• Computers and Concrete
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• v.10 no.3
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• pp.241-258
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• 2012

The need for long-span members increases gradually in recent years, which makes issues not only on ultimate strength but also on excessive deflection of horizontal members important. In building structures, the post-tension methods with unbonded tendons are often used for long-span members to solve deflection problems. Previous studies on prestressed flexural members with unbonded tendons, however, were mostly focused on the ultimate strength. For this reason, their approaches are either impossible or very difficult to be implemented for serviceability check such as deflection, tendons stress, etc. Therefore, this study proposed a flexural behavior model for post-tensioned members with unbonded tendons that can predict the initial behavior, before and after cracking, service load behavior and ultimate strength. The applicability and accuracy of the proposed model were also verified by comparing with various types of test results including internally and externally post-tensioned members, a wide range of reinforcement ratios and different loading patterns. The comparison showed that the proposed model very accurately estimated both the flexural behavior and strength for these members. Particularly, the proposed model well reflected the effect of various loading patterns, and also provided good estimation on the flexural behavior of excessively reinforced members that could often occur during reinforcing work.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.475-480
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• 2003

Latex modification of concrete provides the material with higher flexural strength. This increase in flexural strength can attribute to the crack-arresting action of polymer in concrete, and also to the bonding they provide between the matrix and aggregates. This experimental study presents the fracture behavior of 12 flexural reinforced concrete beams repaired or strengthened by latex-modified concrete with the main experimental variables such as overlay thickness, strength thickness, and shear reinforcement. The results are as follow: All beam specimens having shear reinforcement were failed by delamination rupture at concrete interface at about 80% of ultimate loading after flexural cracking. All specimens overlayed and strengthened by latex-modified concrete (LMC) showed higher ultimate flexural strength than OPC control specimen, but lower than LMC control specimen. This increase in flexural strength could attribute to the high bonding they provide between the matrix and aggregates. All specimens except two shear unreinforced showed quite similar and consistent displacement behavior. The effect of overlay and strength thickness on the load-displacement relationship were a small at this study.

• Journal of the Korean Society of Safety
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• v.27 no.5
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• pp.141-147
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• 2012

Recently, the external prestressed concrete structures are increasingly being built. The mechanical behavior of prestressed concrete beams with external tendon is different from that of normal bonded PSC beams in that the increment of tendon stress was derived by whole member behavior. By this reason, the ultimate stress of external tendon is smaller than that of bonded tendon or internal unbonded tendon. The purposes of the present paper are therefore to improve the mechanical behavior of external unbonded tendon by using partially bonded external tendon and to evaluate the flexural behavior of partially bonded external tendon by the flexural member experiment. From the experimental results, before flexural cracking, there was no difference between external unbonded, partially bonded and bonded tendons. However, after cracking, yielding load of reinforcement, ultimate load, and tendon stress were increased in the sequence of external unbonded, partially bonded and bonded tendon members. The equation of ACI-318 and AASHTO 1994 were not matched with test results and had no correlations. So the newly proposed equation will be needed including the consideration of tendon profile, tendon bonded type, and so on. The proposed partially bonded external tendon in this paper will be a effective basis for the evaluation of external tendons in construction and design.

• Steel and Composite Structures
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• v.10 no.5
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• pp.373-383
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• 2010

This paper presents the experimental studies of the flexural behavior of steel-concrete composite beams. Herein, steel-concrete composite beams were constructed with a welded steel I section beam and concrete slab with different material strength. Four simply supported composite beams subjected to two-point concentrated loads were tested and compared to investigate the effect of high strength engineering materials on the overall flexural response, including failure modes, load deflection behavior, strain response and interface slip. The experimental results show that the moment capacity of composite beams has been improved effectively when high-strength steel and concrete are used. Comparisons of the ultimate flexural strength of beams tested are then made with the calculated results according to the methods specified in guideline Eurocode 4. The ultimate flexural strength based on current codes may be slightly unconservative for predicating the moment capacity of composite beams with high-strength steel or concrete.

• KIEAE Journal
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• v.8 no.5
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• pp.61-68
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• 2008

For the recycling of the resources and the preservation of the environment, this study's purpose is to measure flexural behavior of the reinforced concrete beams with the major variables like concrete strength, replacement ratio of the recycled aggregate and the waste foundry sand and the tension reinforcement ratio and to present the data of the recycled aggregate used for the structure design. The experiment on the flexural behavior resulted in the followings. The ultimate strength of recycled R/C beam was manipulated proportionate to the tension reinforcement ratio, however the strength instantly decreased after passing the ultimate load due to the destroyed concrete of the compression side. The deflection at the maximum load varied from the tension reinforcement ratio by 5.5 times. The test specimen with the tension reinforcement ratio less than $0.5{\rho}b$ showed constant curve without change in the load from the yield to the ultimate load in contrast to the distinctive plastic region where the displacement was rising. Although the strain of main tension steel with the reinforcement ratio indicate different, the design of recycled concrete member can be applied for current design code for reinforced concrete structure as the ratio of tension reinforcement district the under the reinforcement ration in a balanced strain condition.

