• Structural Engineering and Mechanics
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• v.30 no.4
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• pp.403-426
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• 2008

Externally bonding fiber reinforced polymer (FRP) sheets with an epoxy resin is an effective technique for strengthening and repairing reinforced concrete (RC) beams under flexural loads. Their resistance to electro-chemical corrosion, high strength-to-weight ratio, larger creep strain, fatigue resistance, and nonmagnetic and nonmetallic properties make carbon fiber reinforced polymer (CFRP) composites a viable alternative to bonding of steel plates in repair and rehabilitation of RC structures. The objective of this investigation is to study the effectiveness of CFRP sheets on ductility and flexural strength of reinforced high strength concrete (HSC) beams. This objective is achieved by conducting the following tasks: (1) flexural four-point testing of reinforced HSC beams strengthened with different amounts of cross-ply of CFRP sheets with different amount of tensile reinforcement up to failure; (2) calculating the effect of different layouts of CFRP sheets on the flexural strength; (3) Evaluating the failure modes; (4) developing an analytical procedure based on compatibility of deformations and equilibrium of forces to calculate the flexural strength of reinforced HSC beams strengthened with CFRP composites; and (5) comparing the analytical calculations with experimental results.

• Structural Engineering and Mechanics
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• v.41 no.2
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• pp.231-242
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• 2012

This research work aims to develop an optimal design using Finite Element (FE) and Genetic Algorithm (GA) methods to replace the traditional concrete and timber material by a Synthetic Polyurethane fibre glass composite material in railway sleepers. The conventional timber railway sleeper technology is associated with several technical problems related to its durability and ability to resist cutting and abrading action of the bearing plate. The use of pre-stress concrete sleeper in railway industry has many disadvantages related to the concrete material behaviour to resist dynamic stress that may lead to a significant mechanical damage with feasible fissures and cracks. Scientific researchers have recently developed a new composite material such as Glass Fibre Reinforced Polyurethane (GFRP) foam to replace the conventional one. The mechanical properties of these materials are reliable enough to help solving structural problems such as durability, light weight, long life span (50-60 years), less water absorption, provide electric insulation, excellent resistance of fatigue and ability to recycle. This paper suggests appropriate sleeper design to reduce the volume of the material. The design optimization shows that the sleeper length is more sensitive to the loading type than the other parameters.

• Steel and Composite Structures
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• v.20 no.6
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• pp.1193-1203
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• 2016

This paper focuses on the analytical behavior of modular circular concrete-filled tubular (CFT) column with enhanced bracing details. To design a full-scale bridge pier of multiple circular concrete-filled tubes, numerical analysis was used to evaluate structural performance according to load directivity. In previous research (Ma et al. 2012, Shim et al. 2014), low cycle fatigue failure at bracing joints was observed, so enhanced bracing details to prevent premature failure are proposed in this analysis. The main purpose of this research is to investigate seismic performance for the diagonal direction load without premature failure at the joints when the structure reaches the ultimate load. The ABAQUS finite-element software is used to evaluate experimental performance. A quasi-static loading condition on a modular bridge pier is introduced to investigate structural performance. The results obtained from the analysis are evaluated by comparing with load-displacement responses from experiments. The concrete-filled tubes with enhanced bracing details showed higher energy dissipation capacity and proper performance without connection failure for a diagonal load.

• Structural Engineering and Mechanics
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• v.43 no.6
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• pp.823-833
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• 2012

An experimental method was suggested for obtaining fracture toughness ($K_{Ic}$) and the tensile strength (${\sigma}_t$) of chopped strand glass fiber reinforced polymer concretes (PC). Semi-circular bend (SCB) specimens subjected to three-point bending were used for conducting the experiments on the PC material. While the edge cracked SCB specimen could be used to evaluate fracture toughness, the tensile strength was obtained from the un-cracked SCB specimen. The experiments showed the practical applicability of both cracked and un-cracked SCB specimens for using as suitable techniques for measuring $K_{Ic}$ and ${\sigma}_t$ in polymer concretes. In comparison with the conventional rectangular bend beam specimen, the suggested SCB samples need significantly less material due to its smaller size. Furthermore, the average values of ${\sigma}_t$ and $K_{Ic}$ of tested PC were approximately 3.5 to 4.5 times the corresponding values obtained for conventional concrete showing the improved strength properties of PC relative to the conventional concretes.

