Structural Analysis & Field Testing of a CFRP Wrapped Pier Cap

Transcription

1 University of Toledo University of Cincinnati Structural Analysis & Field Testing of a CFRP Wrapped Pier Cap Dr. Serhan Guner Dr. Douglas Nims Mr. John Morganstern Dr. Victor Hunt Dr. Arthur Helmicki Mr. Mahdi Norouzi October 26 OTEC 2016 Columbus, OH

2 Outline Problem Statement Objectives Structural Analysis Field Testing Preliminary Findings 2

3 Problem Statement I-71 SB Interchange at Fort Hayes. Designed in 1961 for three lanes of traffic. Original 3 lanes Original Pier Cap 3

4 Problem Statement In 2011, two more lanes & a new pier cap added. New Pier Cap Original Pier Cap (Focus of this study) New 2 lanes Original 3 lanes Live load on the original pier cap increased. Shear & flexure overloads. 4

5 Problem Statement ODOT retrofitted the cap with CFRP composites 5

6 Problem Statement Retrofit design was done based on ACI 440, which contains many assumptions. Actual contribution of the CFRP to the load carrying capacity is unknown. ODOT wanted scientific evidence on the contribution of CFRP. Does CFRP wrap indeed work? 6

7 Objectives Understand the behaviour of the cap before and after the retrofit. Use structural analysis. Measure CFRP strains & validate analysis results. Develop a controlled truck testing procedure. Consider ambient traffic, daily thermal changes, and truck loading. Understand CFRP contributions to response. Provide recommendations for future retrofits. -- 7

8 Bridge Background Bridge FRA L at Forth Hayes Interchange Original Construction as per 1961 specifications 8

9 Bridge Background North and South piers make up a 3 span bridge Both stepped between bearings, supported by 3 circular columns North pier is the focus of this study. 9

10 Bridge Background Total length of the cap 55 ft (16.8 m) 10

11 Bridge Background 7 bearing pads, equally spaced. Section depth 4-3 (1300 mm) 11

12 Bridge Background Entire cap is a disturbed region & deep beam. 12

13 Bridge Background Light amounts of shear reinforcement. No skin reinforcement. 13

14 Bridge Background Section is designed for negative flexure. 14

15 CFRP Retrofit Procedure New pier was built. Bridge deck was widened. Traffic was shifted to the new pier cap. Existing cap was wrapped while no live traffic load. New Pier Cap Existing Pier Cap 15

16 CFRP Retrofit Procedure Epoxy applied then CFRP wrapped over 16

17 CFRP Retrofit (Shear) Primary Fiber Directions 17

18 CFRP Retrofit (Flexure) Primary Fiber Directions 18

19 CFRP Retrofit Procedure Flexure Strengthening SikaWrap Cured Laminate Thickness = 0.02 (0.5 mm) Tensile strength = 105 ksi (725 MPa) Shear Strengthening Mod. of Elast. = 8,200 ksi (56,500 MPa) Elongation at break = 1.0 % (10 me) Flexure Strengthening 19

20 Linear-Elastic Analysis Understand the linear strain field. Assess contributions of CFRP composite. Locate high strain locations for field testing

21 Loading Load analysis is performed in Two critical load cases: Load Case #12: trucks in two west southbound lanes Load Case #16: trucks in central southbound lane 21

22 Truck location Load Case #12 Truck location 22

23 Load Case #16 Truck location 23

24 Linear-Elastic Analysis Un-Retrofitted Model (Dead Load Only) 123 kips each 550 kn Z N X Shell Element E c = 3,800 ksi (26,200 MPa) f c = 4.0 ksi (27.6 MPa) Possion s Ratio = 0.2 Mesh aspect ratio = 1.0 approx. 24

25 Displacements and Principal Stresses Max Tensile Stress = 0.65 ksi (4.5 MPa) Strain = 171 μe Tens. (+) psi Z N X Δ = (0.12 mm) Max Compressive Stress = 1.68 ksi (11.6 MPa) Strain = 442 μe Δ = (1.65 mm) Comp. (-) psi 25

