DN Staff

July 10, 2001

2 Min Read
Super-size shocks sure up civil structures

Friday, December 15, 2000

North Tonawanda, NY-Today, more and more civil engineers are turning to mechanical engineers to help meet seismic requirements, reduce the mass, and in some cases actually decrease the cost of bridges, buildings, and other structures.

For example, at the Seattle Mariners' SAFECO stadium, Taylor Devices supplied eight 24-ft long dampers weighing 4.5 tons each that serve as buffers between the stadium's side columns and the retractable roof sections that they support. The company has shipped 16 of the world's largest shock absorbers for the new Cape Girardeau Bridge that is nearing completion and spans the Mississippi River between Illinois and Missouri. It is also working to reduce the mass of a 55 story building in Mexico City to keep the soil bearing stress within legal limits.

The dampers reduce stress and deflection simultaneously so that, for example, SAFECO stadium's 20-million-lb roof won't collapse in the event of an earthquake. And according to Taylor Devices President Doug Taylor, dampers saved $5 million in steel costs. But the real challenge, says Taylor, was interfacing between the stadium's roof and the crane mechanism because it joins rigid machine-like crane products with the more flexible civil engineering structure.

"Normally, civil engineers tend to use stress-based calculations," explains Taylor, "while mechanical engineers use strain-based calculations. Stress-based designs minimize the use of material, and result in low-cost, lightweight structures that are aesthetically pleasing. Strain-based designs typically yield much stiffer structures."

Initial testing indicated that the roof flexed too much under seismic forces, and started showing failure points where it connects to its supporting columns. "A seismic input, perpendicular to the axis of motion of the roof, tended to buckle the structure at the hinge or knee connection between the roof and the support trusses that actually connect it to the moving runway," explains Taylor.

So mechanical engineers came up with a solution that involved adding some six million lbs of steel to the structure, which was unacceptable to the civil engineers and architects because it would be too heavy and unattractive. Taylor engineers came back with a damping proposal to reduce loading in the structure under seismic input. Designed to sop up the energy produced by an earthquake, the dampers deflect up to 2.5 ft of movement, and absorb 1.1 million lbs of force.

"Damping not only reduces loading in the structure and keeps the design attractive," says Taylor, "but it saves an estimated $5 million in net project costs. So instead of adding an extra $6 million in steel costs, the design requires only $1 million worth of dampers to reduce the loads down to a point where we have an optimal design." For more information about Taylor's dampers visit www.shockandvibration.com.

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