Limit State Design Method Research Articles

Reliability analysis of laterally loaded piles for an offshore wind turbine support structure using response surface methodology

With an increasing demand of a renewable energy, new offshore wind turbine farms are being planned in some parts of the world. Foundation installation asks a significant cost of the total budget of offshore wind turbine (OWT) projects. Hence, a cost reduction from foundation parts is a key element when a cost-efficient designing of OWT budget. Mono-piles have been largely used, accounting about 78% of existing OWT foundations, because they are considered as a most economical alternative with a relatively shallow-water, less than 30 m of seawater depth. OWT design standards such as IEC, GL, DNV, API, and Eurocode are being developed in a form of reliability based limit state design method. In this paper, reliability analysis using the response surface method (RSM) and numerical simulation technique for an OWT mono-pile foundation were performed to investigate the sensitivities of mono-pile design parameters, and to find practical implications of RSM reliability analysis.

Analysis of Design Live Load of Railway Bridge Through Statistical Analysis of WIM Data for High-speed Rail

In this paper, the live load model for the design of high-speed railway bridge is analyzed by statistic and probabilistic methods and the safety level that is given by the load factors of the load combination is analyzed. This study is a part of the development of the limit state design method for the railway bridge, and the train data collected from the Gyeongbu high-speed railway for about one month are utilized. The four different statistical methods are applied to estimate the design load to match the bridge design life and the results are compared. In order to examine the safety level that the design load combination of the railway bridge gives, the reliability indexes are determined and the results are analyzed. The load effect from the current design live load for the high-speed rail bridge which is 0.75 times of the standard train load is came out greater than at least 30-22% that from the estimated load from the measured data. If it is judged based on the ultimate limit state, there is a possibility of additional reduction of the safety factors through the reliability analysis.

초박층 폴리머콘크리트 포장적용을 위한 매개변수 해석

경제성장 및 물류증가로 인하여 장대교량에 대한 수요가 증가하고 있다. 장지간을 가진 교량 건설을 위해서는 자중 감소가 필수적이며, 이를 위한 노력의 일환으로 초박층 포장재에 대한 연구 및 개발이 진행되고 있다. 국내 설계기준을 살펴보면, 이전 도로교설계기준(2010)에서는 포장이 가지는 강성을 강바닥판에 고려하지 않아 보수적인 설계가 이루어져 왔으나, 최근 개정된 설계기준인 도로교설계기준(2012, 한계상태설계법)에서는 일정한 조건 하 포장이 가지는 강성을 강바닥판에 반영하는 것을 허용하고 있다. 하지만 초박층 교면포장이 강바닥판에 미치는 영향에 대한 연구는 미비한 실정이며, 진행된 연구 또한 거동 특성 및 피로응력에 대한 연구로 한정되어 왔다. 본 연구에서는 포장강성의 반영/미반영, 교면 포장재료, 포장 두께 및 강바닥판 두께를 매개변수로 하여 이에 따른 강바닥판의 처짐과 전단응력의 변화 및 추세를 알아보고 또한 이를 바탕으로 강바닥판에 초박층 교면포장 강성 적용의 효율성을 알아보았다. Base on Korean design code, previous design code had not considered the effect of pavement on the orthotropic steel deck, however recent design code (Limit State Design Method, 2012) allowed to consider the effect of pavement on the orthotropic steel deck, and efforts to apply the stiffness of pavement to the deck continue. Meanwhile, research on the effect of ultra thin bridge deck overlay on the orthotropic steel deck is inadequate, previous study was limited in about fatigue stress and performance between pavement layer and the orthotropic steel deck. In this study, according to changing of pavement layer stiffness application, pavement materials, pavement thickness and steel deck thickness, analysis of deflection. In addition to base on this result, consider effectiveness of ultra-thin pavement stiffness application on the orthotropic steel deck.

