Probabilistic failure analysis of underground flexible pipes

Kong Fah Tee,Lutfor Rahman Khan,Hua-Peng Chen 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.47 No.2

Methods for estimating structural reliability using probability ideas are well established. When the residual ultimate strength of a buried pipeline is exceeded the limit, breakage becomes imminent and the overall reliability of the pipe distribution network is reduced. This paper is concerned with estimating structural failure of underground flexible pipes due to corrosion induced excessive deflection, buckling, wall thrust and bending stress subject to externally applied loading. With changes of pipe wall thickness due to corrosion, the moment of inertia and the cross-sectional area of pipe wall are directly changed with time. Consequently, the chance of survival or the reliability of the pipe material is decreased over time. One numerical example has been presented for a buried steel pipe to predict the probability of failure using Hasofer-Lind and Rackwitz-Fiessler algorithm and Monte Carlo simulation. Then the parametric study and sensitivity analysis have been conducted on the reliability of pipeline with different influencing factors, e.g. pipe thickness, diameter, backfill height etc.

Probabilistic failure analysis of underground flexible pipes

Tee, Kong Fah,Khan, Lutfor Rahman,Chen, Hua-Peng Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.47 No.2

Methods for estimating structural reliability using probability ideas are well established. When the residual ultimate strength of a buried pipeline is exceeded the limit, breakage becomes imminent and the overall reliability of the pipe distribution network is reduced. This paper is concerned with estimating structural failure of underground flexible pipes due to corrosion induced excessive deflection, buckling, wall thrust and bending stress subject to externally applied loading. With changes of pipe wall thickness due to corrosion, the moment of inertia and the cross-sectional area of pipe wall are directly changed with time. Consequently, the chance of survival or the reliability of the pipe material is decreased over time. One numerical example has been presented for a buried steel pipe to predict the probability of failure using Hasofer-Lind and Rackwitz-Fiessler algorithm and Monte Carlo simulation. Then the parametric study and sensitivity analysis have been conducted on the reliability of pipeline with different influencing factors, e.g. pipe thickness, diameter, backfill height etc.

Structural reliability analysis using response surface method with improved genetic algorithm

Yongfeng Fang,Kong Fah Tee 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.62 No.2

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.

Analysis of structural dynamic reliability based on the probability density evolution method

Fang, Yongfeng,Chen, Jianjun,Tee, Kong Fah Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.45 No.2

A new dynamic reliability analysis of structure under repeated random loads is proposed in this paper. The proposed method is developed based on the idea that the probability density of several times random loads can be derived from the probability density of single-time random load. The reliability prediction models of structure based on time responses under several times random loads with and without strength degradation are obtained by using the stress-strength interference theory and probability density evolution method. The resulting differential equations in the prediction models can be solved by using the forward finite difference method. Then, the probability density functions of strength redundancy of the structures can be obtained. Finally, the structural dynamic reliability can be calculated using integral method. The efficiency of the proposed method is demonstrated numerically through a speed reducer. The results have shown that the proposed method is practicable, feasible and gives reasonably accurate prediction.

Reliability analysis of repairable k-out-n system from time response under several times stochastic shocks

Yongfeng Fang,Wenliang Tao,Kong Fah Tee 국제구조공학회 2014 Smart Structures and Systems, An International Jou Vol.14 No.4

The model of unit dynamic reliability of repairable k/n (G) system with unit strengthdegradation under repeated random shocks has been developed according to the stress-strength interferencetheory. The unit failure number is obtained based on the unit failure probability which can be computed fromthe unit dynamic reliability. Then, the transfer probability function of the repairable k/n (G) system is givenby its Markov property. Once the transfer probability function has been obtained, the probability densitymatrix and the steady-state probabilities of the system can be retrieved. Finally, the dynamic reliability of therepairable k/n (G) system is obtained by solving the differential equations. It is illustrated that the proposedmethod is practicable, feasible and gives reasonable prediction which conforms to the engineering practice.

