The Seismic Design and Performance of Reinforced Concrete Beam-Column Knee Joints in Buildings

2003 ◽  
Vol 19 (4) ◽  
pp. 863-895 ◽  
Author(s):  
Leslie M. Megget
Keyword(s):  
Reinforced Concrete ◽  
New Zealand ◽  
Concrete Beam ◽  
Reinforced Concrete Beam ◽  
Knee Joints ◽  
Joint Zone ◽  
Displacement Ductility ◽  
Cover Concrete ◽  
Joint Shear ◽  
And Performance

The seismic performance of eleven half-scale and three full-sized reinforced concrete beam-column knee joints was tested under inelastic cyclic loading. Twelve joints were designed to the current New Zealand Concrete Standard, NZS 3101 while the remaining two were designed to the 1964 New Zealand Code, which contained few seismic provisions. All the 1995 designs approached or exceeded their nominal beam strengths in both directions and only degraded in strength at displacement ductility factors greater than 2, while the 1960 designs failed prematurely in joint shear at about 70% of the beam nominal strengths. Many of the half-scale joints failed when cover concrete split off in the joint zone, allowing loss of anchorage and slip of the top beam bars. Two full-scale joints were designed to carry the maximum specified code joint shear stress (0.2 fc′), and one subsequently failed due to joint shear when the concrete compressive strength did not reach the specified design value. A third full-size joint was tested with distributed beam reinforcement. This joint performed in a ductile manner to displacement ductility 4 but failed in the second cycle at that displacement, due to buckling of several rows of beam bars.

The seismic behaviour of small reinforced concrete beam-column knee joints

1998 ◽  
Vol 31 (4) ◽  
pp. 215-245 ◽  
Author(s):  
Leslie M. Megget
Keyword(s):  
Shear Stress ◽  
Reinforced Concrete Beam ◽  
The United States ◽  
Knee Joints ◽  
Seismic Behaviour ◽  
Moment Capacity ◽  
Displacement Ductility ◽  
Nominal Strength ◽  
Frame Buildings ◽  
Joint Shear

The majority of research into beam-column knee joints has been conducted with monotonic loading. Many of these joints failed to reach their member moment capacity, especially under opening moments, while a few cyclic knee joint tests have been completed in the United States this decade. This paper describes the cyclic testing of 8 small knee joints designed to the 1995 New Zealand Concrete Standard. In addition two joints designed and detailed to the 1965 N.Z. Concrete Code were also tested. Joints with U-bar anchorages performed better than joints with standard 90 degree hook details on beam and column bars. The current Concrete Standard (NZS3101:1995) designs usually attained their nominal moment capacity in both directions up to and including ductility 4 displacements, but subsequently strengths fell off at higher ductilities. Joints with extra diagonal bars across the inner comer were able to sustain their nominal member strengths to higher ductility levels, especially under opening moments. A maximum horizontal joint shear stress of 0.12 f’c, for knee joints, in ductile frame buildings is recommended, where this limit is 60% of the current NZS3101:1995 Standard recommendation. An approximate 25% degradation of the joint shear stress occurred as displacement ductility factors increased from 1 to 8. The 1960's designed joints behaved poorly, as expected, with joint shear and anchorage failures occurring, in both moment directions, at strength levels below the beam's nominal strength. A maximum joint shear stress of only 0.072 f’c was reached and this fell to about a third of that stress between displacement ductility factors of 1 and 4 under closing moments.

Experimental evaluation of seismic response for reinforced concrete beam–column knee joints with irregular geometries

2016 ◽  
Vol 19 (12) ◽  
pp. 1889-1901
Author(s):  
Min Wang ◽  
Dichuan Zhang ◽  
Jainping Fu
Keyword(s):  
Reinforced Concrete ◽  
Knee Joint ◽  
Large Scale ◽  
Concrete Beam ◽  
Reinforced Concrete Beam ◽  
Knee Joints ◽  
Seismic Capacity ◽  
Bond Slip ◽  
Irregular Geometries ◽  
Irregular Geometry

Regular reinforced concrete beam–column knee joints are typically framed by beams and columns with similar heights. However, complexities in modern architecture layouts may result in irregular geometries for the knee joint. The irregular geometry refers to significant differences in the height for the beam and the column framing into the joint. For example, the height of the beam is considerably larger than that of the column, and vice versa. Seismic performance and behavior for the regular knee joint have been well examined through previous experimental research. However, the knee joint with irregular geometry (termed here as irregular knee joint) may have different seismic behaviors compared to the regular knee joint because the irregular geometry can produce different demands, stiffness, strength, and reinforcing bond conditions. Therefore, this article evaluates seismic behavior of the irregular knee joint including failure mode, strength and stiffness degradation, deformation capacity, bond-slip of reinforcement, and energy dissipation capacity through four large-scale static cyclic tests. The test results show that in general the irregular knee joint designed to the current code has low seismic capacity due to poor bond conditions of the reinforcement inside the joint.

scholarly journals Seismic performance of two full size reinforced concrete beam-column joint units

1975 ◽  
Vol 8 (1) ◽  
pp. 38-69
Author(s):  
R. W. G. Blakeley ◽  
L. M. Megget ◽  
M. J. N. Priestley
Keyword(s):  
Reinforced Concrete ◽  
Seismic Performance ◽  
Concrete Beam ◽  
Reinforced Concrete Beam ◽  
Joint Region ◽  
Displacement Ductility ◽  
Full Size ◽  
Frame Building ◽  
Column Joint ◽  
Design Construction

The design, construction and testing of two large reinforced concrete beam-column assemblies, representing an interior and an exterior joint, are described. Member details were based on an actual frame building designed by the M.W.D. Extensive results are presented which indicate very satisfactory behaviour particularly in the joint region. Hinges formed in the beams in all cases, and stable behaviour was obtained at displacement ductility factors of up to 6 and 8 for the interior and exterior test units respectively. Results are assessed in terms of design assumptions, and tentative design recommendations are made.

Experimental and analytical investigations of reinforced concrete beam-column joints retrofitted by single haunch

2020 ◽  
Vol 23 (15) ◽  
pp. 3171-3184
Author(s):  
Ebrahim Emami ◽  
Ali Kheyroddin ◽  
Mohhamad Kazem Sharbatdar
Keyword(s):  
Reinforced Concrete ◽  
Concrete Beam ◽  
Peak Load ◽  
Vulnerability Index ◽  
Reinforced Concrete Beam ◽  
Stiffness Ratio ◽  
Limit States ◽  
Joint Shear Strength ◽  
Analytical Results ◽  
Joint Shear

Recently, the single haunch with specifications such as less invasive and architectural consistency, and easy to practice have been adopted as one of the considered retrofitting options for deficient reinforced concrete beam-column joints. In this article, by analytical evaluation, the influence parameters such as haunch to beam stiffness ratio, haunch inclination angles, and mounted position were investigated. Analytical equations were also proposed for haunch to beam stiffness ratio in terms of both shear interaction between haunch and beam-column members and reduction of joint shear demand. Moreover, five exterior beam-column joint sub-assemblies were fabricated afterwards four of those retrofitted by various cross-sectional area of single steel haunch. Then, all of these beam-column joints and remaining one (as-built joint) were experimentally subjected to cyclic loading. To validate the analytical results, the experimental responses in four limit states including first diagonal core crack in as-built joint, drift ratio 2%, the first diagonal core crack in all the joints, and ultimate state (peak load) were provided for comparison. Also, by definition of an index as vulnerability index in fraction ratio of available joint shear force to joint shear strength predicted by international codes, the obtained vulnerability index of experimental responses were compared to analytical results.

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