Presentation on theme: "Update of ASCE 41 Concrete Provisions Kenneth Elwood, Univ. British Columbia Craig Comartin, CDComartin Inc. Jon Heintz, ATC Dawn Lehman, Univ of Washington."— Presentation transcript:
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 SEAONC 2007 Excellence in Structural Engineering Awards Andrew Mitchell, Degenkolb Jack Moehle, UC Berkeley Mark Moore, Forell/Elsesser Michael Valley, MKA John Wallace, UCLA
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
Example: Improved reliability, clearly expressed Parameter a for flexure-shear columns: conservative unconservative Proposed FEMA 356
Examples of other changes p
Impact on REAL projects Elevation shear-critical captive columns V V
Impact on REAL projects FEMA 356 LSASCE 41 Supp. LS FEMA 356 CPASCE 41 Supp. CP BSE-1 BSE-2 Shear-Critical Columns
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!!
Acknowledgments American Society of Civil Engineering Chris Poland Jim Rossberg Federal Emergency Management Agency Cathleen Carlisle PEER Center Laura Lowes – University of Washington
Update of ASCE 41 Concrete Provisions SEAONC 2007 Excellence in Structural Engineering Awards 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 Andrew Mitchell, Degenkolb Engineers Jack Moehle, UC Berkeley Mark Moore, Forell/Elsesser Michael Valley, Magnusson Klemencic John Wallace, UCLA 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. Stiffness Models: Walls: Columns: Slab-Column Connections: Acceptance Criteria: c Q Q y 1.0 A BC DE f F d e g h k calc /k meas ProposedFEMA 356 Mean Min Max cov0.36 Highlights: Low axial-load columns and beams: EI eff FEMA 356 = 0.5EI g EI eff Supp = 0.3EI g Beam-Column Joints: FEMA 356: rigid zone Supplemental: Dependent on M nc / M nb New models provide better estimate of measured stiffness from 57 beam- column sub-assembly tests. Accounts for slip from B-C joints. Accounts for shear deformations in B-C joints. Highlights: New development length model. Lap splices typical of older columns: f s Supp / f s FEMA 356 = 1.45 Flexure-controlled columns. p depends on axial load and Flexure-shear failure mode. p depends on axial load and and v Secondary shear-critical columns. Low axial loads: FEMA 356 (CP) p = rad Supp. (CP) p = to 0.06 rad High axial loads: FEMA 356 (CP) p = rad Supp. (CP) p = 0.0 to rad Highlights: Tri-linear backbone for walls controlled by shear. Relax confinement requirements. Considered as confined if: A sh > 0.75A sh ACI s < 8d b 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: total Supp = 2.0% (Sec. - CP) High axial load: total Supp = 1.0% (Sec. - CP) Calibrated to experimental shear axial failure Proposed Condition i vs. FEMA 356 Conforming Proposed Condition ii vs. FEMA 356 Non-Conforming (MPa) Highlights: Specific parameters for PT slab- column connections. RC modeling parameters and acceptance criteria revised based on new data. -continuity reinforcement values -no continuity reinforcement 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.