Using Acoustic Sensors to Monitor Structural Cable Performance

Michael S. Higgins, P.E.Pure Technologies410-309-7050

What is a Structural Cable?

Cable Performance History

• Suspension Bridges over 120 years

• Post tensioning tendons and stay cables more recent

• Performance has been excellent

• How do we inspect/assess a cable?

Challenges of Assessing a Cable

• Main structural elements are hidden

• Corrosion or fatigue problems can be localized

• Corrosion or fatigue will not necessarily produce visual evidence

How to Assess a Cable?Conventional inspections rely on visual inspections

Grouted Stay Cable

Suspension Bridge Cable

Post Tensioning Tendon

Limitation of visual inspections

Inspecting a 20-foot length of cable with wedging at 8 points exposes less than 0.1% of the wire for a typical suspension bridge (4,000 foot main cable with 15,000 wires).

(Robert Nickerson (1998), “Safety Appraisal of Suspension Bride Main Cables”, National Cooperative Highway Research Program, Transportation Research Board, Contractor’s Report fro a Workshop in Newark, NJ)

Unexposed

ExposedHow Much of the Cable is Inspected?

Extrapolation?

Limitation of Visual InspectionsAcoustic Health Monitoring for Cables

• Electronically monitor acoustic events being transmitted through a structure

• Identify acoustic event associated corrosion/fatigue problem

• Proven to reliably detect wire failures in cables and tendons

Limitation of Visual InspectionsCables & Acoustic Monitoring

• Wire failures generate significant energy release

• A few sensors can monitor entire length of cables

• Wire failures can be distinguished from ambient noise

How Does Acoustic Monitoring Work?

WWW Data Center

ReportDAQWire Break

Bridge

Limitation of Visual InspectionsFiltering Ambient Noise

Limitation of Visual InspectionsFiltering Ambient Noise

Limitation of Visual InspectionsQuincy Bayview Bridge

Limitation of Visual InspectionsSensors on the Quincy Bayview

Limitation of Visual InspectionsSensors on the Quincy Bayview

Limitation of Visual InspectionsCabling on the Quincy Bayview

Limitation of Visual InspectionsData Acquisition System on the Quincy Bayview

Limitation of Visual InspectionsNear Real Time Availability of Data

Limitation of Visual InspectionsNear Real Time Availability of Data

Insert screen capture

Limitation of Visual InspectionsNear Real Time Availability of Data

Challenges of Continuous Monitoring

• Software problems (e.g. viruses)

• Power outages

• Operating system freezes

• Power outages

• Lightening strikes

• Durability

Other Operating Acoustic Monitoring Systems

Other Operating Acoustic Monitoring Systems

Suspension Bridge Monitoring Systems

Suspension Bridge Monitoring Systems

Post-Tensioned Bridges

Who is Pure Technologies?Combining Video and Other Sensors

Who is Pure Technologies?Combining Video and Other Sensors

Limitation of Visual InspectionsComplete Structural Monitoring

Wacker Drive, Chicago, IL• Acoustic• Extensometers• Strain Gages• Tiltmeters• Thermocouples• Humidity• Load Cells

Limitation of Visual InspectionsReasons for Structural Health Monitoring Systems

1. Problematic Structure

2. Proactive inspection/assessment