1. Beam-Column Connections
Jack Moehle
University of California, Berkeley
with contributions from
Dawn Lehman and Laura Lowes
University of Washington, Seattle

2. Outline design of new joints existing joint details
failure of existing joints in earthquakes
general response characteristics
importance of including joint deformations
stiffness
strength
deformation capacity
axial failure

3. Special Moment-Resisting Frames - Design intent -
Vcol
For seismic design, beam yielding defines demands w
Mpr
Mpr
Mpr
Beam lc
Describe how the joint demands are obtained. Sketch in the beam Mp values, then the corresponding beam shears. Note that the newer 352 document, under ballot, uses the slab effective width in tension as we talked about previously. The vertical line through the joint is to represent the column, use statics to estimate the column shear. Show actions on the joint. Vp Vp
lnb Vp
Mpr
Vcol
Beam Section

4. Joint demands (b) internal stress resultants acting on joint
1.25Asfy
C2 = Ts2
Ts1 =
C1 = Ts2
Vcol
Vb1
Vb2
Joint demands
Never really covered this one, though we have talked about how the boundary conditions around a joint affect strength.
(c) joint shear
Vcol
Ts1 C2
Vu =Vj = Ts1 + C1 - Vcol
(a) moments, shears, axial loads acting on joint

5. Joint geometry (ACI Committee 352)
Interior A.1
c) Corner
A.3
b) Exterior
A.2
d) Roof
Interior B.1
e) Roof
Exterior B.2
f) Roof
Corner B.3
Self explanatory. I would show this transparency, then sketch in the geometries.
ACI 352

6. Joint shear strength - code-conforming joints -
Classification
/type
interior
exterior
corner
cont. column 20 15 12
Roof 8
Values of g (ACI 352)
Define the values of joint shear strength
ACI 352

7. Joint Details - Interior
hcol  20db
ACI 352

8. Joint Details - Corner
 ldh
ACI 352

9. Code-conforming joints

10. Older-type beam-column connections

11. Survey of existing buildings
Mosier

12. Joint failures

13. Studies of older-type joints
The figure show the reference specimen. Approximately 2/3 of full scale. An interior joint in an exterior frame. And was constructed without transverse beams. The longitudinal bars in the columns and beams have been grooved to permit placing the strain guages and minimize distrubance ot bond capacity.
This photograph shows the specimen in the laboratory. The specimen was tested by loading the beams. The dipslacement history is indicated. We subjected the specimen to increasing levels of drift including drifts of 0.5%, 1%, 1.5%, 2%, 3%, 4%, and 5%.
The specimen was not expected to loose axial load carrying capacity unless the bars buckled. However, the tests would be carried out until loss of the majority of the lateral load carrying capacity
Lehman

14. Damage progression interior connections
Lehman

15. Effect of load history interior connections
Impulsive loading history
Envelope for standard
cyclic history
Column Shear (k)
Column Bar
The column force-drift response of the specimen is indicated. We note a significant decrease in strength from cycle 1 to cycle 2 at a drift of 3%. In additon, we see that the energy dissipation capacity of the subassemblage is reduced relative to a “ductile” response.
It is instructive to consider the damage at various drift levels.
At 0.5% drift (yield of the longitudinal bars occurred between drift of 0.5% and 0.75%), we not cracking in the joint region. After the first cycle to 3% drift, we see significant damage to the joint region. And at 5% drift we see more extensive damage to the joint region as well as damage to the beams and the columns.
Therefore, although the performance of the joint may not meet the expectation for a new joint, for an existing joint, we would expect the joint to sustain the lateral load carrying capacity until a drift of 3% and it axial load carrying capacity was sustained throughout, even cycling to 5% drift 5 times. These results have significant implications for the need to retrofit or not retrofit the joints. -6 -4 -2 2 4 6
Story Drift
Lehman

16. Damage at 5% drift
Standard Loading
Impulsive Loading
Lehman

17. Contributions to drift interior connections
“Joints shall be modeled as either stiff or rigid components.” (FEMA 356)
Specimen CD15-14
Lehman

18. Evaluation of FEMA-356 Model interior connections18 16 14 12 10
Joint Shear Factor
FEMA 8
PEER-14 6
CD15-14
CD30-14 4
PADH-14
PEER-22 2
CD30-22
PADH-22
0.005
0.01
0.015
0.02
0.025
0.03
Joint Shear Strain
Lehman

