• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6C
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• pp.367-377
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• 2008

As part of study to develop LRFD (Load and Resistance Factor Design) codes for foundation structures in Korea, resistance factors for static bearing capacity of driven steel pipe piles were calibrated in the framework of reliability theory. The 57 data sets of static load tests and soil property tests conducted in the whole domestic area were collected and these load test piles were sorted into two cases: SPT N at pile tip less than 50, SPT N at pile tip equal to or more than 50. The static bearing capacity formula and the Meyerhof method using N values were applied to calculate the expected design bearing capacities of the piles. The resistance bias factors were evaluated for the two static design methods by comparing the representative measured bearing capacities with the expected design values. Reliability analysis was performed by two types of advanced methods: the First Order Reliability Method (FORM), and the Monte Carlo Simulation (MCS) method using resistance bias factor statistics. The target reliability indices are selected as 2.0 and 2.33 for group pile case and 2.5 for single pile case, in consideration of the reliability level of the current design practice, redundancy of pile group, acceptable risk level, construction quality control, and significance of individual structure. Resistance factors of driven steel pipe piles were recommended based on the results derived from the First Order Reliability Method and the Monte Carlo Simulation method.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4A
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• pp.323-329
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• 2011

Most current design codes of concrete structures adopt the partial safety factor format to assure the proper safety margin or reliability against various limit states as a practical design tool. The safety factors, load and resistance factors and so on, are determined based on the theory of structural reliability, which takes into account the statistical uncertainties of both loads and resistances. The establishment of statistical models for load and resistance should be preceded the application of reliability theory. In this paper, especially the influence of the statistical variations of resistance models, which are described in terms of strength of concrete, strength of reinforcements and sectional dimensions and so on, are examined and the probabilistic models for resistance of reinforced concrete members were developed. The statistical data were collected on local tests and experiments in Korea and the Monte Carlo simulation (MCS) technique was used. The results of this paper may be useful and valuable in calibration of design code in this country.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.1
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• pp.13-24
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• 2019

This paper brings up fallacy of material factors specified for the design of concrete members in the current Korean limit state design code for highway bridges, and proposes new material factors based on a robust optimization scheme to overcome the fallacy. It is shown that the current load factors in the code and the proposed material factors lead to a much higher reliability index than the target index. The load factors are adjusted to yield the target reliability index using the inverse reliability analysis. A reliability-based approach following the basic concept of Eurocode is formulated to determine material factors as well as load factors. The load-material factors obtained by the proposed reliability-based approach yield a lower reliability level than the target index. Drawbacks of the basic concept of Eurocode are discussed. It is pointed out that differences in the uncertainties between materials and members may cause the lower reliability index of concrete member than the target.

• 지반과기술
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• v.8 no.1
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• pp.39-44
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• 2011

• Land and Housing Review
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• v.3 no.3
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• pp.279-286
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• 2012

The limit states design method is replacing the allowable stress design method worldwide, e.g. the design code of ISO and various construction codes of Korea are adopting the reliability based limit state method. This paper proposed LRFD design value which is one of limit states design method for the PHC bored pile used as building foundation. This paper analysed 81 load test results and the bearing design(Meyerhof method & SPT-CPT conversion method), and proposed LRFD value for each design reliability Index 2.33 and 3.0 for PHC bored pile. LRFD value of PHC bored pile represents 0.36~0.44 for Meyerhof method and 0.24~0.31 for SPT-CPT conversion method according to the deign reliability index.

