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. Slab-Column Connections
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
0.01
0.02
0.03
0.04
0.05
0.06
0.07
plastic rotation (rad)

5. 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

6. Examples of other changesqp

7. Impact on REAL projectsV 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. 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 = rad Supp. (CP) qp = to 0.06 rad High axial loads: FEMA 356 (CP) qp = rad Supp. (CP) qp = 0.0 to 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