Steel Reservoir Seismic Design Criteria
Transcript of Steel Reservoir Seismic Design Criteria
Steel Reservoir Seismic Design Criteria
May 8, 2013
Jon Conner, P.E.
RH2 Engineering
• Damage/failure modes • Ground motions • Structural design • Detailing
Seismic Design Criteria
Seismic Design Notes
• The goals of seismic restraint are to prevent collapse and protect life
• Essential facilities are designed for 50% higher loads than ordinary facilities
• Current code uses a cost-versus-risk approach – In a 50-year timeframe, there is a 2% probability that
an earthquake larger than the design earthquake will occur
– This is equivalent to a 2,500 year return period for the design earthquake
• The code does NOT limit property damage or guarantee functionality
Existing Tanks at Risk
• Older reservoirs • Tall and slender • Inadequate foundation size • Inadequate anchorage
o Straps or small bolts
Possible Damage Modes 1. Anchorage – Primary: Anchor stress
Possible Damage Modes
1. Anchorage Failure
– Secondary: Floor cracking
Small Diameter Bolts
Anchor Straps
Large Diameter Bolts with Anchor Chairs
Retrofit Example - 50 feet by 50 feet - 725,000 gallons
• MicroPile Retrofit
– Useful on small properties where foundation cannot be expanded
– Provides resistance to uplift and bearing without adding much mass
Possible Damage Modes 2. Soil Settlement
(inadequate foundation)
Inadequate Foundation
Possible Damage Modes
3. Shell Buckling (elephant foot)
Potential Buckling Solutions
• Stiffen shell
• Add interior ballast ring
• Lower water level
Possible Damage Modes 4. Sloshing Damage
5. Soil Stability
Ground Motion
• Based on ASCE 7 (US)
– Site-specific based on location and soil type
– Also used by IBC
• Max Considered EQ
– 2% probability in 50 years
– 2,500-year return
– Previously 500-year return
Developed by USGS &
Design Model
Detailing • Freeboard
• Ventilation
• Piping
Piping Connections
• Allow for relative displacements • Prepare for emergency shut down • Isolate damaged sections
Questions?