• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.24-32
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• 2002

The modified compression field theory is already applied in shear problem at some code(AASHTO-1998) partly. Nominal shear strength of concrete beam is sum of the concrete shcar strength and the steel shear strength in the current design code. But Torsional moment strength of concrete is neglected in the calculation of the nominal torsional moment strength of concrete beam In the current revised code. Tensile stress of concrete strut between cracks is still in effect due to tension stiffening effect. But The tensile stresses of concrete after cracking are neglected in bending and torsion In design. The torsional behavior is similar to the shear behavior in mechanics. Therefore the torsional moment strength of concrete should be concluded in the nominal torsional moment strength of reinforced concrete beam. This paper shows that the torsional moment strength of concrete is caused by the average principal tensile stress of concrete. To verify the validity of the proposed model, the nominal torsional moment strengths according to two ACI codes (89, 99) and proposed model are compared to experimental torsional moment strengths of 55 test specimens found in literature. The nominal torsional moment strengths by the proposed model show the best results.

• Steel and Composite Structures
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• v.27 no.4
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• pp.401-416
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• 2018

Composite beams with web openings are vulnerable to Vierendeel bending failure. The available methods provide quite conservative estimates of Vierendeel bending resistance. An alternative design method to compute the resistance was proposed in this study, based on quadratic nonlinear interactions of normalized shear force, axial force and Vierendeel bending moment. The interactions of the top and bottom Tee section must satisfy mutual conditions to prevent the Vierendeel failure. The normalized shear force and Vierendeel bending moment of the composite part were used instead in the top Tee interaction. The top Tee axial force was computed based on force equilibrium. Based on a rigid-plastic model, the composite resistance is estimated using an effective slab width of the vertical shear resistance. On using the proposed method, nonlinear reductions due to shear loads and axial forces are not required, in contrast to prior methods. The proposed method was validated against experiments from literature. The method limitations and accuracy as well as the Vierendeel behavior were investigated by finite element simulations, with varied composite beam parameters. The proposed design loads are less conservative than earlier estimates and deviate less from the simulations.

• Structural Engineering and Mechanics
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• v.82 no.5
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• pp.595-609
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• 2022

Prestressed composite steel-concrete beams are still a technology restricted to repair sites of large-scale structures and spans. One of the reasons for that is the absence of standard frameworks and publications regarding their design and implementation. In addition, the primary normative codes do not address this subject directly, which might be related to a scarcity of papers indicating methods of design that would align the two technics, composite beams and external prestressing. In this context, this paper proposes methods to analyze the sizing of prestressed composite beams submitted to pre-tension and post-tension with a straight or polynomial layout cable. This inquiry inspected a hundred and twenty models of prestressed composite beams according to its prestressing technology and the eccentricity and value of the prestressing force. The evaluation also included the ratio between span and height of the steel profile, thickness and typology of the concrete slab, and layout of the prestressing cables. As for the results, it was observed that the eccentricity of the prestressing force doesn't significantly influence the bending resistance. In prestressed composite beams subjected to a sagging moment, the ratio L/d can reach 35 and 30 for steel-concrete composite slabs and solid concrete slabs, respectively. Considering the negative bending moment resistance, the value of the L/d ratio must be less than or equal to 25, regardless of the type of slab. When it comes to the value of the prestressing force, a variation greater than 10% causes a 2.6% increase in the positive bending moment resistance and a 4% decrease in the negative bending moment resistance. The pre-tensioned composite beams showed a superior response to flexural-compression and excessive compression limit states than the post-tensioned ones.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.11
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• pp.105-117
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• 1972

