1. Shear Capacity of Composite Steel Girder at Simple Support Virtis/Opis User Group Conference Nashville, TN, August 3-4, 2010 George Huang, PhD, PE California Department of Transportation

2. Outline Background Background AASHTO Specification Review AASHTO Specification Review Concrete Deck Lab Test by Shanmugam Concrete Deck Lab Test by Shanmugam Bridge Field Test By Au Bridge Field Test By Au Proposed Capacity Calculation Method Proposed Capacity Calculation Method Proposed Virtis Enhancement Proposed Virtis Enhancement

3. Background Many composite steel bridges designed before 70’s were re-rated with LFR. Many composite steel bridges designed before 70’s were re-rated with LFR. Some bridges have much smaller ratings due to shear deficiency at support. Some bridges have much smaller ratings due to shear deficiency at support. Based on new rating results, permit vehicles would often not be allowed on these bridges. Based on new rating results, permit vehicles would often not be allowed on these bridges.

4. Background Traffic histories show that permit vehicles have travelled on these bridges for over 40 years. Traffic histories show that permit vehicles have travelled on these bridges for over 40 years. Bridge field inspections found there was no distress on the steel girder or concrete deck near support for most bridges. Bridge field inspections found there was no distress on the steel girder or concrete deck near support for most bridges. What is the correct rating? What is the correct rating?

5. Bridge Example Bridge Number: 50-0316 Bridge Number: 50-0316 Bridge Name: Route 46/5 Separation Bridge Name: Route 46/5 Separation Year Built: 1967 Year Built: 1967 Bridge width = 44’ ; depth = 4’-11” Bridge width = 44’ ; depth = 4’-11” Spans: 83’, 90’, 90’, and 83’ Spans: 83’, 90’, 90’, and 83’ Super-Structure: Simple Span Composite Weld Steel Plate Girders (4) spacing@12’ Super-Structure: Simple Span Composite Weld Steel Plate Girders (4) spacing@12’ Design Live Load: HS 20-44 Design Live Load: HS 20-44

6. Br. No. 50-0316

8. General Plan

9. Typical Section & Girder Layout

10. Girder Details at Support

11. Changes in Ratings Working Stress Rating (1974) Working Stress Rating (1974) HS 20 Inventory Rating Factor = 1.12 P13 Operating Rating Factor = 1.27 Control Case: Interior Girder, Moment at middle of span 2 (Shear was not rated) Load Factor Rating (2010) Load Factor Rating (2010) HS 20 Inventory Rating = 0.75 P13 Operating Rating Factor = 0.62 P13 Operating Rating Factor = 0.62 Control Case: Interior Girder, Shear at supports of span 1

12. California Permit Trucks

13. Reason for Shear Deficiency Original Design Error? Original Design Error? Design Code Changes? Design Code Changes? If shear at simple support is ignored, the inventory rating factor will be greater than 1.0 If shear at simple support is ignored, the inventory rating factor will be greater than 1.0

14. General Structure Details Near Support

15. Changes in Design Specification Before AASHTO introduced LF for steel structure in 1973, bridges were designed with Working (Allowable) Stress method. Before AASHTO introduced LF for steel structure in 1973, bridges were designed with Working (Allowable) Stress method. In 1973 AASHTO (11th Ed.) Standard Specifications, shear capacities at interior and first panel locations were the same for both WS and LF. The equation is similar to the one used for an interior panel. In 1973 AASHTO (11th Ed.) Standard Specifications, shear capacities at interior and first panel locations were the same for both WS and LF. The equation is similar to the one used for an interior panel.

16. Changes in Design Specification In 1977 AASHTO 12 th ed., a lower shear capacity equation was introduced at the first panel location for WSD; In 1977 AASHTO 12 th ed., a lower shear capacity equation was introduced at the first panel location for WSD; In the 1978 AASHTO Interim Specifications, a lower shear capacity equation was introduced at the first panel location for LFD; In the 1978 AASHTO Interim Specifications, a lower shear capacity equation was introduced at the first panel location for LFD;

17. Changes in Design Specification In the 1983 AASHTO 13 th ed., chapter layout becomes similar to the current Standard Spec. In the 1983 AASHTO 13 th ed., chapter layout becomes similar to the current Standard Spec. In the1984-1986 Interim Specification, the current shear capacity equation at the first panel was introduced for the Load Factor method In the1984-1986 Interim Specification, the current shear capacity equation at the first panel was introduced for the Load Factor method

18. Shear Capacity Equations (LF) Other than the first panel: Other than the first panel:(10-114) At the first panel: (10-119) Where :V p = 0.58F y Dt w C = (buckling shear stress)/(shear yielding stress)

19. Resistance Due to Post-Buckling The second term in Eq. (10-114) is the additional shear capacity provided by post- buckling resistance due to web tension-field action. This additional shear capacity is ignored at the first panel location. The second term in Eq. (10-114) is the additional shear capacity provided by post- buckling resistance due to web tension-field action. This additional shear capacity is ignored at the first panel location.

