Vasileios MELISSIANOS
Vasileios Melissianos holds a degree in civil engineering with major in structural engineering (National Technical University of Athens, NTUA, Greece, 2009), an M.Sc. in Analysis and Design of Earthquake Resistant Structures (NTUA, 2010), and a Ph.D. (NTUA, 2016). Dr Melissianos joined the Institute of Steel Structures at NTUA in 2011 as a Ph.D. candidate and now works as a post-doctoral researcher and member of The Lambda Lab group. Vasileios’ research focuses on the seismic risk assessment of structures and industrial infrastructure, using nonlinear analysis methods, detailed finite element modeling, and probabilistic methods. He has, also, worked on problems related to the geometrical and material nonlinearities of steel structures. He is an active researcher with participation in national and international research projects funded by Greek and European agencies and publications of journal and conference papers. Moreover, he has teaching experience in undergraduate courses (e.g. rigid body mechanics, steel structures, nonlinear behavior of steel structures) and two-year professional experience as a site engineer in civil engineering projects within oil and gas industrial facilities. Vasileios is a licenced civil engineer as a member of the Technical Chamber of Greece since 2009.
JOURNAL PAPERS
Now - 2013
Karaferis N.D., Melissianos V.E., Vamvatsikos D. (2024). Mechanical modeling, seismic fragility, and correlation issues for groups of spherical pressure vessels, Acta Mech, 235:1563-1582.
Abstract | A roadmap is outlined for determining comprehensive seismic fragility curves for (single or groups of) spherical pressure vessel structures commonly found in oil refineries. The developed modeling techniques aim to strike a balance between accuracy and computational efficiency, with a focus on capturing the most pertinent failure modes relevant to these structural types. First, a set of “partial” fragilities is determined based on each vessel’s fill ratio, as the response varies substantially depending on the amount of liquid content. Considering that a seismic assessment process invariably involves simultaneous consideration of such partial fragilities, a Monte Carlo-based approach is employed for their combination. The results naturally depend on the level of correlation employed, but can be almost perfectly matched by simpler analytical methods in the edge cases of full and zero correlation.
Melissianos V.E., Vamvatsikos D., Danciu L., Basili R. (2024). Design Fault Displacement for Lifelines at Fault Crossings: The Code-Based Approach for Europe. Bulletin of Earthquake Engineering, 22: 2677-2720.
Abstract | The earthquake-resistant design of lifelines, such as pipelines, tunnels and bridges, is based on the reliable representation and estimation of the seismic loading. In the case of lifeline–fault crossings, the design fault displacement is typically derived from estimates based on fault dimensions via empirical fault scaling relations for a given “design” scenario event. This approach comes with an unknown level of safety because the fault productivity and the actual distribution of earthquake events are essentially disregarded. To overcome this challenge, a simplified approach is proposed by statistically analyzing the outcome of probabilistic fault displacement hazard analyses (PFDHAs). A selection of faults from the 2020 European Fault-Source Model is used to build the logic tree and to set the range of parameters considered in the PFDHAs. The methodology allows the (mostly conservative) approximation of the fault displacement corresponding to any given return period based on readily available data, namely fault productivity, fault mechanism, fault length, and lifeline crossing location on the fault. The proposed methodology has been proposed and adopted as an informative Annex in prEN 1998-4:2022.
Kazantzi A.K., Karaferis N.D., Melissianos V.E., Vamvatsikos D. (2024). Acceleration-sensitive ancillary elements in industrial facilities: alternative seismic design approaches in the new Eurocode. Bulletin of Earthquake Engineering, 22: 109-132.
Abstract | The Eurocode 8—Part 4 approaches, per their December 2022 update, are presented for the design of acceleration-sensitive industrial ancillary components. The seismic performance of such nested and/or supported ancillary elements, namely mechanical and electrical equipment, machinery, vessels, etc. is critical for the safety and operability of an industrial facility in the aftermath of an earthquake. Of primary importance are the structural characteristics of the supporting structure and the supported component, pertaining to resonance, strength, and ductility, and whether these are known (and to what degree) during initial design and/or subsequent modifications and upgrades. Depending on the availability and reliability of information on the overall system, the Eurocode methods comprise (a) a detailed component/structure-specific design accounting for all pertinent component and building characteristics, equivalent to typical building design per Eurocode 8—Part 1–2, (b) a conservative approach where a blanket safety factor is applied when little or no such data is available, and (c) a ductile design founded on the novel concept of inserting a fuse of verified ductility and strength in the load path between the supporting structure and the ancillary element. All three methods are evaluated and compared on the basis of a case-study industrial structure, showing how an engineer can achieve economy without compromising safety under different levels of uncertainty.
