Environmental Problems of Space Flight Structures. 2. Meteoroid Hazard

Environmental problems of space flight structures - part 2, meteoroid hazard

Exposure modelling and loss estimation for seismic risk assessment of residential buildings: innovative methods and applications

Defining the seismic hazard, assessing the vulnerability of the main components of the built environment and, consequently, estimating the expected losses are key steps for setting up effective post-event emergency plans as well as medium-long term mitigation strategies. Despite the significant knowledge advancements achieved in the last years, several points need to be further developed. Among them the collection of reliable building inventories, the selection of appropriate measures of seismic intensity and the definition of accurate loss estimation models still propose some challenges for the scientific community. The present PhD thesis aims at providing a contribution in this direction. After a comprehensive state of the art on seismic risk components along with a literature review focused on the main models to estimate the expected seismic losses, some new procedures related to hazard, exposure and loss estimation, have been proposed and applied. Firstly, a model aimed at estimating the direct economic losses (i.e., building repair costs) has been developed by improving the models currently available in the literature. These models generally account for only the severity of damage (i.e., the maximum damage level), while damage extension and distribution, especially along the building height, are implicitly considered in the repair cost values. If on the one side, the assessment of safety condition depends essentially on damage severity, on the other side, damage extension strongly affects the estimation of economic impact. In this regard, the proposed model allows to explicitly consider both damage severity and distribution along the building height. The model is applicable to both Reinforced Concrete (RC) and masonry building types. It requires the determination of the more frequent damage distributions throughout the building height. At the current state, the procedure has been specifically implemented for existing Reinforced Concrete (RC) building types by performing Non-Linear Dynamic Analyses (NLDAs). As for seismic hazard, correlations between macroseismic intensities and ground motion parameters have been derived processing data related to Italian earthquakes occurred in the last 40 years. Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV) and Housner Intensity (IH) as instrumental measures, and European Macroseismic Scale (EMS-98) and Mercalli-Cancani-Sieberg (MCS) as macroseismic measures, have been considered. The correlations can be used both to adopt empirical damage estimation methods (e.g., Damage Probability Matrices) and to convert the macroseismic data of historical earthquakes into instrumental intensity values, more suitable to risk analyses and design practice. Concerning exposure, an innovative methodology has been developed to convert the information on the typological characteristics collected through the AeDES form (currently used in Italy in post-earthquake usability surveys) to recognized international standards such as the taxonomy proposed by the Global Earthquake Model (GEM) and the EMS-98 building types. The methodology allows to fully exploit the exposure and vulnerability data of post-earthquake surveys related to the Italian built environment and to define an exposure model in terms of risk-oriented classes more suitable for large-scale risk assessments. Furthermore, an approach based on the integration of data collected with the CARTIS procedure (i.e., a protocol used in Italy for the typological-structural characterization of buildings at regional scale) and using the RRVS web-based platform (i.e., for a remote visual screening based on satellite images) has been proposed and specifically applied to the village of Calvello (Basilicata region, Southern Italy). This approach represents a useful tool for compiling residential building inventories in a quick and inexpensive way thus being very suitable in data-poor and economically developing countries. To better illustrate the proposed methodological developments, some applications are provided in the last part of the thesis. The first one proposes a comparison among the results obtained applying some casualty estimation models available in the literature using the vulnerability and damage data collected in the L’Aquila urban area after the 2009 earthquake (data available on the Observed Damage Database Da.D.O. platform). After, by using the same data source, an exposure model in terms of EMS-98 types based on the 2009 post-earthquake data has been implemented for the residential buildings of L'Aquila town and the surrounding municipalities involved in the usability assessment surveys. The third - expansive - application deals with the seismic risk assessment of the Val d’Agri area (Basilicata region, Southern Italy). This area has a strategic role for Italy due to the large quantities of oil extracted from local deposits, making available large resources deriving from royalties. Specifically, earthquake damage scenarios for the residential building stock of 19 villages have been prepared. Considering a seismic vulnerability distribution obtained from the integration of a building-by-building inventory and information collected with the CARTIS and RRVS approaches, the expected losses deriving from a seismic event with an exceedance probability of 10% in 50 years (475 years return period) have been determined. Finally, an action plan for the seismic risk mitigation, essentially based on the reduction of vulnerability of the building stock through a structural strengthening program, has been proposed and specifically applied to one of the villages in the area under study

Existing Empirical Fragility and Vulnerability Functions: Compendium and Guide for Selection

This document reviews existing empirical vulnerability and fragility functions worldwide collected until April 2014 in terms of their characteristics, data sources, and statistical modelling techniques. A qualitative rating system is described and applied to all reviewed functions to aid users to choose between existing functions for use in seismic risk assessments. The MS Access database developed by GEM VEM of all reviewed empirical functions and associated ratings is also described in this document. The database may be freely downloaded and includes all existing empirical vulnerability and fragility functions