This experiment has been made to study the relationship between several characters affecting the field lodging and to establish some useful standards for selection of lodging resistant varieties and to classify the degree of lodging resistance in wheat and barley varieties of different sources. The experiment was carried at the Crop Experiment Station, Suwon in 1968. The results obtained are summarized as followings. a. The lodging index modified with bending moment of culm at breaking seemed to be the most useful character in checking the lodging resistance. Highly significant positive correlation (Barley; r=0.40-0.67, Wheat; r=0.46-0.68) was obtained between the lodging index and actual field lodging. b. Between two essential components expressing bending stiffness of the culm, the bending moment at breaking and secondary moment of inertia, a highly significant positive correlation (Barley; r=0.59, wheat; r=0.46-0.53) was observed. c. The bending stiffness of culm got stronger as the dry weight per unit culm, which express the quantity of accumulated dry matters in culm, increased. The correlation coefficient between those two factors was 0.35 to 0.40 in barley and 0.33 to 0.76 in wheat respectively. d. In both wheat and barley, highly significant negative correlation between lodging index and the other factors such as dry weight per unit culm (Barley; r=-0. 51 to -0.70, Wheat; r=-0.65 to -0.83) and bending moment of culm at breaking (Barley; r=-0.29 to -0.69, Wheat: r=-0.54 to -0.89) were observed. Particulary, weight of culm at breaking, secondary moment of inertia and section modulus showed significant negative correlation with lodging index in wheat. e. Outside diameter of culm expressed more intimate relationship with physical characteristics of culm than inside diameter and also showed highly significant correlation with weight of culm at breaking (Barley; r=0.42-0.56, Wheat; r=0.39-0.44) and with bending moment of culm at breaking (Barley; r=0.40-0.41, Wheat; r=0.38-0.49) and with secondary moment of inertia (Barley; r=0.56-0.57, Wheat; r=0.28-0.98) and with section modulus (Wheat; r=0.22-0.96). Between the thickness of culm and physical characteristics of culm also showed the positive correlation. f. There was positive correlation between the culm length and actual field lodging in several groups of variety among the varieties tested. But the culm length seemed to undesirable as a selection measure for the selection of the lodging resistant variety considering the stiffness of culm. g. In classification of lodging resistance for the varieties tested, many Korean barley varieties expressed excellent lodging resistant than wheat, but most of the wheat and barley varieties from Japan considered quite resistant to lodging. h. In selection of lodging resistant varieties, lodging index lower than 1.67 in barley and 1. 76 in wheat considered highly resistant to actual field lodging.

• Journal of the Korean Wood Science and Technology
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• v.36 no.4
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• pp.58-65
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• 2008

Most connections for the glulam structural members consisted of connector and fastener. The mechanical behaviour of the connection can be occurred by the dowel bearing resistance and wood shear by the fastener. This study aims at the examination of the shear properties for the small specimen with lamination components and for the full-sized pin connection and the moment resisting property for the double shear full-sized pin connection using structural column and beam members. Small specimens including glue line shows greater density and shear strength by the lamination effect than other specimens. It is needed that estimations of double shear property and moment resistance for the pin connections should be adjusted in some degree. For the better and safe estimation of moment resistance strength for the column-beam pin connection, however, the shear strength of small specimens should be deducted by 10%.

• The korean journal of orthodontics
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• v.31 no.1 s.84
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• pp.15-24
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• 2001

In order to achieve a desirable tooth movement, it is of great importance to control the M/F ratio and to know the location of the center of resistance. The purpose of this study was to locate the center of resistance and the axis of rotation, and to estimate the stress distribution in the periodontal ligament with experimental model. After preparing a model of an upper canine with a simulated periodontal ligament and alveolar bone, the force and moment were applied. The tooth movement was traced using measuring device with LVDTs(Linear variable differential transformers) that can measure three dimensional tooth movement in real time. The results were as follows. 1. The location of center of resistance by transverse force was $29\%$ of root length measured from alveolar crest to apex regardless of force magnitude. The position of the center of resistance is more coronal than that of two-dimensional model($42\%$). 2. The center of resistance and the axis of rotation coincide when couple moment was applied. 3. As the magnitude of moment increases, tooth tends to extrude irrespective of the direction of the moment. 4. The relationship between location of force and axis of rotation (a x b = $49.6\;mm^2$) was obtained. A tooth movement can be predicted through this formula. 5. The centers of rotation by transverse force were plotted linearly.

