asce 41 ad hoc committee supplement revisions to chapter 6 of asce 41, seismic rehabilitation of...

ASCE 41 Ad Hoc CommitteeSupplement Revisions to Chapter 6 of ASCE 41,Seismic Rehabilitation of Existing Buildings

Kenneth Elwood, UBC (Chair)Craig Comartin, EERIJon Heintz, ATCDawn Lehman, Univ of WashingtonAdolfo Matamoros, Univ of Kansas

PEER 2007 Annual Meeting - San Francisco, January 19, 2007

Andrew Mitchell, DegenkolbJack Moehle, UC BerkeleyMark Moore, R&CMichael Valley, MKAJohn Wallace, UCLA

Timeline

EERI/PEER Technical Seminars (Jan-Feb 2006)ASCE 41 Public Comments on Chapter 6 (Mar 2006)ASCE 41 Commentary Changes (Apr 2006)ASCE 41 Ad Hoc Committee Kick-off meeting, 29 June 2006 Bi-weekly meetings Completed revisions, 1 Dec 2006 ASCE 41 review group provided comments Final changes completed, 19 Dec 2006 ASCE 41 voted to consider modifications, 19 Jan 2007

ASCE 41 Supplement No. 1 released - ?? 2007

Committee ScopeTo develop Supplement No. 1 revisions to ASCE 41 to address negative comments withdrawn during the public comment period.

Focus on integrating recent research presented at the EERI/PEER seminars titled, New Information on the Seismic Performance of Existing Concrete Buildings.

Scope limited to Chapter 6 – Concrete. Although some limited changes are proposed for

Chapter 2 to ensure clarity of changes in Chapter 6.

Focused on modifications the committee felt were critical to the outcome of assessments using ASCE 41.

Components addressedColumns Substantive changes to modeling parameters,

acceptance criteria, and stiffness based on new data.Beam-Column Joints Changes to stiffness models.

Slab-Column Connections Modeling recommendations Substantive changes to modeling parameters and

acceptance criteria based on new data. Addition of PT slabs

Walls Substantive changes to modeling parameters and

confinement requirements.Acceptance criteria and alternative criteria Clarification within Chapter 2

ColumnsSummary of Changes

1. Effective stiffness modified for low axial loads (6.3.1.2).

2. Lap splice requirements changed (6.3.5).

3. Changed format and values in Tables 6-8 and 6-12 to account for flexure-shear failures (6.4.2.2.1).

4. Added information on probabilities of failure (C6.4.2.2.1).

Columns (Table 6-8)Deformation capacities

Methodology for modifications: Explicitly account for flexure-shear failure mode. Account for scatter in data. Select target probabilities of failure.

drift at 20% loss in lateral strength - Flexure failures: Pf < 35% - all others: Pf < 15%

drift at loss of axial load capacity - all failure modes: Pf < 15%

Q

a

b


Methodology for modifications (cont.) Columns with low axial loads can sustain

gravity loads well beyond lateral-load failure. Axial-load failure can occur suddenly after

lateral load failure for: columns with high axial loads (P=0.6Agf’c ) very light transverse reinforcement (”≤0.0005)

To account for this a and b parameters converge to a single value.

High axial load and very light transverse reinforcement: Zero plastic rotation capacity!

Proposed Condition i vs. FEMA 356 “controlled by flexure”

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)

P/A

gf'c

a (” =0.006)

b (” =0.006)

a (” =0.002)

b (” =0.002)

a - FEMA 356

b - FEMA 356

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


P/A

gf'c

a (” =0.006)

b (” =0.006)

a (” =0.002)

b (” =0.002)

a - FEMA 356

b - FEMA 356

3 'cv f

6 'cv f3 'cv f

6 'cv f

proposed

conforming transverse reinforcement

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


P/A

gf'

c

a (” =0.006)

b (” =0.006)

a (” =0.002)

b (” =0.002)

a - FEMA 356

b - FEMA 356

3 '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


P/A

gf'

c

a (” =0.006)

b (” =0.006)

a (” =0.002)

b (” =0.002)

a - FEMA 356

b - FEMA 356

a (” =0.006)

b (” =0.006)

a (” =0.002)

b (” =0.002)

a - FEMA 356

b - FEMA 356

3 'cv f

6 'cv f proposed

nonconforming transverse reinforcement

Proposed Condition i vs. FEMA 356 “controlled by flexure”

