Update of ASCE 41 Concrete Provisions

Kenneth Elwood, Univ. British ColumbiaCraig Comartin, CDComartin Inc.Jon Heintz, ATCDawn Lehman, Univ of WashingtonAdolfo Matamoros, Univ of Kansas

SEAONC 2007 Excellence in Structural Engineering Awards

Andrew Mitchell, DegenkolbJack Moehle, UC BerkeleyMark Moore, Forell/ElsesserMichael Valley, MKAJohn Wallace, UCLA

Scope of WorkConcrete 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

ColumnsSlab-Column Connections

WallsJoints

Example: Onset of column shear failure

3 'cv f

0

0.2

0.4

0.6

0.8

1.0

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

plastic rotation (rad)

'g cP A fFEMA 356

Proposed, (” =0.0005)

Proposed, (” =0.006)

Example: Improved reliability, clearly expressed

Parameter “a” for “flexure-shear” columns:

'g c

PA f

p meas

p calc

conservative

unconservative01

5

10

0.0 0.2 0.4 0.6

Proposed

FEMA 356

Examples of other changes

0

0.5

1

1.5

2

columnstiffness for

low axial load

max steelstress fortypical lap

splice

slab-columnqp at

punching(Vg/Vo=0.2,continuity)

wall drift atshear failure

(low axial load)

wall drift ataxial failure(high axial

load)

Pro

po

sed

/ F

EM

A 3

56

p

Impact on REAL projects

Elevation

shear-critical “captive” columns

V

V

Impact on REAL projects

Life Safety

0

1,000

2,000

3,000

4,000

5,000

6,000

0.000 0.002 0.004 0.006 0.008 0.010

Total Hinge Rotation (rad)

Hin

ge M

omen

t (k

ip-in

)

Collapse Prevention

0

1,000

2,000

3,000

4,000

5,000

6,000

0.000 0.002 0.004 0.006 0.008 0.010

Total Hinge Rotation (rad)

Hin

ge M

omen

t (k

ip-in

)

FEM

A 3

56 L

S

ASC

E 4

1 S

upp.

LS FEM

A 3

56 C

P

ASC

E 4

1 S

upp.

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 ColumbiaCraig Comartin, CDComartin Inc.Jon Heintz, Applied Technology CouncilDawn Lehman, Univ of WashingtonAdolfo Matamoros, Univ of Kansas

Andrew Mitchell, Degenkolb EngineersJack Moehle, UC BerkeleyMark Moore, Forell/ElsesserMichael Valley, Magnusson KlemencicJohn Wallace, UCLA

Rigid end zone Rigid end zonesRigid end zone

b) M nc/M

nb < 0.8 c) 0.8 M nc/M

nb 1.2a) M nc/M

nb > 1.2

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:

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

plastic rotation (rad)

a (” =0.006)b (” =0.006)a (” =0.002)b (” =0.002)a - FEMA 356b - FEMA 356

'g

cP

Af

3 'cv f

6 'cv f3 'cv f

6 'cv f

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

plastic rotation (rad)

a (” =0.006)b (” =0.006)a (” =0.002)b (” =0.002)a - FEMA 356b - FEMA 356

'g

cP

Af

3 'cv f

6 'cv f3 'cv f

6 'cv f (a)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

plastic rotation (rad)

a (” =0.006)b (” =0.006)a (” =0.0005)b (” =0.0005)a - FEMA 356b - FEMA 356

(b)

'g

cP

Af

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

plastic rotation (rad)

a (” =0.006)b (” =0.006)a (” =0.0005)b (” =0.0005)a - FEMA 356b - FEMA 356

(b)

'g

cP

Af

0

2

4

6

8

10

12

14

16

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Condition ii - proposed'controlled by flexure' - FEMA 356

0

1

2

3

4

5

6

7

8

9

10

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Condition ii - proposed

'controlled by flexure' - FEMA 356

c

Q Qy

1.0

A

B C

D Ef

F

de

g

∆ h

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

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

Mnc/Mnb

New models provide better estimate of measured stiffness from 57 beam-column sub-assembly tests.

Accounts for slip from B-C joints.

Accounts for sheardeformations in B-C joints.

Highlights:New development length model.

Lap splices typical of older columns:fs Supp / fs 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 = 0.004 radSupp. (CP) p = 0.006 to 0.06 rad

High axial loads:FEMA 356 (CP) p = 0.004 radSupp. (CP) p = 0.0 to 0.008 rad

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 approximatelyconstant 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 data:

@ shear failure

@ axial failure

'g c

PA f

'g c

PA f

pm

eas

pta

ble

pm

eas

pta

ble

Proposed Condition i vs. FEMA 356 Conforming

Proposed Condition ii vs. FEMA 356 Non-Conforming

3 'cv f

4 'cv f

(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.

M

M

Elastic slab beam

Elastic column

Column plastic hinge

Joint region

Plastic hinges for slab beamsor for torsional element

Elastic relation for slab beamor column

Slab-beam plastic hinge

Torsional connection element

M

M

M

M

Elastic slab beam

Elastic column

Column plastic hinge

Joint region

Plastic hinges for slab beamsor for torsional element

Elastic relation for slab beamor column

Slab-beam plastic hinge

Torsional connection element

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.

0 1 2 3 4( f y)M IN

0

1

2

3

Vte

st /

Vn

(FE

MA

356

)

O n e C u rta inT w o C u rta in s fy)m in= 0 .2 5 % * 4 1 4 M P a

fy)m in= 0 .1 5 % * 4 1 4 M P a

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1G rav ity S h ea r R a tio (V g /V 0), w h ere V 0 = 4 f 'c

1 /2b od

0

0.01

0.02

0.03

0.04

0.05

0.06

Dri

ft R

atio

(T

otal

Rot

atio

n) a

t Pun

chin

g

R C co n n ection s/S u b a ssem b lies

E d ge co n n ection s

A S C E 41 - C o n tin u ity (C )

A S C E 41 - N o C on tin u ity (N C )

F E M A 3 5 6 - C /N C

A C I 3 1 8 -0 5 2 1 .11 .5 L im it

R ef: K an g & W allace , A C I 1 0 3 (4 ), 2 0 0 6