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1.
Toshiaki Nanazawa Tetsuya Kouno Gaku Sakashita Kazunori Oshiro 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2019,13(3):166-175
ABSTRACTThis paper shows the development of a partial factor design method on the bearing capacity of pile foundations for Japanese Specifications for Highway Bridges. Firstly, estimation design equations on the bearing capacities of pile foundations are improved by analysis of pile load test results and uncertainties in the bearing capacities are evaluated. Secondly, the reliabilities of pile foundations designed by the former specifications are evaluated based on reliability analysis considering the uncertainties in the bearing capacities and coefficients of subgrade reaction. Finally, a partial factor design method is developed based on the target reliability index obtained based on the conventional pile installation method by the pile installation methods. The factors are different for each pile installation method. 相似文献
2.
针对特定场地下土工构筑物的正常使用极限状态,采用近年发展的几何可靠性方法计算了多种构筑物的可靠度指标。考虑同一场地下的钻孔灌注桩、抗浮锚杆和CFG桩单桩加载变形测试曲线的离散性,各曲线回归参数呈现差异并可作为随机变量,进而探讨了各曲线回归参数间的相关性及联合分布特性。基于这些回归参数的联合发散概率密度等值线,即随机变量刚好达到极限承载能力状态,该几何可靠性算法可在随机变量的原始空间求得土工构筑物的可靠度指标。通过比对该几何可靠度指标与常规的一次可靠性算法成果,验证了该几何可靠性计算技术的可行性。计算表明,几何可靠性评价模型实施简便,易于被工程技术人员接受。 相似文献
3.
Design charts that enable quick determination of the probability distribution parameters related to the ultimate bearing capacity of shallow foundations resting on (c = 0) soils are developed. These charts are intended to assist foundation designers and analysts in studying the reliability of structures as related to the capacity of the foundation system. The approach presented herein provides a more reliable alternative to foundation design and analysis than the current conventional design procedure which employs the assumption of an appropriate factor-of-safety. © Rapid Science Ltd. 1998 相似文献
4.
Sara Khoshnevisan Lei Wang C. Hsein Juang 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2016,10(2):121-134
This paper provides a simplified procedure for reliability-based robust geotechnical design (RGD) using spreadsheet. In the RGD methodology, design robustness is achieved by adjusting “design parameters” without reducing the uncertainties in noise factors. This design approach generally involves a multi-objective optimisation, which is computationally challenging. To improve the efficiency of the RGD methodology, the design robustness is evaluated in terms of sensitivity index and the safety requirement is evaluated using mean value first order second moment (MFOSM). To ease the concern that the reliability index obtained with MFOSM may not be sufficiently accurate, a mapping function that relates MFOSM to a more accurate method such as first order reliability method is introduced. To further improve the efficiency of the proposed simplified RGD method, a new simplified procedure along with a more accurate robustness measure is developed that eliminates the need for multi-objective optimisation. With these modifications, the proposed simplified RGD method can efficiently be implemented in a single Excel spreadsheet. The proposed simplified method, which goes beyond any existing reliability-based RGD methods in terms of ease of use and computational efficiency, is illustrated in this paper with an example of robust design of drilled shaft in clay. 相似文献
5.
Eurocode 7, the new European standard for geotechnical design, is based on the limit state design method, with partial factors and characteristic parameter values. An objective of the Eurocodes is that the chosen partial factors should achieve reliability levels for a structure close to a prescribed target value. The target ultimate limit state reliability index for a medium risk structure for 50 years is 3.8. This paper examines the reliability of an inclined-eccentrically and vertically loaded square foundation designed using all three Design Approaches in Eurocode 7 with the recommended partial factor values given in EN1997-1. The reliabilities obtained using the three Design Approaches are compared with the target reliability value and the reliabilities of traditional designs using overall factors of safety. The paper provides evidence that Eurocode 7 gives more consistent reliabilities for a greater range of parameter values than the traditional allowable stress method and demonstrates the importance of selecting appropriate characteristic values. 相似文献
6.