• Steel and Composite Structures
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• v.24 no.3
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• pp.369-382
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• 2017

This study investigates the reliability of the performance levels of moment resisting steel frames subjected to lateral loads such as wind and earthquake. The reliability assessment has been performed with respect to three performance levels: serviceability, damageability, and ultimate limit states. A four-story moment resisting frame is used as a typical example. In the reliability assessment the uncertainties in the loadings and in the capacity of the frame have been considered. The wind and earthquake loads are assumed to have lognormal distribution, and the frame resistance is assumed to have a normal distribution. In order to obtain an appropriate limit state function a linear relation between the loading and the deflection is formed. For the reliability analysis an algorithm has been developed for determination of limit state functions and iterations of the first order reliability method (FORM) procedure. By the method presented herein the multivariable analysis of a complicated reliability problem is reduced to an S-R problem. The procedure for iterations has been tested by a known problem for the purpose of avoiding convergence problems. The reliability indices for many cases have been obtained and also the effects of the coefficient of variation of load and resistance have been investigated.

• Steel and Composite Structures
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• v.15 no.6
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• pp.705-724
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• 2013

The behaviour of steel column at elevated temperature is significantly different than that at ambient temperature due to its changes in the mechanical properties with temperature. Reported literature suggests that steel column may become vulnerable when exposed to fire condition, since its strength and capacity decrease rapidly with temperature. The present study aims at investigating the lateral load resistance of non-insulated steel columns under fire exposure through finite element analysis. The studied parameters include moment-rotation behaviour, lateral load-deflection behaviour, stiffness and ductility of columns at different axial load levels. It was observed that when the temperature of the column was increased, there was a significant reduction in the lateral load and moment capacity of the non-insulated steel columns. Moreover, it was noted that the stiffness and ductility of steel columns decreased sharply with the increase in temperature, especially for temperatures above $400^{\circ}C$. In addition, the lateral load capacity and the moment capacity of columns were plotted against fire exposure time, which revealed that in fire conditions, the non-insulated steel columns experience substantial reduction in lateral load resistance within 15 minutes of fire exposure.

• Earthquakes and Structures
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• v.17 no.1
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• pp.49-61
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• 2019

A novel asymmetrical resistance friction damper (ARFD) was proposed in this study to be applied on a rocking column base. The damper comprises multiple steel plates and was fastened using high-strength bolts. The sliding surfaces can be switched into one another and can cause strength to be higher in the loading direction than in the unloading direction. By combining the asymmetrical resistance with the restoring resistance that is generated due to an axial load on the column, the rocking column base can develop a self-centering behavior and achieve high connection strength. Cyclic tests on the ARFD proved that the damper performs a stable asymmetrical hysteretic loop. The desired hysteretic behavior was achieved by tuning the bolt pretension force and the diameter of the round bolt hole. In this study, full-scale, flexural tests were conducted to evaluate the performance of the column base and to verify the analytical model. The results indicated that the column base exhibits a stable self-centering behavior up to a drift angle of 4%. The decompression moment and maximum strength reached 42% and 88% of the full plastic moment of the section, respectively, under a column axial force ratio of approximately 0.2. The strengths and self-centering capacity can be obtained by determining the bolt pretension force. The analytical model results revealed good agreement with the experimental results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4B
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• pp.323-332
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• 2011

In order to properly manage trees in rivers, the impact of trees on flooding and their ecological characteristics need to be considered and a plan needs to be established. The hydraulic impact by trees is reduction of conveyance and hydraulic structure's function due to overturn arising from flow force. A field pulling test was carried out to measure the critical resistance force for when trees break in order to discover the level of resistance that trees inside the river have to external force. The relevant factors for discovering the critical breaking moment for trees include tree species, which determines the external characteristic of trees, tree diameter at breast height, and tree height. In this study, the correlation between critical breaking moment and diameter at breast height were used. The tree's limit or critical breaking moment was tested using 100 shrubs and tall trees with a breast height diameter of 4.9 to 32.8 cm. It was difficult to derive a correlation between diameter at breast height and critical breaking moment when shrubs and tall trees were being considered together, but when only tall trees were considered, a consistent correlation was found between them.