• Journal of Korean Society of Steel Construction
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• v.24 no.2
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• pp.137-147
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• 2012

This paper describes an experimental study on the mechanical characteristic and behavior of a structure that has a joint between the reinforced concrete (RC) member and steel plate concrete (SC) member. An out-of-plane flexural test on an L-type test specimen and in-plane shear test on an I-type test specimen were carried out by means of repeated cyclic loading until their failure. Based on the results, the former showed pull-out failure mode of anchored vertical bars while the latter exhibited flexural failure mode of the basement member. These results reveal that the maximum capacity of the specimens is 96% and 82%, respectively, compared with the theoretical value.

• 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.

• Journal of Korean Association for Spatial Structures
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• v.15 no.2
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• pp.69-77
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• 2015

Ultra High Performance Fiber Reinforced Concrete (UHPFRC) has a outstanding tensile hardening behaviour after a crack develops, which gives ductility to structures. Existing shear strength model for fiber reinforced concrete is entirely based on crack opening behavior(mode I) which comes from flexural-shear failure, not considering shear-slip behavior(mode II). To find out the mode I and mode II behavior on a crack in UHPFRC simultaneously, maximum shear strength of cracked UHPFRC is investigated from twenty-four push-off test results. The shear stress on a crack is derived as variable of initial crack width and fiber volume ratio. Test results show that shear slippage is proportional to crack opening, which leads to relationship between shear transfer strength and crack width. Based on the test results a hypothesis is proposed for the physical mechanics of shear transfer in UHPFRC by tensile hardening behavior in stead of aggregate interlocking in reinforced concrete. Shear transfer strength based on tensile hardening behavior in UHPFRC is suggested and this suggestion was verified by comparing direct tensile test results and push-off test results.

• Journal of the Korean Society for Advanced Composite Structures
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• v.4 no.4
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• pp.9-14
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• 2013

In this study, flexural strength properties of SC shear walls were investigated through static pushover test. Failure modes and stiffness characteristics of SC shear walls under lateral loads were inspected by analyzing the experimental results. Main failures of unstiffened SC shear walls were found to be the type of bending shear failure due to the unbonding of the steel plate at the concrete interface. The ductility capacity of SC structures was also confirmed to be improved, which is considered to be a confining effect on steel plates in the longitudinal behavior of SC shear walls.

• Structural Engineering and Mechanics
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• v.86 no.3
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• pp.385-397
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• 2023

This study presents an experiment and analysis to compare the seismic behavior of full-scale reinforced concrete beam-column joint strengthened by prestressed steel strips, externally bonded steel plate, and CFRP sheets. For experimental investigation, five specimens, including one joint without any retrofitting, one joint retrofitted by externally bonded steel plate, one joint retrofitted by CFRP sheets, and two joints retrofitted by prestressed steel strips, were tested under cyclic-reserve loading. The failure mode, strain response, shear deformation, hysteresis behavior, energy dissipation capacity, stiffness degradation and damage indexes of all specimens were analyzed according to experimental study. It was found that prestressed steel strips, steel plate and CFRP sheets improved shear resistance, energy dissipation capacity, stiffness degradation behavior and reduced the shear deformation of the joint core area, as well as changed the failure pattern of the specimen, which led to the failure mode changed from the combination of flexural failure of beams and shear failure of joints core to the flexural failure of beams. In addition, the beam-column joint retrofitted by steel plate exhibited a high bearing capacity, energy consumption capacity and low damage index compared with the joint strengthened by prestressed steel strip, and the prestressed steel strips reinforced joint showed a high strength, energy dissipation capacity and low shear deformation, stirrups strains and damage index compared to the CFRP reinforced joint, which indicated that the frame joints strengthened with steel plate exhibited the most excellent seismic behavior, followed by the prestressed steel strips.

• Structural Engineering and Mechanics
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• v.67 no.1
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• pp.45-52
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• 2018

Several techniques have been developed for shear strengthening of reinforced concrete (RC) members by using fiber reinforced polymer (FRP) composites. However, debonding of FRP retrofits from concrete substrate still deemed as a challenging concern in their application which needs to be scrutinized in details. As a result, this paper reports on the results of an experimental investigation on shear strengthening of RC beams using near surface mounted (NSM) FRP reinforcing bars. The main objective of the experimentation was increasing the efficiency of shear retrofits by precluding/postponing the premature debonding failure. The experimental program was comprised of six shear deficient RC beams. The test parameters include the FRP rebar spacing, inclination angle, and groove shape. Also, an innovative modification was introduced to the conventional NSM technique and its efficiency was evaluated by experimental observation and measurement. The results testified the efficiency of glass FRP (GFRP) rebars in increasing the shear strength of the test specimens retrofitted using conventional NSM technique. However, debonding of FRP bars impeded exploiting all retrofitting advantages and induced a premature shear failure. On the contrary, application of the proposed modified NSM (MNSM) technique was not only capable of preventing the premature debonding of FRP bars, but also could replace the failure mode of specimen from the brittle shear to a ductile flexural failure which is more desirable.

