Search

Fatigue crack propagation tests are carried out on arc-shaped specimens prepared from MDPE gas pipes. Damage zone characterization is achieved using the diamond wafer sectioning technique from partially propagated and prematurely arrested cracks. Damage ahead of the crack-tip is used to assess a damage parameter and reliability based on statistical laws and subsequent use the PHIMECA Software. It is shown that a length and a width associated with a corresponding change in thickness at the fracture surface satisfactorily describe the damage zone size. The 3-parameter Weibull model gives the best reliability behavior and a critical lifetime of 82%. When considering separately both the Dugdale model and experimental damage zone measurements, it is possible to establish the evolution of the reliability index as a function of crack length. It is concluded that the reliability index approach based on damage provides a more consistent representation compared to analytical models. [ABSTRACT FROM AUTHOR]

Soil slope stability is an important concern for constructing any structure on a soil slope. As soil is heterogeneous in nature due to its formation process, soil slope stability analysis cannot be done without considering the variability in the properties of soil. To consider the variability in soil properties, the research approach has shifted towards a probabilistic approach. In this paper, two soft computing techniques i.e., Adaptive Network based Fuzzy Inference System (ANFIS) and Multivariate Adaptive Regression Spline (MARS), are used for reliability analysis of layered soil slope stability. As the soil slope stability mainly depends on three properties of soil i.e., unit weight (?), cohesion (c) and angle of shear resistance (?), these are taken as input variables for the models and factor of safety of slope was taken as output. The stability analysis is carried out using the Morgenstern-Price method. The models were accessed using statistical parameters like NS, RPD, RMSE, R2, PI, GPI. The results showed that although both models performed well, the model MARS outperformed the other. Therefore, MARS can be used as a reliable soft computing technique for analyzing soil slope stability. [ABSTRACT FROM AUTHOR]

Soil uncertainty plays a crucial role in the analysis and design of any geotechnical structure. Reliability based probabilistic method of analysis is particularly suitable to address the situation arising due to soil uncertainties. This paper presents a reliability based probabilistic method of analysis of a finite slope by considering the uncertainty in the cohesion and angle of internal friction of the soil. The reliability index (β) and its corresponding probability of failure (Pf) of the slope are determined using different methods namely Monte-Carlo simulation (MCS) method, First order second moment (FOSM) method and Subset simulation (SS) method. The reliability based probabilistic slope stability analysis has been developed and carried out in a MS-Excel spreadsheet. This spreadsheet mainly analyzes three different models i.e. deterministic model for calculating the factor of safety of the slope, uncertainty model for generating random samples of uncertain parameter of the soil and uncertainty propagation using subset simulation. The stability analysis is carried out using the ordinary method of slices. It is found that the SS method has shown better performance in terms of efficiency and accuracy as compared to the MCS method and FOSM method. Moreover, the study also demonstrate that the SS method can help in understanding the problem and can better assess the risk involved. [ABSTRACT FROM AUTHOR]

• In reliability disintegration, computing reliability index is still a challenge. In this research a impressive reliability algorithm is proposed. • The algorithm is a combination of the particle swarm optimization (PSO) and differential evolution (DE) algorithms. • The proposed algorithm (DEPSO) is implemented in ten numerical nonlinear examples. • This proposed algorithm is much easier than other optimization schemes. • Results illustrate that the proposed algorithm is effective and as simple as the several other methods but more robust and accurate. The accurate estimation of the health (reliability) index is important to estimate probability of failure in the reliability assessment of structures. The conventional first-order reliability methods including the Hasofer-Lind, Rackwitz-Fiessler, and Monte Carlo could lead to unstable, fluctuating, and distorted solutions to nonlinear problems, featuring complicated structural performance functions. The present study aimed to propose a new method by combining the particle swarm optimization and differential evolution algorithms in order to calculate the reliability index. The performance of the proposed method was evaluated by 10 examples from different studies, and the convergence results were compared to the results of studies such as Hasofer-Lind, Rackwitz-Fiessler, Monte Carlo and some other methods. To verify the accuracy of the proposed method, to verify the accuracy of the proposed method, a reliability index chart was applied. The comparisons indicated the high accuracy and speed of the proposed method. Accordingly, in higher order nonlinear problems, the proposed method successfully calculated the reliability index while some failed to solve these problems. [ABSTRACT FROM AUTHOR]

