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

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

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

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

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

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

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 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

Damage progression interior connections Lehman

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

Damage at 5% drift Standard Loading Impulsive Loading Lehman

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

Evaluation of FEMA-356 Model interior connections 18 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

Joint panel deformations Joint Deformation

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

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

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

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

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 (%)

Plastic drift capacity interior connections 30 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

Damage progression exterior connections Pantelides, 2002

Joint behavior exterior connections 15 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, %

Plastic drift capacity 30 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

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

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

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.

Joint failure? sy tcr , psi

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

Joint test summary axial failures identified Tests with axial load failure 0.1 } 0.08 0.03 - 0.07 0.10 - 0.18 0.20 - 0.22 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

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

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

Joint panel deformations Joint Deformation

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

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

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