20. Cause of Shear Deficiency The deficiency is due to the changes in design specification for shear capacity reduction at the first panel in 1977 (WSD) and 1978 (LFD). The deficiency is due to the changes in design specification for shear capacity reduction at the first panel in 1977 (WSD) and 1978 (LFD).

21. How to Solve the “Deficiency” Retrofit the Structure Retrofit the Structureor Modify the Shear Capacity Calculation Equation for Rating Analysis Modify the Shear Capacity Calculation Equation for Rating Analysis

22. Modify Shear Capacity Equation Are the current shear capacity calculation equations too conservative (for rating analysis)? Are the current shear capacity calculation equations too conservative (for rating analysis)? What’s the real shear capacity? What’s the real shear capacity?

23. Assumption for Current Equation Capacity of girder flange is ignored; Capacity of girder flange is ignored; Additional shear stiffener (extra panel) is required to develop post-buckling tension field in web; Additional shear stiffener (extra panel) is required to develop post-buckling tension field in web; Capacity of concrete deck is ignored. Capacity of concrete deck is ignored.

24. In Real Condition Girder flanges do have stiffness, and the composite top flange is much stiffer. Girder flanges do have stiffness, and the composite top flange is much stiffer. Even without extra panel, flange should provide some anchorage to develop some tension effect in the first panel. Even without extra panel, flange should provide some anchorage to develop some tension effect in the first panel. Concrete deck does have some shear capacity. Concrete deck does have some shear capacity.

25. Deck Capacity from Lab Test Lab tests were conducted for composite plate girder. Testing results were published by Shanmugam and Baskar in ASCE Journal of Structural Engineering, Sept. 2003 Lab tests were conducted for composite plate girder. Testing results were published by Shanmugam and Baskar in ASCE Journal of Structural Engineering, Sept. 2003 Concrete deck: Concrete deck: width = 1000 mm (39.4 in) thickness = 150 mm (5.9 in) f’c = 400 MPa (5.8 Ksi)

26. Typical Test Specimen

27. Instruments Layout

28. Test of Steel Girder

29. Test of Composite Girder

30. Description of Test Girders Spg1 and 2 are steel girders only. Spg1 and 2 are steel girders only. cpg1, 2, 3, 4 are composite steel girders with reinforced concrete decks. cpg1, 2, 3, 4 are composite steel girders with reinforced concrete decks. cpg3 and 4 have additional shear bars in the deck. cpg3 and 4 have additional shear bars in the deck.

31. Test Loads: Steel VS Composite (d/t = 250)

32. Test Loads: Steel VS Composite (d/t = 150)

33. Summary of Lab Test The paper concluded the concrete deck did provide additional shear capacity; The paper concluded the concrete deck did provide additional shear capacity; Without shear bars, concrete deck had a sudden failure mode; Without shear bars, concrete deck had a sudden failure mode; With shear bars, concrete deck had a ductile failure mode. With shear bars, concrete deck had a ductile failure mode.

34. Discussion of Lab Test The difference between the maximum elastic shear capacities of cpag1 and spag1 is the same as the difference between spg2 and cpg2 (about 200 KN). This may due to the same concrete deck dimensions used for both cpag1 and cpag2. The difference between the maximum elastic shear capacities of cpag1 and spag1 is the same as the difference between spg2 and cpg2 (about 200 KN). This may due to the same concrete deck dimensions used for both cpag1 and cpag2.

35. Discussion of Lab Test In the load-deflection plot for d/t = 250, the initial elastic stiffness for cpag1and spag1 are about the same. This may imply that the concrete deck is not effective until the steel girder behaviors nonlinearly (or steel web starts to yield and buckle). In the load-deflection plot for d/t = 250, the initial elastic stiffness for cpag1and spag1 are about the same. This may imply that the concrete deck is not effective until the steel girder behaviors nonlinearly (or steel web starts to yield and buckle).

