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Okamoto Structural Engineering Announces First Ambient Vibration Test Conducted on Concrete Digester Tank

LOS ANGELES, CA — Okamoto Structural Engineering (OSE) has conducted the first ever ambient vibration testing on an aboveground, wastewater tank structure. The test was conducted on digester tank No. 5 at the Inland Empire Utility Agency’s (IEUA) Ontario facility.

Erich Axsom, SE, Vice President at OSE, performed in-situ testing using precision sensors by Sensequake, OSE’s technology partner. His tests included six Larzé sensors placed along the tank’s rim to gather ambient (small and natural) vibrations. The field data was sent to Sensequake’s headquarters in Montreal, Canada, where they used their patented 3D-SAM software to model the tank’s current performance state.

The results showed that the tank structure’s fundamental frequency at 90 percent full moves at a natural 5.0 to 9.3 Hz. Ambient vibration testing is now allowing asset owners to accurately take inventory of their critical infrastructure assets. OSE can identify structural integrity problems from the tests or immediately after a major, natural event like an earthquake.

“I was able to capture a tank’s structural properties in just a few hours,” Axsom said.

The Future is Now
Since 2015, customers have benefitted from deploying Sensequake’s technologies on their buildings, bridges, and port assets. The IEUA is a California Municipal Water District that authorized this pilot study to determine how they can use technology to enhance their maintenance program.

“I really enjoyed the conversation and presentation last week," said Travis Sprague, IEUA Principal Engineer. "We are going to sit down with our Asset Management group soon to discuss next steps. In addition, we will share this information with the rest of our Engineering and O&M team. Doing a baseline analysis on our critical structures that cannot be regularly, or ever, inspected is something that I would like to investigate next."

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