• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.11
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• pp.4635-4642
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• 2010

Latex modification of concrete provides the material with higher flexural strength, as well as high bond strength and reduced water permeability. One of the most advantages of the very early-strength latex-modified concrete (VES-LMC) could be the similar contraction and expansion behaviour to normal concrete substrate, which enable to ensure long-term performance. The purpose of this study was to parametric nonlinear flexural nonlinear analysis of RC beam rehabilitated by VES-LMC. The results were as follows; The flexural nonlinear analysis model of RC beam overlaid by VES-LMC in ABAQUS was proposed to predict the load-deflection response, interfacial stress, and ultimate strength. The proposed FE analysis model was verified by comparison of an experimental data and the FE analysis results. The FE analysis results showed that yield point as well as flexural stiffness increased as the depth increased; the stiffness of beam overall increased as the bond stiffness became larger; the bond strength between two different materials is a key factor in composite beam. A parametric study showed that an overlay thickness was a main influencing factor to the behavior of RC beam overlaid by VES-LMC.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.233-240
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• 2013

In this study, experimental research was carried out to evaluate and improve the seismic performance of high strength R/C interior beam-column joints regions using advanced reinforcing detailings and high ductile fiber-reinforced mortar. Five specimens of retrofitted the beam-column joint regions using advanced reinforcing detailings and high ductile fiber-reinforced mortar were constructed and tested for their retrofitring performances. Specimens designed by retrofitting the interior beam-column joint regions (IJIR series) of existing reinforced concrete building showed a stable mode of failure and an increase in load-carrying capacity. Specimens of IJIR series, designed by the retrofitting of advanced reinforcing detailings and high ductile fiber-reinforced mortar in reinforecd beam-column joint regions increased its maximum load carrying capacity by 114.2~123.5% and its energy dissipation capacity by 1.55~1.85 times in comparison with the standard specimen of SIJC with a displacement ductility of 5.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.657-666
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• 2006

The precast concrete beam-column connectors to retrofit an apartment building were investigated experimentally. Five precast concrete beam-column connectors were considered to develop a modified model which was adapted to domestic construction conditions from the DDC(dywidag ductile connection) of Germany. Special H-shape steel hardware was used to decrease the width of column and beams for the construction of external frames in apartments. It was found that the DDC had high joint strength and ductility, however failed in inclined shear crackings in the columns. The modified one showed better behaviors in tests because they did not show critical column crackings at failure. The test result of modified one with grouting was compared to that of the one without grouting within the duct. The one with grouting showed higher strength and ductility in failure than that without grouting.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.443-452
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• 2001

Fatigue behavior of reinforced concrete(RC) and steel fiber reinforced concrete(SFRC) beams has been experimentally investigated. Fatigue behavior influenced by longitudinal reinforcement ratio, volume and type of steel fiber, strength of concrete and load ratio $P_{u}/P_{o}$. It can be observed from experimental results that addition of steel fiber to reinforced concrete beam reduces crack widths and increases stiffness, and thus enhances the behavior in serviceability limit states also for high cyclic fatigue loading.

• Steel and Composite Structures
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• v.39 no.3
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• pp.337-352
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• 2021

The study presented experimental and numerical investigation on the seismic performance of steel reinforced concrete (SRC) L-shaped column- reinforced concrete (RC) beam joints. Various parameters described as steel configuration form, axial compressive ratio, loading angle, and the existence of slab were examined through 4 planar joints and 7 spatial joints. The characteristics of the load-displacement response included the bearing capacity, ductility, story drift ratio, energy-dissipating capacity, and stiffness degradation were analyzed. The results showed that shear failure and flexural failure in the beam tip were observed for planar joints and spatial joint, respectively. And RC joint with slab failed with the plastic hinge in the slab and bottom of the beam. The results indicated that hysteretic curves of spatial joints with solid-web steel were plumper than those with hollow-web specimens. The capacity of planar joints was higher than that of space joints, while the opposite was true for energy-dissipation capacity and ductility. The high compression ratio contributed to the increase in capacity and initial stiffness of the joint. The elastic and elastic-plastic story deformation capacity of L-shaped column frame joints satisfied the code requirement. A design formula of joint shear resistance based on the superposition theory and equilibrium plasticity truss model was proposed for engineering application.