• Journal of the Korean Geotechnical Society
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• v.21 no.10
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• pp.113-122
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• 2005

Application of Limit State Design in geotechnical engineering has become world-widely popular. While LRFD code in the North America presents geotechnical load and resistance factors, the values of resistance factors proposed by these methods are still unstable with limited application. CPT has been widely used for the pile design and various methods have been proposed to estimate the bearing capacity of piles. In this paper, resistance factors for representative pile design methods based on CPT results are evaluated. Field pile load test and CPT results were collected and analyzed in order to obtain necessary statistical data and resistance factors. Resistance factors of the base, shaft, and total capacity are estimated. From fisrt order second moment (FOSM) analysis, resistance factors of $0.30{\sim}0.55$ are estimated for total load capacity.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.845-856
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• 2020

This study proposes a bridge evaluation system for indivisible permit vehicles such as hydraulic cranes. The permit loads for the bridge evaluation are divided into three categories: routine permit loads, special permit 1 loads, and special permit 2 loads. Routine permit and special permit 1 vehicles are allowed to cross a bridge with normal traffic. For these two permits, the standard lane model in the Korean Highway Bridge Design Code was adopted to consider normal traffic in the same lane. Special permit 2 vehicles are assumed to cross a bridge without other traffic. Structural analyses of two prestressed-beam bridges and two steel box girder bridges were conducted for the proposed permit loads. The rating factors of the four bridges for all permit loads were calculated as sufficiently large values for the moment and shear force so that crossing the bridges can be permitted. A reliability assessment of the bridges was performed to identify the reliability levels for the permit vehicles. It was confirmed that the reliability level of the minimum required strength obtained by the load-resistance factors yields the target reliability index of the design code for the permit vehicles.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.12
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• pp.8128-8139
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• 2015

Recently, the necessity of developing the load and resistance factor design(LRFD) for soft ground improvement method has been raised, since the limit state design is requested as international technical standard for the foundation of structures. In this study, to develop LRFD codes for foundation structures in Korea, target reliability index and resistance factor for static bearing capacity of driven steel pipe piles were calibrated in the framework of reliability theory. The 16 data(in Gwangyang) and the 57 data(Korea Institute of Construction Technology, 2008) sets of static load test and soil property tests conducted in the whole domestic area were collected along with available subsurface investigation results. The resistance bias factors were evaluated for the tow static design methods by comparing the representative measured bearing capacities with the expected design values. Reliability analysis was performed by two types of advanced methods : the First Order Reliability Method (FORM), and the Monte Carlo Simulation (MCS) method using resistance bias factor statistics. As a result, when target reliability indices of the driven pipe pile were selected as 2.0, 2.33, 2.5, resistance factor of two design methods for SPT N at pile tip less than 50 were evaluated as 0.611~0.684, 0.537~0.821 respectively, and STP N at pile tip more than 50 were evaluated as 0.545~0.608, 0.643~0.749 respectively. The result from this research will be useful for developing various foundations and soil structures under LRFD.

• Land and Housing Review
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• v.4 no.3
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• pp.279-286
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• 2013

Driving a prefabricated pile is the efficient construction method with low cost and excellent bearing capacity charateristics. But pile drinving method has often been changed to bored pile method with mechanical boring due to the unexpected problems occurred in the various domestic ground condition with landfill. So, pile driving method has more uncertainty than the Bored Pile method. This paper proposed LRFD design value which is one of limit states design method for the PHC driven pile used as building foundation to guarantee the reliable design with reduced uncertainty. This paper analysed 221 dynamic load test results(E.O.I.D : 93, Resrike : 128) and the different methods of estimating bearing design(Meyerhof method & SPT-CPT conversion method), and proposed LRFD value for each design reliability Index 2.33 and 3.0 for PHC driven pile. LRFD value of PHC driven pile represents 0.43~0.55 for Meyerhof method and 0.40~0.49 for SPT-CPT conversion method according to the deign reliability index.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.4
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• pp.1-12
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• 1987

The Advanced First Order Second Moment(AFOSM) method is commonly used to determine partial safety factors in the development of probability based LRFD code. However, design format using load and resistance factors based on this method may result in different reliability levels from specified ones. Reliability-Conditioned(RC) method recently proposed by Ayyub et al. gives partial safety factors which do not affect the target reliability level as specified. However, this method has some numerical difficulties and the procedure is not consistent. The proposed RC/AFOSM combined method has not only numerical consistency, but also results in almost constant partial safety factors with respect to various design conditions, and the resulting reliability levels are very close to specified ones.