHonline.org Thermal stressesConcrete has a temperature coefficient of expansion ofapproximately 5.5*10 (-06). Consider two surfaces incontact with a temperature differential of 25 F.Consider one surface completely restrained,fc’ 4000psipressure strain*E 137.5*10(-6)*57000*fc’ (1/2)pressure 496 psiNow ft modulus of rupture 7.5*fc’(1/2)ft 474 psi 496 psi, n.g. w maximum crack width 0.10*fs*(dc*A) (1/3)*10 (-3)where w in inches, fs in steel stress (ksi), dc cover in inches and A area of concrete symmetricwith rebars divided by the number of rebars. Post-installed anchors are required to perform well bytests with a crack width of 0.012 inch.GENERAL REQUIREMENTS-----------------CONCRETE SPLITTING The rules in Section D.8 refer to spacing, edge distances,and hef (effective embedment depth). They apply to allfailure modes and should be addressed before starting thedesign.QuantityUntorqued Cast-inTorqued --------------Minimum center 4*da6*dacenter spacingMiniumum edgecover6*dadistance 2016 Marvin LieblerPage 6 of 72
www.PDHcenter.comPDHonline Course S293QuantityAdhesiveAnchor-------------Min. ctr-ctrspacingMin. edge (1)distancehef max. isplacementControlled--------6*da10*da (2/3)*ha (2/3)*ha ha-4 ha-4cac,min2*hef4*hef4*hefcac critical edge distance controlled by concretebreakout or bond. Unless determined by test to ACI 355.2(mechanical anchors) or ACI 355.4 (post-installed adhesiveanchors), use the following values:adhesive anchors – 2.0*hefundercut anchors - 2.5*heftorque-controlled expansion anchors - 4.0*hefdisplacement-controlled expansion anchors - 4.0*hefda anchor diameter, in.ha member depth, in.(1) If edge distance less than that shown, substitute da’for da that meets the requirements of minimum centercenter spacing and edge distance. Forces are limitedto an anchor with a diameter of da’.(2) Values here may be reduced if tests according to thedefinition of cac are performed.GROUP EFFECTS (D.3.1.1)Group effects must be considered if anchor spacing is lessless than any of the following values:Failure Concrete breakout in tension3*hefBond strength in tension2*cnaConcrete breakout in shear3*ca1cna projects distance from the center of an anchor shafton one side of the anchor to develop the full bondstrength of an adhesive anchor 2016 Marvin LieblerPage 7 of 72
www.PDHcenter.comPDHonline Course S293www.PDHonline.orgca1 distance from the anchor center to the concrete edgein one direction, in. If shear is applied to theanchor, ca1 is taken in the direction of appliedshear. If tension is applied to the anchor, ca1 isthe minimum edge distance.OTHER (D.2 – D.4)Loads with high fatigue or impact not covered (D.2.4)By Appendix D.Anchors and anchor groups can be designed by (D.3.1)elastic analysis. Plastic analysis may be usedif nominal strength is controlled by ductile steel.Appendix D does not apply to the design of anchors inplastic hinge zones of concrete structures underearthquake loads. These zones are defined as extendedfrom twice the member depth from any column or beamface. These zones also include any other section whereyielding of reinforcement is likely to occur due tolateral displacements.(D.3.3.2)If anchors must be located in these plastic hingezones, they should be designed so that the anchorforces are directly transferred to anchorreinforcement that carries these anchor forces intothe member beyond the anchor region.(RD.3.3.2)Post-installed anchors must meet ACI 355.2 orAQCI 355-4(D3.3.3)Anchors in Seismic Design Category C, D, E, and Fstructures must satisfy all the non-seismicrequirements of Appendix D, as well as additionalrequirements:Tensile Loading(D.3.3.4)Shear Loading(D.3.3.5)Modification factor λa for lightweight(D.3.6)concrete :Cast-in concrete failureλa 1.0Expansion adhesive anchor concrete failure λa 0.8Adhesive anchor bond failureλa 0.6fc’ 10000 psi for cast-in anchors(D.3.7)fc’ 8000 psi for post-installed anchorsFor steel and pullout failure loads, the(RD.4.11) 2016 Marvin LieblerPage 8 of 72
www.PDHcenter.com PDHonline Course S293www.PDHonline.orghighly stressed anchor should be checked.For concrete breakout, the anchors should bechecked as a group.Maximum anchor diameter 4 inches.(D.4.2.2)Adhesive anchor embedment depths must be(D.4.2.3)limited to 4*da hef 20*hefStrength Reduction ϕ factors(D.4.3)Anchors governed by strength of ductilesteel element – tension 0.75 shear 0.65Anchors governed by concrete breakout, sideface blowout, pullout or pryout strengths:LoadElementConditionCategoryϕ----- ------------ ------ShearTension----cast-in headedstuds bolts hooked bolts,post-installedanchorsABAB------ ------------A1A2A3B1B2B3Condition A – supplementary reinforcement ispresent except for pullout andpryoutCondition B – no supplementary reinforcementAnd for pullout and pryoutCategory – applies to post-installed anchorsCategory SensitivityReliability-------- here sensitivity refers to sensitivity toinstallation. 2016 Marvin e 9 of 72
