Giorgio Barone

Reliability, risk and lifetime distributions as performance indicators for life-cycle maintenance of deteriorating structures

Abstract Structural capacity deterioration is among the main causes of increasing failure probabilities of structural systems, thus maintenance interventions are a crucial task for their rational management. Several probabilistic approaches have been proposed during the last decades for the determination of cost-effective maintenance strategies based on selected performance indicators. However, benefits and drawbacks of each performance indicator with respect to the others should be further analyzed. The objective of this paper is to investigate probabilistic approaches based on the annual reliability index, annual risk, and lifetime distributions for life-cycle maintenance of structural systems. Maintenance schedules are obtained for representative series, parallel, and series–parallel systems considering total restoration of component resistances whenever a prescribed threshold, based on a selected performance indicator, is reached. Effects related to different structural configurations and correlation among failure modes are investigated. The superstructure of an existing bridge is used to illustrate the presented approaches.

Optimization of Life-Cycle Maintenance of Deteriorating Bridges with Respect to Expected Annual System Failure Rate and Expected Cumulative Cost

AbstractCivil infrastructure systems are subjected to progressive deterioration resulting from multiple mechanical and environmental stressors. This deterioration process is developed under uncertainties related to load effects, structural resistance, and inspection outcomes, among others. In this context, life-cycle optimization techniques provide a rational approach to manage these systems considering uncertainties and several budgetary and safety constraints. This paper proposes a novel optimization procedure for life-cycle inspection and maintenance planning of aging structures. In this procedure, the structural system effects are accounted for by modeling the structure as a series, parallel, or a series-parallel system whose components are subjected to time-dependent deterioration phenomena. Different possible repair options are considered depending on the damage state and the outcomes of each inspection. For each component, essential or preventive maintenance aiming at reducing the system failure ra...

Hazard-Based Optimum Lifetime Inspection and Repair Planning for Deteriorating Structures

The hazard function is one of the most used lifetime distribution functions in reliability analysis of components and systems. Although it is extensively used in several scientific disciplines, few applications have been proposed in the field of civil infrastructure systems. In this paper, the hazard function is used to provide optimal inspection/repair lifetime planning for deteriorating structures through an iterative procedure. The proposed approach is based on the definition of a threshold value for the hazard function. Constraints are imposed based on both the maximum allowable expected total cost and minimum allowable effectiveness of each intervention. Uncertainties related to damage detection during inspections and attitudes towards repair are considered. An optimization procedure for determining the best threshold value for the hazard function, with target maximum expected failure time, is proposed. The method is applied to an existing deteriorating bridge deck under corrosion.

Fatigue reliability and service life prediction of aluminum naval ship details based on monitoring data

The evolution of naval vessels toward high-speed crafts subjected to severe sea conditions has promoted an increasing interest in lightweight high-strength materials. Due to its strength and weight characteristics, aluminum has been proven especially suitable as construction material for hull structures as well as other vessel parts. However, fatigue in aluminum naval crafts needs to be effectively addressed for the proper life-cycle assessment. Structural health monitoring systems constitute effective tools for measuring the structural response and assessing the structural performance under actual operational conditions. In this article, an approach for using structural health monitoring information in the fatigue reliability analysis and service life prediction of aluminum naval vessels is presented. The accumulated fatigue damage and the fatigue reliability are quantified based on structural health monitoring data acquired under different operational conditions, specified by the ship speeds, sea states, and heading angles. Additionally, an approach for estimating the reliability-based fatigue life under a given operational profile is presented. Seakeeping trial data of an aluminum high-speed naval vessel are used to illustrate the proposed approach.

CVBEM Application to a Novel Potential Function Providing Stress Field and Twist Rotation at Once

AbstractIn this paper, complex variable boundary element method (CVBEM) is used for the solution of de Saint-Venant’s torsion problem in homogenous isotropic elastic beams with a generic cross section, considering a complex potential function related to the stress field. Generally, CVBEM, when used for torsion problems, leads to evaluation of the stress field divided by the twist rotation. The latter has been evaluated by performing a domain integral. In this paper, taking advantage of the aforementioned potential function, it is possible, by applying CVBEM, to evaluate the complete stress distribution and the twist rotation of the cross section and the torsional stiffness factor, performing line integrals only. Numerical results were compared with both analytical and numerical results proposed by other authors, thus assessing the validity of the proposed method.