19. Joint panel deformations
Joint Deformation

20. Joint shear stiffness interior connections
Gc /8
Gc /5 Gc 12 10 8
Joint shear stress (MPa) 6 4 2
0.000
0.005
0.010
0.015
0.020
0.025
0.030
Joint shear strain
Lehman

21. Joint strength effect of beam yielding
1600
1200
Joint Stress (psi)
800
400 1 2 3 4 5 6
Drift (%)
Joint strength closely linked to beam flexural strength
Plastic deformation capacity higher for lower joint shear
Lehman

22. Joint strength interior connections - lower/upper bounds
Joint Shear Failure
Joint failure without yielding near 25.5√f’c
0.4
0.3
Beam Hinging/
Beam Bar Slip
Failure forced into beams between 8.5√f’c and 11√f’c
0.2 vj
/fc’
0.1 10 20 30 40 50 60 L
Lehman

23. Joint strength interior connections
3500
3000
Joint Failures
2500
2000
Joint Stress (psi)
1500
1000
500
Beam Failures
4000
8000
12000
16000
Concrete Strength (psi)
Lehman

24. plastic drift capacity
Joint deformability
1600
plastic drift capacity
1200
vmax
Joint Stress (psi)
800
envelope
0.2vmax
400 1 2 3 4 5 6
Drift (%)

25. Plastic drift capacity interior connections30 25 20 15 10 5
0.01
0.02
0.03
0.04
0.05
0.06
plastic drift angle
Note: the plastic drift angle includes inelastic deformations of the beams

26. Damage progression exterior connections
Pantelides, 2002

27. Joint behavior exterior connections15
2 Clyde
6 Clyde
4 Clyde
5 Clyde
5 Pantelides
6 Pantelides
6 Hakuto
Priestley longitudinal
Priestley transverse 10 5 1 2 3 4 5 6 7
bidirectional loading
Drift, %

28. Plastic drift capacity30
Interior
Exterior 25 20 15 10 5
0.01
0.02
0.03
0.04
0.05
0.06
plastic drift angle
Note: the plastic drift angle includes inelastic deformations of the beams

29. Exterior joint hook detail
hook bent into joint
hook bent out of joint

30. Interior joints with discontinuous bars
Column shear, kips 40 30 20 10 1 2 3 4 5
Drift ratio, %
Beres, 1992

31. Unreinforced Joint Strength
FEMA 356 specifies the following:
No new data. Probably still valid. g
joint
geometry 4 6 10 8 12
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.
Note that the tension force is 1.25 fy, for seismic. The compression force balances the tension force. On the right, show the joint shear.
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.

32. Joint failure? sy
tcr
, psi

33. Joint failure? Lateral Deflection, mm Lateral Load
Drift at “lateral failure”
Drift at “tensile failure”
Drift at “axial failure”
Priestley, 1994

34. Joint test summary axial failures identified
Tests with axial load failure
0.1 }
0.08
Range of g values
0.36
0.06
Drift ratio
Interior
0.04
Exterior, hooks bent in
Exterior, hooks bent out
0.02
Corner
0.05
0.1
0.15
0.2
0.25
0.3
Axial load ratio

35. Suggested envelope relation interior connections with continuous beam bars
stiffness based on effective stiffness to yield
0.015 25
strength = beam strength but not to exceed 20 15
0.02 8 10 5
0.04
Note: the plastic drift angle includes inelastic deformations of the beams

36. Suggested envelope relation exterior connections with hooked beam bars
stiffness based on effective stiffness to yield 25
strength = beam strength but not to exceed 20
0.010 15
connections with demand less
than have beam-yield mechanisms and do not follow this model 10
0.01 5
axial-load stability unknown, especially under high axial loads
0.02
Note: the plastic drift angle includes inelastic deformations of the beams

37. Joint panel deformations
Joint Deformation

38. Methods of Repair (MOR)
Method of Repair
Activities
Damage 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 12
Pagni

39. Interior joint fragility relations
Cosmetic repair
Epoxy injection
Patching
Replace concrete
Replace joint

40. Beam-Column Connections
Jack Moehle
University of California, Berkeley
with contributions from
Dawn Lehman and Laura Lowes
University of Washington, Seattle

41. 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
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, August 2001, Report No. PEER-2002/02, Pacific Earthquake Engineering Research Center, University of California, Berkeley, pp
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
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 , 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 , 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.

42. 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):
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.