Monitoring Structural Response to Earthquakes using

Wireless Sensor Networks

Judith Mitrani

June 18, 2002

Why is Structural Health Monitoring Important?

• Measure changes to applied loads • Evaluate health due to accumulated damage (weather, age, ambient vibrations, natural disasters, “unnatural” disasters)• Evaluate structure after major event (earthquakes, hurricanes, industrial accidents, terrorist attacks)• Use measurements to actively or passively control structure

Instrumentation for Monitoring

• Accelerometers (acceleration)

• GPS (displacement)

• Rate Gyroscopes (dynamic strain)

• Magnetometer (sensor bearings)

• Barometer (pressure)

• Thermistor (temperature)

Lessons Learned from 1994 Northridge Earthquake

• Apartment buildings built with tuck-under parking in the 1960’s and the 1970’s

• Configuration creates a soft-story in the ground floor and torsional modes of vibration

• Important welded connections failed in hundreds of buildings

• Severe damage and even collapse

CUREE Wood-Frame Test at Richmond Field Station

• Build large-scale model of a typical late 1960’s apartment building with tuck-under parking, using 1964 Uniform Building Code (UBC)

• Run series of scaled 1994 Northridge and 1999 Izmit Earthquakes

• Asses the effect of finish materials on structure (exterior stucco, interior gypsum boards, etc.)

• Test effectiveness of most common retrofit

• Detect damage to structure using dense array of wireless sensors

Retrofit for Soft-Stories

3-Story Wood Frame Apartment Building with

Finish Materials

Close-up of Retrofit: Steel Moment Resisting Frame

(mechanism for resisting lateral forces induced by earthquakes)

Why Wireless Motes?

• Easy to Install

• Cheap

• Store Data Onboard

• Expandable Sensor-Board Platform/Flexible Software

• Message Hopping Capabilities

• Remote Communication

Structural Testing in a Controlled Environment

• Footprint of building is 16’W 32’L 27’T

• Longitudinal side completely open on one side for parking

• Shaking table (20’ 20’) produces 3 translational components of motion

• Wireless and conventional sensors used

• Software for sensors by Crossbow Technology, Inc.

• 25 Motes on Glulam Beam

• 25 Motes on First Story Wall

Scaled 1994 Northridge Earthquake on Wood-Frame of Apartment Building

Structural Response to Earthquake

More Civil Engineering Applications:Liquefaction Experiment in Japan

Measured Accelerations

Potential Applications

• Instrument Golden Gate Bridge

• Prompt Post-Event Tagging of Structures

• FEMA Urban Search & Rescue Team

• On-line Health Monitoring (update dynamic model of structure)

• Enabling Technology for Self-Repairing Structures (active control)

Mote Challenges

• Storage• Communication• Numerical Computation Capability• Power• Reliability (in Japan, 50% of the motes thought

they were there for “security” reasons)• Time Synchronization