26 Linear-Elastic Analysis Un-Retrofitted Model (Load Case #12) 168 kips kn Z N X 26

27 Displacements and Principal Stresses Max Tensile Stress = 0.9 ksi (6.2 MPa) Strain = 237 μe Tens. (+) psi Z X N Δ = 0.08 (0.20 mm) Max Compressive Stress = 2.27 ksi (15.7 MPa) Strain = 597 μe Δ = (2.25 mm) Comp. (-) psi 27

28 Linear-Elastic Analysis Un-Retrofitted Model (Load Case #16) 123 kips kn Z N X 28

29 Displacements and Principal Stresses Max Tensile Stress = ksi (4.6 MPa) Strain = 178 μe Tens. (+) psi Z N X Δ = (0.28 mm) Δ = (1.63 mm) Max Compressive Stress = 1.64 ksi (11.3 MPa) Strain = 432 μe Δ = (1.55 mm) Comp. (-) psi 29

30 Result Comparisons Results Max Tip Disp. (in) DL only Case # 12 (LL+DL) Case # 16 (LL+DL) Max stress locations do not change. Max Stresses (ksi) Location of Max Stresses Max strains (micro-strain) Tensile Comp. Tensile Comp. Tensile Comp. Top of Bot of Bearing Bearing Top of Bearing Top of Bearing Bot of Bearing Bot of Bearing Pier to cap connection should be instrumented for field testing. 30

31 Linear-Elastic Analysis Retrofitted Model (Dead Load Only) 123 kips each 550 kn Z N X Orthotropic CFRP Shell Element Hex 117C for Shear E z = 8,200 ksi (56,500 MPa) G xz =2733 ksi G xz =0.5 Hex 230C for Flexure E x = 8,200 ksi (56,500 MPa) G xy =2952 ksi G xy =0.5 31

32 Displacements and Principal Stresses Max Tensile Stress = 0.85 ksi (5.9 MPa) in CFRP Strain = 96 μe Tens. (+) psi Z N X Δ = (0.12 mm) Comp. (-) psi Max Compressive Stress = 1.68 ksi (11.6 MPa) in concrete Strain = 442 μe Δ = (1.65 mm) 32

33 Linear-Elastic Analysis Retrofitted Model (Load Case #12) 168 kips kn Z N X 33

34 Displacements and Principal Stresses Max Tensile Stress = 1.14 ksi (7.9 MPa) Strain = 129 μe Tens. (+) psi Z N X Δ = 0.08 (0.20 mm) Max Compressive Stress = 2.25 ksi (15.5 MPa) Strain = 592 μe Δ = (2.25 mm) Comp. (-) psi 34

35 Result Comparisons Results Max Tip Disp. (in) DL only Case # 12 (LL+DL) Max stress locations do not change. Max Stresses (ksi) Location of Max Stresses Max strains (micro-strain) Tensile Comp. Tensile Comp. Tensile Comp. Top of Bot of Bearing Bearing Top of Bearing Bot of Bearing Pier to cap connection should be instrumented for field testing. 35

36 Nonlinear Pushover Analysis Understand nonlinear bridge response Determine stress/strain conditions for service loads Confirm the governing behaviour and failure mode -- 36

37 What is Nonlinear Pushover Analysis? Create the finite element model. Increase loading monotonically with fixed proportions until structure fails. Applied Load Applied Load Capacity Load Stage Deflection Obtain the load-deflection response. 37

38 Is it permitted in AASHTO? 38

39 What tool to use? VecTor2 used in this study. Developed at the University of Toronto, Canada. Based on the Modified Compression Field Theory (Vecchio and Collins,1986). Adopted by AASHTO LRFD. Verified with hundreds of large-scale experimental specimens. Considers shear and advanced concrete behaviours. 39

40 Concrete Hysteresis 40

41 Reinforcement Hysteresis Seckin (1981) Model 41

42 Concrete Tension Stiffening Modified Bentz (2005) 42

43 Concrete Tension Softening Especially important for members: with no transverse reinforcement with no longitudinal reinforcement for plain concrete fc 1 = max (f c1 1 ;f c12 ) 43

