• Nuclear Engineering and Technology
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• v.45 no.3
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• pp.393-400
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• 2013

Concrete undergoing early frost damage in cold weather will experience significant loss of not only strength, but also of permeability and durability. Accordingly, concrete codes like ACI-306R prescribe a minimum compressive strength and duration of curing to prevent frost damage at an early age and secure the quality of concrete. Such minimum compressive strength and duration of curing are mostly defined based on the strength development of concrete. However, concrete subjected to frost damage at early age may not show a consistent relationship between its strength and durability. Especially, since durability of concrete is of utmost importance in nuclear power plant structures, this relationship should be imperatively clarified. Therefore, this study verifies the feasibility of the minimum compressive strength specified in the codes like ACI-306R by evaluating the strength development and the durability preventing the frost damage of early age concrete for nuclear power plant. The results indicate that the value of 5 MPa specified by the concrete standards like ACI-306R as the minimum compressive strength to prevent the early frost damage is reasonable in terms of the strength development, but seems to be inappropriate in the viewpoint of the resistance to chloride ion penetration and freeze-thaw. Consequently, it is recommended to propose a minimum compressive strength preventing early frost damage in terms of not only the strength development, but also in terms of the durability to secure the quality of concrete for nuclear power plants in cold climates.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.1
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• pp.211-220
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• 2004

This paper presents the evaluation of pullout strengths of expansion anchors and wedge anchors that can cause a failure of the concrete on the basis of the design for anchorage. Tests are conducted for heavy-duty anchors and wedge anchors domestically manufactured and to be installed in plain concrete member. The mainly testing parameters reflected the effects of edge distance. Design of post-installed steel anchors is presented by the Concrete Capacity Design(CCD) in European Organization for Technical Approval. This approach is compared to the well-known provisions, ACI 349-90 specification. The use of both methods to predict the concrete failure load of expansion anchor in uncracked concrete under monotonic loading for important applications is compared. In this study, the concrete tension capacity of fastenings with Heavy-duty Anchors and Wedge Anchors in plain concrete predicted by ACI 349-90 and the Concrete Capacity Design method has been compared with the results of tests.

• Clinics in Shoulder and Elbow
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• v.22 no.2
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• pp.93-99
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• 2019

Background: Modified Phemister operation has been widely used for the treatment of acute acromioclavicular (AC) joint dislocation. Additionally, the use of suture anchor for coracoclavicular (CC) fixation has been reported to provide CC stability. This study was conducted to evaluate the clinical and radiological results of a modified Phemister operation with CC ligament augmentation using suture anchor for acute AC joint dislocation. Methods: Seventy-four patients underwent the modified Phemister operation with CC ligament augmentation using suture anchor for acute AC joint dislocation and were followed-up for an average of 12.3 months. The visual analogue scale (VAS), range of motion, Constant score, and Korean shoulder scoring system (KSS) were used for clinical assessment. Acromioclavicular interval (ACI), coracoclavicular distance (CCD), and acromioclavicular distance (ACD) were obtained to evaluate the radiological assessments. Results: At the last follow-up, the mean VAS Score was 1.7 points, the mean joint range of the forward flexion was $164.6^{\circ}$, external rotation at the side was $61.2^{\circ}$ and internal rotation to the posterior was a level of T12. The mean Constant score and the mean KSS was 82.7 points and 84.2 points, respectively. At the mean ACI, CCD, and ACD, significant differences were found preoperatively and at the last follow-up. When the ACI, CCD, and ACD were compared with the contralateral unaffected shoulder at the last follow-up, the affected shoulders had significantly higher values. Conclusions: The modified Phemister operation with CC ligament augmentation using suture anchor is clinically and radiologically effective at acute AC joint dislocation.