Providing safety and reliability in the design of the offshore ice-resistant stationary oil and gas structures

Safety and reliability factors, assumed in Russian and international standards, as well as the main provisions of design of offshore oil and gas structures are considered in the article. The reasons for structures destruction are classified. The analysis showed that the main design provisions and methodology of calculations related to provision of safe and reliable operation of offshore oil and gas structures by different standards are not fundamentally different: the required degree of reliability of the structure is set depending on the social and economic consequences of possible hydrodynamic accidents; calculations are based on the limit states design method using partial safety factors; etc. However, the factors accounting the degree of the structure reliability, partial safety coefficients and load combinations coefficients differ in different standards and methodologies.

Reliability analysis of RC T-beam highway bridges in China based on a virtual bridge dataset

Limit state design method based on probability theory is used in the Chinese highway bridge design codes which adopt partial factors in the design equations. In this paper, a virtual bridge dataset (VBD) including a total of 8064 RC T-beam bridges designed based on the Chinese highway bridge design codes was established. With this VBD, the influences of the different design parameters including span length, girder spacing, concrete grade, reinforcement grade, number of design lanes, and actions on the reliability of the RC T-beams were studied. A Monte-Carlo simulation combined with first order second moment method was employed to calculate the reliability indices of the bridges in the VBD. By conducting a statistical analysis on the calculated reliability indices, it is shown that the reliability indices follow a normal distribution and there is good consistency in the reliability of the bridges with different parameters. Construction cost for the bridges with spans of 16m in the VBD was calculated, indicating that the construction cost increases along with the increase of the reliability indices. Suggestions with regard to the determination of the target reliability of the bridges in multi objects were also proposed.

Sensitivity Analysis by Parametric Study of Load Factor for a Concrete Box Girder Railway Bridge Using Limit State Design

Reliability based limit state design method is replacing traditional deterministic designs such as allowable stress design and/or ultimate strength design methods in world trends. European design code(Eurocode) has adopted limit state design, and Korea road bridge design standard has also recently been transferred to limit state design method. In this trend, Korea railroad design standard is also preparing for adopting the same design concept. While safety factors are determined empirically in traditional design, load combinations as well as load factors are determined by solving limit state equations. General partial safety factors are evaluated by using AFORM(Advanced First Order Reliability Method) in the reliability based limit state design method. In this study sensitivity analysis is carried out for a dead load factor and a live load factor. Relative precisions of the dead load and the live load factors are discussed prior to the AFORM analysis. Furthermore the sectional forces of design and the material quantities required by two different design methods are compared for a PSC box girder railway bridge.

Response modification factor of suspended zipper braced frames

The suspended zipper bracing system is suggested to reduce the flaws of ordinary zipper braced and concentric inverted <i>V</i> braced frames. In the design procedure of suspended zipper bracing systems, columns and top story truss elements are strengthened. This bracing system show different performances and characteristics compared with inverted <i>V</i> braced and ordinary zipper frames. As a result, a different response modification factor for suspend zipper frames is needed. In this research paper, the response modification factor of suspended zipper frames was obtained using the incremental dynamic analysis. Suspended zipper braced frames with different stories and bay lengths were selected to be representations of the design space. To analyze the frames, a number of models were constructed and calibrated using experimental data. These archetype models were subjected to 44 earthquake records of the FEMA-P695 project data set. The incremental dynamic analysis and elastic dynamic analysis were carried out to determine the yield base shear value and elastic base shear value of archetype models using the OpenSEES software. The seismic response modification factor for each frame was calculated separately and the values of 9.5 and 13.6 were recommended for ultimate limit state and allowable stress design methods, respectively.

The performance evaluation of ordinary moment resisting frames designed by performance-based plastic design and limit state design

The performance in terms of interstorey drift ratios and failure pattern of ordinary moment resisting frames designed by performance-based plastic design (PBPD) method and limit state design method have been compared in this paper. For this, different study frames were designed using the force based limit state design method and displacement-based performance-based plastic design method. The PBPD frames were designed taking ductility ratio two. Results of static pushover and time history analysis prove the superiority of the PBPD method when compared in terms of interstorey drift ratio and failure pattern.

