1. Utilization of SHM Methodologies to Detect Trunnion Friction in Tainter Gates
Quincy G. Alexander
Research Civil Engineer
Information Technology Laboratory
19 September 2017

2. Why Monitor Trunnion Friction
Case Study
Folsom Dam Spillway Gate Failure
Sacramento, CA,
July 1995
Gate #3 opened to maintain the flow of the river during a scheduled power plant shutdown
At 2.4 feet operator felt an “unusual vibration” and heard grinding noises
Gate failed releasing approximately 40,000 cfs
40% of Folsom Lake storage released
Lock operator’s responsiveness reduced further damage downstream
Due to the emergency action taken by the Folsom Dam operator when he noticed the failure of the gate, overtopping of Nimbus Dam was prevented and the water released from Folsom Lake was safely conveyed and attenuated.  As a result, the consequences of the gate failure were limited to the damage to the gate and the loss of stored water.  The gates were repaired at a cost of approximately $20 million.

3. Why Monitor Trunnion Friction
Case Study-Lessons Learned
Forensics revealed the cause of the malfunction to be excessive friction at the trunnion
Failure initiated at a diagonal brace
Caused by the corrosion at the pin-hub interface
Operated nearly 40 years with no problems
Failure may have been avoided with:
Routine maintenance (e.g. lubrication)
Protection from weathering
Routine Inspections
Due to the additional friction forces, the loads experienced by the trunnion pin caused increased loading in the gate struts and braces of the gate.  The gate struts are primarily compression members, but friction at the pin-hub interface induced a bending stress during gate operation. In order to better handle these loads, the struts are connected with diagonal braces that take the stress as axial loads. The resulting loads in these members exceeded the capacity of the strut-brace-connection bolts compromising the structural integrity of the gate.  As the gate was operated, the failure initiated at a diagonal brace between the lowest and second lowest struts. Increasing corrosion at the pin-hub interface raised the coefficient of friction and, therefore, the bending stress in the strut and the axial force in the brace. The capacity of the brace connection was exceeded and it failed. This caused the load to redistribute and the failure progressed, eventually buckling the struts.

4. Structural Health Monitoring
ERDC’s view of SHM
Use field observations, numerical simulations, and statistical models to:
Detect damage: location, type, severity
Observe degradation over time
Predict future degradation and reliability
We seek to provide tools, using this framework that will inform:
Maintenance/Repair/Rehab decisions
Operational decisions
Post-emergency evaluations

5. Trunnion Friction Study
Application of SHM paradigm to Trunnion Friction problem
Trunnion friction monitoring was identified as a need by districts
Low-cost
Minimal instrumentation
Output meaningful to operators

6. Trunnion Friction Study
Life safety/economic justification
How is damage defined
What operational and environmental conditions must be considered
Limitations on acquiring data
Operational Evaluation
Limitations….no good sensors available for this application that would allow for direct measurement of friction

7. Trunnion Friction Study
Selecting sensor types, number, and location
Data acquisition hardware
Data storage
Ability to normalize the data
Data Acquisition

8. Trunnion Friction Study
Identification of features that allows one to distinguish between the undamaged and damage cases
Comparing measured response with observations of the degrading system
Validated FEM can be used to introduce flaws and identify features
Feature Extraction
Externally applied moment ~3,378 kip-in
Estimated moment from diagonal strain measurements ~3,606 kip-in
Estimated moment 6.7% over actual
Approach feasible
Physical testing
1/5th scale model
Big cliff bass of design
Strain Measurement
Numerical Model

9. Trunnion Friction Study
Identification of features that allows one to distinguish between the undamaged and damage cases
Comparing measured response with observations of the degrading system
Validated FEM can be used to introduce flaws and identify features
Feature Extraction
Estimated moment ranged from 0.4% to 9% over actual across 10 loading scenarios
Approach feasible
Physical testing
1/5th scale model
Big cliff bass of design
Physical Model

10. Trunnion Friction Study
Using statistical models to transform features into actual performance-level decisions
Implementation of algorithms that operate on the feature to quantify damage
Supervised learning, unsupervised learning/outlier detection
Decision Making

11. Summary
Trunnion friction is a major concern and is difficult to measure
ERDC has developed a low-cost methodology to estimate frictional moments at trunnions
Numerical and physical simulations indicate methodology may provide estimates of frictional moments within a few percent of the actual values
Field demonstration pending

12. Questions? Quincy Alexander 601-634-2905