• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.3
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• pp.87-99
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• 1982

This study proposes a reliability based design criteria for the R.C. superstructures of highway bridges. Uncertainties associated with the resistance of T or rectangular sections are investigated, and a set of appropriate uncertainties associated with the bridge dead and traffic live loads are proposed by reflecting our level of practice. Major 2nd moment reliability analysis and design theories including both Cornell's MFOSM(Mean First Order 2nd Moment) Methods and Lind-Hasofer's AFOSM(Advanced First Order 2nd Moment) Methods are summarized and compared, and it has been found that Ellingwood's algorithm and an approximate log-normal type reliability formula are well suited for the proposed reliability study. A target reliability index (${\beta}_0=3.5$) is selected as an optimal value considering our practice based on the calibration with the current R.C. bridge design safety provisions. A set of load and resistance factors is derived by the proposed uncertainties and the methods corresponding to the target reliability. Furthermore, a set of nominal safety factors and allowable stresses are proposed for the current W.S.D. design provisions. It may be asserted that the proposed L.R.F.D. reliability based design criteria for the R.C. highway bridges may have to be incorporated into the current R.C. bridge design codes as a design provision corresponding to the U.S.D. provisions of the current R.C. design code.

• Journal of Korean Society of Steel Construction
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• v.19 no.1
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• pp.15-27
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• 2007

Over the past decade, labor costs have increased relative to the cost of material hardware according to analysts in the construction industry. Therefore, the minimum weight design, which has been widely adopted in the literature for the optimal design of steel structures, is no longer the most economical construction approach. Presently, although connection- related costs is crucial in determining the most cost-effective steel structures, most studies on this subject focused on minimum-weight design or engaged in higher analysis. Therefore, in this study, we proposed a fabrication scheme for the most cost-effective moment-resisting steel frame structures that resist lateral loads without compromising overall stability. The proposed approach considers the cost of steel products, fabrication, and connections within the design process. The optimal design considered construction realities, with the optimal trade-off between the number of moment connections and total cost was achieved by reducing the number of moment connections and rearranging them using the combination of analysis that includes shear, displacement and interaction value based on the LRFD code and optimization scheme based on genetic algorithms. In this study, we have shown the applicability and efficiency in the examples that considered actual loading conditions.

• Journal of the Korean Society of Safety
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• v.6 no.3
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• pp.56-63
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• 1991

This study investigates reliability based design criteria for the erection members, and proposes practical algorithm which is based on Ellingwood's algorithm for the reliability analysis and the derivation of reliability based criteria. The magnitude of the uncertainties associated with load effects are chosen primarily by considering our level of practice. And thus the uncertainties so obtained are applied for the reliability analysis and the derivation of reliability based design criteria. A target reliability($\beta$$_{o}$=2.0) is selected as an appropriate value by analyzing the reliability levels of our current USD and WSD design standards. Them a set of load and resistance factors corresponding to the target reliability is proposed as a reliability based design provision, and furthermore a set of allowable stresses for steel having same level of reliability with the corresponding LRFD criteria is also prepared for the current WSD design provision. It may be concluded that the proposed LRFD reliability based design provisions and the corresponding allowable stresses give more rational design than the current code for erection membars.s.s.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.214-224
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• 2008

Member force, strain and stress distribution of a section are obtained for optimized standard 25m~45m PSSC composite bridge subjected to dead and live load in order to interpret the effect of prestressing and deformation of tendon. The stress and strain distribution and moment capacity are obtained for both noncomposite and composite section and for allowable stress limit state, yield limit state and strength limit state. Reliability analysis is conducted after assuming limit states for stress and flexural strength. The reliability index for standard PSSC composite bridge which is designed to satisfy the allowable stress for flexural strength are higher than 3.5 which is required reliability indexes on American code for LRFD. Reliability of PSSC girder which is designed based on allowable stress of bridge design code is high for flexural strength.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.2
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• pp.112-121
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• 2013

The calibration of resistance factor in reliability theory for limit state design of gravel compaction piles (GCP) requires a reliable estimate of ultimate bearing capacity. The static load test is commonly used in geotechnical engineering practice to predict the ultimate bearing capacity. Many graphical methods are specified in the design standard to define the ultimate bearing capacity based on the load-settlement curve. However, it has some disadvantages to ensure reliability to obtain an uniform ultimate load depend on engineering judgement. In this study, a well-fitting nonlinear regression model is proposed to estimate the ultimate bearing capacity, for which a nonlinear regression analysis is applied to estimate the ultimate bearing capacity of GCP and the results are compared with those calculated using previous graphical method. Affect the resistance factor of the estimate method were analyzed. To provide a database in the development of limit state design, the load test conditions for predicting the ultimate bearing capacity from static load test are examined.