하한지지력이 현장타설말뚝의 저항계수에 미치는 영향

한계상태설계법의 하나인 하중저항계수설계법의 이용이 북미를 중심으로 점차 확산되고 있는 가운데, 국내에서도 이에 대한 연구가 활발하게 진행되고 있다. 하지만, 국내에서는 자료가 충분히 확보되지 못하여 기초구조물의 설계에 AASHTO에서 제안한 저항계수를 설계에 이용하고 있다. AASHTO에서 제안하고 있는 저항계수는 북미에 보편적으로 존재하는 암반조건을 이용하여 결정된 저항계수로서, 국내지반에 적합한 저항계수를 독자적으로 개발할 필요가 있다. 또한, 기존의 신뢰성 분석 기법에서는 하중저항계수를 결정할 때, 저항의 최소값을 0으로 가정하는 일반적인 대수정규 분포를 이용하기 때문에, 이로부터 산정한 파괴확률은 비현실적이라고 알려져 있다. 따라서, 이를 개선하기 위하여 저항계수를 산정할 때 저항의 하한값이 0이 아닌, 현실적으로 의미가 있는 하한지지력을 이용하는 방법이 최근에 고안되었다. 따라서, 본 연구에서는 국내에서 수행된 현장타설말뚝 13본에 대한 재하시험자료를 면밀히 분석하여 저항계수를 산정한 다음, 현실성 있는 하한지지력을 산정하여 저항계수 값을 보정하였다. 그 결과, 목표신뢰도지수가 3.0일때, 기존의 신뢰성 분석 기법으로부터 산정된 주면저항계수와 선단저항계수는 각각 0.13-0.32, 0.19-0.29 이었으며, 하한지지력을 보정하여 구한 주면저항계수와 선단저항계수는 Carter & Kulhawy 공식의 경우 각각 8%와 13% 증가하였다. Load and Resistance Factor Design (LRFD) is one of the limit state design methods, and has been used worldwide, especially in North America. Also, the study for LRFD has been actively conducted in Korea. However, the data for LRFD in Korea were not sufficient, so resistance factors suggested by AASTTO have been used for the design in Korea. But the resistance factors suggested by AASHTO represent the characteristics of bedrocks defined in the US, therefore, it is necessary to determine the resistance factors for designs in Korea, which can reflect the characteristics of bedrocks in Korea. Also, the calculated probabilities of failure from conventional reliability analyses which commonly use log-normal distribution are not realistic because of the lower tail that can be extended to zero. Therefore, it is necessary to calibrate the resistance factors considering the lower-bound resistance. Thus, this study calculates the resistance factors using thirteen sets of drilled shaft load test results, and then calibrates the resistance factors considering the lower-bound resistance corresponding to a target reliability index of 3.0. As a result, resistance factors from conventional reliability analyses were determined in the range of 0.13-0.32 for the shaft resistance, and 0.19-0.29 for the base resistance, respectively. Also, the lower bounds of resistance were determined based on the Hoek-Brown failure criteria (2002) and GSI downgrading. Considering the lower-bound resistances, resistance factors increased by 0~8% for the shaft, and 0~13% for the base, respectively.

Reliability of corroded thin walled pipes repaired with composite overwrap

Current design codes provide two design methods: allowable stress/strain design and limit state design. Design in the current pipework composite repair codes is based on the allowable design method and only two safety factors are applied to the ultimate strain of the composite layer and to the yield stress of steel. On the other hand, safety factors are applied to each of the load and resistance parameters in the limit state design method. The limit state design method is probabilistic based in which the safety factors are calibrated based on a target reliability index. In this study, an investigation into the reliability of rehabilitated pipelines is conducted. The limit state function is defined based on ASME PCC-2, and reliability analysis is conducted using the AFOSM method. Results show that ASME PCC-2 generally provides adequate safety although the level of safety is not uniform for different percentages of corrosion. Comparing the achieved results and the ISO 2394 target reliability indices, some resistance factors are proposed.