Dasiou M-E., Lachanas C.G., Melissianos V.E., Vamvatsikos D. (2024). Seismic performance of the temple of Aphaia in Aegina island, Greece. Earthquake Engineering and Structural Dynamics, 53(2):573-592
Abstract | The seismic performance assessment of the ancient Temple of Aphaia in Aegina island, Greece, is presented. The Temple of Aphaia was erected around 500BC using porous limestone and is one of the most characteristic examples of Doric architecture. The assessment is performed within a performance-based framework using state-of-the-art tools of earthquake engineering. In the first part, the seismic hazard of the site was calculated using the European Seismic Hazard Model and hazard-consistent records were selected. Then, the Temple was scanned by drone and the point cloud was used to develop the numerical structural model. The Temple was analyzed using the discrete element method. Appropriate engineering demand parameters and limit state thresholds were defined. Fragility curves for the structural elements, namely, columns and architraves, of the Temple were computed via multi-stripe analysis. Finally, the seismic risk of the Temple was evaluated using long-term estimates in terms of return periods of exceeding limit states and total loss. The outcomes of the study offer valuable information to engineers, architects, and archaeologists regarding the current status of the monument in terms of identifying its most vulnerable elements and allowing the prioritization of short- and long-term restoration actions.
Melissianos V.E., Danciu L., Vamvatsikos D., Basili R. (2023). Fault displacement hazard estimation at lifeline–fault crossings: A simplified approach for engineering applications. Bulletin of Earthquake Engineering, 21: 4821–4849
Abstract | Lifelines, such as pipelines, roads, and tunnels, are critical infrastructure and when crossing active tectonic faults, a reliable estimation of the fault displacement in case of an earthquake is required. The first and simplest approach is to use empirical fault scaling relations to compute the design fault displacement, but this may result in an unknown level of safety. Thus, the probabilistic fault displacement hazard analysis (PFDHA) is the appropriate tool to assess the fault displacement hazard within a performance-based framework. Based upon an established PFDHA model, we present a simplified approach for engineering applications focusing on the lifeline–fault crossing along with appropriate simplifications and assumptions to extend its applicability to numerous faults. The aim is to provide a structure-independent approach of PFDHA that can be used when a site-specific study is not required, not possible (e.g., absence of recent sediments for dating past events), or too cumbersome, e.g., for lifeline route selection. Additionally, an in-depth investigation is presented on the key parameters, such as maximum earthquake magnitude, fault length, recurrence rate of all earthquakes above a minimum magnitude, and lifeline-fault crossing site, and how they affect the hazard level. This approach will be the basis for deriving hazard-consistent expressions to approximate fault displacement for use within the Eurocodes. The latter is intended to serve as a compromise between hazard-agnostic fault scaling relations and a comprehensive PFDHA, which requires detailed calculations and site-specific seismological data.
Melissianos V.E. (2022). Onshore Buried Steel Fuel Pipelines at Fault Crossings: A Review of Critical Analysis and Design Aspects. Journal of Pipeline Systems Engineering and Practice, 13(4): 03122002.
Abstract | Onshore buried steel pipeline infrastructure is a critical component of the fuel supply system. Pipeline failure due to seismic actions is socially, environmentally, and economically unacceptable and thus the design of pipelines in geohazard areas, such as fault crossings, remains a hot topic for the pipeline community. There is an intense research effort on the evaluation of the pipeline mechanical behavior and the strength verification at fault crossings. Still, some aspects need in-depth consideration concerning practical applications. A state-of-the-art review is presented on three critical analysis and design aspects, namely, the calculation of the design fault displacement via deterministic and probabilistic methods, the effect of numerical modeling parameters such as soil spring properties, and the alternative pipe protection measures in terms of availability, efficiency, and selection process. The critical review offers a thorough insight into what is available and how to employ it in design, assisting engineers and pipe operators in improving pipe safety.