• Earthquakes and Structures
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• v.23 no.5
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• pp.403-417
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• 2022

Reinforced concrete (RC) structures with low-strength RC columns are rampant in several countries, especially those constructed during the early 1960s and 1970s. The weakness of these structures due to overloading or some natural disasters such as earthquakes and building age effects are some of the main reasons to collapse, particularly with the scarcity of data on the impact of aspect ratio and corner radius on the confinement effectiveness. Hence, it is crucial to investigate if these columns (with different aspect ratios) can be made safe by strengthening them with carbon fiber-reinforced polymers (CFRP) sheets. Therefore, experimental and numerical studies of CFRP-strengthened low-strength reinforced concrete short rectangular, square, and circular columns were studied. In this investigation, a total of 6 columns divided into three sets were evaluated. The first set had two circular cross-sectional columns, the second set had two square cross-section columns, and the third set has two rectangular cross-section columns. Furthermore, FEM validation has been conducted for some of the experimental results obtained from the literature. The experimental results revealed that the confinement equations for RC columns as per both CSA and ACI codes could give incorrect results for low-strength concrete. The control specimen (unstrengthened ones) displayed that both ACI and CSA equations overestimate the ultimate strength of low-strength RC columns by order of extent. For strengthened columns with CFRP, the code equations of CSA and ACI code overestimate the maximum strength by around 6 to 13% and 23 to 29%, respectively, depending on the cross-section of the column (i.e., square, rectangular, or circular). Results of finite element models (FEMs) showed that increasing the layer number of new commonly CFRP type (B) from one to 3 for circular columns can increase the column's ultimate loads by around eight times compared to unjacketed columns. However, in the case of strengthened square and rectangular columns with CFRP, the increase of the ultimate loads of columns can reach up to six times and two times, respectively.

• Structural Engineering and Mechanics
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• v.86 no.3
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• pp.337-348
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• 2023

The optimization of reinforced concrete (RC) cantilever retaining walls is a complex problem and requires the use of advanced techniques like metaheuristic algorithms. For this purpose, an optimization model must first be developed, which involves mathematical complications, multidisciplinary knowledge, and programming skills. This task has proven to be too arduous and has halted the mainstream acceptance of optimization. Therefore, it is necessary to unravel the complications of optimization into an easily applicable form. Currently, the most commonly used method for designing retaining walls is by following the proportioning limits provided by the ACI handbook. However, these limits, derived manually, are not verified by any optimization technique. There is a need to validate or modify these limits, using optimization algorithms to consider them as optimal limits. Therefore, this study aims to propose updated proportioning limits for the economical design of a RC cantilever retaining wall through a comprehensive parametric investigation using the genetic algorithm (GA). Multiple simulations are run to examine various design parameters, and trends are drawn to determine effective ranges. The optimal limits are derived for 5 geometric and 3 reinforcement variables and validated by comparison with their predecessor, ACI's preliminary proportioning limits. The results indicate close proximity between the optimized and code-provided ranges; however, the use of optimal limits can lead to additional cost optimization. Modifications to achieve further optimization are also discussed. Besides the geometric variables, other design parameters not covered by the ACI building code, like reinforcement ratios, bar diameters, and material strengths, and their effects on cost optimization, are also discussed. The findings of this investigation can be used by experienced engineers to refine their designs, without delving into the complexities of optimization.

• Structural Engineering and Mechanics
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• v.88 no.2
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• pp.169-178
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• 2023

Lightweight aggregate concrete (LWAC) has various advantages, but it has limitations in ensuring sufficient ductility as structural members such as reinforced concrete (RC) columns due to its low confinement effect of core concrete. In particular, the confinement effect significantly decreases as the axial load increases, but studies on evaluating the ductility of RC columns at high axial loads are very limited. Therefore, this study examined the effects of concrete unit weight on the seismic performance of RC columns subjected to constant axial loads applied with different values for each specimen. The column specimens were classified into all-lightweight aggregate concrete (ALWAC), sand-lightweight aggregate concrete (SLWAC), and normal-weight concrete (NWC). The amount of transverse reinforcement was specified for all the columns to satisfy twice the minimum amount specified in the ACI 318-19 provision. Test results showed that the normalized moment capacity of the columns decreased slightly with the concrete unit weight, whereas the moment capacity of LWAC columns could be conservatively estimated based on the procedure stipulated in ACI 318-19 using an equivalent rectangular stress block. Additionally, by applying the section lamina method, the axial load level corresponding to the balanced failure decreased with the concrete unit weight. The ductility of the columns also decreased with the concrete unit weight, indicating a higher level of decline under a higher axial load level. Thus, the LWAC columns required more transverse reinforcement than their counterpart NWC columns to achieve the same ductility level. Ultimately, in order to achieve high ductility in LWAC columns subjected to an axial load of 0.5, it is recommended to design the transverse reinforcement with twice the minimum amount specified in the ACI 318-19 provision.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.3
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• pp.93-100
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• 2008

