Beam-Column Connections

Jack MoehleUniversity of California, Berkeley

with contributions fromDawn Lehman and Laura LowesUniversity of Washington, Seattle

Outlinedesign of new jointsexisting joint detailsfailure of existing joints in earthquakesgeneral response characteristicsimportance of including joint deformationsstiffnessstrengthdeformation capacityaxial failure

Special Moment-Resisting Frames - Design intent -

Beam

Beam Section

lnbVp

wMpr

Mpr

Vp

Mpr

Vp

Mpr

lc

Vcol

Vcol

For seismic design, beam yielding defines demands

Joint demands

(a) moments, shears, axial loads acting on joint

(c) joint shear

Vcol

Ts1 C2

Vu =Vj = Ts1 + C1 - Vcol

(b) internal stress resultants acting on joint

Ts2 = 1.25Asfy

C2 = Ts2

Ts1 = 1.25Asfy

C1 = Ts2

Vcol

Vcol

Vb1 Vb2

Joint geometry(ACI Committee 352)

a) Interior A.1

c) Corner A.3

b) Exterior A.2

d) Roof Interior B.1

e) Roof Exterior B.2

f) RoofCorner B.3

ACI 352

Classification/type

interior exterior corner

cont. column

20 15 12

Roof 15 12 8

Values of (ACI 352)

Joint shear strength- code-conforming joints -

hbfVV jcnu'

= 0.85

ACI 352

Joint Details - Interior

hcol 20db

ACI 352

Joint Details - Corner ldh

ACI 352

Code-conforming joints

Older-type beam-column connections

Survey of existing buildings 

Mosier

Joint failures

Studies of older-type joints

Lehman

-80

-60

-40

-20

0

20

40

60

80

-6 -4 -2 0 2 4 6Drift %

Col

umn

Shea

r (K

)

Yield of Beam Longitudinal Reinforcement

Spalling of Concrete Cover Longitudinal

Column Bar Exposed

Measurable residual cracks

20% Reduction in Envelope

Damage progressioninterior connections

Lehman

Effect of load historyinterior connections

-6 -4 -2 0 2 4 6Story Drift

Col

umn

Shea

r (k)

Column Bar

Envelope for standard cyclic history

Impulsive loading history

Lehman

Standard Loading Impulsive Loading

Damage at 5% drift

Lehman

Specimen CD15-14

Contributions to driftinterior connections

“Joints shall be modeled as either stiff or rigid components.” (FEMA 356)

Lehman

Evaluation of FEMA-356 Modelinterior connections

0

2

4

6

8

10

12

14

16

18

0 0.005 0.01 0.015 0.02 0.025 0.03

Joint Shear Strain

Join

t She

ar F

acto

r

FEMAPEER-14CD15-14CD30-14PADH-14PEER-22CD30-22PADH-22

Lehman

Joint panel deformations

Joint Deformation

0.0000

12

Gc /5Gc

Joint shear stiffnessinterior connections

psifc ,20 '

0.005 0.010 0.015 0.020 0.025 0.030Joint shear strainJo

int s

hear

stre

ss (M

Pa)

108642

psifc ,20 '

psifc ,10 '

Gc /8

Lehman

Joint strengtheffect of beam yielding

Join

t Stre

ss (p

si)

0

400

800

1200

1600

0 1 2 3 4 5 6

Drift (%)

• Joint strength closely linked to beam flexural strength• Plastic deformation capacity higher for lower joint shear

Lehman

Yield

Yield

Joint strength interior connections - lower/upper bounds

/fc’

0

0.1

0.3

0.4

0 10 20 30 40 50 60

0.2vj

Beam Hinging/Beam Bar Slip

Failure forced into beams between 8.5√f’c and 11√f’c

Joint Shear Failure

Joint failure without yielding near 25.5√f’c

Lehman

Joint strengthinterior connections

0

500

1000

1500

2000

2500

3000

3500

0 4000 8000 12000 16000

Concrete Strength (psi)

Join

t Stre

ss (p

si)

Joint Failures

Beam Failures

psifc ,10 '

Lehman

Joint deformabilityJo

int S

tress

(psi

)

0

400

800

1200

1600

0 1 2 3 4 5 6

vmax

Drift (%)

