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The search for a bona fide robustness index to quantify the system performance upon unexpected disturbances has been a continuous research effort. Previous studies have largely neglected to reflect the damage evolution feature of a progressive collapse failure. To bridge this important knowledge gap, this paper presents a novel risk-based robustness index for structures prone to disproportionate progressive collapse. Defined on a new concept, referred to as damage evolution curve, the proposed index considers the full spectrum of risk due to initiating events, and rigorously quantifies the impact of intermediate partial damages on the robustness assessment. Examples using a Daniels system, a truss, and an idealised moment-resistant frame are presented to illustrate how the proposed index is applied for assessing the robustness of structures with increasing complexity. In addition, a comprehensive comparative study against four existing robustness indices is carried out. It is shown that the proposed index provides consistent results for different influencing factors, whereas the other indices either respond counter-intuitively or are insensitive to some of the factors. With consideration of intermediate damage and failure consequences, the development of the proposed robustness index represents an important step towards the performance-based design against progressive collapse. [ABSTRACT FROM AUTHOR]

Maintenance flexibility has been promoted as a value driver for long-term public–private partnerships (PPPs). However, the value and risk associated with this value driver have not been properly quantified in the Value for Money (VfM) assessment literature. To bridge the gap, a novel stochastic modelling methodology is proposed to characterize the complex interactions among the lifecycle cost (LCC), performance deterioration and maintenance strategies. Four different maintenance strategies are designed to emulate the practice in the traditional and PPP delivery methods. The LCC includes the direct maintenance cost, user cost, residual value, and payment deduction, the last three often being neglected in VfM assessments. Simulation-based optimization and dynamic programming analysis are used to determine the probability distributions of the LCC and the VfM. A hypothetical highway PPP project under an availability payment model is selected as a case study. The results show that maintenance flexibility is indeed able to reduce the LCC for the private party. However, this private efficiency, if not properly regulated, could cause a reduced asset residual value and an increased user cost, making the public party worse off. In addition, for all potential maintenance strategies, the public sector is found to retain significant lifecycle cost risk, largely in the form of user cost. [ABSTRACT FROM AUTHOR]

Local calibration is an important step before a transportation agency adopts the American Association of State Highway and Transportation Officials' (AASHTO) mechanistic-empirical pavement design guide (MEPDG). This paper presents the challenges of and findings from the local calibration of flexible pavements in provincial highways under the jurisdiction of the Ministry of Transportation of Ontario (MTO). A calibration database was developed that involved a hierarchical framework of the input parameters required for AASHTOWare Pavement ME (the MEPDG software) and the historical field performance data based on the MTO's second-generation pavement management system. A regression analysis is carried out for preliminary calibration of rutting and international roughness index (IRI) models by comparing the predicted distress to observed distress. The analysis suggested that whereas the MEPDG provided fairly unbiased prediction of the IRI value, it often over-predicted the total rutting. Calibrated predicted IRI and rut depth are found for Ontario's local conditions from MEPDG distress prediction models. A further clustering analysis based on Functional Class and geographical zone for the rutting and IRI, respectively, improved the precision of the locally calibrated models. [ABSTRACT FROM AUTHOR]

In this study, the performance of annular liquid tanks as a tuned liquid damper (TLD) in mitigating the vibration of wind turbines was investigated using a numerical model. A proposed hybrid wind tower model composed of a concrete shaft and a steel mast with a height of 150 m was simulated using a single-degree-of-freedom system. The structural domain including the tank wall and a rigid mass was modeled using finite element method, while the fluid domain was simulated by finite volume method using CFX software. A parametric study was carried out to investigate the behavior of annular TLD under harmonic loads for different mass and frequency ratios as well as displacement amplitudes. The damping characteristics of the annular TLD model were derived by comparing the numerical results with an equivalent linear model. In addition, the effectiveness of annular TLD was estimated by comparing the numerically calculated damping ratios with those corresponding to the optimum damping ratio values derived for a particular mass ratio based on the concept of tuned mass damper. It was found that that the annular TLD is effective when the amplitude of excitation is small. Moreover, the response of TLD in terms of nonlinear free surface sloshing and the energy dissipated by the system was discussed. Finally, the effectiveness of annular TLD in reducing the structural response of wind turbine towers under random vibrations was evaluated and discussed. [ABSTRACT FROM AUTHOR]