A NOVEL ANALYTICAL MODEL OF POWER SPECTRAL DENSITY FUNCTION COHERENT WITH EARTHQUAKE RESPONSE SPECTRA

In the most advanced seismic codes earthquake loads are often defined by means of pseudo-acceleration Response Spectra (RS) and the use of modal superposition analysis method is strongly encouraged. The effectiveness of the design procedures is thus limited by the underlying hypotheses, such as the linearity of the system and the reliability of the modal correlation coefficients used to combine the modal responses for MDOF systems. On the other hand, linear systems response statistics could be easily computed by using stochastic analysis tools, once a stochastic characterization of the seismic action is provided. In this paper a few-parameters analytical model for the definition of Power Spectral Density functions (PSD) coherent with Response Spectra is proposed. Closed-form relationships between the parameters involved in the definition of the PSD and the RS defined by several international seismic codes are provided. The reliability of this tool is assessed by means of a numerical campaign by comparing stochastic analysis and Monte-Carlo simulations. By using the proposed approach, the seismic action can be defined both in terms of RS and in terms of PSD, and, therefore, the engineer can choose the most appropriate analysis tool for his purpose.

Dynamic characterization of fractional oscillators for Fractional Tuned Mass Dampers tuning

A novel formulation for Fractional Tuned Mass Damper (FTMD) devices is proposed in this paper. The FTMD is realized by connecting an oscillating mass to the main structure using a viscoelastic link, realized through elastomeric rubber bearings with fractional derivative constitutive model. A new function, labeled Damped Fractional Frequency, is defined for the fractional oscillator as the analogous of the damped frequency for classic single oscillators. Then, a critical value for the fractional order derivative involved in the damper constitutive law is defined as the limit value for which the DFF is real. It is shown that prevalent elastic or viscous dynamic behaviours are observed for the fractional oscillator when the fractional order derivative assumes values smaller or greater than the critical value, respectively. Finally, the DFF concept is utilized to opportunely tune the FTMD to its main structure, analogously to classic Tuned Mass Damper devices. Applications to a system excited by stochastic loads are presented, using the classic tools of stochastic analysis to determine the system response statistics and measure the performance of the FTMD.

Exact Closed-Form Fractional Spectral Moments for Linear Fractional Oscillators Excited by a White Noise

In the last decades the research community has shown an increasing interest in the engineering applications of fractional calculus, which allows to accurately characterize the static and dynamic behaviour of many complex mechanical systems, e.g. the non-local or non-viscous constitutive law. In particular, fractional calculus has gained considerable importance in the random vibration analysis of engineering structures provided with viscoelastic damping. In this case, the evaluation of the dynamic response in the frequency domain presents significant advantages, once a probabilistic characterization of the input is provided. On the other hand, closed-form expressions for the response statistics of dynamical fractional systems are not available even for the simplest cases. Taking advantage of the Residue Theorem, in this paper the exact expressions of the spectral moments of integer and complex orders (i.e. fractional spectral moments) of linear fractional oscillators driven by acceleration time histories obtained as samples of stationary Gaussian white noise processes are determined.

Stochastic analysis of fractional oscillators by equivalent system definition

Fractional oscillators have been recently proposed as damping devices under the configuration of Fractional Tuned Mass Dampers (FTMD), realized by connecting an oscil- lating mass to the primary structure through a viscoelastic link with inherent fractional con- stitutive law. The characteristic tuning frequency for the FTMD has been identified with the Damped Fractional Frequency (DFF), defined as the frequency at which the squared abso- lute value of the transfer function of the device attains its relative maximum. The definition of the DFF constitutes an interesting step towards the analysis of fractional oscillators in the frequency domain. In this paper, a simplified frequency domain approach is presented for the design of fractional oscillators subjected to stationary white noise. The analysis of the frac- tional oscillator is performed by using an equivalent single degree of freedom system with linear viscous damping. The aim is to obtain a clear understanding of the physical dynamic effects of the variations in the fractional oscillator parameters, in terms of damping and natu- ral frequencies. Moreover, the use of an equivalent system allows for the straightforward ap- plications of stochastic analysis to determine an approximate closed-form expression of the response variance.