Kazantzi A.K., Karaferis N.D., Melissianos V.E., Bakalis K., Vamvatsikos D. (2022). Seismic fragility assessment of building-type structures in oil refineries. Bulletin of Earthquake Engineering, 20: 6853–6876.
Abstract | A seismic fragility assessment methodology is presented for equipment-supporting reinforced concrete and steel buildings that are typically encountered in oil refineries. Using a suite of hazard-consistent ground motions and reduced-order models, incremental dynamic analysis is performed to obtain the seismic demand of the structural systems examined. Appropriate drift- and floor acceleration-sensitive failure modes are considered to define the limit state capacities of the supporting structure and the nested non-structural process equipment. Special care is exercised on the demand and capacity representation of structural and non-structural components, offering a transparent roadmap for undertaking analytical fragility assessment for equipment-supporting buildings typical to an oil refinery. The findings and the proposed methodology can be exploited by designers and facility managers for mitigating the risk of failure prior to the occurrence of an earthquake event, for designing the pertinent structures and their non-structural components by means of a risk-aware performance-based methodology, or as feed data in early warning systems.
Karaferis N.D., Kazantzi A.K., Melissianos V.E., Bakalis K., Vamvatsikos D. (2022). Seismic fragility assessment of high-rise stacks in oil refineries. Bulletin of Earthquake Engineering. 20:6877–6900.
Abstract | The seismic fragility is assessed for typical high-rise stacks encountered in oil refineries, namely process towers, chimneys, and flares. Models of varying complexity were developed for the structures of interest, attempting to balance computational complexity and accuracy regarding the structural dynamic and strength properties. The models were utilized along with a set of hazard-consistent ground motions for evaluating the seismic demands through incremental dynamic analysis. Demand/capacity-related uncertainties were explicitly accounted for in the proposed framework. Damage states were defined for each of the examined structure considering characteristic serviceability and ultimate limit states. Τhe proposed resource-efficient roadmap for the analytical seismic fragility assessment of typical high-rise stacks, as well as the findings of the presented research work are available to be exploited in seismic risk assessment studies of oil refineries.
Melissianos V., Vamvatsikos D., Gantes C.J. (2020). Methodology for failure mode prediction of onshore buried steel pipelines subjected to reverse fault rupture. Soil Dynamics and Earthquake Engineering, 135: 106116
Abstract | Oil and gas buried steel pipelines are vulnerable to permanent ground displacements, such as those resulting from tectonic fault activation. The dominant failure mechanism is strongly dependent on the type of faulting. The more complex case is the reverse fault type because the crossing pipeline is significantly compressed and bent and consequently, it may fail due to local buckling, upheaval buckling or tensile weld fracture. Which among those failure modes will be critical, depends on a set of parameters, comprising fault crossing geometry, diameter to thickness ratio (D/t) of the pipeline, pipeline steel grade, and backfill soil properties. An extensive parametric study is carried out, followed by statistical processing of the results in order to formulate simplified statistical models for the prediction of the predominant failure mode according to criteria set by the American Lifelines Alliance and EN 1998-4 standards. The study thus offers the first comprehensive attempt to quantify the qualitative criterion that deeply buried pipes with high D/t ratio tend to buckle locally, while shallowly buried pipes with low D/t ratio tend to buckle globally. Pipe designers may use the provided expressions to predict the predominant failure mode in order to either apply the necessary seismic countermeasures or re-design the pipeline if necessary.
Melissianos V., Vamvatsikos D., Gantes C.J. (2017). Performance-based assessment of protection measures for buried pipes at strike-slip fault crossings. Soil Dynamics and Earthquake Engineering, 101: 1-11
Abstract | Onshore buried steel pipelines are vulnerable to fault rupture, where large ground displacements are imposed on the crossing pipe and thus protection measures are often necessary to avoid failure. A three-step methodology based on the framework of performance-based earthquake engineering is presented on assessing the effectiveness of protection measures against the consequences of strike-slip faulting on pipes. Firstly, the randomness of the fault movement is quantified, next the pipeline mechanical behavior is numerically assessed and finally the results are combined to extract the strain hazard curves, which are easy-to-handle engineering decision making tools. The various protection measures used in engineering practice or proposed in the literature are evaluated through the mean annual rate of exceeding strain values, also including a simple safety checking format at the strain level. Conclusions are extracted from the proposed assessment methodology on the efficiency of measures with reference to engineering practice and safety requirements of the pipeline operator.
