• Steel and Composite Structures
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• v.13 no.4
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• pp.309-325
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• 2012

The risk of progressive collapse in steel framed buildings under fire conditions is gradually rising due to the increasing use of combustible materials. The fire resistance of such steel framed buildings is evaluated by fire tests. Recently, the application of performance based fire engineering makes it easier to evaluate the fire resistance owing to various engineering techniques and fire science. The fire resistance of steel structural members can be evaluated by the comparison of the limiting temperatures and maximum temperatures of structural steel members. The limiting temperature is derived at the moment that the failure of structural member results from the rise in temperature and the maximum temperature is calculated by using a heat transfer analysis. To obtain the limiting temperatures for structural steel of grades SS400 and SM490 in Korea, tensile strength tests of coupons at high temperature were conducted. The limiting temperatures obtained by the tensile coupon tests were compared with the limiting temperatures reported in the literature and the results of column fire tests under four types of loading with different load ratios. Simple limiting temperature formulas for SS400 and SM490 steel based on the fire tests of the tensile coupons are proposed. The limiting temperature predictions using the proposed formulas were proven to be conservative in comparison with those obtained from H-section and hollow section column fire tests.

• Computers and Concrete
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• v.3 no.6
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• pp.389-400
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• 2006

This paper presents the investigations towards developing a better understanding on the contribution of steel fibers on the tensile strength of high-performance fiber reinforced concrete (HPFRC). An extensive experimentation was carried out with w/cm ratios ranging from 0.25 to 0.40 and fiber content ranging from zero to 1.5 percent with an aspect ratio of 80. For 32 concrete mixes, flexural and splitting tensile strengths were determined at 28 days. The influence of fiber content in terms of fiber reinforcing index on the flexural and splitting tensile strengths of HPFRC is presented. Based on the test results, mathematical models were developed using statistical methods to predict 28-day flexural and splitting tensile strengths of HPFRC for a wide range of w/cm ratios. The expressions, being developed with strength ratios and not with absolute values of strengths and are applicable to wide range of w/cm ratio and different sizes/shapes of specimens. Relationship between flexural and splitting tensile strengths has been developed using regression analysis and absolute variation of strength values obtained was within 3.85 percent. To examine the validity of the proposed model, the experimental results of previous researchers were compared with the values predicted by the model.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.223-234
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• 2016

In this study, direct tension test for hybrid steel fiber reinforced ultra-high performance concrete (UHPC) containing two different steel fibers with a length of 16 and 19 mm was performed to investigate the fracture behavior of UHPC. Test results showed that crack strength and tensile strength, and fracture energy increased with increasing the fiber volume ratio. Based on the test results, the peak cohesive stress at the crack tip, tensile strength, and fracture energy depending on the fiber volume ratio were proposed. The proposed tensile strength of UHPC was suggested as a function of the fiber volume ratio and compressive strength. The peak cohesive stress at the crack tip and fracture energy were also proposed as a function of the tensile strength. The predicted values were relatively agree well with the test results. Thus, the proposed equations is expected to be applicable to UHPC with a compressive strength of 140~170 MPa and a fiber volume ratio of less than 2%.

• Journal of Korean Society of Steel Construction
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• v.14 no.1
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• pp.121-130
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• 2002

This paper presents the tensile behavior of a Concrete-Filled Square Steel Tubular (CFT) column to H-beam welded connections. These connections were externally reinforced with T-shaped stiffeners at the junction of CFT column and beam. The tensile loading tests of eighteen tee-joint connections and finite element analysis using ANSYS were carried out. The main parameters of tests are as follows: 1) the thickness of Square Steel Tubular Column : 6 mm, 9 mm, 2) the strength ratios of tensile strength of horizontal stiffeners to tensile strength of beam flange : 70 %, 100 %, 150 %, 3) the strength ratios of shear strength of vertical stiffeners to tensile strength of beam flange : 80 %, 115 %, 160 %. The results of the tests demonstrate that overall behavior and failure modes of all the specimens are governed mainly by the horizontal stiffeners rather than the vertical stiffeners, and the vertical stiffener played only a role in transferring load introduced from beam to column.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.234-238
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• 2006

In this research, an analysis of damaged instance and forming fault for disc part in automotive steel wheel was performed. Rolled steel material, which had been used in the manufacturing of the damaged disc part, was prepared for tensile test, quantitative analysis of chemical component and acquirement of scanning electron microscope images. Although the results of mechanical properties and chemical component ratio for the material satisfied the suggested specification, some material inherent problem was found in the scanning electron microscope images. Finally, in an analysis of chemical component for the damaged disc part used in road condition, mismatching of chemical component ratio between the suggested specification and test result was found.

• Computers and Concrete
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• v.25 no.6
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• pp.509-516
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• 2020

Adding fibers improves concrete performance in respect of strength and plasticity. There are numerous fibers for use in concrete that have different mechanical properties, and their combination in concrete changes its behavior. So, to investigate the behavior of the fiber reinforced concrete, an in vitro study was conducted on concrete with different fiber compositions including different ratios of steel, polypropylene and glass fibers with the volume of 1%. Two forms of fibers including single-stranded and aggregated fibers have been used for testing, and the specimens were tested for compressive strength and dividable tensile strength (splitting tensile) to determine the optimal ratio of the composition of fibers in the concrete reinforced by hybrid fibers. The results show that the concrete with a composition of steel fibers has a better performance than other compounds. In addition, by adding glass and propylene fibers to the composition of steel fibers, the strength of the samples is reduced. Also, if using the combination of fibers is required, the use of a combination of glass fibers with steel fibers will provide a better compressive strength and tensile strength than the combination of steel fibers with propylene.

