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
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
Components addressed
Columns
Slab-Column
Connections
Joints
Walls
Example:
Onset of column shear failure
1.0
P Ag f c '
v  3 fc '
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
plastic rotation (rad)
0.06
0.07
Example:
Improved reliability, clearly expressed
Parameter “a” for “flexure-shear” columns:
 p meas
 p calc
Proposed
10
FEMA 356
5
conservative
1
0
0.0
0.2
0.4
P
Ag f c '
0.6
unconservative
Examples of other changes
Proposed / FEMA 356
2
1.5
1
0.5
0
column
stiffness for
low axial load
max steel
stress for
typical lap
splice
slab-column
p at
qp
punching
(Vg/Vo=0.2,
continuity)
wall drift at
shear failure
(low axial load)
wall drift at
axial failure
(high axial
load)
Impact on REAL projects
V
V
shear-critical “captive” columns
Elevation
Impact on REAL projects
Shear-Critical Columns
Life
Safety
BSE-1
Prevention
Collapse
BSE-2
2,000
1,000
0
0.000
0.002
0.004
0.006
Total Hinge Rotation (rad)
0.008
ASCE 41 Supp. CP
3,000
5,000
4,000
FEMA 356 CP
4,000
ASCE 41 Supp. LS
5,000
Hinge Moment (kip-in)
6,000
FEMA 356 LS
Hinge Moment (kip-in)
6,000
3,000
2,000
1,000
0
0.010
0.000
0.002
0.004
0.006
Total Hinge Rotation (rad)
0.008
0.010
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
Proposed Condition i vs.
FEMA 356 Conforming
 New development length model.
Lap splices typical of older columns:
fs Supp / fs FEMA 356 = 1.45
Accounts for shear
deformations in
B-C joints.
 Beam-Column Joints:
FEMA 356: ”rigid zone”
Supplemental: Dependent on
Mnc/Mnb
Rigid end zone
Rigid end zone
a) Mnc/Mnb > 1.2
b) Mnc/Mnb < 0.8
 New models provide better estimate
of measured stiffness from 57 beamcolumn sub-assembly tests.
Rigid end zones
c) 0.8  Mnc/Mnb 1.2
kcalc/kmeas
v  6 fc '
v  3 fc '
0.8
P Ag f c '
0.7
0.6
0.5
Mean
Walls:
1.22
@ shear failure
10
8
6
4
0.3
2
0.2
0.1
0
0.0
0
0
 Flexure-shear failure mode.
p depends on axial load and r” and v
0.01
0.02
0.03
0.04
0.05
0.06
0.1
0.2
0.3
Proposed Condition ii vs.
FEMA 356 Non-Conforming
 Secondary shear-critical columns.
Low axial loads:
FEMA 356 (CP) p = 0.004 rad
Supp. (CP) p = 0.006 to 0.06 rad
0.8
0.7
0.6
0.5
0.4
Condition ii - proposed
'controlled by flexure' - FEMA 356
@ axial failure
7
6
5
4
3
2
0.2
1
0.1
0
0.0
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.1
0.2
0.07
plastic rotation (rad)
Acceptance Criteria:
Min
 Tri-linear backbone for walls
controlled by shear.
0.19
B
F
Max
 Increase shear stress limits.
Deformation capacity approximately
constant for v  4 fc '
 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)
Highlights:
 Specific parameters for PT slabcolumn connections.
C
2.52
5.18
D
f
E
c
A
cov
0.36
∆
h
 RC modeling parameters and
acceptance criteria revised based
on new data.
-continuity reinforcement
 mvalues
-no continuity reinforcement
 m-svalues
0.36
3
Vtest / Vn (FEMA 356)
 Relax confinement requirements.
Considered as confined if:
Ash > 0.75Ash ACI
s < 8db
0.41
d
g
1.0
2
Drift Ratio (Total Rotation) at Punching
0.06
Highlights:
RC connections/Subassemblies
Edge connections
ASCE 41 - Continuity (C)
ASCE 41 - No Continuity (NC)
FEMA 356 - C/NC
0.05
0.04
One Curtain
Two Curtains
r fy)min=0.25%*414 MPa
r fy)min=0.15%*414 MPa
0
0
1
2
3
(r fy)MIN (MPa)
4
 Modeling recommendations:
Guidance on stiffness and
nonlinear models to model
influence of punching.
 Allow for secondary nonductile
elements to lose lateral load
capacity, but still sustain gravity
loads.
Ref: Kang & Wallace, ACI 103(4), 2006
0.02
0.01
ACI 318-05 21.11.5 Limit
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Gravity Shear Ratio (Vg /V0), where V0 = 4 f
0.8
'c1/2bod
0.9
Elastic column
Column plastic hinge
Torsional connection element
Slab-beam plastic hinge
Joint region
Elastic slab beam
1
Highlights:
0.03
0
M
M

Plastic hinges for slab beams
or for torsional element
0.7
8
v  3 fc '
Slab-Column Connections:
e
0.6
10
(b)
a (r” =0.006)
b (r” =0.006)
a (r” =0.0005)
b (r” =0.0005)
a - FEMA 356
b - FEMA 356
0.9
0.5
Ag f c '
9
1
2.59
Q
Qy
0.4
P
0.07
plastic rotation (rad)
High axial loads:
FEMA 356 (CP) p = 0.004 rad
Supp. (CP) p = 0.0 to 0.008 rad
FEMA 356
12
0.4
0.3
Proposed
Condition ii - proposed
'controlled by flexure' - FEMA 356
14
(a)
a (r” =0.006)
b (r” =0.006)
a (r” =0.002)
b (r” =0.002)
a - FEMA 356
b - FEMA 356
0.9
 Flexure-controlled columns.
p depends on axial load and r”
Calibrated to experimental data:
16
1
P Ag f c '
 Low axial-load columns and beams:
EIeff FEMA 356 = 0.5EIg
EIeff Supp = 0.3EIg
v  6 fc '
 p table
Highlights:
Highlights:
v  3 fc '
 p meas
Columns:
Accounts for slip
from B-C joints.
Stiffness Models:
Andrew Mitchell, Degenkolb Engineers
Jack Moehle, UC Berkeley
Mark Moore, Forell/Elsesser
Michael Valley, Magnusson Klemencic
John Wallace, UCLA
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
 p table
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.
 p meas
Abstract:

Elastic relation for slab beam
or column
SEAONC 2007 Excellence in Structural Engineering Awards
1
 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.
0.3
P
0.4
Ag f c '
0.5
0.6
0.7