Melissianos V., Vamvatsikos D., Gantes C.J. (2017). Performance assessment of buried pipelines at fault crossings. Earthquake Spectra, 33(1): 201-218
Abstract | A methodology for seismic performance assessment of onshore buried steel pipelines at fault crossings is presented. Probabilistic fault displacement hazard analysis is performed at first to determine the magnitude of the three fault displacement components in space. Next, three-dimensional (3-D) structural analysis of the pipeline via a nonlinear beam-type finite element model allows accounting for the different effect of imposed displacements in each axis. Finally, convolving of seismic hazard and structural response results in joint hazard surfaces of compressive and tensile strains that can be used to estimate the mean annual rate of exceeding any limit-state of interest under the influence of demand and capacity uncertainty.
Melissianos, V. E., Lignos, X. A., Mpachas, K., and Gantes, C. J. (2017). Experimental Investigation of Pipes with Flexible Joints under Fault Rupture. Journal of Constructional Steel Research, 128: 633-68
Abstract | Objective of the present study is the experimental investigation and comparison of the response of continuous pipes and pipes with internal flexible joints under imposed transverse displacement, modeling seismic fault rupture. Three-point bending tests were performed modeling the deformation of buried pipes subjected to fault offset. The introduction of flexible joints between adjacent pipeline parts is proposed as an alternative protection measure to reduce developing strains due to such offsets. Indeed, experimental results confirmed very significant contribution of flexible joints in strain reduction, thus providing strong promise of effective protection of buried pipes from the principal failure modes occurring in such cases, i.e. local buckling of pipe wall and tensile fracture of girth welds between adjacent pipeline segments. Experimental results have been sufficiently reproduced by numerical simulation accounting for geometric and material nonlinearities and incorporating longitudinal residual stresses due to seam weld. The numerical analyses and corresponding results are also presented in detail.
Gantes, C. J., and Melissianos, V. E. (2016). Evaluation of Seismic Protection Methods for Buried Fuel Pipelines Subjected to Fault Rupture. Frontiers in Built Environment, 2:34
Abstract | Buried steel fuel pipelines are critical lifelines for the society and the economy but are very vulnerable to earthquake-induced ground failure. Traversing seismic areas inevitably results in several pipe-fault crossings. Fault rupture forces a buried pipeline to undergo deformations that could be substantial and heavily endanger its integrity. Due to the grave consequences of a potential pipe failure, mitigating measures are commonly applied at pipe-fault crossings to reduce the effects of a potential fault activation. In this paper, a comparative review of several measures that are used in practice or have been proposed in the technical literature is presented. Numerical analyses are then carried out to compare the effectiveness of commonly used measures and to extract conclusions regarding their applicability. Results indicate that the most efficient among the evaluated measures are pipe placement within culverts and use of flexible joints. Trench backfilling with pumice is a moderately effective measure in terms of pipe protection, while steel grade upgrade, wall thickness increase, and pipe wrapping with geotextile are found to be insufficient protection methods.
Melissianos, V. E., Korakitis, G. P., Gantes, C. J., and Bouckovalas, G. D. (2016). Numerical Evaluation of the Effectiveness of Flexible Joints in Buried Pipelines Subjected to Strike-Slip Fault Rupture. Soil Dynamics and Earthquake Engineering, 90: 395-410
Abstract | Buried steel pipelines transport large amounts of fuel over long distances and inevitably cross active tectonic seismic faults when seismic areas are traversed. Eventual fault activation leads to large imposed displacements on the pipeline, which may then fail due to local wall buckling or tensile weld fracture, having grave financial, social and environmental consequences. In this paper, flexible joints are evaluated as an innovative mitigating measure against the consequences of faulting on pipelines. Joints are introduced in the pipeline in the fault vicinity, aiming at absorbing the developing deformation through relative rotation between adjacent pipeline parts, which then remain relatively unstressed. The effectiveness of flexible joints is numerically evaluated through advanced 3D nonlinear finite element modeling. Extensive parametric analysis is carried out to determine the effect of pipeline – fault crossing angle, fault offset magnitude, joint angular capacity, burial depth and diameter over thickness ratio on the joint efficiency. The uncertainty regarding the fault trace is also addressed.