Investigation of plasma contactors for use with orbiting wires

The proposed Shuttle-based short tether experiments with hollow cathodes have the potential for providing important data that will not be obtained in long tether experiments. A critical property for hollow cathode effectiveness as a plasma contactor is the cross magnetic field conductivity of the emitted plasma. The different effects of hollow cathode cloud overlap in the cases of motion-driven and battery-driven operation are emphasized. The calculations presented on the size and shape of the hollow cathode cloud improve the qualitative picture of hollow cathodes in low Earth orbit and provide estimates of time constants for establishing the fully-expanded cloud. The magnetic boundary value problem calculations indicate the way in which the magnetic field will effect the shape of the cloud by resisting expansion in the direction perpendicular to the field. The large-scale interactions of the system were also considered. It was concluded that recent plasma chamber experiments by Stenzel and Urrutia do not model an electrodynamic tether well enough to apply the results to tethered system behavior. Orbiting short tether experiments on hollow cathodes will provide critical information on hollow cathode performance and the underlying physics that cannot be obtained any other way. Experiments should be conducted as soon as funding and a suitable space vehicle are available

Aeronautical engineering: A continuing bibliography with indexes (supplement 232)

This bibliography lists 422 reports, articles, and other documents introduced into the NASA scientific and technical information system in October, 1988

Rolling-contact bearing reference summary

Design and performance of rolling contact bearing

Framework for Seismic Vulnerability Assessment of RC High-rise Wall Buildings

With population growth and urbanization, the number of high-rise buildings is rapidly growing worldwide resulting in increased exposure to multiple-scenario earthquakes and associated risks. The wide range in the frequency content of expected ground motions impacts the seismic response and vulnerability of this class of structures. While the seismic vulnerability of some high-rise building classes has been evaluated, the vulnerability of these structures under multiple earthquake scenarios is not fully understood, highlighting the pressing need for the development of a framework to address this complex issue. This study aims to establish a refined framework to assess the seismic vulnerability of RC high-rise wall buildings in multiple-scenario earthquake-prone regions. A deeper understanding of the responsive nature of these structures under different seismic scenarios is developed as a tool to build the framework. The framework is concluded with analytically-driven sets of Seismic Scenario-Structure-Based (SSSB) fragility relations. Different nonlinear modelling approaches, software, and key parameters contributing to the nonlinear analytical models of RC high-rise wall structures are investigated and verified against full-scale shake table tests through a multi-level nonlinear modelling verification scheme. The study reveals the superior performance of 4-noded fibre-based wall/shell element modelling approach in accounting for the 3D effects and deformation compatibility. A fundamental mode damping value in the range of 0.5% is found sufficient to capture the inelastic response when initial stiffness-based damping matrix is employed. A 30-storey reference wall building located in the multiple-scenario earthquake-prone city of Dubai (UAE) is fully designed and numerically modelled as a case study to illustrate the proposed framework. A total of 40 real earthquake records, representing severe distant and moderate near-field seismic scenarios, are used in the Multi-Record Incremental Dynamic Analyses (MRIDAs) along with a new scalar intensity measure. A methodology is proposed to obtain reliable SSSB definitions of limit state criteria for RC high-rise wall buildings. The local response of the reference building is mapped using Net Inter-Storey Drift (NISD) as a global damage measure. The study reveals that for this class of structures, higher modes shift the shear wall response from flexure-controlled under severe distant earthquakes to shear-controlled under moderate near-field events. A numerical parametric study employing seven RC high-rise wall buildings with varying height is conducted to investigate the effect of total height on the local damage-drift relation. The study reveals that, for buildings with varying heights and similar structural system, NISD is better linked to the building response and well correlated to structural member damage, which indicates that only one set of SSSB limit state criteria is necessary for a range of buildings. The study concludes with finalising the layout of the proposed refined framework to assess the seismic vulnerability of RC high-rise wall buildings under multiple earthquake scenarios. A methodology to develop refined fragility relations is presented where the derived fragility curves are analysed, compared, and correlated to varying states of damage. Finally, a methodology to develop Cheaper (simplified) Fragility Curves (CFC) using the defined limit state criteria with a lower number of records is proposed along with a new record selection criterion and fragility curve acceptance procedure. It is concluded that fairly reliable CFCs can be achieved with 5 to 6 earthquake records only

Multicriteria decision making for selecting an optimal survey approach for large building portfolios

Technological advances and innovations have led to various pre- and post-disaster data collection alternatives to traditional sidewalk surveys. Hence, selecting a suitable survey approach may be challenging for different decision-makers. This paper proposes a multicriteria decision-making (MCDM) method to choose the optimal survey approach to gather exposure information needed for reliable multi-hazard risk assessment of large building and infrastructure portfolios. Both deterministic and stochastic implementations of MCDM are investigated, considering primary sources of aleatory and epistemic uncertainties. The applicability of the proposed framework is demonstrated for a portfolio of 13,200 buildings in a hypothetical multi-hazard prone region. The results show that informed decisions on identifying an optimal survey technique could be efficiently derived using MCDM and a number of relevant criteria. The proposed methodology can support various decision-makers in pre- and post-disaster risk modeling and management/reduction