• Structural Engineering and Mechanics
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• v.5 no.5
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• pp.625-634
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• 1997

Reinforced concrete (RC) interior beam-column joints with high-strength materials: concrete compressive strength of 100 MPa and the yield strength of longitudinal bars of 685 MPa, were analyzed using three-dimensional (3-D) nonlinear finite element method (FEM). Specimen OKJ3 of joint shear failure type was a plane interior joint, and Specimen 12 of beam flexural failure type was a 3-D interior joint with transverse beams. Though the analytical initial stiffness was higher than experimental one, the analytical results gave a good agreement with the test results on the maximum story shear forces, the failure mode.

• Earthquakes and Structures
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• v.16 no.5
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• pp.533-546
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• 2019

This study presents an experimental investigation on six beam-column joint specimens under the lateral cyclic loading. The aim was to explore the effectiveness of steel fiber-reinforced concrete (SFRC) in reducing the transverse shear stirrups in beam-column joints of the reinforced concrete (RC) frames with strong-columns and weak-beams. Two RC and four SFRC specimens with different types of reinforcement detailing and steel fibers of volume fraction in the range of 0.75-1.5% were tested under gradually increasing cyclic displacements. The main parameters investigated were lateral load-resisting capacity, hysteresis response, energy dissipation capacity, stiffness degradation, viscous damping variation, and mode of failure. Test results showed that the diagonally bent configuration of beam longitudinal bars in the beam-column joints resulted in the shear failure at the joint region against the flexural failure of beams having straight bar configurations. However, all SFRC specimens exhibited similar lateral strength, energy dissipation potential and mode of failure even in the absence of transverse steel in the beam-column joints. Finally, a methodology has been proposed to compute the shear strength of SFRC beam-column joints under the lateral loading condition.

• Earthquakes and Structures
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• v.25 no.4
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• pp.283-296
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• 2023

This paper presents experimental and numerical studies of seismic performance on reinforced concrete (RC) wide beam (WB) joints. Two RC-WB joint specimens and one conventional RC joint specimen were fabricated using the reinforcing details of longitudinal reinforcing bars in a beam as a variable, and quasi-static cyclic loading tests were performed. The results were used to compare and analyze the load-drift ratio relationship, failure mode, and seismic performance of the specimens quantitatively. In addition, a finite element (FE) analysis of the RC-WB joint was conducted, and the rationality of the FE model was validated by comparing it with the test results. Based on the FE model, a parametric study was conducted, where the ratio of longitudinal reinforcing bars placed on the outer and inner parts of the joint (𝜌_ex/𝜌_in) was a key variable. The results showed that, in the RC-WB joint, an increase of 𝜌_ex/𝜌_in leads to more severe damage to concrete, which reduces the seismic performance of the RC-WB joints.

• Earthquakes and Structures
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• v.23 no.5
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• pp.463-472
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• 2022

Reinforced concrete (RC) beam column joints (BCJ) have mostly exhibited poor seismic performance during several past earthquakes, typically due to the poor-quality concrete or lack of reinforcement detailing typical of pre-code design practice. The present study is motivated towards numerical simulation and seismic fragility assessment of one such RC-BCJ. The BCJ is loaded to failure and strengthened using Ultra High Performance-Hybrid Fiber Reinforced Concrete (UHP-HFRC) jacketing. The strengthening is performed for four different BCJ specimens, each representing an intermediate damage state before collapse. viz., slight, moderate, severe, and collapse. From the numerical simulation of all the BCJ specimens, an attempt is made to correlate different modelling and design parameters of the BC joint with respect to the damage states. In addition, seismic fragility analysis of the original as well as the retrofitted damaged BCJ specimens show the relative enhancement achieved in each case.

• Journal of the Earthquake Engineering Society of Korea
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• v.19 no.6
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• pp.283-292
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• 2015

In the moment frame subjected to earthquake loads, beam-column joint is structurally important for ductile behavior of a system. ACI Committee 352 proposed guidelines for designing beam-column joint details. The guidelines, however, need to be updated because of the lack of data regarding several factors that may improve the performance of joints. The purpose of this study is to investigate the seismic performance of reinforced concrete exterior joints with high-strength materials and unbonded tendons. Three specimens with different joint shear demand-to-strength ratios were constructed and tested, where headed bars were used to anchor the beam bars into the joint. All specimens showed satisfactory seismic behavior including moment strength of 1.3 times the nominal moment, ductile performance (ductility factor = at least 2.4), and sufficiently large dissipated energy.

