• Journal of the Korean Geotechnical Society
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• v.24 no.5
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• pp.37-54
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• 2008

The standard construction manual of the SDA (Separated Doughnut Auger) piling method was proposed so that the resisting capacity of the augered piles could work effectively. 438 dynamic pile load tests were performed on 379 test piles, which were installed at 36 sites in Korea by the SDA piling method with application of various water-cement ratio of cement milks. The dynamic pile load test results showed that the bearing capacity of the SDA augered piles depended on the water-cement ratio of cement milks. And couple of the formulas were presented according to water-cement ratio and various grounds to estimate quantitatively both the unit end bearing and the unit frictional capacity of the SDA augered piles. It was also considered that the water-cement ratio of cement milks exerts an influence on the bearing capacity of the SDA augered piles. The presented formulas were compared with the existing formulas, which were presented by several standard design codes to design the augered piles.

• Journal of Fashion Business
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• v.27 no.2
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• pp.39-51
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• 2023

The purpose of this study was to effectively improve the thigh muscles of adult women working from home due to COVID-19. In this study, ten adult women working from home performed 1) an electromyography test, 2) a static balance test on a balance board, and a 3) dynamic balance test by squatting on a Bosu ball four times: before electric muscle stimulation (EMS), after EMS, after high-intensity circuit training (HICT), and after EMS plus HICT. For this test, EMS was attached to a medical knee support to manufacture an EMS knee band that could be easily worn regardless of the location. For the experiment, EMS(electric muscle stimulation) was attached to the medical knee protector to manufacture an EMS knee band that can be easily worn regardless of location, and was measured based on the right foot. The study results confirmed that in all tests (electromyography test, static balance test on the balance board, and dynamic balance test by squatting on a Bosu ball), thigh strength improved in the order of treatment before EMS, after EMS, after HICT, and after EMS plus HICT. The study showed that people working from home or with activity restrictions due to COVID-19 had better exercise effects when wearing the EMS knee band and performing HICT, even in a small space.

• Wind and Structures
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• v.34 no.2
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• pp.231-257
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• 2022

Transmission lines systems are important components of the electrical power infrastructure. However, these systems are vulnerable to damage from high wind events such as hurricanes. This study presents the results from a 1:50 scale aeroelastic model of a multi-span transmission lines system subjected to simulated hurricane winds. The transmission lines system considered in this study consists of three lattice towers, four spans of conductors and two end-frames. The aeroelastic tests were conducted at the NSF NHERI Wall of Wind Experimental Facility (WOW EF) at the Florida International University (FIU). A horizontal distortion scaling technique was used in order to fit the entire model on the WOW turntable. The system was tested at various wind speeds ranging from 35 m/s to 78 m/s (equivalent full-scale speeds) for varying wind directions. A system identification (SID) technique was used to evaluate experimental-based along-wind aerodynamic damping coefficients and compare with their theoretical counterparts. Comparisons were done for two aeroelastic models: (i) a self-supported lattice tower, and (ii) a multi-span transmission lines system. A buffeting analysis was conducted to estimate the response of the conductors and compare it to measured experimental values. The responses of the single lattice tower and the multi-span transmission lines system were compared. The coupling effects seem to drastically change the aerodynamic damping of the system, compared to the single lattice tower case. The estimation of the drag forces on the conductors are in good agreement with their experimental counterparts. The incorporation of the change in turbulence intensity along the height of the towers appears to better estimate the response of the transmission tower, in comparison with previous methods which assumed constant turbulence intensity. Dynamic amplification factors and gust effect factors were computed, and comparisons were made with code specific values. The resonance contribution is shown to reach a maximum of 18% and 30% of the peak response of the stand-alone tower and entire system, respectively.