Melissianos, V. E., and Gantes, C. J. (2016). Buckling and Post-Buckling Behavior of Beams with Internal Flexible Joints Resting on Elastic Foundation Modeling Buried Pipelines. Structures, 7: 138-152
Abstract | The buckling and post-buckling behavior of axially loaded Winkler beams with flexible internal hinges is addressed, aiming to provide a background for the investigation of upheaval buckling of buried pipelines equipped with flexible joints for their protection against activation of reverse seismic faults. In order to acquire qualitative understanding of the interaction between the hinge stiffness and the soil stiffness for different cases, the beams under investigation are considered as either simply-supported or clamped. At first, elastic critical buckling loads and corresponding eigenmodes are numerically obtained using linearized buckling analysis, and eigenmode cross-over is investigated considering soil and hinge rotational stiffness. Geometrically nonlinear analyses with imperfections (GNIA) are then performed, indicating for most cases descending post-buckling paths, thus unstable post-buckling behavior, with the exception of cases of very soft soil. The sensitivity of the response to initial imperfection shape and magnitude is also addressed, to identify their impact on the post-buckling behavior. Beam buckling behavior is moreover examined by considering the beam being surrounded by soil exhibiting different stiffness in the upward and the downward direction. The results are compared to the case of a continuous beam, in order to highlight the impact of internal hinges on the beam overall buckling behavior.
BOOKS & CHAPTERS IN EDITED BOOKS
Now - 2017
Melissianos V.E., Vamvatsikos D., Danciu L., Basili R. (2024). Design Fault Displacement for Lifelines at Fault Crossings: The Code-Based Approach for Europe. Bulletin of Earthquake Engineering, 22: 2677-2720.
Abstract | The earthquake-resistant design of lifelines, such as pipelines, tunnels and bridges, is based on the reliable representation and estimation of the seismic loading. In the case of lifeline–fault crossings, the design fault displacement is typically derived from estimates based on fault dimensions via empirical fault scaling relations for a given “design” scenario event. This approach comes with an unknown level of safety because the fault productivity and the actual distribution of earthquake events are essentially disregarded. To overcome this challenge, a simplified approach is proposed by statistically analyzing the outcome of probabilistic fault displacement hazard analyses (PFDHAs). A selection of faults from the 2020 European Fault-Source Model is used to build the logic tree and to set the range of parameters considered in the PFDHAs. The methodology allows the (mostly conservative) approximation of the fault displacement corresponding to any given return period based on readily available data, namely fault productivity, fault mechanism, fault length, and lifeline crossing location on the fault. The proposed methodology has been proposed and adopted as an informative Annex in prEN 1998-4:2022.
Melissianos, V.E., Gantes, C.J. (2017). Numerical Modeling Aspects of Buried Pipeline—Fault Crossing. In: Papadrakakis, M., Plevris, V., Lagaros, N. (eds) Computational Methods in Earthquake Engineering. Computational Methods in Applied Sciences, vol 44. Springer, Cham.
Abstract | Onshore buried steel pipelines transporting oil and gas play a major role in the energy supply chain. Hence, when seismic areas are transversed, fault crossing might be inevitable, which may heavily endanger the pipeline integrity. Thus, the design of buried pipelines at fault crossing remains a research topic of great interest both for the industry and the academia. Experimental, analytical and numerical approaches are used for that purpose. In this chapter, the numerical modeling of pipelines subjected to faulting is addressed and the advantages and disadvantages of the available numerical approaches are highlighted. The impact of fault type on the pipeline mechanical behavior is investigated and numerical considerations, such as the geometrical nonlinearity, the ovalization and the internal pressure are evaluated using a simple, well-established and reliable numerical approach. The outcome of this study provides useful information and guidelines to practicing engineers for the analysis and design of buried pipelines at fault crossings.
