Transcription
Module 2 –AASHTO ABC GuideSpecifications, SeismicDesign Requirements forConnectionsLee Marsh, Ph.D., P.EDeputy Director – America’s Technical Excellence CenterGreg Banks, P.E., S.EProject Manager and Senior Bridge Engineer
AASHTO LRFD Guide Specifications for ABCAASHTO Guide Specifications for ABCNCHRP 12-102 Final Report providesadditional commentary and background2
OutlineI. Overview of AASHTO LRFD Guide Specifications for ABC- SeismicII. Seismic Design for ABC (3.4)III. Seismic Connection Design and Detailing (3.6.4-7 & 3.4.12)OverviewSeismic DesignConnections3
I. Overview of Guide Specifications for ABC- Seismic Aims to ensure minimal damage of the structure under moderateearthquake and collapse prevention under rare earthquakes. Adopts a Type I design strategy exclusively (inelastic behavior underductile limit state should occur only in the substructure). Written to supplement (not to replace) the current specifications. Future editions of Guide Specifications for ABC are expected toincorporate ongoing ABC seismic research.OverviewSeismic DesignConnections4
II. Seismic Design for ABC (3.4) Force-Based Design(AASHTO LRFD, 2017)OR Displacement-Based Design(AASHTO SGS, 2011)Regardless of the seismic analysis/design method the EarthquakeResisting Systems (ERS) and Elements (ERE) shall be identified.OverviewSeismic DesignConnections5
II. Seismic Design for ABCFibFdForce, FFBrittle LinksDuctile LinkBrittle LinksFDuctile Behavior, Fd All FibBrittle Behavior, Any Fib FdDisplacement, OverviewSeismic DesignConnections6
II. Seismic Design for ABC (3.4)CP – Capacity Protected(Non-ductile)ED – Energy Dissipating(Ductile)The Designer should evaluate the implications ofusing prefabricated elements and/or connectionsin or near the plastic hinge zones.OverviewSeismic DesignConnections7
II. Seismic Design for ABC (3.4)All members of the ERSmust have sufficientstrength and ductility toform the intendedstructural plasticmechanism.OverviewSeismic DesignConnections8
II. Seismic Design for ABC (3.4) Ensure continuity of load path under load reversals. Ensure development of cyclic inelastic deformations. Realize that maximum demands typically occur at connections ofprefabricated elements. Limit the occurrence of conditions leading to rapid loss ofresistance (local buckling, stress concentrations, etc.)DETAILING IS IMPORTANT!OverviewSeismic DesignConnections9
II. Seismic Design for ABCAll connections and Earthquake Resisting Elements(EREs) in the GS for ABC only permitted with theOwner’s approval.OverviewSeismic DesignConnections10
III. Seismic Connection Design and Detailing (3.6)Other details are permitted provided that:1. They are approved by the Owner,AND2. The designer demonstrates adequate load transferwith consideration for compatibility of deformationsand constitutive relations of materials.OverviewSeismic DesignConnections11
III. Seismic Connection Design and Detailing (3.6) Mechanical bar connectors (3.6.4) Grouted duct connections (3.6.5) Pocket connections (3.6.6) Socket connections (3.6.7) Two-stage integral pier cap (3.6.12)Mechanical connectorsGrouted ductPocketSocketTwo-stage integral12
3.6.4 Mechanical Bar ConnectorsNote: No more than one connector per bar inplastic hinge zone is allowed (3.6.4.4) so thisdetail does not meet the GS for ABC.PC ColumnPC ColumnGrouted SleeveCoupler (GC)Headed BarCoupler (HC)FootingSource: Haber et al.,(2013)Mechanical connectorsGrouted ductPocketSocketTwo-stage integral13
3.6.4 Mechanical Bar Connectors Connector Types as defined in ACI 318-14StressfufyStrain Type 1: Capacity (1.25 fy )AbAb Type 2: Capacity (fu )AbBarConnectorBar(Limited to bars with fy 60 ksi)Mechanical connectorsGrouted ductPocketSocketTwo-stage integral14
3.6.4 Mechanical Bar Connectors2DcType 1 connector: not allowedColumnDcMechanical connectorsGrouted ductPocketSocketTwo-stage integral15
3.6.4 Mechanical Bar Connectors For SDC A/Seismic Zone 1.Plastichingezone(PHZ)Type 2: Allowed Seismic SDCs C&D/Zones 3&4w/ add’l requirements(3.6.4.4).ColumnMechanical connectors Seismic SDC B/Zone 2 withOwner’s approval.Grouted ductPocketSocketTwo-stage integral16
