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Evidence of SeismicResistance of HelicalFoundationsHoward A. Perko, Ph.D., P.E.Magnum Piering, Inc.November 2007DFI Helical Foundations andTie-Backs SeminarOutline IBC Seismic LoadsSeismic Case StudiesSeismic Damping of Helical PilesExample Seismic DesignNovember 2007DFI Helical Foundations andTie-Backs Seminar1
Earthquake Loads (IBC 2006) Design to Resist Earthquake Loads– Exceptions: One and Two-Family Dwellings in Seismic Design CategoriesA, B, or C where mapped short-period response 0.4 g Wood Frame Buildings in Accordance with Section 2308 Agricultural Storage Structures– Seismic Design Category Based on Occupancy and Severity of Ground Motion– Site Class Classification based on Soils PresentNovember 2007DFI Helical Foundations andTie-Backs SeminarSeismic Design of Piers or Piles (IBC 2006) Seismic Design Category C– Interconnect Piles or Pile Caps with Ties Capable of Tension or Compression Force, FsFs 0.1 x Pc x SDSPc Higher Column Load– Connection of Piles to Pile Cap Provide Transverse Steel as Required for Column Provide Tension Connection– Pile Splices Develop Full Tensile Strength of Pile, or Designed to Resist Seismic Load CombinationsNovember 2007DFI Helical Foundations andTie-Backs Seminar2
Seismic Design of Piers or Piles (IBC 2006) Seismic Design Category D, E, or F– Meet Requirements of Seismic Design Category C– Design Details for Piles Designed to Withstand Maximum Imposed Ground Motions– Lateral Resistance to Structure Seismic Forces– Liquefiable Strata– Connection of Piles to Pile Cap Design Tension Connection for lesser of– 1.3 x Mechanical Tensile Capacity of Pile– 1.3 x Pullout Capacity of Pile– Seismic Load Combinations Design Moment Connection for lesser of– Mechanical Axial, Shear, and Moment Capacity of Pile– Seismic Load CombinationsNovember 2007DFI Helical Foundations andTie-Backs SeminarEarthquake Loads (IBC 2006) Vertical Component, EV– EV 0.25 SDS D where, SDS Short Period Design Acceleration D Dead Load Horizontal Component, EH– EH ρ QE where, ρ Redundancy Factor (1 to 1.5)QE Horizontal Seismic Forces (CS W “Base Shear”)CS Seismic Response Coefficient (I SDS/R “Simplified”W Weight of Structure (Dead Select Live LoadsR Response Modification Coefficient (1.5 to 8)November 2007DFI Helical Foundations andTie-Backs Seminar3
Seismic Design Category (2006 IBC)Seismic Design Category E:Occupancy I, II, or IIIwith SD1 0.75Seismic Design Category F:Occupancy IVwith SD1 0.75November 2007DFI Helical Foundations andTie-Backs SeminarOccupancy Category (IBC 2006) I : Agricultural and Storage FacilitiesII: Other StructuresIII: High Occupancy StructuresIV: Essential FacilitiesNovember 2007DFI Helical Foundations andTie-Backs Seminar4
Earthquake Loads (IBC 2006) Adjusted Maximum Acceleration– SMS Fa Ss Design Acceleration– SDS 2/3 SMSNovember 2007DFI Helical Foundations andTie-Backs Seminar0.2 s Acceleration, Ss (2006 IBC)November 2007DFI Helical Foundations andTie-Backs Seminar5
Site Coefficients (2006 IBC)November 2007DFI Helical Foundations andTie-Backs SeminarSite Class Definitions (2006 IBC)November 2007DFI Helical Foundations andTie-Backs Seminar6
Residence, Northridge, CANovember 2007DFI Helical Foundations andTie-Backs SeminarShopping Mall, Northridge, CANovember 2007DFI Helical Foundations andTie-Backs Seminar7
Common Pile FailuresNovember 2007DFI Helical Foundations andTie-Backs SeminarNovember 2007DFI Helical Foundations andTie-Backs Seminar8
DFI Helical Foundations andTie-Backs SeminarNovember 2007DampingCap Displacement Amplitude (mm)3530MeasuredComputed, Damping Ratio 0%25Computed, Damping Ratio 20%201510500123456Frequency (Hz)November 2007DFI Helical Foundations andTie-Backs Seminar9
Damping Pile Head Accelerations can beReduced by 60% due to Damping(Tabesh and Poulos, 1999)November 2007SeismicParameters:DFI Helical Foundations andTie-Backs Seminar0.2 s Acceleration, Ss (2006 IBC)SS 0.50Gatlinburg, TNNovember 2007DFI Helical Foundations andTie-Backs Seminar10
SeismicParameters:Site Class Definitions (2006 IBC)SS 0.50Site Class DNovember 2007SeismicParameters:DFI Helical Foundations andTie-Backs SeminarSite Coefficients (2006 IBC)SS 0.50Site Class DFa 1.4November 2007DFI Helical Foundations andTie-Backs Seminar11
