GT STRUDL Users Group 22 nd Annual Meeting & Training Seminar June 24, 2010

1. GT STRUDL Users Group22nd Annual Meeting & Training SeminarJune 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 Background Test Speciemens Top-strand Effect GT STRUDL Model Practical Modeling Technique for Transfer Length

3. 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

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

5. Background fps fse Ld 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 ACI AASHTO Lt Lfb Practical Modeling Technique for Transfer Length

6. Background fse Lt Transfer Length • The bonded length of strand required to transfer the prestress force in the strand to the surrounding concrete Lt= 50db ACI Lt = 60db AASHTO Practical Modeling Technique for Transfer Length

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

8. Background Deformed Bar > 12” Top-strand Effect • Provisions exist for development length of deformed bars • Ld 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 Practical Modeling Technique for Transfer Length

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

10. Background 12 ft 12 ft Block A Block B 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 Practical Modeling Technique for Transfer Length

11. Test Speciemens 30 in. 5 in. 4 in. 24 in. 2 in. 8 in. Large 24 in. 24 in. 3 in. 2 in. 4 in. 4 in. 17 in. 19 in. 2 in. 2 in. 8 in. 8 in. Medium Small T-beams ½” f regular ½” f special 0.6” f Practical Modeling Technique for Transfer Length

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

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

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

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

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

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

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

19. Test Specimens Transfer Length 100 mmspacing 50 mmspacing Practical Modeling Technique for Transfer Length

20. Test Specimens 100 mmspacing 50 mmspacing Transfer Length ≈ 30,000 measurements Practical Modeling Technique for Transfer Length

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

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

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

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

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

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

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

28. 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 Practical Modeling Technique for Transfer Length

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

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

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

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

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

34. Top-strand Effect Transfer Length(Proposed Transfer Length Eq.) z = 1 z = 2 R2 = 0.176 R2 = 0.206 Practical Modeling Technique for Transfer Length

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

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

37. GT STRUDL Model Practical Modeling Technique for Transfer Length

38. GT STRUDL Model Practical Modeling Technique for Transfer Length

39. GT STRUDL Model Practical Modeling Technique for Transfer Length

40. GT STRUDL Model A1 A2 A3 A4 A5 A6 A7 AB-1 AB-2 AB-3 AB-4 AB-5 AB-6 B1 B2 B3 B4 B5 B6 B7 BC-1 BC-2 BC-3 BC-4 BC-5 BC-6 C1 C2 C3 C4 C5 C6 C7 $$=================================================== $$ 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' Practical Modeling Technique for Transfer Length

41. 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. C1 C2 C3 C4 C5 (-1,2) (0,2) (1,2) (3,2) (5,2) Practical Modeling Technique for Transfer Length

42. 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' Cd0 Cd1 Cd2 Cd3 Cd4 STRND-0 STRND-1 STRND-2 STRND-3 Practical Modeling Technique for Transfer Length

43. 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 250 kip/in. 200 kip/in. 150 kip/in. 100 kip/in. 50 kip/in. Practical Modeling Technique for Transfer Length

44. GT STRUDL Model $$================================================================== $$ SPECIFY TEMPERATURE LOADINGS $$================================================================== LOADING 'TRANSFER' '-1100 TEMPERATURE CHANGE' MEMBER TEMPERATURE LOADS 'STRND-0' TO 'STRND-3' AXIAL -1100 Cd4 Cd0 Cd1 Cd2 Cd3 STRND-0 STRND-1 STRND-2 STRND-3 Practical Modeling Technique for Transfer Length

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

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

47. GT STRUDL Model Practical Modeling Technique for Transfer Length

48. GT STRUDL Model Practical Modeling Technique for Transfer Length

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