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?