The first order reliability method (FORM) is efficient, but it has limited accuracy; the second order reliability method (SORM) provides greater accuracy, but with additional computational effort. In this study, a new method which integrates two quasi-Newton approximation algorithms is proposed to efficiently estimate the second order reliability of geotechnical problems with reasonable accuracy. In particular, the Hasofer–Lind–Rackwitz–Fiessler–Broyden–Fletcher–Goldfarb–Shanno (HLRF–BFGS) algorithm is applied to identify the design point on the limit state function (LSF), and consequently to compute the first order reliability index; whereas the Symmetric Rank-one (SR1) algorithm is nested within the HLRF–BFGS algorithm to compute good approximations, yet with a reduced computational effort, of the Hessian matrix required to compute second order reliabilities. Three typical geotechnical problems are employed to demonstrate the ability of the suggested procedure, and advantages of the proposed approach with respect to conventional alternatives are discussed. Results show that the proposed method is able to achieve the accuracy of conventional SORM, but with a reduced computational cost that is equal to the computational cost of HLRF–BFGS-based FORM. 相似文献
7.
A practical and efficient approach of implementing second‐order reliability method (SORM) is presented and illustrated for cases related to foundation engineering involving explicit and implicit limit state functions. The proposed SORM procedure is based on an approximating paraboloid fitted to the limit state surface in the neighborhood of the design point and can be easily carried out in a spreadsheet. Complex mathematical operations are relegated to relatively simple user‐created functions. The failure probability is calculated automatically based on the reliability index and principal curvatures of the limit state surface using established closed‐form SORM formulas. Four common foundation engineering examples are analyzed using the proposed method and discussed: immediate settlement of a flexible rectangular foundation, bearing capacity of a shallow footing, axial capacity of a vertical single pile, and deflection of a pile under lateral load. Comparisons with Monte Carlo simulations are made. In the case of the laterally loaded pile, the friction angle of the soil is represented as a one‐dimensional random field, and pile deflections are computed based on finite element analysis on a stand‐alone computer package. The implicit limit state function is approximated via the response surface method using two quadratic models. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
8.
The evaluation of variability in ultimate pile capacity from the load-settlement data is useful in the context of code calibration and reliability based design in pile foundations. This paper examines the applicability of two non-linear analytical methods to calculate the load-settlement response of piles using actual test data in terms of percentage deviation from the measured capacity. The degree of agreement associated with each method with respect to field test data is quantified using two different failure criteria (FHWA and Eurocode) for determination of the ultimate load of pile. The analytical methods are used to quantify the variability associated with the soil-pile interface parameters and ultimate capacity using Monte Carlo simulations, which is useful in load-resistance factored/reliability design of pile foundations. Study reveals that variability depends on the method of analysis, percent deviation of prediction from measured values and failure criteria. 相似文献
9.
Excavation projects related to urban redevelopment and infrastructure improvement are often governed by serviceability-based design, rather than failure prevention criteria. Deformation tolerance specifications are often prescribed based on minimizing potential damage to adjacent structures. A risk-based approach to serviceability performance that systematically incorporates design parameter uncertainty will allow engineers to address soil uncertainty in performance-based design. This paper demonstrates the use of various kinds of reliability methods, such as response surface method (RSM), first-order reliability method (FORM), second-order reliability method (SORM), adaptive importance sampling (AIS), Monte Carlo simulation (MCS) and system reliability, to assess the risk of stability and/or serviceability failure of an entire excavation support system throughout the entire construction process. By considering multiple failure modes (including serviceability criteria) of an excavation, the component and system reliability indices for each excavation step are assessed during the entire excavation process. Sensitivity analyses are conducted for the system reliability calculations, which demonstrate that the adjacent structure damage potential limit state function is the dominant factor for determining excavation system reliability. An example is presented to show how the serviceability performance for braced excavation problems can be assessed based on the system reliability index. 相似文献
10.
根据朗金土压力公式,以常规设计为基础,建立了分步开挖、无粘性土时主动土压力荷载增加的极限状态方程:采用可靠度分析的AFOSM法,分析了分步开挖时土压力计算中应注意的问题。并分析研究了土性参数对土压力计算可靠性的影响,最后得出了四点结论。 相似文献
11.