• Steel and Composite Structures
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• v.38 no.4
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• pp.365-380
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• 2021

Although traditional steel-concrete composite beams have excellent structural characteristics, it cannot meet the requirement of quick assembly and repair in the engineering. This paper presents a study on static behavior of bolt connected steel-concrete composite beam without post-cast zone. A three-dimensional finite element model was developed with its accuracy and reliability validated by available experimental results. The analysis results show that in the normal service stage, the bolt is basically in the state of unidirectional stress with the loss of pretightening can be ignored. Parametric studies are presented to quantify the effects of the post-cast zone, size and position of splicing gap on the behavior of the beam. Based on the studies, suggested size of gap and installation order were proposed. It is also confirmed that optimized concrete slab in mid-span can reduce the requirement of construction accuracy.

• Journal of the Korea Concrete Institute
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• v.27 no.6
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• pp.677-685
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• 2015

In a will to subdue the brittleness as well as the low tensile and flexural strengths of ordinary concrete, researches are being actively watched worldwide on steel fiber-reinforced Ultra High Performance Concrete (UHPC) obtained by admixing steel fibers in ultra high strength concrete. For the purpose of maximizing advantage of UHPC, this study removes the upper flange of the steel girder to apply an inverted T-shape girder for the formation of the composite beam. This paper intends to evaluate the behavior of the shear connectors and the flexural characteristics of the composite beam made of the inverted T-shape girder and UHPC slab using 16 specimens considering the compressive strength of concrete, the mixing ratio of steel fiber, the spacing of shear connectors and the thickness of the slab as variables. In view of the test results, it seemed that the appropriate stud spacing should range between 100 mm and 2 or 4 times the thickness of the slab. Moreover, the relative displacement observed in the specimens showed that ductile behavior was secured to a certain extent with reference to the criteria for ductile behavior suggested in Eurocode-4. The specimens with large stud spacing exhibited larger values than given by the design formula and revealed that the shear connectors developed larger ultimate strength than predicted owing to the action of UHPC and steel after non-composite behavior. Besides, the specimens with narrow stud spacing failed suddenly through compression at the upper chord of UHPC before reaching the full capacity of the shear connectors.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.2
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• pp.181-190
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• 2005

The objective of this work is to study the flexural strengthening effectiveness of Carbon Fiber Mesh (CFM) in reinforced concrete beams. Flexural strengthening for a simply supported reinforced concrete (RC) beam using CFM is developed by bonding CFM to the soffit of the beam. In this experimental program, five medium-sized reinforced concrete beams strengthened with CFM are tested in bending to evaluate reinforcing effects of the CFM. The beams are designed to have high shear capacity so that expected dominant failure mode of specimens is bending. The reinforcing effect of CFM is small at crack initiation, but is considerable in flexural rigidity of the beam after crack initiation. In comparing the behaviors of strengthened and virgin beams each other, it is shown that the strength of RC beams can be enhanced by attaching CFM. A fairly good agreement between the measured values and the calculated ones is obtained at both the cracking strength and yield strength of the strengthened beams.

• Journal of the Korea Institute of Building Construction
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• v.10 no.6
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• pp.67-75
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• 2010

In this paper, by using steel fiber, polypropylene fiber and these two hybrid fibers, the fire resistance performance and explosive properties of High Strength Concrete (HSC) with specified compressive strength of 40MPa are discussed. The paper also examines the bending resistance of the beam and the shearing resistance properties of non-reinforced HSC beam. This research helps to clarify the fire resistance of fiber HSC and its anti-explosion methods. The test results show that crack generation, explosion and carbonization can be effectively restrained when HSC is mixed with hybrid fibers under high temperature; furthermore, the maximum internal force and ductility are increased and the initial cracking can be restrained in the mechanical test.

• Steel and Composite Structures
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• v.19 no.3
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• pp.735-757
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• 2015

Composite bonding steel plate (CBSP) is a newly developed type of structure strengthened technique applicable to the existing RC beam. This composite structure is applicable to strengthening the existing beam bearing high load. The strengthened beam consists of two layers of epoxy bonding prestressed steel plates and the RC beam sandwiched in between. The bonding enclosed and prestressed U-shaped steel jackets are applied at the beam sides. This technique is adopted in case of structures with high longitudinal reinforcing bar ratio and impracticable unloading. The prestress can be generated on the strengthening steel plates and jackets by using the CBSP technique before loading. The test results of full-scale CBSP strengthened beams show that the strength and stiffness are enhanced without reduction of their ductility. It is demonstrated that the strain hysteresis effect can be effectively overcome after prestressing on the steel plates by using such technique. The applied plates and jackets can jointly behave together with the existing beam under the action of epoxy bonding and the mechanical anchorage of the steel jackets. The simplified formulas are proposed to calculate the prestress and the ultimate capacities of strengthened beams. The accuracy of formulas was verified with the experimental results.