• Restorative Dentistry and Endodontics
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• v.47 no.1
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• pp.4.1-4.13
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• 2022

Objectives: This study evaluated the effects of different smear layer preparations on the dentin permeability and microtensile bond strength (µTBS) of 2 self-etching adhesives (Clearfil SE Bond [CSE] and Clearfil Tri-S Bond Universal [CTS]) under dynamic pulpal pressure. Materials and Methods: Human third molars were cut into crown segments. The dentin surfaces were prepared using 4 armamentaria: 600-grit SiC paper, coarse diamond burs, superfine diamond burs, and carbide burs. The pulp chamber of each crown segment was connected to a dynamic intra-pulpal pressure simulation apparatus, and the permeability test was done under a pressure of 15 cmH₂O. The relative permeability (%P) was evaluated on the smear layer-covered and bonded dentin surfaces. The teeth were bonded to either of the adhesives under pulpal pressure simulation, and cut into sticks after 24 hours water storage for the µTBS test. The resin-dentin interface and nanoleakage observations were performed using a scanning electron microscope. Statistical comparisons were done using analysis of variance and post hoc tests. Results: Only the method of surface preparation had a significant effect on permeability (p < 0.05). The smear layers created by the carbide and superfine diamond burs yielded the lowest permeability. CSE demonstrated a higher µTBS, with these values in the superfine diamond and carbide bur groups being the highest. Microscopic evaluation of the resin-dentin interface revealed nanoleakage in the coarse diamond bur and SiC paper groups for both adhesives. Conclusions: Superfine diamond and carbide burs can be recommended for dentin preparation with the use of 2-step CSE.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2A
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• pp.149-159
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• 2010

This paper presents an experimental study on the structural behavior of composite CFT truss girder bridge with full depth precast panels. The length of span is 20,000 mm. The CFT truss girder is a tubular truss composed of chord members made of concrete-filled and hollow circular tubes. To determine fundamental structural characteristics such as the strength and deformation properties of composite CFT truss girder bridge, static and dynamic tests were conducted. The natural frequencies calculated by the FEM are in good agreement with experimental results obtained from dynamic test. Bracing have only a small effect on the natural frequencies of composite CFT truss girder bridge as indicated by the FEM results. The yield strength and deformation of the composite CFT truss girder bridges were investigated through a static bending test. Besides, the test results showed that uniform distribution of shear connectors can be applicable in composite CFT truss girder bridges.

• Journal of the Korean Geotechnical Society
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• v.40 no.3
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• pp.19-31
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• 2024

In Korea, driven piles are generally penetrated up to weathered rock or harder strata. Friction piles have been used to some extent in the southwest coastal area with deep soils; however, friction piles are not extensively due to uncertainties about construction quality. The embedded pile construction method is primarily used due to noise and vibration complaints. However, in Southeast Asian countries (e.g., Cambodia, Myanmar, and Vietnam), where soft sediments are deep, the driven pile method is commonly used due to its economic advantages. Construction companies are increasingly entering overseas construction markets, e.g., Southeast Asia; thus, it is necessary to understand the behavior of driven friction piles in the soil and improve on-site engineering management to gain market competitiveness in these countries. In this study, the bearing capacity of friction piles driven into clayey coastal soils in Vietnam with time-dependent characteristics was evaluated based on the dynamic and static pile load tests. Based on the results, a modified Danish formula is proposed for on-site quality management.

• Computers and Concrete
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• v.34 no.1
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• pp.33-48
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• 2024

This paper presents the detailed experimental and analytical investigation on the evolution of static (E_s) and dynamic modulus of elasticity (E_d) of concrete having 0%, 35%, and 50% FA used as partial cement replacement. Destructive and non-destructive tests were conducted on cylindrical specimens to evaluate the compressive strength and MoE of concrete in compression at the age of 28, 56, 90, and 150 days for all mixes. Experimental results show that the concrete having 35% FA achieved compressive strength and MoE similar to plain concrete at the age of 90 days, while 50% FA concrete attained satisfactory compressive strength and MoE at the age of 150 days. The comprehensive statistical analysis has been carried out in two ways on the basis of the experimental results. Firstly, the 28-day crushing strength of plain concrete in compression was used to design the models for the prediction of E_s and E_d of fly ash concrete at any age and percentage replacement of FA. Secondly, using the values of UPV and RHN, models have been developed to predict the age or time-dependent E_s and E_d of fly ash concrete. These models will be helpful in assessing the E_s and E_d of fly ash concrete without knowing the 28-day crushing strength of plain concrete in compression in the laboratory. Hence, the suggested models in the present study will be beneficial in conducting the health assessment of fly ash based concrete structures.

