• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.6
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• pp.41-49
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• 2014

In order to investigation splitting bond strength of the deformed longitudinal reinforcing bars in the R C members strengthened laterally with the external steel-band, a total 9 sets of test re-bars with and without active confining force given by the external steel-band are pulled monotonically until failure. Test results indicate that the bond strength becomes higher with the increase in number of steel-band sets and their initial stress magnitude. This is due to the active confining force given by the steel-band, and passive confining forces given by the steel-band and transverse reinforcements, in which the passive confinement effect varies depending on the magnitude of active confining force. An equation to estimate the splitting bond strengths for the R C members strengthened laterally with the external steel-band is developed based on the several experimental results of the present study.

• Computers and Concrete
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• v.7 no.3
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• pp.203-220
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• 2010

In the present study, exterior beam-column sub-assemblage from a regular reinforced concrete (RC) building has been considered. Two different types of beam-column sub-assemblages from existing RC building have been considered, i.e., gravity load designed ('GLD'), and seismically designed but without any ductile detailing ('NonDuctile'). Hence, both the cases represent the under-designed structure at different time frame span before the introduction of ductile detailing. For designing 'NonDuctile' structure, Eurocode and Indian Standard were considered. Non-linear finite element (FE) program has been employed for analysing the sub-assemblages under cyclic loading. FE models were developed using quadratic concrete brick elements with embedded truss elements to represent reinforcements. It has been found that the results obtained from the numerical analysis are well corroborated with that of experimental results. Using the validated numerical models, it was proposed to correlate the energy dissipation from numerical analysis to that from experimental analysis. Numerical models would be helpful in practice to evaluate the seismic performance of the critical sub-assemblages prior to design decisions. Further, using the numerical studies, performance of the sub-assemblages with variation of axial load ratios (ratio is defined by applied axial load divided by axial strength) has been studied since many researchers have brought out inconsistent observations on role of axial load in changing strength and energy dissipation under cyclic load.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.1
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• pp.147-155
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• 1999

The purpose of this study is to investigate the strength and ductility of reinforced concrete columns subject to axial load experimentally for several variables of reinforcements and propose foundational research date for reinforcement design of column. In the test a total of eleven specimens, which are all $20{\times}20{\times}60cm$ in size and differently reinforced with steel plate, has been used. The main variables of reinforcement considered in the test are the width of steel plate, the thickness of steel plate. Based on the test results, the effect of the main variables on the strength and ductility of reinforced concrete column have been scrutinized. The strength of reinforced concrete columns are that C-2 series on strengthed with 2mm thickness steel plate are smaller than C-4 series on strengthed with 4mm steel plate. Thick steel plate of reinforced expected utilizer than the other on strength increase and specimens to be large width steel plate of each system are the utiltzer on strength increase. Ductility of C-0 specimen is 1.60, C-2 series is 2.38, C-4 series 2.63 Compare efficiency of ductility increase with each specimens, in narrow width condition (2cm, 4cm) C-2 series is more efficiency, in wide width condition (8cm, 10cm) C-4 series is more efficiency.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.35-44
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• 2017

In this study, steel fiber-reinforced concrete beams with ordinary steel reinforcements, that are below minimum steel reinforcement amount specified in domestic concrete structure design code, were tested in flexure until failure. Steel reinforcement ratio considered were 44%, 66%, 78% and 100% of the minimum steel reinforcement. Considered steel fiber volume fractions were 0.25%, 0.50%, 0.75% and 1.00%. In results, it is confirmed that steel fibers greatly improve crack performance. Also, the steel fibers contributed to increment in yield load not in ultimate load. But the increment was not greater than the reduction by steel reinforcement reduction. The use of steel fibers in RC beams lightly reinforced below the minimum reinforcement ratio specified design code reduced ductility greatly. Consequently, steel reinforcement ratio in steel fiber-reinforced beams lightly reinforced below the minimum steel reinforcement should be increased in order to enhance proper ductility.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.1
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• pp.95-102
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• 2002

The flexural behavior of the reinforced concrete (RC) structure upgraded by external reinforcements was examined in this study. It is well known that the incorporation of carbon fiber sheet (CFS) with concrete is one of the most effective ways to strengthen the RC structure. Complete bonding is required between CFS and concrete in order to make the RC structure provide its full function until the time the Re structures serve. Many studies have reported that construction deficiencies have caused the debonding of the CFS from concrete before the RC structure with CFS reaches its ultimate capacity. This research took a systematic look at the failure mechanism, macroscopic load-deformation characteristics, the maximum load applied, and maximum bending moment when construction deficiencies exist. The results of the experiment conducted were compared with theoretically derived values. In the future, the results of this investigation will help minimize the factors of construction deficiencies, which may occur when CFS is used to reinforce a RC structure. The experiment was manipulated with steel reinforcement ratio and piles of CFS on a total of 14 beams ($20cm{\times}30cm{\times}240cm$). The results showed that internal moment capacity increased even when construction deficiencies existed. However, RC structures with CFS in the field still contain a considerable level of potential risks.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.1
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• pp.131-139
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• 2012

