Fatigue analysis of an offshore wind turbine in Mediterranean sea under a probabilistic framework

Wind Turbines constitute a sustainable and effective solution for the production of energy using wind power. Offshore wind turbines especially are becoming of special interest. However, their design poses great challenges, since an offshore structure is subject to combined wind and wave dynamic loading that is characteristic of the site of installation. The purpose of this paper is to provide a case study of fatigue life assessment for the cross-section at mudline (foundation) of a standard offshore wind turbine with a monopile design, under a probabilistic framework, and assuming the diameter and thickness of the examined cross- section as the design variables. Two potential sites of construction in the Aegean Sea of Greece (part of Mediterranean Sea) were examined. A probabilistic approach was employed in order to determine the fatigue life based on anemological data at each of the two sites of interest. At its basis is an extensive Monte Carlo simulation of wind (velocity) and wave (height, period) characteristics. The results show the dependence of fatigue life on the local wind and wave conditions, the cross-section size (e.g. diameter and thickness of the foundation’s pile) and the welded connection detail. All in all, the more benign conditions in the Aegean allow simpler connection details and smaller in size cross-section of foundation pile’s cross-section to still have acceptable performance

A Socioeconomic Model For Estimating Indirect Consequences Of Earthquake Hazards To Cultural Heritage Communities

A socioeconomic model of the residents and visitors (i.e., users) and the local economy (i.e., production and consumption of goods, services, and small businesses) is proposed to simulate the core functions of a cultural heritage community. Given the direct infrastructure damages of an event, as those are derived by vulnerability and hazard assessment, the model is able to quantify the indirect losses per critical business sector as they evolve over time. This is accomplished by first deriving downtime estimates per sector, propagating the resulting disruptions through the demand-supply chain of the community, and then tracking their eventual recovery. The model is designed to accommodate the salient socioeconomic characteristics of the cultural heritage community, by giving heed to effects such as the adaptive behavior of the site visitors and the occurrence of an adverse event during a high or a low season for tourism. The methodology is finally illustrated and verified on the basis of several earthquake scenarios derived for the historical city of Rhodes, highlighting the potential usage of the tool during risk mitigation planning and post-event decision-making

Exposure, Vulnerabilities, And Scenario Seismic Risk Assessment For The City Of Granada

A model is developed for the seismic risk assessment of the city of Granada, Spain, focusing on the building stock. For its implementation, in-house software is coded in the objectoriented programming language Python. Firstly, the assets of interest, in this case the different buildings, are identified and classified according to the taxonomy of the 2020 European Seismic Risk Model, appropriately customized for the characteristics of the local stock. The exposure model is created using the geographical position of each building and aggregating them per city block. Seismic hazard is determined via the 2020 European Seismic Hazard Model. An eventbased probabilistic seismic hazard approach is employed, generating a stochastic event set for a 10,000 year investigation period, together with corresponding spatially-correlated ground motion fields via the OpenQuake platform. For simplicity, a single intensity measure is employed to characterize all buildings. Suitable vulnerability functions are selected to calculate loss. Results are obtained per block for the damage of buildings in terms of assigning them to different damage states as well as defining the cost of replacement. The resulting consequences are grouped across different functions and lines of business. The focus is on offering a preliminary determination of the disruption caused by each event in support of socioeconomic impact modelling within the HYPERION EU project.Financial support has also been provided by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the "2nd Call for H.F.R.I. Research Projects to support Faculty Members & Researchers", Project "TwinCity: Climate-Aware Risk and Resilience Assessment of Urban Areas under Multiple Environmental Stressors via MultiTiered Digital City Twinning" (Grant Agreement 2515)

Prescriptive Approaches in Performance-Based Design? A Case-Study on Base Isolation

The collapse performance of code-designed base-isolated structures has recently received considerable criticism, having been found to be deficient vis-à-vis conventional buildings in several situations. As a remedy, prescriptive minima with a tenuous probabilistic justification have been recommended in the literature for the bearing deformation capacity. These are independent of structure or site characteristics, yet they are already finding use in design. We put this concept to the test by means of a case study of a seismically isolated steel structure that rests on the roof of two adjacent high-rise reinforced concrete towers. To seismically isolate the steel structure, Friction Pendulum Bearings (FPBs) are used, and their displacement capacity is determined to comply with a performance objective of 1% probability of collapse in 50 years. The case study possesses two salient features that distinguish it from pertinent past investigations. The first is that the isolated steel structure rests on top of two others and consequently it is subjected to narrow-band roof acceleration time histories, shaped by the filtering of the ground motion excitation through the supporting buildings. The second is that the two supporting towers have different modal characteristics, thus displacement demands imposed to the FPBs are mainly affected by their in-phase or out-of-phase movement. Overall, a case-specific true performance-based design is shown to achieve the desired safety while requiring 1.5 times lower displacement capacities for the bearings, when compared to prescriptive performance-based approaches.This project has received funding from the European Unions Horizon 2020 research and innovation programme under grant agreement No 769129