Proposed Condition ii vs. FEMA 356 “controlled by flexure”

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07


P/A

gf'c

a (” =0.006)

b (” =0.006)

a (” =0.0005)

b (” =0.0005)

a - FEMA 356

b - FEMA 356

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07


P/A

gf'c

a (” =0.006)

b (” =0.006)

a (” =0.0005)

b (” =0.0005)

a - FEMA 356

b - FEMA 356

a (” =0.006)

b (” =0.006)

a (” =0.0005)

b (” =0.0005)

a - FEMA 356

b - FEMA 356

Conforming Nonconforming

3 'cv f 3 '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


P/A

gf'c

a (” =0.006)

b (” =0.006)

a (” =0.0005)

b (” =0.0005)

a - FEMA 356

b - FEMA 356

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


P/A

gf'c

a (” =0.006)

b (” =0.006)

a (” =0.0005)

b (” =0.0005)

a - FEMA 356

b - FEMA 356

a (” =0.006)

b (” =0.006)

a (” =0.0005)

b (” =0.0005)

a - FEMA 356

b - FEMA 356

6 'cv f


P/A

gfc’

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07

a (” =0.006)

b (” =0.006)

a (” =0.0005)

b (” =0.0005)

a - FEMA 356

b - FEMA 356


P/A

gfc’

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07

a (” =0.006)

b (” =0.006)

a (” =0.0005)

b (” =0.0005)

a - FEMA 356

b - FEMA 356

a (” =0.006)

b (” =0.006)

a (” =0.0005)

b (” =0.0005)

a - FEMA 356

b - FEMA 356

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


P/A

gf'c

a (” =0.006)

b (” =0.006)

a (” =0.0005)

b (” =0.0005)

a - FEMA 356

b - FEMA 356

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


P/A

gf'c

a (” =0.006)

b (” =0.006)

a (” =0.0005)

b (” =0.0005)

a - FEMA 356

b - FEMA 356

a (” =0.006)

b (” =0.006)

a (” =0.0005)

b (” =0.0005)

a - FEMA 356

b - FEMA 356

0

1

2

3

4

5

6

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Condition i - proposed

'controlled by flexure' - FEMA 356

`


Evaluate “a” for Condition i columns:

'g c

PA f

(

/(3

/)

tota

lm

eas

pef

f

tabl

e

ME

IL

Pf = 30%Pf = 6%

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Condition ii - proposed



Evaluate “a” for Condition ii columns:

'g c

PA f

(

/(3

/)

tota

lm

eas

pef

f

tabl

e

ME

IL

Pf = 6%Pf = 0.1%

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



Evaluate “b” for columns with axial-load failures:

'g c

PA f

(

/(3

/)

tota

lm

eas

pef

f

tabl

e

ME

IL

Pf = 13%Pf = 7%

Beam-Column JointsSummary of Changes

1. Rigid end-zone models (6.4.2.2.1)2. Strength section created

(6.4.2.3.2) 3. Definition of “conforming”

transverse reinforcement.4. Clarifications to Tables 6-9 and 6-

10Substantive changes to Tables 6-9 and 6-10 were discussed by committee, however the committee did not feel the changes were urgent and proposed modifications were better left to a more deliberative process.

Beam-Column JointsRigid end-zone models

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

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

FEMA 356:

Proposed:

0

20

40

60

80

100

120

140

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0


FEMA 356*

Proposed*

* Includes beam and column stiffness models, in addition to rigid end zone models.

Walker, Lehman, LowesDrift (%)

Colu

mn S

hear

(kip

s)

Drift (%)


Lowes and Lehman

Lowes collected a database of 57 beam-column subassemblies from 13 test programs.kmeas based on first significant load cycle.

