• Steel and Composite Structures
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• v.29 no.3
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• pp.405-422
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• 2018

In this research, experimental tensile test and manufacturing of carbon nanotube reinforced composite beam (CNTRC) is presented. Also, bending, buckling, and vibration analysis of CNTRC based on various beam theories such as Euler-Bernoulli, Timoshenko and Reddy beams are considered. At first, the experimental tensile tests are carried out for CNTRC and composite beams in order to obtain mechanical properties and then using Hamilton's principle the governing equations of motion are derived for Euler Bernoulli, Timoshenko and Reddy theories. The results have a good agreement with the obtained results by similar researches and it is shown that adding just two percent of carbon nanotubes increases dimensionless fundamental frequency and critical buckling load as well as decreases transverse deflection of composite beams. Also, the influences of different manufacturing processes such as hand layup and industrial methods using vacuum pump on composite properties are investigated. In these composite beams, glass fibers used in an epoxy matrix and for producing CNTRC, CNTs are applied as reinforcement particles. Applying two percent of CNTs leads to increase the mechanical properties and increases natural frequencies and critical buckling load and decreases deflection. The obtained natural frequencies and critical buckling load by theoretical method are higher than other methods, because there are some inevitable errors in industrial and hand layup method. Also, the minimum deflection occurs for theoretical methods, in bending analysis. In this study, Young's and shear modulli as well as density are obtained by experimental test and have not been used from the results of other researches. Then the theoretical analysis such as bending, buckling and vibration are considered by using the obtained mechanical properties of this research.

• Journal of the Korean GEO-environmental Society
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• v.17 no.11
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• pp.45-53
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• 2016

A precast panel wall system resists against the horizontal earth pressure by increasing the shear strength of ground by reinforcement connected to the panel. The application of precast panel wall system is growing to lately minimize the earth work and environmental damage caused by large cut slope and to use the limited land effectively. The ground adhered panel wall system is the construction method that has the panel engraved with natural rock shape to improve the landscape. This system is developed to complete Top-Down method, and it is possible to have vertical cut, and to adhere to in-situ ground, improve construction ability by minimizing the ground relaxation and exclusion the trench and backfill process. In this study the field tests were performed to verify the construction ability about the vertical cut and complete Top-Down process and the construction behavior of ground adhered panel wall system was analyzed by large scale loading test and measurement results during loading test.

• Journal of the Korean Geotechnical Society
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• v.31 no.2
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• pp.65-73
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• 2015

The bank revetment work which is conducted on the slope of river bank to protect against flowing water as a geotechnical structure has been applied as an average value of critical tractive force based on domestic and international standard design. Currently, an appropriate evaluation is needed for the hydraulic stability and geotechnical behavior analysis of bank revetments because of the effects of climate change and ambiguous design criterion. This study has compared the critical tractive forces of soil improvement material and conventional materials used for the bank revetment work. Through various experiments, the shear strength of mixtures with soil improvement material was investigated by curing time and mixture ratio. It was found that the critical tractive force of the mixture obtained from a scour test is suitable to the reinforcement of the slope of river bank which has problems such as seepage erosion and scour.

• 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.

• Korean Journal of Materials Research
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• v.22 no.9
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• pp.454-458
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• 2012

Various adhesive materials are used in flip chip packaging for electrical interconnection and structural reinforcement. In cases of COF(chip on film) packages, low temperature bonding adhesive is currently needed for the utilization of low thermal resistance substrate films, such as PEN(polyethylene naphthalate) and PET(polyethylene terephthalate). In this study, the effects of anhydride and dihydrazide hardeners on the low-temperature snap cure behavior of epoxy based non-conductive pastes(NCPs) were investigated to reduce flip chip bonding temperature. Dynamic DSC(differential scanning calorimetry) and isothermal DEA(dielectric analysis) results showed that the curing rate of MHHPA(hexahydro-4-methylphthalic anhydride) at $160^{\circ}C$ was faster than that of ADH(adipic dihydrazide) when considering the onset and peak curing temperatures. In a die shear test performed after flip chip bonding, however, ADH-containing formulations indicated faster trends in reaching saturated bond strength values due to the post curing effect. More enhanced HAST(highly accelerated stress test) reliability could be achieved in an assembly having a higher initial bond strength and, thus, MHHPA is considered to be a more effective hardener than ADH for low temperature snap cure NCPs.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.53-67
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• 2001

In this study the pilot test of CGS as injection method by low slump mortar was performed and the results were analyzed in order to find out the application of this method and effect of settlement restraint. The site far pilot test is adjacent to apartments supported by pile foundations. Sand drain method was performed previously as countermeasures against settlement, but settlement occur continuously because this ground is very soft. Site investigations such as SPT, DCPT and vane shear test were performed to determine the characteristics of ground improvement. Field measurements and FDM analysis were performed on purpose to find out the displacement of ground during injection works. From the results of this study, CGS method can be optimized by the control of diagram, space, depth, injection material, and injection pressure. CGS improved soft ground compositely by the bearing effect of CGS columns and reinforcement of adjacent ground. Considering that increase of N value is about 2.1, CGS can be considered as an effective method to increase the bearing capacity as well as to stop the settlement of soft ground. It is also expected to be economic and effective in improvement of ground when it is used in applicable sites.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.4
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• pp.659-665
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• 2016