36. Bridge Field Testing Au, Lam and Tharmabala (the Bridge Office of the Ministry of Transportation of Ontario) published “Investigation of shear resistance of steel bridge girders by load testing and monitoring of load response data under highway traffic conditions” in Canadian Journal of Civil Engineering, 2009. Au, Lam and Tharmabala (the Bridge Office of the Ministry of Transportation of Ontario) published “Investigation of shear resistance of steel bridge girders by load testing and monitoring of load response data under highway traffic conditions” in Canadian Journal of Civil Engineering, 2009.

37. Reason for the Testing During rehabilitation, a strength evaluation revealed a significant deficiency in the shear resistance of existing girders at support locations. During rehabilitation, a strength evaluation revealed a significant deficiency in the shear resistance of existing girders at support locations. Bridge girders showed no signs of distress Bridge girders showed no signs of distress

38. Scope of Testing Program Monitor real stresses in end panels of two selected girders when subjected to Monitor real stresses in end panels of two selected girders when subjected to (i) a test truck with known axle loads and (ii) normal highway traffic loading Calibrate observed stresses against theoretically expected responses in girders Calibrate observed stresses against theoretically expected responses in girders Calculate the live load capacity factor using shear data derived from field measurements Calculate the live load capacity factor using shear data derived from field measurements

39. Traffic Layout and Typical section

40. Traffic Lane Layout – Span K

41. Transverse Section –Span K

42. Bridge Instrumentation details

44. Testing Truck and Location

45. Canadian Highway Bridge Design Code (CHBDC)

46. Based on CHBDC Total shear capacity = 1.01x1071 Total shear capacity = 1.01x1071 = 1081.71 KN = 1081.71 KN Available live load shear capacity Available live load shear capacity =1.01x1071 – 988 =93.71 KN or 94 KN Un-factored dead load shear can be calculated as 861 KN Un-factored dead load shear can be calculated as 861 KN

47. Field Measurement Prorated from the measurement, the factored live load is estimated at 437 KN; Prorated from the measurement, the factored live load is estimated at 437 KN; Based on the maximum vertical shear strain measured under normal traffic, the largest shear force under live load is estimated at 606 KN Based on the maximum vertical shear strain measured under normal traffic, the largest shear force under live load is estimated at 606 KN

48. Summary of Live Load Capacity

49. Conclusion of the Paper The actual steel girder shear capacity at simple support is larger than that calculated by design code (CHBDC). The actual steel girder shear capacity at simple support is larger than that calculated by design code (CHBDC). The actual live load in the steel girder is smaller than that calculated by design code. The actual live load in the steel girder is smaller than that calculated by design code. The bridge has enough shear capacity (F=1.39) to carry the design live loads. The bridge has enough shear capacity (F=1.39) to carry the design live loads.

50. Total Steel Shear Capacity Paper suggested the total shear capacity of the steel girder was 1594 KN, which was the sum of measured live load force (606 KN) and the FACTORED shear force (988 KN) due to existing dead load; Paper suggested the total shear capacity of the steel girder was 1594 KN, which was the sum of measured live load force (606 KN) and the FACTORED shear force (988 KN) due to existing dead load; And in order to reach this 1594 KN based on the CHBDC, 38% of post-buckling shear component had to be included. And in order to reach this 1594 KN based on the CHBDC, 38% of post-buckling shear component had to be included.

51. Discussion of Total Shear Capacity Deck could carry some loads. However, since there was no distress, it might assumed that most dead load was taken by steel girder; Deck could carry some loads. However, since there was no distress, it might assumed that most dead load was taken by steel girder; Only the non-factored dead load (861 KN) should be included; Only the non-factored dead load (861 KN) should be included; The total least shear capacity might be 1467 KN (not 1594 KN). The total least shear capacity might be 1467 KN (not 1594 KN).

52. AASHTO VS CHBDC At first panel: At first panel: AASHTO: Vu = 1135 KN (255.2 Kips) AASHTO: Vu = 1135 KN (255.2 Kips) CHBDC: Vu = 1.01x1071 KN =1082 KN CHBDC: Vu = 1.01x1071 KN =1082 KN AASHTO/CHBDC = 1.05 AASHTO/CHBDC = 1.05 At interior panel: At interior panel: AASHTO: Vu = 2559 KN (575.3 Kips) AASHTO: Vu = 2559 KN (575.3 Kips) CHBDC: Vu = 1.01x2436 KN = 2460 KN AASHTO/CHBDC = 1.04 CHBDC: Vu = 1.01x2436 KN = 2460 KN AASHTO/CHBDC = 1.04

53. AASHTO VS CHBDC Equivalent dead load factor Equivalent dead load factor CHBDC = 1.15, AASHTO = 1.3 Live load factor Live load factor CHBDC = 1.42, AASHTO = 1.3 Rating factor for live loads Rating factor for live loads CHBDC = 0.10, AASHTO = 0.02

54. Need New Approach to Calculate Shear Capacity Based on lab testing, field testing results, and bridge ratings and field inspections of several bridges in California, there is a need for a new approach. Based on lab testing, field testing results, and bridge ratings and field inspections of several bridges in California, there is a need for a new approach.

