Robert J. Connor Ryan Sherman Francisco Martin Will ...

Robert J. Connor

Ryan Sherman

Matt Hebdon

Francisco Martin

Will Collins

Jason Lloyd

AASHTO SCOBS

Saratoga Springs, NY

April 20, 2015

Projects Underway

TPF-5(238) - Design and Fabrication

Standards to Eliminate Fracture Concerns

in Steel Members Traditionally Classified

as FCMs

TPF-5(253) - Evaluation of Member Level

Redundancy in Built-up Steel Members

Projects Underway

NCHRP Project 12-87a – Looking at

System Analysis of FC Bridges

NSBA/AISI Twin Tub Girder FC Analysis

Integrated Fracture Control Plan

Must recognize and accept:

Defects exist

Bridges experience variable loading

Materials are variable

Inspection methods have limitations

Components of Integrated FCP:

Material properties

Fabrication guidelines

In-service inspections

Design considerations

Outcomes of Integrated FCP

Confidence/Life Safety

Treat fracture like any other limit state

○ Statistical understanding of fracture behavior

Pf and β can equivalent to other limit states

○ Approach fracture like all limit states in LRFD

Economic

Reduce required “hands-on” inspections

○ Set rational interval w/o compromising reliability

Better allocation of inspection resources

FCP Considerations: Material Variability

Scatter in toughness data

FCP Considerations: Material Variability

Scatter in toughness data

Statistical characterization possible

FCP Considerations: In-service Inspections

Probability of Detection (POD)

POD Testing

TPF 5(253) - “Evaluation of Member Level

Redundancy in Built-up Steel Members”

Project Update – April 2015

Member-level Redundancy

Built-up members

Consist of several individual components

○ Could prevent cracks from propagating through

entire member

Common strategy in other industries to reduce

complete member fracture susceptibility

Not explicitly accounted for in highway bridges

○ (though we know it exists)

TPF 5(253) - “Evaluation of Member Level

Redundancy in Built-up Steel Members”

Establish fracture resistance and remaining

fatigue life AFTER one component fails

Testing Method:

Crack a component Controlled location (angle/cover plate)

○ Notch specimen

○ Not looking at initial fatigue life – already documented

Grow crack in fatigue

Cool beam to AASHTO Zone 3 temp. Much colder often used (-100F)

Load to induce a fracture If no fracture, repeat

Fatigue ‘failed’ beam to determine fatigue resistance after a component fails

Test Setup

Cooling Chamber

-60°F (Zone 3)

Sometimes much less!!

Specimen Preparation

Riveting

Experimental Research Program

Test specimens

20

Specimen sizes

23” Web Plate Specimen L5x3½”x3/8” flange angles

1/2” or 5/8” single cover plate

46” Web Plate Specimen L6x6x3/4” flange angles

3/4” single cover plate

36” Web Plate Specimen L6x6x3/4” flange angles

3/4” double cover plate

30” Web Specimen L6x6x3/4” flange angles

1” single cover plate

Load Redistribution as Cracks

Grow in First Component

Very difficult to get cracks to “fracture” on their own

26 “attempts”

1 “natural” fracture

4 induced with – driven wedges (“Mr. Fracture”)

No fractures “jumped” into uncracked components

Strain measurements and FEA point to load redistribution

Cracked component sheds load to stiffer uncracked

components

Not simple “P/A” fracture mechanics problem

Lack of Fracture not due to High Toughness

0

10

20

30

40

50

60

70

80

90

-100 -80 -60 -40 -20 0 20 40 60 80

Ene

rgy,

ft-

lbs

Temperature, Deg F

CVN Data – 23-1, 23-2, 23-3, 46-1, 46-2

Plate A (36-48FL)

Plate B (23FL)

Plate C (36-48CP)

Plate D (23-1/2CP)

Plate E (23-5/8CP)AASHTO SPEC.

Zone 3

Zone 2

Zone 1

CVN @

Temp of

Tests

Alternative Method to Inducing Fracture

Developed

Alternate fracture method

Hardfacing weld rod

○ Hard material (Rc = 59)

○ Low toughness

○ Microcracks form to relieve residual stresses

24

“Mr. Fracture”!

Test on Girder Specimen

Failure Mode of 1st Component

Specimen

# of

Fracture

Attempts

Method Failure Mode of

1st Component

Fracture Prop. to

Uncracked

Components?

23-1 4 Fatigue Crack Growth Fatigue NO



36-1 4 Fatigue Crack Growth* Fatigue NO

36-2 1 Hardfacing Weld Fuse Fatigue NO

36-2b 3 Driven Wedges Fracture NO

36-3 1 Driven Wedges Fracture NO




46-3 1 Fatigue Crack Growth Fracture NO


28

Fatigue Life

With Previous Research

29

Drilled Holes

Punched

Holes

Out-of-plane Behavior

Specimen 46-5

46” web plate, L6x6x¾” Flange Angles,

¾” Cover Plate

Severed Flange Angle

Loaded to 0.55Fy of

original net section

0.034” Out-of-plane

deflection (~1/32”)

30

Severed Flange Angle

Web Plate

Girder Bottom Flange

Finite Element Modeling Stress distribution

31

Failed flange angle

Results to Date

No fractures “jumped” into uncracked

components

“Natural” fracture of 1st primary component in

only 1 case

Larger member (proportions) being

investigated in FEA and experimental

○ e.g. 1”+ thick CP)

Results to Date

Cat D for drilled holes after 1st component failure

Worse for punched

FEA parametric studies for Sr calculation in process

Effect of unsymmetric failure

Does not appear to be an issue

Evaluation approach may be as simple as:

SrAF = SrNETKbKg

Check Mc/InetAF - simple software developed

Calculation of rational inspection interval

assuming one component failed If not infinite life, hands inspection at extended (calculated)

interval appropriate

Redundancy Evaluation Software

Proposed Deliverable Timeline

Focus on wrapping up work on riveted

members subjected to flexure

Deliver draft evaluation guidelines to FHWA / T-

18 / T-14 for consideration in Summer 2015

Include inspection guidance

Work on bolted members to continue

Investigating different plate geometry

Wrap up bolted early 2016

Proposed Deliverables

Axial (truss) members

TPF panel requested testing of axial

members

Behavior may be different than

bending

2,000 kip capacity machine in

fabrication

Will be utilized by both

TPF-5(253) and TPF-5(238)

Questions?

Steel

Bridge

Research

Inspection

Training

Engineering

S-BRITE Status

Unique Training

Environment

Various Components

I-35W

Components

Lafayette St. Bridge Fractured Girder (Minnesota)

Even Complete

Bridges

2015 Planned S-BRITE Activities

Continue with training

New courses for 2015 “Implementing Effective Retrofits in Selected Steel

Bridge Details” ○ Includes hands-on retrofit implementation

“Welding 101”

Continue with DEN

Proposed pooled fund tasks Virtual Bridge Inspection Pilot Study

Development of Tools for Corrosion and Damage Measurement using 3D Imaging

Roll out “Steel Property Material Archive”

Development of Tools for Corrosion and

Damage Measurement using 3D Imaging

Virtual Bridge Inspection Pilot Study

Steel Property Material Archive

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