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Update of ASCE 41 Concrete Provisions

Update of ASCE 41 Concrete Provisions. Kenneth Elwood, Univ. British Columbia Craig Comartin, CDComartin Inc. Jon Heintz, ATC Dawn Lehman, Univ of Washington Adolfo Matamoros, Univ of Kansas. Andrew Mitchell, Degenkolb Jack Moehle, UC Berkeley Mark Moore, Forell/Elsesser

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Update of ASCE 41 Concrete Provisions

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  1. Update of ASCE 41 Concrete Provisions Kenneth Elwood, Univ. British Columbia Craig Comartin, CDComartin Inc. Jon Heintz, ATC Dawn Lehman, Univ of Washington Adolfo Matamoros, Univ of Kansas Andrew Mitchell, Degenkolb Jack Moehle, UC Berkeley Mark Moore, Forell/Elsesser Michael Valley, MKA John Wallace, UCLA SEAONC 2007 Excellence in Structural Engineering Awards

  2. Scope of Work • Concrete Chapter of ASCE 41 • Research from PEER and elsewhere • EERI/PEER seminars New Information on the Seismic Performance of Existing Concrete Buildings • Compelling and urgent findings

  3. Components addressed Slab-Column Connections Columns Joints Walls

  4. Example: Onset of column shear failure 1.0 FEMA 356 0.8 Proposed, (r” =0.0005) 0.6 Proposed, (r” =0.006) 0.4 0.2 0 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 plastic rotation (rad)

  5. Proposed FEMA 356 Example: Improved reliability, clearly expressed Parameter “a” for “flexure-shear” columns: 10 5 conservative 1 0 unconservative 0.0 0.2 0.4 0.6

  6. Examples of other changes qp

  7. Impact on REAL projects V V shear-critical “captive” columns Elevation

  8. Impact on REAL projects Shear-Critical Columns BSE-1 BSE-2 FEMA 356 LS ASCE 41 Supp. LS FEMA 356 CP ASCE 41 Supp. CP

  9. Impact on REAL projects • Impact on “bottom line”: • New stiff shear wall or column strengthening needed based on FEMA 356 • No retrofit needed to address columns based on ASCE 41 Supplement. = less disruption and $$$$ Savings • End result = more retrofit projects done and reduced seismic risk!!

  10. Acknowledgments • American Society of Civil Engineering • Chris Poland • Jim Rossberg • Federal Emergency Management Agency • Cathleen Carlisle • PEER Center • Laura Lowes – University of Washington

  11. Q Qy e d g 1.0 B C F D E f c A ∆ h Update of ASCE 41 Concrete Provisions Abstract:A supplement to ASCE/SEI 41 Seismic Rehabilitation of Existing Buildings has been developed for the purpose of updating provisions related to existing reinforced concrete buildings. Based on experimental evidence, the proposed supplement includes revisions to stiffness models for beams, columns and beam-column joints, and substantive revisions to acceptance criteria for reinforced concrete columns, structural walls, and slab-column frames. These revisions will result in substantially more accurate, and in most cases more liberal, assessments of structural capacity of concrete components in seismic retrofit projects. Andrew Mitchell, Degenkolb Engineers Jack Moehle, UC Berkeley Mark Moore, Forell/Elsesser Michael Valley, Magnusson Klemencic John Wallace, UCLA Proposed Condition i vs. FEMA 356 Conforming Columns: Calibrated to experimental data: Stiffness Models: Accounts for slip from B-C joints. • Highlights: • New development length model.Lap splices typical of older columns:fs Supp / fs FEMA 356 = 1.45 • Flexure-controlled columns.qp depends on axial load and r” • Flexure-shear failure mode.qp depends on axial load and r” and v • Secondary shear-critical columns. Low axial loads: FEMA 356 (CP) qp = 0.004 rad Supp. (CP) qp = 0.006 to 0.06 radHigh axial loads: FEMA 356 (CP) qp = 0.004 rad Supp. (CP) qp = 0.0 to 0.008 rad • Highlights: • Low axial-load columns and beams:EIeffFEMA 356 = 0.5EIgEIeff Supp = 0.3EIg • Beam-Column Joints: FEMA 356: ”rigid zone” Supplemental: Dependent on SMnc/SMnb • New models provide better estimate of measured stiffness from 57 beam-column sub-assembly tests. @ shear failure Accounts for sheardeformations in B-C joints. Proposed Condition ii vs. FEMA 356 Non-Conforming @ axial failure Kenneth Elwood, Univ of British Columbia Craig Comartin, CDComartin Inc. Jon Heintz, Applied Technology Council Dawn Lehman, Univ of Washington Adolfo Matamoros, Univ of Kansas Acceptance Criteria: Walls: Slab-Column Connections: • Highlights: • Tri-linear backbone for walls controlled by shear. • Relax confinement requirements. Considered as confined if:Ash > 0.75Ash ACI s < 8db • Increase shear stress limits. Deformation capacity approximately constant for • No penalty for walls with one curtain of reinforcement. • Shear-controlled walls dependent on axial load. Low axial load: qtotal Supp = 2.0% (Sec. - CP) High axial load: qtotal Supp = 1.0% (Sec. - CP) • Highlights: • Specific parameters for PT slab-column connections. • RC modeling parameters and acceptance criteria revised based on new data. -continuity reinforcement m values -no continuity reinforcement m-s values • Modeling recommendations: Guidance on stiffness and nonlinear models to model influence of punching. • Highlights: • Allow for secondary nonductile elements to lose lateral load capacity, but still sustain gravity loads. • Facilitate development of more liberal acceptance criteria of other materials. • “Alternative Acceptance Criteria” Backbone created using peak of first cycle of each increment of loading (or deformation). - less exaggeration of rate of degradation. - more realistic backbone. (MPa) SEAONC 2007 Excellence in Structural Engineering Awards

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