www.PDHcenter.comPDHonline Course S293www.PDHonline.orgBOLT BENDING-----------ACI 318-11 defines stretch length as the length ofanchor extending beyond the concrete, subject totensile load. Code Section D.3.3.4.3 gives four (4)options for anchors and their attachments tostructures in Seismic Design Categories C,D,E and F.Option (a), part 3, says anchors shall transmittension loads by a ductile steel element with astretch length of at least eighht (8) bar diameters.The following analysis is that given in Reference 10with the exception of Z, the plastic modulus.zn portion of moment arm above concrete , in. 0 if clamped at concrete surface by nut andwasher (required for mechanical anchors) 0.5 if not clamped at concrete surfaced0 bolt diameter, in.L stretch length z n*d0, in.Z D 3/12 in. 3Mso bending moment to cause rupture 1.2*futa*ZNsa nominal tensile strength of anchorNua factored load tensionMs resultant flexural resistance of anchorMs Mso*(1-Nua/ϕNsa)α adjustment factor 1 α 2Mv factored bending moment due to factored shearMv Vua*L, Ms if not true, redesign.Vadd term added to factored load shear (Vua) α*Ms/LCheck the interaction of all the governing failureloads with the addition of VaddThe following page shows examples of stretch lengthsand stretch connection. 2016 Marvin LieblerPage 10 of 72
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www.PDHcenter.comPDHonline Course S293www.PDHonline.orgTENSION REINFORCEMENT--------------------As stated in Section D.5.2.9 anchor reinforcementstrength may be used instead of concrete breakoutstrength (ϕNcbg) if the following conditions are met: Anchor reinforcement must be developed on bothsides of the breakout surface. ϕ 0.75 Reinforcement should be placed as close to thesurface as possible. Reinforcement consists of stirrups, ties, orhairpins. Reinforcement mus be less than 0.5*hef from theanchor centerline. Research only done with #5 bars and smaller. It is good for the anchor reinforcement toenclose the surface reinforcement It is generally limited to cast-in anchors.There are three types of reinforcement given by theCode, namely hooked end, headed ends, and straightbars. Only the third is discussed here.Conservatively, for normalweight concrete, no coating,and # 6 bar or smaller,ld fy*ψt*ψe*db/25*λ*fc1 (1/2) whereld development length (in.)ψt 1.3 for 12 in. Cast below bars1.0 elsewhereψe 1.5 for epoxy-coated bars with cover less than3*db and/or clear spacing 6*db1.2 for other epoxy-ccoated bars1.0 for no epoxy coating or galvanizedλ less than or e qual to 0.75 for lightweightconcreteλ 1.0 for normalweight concreteTwo perpendicular sections are shown on the followingpage. 2016 Marvin LieblerPage 12 of 72
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www.PDHcenter.comPDHonline Course S293www.PDHonline.orgSHEAR REINFORCEMENT------------------Section D.6.2.9 states the reinforcement should bedeveloped on each side of the breakout surface or enclosethe anchor and is developed beyond the breakout surface.If either one of these is true, the strength of thereinforcement may be used instead of ϕVn, the reducedconcrete shear strength. The commentary to Section D.6.2.9gives the following details to be followed: Reinforcement should be properly anchored by hairpins(first page following), hooked bars (second pagefollowing), or by stirrups or ties. The hairpins should be in contact with the anchor, andas close to the surface as possible. Research on hairpins was performed on #5 or smallerbards, larger bars with increased bend radii havedecreased effectiveness. Reinforcement can also consist of stirrups and tiesenclosing the edge reinforcement, and must be placedas close to the anchors as possible. Thisreinforcement must be spaced less than both 0.5*ca1and 0.3*ca2 from the anchor centerline. It must bedeveoped on both sides of the breakout surface. Since the anchor reinforcement is below the source ofthe shear, the force in the anchor will be larger thanthe shear force. This may be seen by taking the sum ofthe moments of the shear and anchor forces about apoint inward of the anchor force. Because the momentarm is shorter for the anchor force, it will begreater for balance of moments. A third force, in thesame direction as the applied shear, must also bepresent for balance of forces. ϕ 0.75 for shear models 2016 Marvin LieblerPage 14 of 72
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www.PDHcenter.comPDHonline Course S293www.PDHonline.orgACI FAILURE MODES----------------------This section provides a description of each of theeight (8) failure modes set forth in Appendix D, namelyfour (4) tensile, one (1) bonding, and three (3) shear.The required definitions and citations are shown inAppendices 1 and 2. 2016 Marvin LieblerPage 17 of 72
