PTI 2010 HooverDamBypassBridge

8/18/2019 PTI 2010 HooverDamBypassBridge

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Hoover Dam Bypass Bridge:

Temporary Stay CablesConsiderations for Design, Testing,

Installation and Inspection

by

Michael Schwager, P.E.

Schwager Davis, Inc.

Presented at

2010 PTI Technical Conference

Fort Worth, Texas


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Project Description1,060 foot span cast in place concrete segmental twin

arch bridge with precast segmental columns


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SDI’s Scope of Work Fabricate, furnish and install post-tensioned rock

anchors in the arch skew backs


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SDI’s Scope of Work Fabricate, furnish and install post-tensioned rock

anchors in the stay anchor blocks


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SDI’s Scope of Work Furnish post-tensioning materials, equipment and

technical assistance for precast columns, temporarytowers and bent caps


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SDI’s Scope of Work Furnish temporary stay cable system and provided

technical assistance and inspection services


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Contract Stay Cable Layout

• Backstay Cable Geometry

•

Access for installation & Stressing


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Revised Stay Cable Layout

• Removed Lower Cables

• Brought all Cables to tower top

• Re-routed Backstay Cables• Lowered Forestay Connection


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Stay Cable Design Considerations

•

More critical in many ways than permanent stay cables– Permanent stay cables

• Long term Fatigue

• Corrosion

– Temporary stay cables• Large load variations (wedge bite)

• Angle change due to sag from load variation

• Temporary construction obstacles

• Constructability


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Additional Testing

•

Strand fatigue and wedge testing– Cyclical loading with high angle change(2 Million cycles)

• Critical Anchorage Testing

•

Swaged anchor with adjustable ring nut• Post-Blocking equipment

• Strand Installation equipment


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Load Transfer – Strand to Anchorage

•

Machined Anchor Heads / Wedge Design• Post-Blocking Device


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Installation Challenges


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Forestay – Lower Anchorage


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Dampeners


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Hoover Dam Bypass Bridge

Documents

PTI 2010 HooverDamBypassBridge