1. GT STRUDL GT STRUDL Users Group 22 nd Annual Meeting & Training Seminar June 24, 2010 Practical Modeling Technique for Transfer Length Chris Carroll, Ph.D. Assistant Professor Department of Civil Engineering University of Louisiana at Lafayette

2. Overview Introduction Top-strand Effect Test Speciemens GT STRUDL Model Background Practical Modeling Technique for Transfer Length

3. Introduction Objective Develop a modeling technique for transfer length in finite element models of prestressed concrete members Practical Modeling Technique for Transfer Length

4. Background Development length (standard reinforcing steel) The length required to anchor the reinforcing to fully develop the stress in the reinforcing at the nominal moment capacity of the member (AASHTO) The length of embedment required to prevent slip between reinforcing and the surrounding concrete when that reinforcing is placed in tension (or compression) Practical Modeling Technique for Transfer Length

5. Background Required stress in steel Concrete Strength Location of the barCoating of the barSize of the barDiameter of the bar Cover and confinement Effect of lightweight concrete Required stress in steel Diameter of the bar Development length (standard reinforcing steel) Practical Modeling Technique for Transfer Length

6. Background Development Length The length required to anchor the strand to fully develop the stress in the strand at the nominal moment capacity of a member LtLt L fb f se f ps LdLd ACI AASHTO Practical Modeling Technique for Transfer Length

7. Background Transfer Length The bonded length of strand required to transfer the prestress force in the strand to the surrounding concrete L t = 50d b L t = 60d b LtLt f se ACI AASHTO Practical Modeling Technique for Transfer Length

8. Unconservative Background Transfer Length (Code Provisions) Unconservative Practical Modeling Technique for Transfer Length

9. Practical Modeling Technique for Transfer Length Background Top-strand Effect > 12” Deformed Bar Provisions exist for development length of deformed bars L d multiplied by 1.3 (ACI) and 1.4 (AASHTO) with > 12 inches of fresh concrete below the bar Provisions do not exist for the development or transfer length of prestressing strands

10. Practical Modeling Technique for Transfer Length Background Top-strand Effect a b a b

11. Practical Modeling Technique for Transfer Length Background Top-strand Effect –Is top-strand effect a factor of the amount of concrete beneath the strand? –New hypothesis: Top-strand effect may be a factor of the amount of concrete above the strand rather than the amount below or a combination thereof 12 ft Block ABlock B

12. Practical Modeling Technique for Transfer Length Test Speciemens T-beams 30 in. 4 in. 5 in. 24 in. 2 in. 8 in. Large 3 in. 19 in. 2 in. 4 in. 24 in. Medium 8 in. 24 in. 2 in. 17 in. 2 in. 4 in. Small 8 in. ½”  regular½”  special0.6” 

13. Practical Modeling Technique for Transfer Length Test Specimens 300 ksi 270 ksi NormalInverted A A B B Normal Inverted NormalInverted

14. Practical Modeling Technique for Transfer Length Test Specimens T-beams

15. Practical Modeling Technique for Transfer Length Test Specimens Top-strand blocks 12 ft Block ABlock B 24” 4” 2” 5” 2” 5” 2” 14” 4” A B C C D E F G H

16. Practical Modeling Technique for Transfer Length Test Specimens Top-strand blocks Single Strand Blocks Five Strand Blocks Three Strand Blocks

17. Practical Modeling Technique for Transfer Length Test Specimens Top-strand blocks

18. Practical Modeling Technique for Transfer Length Test Specimens Top-strand blocks

19. Practical Modeling Technique for Transfer Length Test Specimens Top-strand blocks

20. Practical Modeling Technique for Transfer Length Test Specimens Transfer Length 50 mm spacing 100 mm spacing

21. Practical Modeling Technique for Transfer Length Test Specimens Transfer Length 50 mm spacing 100 mm spacing ≈ 30,000 measurements

22. Practical Modeling Technique for Transfer Length Test Specimen Transfer Length

23. Practical Modeling Technique for Transfer Length Test Specimens Bond/Shear Failure

24. Practical Modeling Technique for Transfer Length Test Specimens Bond/Shear Failure

25. Practical Modeling Technique for Transfer Length Test Specimens Bond/Shear Failure

26. Practical Modeling Technique for Transfer Length Test Specimens Bond/Shear Failure

27. Practical Modeling Technique for Transfer Length Test Specimens Bond/Shear Failure

28. Practical Modeling Technique for Transfer Length Test Specimens Bond/Shear Failure

29. Practical Modeling Technique for Transfer Length Top-strand Effect Transfer Length Influence of Release Method Influence of Strand Strength Influence of Strand Diameter/Area Influence of Effective Prestress Influence of Concrete Strength Influence of Time Influence of Casting Orientation Proposed Transfer Length Equation

30. Practical Modeling Technique for Transfer Length Top-strand Effect Transfer Length (Influence of Casting Orientation)

31. Practical Modeling Technique for Transfer Length Top-strand Effect Transfer Length (Influence of Casting Orientation) Amount of Concrete Below Amount of Concrete Above

32. Practical Modeling Technique for Transfer Length Top-strand Effect Transfer Length (Influence of Casting Orientation) Same Amount of Concrete Below Same Amount of Concrete Above