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

Slab-Column Connections (6.4.4) Summary of Changes

1. Editorial changes.2. Expanded commentary on

modeling options.3. Modification of Tables 6-14 and 6-

15 based on new data.4. Specific parameters for PT slab-

column connections.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1G ravity Shear R atio (V g /V c), w here V c = (1/3)f'c

1/2bod

0

0.01

0.02

0.03

0.04

0.05

0.06

Drif

t Ra

tio (

Tot

al R

ota

tion)

at

Pun

chin

g

Isolated RC connections

Subassem blies

Nine-panel frame

Edge connections

Best-Fit line

+/- residuals

ACI 318-05 21.11.5 Lim it

R ef: Kang & W allace, A C I 103(4), 2006

Slab-Column Connections (RC) - Comparison with test data

Proposed “a” (no continuity)

Proposed “a” (continuity)

FEMA 356 “a”

Slab-Column Connections (PT) - Comparison with test data

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1G ravity Shear Ratio (V g /V c), w here V c = (0.29 f'c

1/2+0.3 fpc)bod

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

Drif

t Rat

io (

Tot

al R

otat

ion)

at P

unch

ing Cyclic load history

Best fit relation

Monotonic load history

Best fit relation (All)

ACI 318-05 21.11.5 Lim it

(Best-Fit Line)plus one Res

Ref: Kang & W allace, ACI 103(4), 2006

Proposed “a” (no continuity)

Proposed “a” (continuity)

FEMA 356 “a”

Slab-Column Connections “b” values

“b” defined as point of gravity load collapse, thus: For continuity b > a

Very limited data available to assess “b”. For no continuity a = b

0

0.01

0.02

0.03

0.04

0.05

0.06

0 0.1 0.2 0.3 0.4 0.5 0.6

Gravity shear ratio

"b"

va

lue

s (

rad

)

FEMA 356 with ContinuityProposed with ContinuityFEMA 356 without ContinuityProposed without Continuity

a=b

PT

Walls (6.7)Summary of Changes

1. Columns under discontinuous shear walls.

2. Relax confinement requirements. 3. Increase shear stress limits.4. Introduction of tri-linear backbone for

walls controlled by shear. 5. No penalty for walls with one curtain of

reinforcement.6. Remove limit on reinforcement yield

strength.

Walls (6.7.2.2.2)Tri-linear Backbone

c

Q Qy

1.0

A

B C

D Ef

F

d

e

g

∆ h

New Figure 6.1c a/d < 2.5 walls controlled by

shear. captures shear

cracking.based on model by Sozen and Moehle (1993)

Hidalgo et al. 2002M/Vlw = 0.69 Specimen #8

Displacement (mm)30 35

Load

(kN

)

proposedFEMA 356

Walls (Table 6-19)high axial loads

Recent tests by Wallace suggest failure can occur at low drifts. assume no residual and reduce “e” to 1%

-0.5 0 0.5

Lateral D isplacement (in )

-100

0

100

La

tera

l Lo

ad

(k

ips)

top disp.-exp

shear-envelope

shear-backbone

3 x Yield

Axial collapse

La

tera

l Lo

ad

Drift Ratio 1%1%

proposed

FEMA 356

Chapter 2Two sections modified: Deformation and Force-Controlled Actions

(2.4.4.3) ensure clarity of changes in Chapter 6; maintain consistency between the chapters; transparency of design intent to the user; and facilitate development of more liberal

acceptance criteria of other materials.

Alternative Modeling Parameters and Acceptance Criteria (2.8) Address over-estimation of degradation from

current procedures.

Alternative Modeling Parameters and Acceptance Criteria

Force

Deformation

Backbone curve

A smooth "backbone" curve shall be drawn through the intersection of the first cycle curve for the (i)th deformation step with the second cycle curve of the (i-1)th deformation step, for all i steps

FEMA 356, 2.8.3 (1.2):

Results in exaggeration of strength degradation, which in turn leads to overestimation of displacement demands.


