• Korean Journal of Agricultural Science
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• v.46 no.4
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• pp.723-735
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• 2019

The power-train is the most important component of an agricultural tractor. In this study, the strength of the driving gear transmission of an 82 kW-class tractor was analyzed using equivalent torque during plow tillage. The load measurement system consisted of an engine revolution speed sensor, torque-meters, revolution speed sensors for four axles, and pressure sensors for two hydraulic pumps. The load data were measured during plow tillage for four speed stages: F2 (2.78 km/h), F5 (5.35 km/h), F7 (7.98 km/h), and F8 (9.75 km/h). Aspects of the gear-strength such as bending stress, contact stress, and safety factors were analyzed under two torque conditions: the equivalent torque at the highest plow load for the F8 speed stage and the maximum engine torque. The simulation results using KISSsoft showed that the maximum engine torque conditions had a lower safety factor than did the highest equivalent torque condition. The bending safety factors were > 1 at all gear stages, indicating that gear breakage did not occur under actual measured operating conditions, nor under the maximum torque conditions. However, the equivalent torque condition in the contact stress safety factor was > 1, and the maximum torque condition was < 1 at the first gear pair. The method of analysis using the equivalent torque showed lower stress and higher safety factor than did the method using maximum torque. Therefore, when designing a tractor by applying actual working torque, equivalent torque method would support more reliable product development.

• Earthquakes and Structures
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• v.2 no.1
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• pp.65-88
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• 2011

A new method for the seismic design of plane steel moment resisting frames is developed. This method determines the design base shear of a plane steel frame through modal synthesis and spectrum analysis utilizing different values of the strength reduction (behavior) factor for the modes considered instead of a single common value of that factor for all these modes as it is the case with current seismic codes. The values of these modal strength reduction factors are derived with the aid of a) design equations that provide equivalent linear modal damping ratios for steel moment resisting frames as functions of period, allowable interstorey drift and damage levels and b) the damping reduction factor that modifies elastic acceleration spectra for high levels of damping. Thus, a new performance-based design method is established. The direct dependence of the modal strength reduction factor on desired interstorey drift and damage levels permits the control of deformations without their determination and secures that deformations will not exceed these levels. By means of certain seismic design examples presented herein, it is demonstrated that the use of different values for the strength reduction factor per mode instead of a single common value for all modes, leads to more accurate results in a more rational way than the code-based ones.

• Journal of the Korean Society of Safety
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• v.21 no.5 s.77
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• pp.17-21
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• 2006

In this study, SPCC cross-tension type specimens produced under various spot welding conditions were tensile and fatigue tested. Decrease of 2 kA in normal current condition of 10 kA caused a large amount of reduction in both static joining strength and fatigue life. And 2 kA increase resulted in increase of static joining strength and an increase in low cycle regime but a decrease in high cycle regime, revealing the fact that fatigue strength rather than static joining strength would be a major factor during design process in view of the body endurance. As a results of estimating the fatigue lifetimes of various types of spot weld specimens. equivalent stress intensity factor is the proper parameter for predicting the lifetimes of various types of specimens. which can be expressed as ${\Delta}K_{eq}(N/nm^{1.5})=11550N^{-0.36}_{f}$.

• Earthquakes and Structures
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• v.12 no.4
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• pp.397-407
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• 2017

To estimate the structural seismic demand, some methods are based on an equivalent linear system such as the Capacity Spectrum Method, the N2 method and the Equivalent Linearization method. Another category, widely investigated, is based on displacement correction such as the Displacement Coefficient Method and the Coefficient Method. Its basic concept consists in converting the elastic linear displacement of an equivalent Single Degree of Freedom system (SDOF) into a corresponding inelastic displacement. It relies on adequate modifying or reduction coefficient such as the inelastic deformation ratio which is usually developed for systems with known ductility factors ($C_{\mu}$) and ($C_R$) for known yield-strength reduction factor. The present paper proposes a rational approach which estimates this inelastic deformation ratio for SDOF bilinear systems by rigorous nonlinear analysis. It proposes a new inelastic deformation ratio which unifies and combines both $C_{\mu}$ and $C_R$ effects. It is defined by the ratio between the inelastic and elastic maximum lateral displacement demands. Three options are investigated in order to express the inelastic response spectra in terms of: ductility demand, yield strength reduction factor, and inelastic deformation ratio which depends on the period, the post-to-preyield stiffness ratio, the yield strength and the peak ground acceleration. This new inelastic deformation ratio ($C_{\eta}$) is describes the response spectra and is related to the capacity curve (pushover curve): normalized yield strength coefficient (${\eta}$), post-to-preyield stiffness ratio (${\alpha}$), natural period (T), peak ductility factor (${\mu}$), and the yield strength reduction factor ($R_y$). For illustrative purposes, instantaneous ductility demand and yield strength reduction factor for a SDOF system subject to various recorded motions (El-Centro 1940 (N/S), Boumerdes: Algeria 2003). The method accuracy is investigated and compared to classical formulations, for various hysteretic models and values of the normalized yield strength coefficient (${\eta}$), post-to-preyield stiffness ratio (${\alpha}$), and natural period (T). Though the ductility demand and yield strength reduction factor differ greatly for some given T and ${\eta}$ ranges, they remain take close when ${\eta}>1$, whereas they are equal to 1 for periods $T{\geq}1s$.