0.2vmax

plastic drift capacity

envelope

Plastic drift capacityinterior connections

0

5

10

15

20

25

30

0 0.01 0.02 0.03 0.04 0.05 0.06

plastic drift angle

psif

v

c

jo ,'

int

Note: the plastic drift angle includes inelastic deformations of the beams

Damage progressionexterior connections

Pantelides, 2002

Joint behaviorexterior connections

2 Clyde6 Clyde4 Clyde5 Clyde

5 Pantelides 6 Pantelides 6 Hakuto Priestley longitudinal Priestley transverse

psif

v

c

jo ,'

int

15

0 1 2 3 4 5 6 7

10

5

0

Drift, %bidirectional loading

Plastic drift capacity

0

5

10

15

20

25

30

0 0.01 0.02 0.03 0.04 0.05 0.06

plastic drift angle

psif

v

c

jo ,'

int

Note: the plastic drift angle includes inelastic deformations of the beams

InteriorExterior

Exterior jointhook detail

hook bent into joint

hook bent out of joint

Interior joints with discontinuous bars

Column shear, kips

40

30

20

10

00 1 2 3 4 5Drift ratio, %Beres, 1992

• Assuming bars are anchored in joint, strength limited by strength of framing members, with upper bound of 25. For 25 ≥ ≥ 8, joint failure may occur after inelastic response. For ≤ 8, joint unlikely to fail.

Unreinforced Joint StrengthbhfV cj

'

jointgeometry

4

6

10

8

12

FEMA 356 specifies the following:

• No new data. Probably still valid.

• Assuming bars are anchored in joint, strength limited by strength of framing members, with upper-bound of 15. For 15 ≥ ≥ 4, joint failure may occur after inelastic response. For ≤ 4, joint unlikely to fail.

Joint failure?

ycr

cr

'

'

616

c

yccr

ff

, psi

Joint failure?

Drift at “tensile failure”

Drift at “axial failure”

Late

ral L

oad

Lateral Deflection, mm

Drift at “lateral failure”Priestley, 1994

0

0.02

0.04

0.06

0.08

0.1

0 0.05 0.1 0.15 0.2 0.25 0.3

Axial load ratio

Drif

t rat

io }Interior

0.03

- 0.

07

0.10

- 0.

18

0.20

- 0.

22

Range of values

Joint test summaryaxial failures identified

Tests with axial load failure

0.36

Exterior, hooks bent in

Exterior, hooks bent out

Corner

'cj fv

Suggested envelope relationinterior connections with continuous beam bars

psif

v

c

jo ,'

int 25

20

15

10

5

0

0.015

0.04 0.02

8

psifc ,25 'strength = beam strength but not to exceed

stiffness based on effective stiffness to yield

Note: the plastic drift angle includes inelastic deformations of the beams

axial-load stability unknown, especially under high axial loads

Suggested envelope relationexterior connections with hooked beam bars

psif

v

c

jo ,'

int 25

20

15

10

5

0

0.010

0.02 0.01

strength = beam strength but not to exceed psifc ,12 '

stiffness based on effective stiffness to yield

connections with demand less than have beam-yield mechanisms and do not follow this model

'4 cf

Note: the plastic drift angle includes inelastic deformations of the beams

Joint panel deformations

Joint Deformation

Methods of Repair (MOR)Method of

Repair ActivitiesDamag

e States

0. Cosmetic Repair

Replace and repair finishes 0-2

1. Epoxy Injection

Inject cracks with epoxy and replace finishes

3-5

2. Patching Patch spalled concrete, epoxy inject cracks and replace finishes

6-8

3. Replace concrete

Remove and replace damaged concrete, replace finishes

9-11

4. Replace joint Replace damaged reinforcing steel, remove and replace concrete, and replace finishes

12Pagni

Interior joint fragility relations

0.0 1.0 2.0 3.0 4.0 5.0 6.000.10.20.30.40.50.60.70.80.91

Drift (%)

MOR 0MOR 1MOR 2MOR 3MOR 4

0.0 1.0 2.0 3.0 4.0 5.0 6.000.10.20.30.40.50.60.70.80.91

Drift (%)

MOR 0MOR 1MOR 2MOR 3MOR 4

MOR 0MOR 1MOR 2MOR 3MOR 4

MOR 0MOR 1MOR 2MOR 3MOR 4Pr

obab

ility

of R

equi

ring

a M

OR

Cosmetic repairEpoxy injectionPatchingReplace concreteReplace joint

Beam-Column Connections

Jack MoehleUniversity of California, Berkeley

with contributions fromDawn Lehman and Laura LowesUniversity of Washington, Seattle

References• Clyde, C., C. Pantelides, and L. Reaveley (2000), “Performance-based evaluation of exterior reinforced

concrete building joints for seismic excitation,” Report No. PEER-2000/05, Pacific Earthquake Engineering Research Center, University of California, Berkeley, 61 pp.