Resulting backbone curve applying FEMA 356 2.8.3(1.2) is suspect


A smooth "backbone" curve shall be drawn through each point of peak displacement during the first cycle of each increment of loading (or deformation).

Proposed, 2.8.3 (1.2):

SummaryColumns Substantive changes to modeling parameters,

acceptance criteria, and stiffness based on new data.Beam-Column Joints Changes to stiffness models.

Slab-Column Connections Modeling recommendations Substantive changes to modeling parameters and

acceptance criteria based on new data. Addition of PT slabs

Walls Substantive changes to modeling parameters and

confinement requirements.Acceptance criteria and alternative criteria Clarification within Chapter 2

Columns (6.3.1.2)Effective Stiffness

Proposed model accounts for bar slip from foundation or beam-column joints.Data suggests effective stiffness is closer to 0.2EIg for low axial loads, but committee did not want to underestimate stiffness for columns in wall buildings.

FEMA 356

Proposed Figure C6-1:

Columns (6.3.5)Development and splices of reinforcement

FEMA 356 model does not reflect the intent of the ACI development length equation to develop 1.25 times nominal fy.Committee adopted modified version of model by Cho and Pincheira (2006):

2 / 3

1.25 bs y

d

lf f

l

expected or lower-boundyield strength

Lower bound yield strength

Accounts for increasing slip with longer lb

Columns (6.3.5)Development and splices of reinforcement

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.2 0.4 0.6 0.8 1 1.2 1.4

FEMA 356

proposed, force-controlled

proposed, deformation-controlled

b dl l

fs /

fy

nom

inal

New Table 6-8

~Flexure failures

~Flexure-shear failures

~Shear failures

trans. reinf. ratio

High axial load cases

Table 6-8 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures- Reinforced Concrete Columns

Modeling Parameters3 Acceptance Criteria3, 4

Plastic Rotations Angle, radians

Performance Level

Component Type Plastic Rotations Angle, radians

Residual Strength

Ratio Primary Secondary Conditions a b c IO LS CP LS CP

Condition i. 1 2

'g c

P

A f v

w

A

b s

0.1 0.006 0.035 0.060 0.2 0.005 0.026 0.035 0.045 0.060

0.6 0.006 0.010 0.010 0.0 0.003 0.008 0.009 0.009 0.010

0.1 0.002 0.027 0.034 0.2 0.005 0.020 0.027 0.027 0.034

0.6 0.002 0.005 0.005 0.0 0.002 0.003 0.004 0.004 0.005

Condition ii. 1 2

'g c

P

A f v

w

A

b s

'w c

V

b d f

0.032 0.060 0.2 0.005 0.024 0.032 0.045 0.060 0.025 0.060 0.2 0.005 0.019 0.025 0.045 0.060 0.010 0.010 0.2 0.003 0.008 0.009 0.009 0.010 0.008 0.008 0.2 0.003 0.006 0.007 0.007 0.008 0.012 0.012 0.0 0.005 0.009 0.010 0.010 0.012 0.006 0.006 0.0 0.004 0.005 0.005 0.005 0.006 0.004 0.004 0.0 0.002 0.003 0.003 0.003 0.004 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Condition iii. 1 2

'g c

P

A f v

w

A

b s

0.0 0.060 0.0 0.0 0.0 0.0 0.045 0.060 0.0 0.008 0.0 0.0 0.0 0.0 0.007 0.008 0.0 0.006 0.0 0.0 0.0 0.0 0.005 0.006 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Condition iv. Columns controlled by inadequate development or splicing along the clear height1 2

'g c

P

A f v

w

A

b s

0.0 0.060 0.4 0.0 0.0 0.0 0.045 0.060 0.0 0.008 0.4 0.0 0.0 0.0 0.007 0.008 0.0 0.006 0.2 0.0 0.0 0.0 0.005 0.006 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

1. Refer to Section 6.4.2.2.2 for definition of conditions i, ii, and iii. Where more than one of the conditions i, ii, iii, and iv occurs for a given component, use the minimum appropriate numerical value from the table.

