• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1519-1519
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• 2001

The aim of this work was to test the feasibility of NIRS in analysing textural characteristics of “Pasta Filata” cheese during the shelf-life. For this purpose, 128 samples of “Pasta Filata” cheese, subdivided into two sets on the basis of the wax used to avoid mechanical damages (paraffin, biodegradable wax), were analysed by using an InfraAlyzer 500 (Bran+Luebbe). Analyses were performed at room temperature. Samples were cut into small cylinders (D=3.2 cm, height = 1 cm), in agreement with literature information. Data were processed by using Sesame Software (Bran+Luebbe). Samples were analysed, during the shelf-life, at 90 and 120 days. In parallel, textural characteristics were detected carrying out a compression method by using an Universal Testing Machine Instron model 4301 (Instron Corporation, Canton, Massachusetts). As compression probe was used a cylinder (D = 5.8 cm, height = 3.7 cm) and a speed rate of 20mm/min was applied. The load at 20 mm of compression was recorded on sample cylinders of 1.7 cm (D) by 2 cm (height). Qualitative analysis of full spectra showed the possibility to gather samples on the basis of the days of shelf-life. The textural characteristics of cheese during the shelf-life was evaluated by comparing NIRS data with rheological results. The best correlation was obtained applying MLR to the first derivative of normalized absorbance values at seven wavelengths. Load values were plotted against the NIR prediction values based on first derivatives. NIRS proved to be an useful tool in classifying samples on the basis of the shelf-life period as well as in predicting their textural characteristics ($R^2$= 0.916, SEC = 0.192, SEP = 0.248, SEV = 0.345).

• Earthquakes and Structures
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• v.15 no.5
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• pp.499-511
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• 2018

This paper aims to investigate the seismic performance of the prestressed steel strips retrofitted RC beam-column joints. Two series of joint specimens were conducted under compression load and reversed cyclic loading through quasi-static tests. Based on the test results, the seismic behavior of the strengthened joints specimens in terms of the failure modes, hysteresis response, bearing capacity, ductility, stiffness degradation, energy dissipation performance and damage level were focused. Moreover, the effects of the amount of the prestressed steel strips and the axial compression ratio on seismic performance of retrofitted specimens were analyzed. It was shown that the prestressed steel strips retrofitting method could significantly improve the seismic behavior of the RC joint because of the large confinement provided by prestressed steel strips in beam-column joints. The decrease of the spacing and the increase of the layer number of the prestressed steel strips could result in a better seismic performance of the retrofitted joint specimens. Moreover, increasing the axial compression ration could enhance the peak load, stiffness and the energy performance of the joint specimens. Furthermore, by comparison with the specimens reinforced with CFRP sheets, the specimens reinforced with prestressed steel strips was slightly better in seismic performance and cost-saving in material and labor. Therefore, this prestressed steel strips retrofitting method is quite helpful to enhance the seismic behavior of the RC beam-column joints with reducing the cost and engineering time.

• Journal of Korean Society of Steel Construction
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• v.20 no.2
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• pp.279-288
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• 2008

In this study, the slip behavior of high-tension bolted joints subjected to compression force is investigated through 3D finite element analysis and experiments. The relation with sliding load, bolt deformation, and failure load are studied with the metal thickness affecting the bolted joint. The post-sliding behavior considering bolt stiffness is presented and compared with the results by finite element and experiments. The finite element model is constructed by solid elements in ABAQUS, in consideration of all the friction effects between metal plates and bolts. The stress-strain relations in the literature are used, and the sliding displacements and axial stresses around the bolt connection are investigated. The flexural buckling of species happened when the plate thickness is less than the bolt diameter. However, the shear failures of bolt occurred in the opposite case.

