The 100-million-gallon Stacy Park Reservoir is the major water source for the City of St. Louis. As the result of a Metropolitan Area Seismic Hazards Study, the City decided to retrofit the reservoir to withstand the worst earthquake that might occur within a 2,500 year period. The City was concerned that any retrofit minimize interruption of service, not degrade water quality and minimize costs.

Stacy Park is a partially buried concrete reservoir measuring 600 feet by 800 feet with a depth of 35 feet. The reservoir has a concrete post-tensioned slab roof which is divided into eight segments. The individual segments are separated from each other by 5.5-foot-wide expansion joints. The slabs are supported by interior columns and beam frames, and on the exterior walls. The walls provide vertical support, but the slab is able to slide freely in both horizontal directions.

Horner & Shifrin provided two preliminary designs with cost estimates. Alternate No. 1 uses viscous dampers to link individual slabs together, and then to the exterior walls. A viscous damper works on very similar principles to a shock absorber in an automobile. Alternate No. 2 consists of concrete shear walls, cast inside the reservoir between the columns. This alternate would involve taking the reservoir out of service and employing a temporary reservoir to be used during the construction period.

The preliminary designs bore out Horner & Shifrin's early assessment. The passive damping system will cost substantially less than shear walls saving $4.5 million, take less time to construct, will not interfere with operations and will protect water quality by not interfering with water flow through the reservoir.

This is the first application of passive damping to a water reservoir in the United States and is another example of creative and innovative engineering provided by Horner & Shifrin.

	"2003 Excellence in Structural Engineering Award, Buildings under $5 Million" Structure Magazine
	"2003 Engineering Excellence Award" Consulting Engineers Council of Missouri
	"Honor Award" American Council of Engineering Companies of Missouri in 2003
	"Honorable Mention, Non-Building Catagory" Structural Engineers Association fo Kansas and Missouri in 2003