The effect of rice husk ash admixed with treated sisal fibre on properties of lateritic soil as a road construction material was studied. The natural soil falls under A-7-6(10) classification using the American Association of State Highway and Transportation Officials (AASHTO) classification and CL (Lean Clay) according to Unified Soil Classification System (USCS). Treatment of the soil was done with Rice Husk Ash (RHA) and treated Sisal Fibre (SF) in stepped concentrations of 0, 2, 4, 6, 8% and 0, 0.25, 0.5, 0.75, 1.0% by dry weight of soil, respectively. Preliminary test, compaction test (using British Standard light (BSL) energy) and unconfined compressive strength (UCS) test were carried out. Analysis of variance was carried out using Microsoft Excel Analysis Tool Pak Software Package. Mini-tab R15 Software was used for regression analysis. Laboratory results were used to generate reliability indices using a FORTRAN based first order reliability program. Outcome of the laboratory tests show that MDD decreased from 1.85 mg/m3 for the natural soil to 1.73 mg/m3 at 0% RHA/1% SF content. The OMC increased from 18% for the natural soil to 26.5% at 6% RHA/1% SF content. The UCS increased from 100.57 kN/m2 for the natural soil to 139.38 kN/m2 at 0% RHA/0.25%SF content by dry weight of soil. The increasing trend continued to 696.63 kN/m2 at optimum 6% RHA/0.75%SF content by dry weight of soil, which met the regulatory minimum UCS value of 687–1373 kN/m2 for pavement applications. Reliability indices varied for all the variables considered with MDD and OMC having more significant effect on the UCS. Based on the results obtained, an optimum blend of 6%RHA/0.75% SF content by dry weight of soil is recommended for used as sub-based material for lightly trafficked roads. [ABSTRACT FROM AUTHOR]

Copyright of Revista Ciência Agronômica is the property of Revista Ciencia Agronomica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Estimations of global solar radiation based on a model of using normalized clearness index and normalized sunshine duration for a period of up to 25 years (1985-2010) for Ikeja (06.39°N, 03.20°E), Enugu (06.280N, 07.350E), and Kano (12.03 N, 08.32E), Nigeria for each climatological stations were established. The monthly average total solar radiation was also estimated. The reliability index of the calculation varies from 2.4 to 2.6 percent. The overall results show that for Kano, the received radiation on the plane surface is higher than for Ikeja and Enugu. [ABSTRACT FROM AUTHOR]

Uncommon structural fire engineering designs must demonstrate adequate safety, in principle, through a balancing of the uncertain future costs and benefits of safety investments. In structural design for normal load conditions (‘ambient design’) this level of detail is commonly avoided through the application of reliability targets. In order to inform the development of reliability targets for structural fire design, the background of the ambient reliability targets is discussed. It is found that different common ambient reliability targets are broadly comparable when taking into account differences in assumptions and applications. As recent reliability targets have been informed by simplified cost-optimizations, the derivation of such a model is presented. The derivation allows identification of possible pitfalls when extending ambient reliability targets to structural fire design. It is concluded that ambient safety targets cannot readily be scaled as a function of the fire occurrence rate for application to structural fire engineering problems. The underlying cost-optimization model is, however, applicable as a concept. A number of issues requiring further attention are identified. [ABSTRACT FROM AUTHOR]

Most of the construction works carried out on masonry objects are associated with the strengthening of existing elements or assessment of their load capacity to additional load resulting from the change of use. In this situation, the proposed design solutions should always be part of a comprehensive design assessment taking into account the relevant inputs and including information on the actual material properties and the effects of interactions. The use of probabilistic design to evaluate masonry structures enables more economical approach to the issue of possible repairs and reinforcement than the commonly used method of partial factors. In the paper the normalized procedure of semi-probabilistic calculation of load capacity of masonry units and full probabilistic design, recommended in Eurocode 0 [1] are presented and compared. Because of the natural variability of the masonry structures, the information on its real mechanical properties should be obtained from in situ studies. Due to the lack of sufficient number of tests carried out on the masonry structures as well as unknown variation coefficients and distribution parameters, the analyses conducted in the article are limited to basic variables adopted for the probabilistic model based on experimental results described in the literature. The influence of each variable on the reliability index by providing sensitivity coefficients was determined. The basic element of masonry structures such as the lintel masonry was the subject of the analysis. [ABSTRACT FROM AUTHOR]