44 Concrete Variable Crack Spacing Crack spacing required by MCFT and DSFM for crack width calculation, crack check and crack slip. Variable crack spacing for each concrete layer for both sm x and sm y as per Collins and Mitchell (2001) 44

45 Local Crack Calculations 45

46 Out-of-Plane Confinement Case 1 Case 2 Taken into account as concrete elastic strain offset Based on Kupfer et al. (1969) 46

47 Reinforcement Dowel Action Included into the global frame analysis Dowel Stiffness based on He and Kwan (2001) Average shear strains are used. Resisting moment is into fixed end forces. 47

48 Reinforcement Buckling RDM Model (Akkaya, Guner and Vecchio, 2016) Intermediate point Two different stiffnesses 48

49 Model Details 49

50 Mesh and Loading 50

51 Material Modeling 51

52 Load Stages 8 & 9 Load Stage 8: (80% of Serv. Load) No Cracking Load Stage 9: First Cracking 0.01 in (0.34 mm) 52

53 Load Stage 10 (Service Loads) Load Stage 10: Max Crack Width = 0.05 in (1.3 mm) Wrapped Unwrapped Wrapped 53

54 Reinforcement Stresses Load Stage 10: Max rebar stress = 11.1 ksi (77 Mpa) 30% of yield Min rebar stress = -9.3 ksi (-63.9 Mpa) 54

55 Displacements Deflections Load Stage 10: Max displacement = 0.15 in. (3.7 mm) Criteria = Span/300 = 0.35 in. (8.8 mm) 55

56 Concrete Principal Tensile Strains Load Stage 10: Max tensile strain = 1.44 x 10-3 in./in. 56

57 Concrete Principal Compressive Strains Load Stage 10: Max comp. strain = x 10-3 in./in. 57

58 Load Stage 25 (Failure Conditions) Load Stage 25: Failure Mode= Ductile Shear-Flexure 58

59 Reinforcement Stresses Load Stage 25: Max rebar stress = 40 ksi (275 MPa) 100% of yield Min rebar stress = - 40 ksi (-275 Mpa) 59

60 Nonlinear Analysis Results Verified the service load conditions. Crack pattern matches with actual conditions. Verified concrete and rebar stresses. Verified that the cap fails in a combined flexural-shear mode

61 Field Test #1 for Ambient Traffic (June 2016) 61

62 Gauge Locations 2 BDI gages on top concrete (#2987) 5 sets of 3 vibrating wire gauges on top fiber 2 BDI gauges on bottom fiber 1 BDI gauge on concrete (#2989) BDI Rosette (#3002) Plan Elev. 2 BDI gauges on bottom fiber 62

63 Gauge Installation West Cantilever under gore area Analysis of Frames under Blast Loads 63 S. Guner

64 Gauge Installation Analysis of Frames under Blast Loads 64 S. Guner

65 Gauge Installation BDI gauge rosette in compression zone on CFRP Clear Lexan Template 65

66 Gauge Installation 1 BDI gauge at bottom of pier cap at west midspan Plan 66

67 Gauge Installation Vibrating Wire Strain Gauge on top CFRP Geokon Model

68 Test Results (BDI Gauges) BDI #2989 BDI #2987 BDI # μe for ambient traffic 68

69 Strain (μe) Test Results (Vibrating Wire Gauges) μe drift for Superglue over one month No drift for epoxies: Sika 3001 & 3M DP460 69

70 Preliminary Conclusions 1. Pier cap safety is confirmed by structural analysis. 2. Service cracking pattern is captured by analysis. 3. Governing response is confirmed as flexure-shear. 4. Ambient traffic field testing confirmed that the CFRP picks up strain. 5. Analysis showed that CFRP does not significantly contribute to stiffness and response under ambient traffic. 6. Stage #2 testing data analysis is underway. 70

71 University of Toledo University of Cincinnati Questions & Comments? Structural Analysis & Field Testing of a CFRP Wrapped Pier Cap Serhan Guner Douglas Nims John Morganstern Victor Hunt Arthur Helmicki Mahdi Norouzi October 26 OTEC 2016 Columbus, OH

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