55. Proposed New Shear Capacity Eq. for Composite Plate Girder Total shear capacity includes both steel and concrete deck Total shear capacity includes both steel and concrete deckwhere m and n are two proposed new parameters

56. Concrete Capacity Calibration Based on information from Shanmugam’s paper: Based on information from Shanmugam’s paper: b c =1000 mm(39.37 in), t c =150 mm (5.9 in) b c =1000 mm(39.37 in), t c =150 mm (5.9 in) f’ c = 40 MPa (5801 psi), estimated V c = 200 KN (44961 lbs) then n = 2.54 to be conservative, use phi = 0.85 with n = 2 phi = 0.85 with n = 2

57. Steel Capacity Calibration Based on information from Au’s paper: Based on information from Au’s paper: Web depth D = 2438 mm (96”) Web thickness t w = 9.53 mm (3/8”) Trans. stiffener spacing d 0 = 1534mm(60”) Fy = 230 MPa (33 ksi) Then C = 0.37 Vp = 0.58FyDt w = 689 Kips

58. Steel Capacity Calibration Ignoring the deck and using the estimated least shear capacity of 1467 KN (331.8 kips). Based on Ignoring the deck and using the estimated least shear capacity of 1467 KN (331.8 kips). Based on then m = 0.24 Since the girder was still in elastic, the actual m should be larger than 0.24. Since the girder was still in elastic, the actual m should be larger than 0.24. m = 0.25 may be used. m = 0.25 may be used.

59. Steel Capacity Calibration Please note: The higher measured steel capacity may be due to the equation used to calculate buckling shear stress being too conservative; The higher measured steel capacity may be due to the equation used to calculate buckling shear stress being too conservative; The actual shear force in the steel girder could be smaller than 1467KN, but the actual steel girder capacity could be larger; The actual shear force in the steel girder could be smaller than 1467KN, but the actual steel girder capacity could be larger;

60. Rate Br. 50 -316 with Proposed Method Girder dimension: Girder dimension: Top flange: 5/8” x 12” Top flange: 5/8” x 12” Web: 5/16” x 45” Web: 5/16” x 45” Bot. flange: 7/8” x 20” Bot. flange: 7/8” x 20” Spacing of shear stiffener: 34.7” Spacing of shear stiffener: 34.7” calculated: C = 0.804, Vp = 293.6 Kips calculated: C = 0.804, Vp = 293.6 Kips CVp = 236.1 Kips CVp = 236.1 Kips with m=.25 Vu,s = 246.0 Kips with m=.25 Vu,s = 246.0 Kips

61. Rate Br. 50 -316 with Proposed Method Minimum deck thickness: 8.25” Minimum deck thickness: 8.25” Effective deck width: 99” Effective deck width: 99” f’c = 3250 psi f’c = 3250 psi with phi = 0.85 and n=2 Vu,c = 79.1 Kips Total shear capacity Vu = 246+79 = 325 Kips

62. Rate Br. 50 -316 with Proposed Method Inventory Rating for HS20 Virtis: RF = 0.75 proposed: RF = 1.22 proposed: RF = 1.22 Operating Rating for Permit P13 Virtis: RF = 0.62 proposed: RF = 1.01 proposed: RF = 1.01

63. Proposed Virtis Enhancement If Virtis has the option for user to define capacities at any point, user may use proposed method to calculate composite steel plate girder shear capacity near support and to replace the shear capacity based on the AASHTO LFD Specification. If Virtis has the option for user to define capacities at any point, user may use proposed method to calculate composite steel plate girder shear capacity near support and to replace the shear capacity based on the AASHTO LFD Specification. This option may be used for locations, where capacity has to be manually calculated, such as hinge, splices, or structure damage. This option may be used for locations, where capacity has to be manually calculated, such as hinge, splices, or structure damage.

64. Questions?