• Journal of the Korean Geotechnical Society
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• v.28 no.6
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• pp.5-17
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• 2012

The moment responses of electric pole foundations for a railway were investigated using real-scale load tests. Large overturning moments were applied to two circular rigid piles with a 0.75 m diameter and a 2.5 m embedded depth; the circular rigid piles were installed in an actual railway embankment fill. Two different loading directions-toward the fill slope and toward the track -were applied to evaluate the influence of the fill slope on the moment capacities of the foundations. It was found that the failure of the foundations that were constructed according to Korean railway practices exhibited a sudden overturning pattern without any significant pre-failure displacement. The moment capacity toward the fill slope was less than the moment capacity toward the track by 30%. From the test results, the geometry factor (K), which accounted for the reduction of the moment capacity, due to the fill slope, was 0.7. Moment capacities determined from the load tests were compared with those predicted from three existing design methods, and their applicability was discussed.

• Journal of Aerospace System Engineering
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• v.16 no.6
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• pp.64-73
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• 2022

This study aimed to design a 3D fairing shape to reduce the air resistance of commercial vehicles. Rankine Half Body was applied to design the fairing shape, and the design was verified through aerodynamic analysis. Aerodynamic loads were calculated considering the speed conditions of commercial vehicles and gust conditions to ensure the structural safety of the fairing. A glass fibre/epoxy composite material was used to design a fairing structure that satisfied the safety factor 3. The structural safety of the lightest fairing was confirmed through structural analysis.

• Journal of Korean Society of Steel Construction
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• v.18 no.6
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• pp.707-716
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• 2006

The optimization of the direct design system of semi-rigid steel frames using advanced analysis and genetic algorithm was presented. Advanced analysis can predict the combined nonlinear effects of connection, geometry, and material on the behavior and strength of semi-rigid frames. Geometric nonlinearity was determined using stability functions. On the other hand, material nonlinearity was determined using the Column Research Council (CRC) tangent modulus and parabolic function. The Kishi-Chen power model was used to describe the nonlinear behavior of semi-rigid connections. The genetic algorithm was used as the optimization technique. The objective function was assumed as the weight of the steel frame, with the constraint functions accounting for load-carrying capacities, deflections, inter-story drifts and ductility requirement. Member sizes determined by the proposed method were compared with those derived using the conventional method.

• Journal of Korean Society of Steel Construction
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• v.20 no.4
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• pp.469-481
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• 2008

The inelastic design of the three-span continuous composite plate girder with consideration of moment redistribution over the interior pier is performed using the LRFD method. The design of the girder section, based on the inelastic method, is compared with that by the conventional elastic design. The length of the center span for the three-span continuous bridge ranges from 40m to 70m and the relative ratio of the span length is assumed to be 4:5:4. Although the AASHTO- LRFD specifications are applied in the design of the composite girder, the recently proposed new design live load is used. After determining the maximum positive and negative sections by the elastic design for various limit states, the amount of moment redistributed to the maximum positive moment section is calculated. With the increased design moment due to moment redistribution from the interior pier, the maximum positive section designed by the elastic method is checked for the strength limit state and the service limit state. The maximum negative moment section is redesigned by reducing the size of the steel girder relative to the section designed by the elastic method and the new section is checked for the service limit state. Based on the design results for the five bridges considered in this study, it is estimated that about 23% of steel can be saved in the interior pier section if it is designed by the inelastic method compared with that designed by the elastic method.

• Journal of Korean Society of Steel Construction
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• v.23 no.2
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• pp.189-198
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• 2011

Many new structural systems have been developed to build free-form structures, which is the new architectural trend for aesthetic beauty. The diagrid system resists both gravity and later loads, with its perimeter-diagonal columns. In the current seismic-design provisions, however, a seismic-performance factor for a new structural system has not yet been provided. ATC-63 provides a new methodology for defining various seismic-performance factors, including the response modification factor. In this paper, nonlinear static and dynamic analyses were conducted for the 3D diagrid frame, with each load applied at $0-180^{\circ}$ degrees. Through these analyses, the seismic performance of the diagrid system was evaluated.