• Journal of Biosystems Engineering
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• v.33 no.3
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• pp.151-156
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• 2008

This study was conducted to evaluate ride vibrations experienced by tractor operators during plowing, rotovating, and transporting operations in Korea. Field data of ride vibrations were taken at the operator-seat interface from 49 tractors and analyzed on the basis of ISO 2631-1 and EU Directive 2002/44. Of the measured ride vibrations 15.4% in the plowing and 12.5% in farm road transport exceeded the 8-hour fatigue decreased proficiency boundary in the fore and aft directions at frequencies from 1 to 5 Hz. 93.9% exceeded the 8-hour potential health risk of ISO 2631-1. The ride vibrations exceeding the 8-hour exposure limit were 38.5% in plowing, 31.6% in rotovating, 100% in farm road transport and 88.9% in concrete road transport. Although most tractor operators were not exposed to ride vibrations greater than the 8-hour exposure limit value (ELV) of EU Directive 2002/44, 7.7% of the operators in the plowing experienced greater vibrations than the ELV in the fore-aft direction. Farm road transport produced greater vibrations than any other operations. Concrete road transport, plowing and rotovating operations followed next. Limit criteria for ride vibration exposure differ depending upon the guidelines. Exposure limit of the health guidance caution zone of ISO 2631-1 is lowest among its kinds.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.1
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• pp.83-92
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• 1987

Fatigue fracture of reinforced concrete structures are characterized by considerably larger strains and microcracking as compared to fracture of R.C. structures under static loading. The strain of stirrup is increased suddenly by the occuring of inclined crack and the average strain ${\epsilon}_{\omega}$ of all stirrups in a structure at maximum load increase approximately in proportion to log N. The structures critical in longitudinal reinforcement seemed to have an endurance limit of 60~70 percent of static ultimate strengths for 1,000,000 cycles. In this test, the average fatigue strength at 1,000,000 cycles for all structures tested was approximately 65 percent of the static ultimate strength.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3D
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• pp.271-278
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• 2010

Semi rigid pavement is a pavement type using advantages of both flexibility of asphalt pavement and rigidity of concrete pavement by infiltrating cement paste into voids of open graded asphalt mixtures. The semi rigid pavement has better smoothness and smaller driving vibration or noise comparing to the concrete pavement, and has smaller permanent deformation and has temperature falling effect comparing to the asphalt pavement. The temperature falling effect were investigated at a semi rigid overlay pavement test section, and the temperature falling and water retaining effects were verified by measuring the temperature and weight of specimens at a housetop. Horizontal and vertical stresses and strains were compared by structural analysis of the semi rigid pavement and asphalt pavement using the Abaquser o, a commercial 3D finite element analysis program. The results were verified by Bisar 3.0, a multi-layered elastic analysis program. Performance of the semi rigid pavement and asphalt pavement were compared by predicting fatigue cracking based on the structural analysis results.

• International Journal of Highway Engineering
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• v.11 no.2
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• pp.111-120
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• 2009

This paper presents a fundamental findings of the functional and structural performance of the porous asphalt concrete coated with MMA resin. To evaluate the structural performance, cantabro, wheel tracking, moisture sensitivity and indirect tensile fatigue tests are performed. The tests results show that the cantabro loss is reduced three times and fatigue resistance is significantly increased after the specimens are coated with MMA resin. However there are little changes in the rutting and moisture damage resistances before and after the coating. Air voids, permeability and BPT(British Pendulum Test) tests are conducted to study the functional performance. It is observed form the tests that the air voids and permeability are slightly decreased after the coating. However, the changes in the air voids and permeability are negligible. The skid resistance of the coated specimens is lower than reference specimens. However, the skid resistance is maintained beyond the level of the reference specimens when silica sands are chipped on top of the coated surface.

• International Journal of Highway Engineering
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• v.1 no.2
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• pp.155-168
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• 1999

Asphalt pavement tends to rut in high temperature and to crack in cold temperature. The performance of asphalt pavement can be deteriorated by korean weather condition which has the four distinct seasons. In this study, the typical sections that may minimize rutting and fatigue were analyzed through the numerical model tests. The layered elastic theory , finite element method and visco elastic theory were utilized for these numerical model tests. From the various numerical model tests, it is found that an optimum design procedure was recommended. It was increasing the thickness of asphalt stabilized base with fixing the wearing course as 5cm the minimum specified thickness. The section was most beneficial in resting rutting and fatigue. From the analysis of the relative index on tensile strain and cost analysis, it was recommended that the thickness ratio of subbase and asphalt concrete is 1.0$\sim$2.5.

• The Journal of the Convergence on Culture Technology
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• v.9 no.6
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• pp.1057-1063
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• 2023

The urban railway sleeper floating track, the subject of this study, is an anti-vibration track to reduce vibration transmitted to the structure. currently, the replacement cycle of resilience pad for sleeper floating tracks is set and operated based on load. however, most previous studies were conducted on load-based structural safety aspects, such as fatigue life evaluation of sleeper anti-vibration pads and increase in track impact coefficient and track support stiffness due to increase in spring stiffness. therefore, in this study, we measure the vibration acceleration of the ballast for each analysis section and use the results of 7 million fatigue tests to calculate the spring stiffness of the resilience pad for each section. the spring stiffness of the resilience pad calculated for each section was set as the analysis data and the concrete vibration acceleration was derived analytically. the adequacy of analysis modeling was verified as the analyzed concrete bed vibration acceleration for each section was within the field-measured concrete bed vibration acceleration range. using the vibration acceleration curve according to the derived spring stiffness change, the spring stiffness of the resilience pad is estimated from the measured vibration acceleration. therefore, we would like to present a technique that can estimate the spring stiffness of resilience pad of a running track using the vibration acceleration of the measured concrete bed.