2. Where P > 0.7Agf’c, the plastic rotation angles shall be taken as zero for all performance levels unless columns have transverse reinforcement consisting of hoops with 135 degree hooks spaced at d/3 and the strength provided by the hoops (Vs) is at least three-fourths of the design shear. Axial load, P, shall be based on the maximum expected axial loads due to gravity and earthquake loads

3. Linear interpolation between values listed in the table shall be permitted.

4. Primary and secondary component demands shall be within secondary component acceptance criteria where the full backbone curve is explicitly modeled including strength degradation and residual strength in accordance with Section 3.4.3.2.


Condition selected based in ratio of plastic shear demand to shear strength:

Transverse Reinforcement Details ACI conforming

details with 135° hooks

Closed hoops with 90° hooks

Other (including lap spliced transverse reinforcement)

Vp/(Vn/k) ≤ 0.6 i ii ii 1.0 ≥ Vp/(Vn/k) > 0.6 ii ii iii Vp/(Vn/k) > 1.0 iii iii iii

downgraded

downgraded

no change

Note: The restriction on the effectiveness of transverse reinforcement with 90 degree hooks in regions of moderate and high ductility (Shear and Torsion 6.3.4) has been removed for ASCE41 Supplement 1, but has been maintained for lap spliced transverse reinforcement.

Columns (6.4.2.4)Acceptance Criteria

The following is removed from 6.4.2.4.2:

Not required since shear-critical columns are now considered deformation-controlled and Table 6-8 is used.

For columns designated as primary components and for which calculated design shear exceeds design shear strength, the permissible deformation for the Collapse Prevention Performance Level shall not exceed the deformation at which shear strength is calculated to be reached; the permissible deformation for the Life Safety Performance Level shall not exceed three quarters of that value.




Performance Level


Residual Strength


Condition i. 1 2

'g c

P

A f v

w

A

b s

0.1 0.006 0.035 0.060 0.2 0.005 0.026 0.035 0.045 0.060

0.6 0.006 0.010 0.010 0.0 0.003 0.008 0.009 0.009 0.010

0.1 0.002 0.027 0.034 0.2 0.005 0.020 0.027 0.027 0.034

0.6 0.002 0.005 0.005 0.0 0.002 0.003 0.004 0.004 0.005

Condition ii. 1 2

'g c

P

A f v

w

A

b s

'w c

V

b d f

0.032 0.060 0.2 0.005 0.024 0.032 0.045 0.060 0.025 0.060 0.2 0.005 0.019 0.025 0.045 0.060 0.010 0.010 0.2 0.003 0.008 0.009 0.009 0.010 0.008 0.008 0.2 0.003 0.006 0.007 0.007 0.008 0.012 0.012 0.0 0.005 0.009 0.010 0.010 0.012 0.006 0.006 0.0 0.004 0.005 0.005 0.005 0.006 0.004 0.004 0.0 0.002 0.003 0.003 0.003 0.004 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Condition iii. 1 2

'g c

P

A f v

w

A

b s

0.0 0.060 0.0 0.0 0.0 0.0 0.045 0.060 0.0 0.008 0.0 0.0 0.0 0.0 0.007 0.008 0.0 0.006 0.0 0.0 0.0 0.0 0.005 0.006 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0


'g c

P

A f v

w

A

b s

0.0 0.060 0.4 0.0 0.0 0.0 0.045 0.060 0.0 0.008 0.4 0.0 0.0 0.0 0.007 0.008 0.0 0.006 0.2 0.0 0.0 0.0 0.005 0.006 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

1. Refer to Section 6.4.2.2.2 for definition of conditions i, ii, and iii. Where more than one of the conditions i, ii, iii, an d iv occurs for a given component, use the minimum appropriate numerical value from the table.