• Journal of the Korea Institute of Building Construction
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• v.2 no.4
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• pp.177-182
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• 2002

The purpose of this study is to develope the strength prediction model by Maturity Method. A maturity function is a mathematical expression to account for the combined effects of time and temperature on the strength development of a cementious mixture. The method of equivalent ages is to use Arrhenius equation which indicates the influence of curing temperature on the initial hydration ratio of cement. For the experimental factors of this study, we selected the concrete mixing of W/C ratio 45, 50, 55 and 60% and curing temperature 5, 10, 20 and $30^{\circ}C$. And we compare and evaluate with logistic model that is existing strength prediction model, because we have to verify adaption possibility of new strength prediction model which is proposed by maturity method. As the results, it is found that investigation of the activation energy that are used to calculate equivalent age is necessary, and new strength prediction model was proved to be more accurate in the strength prediction than logistic model in the early age. Moreover, the use of new model was more reasonable because it has low SSE and high decisive factor.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.6
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• pp.166-174
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• 2013

This study investigates the strength durability on the results of structural and vibration analysis due to the shape of excavator wheel. As model 2 has the least stress by comparing three models with maximum equivalent stress, model 2 has most durability among three models at static analysis. Maximum equivalent stress is shown at the bottom part contacted with ground and this part on wheel is most affected by load in cases of all models. Safety factor can be decided with the value of 2.3 by considering the yield stress of this model. The range of maximum harmonic response frequencies becomes 6900 to 7000Hz. As model 2 has the least total deformation and equivalent stress at these critical frequencies, model 2 has the most durability at vibration analysis among three models. The structural and vibration analysis results in this study can be effectively utilized with the design of excavator wheel by investigating prevention and durability against its damage.

• Steel and Composite Structures
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• v.13 no.1
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• pp.47-70
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• 2012

To enhance cable stiffness, this paper proposed a combined application of carbon fiber reinforced polymers (CFRP) and steel materials, resulting in a novel type of hybrid stay cable system especially for the cable-stayed bridges with main span lengths of 1400~2800 m. In this combination, CFRP materials can conserve all their advantages such as light weight and high strength; while steel materials help increase the equivalent stiffness to compensate for the low elastic modulus of CFRP materials. An increase of the equivalent stiffness of the hybrid stay cable system could be further obtained with a reasonable increase of its safety factor. Following this concept, a series of parametric studies for the hybrid stay cable system with the consideration of stiffness and cost were carried out. Three design strategies/criteria, namely, best equivalent stiffness with a given safety factor, highest ratio of equivalent stiffness to material cost with a given safety factor, and best equivalent stiffness under a given cost were proposed from the stiffness and cost viewpoints. Finally, a comprehensive design procedure following the proposed design strategies was suggested. It was shown that the proposed hybrid stay cable system could be a good alternative to the pure CFRP or traditional steel stay cables in the future applications of super long span bridges.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1993.10a
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• pp.240-247
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• 1993

The precise prediction of reserved carrying capacity of bridge as a system is extremely difficult especially when the bridges are highly redundant and significantly deteriorated or damaged. This paper is intended to propose a new approach for the evaluation of reserved system carrying capacity of bridges in terms of equivalent system-strength, which may be defined as a bridge system-strength corresponding to the system reliability of the bridge. This can be derived from an inverse process based on the concept of FOSM form of system reliability index. It may be emphasized that this approach is very useful for the evaluation of the deterministic system redundancy and reserve strength which are measured in terms of either probabilistic system redundancy factor and reserve factor or deterministic system redundancy factor and reserve factor. The system reliability of bridges is formulated as a parallel-series model obtained from the FAM(Failure Mode Approach) based on the major failure mechanisms. AFOSM and IST methods are used for the reliability analysis of the proposed models. The proposed approach and method for the system redundancy and reserve safety/strength are applied to the safety assessment of actual RC and steel box-girder bridges. The results of the evaluation of reserved system safety or bridge system-strength in terms of the system redundancy and the system safety/strength are significantly different from those of element reliability-based or conventional methods.

• Journal of the Korea Institute of Building Construction
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• v.20 no.5
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• pp.409-416
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• 2020

In this paper, strength correction factors of the concretes incorporating ordinary Portland cement(OPC), fly ash(FA) and blast furnace slag(BS) with 50% of water to binder ratio due to temperature drop for standard room temperature(20±3℃) are provided. For this, strength development was done based on equivalent age method. For calculating the equivalent age, apparent activation energy was obtained with 24.69 kJ/mol in OPC, 46.59 kJ/mol in FA, 54.59 kJ/ol in BS systems. According to the estimation of strength development of the concretes, the use of FA and BS resulted in larger strength drop than that of OPC under low temperature compared to standard room temperature. Hence, strength correction factors(Tn) for OPC, FA and BS are suggested within 4~17℃ with every 3MPa levels.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.303-310
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• 2003

Small-scale models have been frequently used for experimental evaluation of seismic performance because of limited testing facilities and economic reasons. However, there are not enough studies on similitude law for analogizing prototype structures accurately with small-scale models, although conventional similitude law based on geometry is not well consistent in the inelastic seismic behavior. When fabricating prototype and small-scale model of reinforced concrete structures by using the same material, added mass is demanded from a volumetric change and scale factor could be limited due to size of aggregate. Therefore, it is desirable that different material is used for small-scale models. Thus, a modified similitude law could be derived depending on geometric scale factor and equivalent modulus ratio. In this study, compressive strength tests are conducted to analyze equivalent modulus ratio of micro-concrete to normal-concrete. Equivalent modulus ratios are divided into elastic, weak nonlinear and strong nonlinear phases, which are based on ultimate strain level. Therefore, an algorithm adaptable to the pseudodynamic test, considering equivalent three phase similitude law based on seismic damage levels, is developed. In addition, prior to tile experiment, it is verified numerically if tile algorithm is applicable to the pseudodynamic test.