To Confirm Structural Coefficient for Design of Penstocks in Hydropower Stations by Partial Factors-Based Method

When confirming the partial factors in design formulas by the probability-based limit states design method (PLSDM), the structural coefficient can determined by two methods. On one hand, the structural coefficient is determined by the engineering experience calibration method, which is calculated by decomposition of the safety coefficient in the former specifications SD144-85. On the other hand, it can be determined by the probability analysis method and optimization calculation based on the target reliability index resulted from reliability calibration analysis. The appropriate value is finally determined by synthesizing results of the two methods.

콘크리트 옹벽구조물의 한계상태설계법 적용성 평가

국내에서는 외국현장에서 사용되고 있는 한계상태설계법을 도입하기 위하여 연구가 일부 진행 중이다. 국내외 한계상태 설계법에서는 말뚝기초, 얕은기초 등 비교적 데이터베이스를 구축하기 쉬운 분야로 설계기준이 마련되고 있으나 옹벽 등에 대하여 재하시험이 어려운 실정으로 옹벽의 한계상태설계법에 관한 연구는 미흡한 실정이다. 본 연구는 2008년도에 제정된 국내 도로옹벽 표준도를 기준으로 옹벽구조물의 한계상태설계법의 적용성 평가에 관한 연구이다. 옹벽의 활동과 전도에 대한 안전율을 LRFD 설계기준을 이용하여 범용 한계상태설계법 프로그램의 해석결과와 비교 검토하였다. 또한 해석결과의 비교를 위하여 테일러 급수를 이용한 간편 신뢰성 분석을 실시하였다. 옹벽단면의 LRFD 검토 결과 허용응력설계법에 비해 안전율이 낮게 나타났으며, 한계상태설계 도입을 통해 옹벽의 단면을 감소시켜 경제성을 확보할 수 있을 것으로 판단된다. 향후 신뢰성 확보를 위해 지반 데이터의 사전평가 연구가 필요하며, 그라운드 앵커와 같은 지보재가 적용되는 옹벽의 한계상태설계법 적용, 평가에 관한 연구도 필요하다. Nowadays, some studies are performed in order to introduce the Limit State Design method widely used in foreign work sites. LRFD (Load Resistance Factor Design) method is widely used in the fields in which the data accumulation is possible - such as deep foundations, and shallow foundations, etc. The limit state design in the retaining walls is insufficient in the country owing to difficulties applying load tests. The limit state design method for retaining wall structures are studied based upon the National Retaining wall Design Standard legislated in 2008 by Ministry of Land, Transport, and Maritime Affairs. In this paper several retaining walls were calculated according to LRFD design criteria analysis using the general program with limit state design method and the factor of safety for sliding and overturning. Comparing with their results, the Taylor's series simple reliability analysis was performed. In the analysis results of retaining wall section, safety factors calculated by LRFD were found to be lowered than those calculated in current WSD, and it is possibly judged to be economic design by changing wall dimensions. In the future, pre-assessment of the geotechnical data for ensuring the reliability and the studies including reinforced retaining walls with ground anchor are needed.

Limit states design for tunnels: related researches and present state of application