A new computing method is proposed for reliable analysis. The limit state function is implicit and nonlinear in reliability analysis of slopes and is difficult to apply by traditional reliability methods, especially in large‐scale project applications. Relevance vector machines (RVMs) are capable of approximating the limit state function without the need for additional assumptions regarding the function form, as opposed to traditional polynomial response surfaces. RVMs were adapted to obtain the limit state function. We propose an RVM‐based response surface method combined with the first‐order reliability method for slope reliability analysis and describe its step‐by‐step implementation. The reliability index obtained from the proposed method shows excellent agreement with traditional response surface method results. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
12.
13.
CFG桩复合地基承载力可靠度分析 总被引：8，自引：1，他引：7
利用可靠度理论对从国内收集到的25组CFG桩复合地基承载力试验数据进行了概率统计处理。借助无量纲计算模式,计算不同载荷组合下CFG桩复合地基承载力的可靠度指标,并分析了各随机变量对可靠度指标的影响程度。为评价常
用经验公式 的可靠性提供一定的参考。 相似文献
14.
Ahmad Shlash Alawneh Osama K. Nusier Ahmed Abdul-Ezel Al-Mufty 《Geotechnical and Geological Engineering》2006,24(3):637-660
A reliability based method was used to design and analyse shallow foundations using first-order Taylor series approximation.
The computer program Mathcad was used to facilitate all mathematical and computional efforts. This method is an effective
tool to assist the foundation designers and analyists to investigate how reliable their designs or analyses are in relation
to the ultimate bearing capacity of the foundations. The approach presented in this paper provides a reliable alternative
for design and analysis of shallow foundations, rather than the conventional design methods, which employs the assumptions
of a specified saftey factor. Several examples were presented for design and analysis of strip footings embedded in sandy
soil, and rectangular and square footings analysis embedded in clayey soils. The program input and output of each example
are also presented and discussed. 相似文献
15.
The resistance factor for pile foundations in load and resistance factor design (LRFD) is traditionally calibrated considering target reliability index (βT) and statistics of load and resistance bias factors. However, the resistance bias factor is hard to quantify statistically. Consequently, the design obtained using the calibrated resistance factor can still miss βT if the variation in resistance bias factor has been underestimated. In this paper, we propose a new resistance factor calibration approach to address this dilemma by considering “feasibility robustness” of design in the calibration process. Herein, the feasibility robustness is defined as a probability that the βT requirement can still be satisfied even in the presence of uncertainty or variation in the computed bearing capacity. For illustration, LRFD approach for pile foundations commonly used in Shanghai, China is examined. Emphasis is placed on re-calibration of resistance factors at various feasibility robustness levels, with due consideration of the variation in the resistance bias factor. A case study is presented to illustrate the use of the re-calibrated resistance factors. The results show that the feasibility robustness is gained at the expense of cost efficiency; in other words, the two objectives are conflicting. To aid in the design decision-making, an optimal feasibility robustness level and corresponding resistance factors are suggested in the absence of a designer’s preference. 相似文献
16.
可靠度分析中梯度求解方法的研究 总被引：2，自引：0，他引：2
在岩土工程的可靠度分析中，功能函数的形式非常复杂，甚至是隐式的。而对于常用的可靠度分析方法，如一阶可靠性方法（FORM）、二阶可靠性方法（SORM）等，一个重要的问题是求功能函数对基本随机变量的梯度。因此，对于隐式的或复杂的显式功能函数，必须采用数值微分方法来求解功能函数的梯度。对于可靠度分析中常用的有限差分法（FDM）及有理多项式法（RPT）这两种数值微分方法，本文详细研究了二者问的异同及其求导结果与步长的关系，指出了对于相同的步长控制系数及取样方式，FDM是RPT在线性情况下的特例；对于连续的线性功能函数，可直接用3点FDM求导：对于连续的非线性功能函数，可用5点RPT求导；对于非连续的功能函数，应采用RPT求导。建议取步长控制系数等于1。 相似文献
17.