• Pantelides, C., J. Hansen, J. Nadauld, L Reaveley (2002, “Assessment of reinforced concrete building exterior joints with substandard details,” Report No. PEER-2002/18, Pacific Earthquake Engineering Research Center, University of California, Berkeley, 103 pp.

• Park, R. (2002), "A Summary of Results of Simulated Seismic Load Tests on Reinforced Concrete Beam-Column Joints, Beams and Columns with Substandard Reinforcing Details, Journal of Earthquake Engineering, Vol. 6, No. 2, pp. 147-174.

• Priestley, M., and G. Hart (1994), “Seismic Behavior of “As-Built” and “As-Designed” Corner Joints,” SEQAD Report to Hart Consultant Group, Report #94-09, 93 pp. plus appendices.

• Walker, S., C. Yeargin, D. Lehman, and J. Stanton (2002), “Influence of Joint Shear Stress Demand and Displacement History on the Seismic Performance of Beam-Column Joints,” Proceedings, The Third US-Japan Workshop on Performance-Based Earthquake Engineering Methodology for Reinforced Concrete Building Structures, Seattle, USA, 16-18 August 2001, Report No. PEER-2002/02, Pacific Earthquake Engineering Research Center, University of California, Berkeley, pp. 349-362.

• Hakuto, S., R. Park, and H. Tanaka, “Seismic Load Tests on Interior and Exterior Beam-Column Joints with Substandard Reinforcing Details,” ACI Structural Journal, Vol. 97, No. 1, January 2000, pp. 11-25.

• Beres, A., R.White, and P. Gergely, “Seismic Behavior of Reinforced Concrete Frame Structures with Nonductile Details: Part I – Summary of Experimental Findings of Full Scale Beam-Column Joint Tests,” Report NCEER-92-0024, NCEER, State University of New York at Buffalo, 1992.

• Pessiki, S., C. Conley, P. Gergely, and R. White, “Seismic Behavior of Lightly-Reinforced Concrete Column and Beam Column Joint Details,” Report NCEER-90-0014, NCEER, State University of New York at Buffalo, 1990.

• ACI-ASCE Committee 352, Recommendations for Design of Beam-Column Connections in Monolithic Reinforced Concrete Structures,” American Concrete Institute, Farmington Hills, 2002.

References (continued)• D. Lehman, University of Washington, personal communication, based on the following resources:

Fragility functions:•Pagni, C.A. and L.N. Lowes (2006). “Empirical Models for Predicting Earthquake Damage and Repair Requirements for Older Reinforced Concrete Beam-Column Joints.” Earthquake Spectra. In press. Joint element:•Lowes, L.N. and A. Altoontash. “Modeling the Response of Reinforced Concrete Beam-Column Joints.” Journal of Structural Engineering, ASCE. 129(12) (2003):1686-1697.•Mitra, N. and L.N. Lowes. “Evaluation, Calibration and Verification of a Reinforced Concrete Beam-Column Joint Model.” Journal of Structural Engineering, ASCE. Submitted July 2005. •Anderson, M.R. (2003). “Analytical Modeling of Existing Reinforced Concrete Beam-Column Joints” MSCE thesis, University of Washington, Seattle, 308 p.Analyses using joint model:•Theiss, A.G. “Modeling the Response of Older Reinforced Concrete Building Joints.” M.S. Thesis. Seattle: University of Washington (2005): 209 p.Experimental Research•Walker, S.*, Yeargin, C.*, Lehman, D.E., and Stanton, J. Seismic Performance of Non-Ductile Reinforced Concrete Beam-Column Joints, Structural Journal, American Concrete Institute, accepted for publication. •Walker, S.G. (2001). “Seismic Performance of Existing Reinforced Concrete Beam-Column Joints”. MSCE Thesis, University of Washington, Seattle. 308 p.•Alire, D.A. (2002). "Seismic Evaluation of Existing Unconfined Reinforced Concrete Beam-Column Joints", MSCE thesis, University of Washington, Seattle, 250 p.•Infrastructure Review•Mosier, G. (2000). “Seismic Assessment of Reinforced Concrete Beam-Column Joints”. MSCE thesis, University of Washington, Seattle. 218 p.