In recent years, the importance of assessment of structural reliability has increased significantly. This is confirmed by the recommendations of the standard PN-EN 1990 in which the rules and requirements to ensure safety, serviceability and durability of the structure are specified. It also sets out the basis for calculation and verification of constructions and provides guidance to ensure their reliability. Reliability design focuses on the ability to meet specific design requirements, taking into account the planned period of use. The concept of the planned period of use should be considered as the adopted in the project interval in which the structure or a part of the structure is to be used for its intended purpose without the need for general repairs. Typically, reliability is expressed in probabilistic metrics - using an index of reliability or probability of failure. Reliability of building structures depends on a number of correlated factors, mainly on the quality of materials, building precision and level of control, protection against environmental influences and maintenance level during exploitation, specific period of use, adopted solutions for the construction materials, design details and technologies, adopted loads (both their values and combinations), standard requirements regarding capacity, exploitation and durability, quality of computational models used in the design process and methods for assessing reliability of the structure. The performed reliability analysis concerns a reinforced concrete foundation, for which reliability index and probability of failure has been specified using the following methods: analytical method FORM, simulation methods FORM and SORM as well as Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

There has been considerable progress in reliabilitybased code development procedures. The load and resistance factors in the 2014 edition of the American Association of State Highway and Transportation Officials' AASHTO LRFD Bridge Design Specifications were determined using statistical parameters from the 1970s and early 1980s. Load and resistance factors were determined by first fixing the load factors and then calculating resistance factors. Load factors were selected so that the factored load corresponded to two standard deviations from the mean value, and the resistance factors were calculated so that the reliability index was close to the target value. However, from a theoretical point of view, the load and resistance factors should be determined as coordinates of the design point that corresponds to less than two standard deviations from the mean. Therefore, the optimum load and resistance factors are about 10% lower than those specified in the AASHTO LRFD specifications. The objective of this paper is to revisit the original calibration and recalculate the load and resistance factors as coordinates of the design point for the Strength I limit state. The analysis was performed for the same types of girder bridges--reinforced concrete T beams, prestressed concrete girders, and steel girders--as in the original calibration presented in the 1999 National Cooperative Highway Research report 368, Calibration of LRFD Bridge Design Code. The recommended new load and resistance factors provide consistent reliability and a rational safety margin. [ABSTRACT FROM AUTHOR]

This research article presents a methodology to identify the critical component of a centrifugal pump and analyze its reliability. Failure analysis of major components of the pump was done, risk priority number was calculated and critical component was identified. The critical component was considered to be composed of two sections. Its reliability was analyzed by mathematical modeling of the first section. A finite element model of the component was developed and stress analysis was done using finite element method, in order to assess the reliability index of the second section. Total reliability of the component was calculated by multiplying the two reliability indices. [ABSTRACT FROM AUTHOR]

Bridge structures are designed on lifetime, which is given in standards and relevant time of design. The design lifetime of bridge structures was 80 years according to expired Slovak standard STN. New design lifetime of the newly designed bridges extends to T d = 100 years by establishing Eurocode STN EN. In the frame of research activities of Department of Structures and Bridges, the theoretical approach for evaluation of existing bridge structures was developed taking into account Eurocodes. However, the problems occur in the case of elder bridges with real lifetime over 100 years, or in the case of remaining lifetime extension over 100 years. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Concrete made of recycled coarse aggregate (RCA) derived from multiple sources can have relative variation in mechanical properties compared with natural aggregate concrete (NAC), resulting in a lower reliability of a recycled aggregate concrete (RAC) beam than that of NAC beam. In this paper, a method is proposed to improve the reliability of beams made with RAC by increasing the reinforcement ratio. According to the equilibrium equations of beams subjected to bending moment, the increase in reinforcement ratio can be achieved by decreasing the RAC design strength. Same mean compressive strengths are assumed for RAC and NAC and four factors are considered including concrete grade, reinforcement grade, reinforcement ratio and the ratio of external loads in reliability analysis. Using NAC beams as a reference and keeping the target reliability index the same as that of RAC beams, the analysis results show that RAC design strength decreases with increase in coefficient of variation (CoV) of RAC compressive strength. When the CoV of RAC compressive strength is 20%, the RAC design strengths are 0.93 and 0.90 times of the NAC design strength with a 95% confidence level for grade C30 and C40 concrete, respectively. [ABSTRACT FROM AUTHOR]