• Steel and Composite Structures
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• v.18 no.5
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• pp.1129-1144
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• 2015

Based on the experiment, this paper focuses on studying flexural behavior of splicing concrete-filled glass fiber reinforced polymer (GFRP) tubular composite members connected with steel bars. The test results indicated the confinement effects of GFRP tubes on the concrete core in compression zone began to produce, when the load reached about $50%P_u$ ($P_u$-ultimate load), but the confinement effects in tensile zone was unobvious. In addition, the failure modes of composite members were influenced by the steel ratio of the joint. For splicing unreinforced composite members, the steel ratio more than 1.96% could satisfy the splicing requirements and the steel ratio 2.94% was ideal comparatively. For splicing reinforced specimen, the bearing capacity of specimen with 3.92% steel ratio was higher 21.4% than specimen with 2.94% steel ratio and the latter was higher 21.2% than the contrast non-splicing specimen, which indicated that the steel ratio more than 2.94% could satisfy the splicing requirements and both splicing ways used in the experiment were feasible. So, the optimal steel ratio 2.94% was suggested economically. The experimental results also indicated that the carrying capacity and ductility of splicing concrete-filled GFRP tubular composite members could be improved by setting internal longitudinal rebars.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2010.05a
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• pp.57-61
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• 2010

In this study, many concrete specimens were tested to investigate the variations of strength characteristics of high-strength concrete due to amount of recycled coarse aggregates, and to investigate the effect of steel-fiber reinforcement on concrete using recycled coarse aggregates. Test results showed that all of the variations of compressive, tensile and flexural strength appeared in linear reduction according to icrease the amount of recycled coarse aggregates, and steel-fiber reinforcement of 0.75% volumn of concrete recovered completely spliting tensile strength and flexual strength and recovered greatly compressive strength of concrete using recycled coarse aggregates of 100% displacement. And test results showed that the shear strength falled rapidly at 30% of replacement ratio so far as 34% of strength reduction ratio, but after that it falled a little within 3% up to the replacement ratio 100%, and steel-fiber reinforcement of 0.75% of concrete volumn recovered completely the deteriorated shear strength, moreover improved the shear strength above 50% rather than that of concrete using natural coarse aggregates.

• Journal of the Korean institute of surface engineering
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• v.37 no.6
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• pp.350-359
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• 2004

Stress corrosion cracking(SCC) characteristics of shot-peened stainless steel containing Ti (0.09 wt%-0.92 wt%) fabricated by the vacuum furnace were investigated using SCC tester and potentiostat. The homogenization and the sensitization treatment were carried out at $1050^{\circ}C$ for 1hr and $650^{\circ}C$ for 5 hr. The samples for SCC were shot-peened using $\Phi$0.6 mm steel ball for 4 min and 10 min. Intergranular and pitting corrosion characteristics were investigated by using EPR and CPPT. SCC test was carried out at the condition of$ 288^{\circ}C$, 90 kgf pressure, water with 8 ppm dissolved oxygen, and $8.3xl0^{-7}$/s strain rate. After the corrosion and see test, the surface of the tested specimen was observed by the optical microscope, TEM and SEM. Specimen with Ti/C ratio of 6.14 showed high tensile strength at the sensitization treatment. The tensile strength decreased with the increase of the Ti/C ratio. Pitting and intergranular corrosion resistance increased with the increase of Ti/C ratio. Stress corrosion cracking strength of shot-peened specimen was higher than that of non shot- peened specimen. Stress corrosion cracking strength decreased with the increase of the Ti/C ratio.

• Structural Engineering and Mechanics
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• v.83 no.5
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• pp.671-680
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• 2022

The shear capacity of beams is an essential parameter in designing beams carrying shear loads. Precise estimation of the ultimate shear capacity typically requires comprehensive calculation methods. For steel fiber reinforced concrete (SFRC) beams, traditional design methods may not accurately predict the interaction between different parameters affecting ultimate shear capacity. In this study, artificial neural network (ANN) modeling was utilized to predict the ultimate shear capacity of SFRC beams using ten input parameters. The results demonstrated that the ANN with 30 neurons had the best performance based on the values of root mean square error (RMSE) and coefficient of determination (R²) compared to other ANN models with different neurons. Analysis of the ANN model has shown that the clear shear span to depth ratio significantly affects the predicted ultimate shear capacity, followed by the reinforcement steel tensile strength and steel fiber tensile strength. Moreover, a Genetic Algorithm (GA) was used to optimize the ANN model's input parameters, resulting in the least cost for the SFRC beams. Results have shown that SFRC beams' cost increased with the clear span to depth ratio. Increasing the clear span to depth ratio has increased the depth, height, steel, and fiber ratio needed to support the SFRC beams against shear failures. This study approach is considered among the earliest in the field of SFRC.