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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.