Advancing Disc Bearing Specifications AASHTO T-2 Columbus, OH June 24, 2014

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2 Advancing Disc Bearing Specifications AASHTO T-2 Columbus, OH June 24, 2014 Paul Bradford, PE, PhD PB Engineering Consultant PBENG

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6 How does it work? - Compression Urethane tries to expand laterally Friction inhibits expansion Disc bulges

7 Disc Bearing Limits Motivation 1. No change since the 1970 s, increase in allowables has not kept up with other materials 2. Excellent field performance for 40 years 3. Tested to much higher levels 4. Higher demands 5. Turn towards elastomeric bearing design methods

8 Current Disc Bearing Limits; 1. Stress (currently 5.0 ksi) 2. Strain (currently 10%) 3. No lower bound Shape Factor 4. No shape factor influence on allowables Thin pads can accommodate higher stresses, but not high strains Thick pads can accommodate higher strains, but not high stresses

9 Shape Factor S=1.50 S=2.00 S=3.00

10 Proposed Disc Bearing Limits Is c c ksi [0.10] [5.00] Individual upper limits based on testing and field history 3. S c 0.24 [N/A, 0.20] Analogous to AASHTO , implicitly sets limits on stress, strain, and shape factor combinations 4. S 1.40 [N/A]

11 SeS = Se Product + Strain Limit S c 0.24 c 0.24 S c ( S) S Thin Pads

12 S c 0.24 SeS = Se Product + Stress Limit E 2 1 S c 0.24E 1 S S 2 c 7.00 ksi ( S) S Thinner Pads

13 Se product - indicator of the max shear strain due to compression c 6S Gent & Lindley Solution, BE 1/76 c c CS c Stanton & Roeder, NCHRP 248 (1982) C varies according to aspect ratio, C = 6.0 for circular bearings

14 Se Product was (is) an implicit constraint in AASHTO specifications EC E c C c 6GS 2 c S c 2.00GS 0.33 (AASHTO ) Equivalent criteria Se Product Material independent Allows for design comparisons between different materials

15 Linear FEA Studies Baseline: S = 2.0 Pad, 62D, E = 10 ksi, nu = Axisymmetric section

16 Linear FEA Studies S=2.00, = 0.10, E = 10 S = 2.0 Pad, 62D, 10% strain

17 Baseline: S = 2.0, 10% strain, 62D Stress (psi) Peak core shear stress = 1.93 ksi Stresses Groove area Radial Coordinate (in) SRR STT SZZ SRZ

18 For baseline pad For proposed pad designs C 1.9 ksi 1.7 ksi 2.3 ksi C Other durometers? Analyses were run with E = 10: C 0.2 E

19 Required Coefficient of Friction; COF R COF R Radial Coordinate (in.) Baseline and Prop S2,e10 Prop S1.5,e14 Prop S3, e8 No real change in required coefficient of friction Move to slightly higher shape factors reduces the average COF R

20 SeS Validation Test Program Test Series 1 - Durometer OD 3.56 ID 1.88 TH A 1.94 S 0.12 ea Dur E Ec e s d R P 42D D D D Test Series 2 - Shape Factor Material - 62D E OD 3.56 ID A S TH Ec ea e s d R P

21 Test Program Test Series 3 - Coupon Tests Sample 0.25 Thickness E>> (in) (in 2 ) 42D 52D 62D 72D 42D 52D 62D 72D 42D 52D 62D 72D S D A ea e e e e s s s s Ec Ec Ec Ec D 52D 62D 72D 42D 52D 62D 72D d d d d P P P P Test Sequence Test Name Test Series Description 1 Exercise 1,2, 3 150% Compression-Deflection 2 Baseline 1,2, 3 100% Compression-Deflection 3 Rotation 1, 2 125% Design Static +.50 Dynamic 4 Post Rotation 1, 2 100% Compression-Deflection 5 Degradation 1 X Vertical Load at Y Temperature in Z Vibration Environment for H hours, where XYZ-H is TBD 6 Post Degradation 1 100% Compression-Deflection

22 Project Brg Tests 11 projects, 38 bearings, circa Fall kips to 2800 kips 5.0 to 7.5 ksi 62D material

23 Test Program

24 Test Program Project Documentation 7.5 ksi, 0.02 radians

25 Test-Predicted Deviation Analysis Calc FEA Mean STDev Material Temperature Procedure Equipment Design

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28 Analytical Solutions Disc with frictionless surfaces 2 ri rr, r 2c 0, 3 rr r 1 0 r G 3 r 2 zz c i Normalized Stress v1 vm p 0 rr E r 3 2 i 1 Ef c 2 f 1 r i 3 c zz r Stress normalized by E E t KS A f

29 Material Tests

30 Force & Displacement Test Data Force Scale Displacement TIme (s) d x 12,000 F

31 Linear Solid Model Standard Linear Solid F Ks Km c

32 Force (kips) Force vs Time F Test Fit FRlx F-Ks F-KmD Time (s)

33 Force Error (lbs) df df

34 10.00 Force at Constant Velocity Free expansion test Force (kips) V=.010 V=.020 Ks only Displacement (Inches)

35 F Free Expansion Results Ks Km c 0? Hypothetical Bonded Results E K' K'' Loss factor Damping ratio 2.00 S Ec K' K'' Loss factor Damping ratio Ks related to molecular network configuration (entropy & int. energy) c, Km related to sliding of molecular segments

36 Moving Forward Complete; SeS Validation Equipment, fine tune load testing procedure Material Test, algorithm, software Finite Elements Results

37 Thank You Acknowledgements: AASHTO T2 Joints & Bearings Committee RJ Watson, Inc. PBENG