www.PDHcenter.com1.PDHonline Course S293www.PDHonline.orgSTEEL STRENGTH OF ANCHOR IN TENSIONThe strength of the anchor itself in tension is afunction of net anchor diameter, ultimate strength,and capacity reduction factor (ϕ). The loads, in turn,are increased by a load factor, depending on the mostrestrictive load combination specified by thegoverning code. This is the strength design method.If the ductile failure is requested (material hasminimum 14% increase in length and minimum 30%reduction in area at tensile failure), all the othertensile failure modes must have higher allowablestrengths so that steel tensile failure governs.A material commonly used for anchor bolts is ASTMF1554, Grade 36. This specification covers hooked,headed, threaded and nutted rods.Appendix D requiresNsa Ase,n*futa whereNsa nominal strength of single anchor, lbfAse,n bolt dia., 0.7854*(D-0.9743/n) 2D is nominal diameter, ichesn is number of thread turns per inchfuta specified tensile stress, psiϕ 0.75Yield stress is 36 ksi and ultimate stress varies from58 to 80 ksi. As noted in Reference 6, two types ofrods are used, threads formed by rolling or cutting.Both have the same roots, so that the root area usedby each in the AISC method (Reference 7) is notchanged.For thread forming by rolling, the rod initialdiameter is, for a nominal 1” diameter bolt, is0.9067”,while that of the rod for thread cutting is0.9755”. This leads to the following comparison: 2016 Marvin LieblerPage 18 of 72
www.PDHcenter.comPDHonline Course S293www.PDHonline.orgRolled ThreadQuantityCut Thread58 ksi Ultimate80 ksi Ultimate------------------ ----------------------------Π*(.9067) 2*futa/4 Π*d 2*futa/4Π*(.9755) 2*futa/437.499 kipNsa59.791 kip28.124 kipϕNsa44.843 kipAppendix D requires:Nsa .7854*(D-.9743/nt) 2*futa whereNsa nominal tensile capacity based on steel aloneD nominal anchor diameter 1 inchnt number of threads per inch, 8 for 1 in. dia.Nsa 35.133 kipϕNsa 0.75*35.133 26.350 kipTo ensure ductility for threads cut, rather thanrolled, for the highest ultimate strength, ϕN for theother capacities must exceed 44.843 kip, not 26.350kip, as it would be if the spread in rod sizes andultimate strengths is neglected. This, however, is notrequired by Appendix D.A second specification is for headed studs, i.e.,threadless headed rods fillet welded to a steel plate,is the AWS D1.1 Section 7 (Ref. 8). futa 65000 psiShank dia.(in.) Head dia.(in.) Head thk.(in.)--------------- -------------- /83/8101-5/81/2 2016 Marvin LieblerPage 19 of 72
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www.PDHcenter.com2.PDHonline Course S293www.PDHonline.orgCONCRETE BREAKOUT STRENGTH OF ANCHOR IN TENSIONThe sketch above shows the basic model for concretebreakout in tension, a brittle failure which occursbefore yielding of the anchor steel, if so designed.The basis of the design procedure is the ConcreteCapacity Design (CCD) method, introduced in the CodeBackground Paper shown as Reference 9. This methodassumes the shape of the fractured area is an invertedpyramid, as shown above, together with a plan view.The model used for basic breakout strength is onewhere ca1 ca2 ca3 ca4 1.5*hef, hef equaling embedmentdistance, and s1 s2 0. This means the failure planesare oriented at arctan(1.0*hef/1.5*hef) 33.7 .For example, assume hef 12 inches, then :Area
A concrete anchor is a steel shaft either cast into concrete at placement or post-installed after the concrete has hardened. Cast-in anchors are threaded shafts with a buried end termination of a hex head, threaded nut, or 90 (L-) or 180 (J-) hook, or headed (non-threaded) studs welded to a surface plate.
the unit), on Connexus Perimeter, this foot has four anchoring points. Total anchors per unit: Connexus Free 12, Connexus Perimeter 10. Six additional anchoring points are used for each Connexus Expansion unit, e.g. Perimeter (1) Expansion 16 anchoring points, Perimeter (2) Expansions 22 anchoring points, etc.
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Forensic Analysis of a Trampoline Peter Chen, P.E., CFEI, ACTAR 2015 PDH Online PDH Center 5272 Meadow Estates Drive Fairfax, VA 22030-6658 Phone & Fax: 703-988-0088 www.PDHonline.org www.PDHcenter.com . www.PDHcenter.com PDHonline Course G523 www.PDHonline.org 2014 Peter Chen Page 2 of 16 .
Aug 04, 2017 · – Attachment in Halfen anchoring bracket. – Weld or screw on the Halfen anchoring bracket at a right angle. – Slide the compact hanger into the Halfen anchoring bracket and secure it with safety screws. – Make sure that the compact hanger and Halfen anchoring bracket are correct
C-A-2016 2015 SIMPSON STRONG-TIE COMPANY INC. 167 Mechanical Anchors Simpson Strong-Tie Anchoring and Fastening Systems for Concrete and Masonry * See page 12 for an explanation of the load table icons. Wedge-All Design Information — Concrete Carbon-Steel Wedge-All Allowable Tension Loads in Normal-Weight Concrete in. (27.6 MPa) Concrete
in accordance with ASTM E488-96 and ASTM E1512-01 for its capability to resist static, dynamic, seismic and wind loads in uncracked concrete for both threaded rod and rebar. Anchoring threaded rods, bolts and rebar dowels into uncracked concrete Short and long term tensile anchoring, including wind,
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