CONFERENCE PAPERS
Now - 2013
Melissianos V.E., Vamvatsikos D., Danciu L., Basili R. (2024). Design Fault Displacement for Lifelines at Fault Crossings: The Code-Based Approach for Europe. Bulletin of Earthquake Engineering, 22: 2677-2720.
Abstract | The earthquake-resistant design of lifelines, such as pipelines, tunnels and bridges, is based on the reliable representation and estimation of the seismic loading. In the case of lifeline–fault crossings, the design fault displacement is typically derived from estimates based on fault dimensions via empirical fault scaling relations for a given “design” scenario event. This approach comes with an unknown level of safety because the fault productivity and the actual distribution of earthquake events are essentially disregarded. To overcome this challenge, a simplified approach is proposed by statistically analyzing the outcome of probabilistic fault displacement hazard analyses (PFDHAs). A selection of faults from the 2020 European Fault-Source Model is used to build the logic tree and to set the range of parameters considered in the PFDHAs. The methodology allows the (mostly conservative) approximation of the fault displacement corresponding to any given return period based on readily available data, namely fault productivity, fault mechanism, fault length, and lifeline crossing location on the fault. The proposed methodology has been proposed and adopted as an informative Annex in prEN 1998-4:2022.
Melissianos V.E., Kazantzi A.K., Karaferis N., Bakalis K., Vamvatsikos D. (2023). Reduced-order models of steel structures for the seismic risk assessment of oil refineries. Proceedings of the 10th Hellenic National Conference on Steel Structures, Athens, Greece.
Abstract | Ensuring the structural and operational integrity of oil refineries in case of an earthquake event is of utmost importance for the society, the environment, and the economy. A potential failure in such critical facilities may trigger a number of undesirable situations, such as fire, injuries, environmental pollution, etc. Hence, improving safety plan and increasing seismic resilience is a necessity that requires the development of reliable models and seismic risk assessment tools. Towards this direction, this paper presents a seismic fragility study of two characteristic steel high-rise stacks encountered in oil refineries, namely a relatively low-rise chimney and a process tower. The developed of reduced-order numerical models, the selection of appropriate engineering demand parameters to capture the seismic response of the structures, the calculation of the fragility curves, and finally the evaluation of the overall seismic response are presented. The results could be exploited in the context of a seismic risk assessment study of an oil refinery, as an integrated system.
[paper]
Melissianos V.E., Karaferis N.D., Kazantzi A.K., Bakalis K., Vamvatsikos D. (2023). Towards seismic resilience of industrial facilities: the case study of an oil refinery. Proceedings of the SECED 2023 Conference, Cambridge, UK.
Abstract | Crude oil refineries are high-importance infrastructure that play a key role in the energy supply chain. Securing the operational and structural integrity of refineries in the aftermath of an earthquake is crucial for avoiding the undesirable consequences of a Natural-Technological (NaTech) incident, such as injuries, environmental pollution, business interruption, and monetary losses. Refineries are designed, constructed, maintained, and operated under a strict framework of standards and regulations. Still, seismic-related NaTech incidents are occurring. Thus, to assess with more confidence and consequently improve, if needed, their seismic resilience, a coherent performance-based framework needs to be utilised, that accounts for the refinery as an integrated system comprising a variety of structural typologies, such as buildings, tanks, and high-rise stacks. These structures have very diverse dynamic properties and hence seismic responses. Towards this objective, a virtual crude oil refinery is examined herein as a case study. The aim is to showcase the steps of a seismic risk assessment framework when applied to such infrastructures, focusing on the evaluation of the seismic hazard, the development of the exposure model, the numerical analysis of the structures, and the preliminary damage assessment of the facility using different earthquake scenarios.
[paper]
Kazantzi A., Karaferis N., Melissianos V.E., Vamvatsikos D. (2023). Design of acceleration-sensitive ancillary elements under uncertainties in the new eurocode. Proceedings of the SECED 2023 Conference, Cambridge, UK.