A simplified approach for including the incidence angle effect in seismic risk assessment

A simplified procedure is developed to consider the azimuthal orientation of buildings when estimating seismic risk. Two square-plan reinforced concrete building models are considered as a testbed, one with similar and one with dissimilar properties along the two principal horizontal axes. The fragility of both structures is analysed using a set of ground motion records rotated to multiple incidence angles to develop orientation-dependent fragility functions. It has been observed that, re-orienting all records so that these structures have the same azimuth vis-à-vis the corresponding epicentre leads to significant differences compared to assuming random orientations. Additional results stemming from single-degree-of-freedom oscillators further confirm such findings, showing a dependence to the proximity to the faults and the level of dissimilarity in the principal horizontal axes of the structure. The end results point to a non-negligible bias in assessment studies when a structure's orientation with respect to governing rupture scenarios is not taken into account. It is shown that the median of fragility curves calculated for un-rotated incidence angles can be bias-corrected through shifted by an amount that depends on the azimuthal orientation and level of axes-dissimilarity of structures.Yeudy F. Vargas-Alzate has been granted an Individual Fellowship (IF) in the research grant program of the Marie Sklodowska-Curie Actions (MSCA), European Union/European (H2020-MSCA-IF-2017) No 799553. This author is deeply grateful to this institution.Peer ReviewedPostprint (published version

Issues in Harmonization of Seismic Performance via Risk Targeted Spectra

Current seismic design code provisions are mainly based on checking structural performance at a single seismic intensity associated with a pre-defined return period. For instance, in EN1998, a ground motion with 10% probability of exceedance in 50 years is used for design. This design procedure, with the inclusion of partial safety factors, is assumed to provide sufficient safety margin against earthquakes for newly designed buildings. Nevertheless, it does not specifically determine the expected seismic risk related to any performance level or limit state. Therefore, it may result in non-uniform risk for buildings located in different sites within a region (or country), even for places with identical design intensities. Instead, ASCE 7-10 incorporates Risk Targeted design maps that suggest the application of suitable spectra adjustment factors, in order to ensure a reasonably low uniform collapse risk. Making use of simplified single degree of freedom structures defined in several configurations of period and ductility, our aim is to test the effectiveness of the adjustment factors computed under different assumptions. It is shown that, although matching is not practically possible, harmonization remains a viable target, offering insights for possible future adoption of Risk Targeted Spectra in forthcoming seismic codes.The second author acknowledges the support of the European Commission via the Horizon 2020 Grant No. 769129 PANOPTIS: Development of a Decision Support System for increasing the Resilience of Transportation Infrastructure based on combined use of terrestrial and airborne sensors and advanced modelling tools

A view of seismic robustness based on uncertainty

A simplified view of robustness and redundancy is presented for the seismic assessment and design of structures. It is argued that the topological simplicity of the seismic load, i.e., its highly correlated nature of application for practically every component in all but the ultra-long structures, means that simpler formulations can be devised compared to blast, wave or wind hazards. In that sense, robustness may be considered to express the influence of structural uncertainties on the seismic performance of the structure, in essence showing the available margin of safety subject to material variability. Quantitatively, a pertinent robustness/redundancy index is defined as the ratio of two different estimates of the mean annual frequency (MAF) of exceeding a limit-state of interest, such as global collapse: On the denominator lies the MAF estimate that incorporates all sources of variability while on the nominator is the estimate that neglects structural uncertainties. It is shown that a simple closed form solution is available that directly relates robustness to the dispersion of response due to model parameter uncertainty. As an example, a steel frame where only beams are allowed to yield is shown to be more robust compared to another version where columns become the sacrificial element.Non UBCUnreviewedThis collection contains the proceedings of ICASP12, the 12th International Conference on Applications of Statistics and Probability in Civil Engineering held in Vancouver, Canada on July 12-15, 2015. Abstracts were peer-reviewed and authors of accepted abstracts were invited to submit full papers. Also full papers were peer reviewed. The editor for this collection is Professor Terje Haukaas, Department of Civil Engineering, UBC Vancouver.Facult

Probabilistic Assessment of Rocking Response for Simply-Supported Rigid Blocks

Abstract: A probabilistic assessment of the rocking and overturning response of a simply-supported rigid block on a horizontal plane is reported. A two-dimensional rectangular block resting on a rough, horizontal, tensionless and cohesionless rigid base at ground surface is considered, subjected to far field horizontal earthquake excitations. The roughness of the interface is assumed to be sufficiently large to prevent sliding, while the flexibility of the block is neglected. Rocking response curves are calculated for increasing ground motion intensity (or, equivalently, decreasing uplift strength) via Incremental Dynamic Analysis (IDA), and results are summarised in the form of 16%, 50 % and 84 % fractile IDA curves. By employing non-linear regression analysis, simple expressions are developed for each fractile of peak response to offer a complete probabilistic characterisation of rocking behaviour. Generalised overturning criteria are proposed covering a wide set of excitations and block parameters