Performance Level


Residual Strength


Condition i. 1 2

'g c

P

A f

v

w

A

b s

0.035 0.060 0.2 0.005 0.026 0.035 0.045 0.060

0.010 0.010 0.0 0.003 0.008 0.009 0.009 0.010

0.027 0.034 0.2 0.005 0.020 0.027 0.027 0.034

0.005 0.005 0.0 0.002 0.003 0.004 0.004 0.005

Condition ii. 1 2

'g c

P

A f

v

w

A

b s

'w c

V

b d f

0.032 0.060 0.2 0.005 0.024 0.032 0.045 0.060

0.025 0.060 0.2 0.005 0.019 0.025 0.045 0.060

0.010 0.010 0.2 0.003 0.008 0.009 0.009 0.010

0.008 0.008 0.2 0.003 0.006 0.007 0.007 0.008

0.012 0.012 0.0 0.005 0.009 0.010 0.010 0.012

0.006 0.006 0.0 0.004 0.005 0.005 0.005 0.006

0.004 0.004 0.0 0.002 0.003 0.003 0.003 0.004

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Condition iii. 1 2

'g c

P

A f

v

w

A

b s

0.0 0.060 0.0 0.0 0.0 0.0 0.045 0.060

0.0 0.008 0.0 0.0 0.0 0.0 0.007 0.008

0.0 0.006 0.0 0.0 0.0 0.0 0.005 0.006

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0


'g c

P

A f

v

w

A

b s

0.0 0.060 0.4 0.0 0.0 0.0 0.045 0.060

0.0 0.008 0.4 0.0 0.0 0.0 0.007 0.008

0.0 0.006 0.2 0.0 0.0 0.0 0.005 0.006

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

1. Refer to Section 6.4.2.2.2 for definition of conditions i, ii, and iii. Where more than one of the conditions i, ii, iii, and iv occurs for a given component, use the minimum appropriate numerical value from the table.




Beam-Column JointsDefinition of “Conforming”

“Joint transverse reinforcement is conforming if hoops are spaced at hc/2 within the joint.”

Based on observation from tests that any reinforcement in the joint will substantially improve the performance.

Beam-Column JointsTable 6-10

Table 6-10 Values of for Joint Strength Calculation

Value of

Condition i: Interior Joints Condition ii: Other Joints

Trans. Reinf.1

Interior joint with transverse

beams

Interior joint without

transverse beams

Exterior joint with transverse

beams

Exterior joint without

transverse beams

Knee joint with or without

transverse beams

C 20 15 15 12 8

NC 12 10 8 6 4

New Table 6-14

Table 6-14 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures- Two-way Slabs and Slab-Column Connections


Plastic Rotation Angle, radians

Performance Level

Component Type Plastic Rotation Angle, radians

Residual Strength

Ratio Primary Secondary

Conditions a b c IO LS CP LS CP

i. Reinforced Concrete slab-column connections1

o

g

V

V 2 Continuity Reinforcement3

Yes 0.035 0.05 0.2 0.01 0.026 0.035 0.035 0.05

Yes 0.03 0.04 0.2 0.01 0.023 0.03 0.03 0.04

Yes 0.02 0.03 0.2 0 0.015 0.02 0.02 0.03

Yes 0 0.02 0 0 0 0 0 0.02

No 0.025 0.025 0 0.01 0.02 0.02 0.02 0.025

No 0.02 0.02 0 0.01 0.015 0.015 0.015 0.02

No 0.01 0.01 0 0 0.008 0.008 0.008 0.01

No 0 0 0 0 0 0 0 0

No 0 0 0 --3 --3 --3 --3 --3

ii. Post-Tensioned slab-column connections1

o

g

V

V 2 Continuity Reinforcement3

Yes 0.035 0.05 0.4 0.01 0.026 0.035 0.035 0.05

Yes 0.005 0.03 0.2 0 0.003 0.005 0.025 0.03

Yes 0 0.02 0.2 0 0 0 0.015 0.02

No 0.025 0.025 0 0.01 0.02 0.02 0.02 0.025

No 0 0 0 0 0 0 0 0

No 0 0 0 --4 --4 --4 --4 --4

iii. Slabs controlled by inadequate development or splicing along the span1

0 0.02 0 0 0 0 0.01 0.02

iv. Slabs controlled by inadequate embedment into slab-column joint1

0.015 0.03 0.2 0.01 0.01 0.015 0.02 0.03

1. Where more than one of the conditions i, ii, iii, and iv occurs for a given component, use the minimum appropriate numerical value from the table.

