Most of the diffusion models of chloride ions in reinforced concrete (RC) elements proposed in literature are related to an isotropic homogeneous semi-infinite medium. This assumption reduces the mathematical complexity, but it is correct only for plane RC elements. This work proposes a comparison between the diffusion model of chloride ions in RC circular columns and in RC slab elements. The durability of RC cylindric elements estimated with the circular model instead of the plane model is shown to be shorter. Finally, a guideline is formulated to properly use the standard and more simple plane model instead of the circular one to estimate the time to corrosion initiation of cylindrical RC elements.Keywords: chloride ions diffusion, circular column, time to corrosion initiation, pitting corrosion of rebars. List of Symbols erf ðÞError function tTime from the beginning of the exposure to chloride solution t crTime to corrosion initiation x Perpendicular distance from external surface in the slab model w/c Water-cement ratio C(x, t) or C(q 1 , t)Chloride concentration in RC structural member at the distance x or q 1 from the external surface at time t from the first exposure to chloride solution C 0Chloride concentration on the external surface of the RC structural member C cr Chloride threshold concentration for the beginning of the depassivation D (cm 2 /year) Diffusion coefficient R Radius of the circular cross-section q Radial distance from the centre in a circular modelRadial distance from the external surface in a circular model erf
This paper deals with the reduction of vibrations caused by wind load in slender structures. The structure is modeled as a Single-Degree-of-Freedom system and the wind load is estimated through the pre-filter technique: the aerodynamic force is a function of White Noise filtered by a simple oscillator. Two optimization criteria to calculate the best values of the frequency and the damping ratio of the Tuned Mass Damper (TMD) are compared here. The aim of the first criterion is the reduction of the displacement of the top end of the structure, while the aim of the second criterion is the reduction of the inertial acceleration of the top end of the structure. The comparison of the two criteria is carried out through sensitivity analyses for different environmental conditions and system configurations. The comparison shows that the acceleration criterion is more attractive only for some conditions. Moreover, it is plain that the different efficiencies of the TMD optimized through each of two criteria are related to the mass ratio. Finally, the optimization criteria are applied to estimate the TMD design parameters to reduce the vibrations due to wind load in a lighting tower.
LIQUEFACT was a EU H2020 funded project to investigate earthquake induced liquefaction potential across Europe and develop a series of tools to understand better the impacts that earthquake induced liquefaction disaster events have on the resilience of built assets and communities. A resilience assessment and improvement framework was developed to provide the theoretical underpinning for the LIQUEFACT project and to provide practical guidance on the assessment of built assets to Earthquake Induced Liquefaction Disaster events through the LIQUEFACT software tool and built asset management planning framework. This paper outlines the theoretical basis to the resilience assessment and improvement framework and built asset management planning framework and presents the results from a validation exercise through their application to a hypothetical healthcare scenario. The paper also describes the different stages of the research that led to the definition of the resilience assessment and improvement framework and built asset management planning framework. To this end the paper concludes that the resilience assessment and improvement framework and built asset management framework provide a longitudinal, holistic view of disaster vulnerability and resilience that can inform the selection of ground improvement mitigation actions to improve business continuity and resilience planning.
As cities become larger and more densely populated the impacts of major earthquake events on city communities become more severe. Improving community resilience to earthquake events relies on the complex relationships that exist between different community stakeholder groups (citizens, businesses, community groups, emergency services, critical infrastructure providers, politicians etc.). This paper reports results from a major EU funded study (LIQUEFACT) that developed a tool for assessing community resilience to Earthquake Induced Liquefaction Disaster (EILD) events. The tool is based on a customised version of the UNDRR Disaster Resilience Scorecard for Cities. The paper reviews alternative approaches to measuring community resilience and describes the process used in the LIQUEFACT project to develop and validate the customised scorecard. The paper presents the results of a questionnaire survey to identify the best generic approach to measure community resilience and a series of semi-structured group interviews to define a range of specific metrics for assessing community resilience to EILD events; and the results of a validation workshop to assess the effectiveness and usability of the customised scorecard. The paper concludes that it is possible to develop a customised version of the UNDRR Scorecard at an appropriate level of granularity to support improved community resilience to earthquake induced soil liquefaction disaster events. The paper also presents key lessons that could assist those developing similar customised versions of the UNDRR scorecard for use in different geographical settings or against different disaster scenarios.
Tuned mass dampers are frequently used for passive control of vibrations in civil structures subject to seismic and wind actions. Their efficiency depends on selection of their mechanical properties in relation to main system and excitation characteristics. This paper proposes an optimum design strategy of single tuned mass dampers to control vibrations of principal mode of structures excited by earthquake ground motion. The main purpose of the paper is to investigate the influence of the time modulation of earthquake excitation upon the optimal tuned mass dampers design parameters: frequency and damping ratio. The study is based on numerical analyses carried out with different stochastic models for earthquakes: a simple filtered white noise model and two time modulated filtered white noise models. The numerical analyses are carried out to solve an optimization problem with a performance index defined by the reduction of the standard deviation of either the structure displacement or its inertial acceleration as objective function. To complete the work, the influence of the bandwidth excitation over the values of the optimal tuned mass damper parameters is investigated, as well the optimum mass ratio and the structure frequency. The results of the numeral analyses carried out infer that the earthquake excitation characteristics, including its modulation in time domain, highly affect the optimum tuned mass damper design parameters values.
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