The use of fiber reinforced polymer (FRP) composites is significantly growing in construction and infrastructure applications where durability under harsh environmental conditions is of great concern. In order to examine the applicability of FRP rebar as a reinforcement in flexural member, flexural tests were conducted. 12 beams with different FRP materials such as CFRP, GFRP and Hybrid FRP and reinforcement ratio were tested and analyzed in terms of failure mode, moment-deflection, flexural capacity, ductility index and sectional strain distribution. The test results were also compared with the theoretical model represented in ACI 440.1R06. Test results indicate that the flexural capacity of the beams reinforced by FRP bars can be accurately predicted using the ultimate design theory. They also show that the current ACI model for computing the deflection overestimates the actual deflection of GFRP series and underestimates the deflection of CFRP series.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.1 no.1
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• pp.33-42
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• 1981

Current standard code for R.C. design consists of two conventional design parts, so called WSD and USD, which are based on ACI 318-63 and 318-71 code provisions. The safety factors of our WSD and USD design criteria which are taken primarily from ACI 318-63 code are considered to be not appropriate compared to out country's design and construction practices. Furthermore, even the ACI safety factors are not determined from probabilistic study but merely from experiences and practices. This study investigates the safety level of R.C. flexural members designed by the current WSD safety provisions based on Second Moment Reliability theory, and proposes a rational but efficient way of determining the nominal safety factors and the associated flexural allowable stresses of steel bars and concretes in order to provide a consistent level of target reliability. Cornell's Mean First-Order Second Moment Method formulae by a log normal transformation of resistance and load output variables are adopted as the reliability analysis method for this study. The compressive allowable stress formulae are derived by a unique approach in which the balanced steel ratios of the resulting design are chosen to be the corresponding under-reinforced sections designed by strength design method with an optimum reinforcing ratio. The target reliability index for the safety provisions are considered to be ${\beta}=4$ that is well suited for our level of construction and design practices. From a series of numerical applications to investigate the safety and reliability of R.C. flexural members designed by current WSD code, it has been found that the design based on WSD provision results in uneconomical design because of unusual and inconsistent reliability. A rational set of reliability based safety factors and allowable stress of steel bars and concrete for flexural members is proposed by providing the appropriate target reliability ${\beta}=4$.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.407-414
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• 2012

The purpose of this study is to experimentally investigate the shear behavior of reinforced concrete beams embedded with GFRP (glass fiber reinforced polymer) plate with openings. In this study, the parameters include the shape of reinforcement, reinforcement area, and thickness and width of reinforcements. The test was performed on 9 specimens with shear spanto-depth ratio of 2.8. When the reinforcement area was varied, the GFRP plate showed 3.6 times greater shear strength than steel stirrup. The test result showed that shear strength increased as reinforcement area increased. Also, when the shape of a parallelogram GFRP plate was used, it showed higher shear strength than that with rectangular shape. Effect of thickness and width of reinforcement showed that shear capacity increased as width increased. For a comparison study, a calculation of the shear strength of reinforced beams with GFRP plate based on the ACI 318M-08 was compared with the test results. The test results were compared with the maximum shear reinforcement areas required by ACI 318M-08, CSA-04, and EC2-02 provision.

• Journal of the Korean Society of Food Science and Nutrition
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• v.46 no.3
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• pp.343-349
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• 2017

The study was conducted to compare quality characteristics and antioxidant activities of aged black chestnut inner shells (ACI) and raw chestnut inner shells (RCI). RCI were aged for 15 days at high humidity and temperature. As storage time progressed, the pH level decreased while acidity increased. The sugar concentration ($^{\circ}Brix$) and reducing sugar concentration (%) increased during storage, whereas L (lightness) decreased. Compared with RCI, L value of ACI was darker than that of RCI after 9 days of storage. In the Hunter color system, L and a (redness) values of ACI were higher than those of RCI, whereas there was no visible difference in degree of aging. Although total phenol contents increased with degree of aging, phenol contents of ACI increased more than those of RCI after 9 days of aging. $IC_{50}$ values for 1,1-diphenyl-2-picrylhydrazyl and hydroxyl radical scavenging activities decreased with degree of aging. Based on these results, it is suggested that aged black chestnut inner shells were appropriate in terms of both physicochemical and antioxidative activities.