A New, Cost Effective Single Sensor Approach to SHM

Trouble Maintaining 612,677 Bridges Nationwide

54,259 of the nation’s 612,677 bridges are rated “structurally deficient.”  Americans cross these deficient bridges 174 million times daily. The average age of a structurally deficient bridge is 67 years, compared to 40 years for non-deficient bridges. One in three (226,837) U.S. bridges have been identified to need repairs.


Source : CNN Report , Feb 2018

Structurally Deficient Bridges | SignaBridge
Structurally Deficient Bridges(comparison of ratings for key items)
Bridge Health Monitoring and Maintenance | SignaBridge

92% Budget Deficit in Bridge Repair

  • $150 billion is needed to repair all the deficient bridges in the US – against an annual budget of only $8 billow available for maintenance. (2017 figures)
  • 160,000+ bridges are structurally deficient and need a significantly increased repair/maintenance budget.
  • Only 8% of the required repair budget is available.
  • Structural Health Monitoring (SHM) or a sensor-based auditing system is required to quickly understand which bridge to repair and where the repairs should occur. An extremely accurate process is required to avoid unnecessary repair.
  • But…present day SHM is expensive!

What is SHM? Sensor-based Structural Health Monitoring?

Sensor Based Structural Health Monitoring | SignaBridge

SHM – Present Methods: Expensive, Logistically Challenging, Labor intensive

The direct method, though expensive, is predominantly used in Structure Health Monitoring. Deflection/Strain monitoring techniques are used in the direct method.

Strain Gauge | SignaBridge
Strain Gauge

Strain gauge and laser operated light sensors are used for this purpose. It is monitored manually or by integrating it with IOT.

The position of a structure is observed with respect to a static base. High impact or self-weight over time can cause deflection, which can be observed and action is taken accordingly.

Structural Health Monitoring | SignaBridge

High Cost of Existing SHM

The main challenge in the transition of traditional SHM technique from R&D to practical field implementation is Economics or Cost of the whole process.

Some of the cost-intensive challenges are:

  • Labor intensive sensor deployment and maintenance
  • Sensor system cost
  • Powering the sensor system
  • Data transmission and interpretation.

Example -> Lehigh River Bridge, SR-33

The bridge was targeted for a 3-year monitoring program.

The direct equipment cost was 40% of the total monitoring cost whereas the costs of labor and other related items were 60% of the total monitoring cost.

Structural Health Monitoring Equipment | SignaBridge
Structural Health Monitoring System | SignaBridge

SHM – Structural Health Monitoring System: A new Less Expensive Compact Solution

MachineSense (by SignaGuard) Solution:

  • One Sensor, three functions: vibration, gyroscope, and magnetometer
  • Natural Frequency (3 axes) + 3 axis deflection data using Gy and Mg
  • Compact, wireless connected, Cloud connected, 3 layers of Edge
  • 100s of SHM sensors can be mounted on a Bridge within hours!
  • Data and Analytics flow within minutes of installation
  • Alarm/SMS to Bridge Authority, Police – Automated
Structural Health Monitoring Analysis | SignaBridge
Deflection trend of Girder in Haldiram Bridge , Kolkata (in mm)
Smart SHM using Multisensing and Edge | SignaBridge
Data Flow: Smart SHM using Multisensing and Edge

MachineSense (by SignaGuard) Approach reducing high cost of SHM

Sensor Component Analyzer | SignaBridge

MachineSense (by SignaGuard) sensors are capable of collecting 9 axis vibration data including a triaxial accelerometer, a gyroscopic sensor, and a magnetometer. One can compute 3 axis deflection, strain, angular velocity, acceleration, and other required parameters.


DataHub (single-board computer) is the brain of our sensor. It receives the sensor data via Bluetooth. It performs high-end signal processing and machine learning using edge computing technology to produce understandable metadata. The metadata is sent to the cloud via wifi to store and to present in the visualization interface.

Component Analyzer | SignaBridge

The whole ecosystem of Sensor, Datahub and Cloud is connected using an advanced IoT onboarding feature which is very easy to install and everything gets synchronized in less than 100 seconds.

