Papers by Keyword: Failure Probability

Abstract: The properties and the performance of Thermally Stable Diamond Composite (TSDC) directly affect the applications of TSDC in engineering. The failure risk of the TSDC cutting tips during a cutting process is affected by many factors, including the Depth of Cut (DOC) of the pick with the TSDC tip. The DOC is an important indicator in mining and construction industries because it directly affects productivity and pick failures. In existing studies, DOC is usually treated as a deterministic variable. However, due to the drum vibration during a cutting process, the DOC during production often varies randomly around its nominal value. This study investigates the influence of the randomly varied DOC on the performance and failure characteristics of TSDC tipped rock cutting picks, in combination with random resultant angle. Monte Carlo simulation method is applied. It is found that the variation in DOC can have considerable influence on the failure characteristics of the TSDC cutting tips, although this influence is affected by the resultant angle and attack angle. This characteristic is important for optimising the design and application of the TSDC tipped picks.

Abstract: This paper deals with the study of stochastic parameters of external loads, which are used in the tasks of determining the level of reliability of steel storage capacities. To describe the random load process, the normal law and the double exponential distribution of Gumbel were used. It was formulated the technique of transition from the study of the entire random process to the consideration of its maximums. It was obtained quantitative values of the stochastic characteristics of snow and wind loads on the territory of Ukraine, without reference to the zoning maps. A general procedure for determining the probability of failure was formulated, depending from a given characteristic maximum. This index corresponds to the basic level of load. The average intersection of this level by a random load process is equal to one. Analytical formulas are obtained to determine the scale and position of the double exponential distribution of Gumbel, which depend on the characteristic maximum, as well as formulas, which help to calculate the statistical characteristics (standard, expected value and coefficient of variation) of the random value of the load maximums. The possibility of using this approach is theoretically confirmed when the density distribution of the ordinate of a random process follows the normal law. It was proposed expressions for the parameters of the distribution maximums of the random processes, which are described by the polynomial exponent and the Weibull law.

Abstract: Thermally Stable Diamond Composite (TSDC) tips have attracted a great attention of rock cutting industry due to the higher thermal stability and high wear resistance of TSDC. To make the TSDC tipped picks practical for real application, it is important to understand the failure behavior of the TSDC tips for rock cutting. One of the failure characters of TSDC tips is random failures. In this paper, a method is proposed to calculate the failure probability of TSDC tips for cutting individual rock segments. This method enables to link the segment length to the failure probability of the tip for cutting the segment. A numerical case study is presented to validate the method. The method can effectively reduce the impact of the number of segments on failure probability estimation accuracy.

Abstract: This study investigated optimum design methods for frame buildings with focus on minimization of economic costs. The methods discussed are intended to provide sufficient reserves for reliability of load-bearing steel structures. The analyzed mathematical models enable to assess seismic resistance of a structure and implement optimum design methods according to the selected key criterion. The available mathematical models assessing economic efficiency of metalwork reinforcement need further development. The model based on the principle of balanced risk is considered as the most appropriate for the study of structural reliability for industrial buildings. This model allows to assess the expected damage as compared with the initial spending on seismic protection. The focus is on setting and implementation of the task whose limiting condition provides equality between expenditures for reinforcement of damaged steel structures and those for damage prevention activities. Minimum of economic costs for construction or reconstruction of a structure is taken as the optimality criterion. This takes into account accumulation of damages within the standard life cycle and changes in stiffness of materials. Assessment of damage risk is based on the life cycle of a structure, its seismic resistance class and spending on damage repair. The study suggests a number of structural solutions that enable to reduce deformation of steel parts of the frame.

Abstract: In the paper small-sample double-loop optimization method is employed to find selected design parameters of a single-span post-tensioned composite bridge to ensure its reliability and load-bearing capacity. The selected approach consists in nesting the computation of the failure probability with respect to the current design within the optimization loop. The analyzed bridge is made of precast post-tensioned concrete girders, each composed of six segments that are connected by the transverse joints. Bridge spatial deterioration brings uncertainty into actual values of concrete strength in transversal joints and of actual loss of pre-stressing. Due to their significant effect on the bridge load-bearing capacity, both were considered as uncertain design parameters with the aim to find their critical values corresponding to desired reliability level and load-bearing capacity.

Abstract: The evaluation of existing bridge structures is the most important process in the global Bridge Management System (BMS) because of providing the basic information about existing bridges required from the viewpoint of decision making process related to the optimal bridge maintenance and rehabilitation strategy. The theoretical approach using conditional probability and the positive effect of the inspection was developed. The new information concerning the actual structure condition is used in this mathematical model. This information is not available in the process of the new structure design [1]. The work is focused on structures subjected to bending [2]. The reinforced concrete beam elements with or without degradation were investigated. The corrosion of reinforcement bars was used as material degradation. The biggest effect of the inspection was obtained for members, which do not degrade. Hereby, the negative effect of degradation on reliability index is also demonstrated.

Abstract: During the process of being used, engineering structures will undergo material aging and structural damage with time passing by under the combined influence of internal factors including load, environment and structural material[1], and accumulation of such damages will cause decrease of bearing capacity, durability and reliability. Among various factors influencing the reliability of in-service structures, ultimate bearing capacity plays the decisive role in safety. In this paper, the fourth-order moment of limit state function is inferred through calculation of failure probability of in-service structures, and thus safety and durability of in-service structures can be ensured.

Abstract: The paper deals with the problems of ceramic head of hip joint endoprosthesis destructions, and with assessing the impact of shape deviations of conical surfaces on the tensile stress under ISO 7206-5 loading. The failure of the hip joint endoprosthesis ceramic head has always traumatic consequences for the patient, since a part of or even the whole endoprosthesis has to be reoperated. Hence, it is desired to reduce the number of implant re-operations to the minimum. Therefore the computational modelling of the stress of the head was realised. The shape deviations of the ideal contact cone areas of the head and stem are parameters that significantly influence the tensile stress in the head and its reliability. The assumed shape deviations of the head’s and stem’s cones are macro shape deviations (different cone taper) and micro shape deviations (unevennes) measured using the IMS-UMPIRE equipment. The stress state in the ceramic heads was solved using the FEM and head’s failure probability is based on the Weibull weakest link theory [4, 5 and 9].

Abstract: This paper introduces a new method, named E-Bayesian estimation method, to estimate failure probability. In the case of zero-failure data, the definition of E-Bayesian estimation of failure probability is provided; moreover, the formulas of E-Bayesian estimation and hierarchical Bayesian estimation and the property of E-Bayesian estimation of the failure probability are also provided. For the estimate failure probability, in the following sections we will see simple the E-Bayesian estimation method is method than hierarchical Bayesian estimation method. Finally, the calculated results of bearing show that the proposed method is feasible and convenient in engineering application.

Abstract: The landslide disaster tends to cause safe hidden trouble to the normal operation of the pipeline and pipeline is likely to take place accident and get failed under the action of a landslide. According to the theory of winkler, in the condition of pipeline landslide, the mechanical model is established and calculated the stress distribution under different landslide scale. According to the calculation result, the dangerous section of pipe is obtained. Based on the pipeline's own strength and pipeline working stress in the landslide, the limit state equation of the pipes is set up by using the third strength theory. Finally according to the distribution of stress and strength, the pipeline reliability index and failure probability are obtained by means of the first order second moment method improved. The achievement of this paper has great value .to the buried gas pipeline risk assessment. Key words: landslides; The third strength theory; The first order second moment method; Reliability index; Failure probability