This paper develops a multiple response surfaces approach to approximate the limit state function for slope failure by second‐order polynomial functions, to incorporate the variation of the most probable slip surfaces, and to evaluate the slope failure probability pf. The proposed methodology was illustrated through a cohesive soil slope example. It is shown that the pf values estimated from multiple response surfaces agree well with those pf values that have been obtained by searching a large number of potential slip surfaces in each Monte Carlo simulation (MCS) sample. The variation of number of the most probable slip surfaces is studied at different scale of fluctuation (λ) values. It is found that when full correlation assumed for each of random fields (i.e., spatial variability is ignored), the number of the most probable slip surfaces is equal to the number of random fields (in this study, it is 3). When the spatial variability grows significantly, the number of the most probable slip surfaces or number of multiple response surfaces firstly increases evidently to a higher value and then varies slightly. In addition, the contribution of a specific most probable slip surface varies dramatically at different spatial variability level, and therefore, the variation of the most probable slip surfaces should be accounted for in the reliability analysis. The multiple response surfaces approach developed in this paper provides a limit equilibrium method and MCS‐based means to incorporate such a variation of the most probable slip surfaces in slope reliability analysis. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
18.
提出了基于支持向量机（SVM）的边坡可靠度分析新算法。该方法采用均匀设计确定样本点,通过一定数量的确定性计算来训练SVM,拟合边坡的功能函数;采用一阶可靠度方法（FORM）和迭代算法优化SVM模型,获得可靠度指标和验算点信息;在SVM模型基础上进一步通过二阶可靠度方法（SORM）和蒙特卡罗模拟（MCS）计算边坡的失稳概率。以两个典型边坡为例,通过与其他方法比较,证明了该方法的准确性和高效性。结果表明：提出的在标准正态空间（U空间）中取样并构建SVM,在原始空间（X空间）中计算功能函数的算法,有效地解决了具有相关非正态分布变量的可靠度分析问题,并且可很容易扩展到SORM的计算。算例结果证明,该方法的精度高于FORM;而效率优于MCS。分析过程中,边坡安全系数计算和可靠度分析相互独立。因此,该方法既适用于具有显式功能函数的简单问题,也适用于需要软件计算安全系数的实际边坡问题。 相似文献
19.
A method based on the linearization of the limit state functions (LSFs) is applied to evaluate the reliability of series geotechnical systems. The approach only needs information provided by first order reliability method (FORM) results: the vector of reliability indices, β, of the LSFs composing the system; and their correlation matrix, R. Two common geotechnical problems—the stability of a slope in layered soil and a circular tunnel in rock—are employed to demonstrate the simplicity, accuracy and efficiency of the suggested procedure, and advantages of the linearization approach with respect to alternative computational tools are discussed. It is also found that, if necessary, the second order reliability method (SORM)—that approximates the true LSF better than FORM—can be employed to compute better estimations of the system’s reliability. 相似文献
20.
This paper presents a practical procedure for assessing the system reliability of a rock tunnel. Three failure modes, namely, inadequate support capacity, excessive tunnel convergence, and insufficient rockbolt length, are considered and investigated using a deterministic model of ground-support interaction analysis based on the convergence–confinement method (CCM). The failure probability of each failure mode is evaluated from the first-order reliability method (FORM) and the response surface method (RSM) via an iterative procedure. The system failure probability bounds are estimated using the bimodal bounds approach suggested by Ditlevsen (1979), based on the reliability index and design point inferred from the FORM. The proposed approach is illustrated with an example of a circular rock tunnel. The computed system failure probability bounds compare favorably with those generated from Monte Carlo simulations. The results show that the relative importance of different failure modes to the system reliability of the tunnel mainly depends on the timing of support installation relative to the advancing tunnel face. It is also shown that reliability indices based on the second-order reliability method (SORM) can be used to achieve more accurate bounds on the system failure probability for nonlinear limit state surfaces. The system reliability-based design for shotcrete thickness is also demonstrated. 相似文献