The lateral reinforcements of concrete such as hoops and spiral bars are known to confine concrete to compensate the strength loss due to fire by reducing explosive spalling and improving the capacity of ductility. In this context, a study was conducted to investigate the residual mechanical properties of confined and unconfined concrete($f_{ck}$=60MPa) after a single thermal cycle at 300, 600, $800^{\circ}C$. The main parameters required to establish the stress-strain relationship are the peak stress, the elastic modulus, and the strain at peak stress. The knowledge of the residual mechanical properties of concrete is necessary whenever the thermally damaged structure is required to bear a significant share of the loads, even after a severe thermal accident. Based on the results obtained in this study, the residual stress of confined concrete under thermal damage is higher according to the level of confinement and the larger strain made it to have better ductility. The decreasing ratio of elastic modulus from the relationship of stress and strain was also smaller than that of unconfined concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.102-109
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• 2010

This paper investigates the bond behavior of reinforced concrete beams having high-strength transverse reinforcement. A total of four reinforced concrete beams were tested in this study to estimate the bond capacity of the proposed U-shape reinforcement. The proposed U-shape reinforcement not only has a simple structure to install, but also can increase the bond capacity of reinforced concrete beams by controling bond cracks. This study follow the test method proposed by Ichinose to obtain the bond stress and the bond slip of the specimens. The main test parameters were the yield strength, ratio, and reinforcing types of transverse reinforcements. It was found that the proposed U-shape reinforcement was able to effectively improve the bond performance of reinforced concrete beams with high-strength transverse reinforcement.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.218-225
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• 2021

The purpose of this study is to present a rational analytical method for predicting the behavioral characteristics from crack occurrence to fracture for a one-way CFRP grid reinforced concrete slab specimen. A total of four specimens were selected by Zhang et al.(2004) as the main experimental variables for CFRP grid amount, material properties and loading method. Analysis was performed through the Nonlinear Finite Element analysis program(RCAHEST), which applied the newly modified constitutive relational equations by the author. The mean and coefficient of variation for maximum moment from the experiment and analysis results was predicted 1.38 and 7 %. The mean and coefficient of variation for displacement corresponding maximum moment from the experiment and analysis results was predicted 1.41and 9.8 %. The prediction results for the behavioral characteristics from crack occurrence to fracture were verified and evaluated. It is judged that additional research is needed to secure various experimental results and to develop a more reliable analytical method.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.4
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• pp.103-112
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• 2019

This study proposes a system to control the bulging phenomenon occurring in the reinforced earth retaining wall and to evaluate the reliability of the system by field experiment. In this study, drainage facilities were not installed in order to induce reinforcement earth retaining wall bulging, and the bulging was induced by rainfall. The induced bulging displacement exceeded the horizontal displacement criterion during the construction of FHWA. The retaining wall block was drilled and grouting was performed by inserting the nail into the drilling hole. The wire mesh is installed on the reinforcing surface and the head of the nail is connected horizontally so that the blocks of the reinforcing earth retaining wall can be supported with each other. In order to protect the reinforcements, the reinforcement surface was closed with shotcrete and a measuring device was installed to detect the progress of the displacement. After the reinforcement, the bulging were not found to progress any more, confirming the reliability of the system.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.197-205
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• 2020

In 2014, The Housing Act amended to allows vertical extension and increases the units of housing (or total floor area) to site. Currently, the feasibility of performing vertical extension is evaluated based on safety diagnosis provisions and manuals with 1st investigation stage on slope, uneven settlement, load-bearing capacity, and durability. However, a need for more reasonable evaluation criteria for the investigation is still required because there had not been any other case study on the diagnosis for the vertical extension, and the engineering basis on evaluation criteria were not suggested. Accordingly, this study is intended to suggest feasible evaluation criteria on the carbonation, chloride ion contents, corrosion of reinforcements, crack and surface deterioration of concrete for durability assessment by codes and standards of domestic and foreign countries. The results of this study are expected to be beneficial for establishing more reasonable durability evaluation criteria, and in turn, more reliable assessment protocol for vertical extension.