• Journal of the Korea Concrete Institute
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• v.20 no.6
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• pp.809-820
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• 2008

A new modified full scale double tee slabs with the length of nib plate - 1,500 mm were suggested, designed, and experimentally evaluated up to the loading of flexural failure. This slabs were composed of the tee section which was same to original PCI double tee and the plate section which was modified in a new shape, and the prestressing force was applied at the bottom of tee section only. This specimens were made from the domestic precast factory. The safety and serviceability of the modified nib plate with the dapped ends were evaluated up to the ultimate flexural strength of tee section. As the experimental loading increased, the flexural crackings developed first in the bottom of the slab and they changed to the increased flexural shear and inclined shear crackings in the nib and dapped portion of the double tees. The suggested modified double tee slabs failed in ductile above the design loading with many evenly distributed flexural crackings. The thickness of nib plate - 250 mm does not show any cracking under the service loading and show several minor flexural cracking up to the ultimate state of tee portion. The proposed specimens were satisfied with the strength and ductility requirements in the design code provisions in the tests. Additional experimental tests are required to reduce the depth and tensile reinforcement of nib plate concrete for the practical use of this system effectively.

• Journal of the Korea Concrete Institute
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• v.25 no.1
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• pp.91-98
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• 2013

The pre-tensioned spun high strength concrete (PHC) pile has poor load carrying capacity in shear and flexure, while showing excellent axial load bearing capacity. The purpose of this study is to evaluate the flexural performance of the concrete-infilled composite PHC (ICP) pile which is the PHC pile reinforced with infilled concrete, transverse and longitudinal reinforcement for the improvement of shear and flexural load carrying capacity. The ICP pile specimen was designed to make allowable axial compression and bending moment higher load bearing capacity than those determined through the investigation of abutment design cases. The allowable axial compression and bending moment of the ICP pile was obtained using the program developed for calculating the axial compression - bending moment interaction. Then, ICP pile specimens were manufactured and flexural tests were performed. From the test results, it was found that the maximum bending moment of the ICP pile was approximately 45% higher than that of the PHC pile and the safety factor of ICP pile design was about 4.5 when the allowable bending moment was determined to be 25% of the flexural strength.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.961-972
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• 2002

Flat plate structures under lateral load are susceptible to the brittle shear failure of plate-column connection. To prevent such brittle failure, strength and ductility of the connection should be ensured. However, according to previous studies, current design methods do not accurately estimate the strength of plate-column connection. In the present study, parametric study using nonlinear finite element analysis was performed for interior connections. Based on the numerical results, a design method for the connection was developed. At the critical sections around the connection coexist flexural moment and shear developed by lateral and gravity loads, and maximum allowable eccentric shear stresses were proposed based on the interactions between the flexural moment and shear, The proposed method can precisely predict the strength of the connection, compared with the current design provisions. The predictability of the proposed method was verified by the comparisons with existing experiments and nonlinear numerical analyses.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.59-67
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• 2014

In tension lap splices of straight deformed bars, KCI Code (KCI2012) and ACI Code (ACI318-11) requires that the lap lengths for class B splice are 1.3 times as development length. KCI2012 contains development length provisions for the use of headed deformed bars in tension and does not allow their tension lap splices. The purpose of this experimental study is to evaluate that KCI2012 equation for the development length, $l_{dt}$, of headed bars can be used to calculate the lap length, $l_s$, of headed deformed bars in grade SD400 and SD500, having specified yield strength of 400 and 500 MPa. Test results showed that specimens with $l_s$ equal to $1.3l_{dt}$ had maximum flexural strengths as 1.16~1.31 times as the nominal flexural strengths, flexural failure mode, and ductility. These observations indicate that $1.3l_{dt}$ is suitable to the tensile lap length of headed deformed bars in grade SD400 and SD500.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.3
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• pp.1-10
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• 2022

For the composite section of corrugated steel sheet and concrete, which is often used in soil structures, a conservative design method based on the ultimate strength state is still applied due to the difficulty of the analysis of compatibility condition. In this study, plastic analysis was performed on the flexural and axial strength of the composite section using two limit state design methods, LRFD and LSD. As a result of the analysis of the experimental results, the LRFD analysis value was interpreted as a conservative results for compressive strength, and it was analyzed that the effect of the concrete compressive strength was greater than the steel ratio of the steel plate. The flexural strength was analyzed to be in good agreement with the experimental results by the LSD analysis. From the parametric analysis on the design variables, the hogging moment, which is affected by the tensile strength of the steel plate, slightly decreased the increasing rate of the strength due to the influence of the bolts connection, but the sagging moment linearly increased according to the increment of steel reinforcement ratio.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.6
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• pp.399-405
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• 2023

This study presents an optimal seismic design method based on genetic algorithms to induce beam-hinge collapse mechanisms in reinforced concrete moment frames. Two objective functions are used. The first minimizes the cost of the structure and the second maximizes the energy dissipation capacity of the structure. Constraints include strength conditions of columns and beams, minimum conditions for column-to-beam flexural strength ratio, and conditions for preventing plastic hinge occurrence of columns. Linear static analysis is performed to evaluate the strength of members, whereas nonlinear static analysis is carried out to evaluate energy dissipation capacity and occurrence of plastic hinges. The proposed method was applied to a four-story example structure, and it was confirmed that solutions for inducing a beam-hinge collapse mechanism are obtained. The value of the column-beam flexural strength ratio of the obtained design was found to be larger than the value suggested by existing seismic codes. A more robust strategy is needed to induce a beam-hinge collapse mode.

• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.171-179
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• 2014

The purpose of this study is to evaluate the structural performance of DH beams. DH beam construction method uses thin steel plates as form-works and structural elements. The prefabricated plates and rebars of DH beams were transported to a construction site and erected for casting concrete at the site. In this study, the contribution of steel plates to the flexural strength was evaluated since the plates were expected to play a role as reinforcements. Five test specimens were made for experimental and analytical studies. They consisted of two DH beams for the positive moment test and two DH beams for the negative moment test and a RC beam for the comparison purpose. Test results on DH beams were compared with design equations and the RC beam test result. It was proven that DH beams demonstrated the good flexural behavior showing sufficient strengths and deformation capacities. Flexural strengths, principal strains of concrete, and rebar stresses were evaluated through nonlinear finite element analyses for two test beams. The analyses also showed that steel plates can contribute to the enhancement of flexural strength of DH beams. Based on experimental and analytical studies, it was concluded that steel plates of DH beams can be used as good flexural reinforcements.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.193-200
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• 2023

This paper investigates the effect of directional alignment of steel fibers using an electromagnetic field on the flexural fracture behavior of steel fiber reinforced concrete. A specially designed and manufactured solenoid, capable of aligning steel fibers in the longitudinal direction of the beam specimen, was employed for this purpose. Beam specimens with a design strength of 30 MPa were produced, and failure tests were conducted on specimens exposed to electromagnetic fields and those without exposure. Experimental variables included the mixing ratio and aspect ratio of steel fibers. The results of the experiments revealed a slight increase in flexural strength and crack mouth opening displacement at the maximum load for specimens exposed to the electromagnetic field. Notably, a significant enhancement in fracture energy was observed.

• Magazine of the Korea Concrete Institute
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• v.10 no.5
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• pp.109-115
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• 1998

철근콘크리트 구조물이 과소설계되어 있거나 과다 하중이 작용하게 되면 그 구조물의 구조성능을 파악하여 보수.보강을 시행하게 된다. 최근에 가장 맣이 사용되는 보수.보강 재료로는 특히 휨내력을 보강하는데 탄소섬유를 들 수 있다. 탄소섬유쉬트는 내열성과 내호염성에 있어서 회재가 발생할 경우 보강재료로서 충분한 성능을 가지고 있다. 그러나 이를 접착시키는데 사용되는 에폭시는 유기계 물질로서 화재시 유독가스가 발생하고 내열성능도 30$0^{\circ}C$정도에도 지탱하기 어려워 화재 발생이 가능한 구조물에 사용하기 어렵다. 이 연구에서는 무기계 폴리머 복합재료로 접착된 탄소섬유를 고온(약 800~100$0^{\circ}C$, 1시간)으로 가열한 후 가열된 섬유판의 인장, 휨 전단내력을 검토하여 내열성능을 파악하고 이 섬유쉬트로 보강한 철근콘크리트 부재의 휨 성능을 실험적으로 규명하여 화재의 위험이 있는 구조물에 구조적인 보강재료로 사용이 가능한가를 검토하였다. 연구 결과, 개발된 무기계 폴리머 복합체는 인장강도, 휨강도 및 접착강도가 유기계 접착제와 유사하게 나타났고 800~100$0^{\circ}C$ 정도로 1시간 가열한 이후에도 상온 시험체 휨내력과 전단내력의 63%, 33% 정도를 유지하여 화재의 위험이 있는 부위에도 사용이 가능한 것으로 판단되었다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.4
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• pp.11-22
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• 2023

In this study, a structural concrete square beam was developed using the centrifugal molding technique. In order to secure the bending stiffness of the cross section, the hollow rate of the cross section was set to 10% or less. Instead of using the current poor mixture of concrete, a special formwork for producing a centrifugal square beam was manufactured, and a concrete mixing ratio with a high slump (150-200) and a design strength of 100 MPa or more was developed and applied. The produced centrifugally formed rectangular beams were subjected to performance tests according to the standard bending and shear test standards for centrifugally formed members. The static load test results for the four specimens exceeded both the nominal bending strength and nominal shear strength, which are design values through structural design, proving the structural reliability of the ultra-high-strength centrifugally formed square beam.