PCI 6 th Edition

1. PCI 6th Edition Headed Concrete Anchors (HCA)

2. Presentation Outine • Research Background • Steel Capacity • Concrete Tension Capacity • Tension Example • Concrete Shear Capacity • Shear Example • Interaction Example

3. Background for Headed Concrete Anchor Design • Anchorage to concrete and the design of welded headed studs has undergone a significant transformation since the Fifth Edition of the Handbook. • “Concrete Capacity Design” (CCD) approach has been incorporated into ACI 318-02 Appendix D

4. Headed Concrete Anchor Design History • The shear capacity equations are based on PCI sponsored research • The Tension capacity equations are based on the ACI Appendix D equations only modified for cracking and common PCI variable names

5. Background forHeaded Concrete Anchor Design • PCI sponsored an extensive research project, conducted by Wiss, Janney, Elstner Associates, Inc., (WJE), to study design criteria of headed stud groups loaded in shear and the combined effects of shear and tension • Section D.4.2 of ACI 318-02 specifically permits alternate procedures, providing the test results met a 5% fractile criteria

6. Supplemental Reinforcement Appendix D, Commentary “… supplementary reinforcement in the direction of load, confining reinforcement, or both, can greatly enhance the strength and ductility of the anchor connection.” “Reinforcement oriented in the direction of load and proportioned to resist the total load within the breakout prism, and fully anchored on both side of the breakout planes, may be provided instead of calculating breakout capacity.”

7. HCA Design Principles • Performance based on the location of the stud relative to the member edges • Shear design capacity can be increased with confinement reinforcement • In tension, ductility can be provided by reinforcement that crosses the potential failure surfaces

8. HCA Design Principles • Designed to resist • Tension • Shear • Interaction of the two • The design equations are applicable to studs which are welded to steel plates or other structural members and embedded in unconfined concrete

9. HCA Design Principles • Where feasible, connection failure should be defined as yielding of the stud material • The groups strength is taken as the smaller of either the concrete or steel capacity • The minimum plate thickness to which studs are attached should be ½ the diameter of the stud • Thicker plates may be required for bending resistance or to ensure a more uniform load distribution to the attached studs

10. Stainless Steel Studs • Can be welded to either stainless steel or mild carbon steel • Fully annealed stainless steel studs are recommended when welding stainless steel studs to a mild carbon steel base metal • Annealed stud use has been shown to be imperative for stainless steel studs welded to carbon steel plates subject to repetitive or cyclic loads

11. Stud Dimensions • Table 6.5.1.2 • Page 6-12

12. Steel Capacity • Both Shear and Tension governed by same basic equation • Strength reduction factor is a function of shear or tension • The ultimate strength is based on Fut and not Fy

13. Steel Capacity fVs= fNs= f·n·Ase·fut Where f = steel strength reduction factor = 0.65 (shear) = 0.75 (tension) Vs= nominal shear strength steel capacity Ns= nominal tensile strength steel capacity n = number of headed studs in group Ase= nominal area of the headed stud shank fut= ultimate tensile strength of the stud steel

14. Material Properties • Adapted from AWS D1.1-02 • Table 6.5.1.1 page 6-11

15. Concrete Capacity • ACI 318-02, Appendix D, “Anchoring to Concrete” • Cover many types of anchors • In general results in more conservative designs than those shown in previous editions of this handbook

16. Cracked Concrete • ACI assumes concrete is cracked • PCI assumes concrete is cracked • All equations contain adjustment factors for cracked and un-cracked concrete • Typical un-cracked regions of members • Flexural compression zone • Column or other compression members • Typical precast concrete • Typical cracked regions of members • Flexural tension zones • Potential of cracks during handling

17. The 5% fractile • ACI 318-02, Section D.4.2 states, in part: “…The nominal strength shall be based on the 5 percent fractile of the basic individual anchor strength…” • Statistical concept that, simply stated, • if a design equation is based on tests, 5 percent of the tests are allowed to fall below expected Capacity 5% Failures Test strength

18. The 5% fractile • This allows us to say with 90 percent confidence that 95 percent of the test actual strengths exceed the equation thus derived • Determination of the coefficient κ, associated with the 5 percent fractile (κσ) • Based on sample population,n number of tests • x the sample mean • σ is the standard deviation of the sample set

19. The 5% fractile • Example values of κbased on sample size are: n= ∞ κ = 1.645 n= 40 κ = 2.010 n= 10 κ = 2.568

20. Strength Reduction Factor Function of supplied confinement reinforcement f = 0.75 with reinforcement f = 0.70 with out reinforcement