The limit equilibrium method (LEM) is commonly used for slope design and stability analysis because it is easy to simulate slope and requires short calculating time. However, LEM cannot adequately simulate ploughing failure in a footwall slope with a joint set dipping parallel with slope, e.g. bedding joint set. This study performed parametric study to analyze the influence factors on ploughing failure using UDEC which is a commercial two-dimensional DEM (Distinct Element Method)-based numerical program. The influence of joint structure and properties on stability of a footwall slope against ploughing failure was investigated, and the factor of safety was estimated using the shear strength reduction method. It was found that the stability of footwall slope against ploughing failure strongly relies on dip angle of conjugate joint, and the critical bedding joint spacing and the critical length of slab triggering ploughing failure are also affected by dip angle of conjugate joint. The results obtained from this study can be used for effective slope design and construction including reinforcement.

• Journal of Korean Society of Steel Construction
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• v.16 no.4 s.71
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• pp.493-500
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• 2004

In this study, the effects of ring stiffeners for buckling of cylindrical shells with composite materials were analyzed. The finite element method was used: 3-D beam elements were used for stiffeners and flat shell elements were used for cylindrical shells and were improved by introducing a substitute shear strain. The ring stiffeners were of the transverse rib type. The buckling behaviors of the cylindrical shells were analyzed based on various parameters, such as locations and sizes of stiffeners, diameter/length ratios and boundary conditions of shells, and fiber-reinforced angles. Effective reinforcement was examined by understanding the exact behaviors for buckling. The results of the analysis may serve as references for designs and future investigations.

• Steel and Composite Structures
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• v.9 no.5
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• pp.419-444
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• 2009

Flange and web local buckling in beam plastic hinge regions of steel moment frames can prevent beam-column connections from achieving adequate plastic rotations under earthquake-induced forces. Reducing the flange-web slenderness ratios (FSR/WSR) of beams is the most effective way in mitigating local member buckling as stipulated in the latest seismic design specifications. However, existing steel moment frame buildings with beams that lack the adequate slenderness ratios set forth for new buildings are vulnerable to local member buckling and thereby system-wise instability prior to reaching the required plastic rotation capacities specified for new buildings. This paper presents results from a research study investigating the cyclic behavior of steel I-beams modified by a welded haunch at the bottom flange and reinforced with glass fiber reinforced polymers at the plastic hinge region. Cantilever I-sections with a triangular haunch at the bottom flange and flange slenderness ratios higher then those stipulated in current design specifications were analyzed under reversed cyclic loading. Beam sections with different depth/width and flange/web slenderness ratios (FSR/WSR) were considered. The effect of GFRP thickness, width, and length on stabilizing plastic local buckling was investigated. The FEA results revealed that the contribution of GFRP strips to mitigation of local buckling increases with increasing depth/width ratio and decreasing FSR and WSR. Provided that the interfacial shear strength of the steel/GFRP bond surface is at least 15 MPa, GFRP reinforcement can enable deep beams with FSR of 8-9 and WSR below 55 to maintain plastic rotations in the order of 0.02 radians without experiencing any local buckling.

• Earthquakes and Structures
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• v.11 no.3
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• pp.483-503
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• 2016

This study aims to evaluate seismic performance of existing low and mid-rise reinforced concrete buildings by comparing their displacement capacities and displacement demands under selected ground motions experienced in Turkey as well as demand spectrum provided in 2007 Turkish Earthquake Code for design earthquake with 10% probability of exceedance in 50 years for soil class Z3. It should be noted that typical residential buildings are designed according to demand spectrum of 10% probability of exceedance in 50 years. Three RC building sets as 2-, 4- and 7-story, are selected to represent reference low-and mid-rise buildings located in the high seismicity region of Turkey. The selected buildings are typical beam-column RC frame buildings with no shear walls. The outcomes of detailed field and archive investigation including approximately 500 real residential RC buildings established building models to reflect existing building stock. Total of 72 3-D building models are constructed from the reference buildings to include the effects of some properties such as structural irregularities, concrete strength, seismic codes, structural deficiencies, transverse reinforcement detailing, and number of story on seismic performance of low and mid-rise RC buildings. Capacity curves of building sets are obtained by nonlinear static analyses conducted in two principal directions, resulting in 144 models. The inelastic dynamic characteristics are represented by "equivalent" Single-Degree-of- Freedom (ESDOF) systems using obtained capacity curves of buildings. Nonlinear time history analysis is used to estimate displacement demands of representative building models idealized with (ESDOF) systems subjected to the selected ground motion records from past earthquakes in Turkey. The results show that the significant number of pre-modern code 4- and 7-story buildings exceeds LS performance level while the modern code 4- and 7-story buildings have better performances. The findings obviously indicate the existence of destructive earthquakes especially for 4- and 7-story buildings. Significant improvements in the performance of the buildings per modern code are also obvious in the study. Almost one third of pre-modern code buildings is exceeding LS level during records in the past earthquakes. This observation also supports the building damages experienced in the past earthquake events in Turkey.