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.667-675
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• 2004

This paper presents the failure mode and strengthening design of reinforced concrete slab strengthened with Carbon Fiber Reinforced Polymer(CFRP) grid. Parameters involved in this experimental study are FRP grid reinforcement quantity, repair mortar thickness, the presence of anchor, and strengthening in compression. In this study, there are different failure types with increasing the CFRP grid strengthening reinforcement. On the low strengthening level, CFRP grid in repair mortar cover ruptures. On the moderate strengthening level, there is a debonding shear failure in the interface of carbon FRP grid because of the excessive shear deformation. On the high strengthening level, diagonal shear failure occurs. With the increasing of FRP grid reinforcement, the strengthening effect increased, but the ductility decreased. By limiting the strengthening level, it can be achieved to prevent shear failure which result in sudden loss in the resisting load capacity. CFRP rupture failure is desirable, because CFRP ruptured concrete slab keeps the same load capacity and ductility haying before strengthening even after failure. Finally, design guideline and procedure are given for strengthening of concrete slab with CFRP grid.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.55-63
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• 2015

Post-installed concrete set anchors are installed after the concrete hardened. These anchors increasing usage in development of construction equipment and flexible construction. The anchor loaded in shearing exhibits various failure modes such as steel failure, concrete failure, concrete pryout, depending on the shear strength of steel, the strength of concrete, edge distance and anchor interval, etc,. In this study, the objective is to investigate the effects of the variations like anchor embedment depth, edge distance and concrete strength on experimental and finite element analysis of shear failure behavior of post-installed concrete set anchor for light load embedded in concrete. The results of embedment depth experiments show that concrete strength has much affection on the shallow embedment depth. Concrete strength has no much affection with anchor interval and edge distance parameter and both experimental results occurred same failure mode. By comparing the experimental results that occurred steel failure mode show that as strong as concrete strength are the displacement results are small.

• Geomechanics and Engineering
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• v.11 no.2
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• pp.253-267
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• 2016

The stability of surrounding rock will be poor when the tunnel is excavated through nearly horizontal stratum. In this paper, the instability mechanism of local nearly horizontal stratum in super-large section and deep buried tunnel is revealed by the analysis of the macro failure and micro fracture. A structural model is proposed to explain the mechanics of surrounding rock collapse under the action of stress redistribution and shed light on the macroscopic analytical approach of the stability of surrounding rock. Then, some highly effective formulas applied in the tunnel engineering are developed according to the theory of mixed-mode micro fracture. And well-documented field case is made to demonstrate the effectiveness and accuracy of the proposed analytical methods of mixed-mode fracture. Meanwhile, in order to make the more accurate judgment about yield failure of rock mass, a series of comprehensive failure criteria are formed. In addition, the relationship between the nonlinear failure criterion and $K_I$ and $K_{II}$ of micro fracture is established to make the surrounding rock failure criterion more comprehensive and accurate. Further, the influence of the parameters related to the tension-shear mixed-mode fracture and compression-shear mixed-mode fracture on the propagation of rock crack is analyzed. Results show that ${\sigma}_3$ changes linearly with the change of ${\sigma}_1$. And the change rate is related to ${\beta}$, angle between the cracks and ${\sigma}_1$. The proposed simple analytical approach is economical and efficient, and suitable for the analysis of local nearly horizontal stratum in super-large section and deep buried tunnel.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.93-96
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• 2005

Since the columns with flexure-shear failure have lower ductility than those with flexural failure, shear capacity curve models shall be applied as well as flexural capacity curve in order to determine ultimate displacement for seismic design or performance evaluation. In this paper, a modified shear capacity curve model is proposed and compared with the other models such as the CALTRANS model, Aschheim et al.'s model, and Priestley et al.'s model. Four shear capacity curve models are applied to the 4 full scale circular bridge column test results and the accuracy of each model is discussed. It may not be fully adequate to drive a final decision from the application to the limited number of test results, however the proposed model provides the better prediction of failure mode and ultimate displacement than the other models for the selected column test results.