Advancing Disc Bearing Specificationssp.bridges.transportation.org/Documents/2014 SCOBS... · 2014....

Advancing Disc Bearing Specifications AASHTO T-2

Columbus, OH June 24, 2014

Paul Bradford, PE, PhD PB Engineering Consultant

PBENG

How does it work? - Compression

Urethane tries to expand laterally

Friction inhibits expansion

Disc bulges

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

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

S=2.00

S=1.50

S=3.00

Shape Factor

Proposed Disc Bearing Limits

0.24c

S

0.14c

7.00 ksic

1.40S

3.

4.

[N/A, 0.20]

Is…

[0.10]

[5.00]

[N/A]

Analogous to AASHTO 14.7.5.3.2-3, implicitly sets limits on stress, strain, and shape factor combinations

Individual upper limits based on testing and field history

2.

1.

0.24c

S

Thin Pads

1 1.5 2 2.5 3 3.50.06

0.08

0.1

0.12

0.14

S( )

S

0.24c

S

SeS = Se Product + Strain Limit

0.14c

2

0.241

ES

S

Thinner Pads

21 cE S

0.24c

S

1 1.5 2 2.55

5.5

6

6.5

7

S( )

S

SeS = Se Product + Stress Limit

7.00 ksic

6c cS Gent & Lindley Solution, BE 1/76

c cC S Stanton & Roeder, NCHRP 248 (1982) C varies according to aspect ratio, C = 6.0 for circular bearings

Se product - indicator of the max shear strain due to compression

26CE GS

2.00c GS

c C cE

0.33cS

Equivalent criteria

• Material independent • Allows for design comparisons between different materials

(AASHTO 14.7.5.3.2-3)

Se Product

Se Product was (is) an implicit constraint in AASHTO specifications

Linear FEA Studies

Axisymmetric section

Baseline: S = 2.0 Pad, 62D, E = 10 ksi, nu = 0.485

Linear FEA Studies

S = 2.0 Pad, 62D, 10% strain

S=2.00, = 0.10, E = 10

Baseline: S = 2.0, 10% strain, 62D

Peak core shear stress = 1.93 ksi

-8000

-6000

-4000

-2000

0

2000

4000

6000

0 1 2 3 4 5 6 7

Stre

ss (

psi

)

Radial Coordinate (in)

Stresses

SRR

STT

SZZ

SRZ

Groove area

0.2C E

1.9 ksiC For baseline pad

Other durometers? Analyses were run with E = 10:

For proposed pad designs

1.7 ksi 2.3 ksiC

Required Coefficient of Friction;

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2 2.5 3 3.5 4 4.5 5 5.5 6

CO

F R

Radial Coordinate (in.)

COFR

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 COFR

SeS Validation Test Program

Test Series 1 - Durometer

15.38 OD

3.56 ID

1.88 TH

175.69 A

1.94 S

0.12 ea

Dur E Ec e s d R P

42D 2.20 10.48 0.12 1.296 0.23 0.030 228

52D 4.00 19.05 0.12 2.357 0.23 0.030 414

62D 10.00 47.63 0.12 5.893 0.23 0.030 1035

72D 16.00 76.21 0.09 7.000 0.17 0.022 1230

Test Series 2 - Shape Factor

Material - 62D

10.00 E

15.38 OD

3.56 ID

175.71 A

S TH Ec ea e s d R P

1.50 2.43 32.50 0.140 0.140 4.55 0.34 0.044 799 1.94 1.88 47.64 0.124 0.124 5.89 0.23 0.030 1035

2.50 1.46 72.50 0.096 0.096 6.96 0.14 0.018 1223 3.00 1.21 100.00 0.080 0.070 7.00 0.08 0.011 1230

Test Program

Test Series 3 - Coupon Tests

0.25 Sample Thickness

E>> 2.20 4.00 10.00 16.00

(in) (in2) 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

1.50 1.50 1.77 0.140 0.140 0.140 0.140 0.135 1.00 1.82 4.55 7.00 7.2 13.0 32.5 52.0

2.00 2.00 3.14 0.120 0.120 0.120 0.120 0.088 1.32 2.40 6.00 7.00 11.0 20.0 50.0 80.0

2.50 2.50 4.91 0.096 0.096 0.096 0.096 0.060 1.53 2.78 6.96 7.00 16.0 29.0 72.5 116.0

3.00 3.00 7.07 0.080 0.080 0.080 0.070 0.044 1.76 3.20 7.00 7.00 22.0 40.0 100.0 160.0

42D 52D 62D 72D 42D 52D 62D 72D

d d d d P P P P

0.035 0.035 0.035 0.034 1.8 3.2 8.0 12.4

0.030 0.030 0.030 0.022 4.1 7.5 18.8 22.0

0.024 0.024 0.024 0.015 7.5 13.7 34.2 34.4

0.020 0.020 0.018 0.011 12.4 22.6 49.5 49.5

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 Rotation @ .75 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

Project Brg Tests – 11 projects, 38 bearings, circa Fall 2012

• 350 kips to 2800 kips • 5.0 to 7.5 ksi • 62D material

Test Program

Test Program – Project Documentation

7.5 ksi, 0.02 radians

• Material • Temperature • Procedure • Equipment • Design

Mean 0.023 0.027

STDev 0.201 0.213

Calc FEA

Test-Predicted Deviation Analysis

?

23zz c iG r

r

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

No

rma

lize

d S

tre

ss

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

p0

rr

zz

v M

v 1

2

, 32 0, 1 0i

rr r c rr

rr

r

Analytical Solutions

Disc with frictionless surfaces…

cfE

2

31 i

c

rE

Stress normalized by E

SEt

KA f

2

13

irf

Material Tests

0

10000

20000

30000

40000

50000

60000

70000

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

Forc

e &

Dis

pla

cem

en

t

TIme (s)

Test Data

d x 12,000 F

Scale Displacement

Force

Linear Solid Model

Ks Km

c

F

Standard Linear Solid

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

4.000

4.500

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

Forc

e (

kip

s)

Time (s)

Force vs Time

F Test

Fit

FRlx

F-Ks

F-KmD

-0.02

-0.015

-0.01

-0.005

0

0.005

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

dF

dF

Force Error (lbs)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

0.0000 0.0020 0.0040 0.0060 0.0080 0.0100

Force at Constant Velocity Free expansion test

V=.010

V=.020

Ks only

Displacement (Inches)

Force (kips)

9.617 E

350.715 K'

172.348 K''

0.491 Loss factor

0.246 Damping ratio

2.00 S

48.09 Ec

1478.699 K'

172.348 K''

0.117 Loss factor

0.058 Damping ratio

Free Expansion Results Hypothetical Bonded Results

Ks Km

c

F

0?

Ks related to molecular network configuration (entropy & int. energy) c, Km related to sliding of molecular segments

Moving Forward - 2014

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

Acknowledgements:

AASHTO T2 Joints & Bearings Committee RJ Watson, Inc.

PBENG

Thank You