• Computers and Concrete
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• v.34 no.4
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• pp.409-425
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• 2024

This paper utilizes LS-DYNA software to numerically investigate impact response and damage evaluation of fiber-reinforced polymer (FRP) bars-reinforced ultra-high-performance concrete (UHPC) composite beams (FRP-UHPC beams). Three-dimensional finite element (FE) models are established and calibrated by using literature-based static and impact tests, demonstrating high accuracy in simulating FRP-UHPC beams under impact loading. Parametric analyses explore the effects of impact mass, impactor height, FRP bar type and diameter, and clear span length on dynamic response and damage modes. Two failure modes emerge: tensile failure with bottom longitudinal reinforcement fracture and compression failure with local concrete compression near the impact region. Impact mass or height variation under the same impact energy significantly affects the first peak impact force, but minimally influences peak midspan displacement with a difference of no more than 5% and damage patterns. Increasing static flexural load-carrying capacity enhances FRP-UHPC beam impact resistance, reducing displacement deformation by up to 30%. Despite similar static load-carrying capacities, different FRP bars result in varied impact resistance. The paper proposes a damage assessment index based on impact energy, static load-carrying capacity, and clear span length, correlating well with beam end rotation. Their linearly-fitting coefficient was 1.285, 1.512, and 1.709 for the cases with CFRP, GFRP, and BFRP bars, respectively. This index establishes a foundation for an impact-resistant design method, including a simplified formula for peak midspan displacement assessment.

• International Journal of Highway Engineering
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• v.10 no.1
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• pp.87-95
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• 2008

One way to shield an atypical structure to secure the occupant safety of an impact vehicle is to stack energy absorbing material modules around the structure. To be applicable to a cushion module, material must have enough energy absorbing capabilities while satisfying the safety requirements of the vehicle occupant. Static compression test of the potential materials gives a good indication which material is good for a slacking module. This paper presents the mechanical properties that a cushion material must have to satisfy the safety requirements. Static tests are performed for Quard-Guard system module, sand bag, recycled tires, Geo-Container, Geo-Cell and Expanded Polystyren (EPS) Blocks. Static test results are discussed and EPS block of $30kg/m^{3}$ density showed good potential for a cushion module. To check the dynamic effect of EPS block, drop tests have been made up to 35.6km/h impact speed. Drop test results are compared with static test results and no appreciable difference was found. To improve the EPS module property, making holes to the block is suggested and drop test are performed for the modified blocks. From the drop test results, design values are suggested.

• Tunnel and Underground Space
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• v.22 no.2
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• pp.77-85
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• 2012

In a material, micro-cracks can be progressively occurred, propagated and finally lead to failure when it is subjected to cyclic or periodic loading less than its ultimate strength. This phenomenon, fatigue, is usually considered in a metal, alloy and structures under repeated loading conditions. In underground structures, a static creep behavior rather than a dynamic fatigue behavior is mostly considered. However, when compressed air is stored in a rock cavern, an inner pressure is periodically changed due to repeated in- and-out process of compressed air. Therefore mechanical properties of surrounding rock mass and an inner lining system under cyclic loading/unloading conditions should be investigated. In this study, considering an underground lined rock cavern for compressed air energy storage (CAES), the mechanical properties of a lining system, that is, concrete lining and plug under periodic loading/unloading conditions were characterized through cyclic bending tests and shear tests. From these tests, the stability of the plug was evaluated and the S-N line of the concrete lining was obtained.