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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