대표적인 한계상태설계법은 AASHTO LRFD와 Eurocodes가 있으며, 토목구조물 설계에 폭넓게 적용되고 있다. 그러나 이러한 설계법이 터널설계에 적용될 경우에는 NATM 터널의 라이닝설계와 쉴드터널의 세그먼트 설계에만 제한적으로 적용되고 있다. 최근 유럽에서는 유로코드를 터널설계 전분야에 적용하기 위하여 기준개정(EG12)을 추진하였으나 다른 유로코드(EC2 및 EC3)에 미치는 영향 등을 고려하여 불가피하게 구성하지 않는 것으로 결정되었다. 그러나 여전히 한계상태설계법을 터널설계에 적용하기 위한 연구를 활발히 진행하고 있다. 한계상태설계법은 가까운 장래에 터널을 포함한 토목구조물 설계법의 주류가 될 것이다. 그러므로 Eurocode 7 등 국외 한계상태설계법에 대한 충분한 이해가 중요하며, 국제적인 연구동향을 파악하고 터널설계에 적용하기 위한 연구가 필요하다. The representative Limit State Design(LSD) codes, AASHTO LRFD and Eurocodes, are widely being applied when designing civil structures. However, these codes are only applying tunnel lining design and segments design for shield tunnels. Recently in Europe, the Eurocode 7 committee was trying to create a research group called EG12, but they reluctantly decided not to create EG12 since it could have an impact on some of the other Eurocodes(including Eerocodes 2 and 3). Still there is an effort to continue researching LSD for tunnelling. LSD method will become the norm for the field of civil structural design in the near future. Therefore, it is important to fully understand Eurocode7:Geotechnical design in connection with Eurocode 2 and Eurocode 3. In addition, it is essential to follow international research trends and also to research for application to tunnelling.

Limit State Approach to Sizing and Design of Rectangular Footings

Limit state design was introduced into some standards in the early 1970s followed by expansion of limit state design into all our structural standards. With pad footings, limit state design is only applied to the structural design components such as thickness of the footing, size and distribution of reinforcement required to resist moments and shear forces. However, the size, ie. contact area of the footing required to transmit column loads is determined by working strength techniques whereby a predetermined allowable soil bearing pressureqa is used to transmit the applied permanent action (dead) loads(G) and superimposed action (live) loads (Q). There appears to be a contradiction in two different approaches applied concurrently in footing design. This article considers the application of limit state design method for determining size of rectangular pad footings.

Limit state approach to sizing and design of rectangular footings

Limit state design was introduced into some standards in the early 1970s followed by expansion of limit state design into all our structural standards. With pad footings, limit state design is only applied to the structural design components such as thickness of the footing, size and distribution of reinforcement required to resist moments and shear forces. However, the size, ie. contact area of the footing required to transmit column loads is determined by working strength techniques whereby a predetermined allowable soil bearing pressure qa is used to transmit the applied permanent action (dead) loads (G) and superimposed action (live) loads (Q). There appears to be a contradiction in two different approaches applied concurrently in footing design. This article considers the application of limit state design method for determining size of rectangular pad footings.

도로교설계기준 한계상태설계법을 적용한 RC슬래브교의 상대 안전도 평가

Seoil University(Received July 1, 2013 / Accepted September 22, 2013)Abstract : This paper is intended to provide the background information and justification for Korean highway bridge design code(limit state design)(2012). Limit state design method calculates reliability index and probability of failure through the analysis of the reliability of the experimental database. It has become possible to perform the economical and consistent design by evaluating the safety of a structure quantitatively. In this paper, we used the design specifications of RC slab bridge of superstructure form of Road Design Manual in Part 5 bridge built in highway bridge. This study conducted structural analysis using the method of frame structure theory, design and analysis of bridge by limit state design method, the design code including various standards and Load model applied Korean highway bridge design code limit state design(KHBDC;2012). As a result, it analyzed the effect of safety through comparison. Showing effect of improvement the safety factor and comparing the value of the result, it is determined to be capable of economical design and safety. Furthermore, limit state design method was able to determine many redundant force of cross-section compared with existing design method. It is determined that it can reduce the overall amount because of the reduction of the cross-section and girder depth.Key Words : Korean highway bridge design code, limit state design, road design manual, RC slab bridge, strength ratio

Based on the Reliability of Composite Pile Foundation Design Theory Research

Due to the physical properties of the soil between piles discrete，thus，composite pile foundation 's bearing capacity exists some uncertainty. So far, the study of the reliability of composite pile foundation is transform from the allowable stress method to the probability limit state design method. That is to say probability definite value design method. Therefor , determine the resistance subentry coefficient become the key of the design method. This paper introduces the significance of the subentry coefficient and the subentry coefficient of the composite pile foundation. Through the calculation of engineering examples, this article give the values of the subentry coefficient and provide a reference for the design of composite pile later.