• International Journal of Safety
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• v.11 no.2
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• pp.26-28
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• 2012

In this thesis, fracture tests were carried out in order to investigate the flexural strength behavior of FRC(fiber reinforced concrete) structures. FRC beams were used in the tests, the initial crack load and the ultimate load of the beams were observed under the static loading. According to the results, the ultimate loads increase with the fiber content, and these tendency is clear in the specimens with large fiber aspect ratio. From the results of the regression analysis, practical formulae for predicting the flexural strength of FRC were suggested.

• Journal of the Korean Society for Railway
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• v.7 no.4
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• pp.319-325
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• 2004

In this study, analysis and design programs of bending of RC beams strengthened with fiber sheets are developed by using Visual Basic Language. The program consists two groups, ultimate strength method and nonlinear flexural analysis method. Ultimate strength method regards concrete compressive stress as a rectangular stress block and do not consider tensile stress of concrete and load-deflection curves. On the other hand, nonlinear flexural analysis considers tensile stress of concrete, load-deflection curves, state of stress distribution and failure strain of strengthening material. Also, the analysis method used in this study regards nonlinear flexural stress as compressive stress of concrete. This program can be a good tool for determining the bending strength of strengthened RC beams and estimating the amount of fiber sheets for practical use.

• Steel and Composite Structures
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• v.26 no.2
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• pp.183-196
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• 2018

The traditional prestressed concrete composite box-girders with corrugated steel webs have several drawbacks such as large deflection and potential local buckling. In this study, two methods were investigated to optimize and improve the prestressed concrete composite box-girders with corrugated steel webs. The first method was to replace the concrete bottom slab with a steel plate and the second method was to support the concrete bottom slab on the steel flanges. The behavior of the prestressed concrete composite box-girders with corrugated steel webs with either method was studied by experiments on three specimens. The test results showed that behavior of the optimized and upgraded prestressed concrete composite box-girders with corrugated steel webs, including ultimate bearing capacity, flexural stiffness, and crack resistance, is greatly improved. In addition, the influence of different shear connectors, including perfobond leisten (PBL) and stud shear connectors, on the behavior of prestressed concrete composite box-girders with corrugated steel webs was studied. The results showed that PBL shear connectors can greatly improve the ultimate bearing capacity, flexural stiffness and crack resistance property of the prestressed concrete composite box-girders with corrugated steel webs. However, for the efficiency of prestressing introduced into the girder, the PBL shear connectors do not perform as well as the stud shear connectors.

• Computers and Concrete
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• v.22 no.2
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• pp.209-220
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• 2018

In order to evaluate the effect of hybrid fibers on the flexural performance of tunnel segment at room temperature, twelve reinforced self-consolidating concrete (SCC) symmetric inclination beams containing steel fiber, macro polypropylene fiber, micro polypropylene fiber, and their hybridizations were studied under combined loading of flexure and axial compression. The results indicate that the addition of mono steel fiber and hybrid fibers can enhance the ultimate bearing capacity and cracking behavior of tested beams. These improvements can be further enhanced along with increasing the content of steel fiber and macro PP fiber, but reduced with the increase of the reinforcement ratio of beams. The hybrid effect of steel fiber and macro PP fiber was the most obvious. However, the addition of micro PP fibers led to a degradation to the flexural performance of reinforced beams at room temperature. Meanwhile, the hybrid use of steel fiber and micro polypropylene fiber didn't present an obvious improvement to SCC beams. Compared to micro polypropylene fiber, the macro polypropylene fiber plays a more prominent role on affecting the structural behavior of SCC beams. A calculation method for ultimate bearing capacity of flexural SCC symmetric inclination beams at room temperature by taking appropriate effect of hybrid fibers into consideration was proposed. The prediction results using the proposed model are compared with the experimental data in this study and other literature. The results indicate that the proposed model can estimate the ultimate bearing capacity of SCC symmetric inclination beams containing hybrid fibers subjected to combined action of flexure and axial compression at room temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.751-756
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• 2001

This paper deals with the experimental evaluation of the performance of R.C beams strengthened with aramid, glass and carbon fiber sheets. To evaluate the effects of FRPs on the flexural strengthening of the beams, strengthening ratio is adopted as a main variable. Seven beams were fabricated and strengthened under same tensile strength based on ultimate strength of FRPs and strengthening length. Deflection, flexural stiffness, strain of FRP, ultimate load and failure load are compared to evaluate the effects of FRPs on structural behavior of retrofitted beams. The results shows that little effects of FRPs on behavior of strengthened beams can be estimated and the fail modes are more influenced on structural behavior than that.