SeismicParameters:Earthquake Loads (IBC 2006)SS 0.50Site Class DFa 1.4SDS 0.47 Adjusted Maximum Acceleration– SMS Fa Ss– SMS 1.4 (0.5) 0.7 Design Acceleration– SDS 2/3 SMS– SDS 2/3 (0.7) 0.47DFI Helical Foundations andTie-Backs SeminarNovember 2007SeismicParameters:Occupancy Category (IBC 2006)SS 0.50Site Class DFa 1.4SDS 0.47Occup. IIINovember 2007 I : Agricultural and Storage FacilitiesII: Other StructuresIII: High Occupancy StructuresIV: Essential FacilitiesDFI Helical Foundations andTie-Backs Seminar12
SeismicParameters:Seismic Design Category (2006 IBC)SS 0.50Site Class DFa 1.4SDS 0.47Occup. IIIS.D.C. CNovember 2007SeismicParameters:DFI Helical Foundations andTie-Backs SeminarSeismic Design of Piers or Piles (IBC 2006)SS 0.50Site Class DFa 1.4SDS 0.47 Seismic Design Category C– Interconnect Piles or Pile Caps with TiesOccup. III Capable of Tension or Compression Force, FsS.D.C. CFs 0.1 x Pc x SDS 0.1(50)(0.47) 2.4 kipsFS 2.4 kipsPc Higher Column Load 50 kips– Connection of Piles to Pile Cap Provide Transverse Steel as Required for Column Provide Tension Connection– Pile Splices Develop Full Tensile Strength of Pile, or Designed to Resist Seismic Load CombinationsNovember 2007DFI Helical Foundations andTie-Backs Seminar13
SeismicParameters:Earthquake Loads (IBC 2006)SS 0.50Site Class DFa 1.4SDS 0.47Occup. IIIS.D.C. CFS 2.4 kipsEV 5.9 kips Vertical Component, EV– EV 0.25 SDS Dwhere, SDS Short Period DesignAcceleration D Dead Load– EV 0.25 (0.47) (50 kips)– EV 5.9 kipsNovember 2007DFI Helical Foundations andTie-Backs SeminarWhat About Damping?– Re-do Example with60% DampingNovember 2007DFI Helical Foundations andTie-Backs Seminar14
SeismicParameters:0.2 s Acceleration, Ss (2006 IBC)SS 0.32Gatlinburg, TNSS 0.50 @5% DampingThus, SS 0.32 @60% DampingNovember 2007SeismicParameters:DFI Helical Foundations andTie-Backs SeminarSite Class Definitions (2006 IBC)SS 0.32Site Class DNovember 2007DFI Helical Foundations andTie-Backs Seminar15
SeismicParameters:Site Coefficients (2006 IBC)SS 0.32Site Class DFa 1.5SS 0.321.5November 2007SeismicParameters:DFI Helical Foundations andTie-Backs SeminarEarthquake Loads (IBC 2006)SS 0.32Site Class DFa 1.5SDS 0.32 Adjusted Maximum Acceleration– SMS Fa Ss– SMS 1.5 (0.32) 0.48 Design Acceleration– SDS 2/3 SMSNovember 2007– SDS 2/3 (0.48) 0.32DFI Helical Foundations andTie-Backs Seminar16
SeismicParameters:Occupancy Category (IBC 2006)SS 0.32Site Class DFa 1.5SDS 0.32Occup. IIINovember 2007SeismicParameters: I : Agricultural and Storage FacilitiesII: Other StructuresIII: High Occupancy StructuresIV: Essential FacilitiesDFI Helical Foundations andTie-Backs SeminarSeismic Design Category (2006 IBC)SS 0.32Site Class DFa 1.5SDS 0.32Occup. IIIS.D.C. BNovember 2007DFI Helical Foundations andTie-Backs Seminar17
SeismicParameters:Seismic Design of Piers or Piles (IBC 2006)SS 0.32Site Class DFa 1.5SDS 0.32Occup. IIIS.D.C. BFS naNovember 2007SeismicParameters: Seismic Design Category A&B– No Special Seismic RequirementsDFI Helical Foundations andTie-Backs SeminarEarthquake Loads (IBC 2006)SS 0.32Site Class DFa 1.5SDS 0.32Occup. IIIS.D.C. BFS naEV 4.0 kips Vertical Component, EV– EV 0.25 SDS Dwhere, SDS Short Period DesignAcceleration D Dead Load– EV 0.25 (0.32) (50 kips)– Ev 4.0 kipsNovember 2007DFI Helical Foundations andTie-Backs Seminar18
ComparisonWith 5%Damping:With 60%Damping:SS 0.50SS 0.32Site Class DFa 1.4SDS 0.47Occup. IIIS.D.C. CFS 2.4 kipsEV 5.9 kipsNovember 2007Site Class DFa 1.5SDS 0.32Occup. IIIS.D.C. BFS naEV 4.0 kipsDFI Helical Foundations andTie-Backs SeminarConclusions Historical Use of Helical Piles SuggestsExcellent Earthquake Resistance More Research is Needed into HelicalPile Seismic Damping The Future of Helical Piles may be forSeismic Retrofit or New Foundations inEarthquake Prone AreasNovember 2007DFI Helical Foundations andTie-Backs Seminar19
Conclusions . hurry, before ourGatlinburg house lookslike this . . or this!November 2007DFI Helical Foundations andTie-Backs Seminar20
DFI Helical Foundations and Tie-Backs Seminar Evidence of Seismic Resistance of Helical Foundations Howard A. Perko, Ph.D., P.E. Magnum Piering, Inc. November 2007 DFI Helical Foundations and Tie-Backs Seminar Outline IBC Seismic Loads . Seismic Design of Piers or Piles (IBC 2006) Seismic Design Category D, E, or F