정모멘트부 강합성거더의 공칭휨강도 재평가

이 논문에는 정모멘트를 받는 강합성거더의 공칭휨강도를 평가하기 위한 연구를 수록하였다. 한계상태설계법을 적용한 현행 도로교설계기준(2012)에 제시된 합성거더의 휨강도 규정은 국내에서 생산되는 일반구조용 강재를 사용한 합성거더에 적용할 수 있다. 고성능 강재 HSB600뿐만 아니라 HSB800를 적용한 강합성거더에 적용하기 위해서는 현행 공칭휨강도 평가식을 개선해야될 필요성이 있다. 강합성거더의 공칭휨강도를 평가하기 위하여, 기존에 수행된 연구들을 고찰하였으며 모멘트-곡률해석방법을 이용하여 다양한 단면을 갖는 강합성거더의 극한휨강도와 연성비를 평가하기 위한 변수해석을 수행하였다. 변수해석결과를 토대로 일반강재를 적용한 강합성거더에 대해 기존 평가식보다 덜 보수적인 공칭휨강도 평가식을 제안하였다. 또한 고성능 강재 HSB600과 HSB800을 적용한 강합성거더의 새로운 공칭휨강도 평가식도 함께 제안하였다. This paper presents a research work for the evaluation of the nominal flexural strength of composite girders in positive bending region. Current predicting equations for the nominal flexural strength of composite girders in the 2012 version of the Korea Bridge Design Codes based on Limit State Design Method are able to apply for the composite girders with conventional structural steels. For applying composite girders with high yield strength steels of HSB800 as well as HSB600, there is a need for improving the current predicting equations. In order to investigate the nominal flexural strength of composite girders, previous research works are carefully reviewed and parametric study using a moment-curvature analysis program is conducted to evaluate the ultimate moment capacity and the ductility of a wide range of composite girders. Based on the results of the parametric study, less conservative nominal flexural strength design equations are proposed for conventional composite girders. In addition, new design equations for predicting the nominal flexural strength of composite girders with HSB600 and HSB800 high-performance steels are provided.

How Eurocode 7 has affected geotechnical design: a review

Eurocode 7, the new European standard for geotechnical design, together with the other Eurocodes for structural design, was implemented in 2010, and relevant parts of British Standards that covered the same ground were withdrawn. Since it is a single code covering all aspects of the design of all types of geotechnical structure, including geotechnical investigations and the determination and selection of geotechnical parameters, and since it is based on the limit state design method with partial factors, its implementation has resulted in many changes to geotechnical design practice. These changes to geotechnical design caused by the introduction of Eurocode 7 are reviewed, including the new terminology, the new associated European investigation, testing and execution standards, the way geotechnical parameters are selected, the way geotechnical calculations are carried out and the way safety elements are introduced. Some of the issues that have arisen and difficulties that have been encountered with the introduction of Eurocode 7 are identified, and the plans for the future development of Eurocode 7 are discussed.

PHC 매입말뚝의 하중저항 설계정수 제안

ABSTRACT 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. Key words: PHC Pile, Bored Pile, Limit States Design Method, LRFD(Load and Resistance factored Design Method), Deign Reliability Index 본 논문은 토지주택연구원의 ‘말뚝기초의 설계법 선진화 및 시공법 다양화 연구’의 일부분을 정리한 내용입니다.1) 토지주택연구원, 수석연구원(주저자: jbpark@lh.or.kr)2) 토지주택연구원, 수석연구원(교신저자: parkyb@lh.or.kr)3) 토지주택연구원, 수석연구원