2. Vg = the gravity shear acting on the slab critical section as defined by ACI 318 ; Vo = the direct punching shear strength as defined by ACI 318.

3. Under the heading "Continuity Reinforcement", use "Yes" where the area of effectively continuous main bottom bars passing through the column cage in each direction is greater than or equal to 0.5Vg/(fy). Where the slab is post-tensioned, use "Yes" where at least one of the post-tensioning tendons in each direction passes through the column cage. Otherwise, use "No".

4. Action shall be treated as force-controlled



Based on values, with b>a

Based on values, with b=a

Continuity

Slab-Column Connections Continuity reinforcement

Recommendations for Design of Beam-Column Connections in Monolithic Reinforced Concrete Structures: ACI 352R-02.

Considered continuous if: …the area of effectively continuous main bottom bars passes through the column cage in each direction is greater than or equal to 0.5Vg/(fy). Where the slab is post-tensioned, at least one of the post-tensioning tendons in each direction must pass through the column cage.

0.5 gsm

y

VA

f

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 element1

1Slab-beams and columns only connected by rigid-plastic torsional connection element.

Slab-Column Connections Nonlinear Modeling

Walls (6.7.1.2)Columns under discontinuous shear walls

Columns under discontinuous shear walls Use Section 6.4.2 (Columns)

Take advantage of improvements to columns section.

Table 6.8 will be restrictive due to high axial loads.

Consistency.

New Table 6-18

… … … …… … … …

Table 6-18 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures- R/C Shear Walls and Associated Components Controlled by Flexure

Acceptable Plastic Hinge Rotation4,5 (radians)

Performance Level

Component Type Plastic Hinge Rotation (radians)

Residual Strength


Conditions a b c IO LS CP LS CP

i. Shear walls and wall segments

cww

yss

flt

PfAA

'

' cww flt

V

' Confined

Boundary1

0.1 4 Yes 0.015 0.020 0.75 0.005 0.010 0.015 0.015 0.020

0.1 6 Yes 0.010 0.015 0.40 0.004 0.008 0.010 0.010 0.015

0.25 4 Yes 0.009 0.012 0.60 0.003 0.006 0.009 0.009 0.012

0.25 6 Yes 0.005 0.010 0.30 0.0015 0.003 0.005 0.005 0.010

0.1 4 No 0.008 0.015 0.60 0.002 0.004 0.008 0.008 0.015

0.1 6 No 0.006 0.010 0.30 0.002 0.004 0.006 0.006 0.010

0.25 4 No 0.003 0.005 0.25 0.001 0.002 0.003 0.003 0.005

0.25 6 No 0.002 0.004 0.20 0.001 0.001 0.002 0.002 0.004

1. A boundary element shall be considered confined where transverse reinforcement exceeds 75% of the requirements given in ACI 318 and spacing of transverse reinforcement does not exceed 8db. It shall be permitted to take modeling parameters and acceptance criteria as 80% of confined values where boundary elements have at least 50% of the requirements given in ACI 318 and spacing of transverse reinforcement does not exceed 8db. Otherwise, boundary elements shall be considered not confined.

2. Conventional longitudinal reinforcement consists of top and bottom steel parallel to the longitudinal axis of the coupling beam. Conforming transverse reinforcement consists of: (a) closed stirrups over the entire length of the coupling beam at a spacing d/3, and (b) strength of closed stirrups Vs 3/4 of required shear strength of the coupling beam.

3. For secondary coupling beams spanning <8'-0", with bottom reinforcement continuous into the supporting walls, secondary values shall be permitted to be doubled.



