Update%20of%20ASCE%2041%20Concrete%20Provisions

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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
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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

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Components addressed
Slab-Column Connections
Columns
Walls
Joints
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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)
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Example Improved reliability, clearly expressed

• Parameter a for flexure-shear columns

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5
conservative
1
0
unconservative
0.0
0.2
0.4
0.6
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Examples of other changes
qp
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Impact on REAL projects
V
V
shear-critical captive columns
Elevation
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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
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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!!

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Acknowledgments

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

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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
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 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.

_at_ shear failure
Accounts for sheardeformations in B-C joints.
Proposed Condition ii vs. FEMA 356 Non-Conforming
_at_ axial failure
kcalc/kmeas kcalc/kmeas
Proposed FEMA 356
Mean 1.22 2.59
Min 0.19 0.41
Max 2.52 5.18
cov 0.36 0.36
Acceptance Criteria
Walls
Slab-Column Connections

• Highlights
• Tri-linear backbone for walls controlled by
  shear.
• Relax confinement requirements. Considered as
  confined if Ash gt 0.75Ash ACI
• s lt 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