Advantage of SHM vs NDT( Non Destructive Testing)

SHM ( MachineSense – by SignaGuard) NDT
Data 24×7 for 3 years ( continuous data) Max 24-48 hours
Visualization/collection Anywhere Only in bridge location
Deflection 3 axis , (reduced cost) 1 axis, expensive
Vibration 3 axis with many algorithms  1-3 axis, raw data
 Rotation  3 axis  normally not used
Temp, humidity  Standard Standard
 Strain gauge/ Corrosion Standard  Standard
Structural Health Monitoring | SignaBridge

Why This Low Cost Approach to SHM is Critical

SHM promises to reduce the cost of Bridge Maintenance, but that can happen only if hardware cost, installation cost and maintenance of SHM is negligible to Bridge Maintenance cost

Therefore, the following must be cost-effective for SHM to be effective

  1. HW and System cost
  2. Installation cost
  3. Maintenance of SHM

How New SHM Can Address 92% Deficit in Repair Budget

Stage 1: Inspection:

All bridges are subjected to an audit

Install MachineSense (by SignaGuard) SHM for 7 days for initial data

Expected outcome:

Determine whether a bridge is structurally deficient – needs next level of scrutiny

Stage 2: 24×7 Long Term Monitoring:

If found structurally deficient, selected bridges will be placed under 24×7 monitoring by MachineSense (by SignaGuard) SHM to look out for long term trend of deflection and natural frequency drift.

Stage 3: Alarm to Police

If Stage 1 or 2 reveals critical condition and hazard to public safety, MachineSense (by SignaGuard) SHM will send the alarm if any abnormal deflection or vibration is detected.

Case Study of Kolkata Gate and Haldiram Bridge Using: MachineSense (by SignaGuard) SHM

Installation Details

Installation Sites Kolkata Gate Haldiram Bridge
Sensor 4-Component Analyzer 2-Component Analyzer
Details Each of the 4 Component Analyzers were installed in the middle of two adjacent pillars. One is installed on the Steel girder and another on the steel frame above the bearing.
Installation Pictures of Haldiram Bridge | SignaBridge
Installation Pictures, Haldiram Bridge
Data Hub +4G | SignaBridge
Data Hub +4G Modem Router, acting as Edge Cloud

Continuous Vibration Monitoring to Check Loading Condition by Analyzing Vibration Patterns.

In this way, we are monitoring vibration induced in the sensor by the bridge in real time. Statistical computations enable us to visualize the loads (Cars, Wind or any other external factors).

Vibration monitoring | SignaBridge
Figure shows Vibration peaks caused by the heavy loaded truck during night time in Haldiram Bridge, Kolkata

Deflection Monitoring With The Help of Gyroscope Sensor

Integrity and strength of a structure are determined by how rigid it is, especially for concrete. For the metal structure, it is determined by how much force it can withstand without going into the plastic deformation region.

Fault in a structure leads to the plastic deformation, i.e., the deformation is permanent or incremental and the structure doesn’t return to its original condition by removing the applied force.

All of this can be analyzed just by monitoring deformation/strain.

With the help of the Gyroscopic and Magnetic sensor, we are monitoring angular velocity, which is reflecting the deflection patterns.

Gyroscope Sensor | SignaBridge
The above graph shows the gyroscopic data of September 15th, when more than 80 people were present on the Kolkata gate. It clearly shows deflection in the X axis after morning but repositioned in the afternoon

Impact Analysis by Conducting Automatic Frequency Domain Analysis On The Impact Band in a Time Series Data

  • Heavy vehicles with huge momentum create an impulsive force on the bridge structure. It is like throwing a pebble in a stationary water body, the ripple starts when the pebble hits the water, but it propagates for quite some time.
  • The amplitude of the generated impulsive wave depends on the vehicle, but the frequency response depends mostly on the structure. Thus, frequency domain analysis reveals the natural frequency response of the structure. Any change in the frequency response or abnormal dampening, will reflect fault in the form of strain or crack which may be catastrophic if not checked in time.

Impact forces of Trucks in Time and Frequency Domain

Frequency Domain | SignaBridge
The spectrum of impact data (produced by a truckload on girder), shows frequencies in the range of 0.5- 5 Hz : (100 sample= 1 Hz

Beta Sites and Collaboration

  1. SHM beta opportunity to install on bridges that have been marked as “structurally deficient”.
  2. Looking at the trend and signature of vibration and deflection data – find out the remaining life cycle of the structure.
  3. Find out from vibration pattern – transition from elastic to the plastic domain.
  4. Compare deflection by FEM vs actual measurement to create an alarm condition on a deflection.
  5. Studies of shifting of natural frequencies to detect faults.
Read Case Studies