• Journal of the Korean Society of Safety
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• v.19 no.3 s.67
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• pp.95-100
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• 2004

H-pile can be more easily driven than pipe pile by pile driver and shows high skin friction and plugging effect. And lately It is well grown that the high strength H-pile has been widely used f3r pile foundations. To compare the skin frictions of H piles under different density soil conditions, this paper presents results of a series of model tests on vertically loaded group piles. Model piles made of steel embedded in weathered granite soil were used in this study. Pile arrangements $(2\times2,\;3\tunes3)$, pile space(2D, 4D, 6D), and soil density$(D_r=40\%,\;80\%)$ were tested. The main results obtained from the model tests can be summarized as follows. The series of tests found that compression load for group piles increases as number of piles increase and piles space ratic decrease to $D_r=40\%$ of soil density. The analysis also found that the theoretical value of skin friction for group piles is greater than practical value as piles space ratio increases to $D_r=40\%$ of soil density. Piles showed the greatest difference of the skin friction in case that the pile space ratio(S/D) is 6. The theoretical value by Meyerhof and DM-7 showed 1.83 times and 1.32 times respectively as great as practical value in case of S/D=6 and $2\times2$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.9
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• pp.2189-2194
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• 2009

The automatic hot gas by-pass technique is applied to control the capacity of refrigeration and air-conditioning system when operating at part load. In the scheme, the hot gas from the compressor is extracted and injected into the outlet of an evaporator through a hot gas by-pass valve. Thus, In this paper, the hot gas by-pass scheme for CO2 is discussed and analyzed on the basis of mass and energy conservation law. A comparative study of the schemes is performed in terms of the coefficiency of performance (COP) and cooling capacity. The operating parameters considered in this study include compressor efficiency, superheating degree, outlet temperature of gas cooler and evaporating temperature in the R744 vapor compression cycle. The main results were summarized as follows : the superheating degree, outlet temperature and evaporating temperature of R744 vapor compression refrigeration system have an effect on the cooling capacity and COP of this system. With a thorough grasp of these effect, it is necessary to design the compression refrigeration cycle using R744.

• Computers and Concrete
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• v.27 no.4
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• pp.355-367
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• 2021

This paper investigates the mechanical response of simply supported one-way reinforced concrete slabs under fire through numerical analysis. The numerical model is constructed using the software ABAQUS, and verified by experimental results. Generally, mechanical response of the slab can be divided into four stages, accompanied with drastic stress redistribution. In the first stage, the bottom of the slab is under tension and the top is under compression. In the second stage, stress at bottom of the slab becomes compression due to thermal expansion, with the tension zone at the mid-span section moving up along the thickness of the slab. In the third stage, compression stress at bottom of the slab starts to decrease with the deflection of the slab increasing significantly. In the fourth stage, the bottom of the slab is under tension again, eventually leading to cracking of the slab. Parametric studies were further performed to investigate the effects of load ratio, thickness of protective layer, width-span ratio and slab thickness on the performance of the slab. Results show that increasing the thickness of the slab or reducing the load ratio can significantly postpone the time that deflection of the slab reaches span/20 under fire. It is also worth noting that slabs with the span ratio of 1:1 reached a deflection of span/20 22 min less than those of 1:3. The thickness of protective layer has little effect on performance of the slab until it reaches a deflection of span/20, but its effect becomes obvious in the late stages of fire.

• Journal of the Korean Society of Safety
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• v.37 no.4
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• pp.36-43
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• 2022

Generally, in construction sites, the pipe support installation workers often use support pins of 9~10 mm which are much smaller than the safety standard sizes for work convenience. Although the safety certification standard thickness of the support pins is 11 mm, and the supervisors are often indifferent to this. Hence, products with far lower performance than the pipe support safety certification value of 40,000 N, which is applied in the supporting post-structural review, are used. Accordingly, this acts as a factor causing collapse accidents in the process of pouring concrete at the construction site. Therefore, this study performed compression experiments on new and reused pipe supports to determine how the thickness of the support pins affects the structural compression performance of the pipe support by considering the thickness of the support pins as a critical variable among various factors affecting the pipe support performance. In the course of the study, the compression test of the pipe support (V2, V4) for the new products showed that only 14 (58.3%) of the total 24 samples satisfied the safety certification standard value of 40,000 N, which indicates that more thorough quality control is required in the manufacturing process. Additionally, comparing the thickness of the support pins and their fracture shape shows that the pipes with support length of 4.0 m or longer are much more affected by the buckling of the entire length than the thickness of the support pins. Of the several factors affecting the performance of reused pipe supports, it was found that, similar to the new products, the use of support pins, with thickness of 12 mm rather than 11 mm, can satisfy the safety certification value more appropriately. Therefore, regardless of the state of usage, it could be concluded that it is necessary to use 12 mm products, whose thickness is larger than that of the safety certification standard value of 11 mm, to improve the performance of the pipe supports.

