Water Tanks Seismic Evaluation & Retrofit

  • Location Sammamish & Issaquah, WA
  • Owner Sammamish Plateau Water & Sewer District
  • A Tale of Two Tanks

    Two tanks; one retrofit alternative; $330,000 saved.

Drinking water for 63,000 residents. Tanks 7MG and 297 are both ground-supported, welded carbon steel water storage tanks that needed a seismic check-up. Reid Middleton peer reviewed retrofit costs and considered retrofit alternatives. The seismic evaluation and analysis determined that both tanks could meet performance objectives while reducing the cost of previous seismic retrofit options. The retrofit alternatives developed in collaboration with SPW met desired structural performance objectives and current AWWA seismic provisions. Reid Middleton’s retrofit design alternative minimized the tanks’ operational downtime and resulted in a cost savings of nearly $330,000; approximately 40% less than originally anticipated. Construction will occur only in the winter months while the demand and impact on the water system is the least.

Stress Results of FEM

Deflected Shape of FEM