This paper presents the settlement analysis of shallow foundations resting on granular soils within the framework of probability theory. Two probabilistic approaches of reliability analyses such as point estimation method (PEM) and first order second moment method (FOSM) along with the non-linear finite element analysis are used to evaluate the reliability index (β). The non-linearity of the soil is represented in the finite element model using the hyperbolic model. The hyperbolic parameters: the modulus number K, the exponent n, and the angle of internal friction φ are considered as random variables in the analysis. Numerical examples of strip and circular footings are presented to illustrate the practical applicability of the methods. The probability that the settlement at the centre of the footing may exceed a specified acceptable value is analysed. The results indicate that the random variable φ has a pronounced effect on the expected settlement as compared to the random variables K and n. [ABSTRACT FROM AUTHOR]

In the latest microelectronics industry, the emerging three-dimensional (3D) chip stacking technique using through silicon via (TSV) enables higher integration density that allows greater numbers of interconnections in order to fulfill the urgent requirements of dimensional downscaling and electrical speed enhancement. A high-density pitch of microbumps associated with the wafer-level underfill (WLUF) under a thermal compressions process are utilized to prevent the thermomechanical failures of the microbumps due to variations of thermal expansions of different materials in the 3D package. The use of dummy microbumps has been proposed to find the acceptable thin-layer uniformity and the reliable mechanical performances of the entire packaging structure. The warpage and strain behavior of packaging structure has been simulated by finite element analysis (FEA) and compared with experimental results. The responses were parametrically modeled using Kriging model with respect to compressive force, the thickness of the top chip, and the location of the dummy microbumps. The deterministic design guidance for warpage and strain has been obtained from the Kriging model. Furthermore, the reliability of the design under uncertainty has been investigated. A reliability-based design guidance (RBDG) has been proposed to provide a safety boundary in terms of the allowable reliability index. The proposed method can be utilized as the reliability standard for high-throughput production of 3D integrated circuits (ICs) packaging. [ABSTRACT FROM AUTHOR]

Structural safety and high reliability are most important requirements of aerospace product. Until recently, a design was considered to be robust if all the variables that affected its life had been taken into account and brought under control. So far designers have traditionally handled variability with safety factors. Some safety factors are derived from observation and analysis and in many cases it use to be pure guesswork. In those cases, the bigger the guess, the bigger the risk, the bigger the safety factor resulting in over design which is undesirable in case of aerospace product. In the present paper Latin Hypercube Sampling (LHS) based quasi random polar sampling technique is suggested for structural safety evaluation. The data generated from LHS are selected quasi-randomly to establish structural load & resistance dispersion and it has been used for safety evaluation. This technique is illustrated with a thin cylindrical pressure vessel, which is used extensively in aerospace applications. The proposed technique found to be simple and this technique will be useful to pressure vessel designer during initial design phase. [ABSTRACT FROM AUTHOR]

Abstract: The probability-based prediction and analysis of time-dependent survival probabilities and reliability indexes of non-deteriorating and deteriorating structural members exposed to extreme gravity and climate action effects are presented. A degradation function of reinforced concrete members under corrosion actions and sulphate attacks is discussed. The time-dependent safety margin of particular members as a random finite sequence of auto structural members is analyzed. Their time-dependent survival probability and reliability index values are expressed in simplified analytical manner. The merit of the method of transformed conditional probabilities based on more accurate conventional correlation factors is demonstrated by numerical examples. [Copyright &y& Elsevier]

Abstract: A simplification of probability based approaches on safety assessments and predictions of structural members is discussed. The modelling of time-dependent survival probabilities and reliability indexes of particular and single members is defined in a simple and easy perceptible manner using uniformed correlation factors of their conventional sequences. These factors of safety margin processes are analyzed and demonstrated by numerical example. [Copyright &y& Elsevier]

Abstract: In the frame of research activities of the Department of structures and bridges, the modified reliability levels for existing bridge evaluation were derived. These levels were used for determining the partial safety factors for materials. Moreover, the partial safety factors of steel and concrete were determined depending on the age of the bridge and on the remaining lifetime of the bridge. New modified reliability levels for evaluation of existing bridges affect also the partial safety factors of loads. In the paper, the modification of reliability levels recommended according to Eurocode for bridge members subjected to bending are presented. These adjusted reliability levels should be used for existing bridge evaluation. [Copyright &y& Elsevier]

Abstract: This study aims to find the difference between the slip surface having minimum factor of safety(called critical slip surface in deterministic analysis of slopes) and the slip surface having minimum reliability index(called critical reliability slip surface). The performance function used in reliability analysis was formulated by unbalanced thrust force method and the value of reliability index regarding given potential slip surface was obtained by Rosenbleuth method. The harmony search algorithm was adopted to alter the potential slip surface in order to locate the critical reliability slip surface. One complicated soil slope was analyzed and the results have shown that the critical slip surface is considerably different from critical reliability slip surface for multi-layer slopes and the reliability index of critical slip surface is larger than that of critical reliability slip surface. [Copyright &y& Elsevier]