• Wind and Structures
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• v.37 no.4
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• pp.289-302
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• 2023

Insulating glass units (IGUs) have been widely used in buildings in recent years due to their superior thermal insulation performance. However, because of the panel reciprocating motion and fatigue deterioration of sealants under long-term wind loads, many IGUs have the problem of early failure of watertight properties in real usage. This study aimed to propose a statistical method for wind-induced deflection of IGU panels during the whole life service period, for further precise analysis of the accumulated fatigue damage at the sealed part of the edge bond. By the estimation of the wind occurrence regularity based on wind pressure return period, the events of each wind speed interval during the whole life were obtained for the IGUs at 50m height in Beijing, which are in good agreement with the measured data. Also, the wind-induced deflection analysis method of IGUs based on the formula of airspace coefficient was proposed and verified as an improvement of the original stiffness distribution method with the average relative error compared to the test being about 3% or less. Combining the two methods above, the deformation of the outer and inner panes under wind loads during 30 years was precisely calculated, and the deflection and stress state at selected locations were obtained finally. The results show that the compression displacement at the secondary sealant under the maximum wind pressure is close to 0.3mm (strain 2.5%), and the IGUs are in tens of thousands of times the low amplitude tensile-compression cycle and several times to dozens of times the relatively high amplitude tensile-compression cycle environment. The approach proposed in this paper provides a basis for subsequent studies on the durability of IGUs and the wind-resistant behaviors of curtain wall structures.

• Computers and Concrete
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• v.33 no.3
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• pp.251-264
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• 2024

The present study pertains to the effects of variations in the location and size of drilled web openings on the behavior of fixed-fixed reinforced concrete (RC) beams. For this purpose, a reference bending beam with a transverse opening in each half span was tested to failure. Later, the same beam was modeled and analyzed with the help of finite element software using ABAQUS. Upon achieving close agreement between the experimental and numerical results, the location and size of the web opening were altered to uncover the effects of these factors on the shear strength and load-deflection behavior of RC beams. The experimental failure mode of the tested beam and the numerical results were also verified by theoretical calculations. In numerical analysis, when compared to the reference (D0) specimen, if the distance of the opening center from the support is 0 or h or 2h, reduction in load-bearing capacity of 1.5%-22.8% or 2.0%-11.3% or is 4.1%-40.7%. In other words, both the numerical analyses and theoretical calculations indicated that the beam behavior shifted from shear-controlled to flexure-controlled as the openings approached the supports. Furthermore, the deformation capacities, energy absorption values, and the ductilities of the beams with different opening diameters also increased with the decreasing distance of the opening from supports. Web compression failure was shown to be the predominant mode of failure of beams with large diameters due to the lack of sufficient material in the diagonal compression strut of the beam. The present study indicated that transverse openings with diameters, not exceeding about 1/3 of the entire beam depth, do not cause the premature shear failure of RC beams. Finally, shear damage should be prevented by placing special reinforcements in the areas where such gaps are opened.

• Structural Engineering and Mechanics
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• v.89 no.2
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• pp.181-197
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• 2024

A numerical method is presented in this paper, for buckling analysis of thin arbitrary stiffened composite cylindrical shells under axial compression. The stiffeners can be placed inside and outside of the shell. The shell and stiffeners are operated as discrete elements, and their interactions are taking place through the compatibility conditions along their intersecting lines. The governing equations of motion are obtained based on Koiter's theory and solved by utilizing the principle of the minimum potential energy. Then, the buckling load coefficient and the critical buckling load are computed by solving characteristic equations. In this formulation, the elastic and geometric stiffness matrices of a single curved strip of the shell and stiffeners can be located anywhere within the shell element and in any direction are provided. Moreover, five stiffened composite shell specimens are made and tested under axial compression loading. The reliability of the presented method is validated by comparing its numerical results with those of commercial software, experiments, and other published numerical results. In addition, by using the ANSYS code, a 3-D finite element model that takes the exact geometric arrangement and the properties of the stiffeners and the shell into consideration is built. Finally, the effects of Poisson's ratio, shell length-to-radius ratio, shell thickness, cross-sectional area, angle, eccentricity, torsional stiffness, numbers and geometric configuration of stiffeners on the buckling of stiffened composite shells with various end conditions are computed. The results gained can be used as a meaningful benchmark for researchers to validate their analytical and numerical methods.