33. Practical Modeling Technique for Transfer Length Amount of Concrete Above Amount of Concrete Below Top-strand Effect Transfer Length (Influence of Casting Orientation)

34. Practical Modeling Technique for Transfer Length Top-strand Effect Transfer Length (Proposed Transfer Length Eq.)

35. Practical Modeling Technique for Transfer Length Top-strand Effect Transfer Length (Proposed Transfer Length Eq.)

36. Practical Modeling Technique for Transfer Length Top-strand Effect Transfer Length (Proposed Transfer Length Eq.)

37. Practical Modeling Technique for Transfer Length Top-strand Effect Transfer Length (Proposed Transfer Length Eq.)  = 1  = 2 R 2 = 0.176R 2 = 0.206

38. Practical Modeling Technique for Transfer Length Top-strand Effect Transfer Length (End-slip)

39. Practical Modeling Technique for Transfer Length Top-strand Effect Transfer Length (End-slip)

40. Practical Modeling Technique for Transfer Length Top-strand Effect Conclusions Top-strand effect was more dependent on the amount of concrete cast above the strand On average L t increased ½ in. for every 1 in. reduction in the amount of concrete cast above the strand

41. Practical Modeling Technique for Transfer Length GT STRUDL Model

42. Practical Modeling Technique for Transfer Length GT STRUDL Model

43. Practical Modeling Technique for Transfer Length GT STRUDL Model

44. Practical Modeling Technique for Transfer Length GT STRUDL Model $$=================================================== $$ CONCRETE ELEMENT DATA $$=================================================== TYPE PLANE STRESS GENERATE 6 ELEMENTS ID 'AB-1', 1 FROM 'A1',1 TO 'A2',1 TO 'B2',1 TO 'B1',1 GENERATE 6 ELEMENTS ID 'BC-1', 1 FROM 'B1',1 TO 'B2',1 TO 'C2',1 TO 'C1',1 ELEMENT PROPERTIES TYPE 'IPLQ' THICK 4 'AB-1' TO 'AB-6' 'BC-1' TO 'BC-6‘ CONSTANTS E 3949 - 'AB-1' TO 'AB-6‘ – 'BC-1' TO 'BC-6‘ G 1688 - 'AB-1' TO 'AB-6' - 'BC-1' TO 'BC-6‘ POI 0.17 - 'AB-1' TO 'AB-6' - 'BC-1' TO 'BC-6'

45. Practical Modeling Technique for Transfer Length GT STRUDL Model $$================================================================== $$ SPECIFY JOINT COORDINATES $$================================================================== GENERATE 5 JOINTS ID 'C1',1 X 0. - DIFF -1 2 AT 1 2 AT 2. Y 2. Z 0. C1C2C3C4C5 (-1,2)(0,2)(1,2)(3,2)(5,2)

46. Practical Modeling Technique for Transfer Length GT STRUDL Model $$================================================================== $$ SPECIFY STRAND PROPERTIES $$================================================================== TYPE PLANE TRUSS GENERATE 4 MEMBERS ID 'STRND-0',1 FROM 'Cd0', 1 TO 'Cd1' MEMBER PROPERTIES PRISMATIC AX 0.153 'STRND-0' TO 'STRND-3' Cd0Cd1Cd2Cd3Cd4 STRND-0STRND-1STRND-2STRND-3

47. Practical Modeling Technique for Transfer Length GT STRUDL Model $$=================================================== $$ SPECIFY BOND ELEMENT PROPERTIES $$=================================================== ELEMENT INC 'BOND-1' 'Cd1' 'C1' 'BOND-2' 'Cd2' 'C2' 'BOND-3' 'Cd3' 'C3' 'BOND-4' 'Cd4' 'C4' NONLINEAR SPRING PROPERTIES CURVE 'BOND' FORCE VS DISPL 0.0 0.0 -50.0 -1.0 END ELEMENT PROPS 'BOND-1' TO 'BOND-4' TYPE 'NLS' NONLINEAR SPRING ELEMENT DATA STIFFNESS 'BOND-1' TO 'BOND-4' X CURVE 'BOND' END 50 kip/in. 100 kip/in. 150 kip/in. 200 kip/in. 250 kip/in.

48. Practical Modeling Technique for Transfer Length GT STRUDL Model $$================================================================== $$ SPECIFY TEMPERATURE LOADINGS $$================================================================== LOADING 'TRANSFER' '-1100 TEMPERATURE CHANGE' MEMBER TEMPERATURE LOADS 'STRND-0' TO 'STRND-3' AXIAL -1100 Cd0Cd1Cd2Cd3 Cd4 STRND-0STRND-1STRND-2STRND-3

49. Practical Modeling Technique for Transfer Length GT STRUDL Model 4x4 in. 12 ft concrete prism (k = 50 kip/in.) 4x4 in. 12 ft concrete prism (k = 250 kip/in.) Excel Spreadsheet

50. Practical Modeling Technique for Transfer Length GT STRUDL Model 99% max force

51. Practical Modeling Technique for Transfer Length GT STRUDL Model

52. Practical Modeling Technique for Transfer Length GT STRUDL Model

53. Practical Modeling Technique for Transfer Length GT STRUDL Model 4x24 in. 12 ft concrete block (k = variable) 17 in. deep T-beam with eccentric strands 8 ft deep 96 ft long I-beam (End-zone) ??? Questions