Walls (Table 6-19)Tri-linear BackboneTable 6-19 Modeling Parameters and Numerical Acceptance Criteria for Nonlinear Procedures- R/C Shear Walls and Associated Components Controlled by Shear

Acceptable Total Drift (%) or Chord5 Rotation (radians)1

Performance Level

Component Type Total Drift

Ratio (%), or Chord Rotation

(radians)1 Strength


Conditions d e g c f IO LS CP LS CP

i. Shear walls and wall segments2

'0.05

's s y

w w c

A A f P

t l f

1.0 2.0 0.4 0.20 0.6 0.40 0.75 1.0 1.5 2.0

'0.05

's s y

w w c

A A f P

t l f

0.75 1.0 0.4 0.0 0.6 0.40 0.55 0.75 0.75 1.0

Response dependent on axial load

Hidalgo et al. 2002M/Vlw = 1.0 Specimen #2

40mm

Displacement (mm)

Load

(kN

)

proposedFEMA 356

Walls (6.7.2.3)one curtain of reinforcement

The nominal shear strength of a shear wall or wall segment, Vn , shall be

determined based on the principles and equations given in Chapter 21 of ACI 318, except that the restriction on the number of curtains of reinforcement shall not apply to existing walls.

(MPa)

Walls (6.7.2.3)reinforcement yield strength

The following text is removed from 6.7.2.3:For all shear strength calculations, 1.0 times the specified reinforcement yield strength shall be used.

Factors on yield strength determined by whether action is force or displacement controlled.

Consistency with rest of document.

Walls (6.7.2.3)reinforcement yield strength

Data - Hidalgo et al. 2002

Specimen hw/lw Vu Test Vn ACI 21-7 Vu Test/Vn ACI

(kips) (kips)

1 2.0 44.6 43.5 1.02

2 2.0 60.8 56.5 1.08

4 2.0 72.9 71.1 1.03

6 1.4 69.5 51.1 1.36

8 1.4 84.2 75.3 1.12

Chapter 6Miscellaneous changes

1. Concrete-encased steel sections (6.1)Chapter 6 does not apply to these components.

2. Fig. 6-1 commentary (C6.3.1.2.2)Impact of rapid strength degradation in Fig 6-1 on displacement demands.

3. Usable strain limits (6.3.3.1)Tests for alternative tensile strain limits for reinforcement must include the influence of low-cycle fatigue and spacing of transverse reinforcement.

Deformation and Force-Controlled Actions

Motivation for changes: Columns can sustain shear failures without

loss of axial load capacity. This case not permitted by 2.4.4.3 or

captured by Fig. 2-3:

Deformation and Force-Controlled ActionsNew Figure 2-3:

Deformation and Force-Controlled ActionsNew Figure C2-1:

Although notation used in Fig 2-3 and C2-1 is not ideal, the committee felt further changes in the document would be needed to address this concern.

Walls (Table 6-18)confinement and shear stress limit

ACI confinement provisions too restrictive. High ductility still achieved with:

Ash > 0.75Ash ACI

s < 8db

Moderate ductility still achieved with: Ash > 0.5Ash ACI

s < 8db

Deformation capacities approximately constant for 4 'cv f

Consider as confined

Consider as 80% confined

Thomsen & Wallace, 2004“unconfined boundary”

Confined

Unconfined

Paulay 1986high shear stress

h = 3.3 m = 10.83 ft

(3.94”)

' 'g

3 3

y 3 '

& 0.163 A & Assume conforming

(70 )(130") 700.4" (10.0 ) 4.6

3 0.5 3(~

WALL Goodsir

3750 )(0.5)(4")(59") /12 (4")(59") 3750

0.01(33

, 1985:

00 ) 33

s s c

u

c g w w c

a

A A P f

VPL k kmm

E I ksi psit l f

mm m

0.015(3300 ) 50bm mm mm

(59”)

Conforming

Conforming6 'cv f

3 'cv f

asce 41 ad hoc committee supplement revisions to chapter 6 of asce 41, seismic rehabilitation of...

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