Mode shape expansion with consideration of analytical modelling errors and modal measurement uncertainty

Hua-Peng Chen,Kong Fah Tee,Yi-Qing Ni 국제구조공학회 2012 Smart Structures and Systems, An International Jou Vol.10 No.5

Mode shape expansion is useful in structural dynamic studies such as vibration based structural health monitoring; however most existing expansion methods can not consider the modelling errors in the finite element model and the measurement uncertainty in the modal properties identified from vibration data. This paper presents a reliable approach for expanding mode shapes with consideration of both the errors in analytical model and noise in measured modal data. The proposed approach takes the perturbed force as an unknown vector that contains the discrepancies in structural parameters between the analytical model and tested structure. A regularisation algorithm based on the Tikhonov solution incorporating the L-curve criterion is adopted to reduce the influence of measurement uncertainties and to produce smooth and optimised expansion estimates in the least squares sense. The Canton Tower benchmark problem established by the Hong Kong Polytechnic University is then utilised to demonstrate the applicability of the proposed expansion approach to the actual structure. The results from the benchmark problem studies show that the proposed approach can provide reliable predictions of mode shape expansion using only limited information on the operational modal data identified from the recorded ambient vibration measurements.

Analysis of structural dynamic reliability based on the probability density evolution method

Yongfeng Fang,Jianjun Chen,Kong Fah Tee 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.45 No.2

A new dynamic reliability analysis of structure under repeated random loads is proposed in this paper. The proposed method is developed based on the idea that the probability density of several times random loads can be derived from the probability density of single-time random load. The reliability prediction models of structure based on time responses under several times random loads with and without strength degradation are obtained by using the stress-strength interference theory and probability density evolution method. The resulting differential equations in the prediction models can be solved by using the forward finite difference method. Then, the probability density functions of strength redundancy of the structures can be obtained. Finally, the structural dynamic reliability can be calculated using integral method. The efficiency of the proposed method is demonstrated numerically through a speed reducer. The results have shown that the proposed method is practicable, feasible and gives reasonably accurate prediction.

Repairable k-out-n system work model analysis from time response

Yongfeng Fang,Webliang Tao,Kong Fah Tee 사단법인 한국계산역학회 2013 Computers and Concrete, An International Journal Vol.12 No.6

A novel reliability-based work model of k/n (G) system has been developed. Unit failure probability is given based on the load and strength distributions and according to the stress-strength interference theory. Then a dynamic reliability prediction model of repairable k/n (G) system is established using probabilistic differential equations. The resulting differential equations are solved and the value of k can be determined precisely. The number of work unit k in repairable k/n (G) system is obtained precisely. The reliability of whole life cycle of repairable k/n (G) system can be predicted and guaranteed in the design period. Finally, it is illustrated that the proposed model is feasible and gives reasonable prediction.

Time-variant structural fuzzy reliability analysis under stochastic loads applied several times

Yongfeng Fang,Jianbin Xiong,Kong Fah Tee 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.55 No.3

A new structural dynamic fuzzy reliability analysis under stochastic loads which are applied several times is proposed in this paper. The fuzzy reliability prediction models based on time responses with and without strength degeneration are established using the stress-strength interference theory. The random loads are applied several times and fuzzy structural strength is analyzed. The efficiency of the proposed method is demonstrated numerically through an example. The results have shown that the proposed method is practicable, feasible and gives a reasonably accurate prediction. The analysis shows that the probabilistic reliability is a special case of fuzzy reliability and fuzzy reliability of structural strength without degeneration is also a special case of fuzzy reliability with structural strength degeneration.

Mode shape expansion with consideration of analytical modelling errors and modal measurement uncertainty

Chen, Hua-Peng,Tee, Kong Fah,Ni, Yi-Qing Techno-Press 2012 Smart Structures and Systems, An International Jou Vol.10 No.4

Mode shape expansion is useful in structural dynamic studies such as vibration based structural health monitoring; however most existing expansion methods can not consider the modelling errors in the finite element model and the measurement uncertainty in the modal properties identified from vibration data. This paper presents a reliable approach for expanding mode shapes with consideration of both the errors in analytical model and noise in measured modal data. The proposed approach takes the perturbed force as an unknown vector that contains the discrepancies in structural parameters between the analytical model and tested structure. A regularisation algorithm based on the Tikhonov solution incorporating the L-curve criterion is adopted to reduce the influence of measurement uncertainties and to produce smooth and optimised expansion estimates in the least squares sense. The Canton Tower benchmark problem established by the Hong Kong Polytechnic University is then utilised to demonstrate the applicability of the proposed expansion approach to the actual structure. The results from the benchmark problem studies show that the proposed approach can provide reliable predictions of mode shape expansion using only limited information on the operational modal data identified from the recorded ambient vibration measurements.