21. Notation Definitions • Edges • de1, de2, de3, de4 • Stud Layout • x1, x2, … • y1, y2, … • X, Y • Critical Dimensions • BED, SED

22. Concrete Tension Failure Modes • Design tensile strength is the minimum of the following modes: • Breakout fNcb: usually the most critical failure mode • Pullout fNph: function of bearing on the head of the stud • Side-Face blowout fNsb: studs cannot be closer to an edge than 40% the effective height of the studs

23. fNcb: Breakout fNph: Pullout fNsb: Side-Face blowout Concrete Tension Strength fTn = Minimum of

24. Concrete Breakout Strength Where: Ccrb = Cracked concrete factor, 1 uncracked, 0.8 Cracked AN= Projected surface area for a stud or group Yed,N =Modification for edge distance Cbs = Breakout strength coefficient

25. Effective Embedment Depth • hef= effective embedment depth • For headed studs welded to a plate flush with the surface, it is the nominal length less the head thickness, plus the plate thickness (if fully recessed), deducting the stud burnoff lost during the welding process about 1/8in.

26. Projected Surface Area, An • Based on 35o • AN - calculated, or empirical equations are provided in the PCI handbook • Critical edge distance is 1.5hef

27. No Edge Distance Restrictions • For a single stud, with de,min > 1.5hef

28. Side Edge Distance, Single Stud de1 < 1.5hef

29. Side Edge Distance, Two Studs de1 < 1.5hef

30. Side and Bottom Edge Distance, Multi Row and Columns de1 < 1.5hef de2< 1.5hef

31. Edge Distance Modification • Yed,N = modification for edge distance • de,min = minimum edge distance, top, bottom, and sides • PCI also provides tables to directly calculate fNcb, but Cbs , Ccrb, and Yed,N must still be determined for the in situ condition

32. Determine Breakout Strength, fNcb • The PCI handbook provides a design guide to determine the breakout area

33. Determine Breakout Strength, fNcb • First find the edge condition that corresponds to the design condition

34. Eccentrically Loaded • When the load application cannot be logically assumed concentric. Where: e′N = eccentricity of the tensile force relative to the center of the stud group e′N ≤ s/2

35. Pullout Strength • Nominal pullout strength Where Abrg= bearing area of the stud head = area of the head – area of the shank Ccrp= cracking coefficient (pullout) = 1.0 uncracked = 0.7 cracked

36. Side-Face Blowout Strength • For a single headed stud located close to an edge (de1< 0.4hef) Where Nsb= Nominal side-face blowout strength de1= Distance to closest edge Abrg= Bearing area of head

37. Side-Face Blowout Strength • If the single headed stud is located at a perpendicular distance, de2, less then 3de1 from an edge, Nsb, is multiplied by: Where:

38. Side-Face Blowout • For multiple headed anchors located close to an edge (de1< 0.4hef) Where so= spacing of the outer anchors along the edge in the group Nsb= nominal side-face blowout strength for a single anchor previously defined

39. Example: Stud Group Tension Given: A flush-mounted base plate with four headed studs embedded in a corner of a 24 in. thick foundation slab (4) ¾ in. f headed studs welded to ½ in thick plate Nominal stud length = 8 in f′c = 4000 psi (normal weight concrete) fy = 60,000 psi

40. Example: Stud Group Tension Problem: Determine the design tension strength of the stud group

41. Solution Steps Step 1 – Determine effective depth Step 2 – Check for edge effect Step 3 – Check concrete strength of stud group Step 4 – Check steel strength of stud group Step 5 – Determine tension capacity Step 6 – Check confinement steel

42. Step 1 – Effective Depth

43. Step 2 – Check for Edge Effect Design aid, Case 4 X = 16 in. Y = 8 in. de1 = 4 in. de3 = 6 in. de1 and de3 > 1.5hef = 12 in. Edge effects apply de,min = 4 in.

44. Step 2 – Edge Factor

45. Step 3 – Breakout Strength

46. Step 3 – Pullout Strength

47. Step 3 – Side-Face Blowout Strength de,min = 4 in. > 0.4hef = 4 in. > 0.4(8) = 3.2 in. Therefore, it is not critical

48. Step 4 – Steel Strength

49. Step 5 – Tension Capacity The controlling tension capacity for the stud group is Breakout Strength

50. Step 6 – Check Confinement Steel • Crack plane area = 4 in. x 8 in. = 32 in.2