Effect of joint shear stress on seismic behaviour of interior GFRP-RC beam-column joints

1998 ◽

Vol 31 (4) ◽

pp. 215-245 ◽

Cited By ~ 2

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.

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A Simplified Approach to Joint Shear Behavior Prediction of RC Beam-Column Connections

Earthquake Spectra ◽

10.1193/1.4000064 ◽

2012 ◽

Vol 28 (3) ◽

pp. 1071-1096 ◽

Cited By ~ 14

Author(s):

Jaehong Kim ◽

James M. LaFave

Keyword(s):

Shear Stress ◽

Parameter Estimation ◽

Estimation Method ◽

Stress And Strain ◽

Rc Beam ◽

Peak Response ◽

Experimental Database ◽

Key Points ◽

Shear Stress And Strain ◽

Joint Shear

An extensive experimental database of reinforced concrete (RC) beam-column connections subjected to cyclic lateral loading has been constructed. All cases within the database experienced joint shear failure, either in conjunction with or without yielding of longitudinal beam reinforcement, representing damage within a joint panel that was the main contributor to total lateral deformation. (Cases having damage within a joint panel caused by other premature failure modes (e.g., anchorage failure) are not included in the database.) Using the experimental database, envelope curves of joint shear stress vs. strain behavior were developed by connecting key points such as cracking, yielding, and peak loading. Joint shear stress and strain models at peak response have been developed by a Bayesian parameter estimation method based on the experimental database. At other key points, important influence parameters are also identified by constructing joint shear stress and strain models in conjunction with the Bayesian parameter estimation method. Then, a complete RC joint shear stress vs. strain model (including post-peak behavior) is suggested using simplified joint shear stress and strain models at peak response; effects of key parameters on the suggested behavior models are evaluated. Finally, the ASCE/SEI 41 joint shear behavior model has been examined using the constructed database—specific joint shear strength factors and plastic joint shear deformation values are recommended for use when following that approach.

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Strengthening of seismically deficient exterior beam-column connections using embedded steel bars

MATEC Web of Conferences ◽

10.1051/matecconf/201927601007 ◽

2019 ◽

Vol 276 ◽

pp. 01007

Author(s):

Ridwan ◽

Samir Dirar ◽

Yaser Jemaa ◽

Marios Theofanous ◽

Mohammed Elshafie

Keyword(s):

Shear Stress ◽

Tensile Stress ◽

Superior Performance ◽

Rc Beam ◽

Control Specimen ◽

Concrete Core ◽

Novel Technique ◽

Principal Tensile Stress ◽

Steel Bars ◽

Joint Shear

Several techniques for improving performance of reinforced concrete (RC) beam-column (BC) connections have been developed in last two decades, but these techniques have been criticized for being labourintensive and susceptible to premature de-bonding. To overcome these shortcomings, a novel technique utilising embedded steel bars has been developed in this study for strengthening seismically deficient RC BC connections. This technique involves drilling holes within the joint core. After the drilled holes are cleaned, they are partially filled with epoxy. Finally, steel bars are inserted in the epoxy-filled holes. Two exterior BC connections were constructed and loaded under displacement-controlled cyclic loading. The first specimen was a control specimen designed in accordance with the pre-1970s building codes to represent BC connections requiring strengthening. The second specimen was strengthened with eight 8 mm steel bars embedded within the concrete core in the joint area and epoxied to maintain the bond between the concrete and the steel bars. The strengthened specimen had superior performance compared to that of the control specimen in terms of joint shear stress, normalised principal tensile stress demand and stiffness degradation. The results show that shear stress of the joint was enhanced by about 8% whereas the enhancement in the principal tensile stress demand was 24% compared to that of the control specimen. The results showed that the proposed technique is capable in upgrading the seismic performance of seismically deficient RC BC connections.

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A Nonlinear Macro-Model for the Analysis of Monotonic and Cyclic Behaviour of Exterior RC Beam-Column Joints

Frontiers in Materials ◽

10.3389/fmats.2021.719716 ◽

2021 ◽

Vol 8 ◽

Author(s):

Ernesto Grande ◽

Maura Imbimbo ◽

Annalisa Napoli ◽

Riccardo Nitiffi ◽

Roberto Realfonzo

Keyword(s):

Shear Stress ◽

Linear Regression Analysis ◽

Material Model ◽

Joint Interface ◽

Model Parameters ◽

Multivariate Linear Regression Analysis ◽

Rc Beam ◽

Stress Strain ◽

Experimental Database ◽

Joint Shear

The study presents a numerical investigation on exterior reinforced concrete (RC) beam-column joints under seismic actions based on a macro-modelling approach proposed by the authors in a recent paper. The followed approach makes use of the well-known “scissors model” where two nonlinear rotational springs arranged in series were introduced to schematize the shear behavior of the joint panel and, moreover, the possible occurrence of the debonding of longitudinal steel rebars at the beam-joint interface. In this paper, the scissor model is employed in the context of a novel predictive approach with the twofold objective to: 1) develop a new model for the estimate of the maximum shear strength of RC joints by performing a multivariate linear regression analysis on a set of experimental tests and, 2) define a new multilinear backbone joint shear stress-strain law to be assigned to one of the mentioned springs. In particular, the identification of the shear strain parameters is obtained by performing a sensitivity analysis in which a number of monotonic load-drift numerical curves are derived by varying the strain values in ranges opportunely a-priori defined and compared with the experimental ones to investigate their accuracy. Finally, cyclic analyses on RC joints collected in the experimental database are carried out by considering the backbone joint shear stress-strain law identified in the calibration process. The analyses are performed by using the nonlinear open-source finite element platform, OpenSees, in which the “pinching4” uniaxial material model, available in the software library, is implemented to set the parameters governing the hysteresis rules and pinching effect. To this purpose, five literature proposals suggesting the values to use for such parameters are taken into account and their assessment is presented in the paper. The obtained outcomes have allowed, on the one hand, to identify the proposal providing the best numerical simulations of the experimental results and, on the other end, to draw useful indications on how to further improve the cyclic modelling by opportunely modifying the setting of the “pinching4” material model parameters.

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