Type 2 Connectors in Plastic Hinge Zone for SDCsC&D Seismic Zones 3&4 (3.6.4.4)PHZ 15dbdbOnly grouted sleeve coupler(GC) or headed reinforcementcoupler (HC) allowed.ColumnMechanical connectorsGrouted ductPocketSocketTwo-stage integral17
Type 2 Connectors in Plastic Hinge Zone for SeismicZones 3&4 (Force-based Design) Reduced modification factorPHZLsp[AASHTO ABC EQ. 3.6.4.4.1-1] 0.8 for Lsp 4 db 0.5 for Lsp 4 dbMechanical connectorsGrouted ductPocketSocketTwo-stage integral18
Type 2 Connectors in Plastic Hinge Zone for SeismicZones 3&4 (Displacement-based Design) Use plastic moment capacity based on moment-curvatureanalysis of the column section with no mechanicalconnector. Calculate displacement capacity based on a reduced plastichinge length,.Mechanical connectorsGrouted ductPocketSocketTwo-stage integral19
Type 2 Connectors in Plastic Hinge Zone for SeismicZones 3&4 (Displacement-based Design)Point ofContraflexure 0.65 for GC 0.75 for HC LLspHsp 1 [AASHTO ABC EQ. 3.6.4.4.2-1]MechanicalCouplersRigid FoundationACTUAL CURVATUREDIAGRAMMechanical connectorsGrouted ductPocket“EQUIVALENT”CURVATURE DIAGRAMSocketTwo-stage integral20
Type 2 Connectors in Plastic Hinge Zone for SeismicZones 3&4 (Displacement-based Design)Point ofContraflexure LIf Lsp 4dbz Hsp LspANDIf Hsp 0.5DcMechanical connectorsGrouted ductPocketSocket( )Two-stage integral21
Debonding of Longitudinal Reinforcement forMechanical Connectors in PHZ (3.6.4.5)0.4 % max5000 Ɛye dbl[AASHTO ABC EQ. 3.6.4.5-1] ldMechanical connectorsGrouted ductPocketSocketTo be usedfor jointshear designTwo-stage integral22
3.6.5 GROUTED DUCT CONNECTIONS3 78 6/ASTM A 760(only)0[EQ. 3.6.5.1-1]0.67/ 0 12 51′4(grade 60 bars)1′4 to be taken 8.0 ksiMechanical connectorsSource: Brenes (2006)Grouted ductPocketSocketTwo-stage integral23
3.6.5 GROUTED DUCT CONNECTIONSUHPC Grouted Duct 8dbUHPCGrouted Duct 4dbPC Pier Cap 4dbDebondingdb(#8-#11)fy 75 ksiMechanical connectorsGrouted ductPocketColumnSocketTwo-stage integral24
3.6.6 POCKET CONNECTIONSA[EQ.3.6.6.3-1] / 0 1251′%(grade 60 bars)ASource: Restrepo et al. (2011) 1.5 max agg. 4 in.ASTM A 760(only)SECTION A-AMechanical connectorsGrouted ductPocketSocketTwo-stage integral25
3.6.6 POCKET CONNECTIONSSteel Pipe ThicknessSet:Solve:7Fp5αD’cp(a) Spiral(b) CorrugatedSteel PipeMechanical connectors U D’cpGrouted duct[AASHTO ABC EQ. 3.6.6.4-2] m?@( sFH9 9 cos( )M.NN ECDEFG Max (A BCD EFGHEF IJ KL, 0.060 in)for SDCs B and Zone 25M.NN ECDEFG, 0.40PQR(0SC )T)For Zones 3 & 4 Calculated min. joint shear reinf. for SDCs C & DPocketSocketTwo-stage integral26
3.6.7 SOCKET CONNECTIONSPC CapCIP FootingGrout orConcrete PourEmbeddedPC ColumnEmbeddedPC ColumnWet (cast-in-place)Mechanical connectorsGrouted ductFormed (precast)PocketSocketTwo-stage integral27
3.6.7 SOCKET CONNECTIONSPC Column in Socketif Le 1.5DcRoughening (0.25” )requiredVc, K1, K2, µ(concrete placed against a clean concrete surface)µ limited to 0.5 when Le 1.1 DcLe DcDcMechanical connectorsGrouted ductPocketSocketTwo-stage integral28
3.6.7 SOCKET CONNECTIONSPC Column in SocketMechanical connectorsGrouted ductAdd’l confinementbars at 45oPocketSocketTwo-stage integral29
Intentional roughening required for Le 1.5Dc3.6.7 SOCKET CONNECTIONSDcle ls e cover[AASHTO ABC EQ. 3.6.7.3.1-1]ecoverC1’-0”Le /2BSocket in ShaftSpiral/Hoops RequirementXY 1 0 X0 Z[\] 2a12bLelsLocationA Le /2coverMechanicalHeads, ifusedMechanical connectors( 1.0)Grouted ductA( 0.5)B( 1.0)C( 2.0)[AASHTO ABC EQ. 3.6.7.3.2-1]PocketSocketTwo-stage integral30
3.6.12 TWO-STAGE INTEGRAL PIER CAP1) LOWER PIER CAPMechanical connectors2) GIRDERS ERECTEDGrouted ductPocket3) UPPER-STAGE CAP CASTSocketTwo-stage integral31
3.6.12 TWO-STAGE INTEGRAL PIER CAPJoint Proportioning for SDC C&D or Seismic Zones 3 & 4Ds2Ds1DcBcapMechanical connectorsGrouted ductPocketSocketTwo-stage integral32
Thank you!wsp.com
Outline I. Overviewof AASHTO LRFD Guide Specifications for ABC-Seismic II. Seismic Design for ABC (3.4) III. Seismic Connection Design and Detailing (3.6.4-7 & 3.4.1
