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

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

Slab-Column Connections Components addressed Slab-Column Connections Columns Joints Walls

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 0.01 0.02 0.03 0.04 0.05 0.06 0.07 plastic rotation (rad)

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

Examples of other changes qp

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

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

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 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. 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 Stiffness Models: Accounts for slip from B-C joints. Columns: Proposed Condition i vs. FEMA 356 Conforming Calibrated to experimental data: 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 rad High 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: EIeff FEMA 356 = 0.5EIg EIeff 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 shear deformations in B-C joints. Proposed Condition ii vs. FEMA 356 Non-Conforming @ axial failure kcalc/kmeas Proposed FEMA 356 Mean 1.22 2.59 Min 0.19 0.41 Max 2.52 5.18 cov 0.36 Walls: c Q Qy 1.0 A B C D E f F d e g ∆ h Slab-Column Connections: Acceptance Criteria: 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