In this paper an attempt is made to formulate time dependent reliability analysis of flanged reinforced concrete beam in limit state of deflection. Normal range of flanged beams designed for limit state of safety as per the guidelines of IS 456:2000 for typical range of dead load and live loads are considered for evaluating time dependent failure probabilities. The algorithm takes into account the concrete maturation, tension stiffening, time dependent shrinkage and creep effect, variability related to material properties, dimensions and loads. Deterministic deflection model given in IS code is used to get deflection samples by Monte Carlo simulation technique. Further it is shown that time dependent probabilistic analysis of the structure can be done conveniently from the deterministic time dependent analysis with lognormal probability model at every time instant. There is a good agreement with Monte Carlo simulation technique. The present study demonstrates that structural response in terms of deflection over a given life time is directly related to design criteria used by structural engineer. [ABSTRACT FROM AUTHOR]

Among the various modes of failure of reinforced concrete (RC) cantilever retaining walls, the sliding mode of failure is invariably seen to be the critical mode governing the proportions of the wall. Traditionally, a constant factor of safety (usually 1.5) is adopted in the design of cantilever retaining walls against sliding and overturning instability, regardless of the actual uncertainties in the various design variables. This paper presents the stability analysis of cantilever retaining walls, accounting for uncertainties in the design variables in the framework of probability theory. The first order reliability method (FORM), second order reliability method (SORM) and Monte Carlo simulation (MCS) method are used as alternative ways to evaluate the probability of failure associated with the sliding failure of retaining walls of various heights (ranging from 4 to 8 m). Sensitivity analysis has shown that the angle of internal friction (φ) and the coefficient of friction below the concrete base slab (μ) are the most sensitive random variables. It is shown that cantilever retaining walls, optimally proportioned to achieve a factor of safety of 1.5 against sliding failure, can have significant variations in the reliability index (or probability of failure). In order to achieve consistently a 'target' reliability index (β = 2.5 or 3.0), the factor of safety must be appropriately chosen, accounting for uncertainties, especially with regard to φ and μ. In this paper, easy-to-use design tables have been developed for this purpose. [ABSTRACT FROM AUTHOR]

Computation of the structural reliability index is one of the important factors in structural reliability theory. First-order second-moment algorithm often behaves discretely when the limit state surface is highly nonlinear. So rotation gradient algorithm is presented for computing the structural reliability. The method is based on Hasofer-Lind Rackwitz-Fiessler (HL-RF) algorithm, whose direction vector is determined by the linear combination of the negative gradient direction and former iteration direction vector. The numerical results show that the rotation gradient algorithm possesses the advantages of simplified iteration format and high convergence robust. The algorithm can ensure convergence and stability even the limit state surface is highly nonlinear. [ABSTRACT FROM AUTHOR]

Reliability indices of reinforced concrete flange beams with respect to limit state of deflection designed as per the provisions of IS 456:2000 are found to be non-uniform. Through this paper, an attempt has been made to propose an empirical expression for reliability index of a flanged RC beam in limit state of deflection. This equation will be useful in deciding depth of member for a given span, load with target reliability index in limit state of deflection and also to obtain an estimate of reliability index of the designed RC beam. [ABSTRACT FROM AUTHOR]

Based on the shear strength parameters, the relationship and difference between the two assessment methods (the safety factor method and the reliability index method) for slope stability analysis are investigated. A more accurate calculation formula of the safety factor for homogeneous soil slope with and without the resisting part of circle surface failure is established using analytical method. The effect of resisting soil is regarded as reducing of driving moment. The ratio of the coherence to unit weight is considered to be the only random variable, labeled by Hc. The relationships among the safety factor, the shear strength parameters and failure probability or reliability index are studied in the condition of different distribution and variation mean values or variation coefficients of Hc for different models of purely cohesive slopes. The results reveal that the traditional safety factor method may give unreasonable evaluations, especially for the practical slope project with strong variability of parameters; the calculation value of failure probability (or reliability index) and the position of the cross point in failure probability-safety factor (or reliability-safety factor) curve are strongly influenced by the mean or variability of Hc with normal or log-normal distribution. [ABSTRACT FROM AUTHOR]

Copyright of Baltic Journal of Road & Bridge Engineering (Baltic Journal of Road & Bridge Engineering) is the property of Baltic Journal of Road & Bridge Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)