Structural reliability analysis using response surface method with improved genetic algorithm

For the conventional computational methods for structural reliability analysis, the common limitations are long computational time, large number of iteration and low accuracy. Thus, a new novel method for structural reliability analysis has been proposed in this paper based on response surface method incorporated with an improved genetic algorithm. The genetic algorithm is first improved from the conventional genetic algorithm. Then, it is used to produce the response surface and the structural reliability is finally computed using the proposed method. The proposed method can be used to compute structural reliability easily whether the limit state function is explicit or implicit. It has been verified by two practical engineering cases that the algorithm is simple, robust, high accuracy and fast computation

Application of gamma process and maintenance cost for fatigue damage of wind turbine blade

The blades of offshore wind turbines accumulate structural damage such as fatigue due to aerodynamic loading by various wind speeds during their service time, leading to premature structural failures. This paper investigates the fatigue damage by the blade element momentum theory (BEMT) method and the cost of operation and maintenance by the integrating models. Three prediction models have been proposed for lifetime performance assessment and management of wind turbine blade, i.e. fatigue prediction model (FPM), the reliable stochastic model (SRM) and cost benefit model (CBM). The fatigue model is discussed to reproduce the fatigue damage evolution in composite blades subjected to aerodynamic loadings by cyclical winds. The lifetime probability of fatigue failure of the composite blades is estimated by stochastic deterioration modelling such as gamma process. On the basis of the cost model, an optimised maintenance policy is determined to make optimal maintenance decision for the composite blades. A numerical example is employed to investigate the effectiveness of predicting fatigue damage and estimating the probability of fatigue failure to determine an opportunistic maintenance policy. The results from the numerical study show that the stochastic gamma process together with the fatigue models can provide a useful tool for remaining useful life predictions and optimum maintenance strategies of the composite blades of offshore wind turbines

Substructural identification with incomplete measurement for structural damage assessment

Ph.DDOCTOR OF PHILOSOPH

Education in the Field of Forensic Engineering

The profession of forensic engineering has been used in investigations for causes of failure in various engineering cases and used when engineers require to give testimony in judicial proceedings. Forensic engineering has become a field of professional practice of its own; criteria and procedural methods have been proposed in the United States, UK and Europe. Many professionals and engineering institutions have venture in this field and set basic principles to establish a platform for going forward. This paper will cover the topics in design-construction process, design codes and standards, construction safety codes, standards and regulations, the first steps after failure, legal concerns after a failure, standard of care and case studies. It is hoped that the paper will enlighten the scope and details of the forensic engineering discipline which can be used as a tool for a failure knowledge base for engineering education and learning outcomes

Time series analysis for vibration-based structural health monitoring: A review

Structural health monitoring (SHM) is a vast, interdisciplinary research field whose literature spans several decades with focusing on condition assessment of different types of structures including aerospace, mechanical and civil structures. The need for quantitative global damage detection methods that can be applied to complex structures has led to vibration-based inspection. Statistical time series methods for SHM form an important and rapidly evolving category within the broader vibration-based methods. In the literature on the structural damage detection, many time series-based methods have been proposed. When a considered time series model approximates the vibration response of a structure and model coefficients or residual error are obtained, any deviations in these coefficients or residual error can be inferred as an indication of a change or damage in the structure. Depending on the technique employed, various damage sensitive features have been proposed to capture the deviations. This paper reviews the application of time series analysis for SHM. The different types of time series analysis are described, and the basic principles are explained in detail. Then, the literature is reviewed based on how a damage sensitive feature is formed. In addition, some investigations that have attempted to modify and/or combine time series analysis with other approaches for better damage identification are presented

Time-domain multi-state Markov Model for engine system reliability analysis

A novel reliability-based approach has been developed for multi-state engine systems. Firstly, the output power of the engine is discretized and modeled as a discrete-state continuous-time Markov random process. Secondly, the multi-state Markov model is established. According to the observed data, the transition intensity is determined. Thirdly, the proposed method is extended to compute the forced outage rate and the expected engine capacity deficiency based on time response. The proposed method can therefore be used for forecasting and monitoring the reliability of the multi-state engine utilizing time-domain response data. It is illustrated that the proposed method is practicable, feasible and gives reasonable prediction which conforms to the engineering practice

Structural dynamic reliability evaluation under consideration of fuzzy strength and fuzzy stress

A new dynamic reliability analysis under repeated or multiple series fuzzy loads and fuzzy strength is proposed in this paper. The proposed prediction models of structural dynamic fuzzy reliability with and without strength degeneration are established by using fuzzy theory and stress-strength interference theory. The fuzzy reliability is converted to probability reliability. The results have shown that the proposed model is feasible and practicable

Static and seismic responses of eco-friendly buried concrete pipes with various dosages of fly ash

In this paper, an evaluation based on the detailed failure has been conducted for underground sewage Geopolymer concrete (GPC) pipes under static and seismic loadings with consideration of the optimal time steps in the time-dependent process related to nonlinear behavior of GPC pipes in static and dynamic analyses. The ANSYS platform is employed for improving an advanced FE model for a GPC pipe which can simulate the performance of underground GPC pipes containing various percentages of fly ash (FA) as a Portland cement (PC) replacement. Subsequently, the time-dependent model is used to assess the efficacy of this concrete admixture (FA) in the structural response of the unreinforced GPC pipe in FEM. Indeed, the generated GPC pipe with the three-dimensional model has the potential to capture the nonlinear behavior of concrete which depicts the patterns of tensile cracking and compressive crushing that occur over the applied static loads in the FE model. The main issue in this paper is the assessment of the GPC pipe response typically based on the displacement due to static and seismic loadings. The numerical results demonstrated that the optimal displacement was obtained when the structural response had typically the lowest value for GPC pipes containing 10–30% FA and 20% FA under static and seismic loadings, respectively. Indeed, a reduction by 25% for the vertical displacement of a GPC pipe containing 20% FA was observed compared to that without FA under time-history analysis

Low velocity impact behaviour of sandwich composite structures with e-glass/epoxy facesheets and PVC foam

This study presents the impact behaviour of marine sandwich composite beam structures that manufactured by vacuum-assisted resin infusion process (VARIM). The sandwich composite consists of different thicknesses of upper and lower E-glass fibre-reinforced polymer as facesheets and PVC foam as core material. Low velocity impact tests have been conducted to understand the impact response of the sandwich composite by using a drop-weight impact machine with a hemispherical impactor. Square samples with 100 mm X 100 mm side dimensions were subjected to impact machine at five energy levels of 20J, 40J, 60J, 80J and 100J. The impact loadings have been applied to thicker facesheet of the sandwich composite to obtain impact parameters experimentally. Damage type on thicker facesheets and internal parts of PVC foam have been characterized through the contact force - time, contact force - displacement and contact force - energy curves after the tests. Impact failures that occurred on the upper facesheets, core and lower facesheets of the specimens were observed

A new computational method for structural reliability with Big Data

A new computational method for structural reliability based on big data is proposed in this paper. Firstly, the big data is collected via structural monitoring and is analyzed. The big data is then classified into different groups according to the regularities of distribution of the data. In this paper, the stress responses of a suspension bridge due to different types of vehicle are obtained. Secondly, structural reliability prediction model is established using the stress-strength interference theory under the repeated loads after the stress responses and structural strength have been comprehensively considered. In addition, structural reliability index is calculated using the first order second moment method under vehicle loads that are obeying the normal distribution. The minimum reliability among various types of stress responses is chosen as the structural reliability. Finally, the proposed method has been validated for its feasibility and effectiveness by an example