• Earthquakes and Structures
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• v.12 no.2
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• pp.237-250
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• 2017

There has been increasing attention in many countries on seismic retrofit of old fashioned RC structures in recent years. In such buildings, the joints lack transverse reinforcement and suffer inadequate seismic dimensional requirements and the reinforcement is plain bar. The behavior of the joints is governed by sliding of steel bars and diagonal shear failure is less influential. Different methods to retrofit beam-column joints have been proposed in the literature such as wrapping the joint by FRP sheets, enlargement of the beam-column joint, and strengthening the joint by steel sheets. In this study, an enlargement technique that uses external prestressed cross ties with steel angles is examined. The technique has already been used for substructures reinforced by deformed bars and has advantages such as efficient enhancement of seismic capacity and lack of damage to the joint. Three reference specimens and two retrofitted units are tested under increasing lateral cyclic load in combination with two levels of axial load. The reference specimens showed relatively low shear strength of 0.150${\surd}$($f_c$) and 0.30${\surd}$($f_c$) for the exterior and interior joints, respectively. In addition, relatively brittle behavior was observed and large deformations extended into the panel zone of the joints. The retrofit method has increased ductility ratio of the interior beam-column joints by 63%, and energy dissipation capacity by 77%, relative to the control specimen; For external joints, these values were 11%, and 94%. The retrofit method has successfully relocated the plastic joints far from the column face. The retrofit method has improved shear strength of the joints by less than 10%.

• Earthquakes and Structures
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• v.3 no.1
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• pp.37-57
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• 2012

The behavior of beam-column joints in moment resisting frame structures is susceptible to damage caused by seismic effects due to poor performance of the joints. A good number of researches were carried out to understand the complex mechanism of RC joints considered in current seismic design codes. The traditional construction detailing of transverse reinforcement has resulted in serious joint failures during earthquakes. This paper introduces a new design philosophy involving the use of additional diagonal bars within the joint particularly suitable for low to medium seismic effects in earthquake zones. In this study, ten full-scale interior beam-column specimens were constructed with various additional reinforcement details and configurations. The results of the experiment showed that adding additional bars is a promising approach in reinforced concrete structures where earthquakes are eminent. In terms of overall cracking observation during the test, the specimens with additional bars (diagonal and straight) compared with the ones without them showed fewer cracks in the column. Furthermore, concrete confinement is certainly an important design measure as recommended by most international codes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.6
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• pp.201-211
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• 2011

Many reinforced concrete structures have been constructed at the offshore in Korea and those are exposed in environments for long period. Due to that, the reinforcement of the structure faces possibility of corrosion by the salt damage. Such corrosions are effects on the bond performance between concrete and reinforcing bar as well as the performance of the structure. In this study, the performance of RC structure has been investigated when the reinforcing bars are totally bonded and unbonded in the structure. Through the experimental tests and finite element analyses of beam-column joint with bond and unbonded reinforcing bar, the energy dissipation capacity, strength, and crack distribution are compared and discussed.

• Structural Engineering and Mechanics
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• v.23 no.2
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• pp.129-145
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• 2006

This paper provides an insight into the response of non-seismic reinforced concrete (RC) building frames to excitations of different frequencies through experimental investigation. The results of cyclic loading tests of six full-scale RC beam-column sub-assemblies are presented. The tested specimens did not have any transverse reinforcement inside the joint core, and they were subjected to quasi-static and dynamic loading with frequencies as high as 20 Hz. Some important differences between the cyclic responses of non-seismic and ductile RC frames are highlighted. The effect of excitation frequency on the behavior of non-seismic joints is also discussed. In the quasi-static tests, shear deformation of the joint panel accounted for more than 50% of the applied story drift. The test results also showed that higher-frequency excitations are less detrimental than quasi-static cyclic loads, and non-seismic frames can withstand a higher load and a larger deformation when they are applied faster.

• Journal of the Earthquake Engineering Society of Korea
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• v.17 no.3
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• pp.97-105
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• 2013

In this paper, the a static experiment of on two reinforced concrete (RC) frame sub-assemblages was conducted to evaluate the seismic behaviors of existing RC frames that were not designed to support a seismic load. The specimens were a one span and actual-sized. One of them had two columns with the same stiffness, but the other had two columns with different stiffness values. As Regarding the test results, lots of many cracks occurred on the surfaces of the columns and beam-column joints for the two specimens, but the cover concrete splitting hardly occurred was minimal until the test ends. In the case of the specimen with the same stiffness offor the two columns, the flexural collapse of the left-side column occurred. However, in the case of the specimen with different stiffness values for of the two columns, the beam-column joint finally collapsed, even though the shear strength of the joint was designed to be strong enough to support the lateral collapse load. The nonlinear Nonlinear static analysis of the two specimens was also conducted using the uniaxial spring model, and the analytical results successfully simulated the nonlinear behaviour of the specimens in accordance with the test results.