Abstract | The overall seismic safety and operability of industrial building-type structures located in critical infrastructure facilities, largely depend on the seismic performance of their nested and/or supported ancillary elements, namely mechanical and electrical equipment, machinery, vessels, etc. Hence, on account that (a) no or minimal direct structural damages are anticipated in the equipment-supporting structures per se during moderate or even strong earthquake events since such structures are typically overdesigned and (b) the sustained structural damages are mostly due to the inferior seismic performance of the nested ancillary elements that could trigger a series of adverse cascading incidents (e.g., uncontrolled fires, explosions), significant effort has been
invested towards developing a design framework that could deliver safe designs for the latter. Despite the significant advancements in the relevant field, the development of a robust design framework is often undermined by several uncertainties that come into play in the evaluation of the capacity and demand of such nonstructural components. In particular, critical information that is needed for the design of the ancillary elements, such as the dynamic characteristics of the component and the supporting structure, are often abstract and/or require substantial effort for being retrieved with certain confidence. On that basis, the new Eurocode 8, offers three distinct design options that allow for adjustments in the conservatism that is induced in the design of the acceleration-sensitive ancillary elements according to the availability and reliability of information on the overall system. This study investigates, by means of a case study industrial structure, the extent to which the seismic reliability of an otherwise code-compatible component designed to comply with each one of the three alternative Eurocode design routes, is likely to be undermined for small discrepancies of the assumed properties from their actual values.
[paper]
Melissianos V.E., Vamvatsikos D., Danciu L., Basili R. (2022). Code-Based Approach for Estimating the Seismic Fault Displacement for Earthquake-Resistance Design of Buried Pipelines. Proceedings of the 5th Panhellenic Conference on Earthquake Engineering and Engineering Seismology, Athens, Greece (in greek).
Abstract | Buried steel fuel pipelines are vulnerable to ground deformations caused by the activation of the crossing seismic fault. In such case, pipelines develop excessive deformations and strains as they follow the ground movement. Ensuring the structural and operational integrity of pipelines, which are critical energy infrastructure, is of utmost importance. In contrast to a typical deterministic design approach, where the seismicity is not taken into account, the performance-based approach can provide the required balance between safety and economy. Towards this path, an approximate methodology for calculating the fault displacement for a given return period was developed. This displacement is suitable for the design of pipelines crossing active seismic faults. using the database of faults in Europe, a lot of probabilistic fault displacement hazard analyses were executed. The statistical processing of these results led to the development of a set of simplified analytical relations that allow the calculation of the design fault displacement based only on data that are available to the engineer, without the requirement of specialized geological and seismological studies. The proposed methodology gas been adopted as an informative annex in the new version of EN1998-4.
[paper]
Karaferi E., Melissianos V.,Vamvatsikos D. (2022). A preliminary urban seismic risk model for the City of Rhodes Greece. Proceedings of the 3rd European Conference on Earthquake Engineering and Seismology (3ECEES), Bucharest, Romania.
Abstract | A first-order model is developed for the seismic risk assessment of the water supply network and the structural integrity of the buildings of Rhodes under spatially correlated seismic loading. For its implementation, in-house software is coded in the object-oriented programming language Python. The water supply network is modelled via a graph theory approach and the vulnerability of the buildings takes advantage of the 2020 European Seismic Risk Model. An event-based probabilistic seismic hazard approach is employed, generating ground motion fields for 10,000 years with the OpenQuake platform. The intensity measures used are the peak ground velocity (PGV) for the water pipelines and Sa(1s) for the buildings.
The close correlation of the two allows the creation of spatially cross-correlated PGV and Sa(1s) values that are otherwise not readily available. Results are obtained, per block, for the percentage of people that have no access to water and for the damage of buildings. This is enough to offer a preliminary determination of the disruption caused by each event in terms of available housing and utilities, in support of socioeconomic impact modeling.
[paper]
Kazantzi A.K., Karaferis N.D., Melissianos V.E., Bakalis K., Vamvatsikos D. (2022). Seismic fragility assessment of two low-rise equipment-supporting RC industrial buildings. Proceedings of the 3rd European Conference on Earthquake Engineering and Seismology (3ECEES), Bucharest, Romania.
Abstract | Open-frame reinforced concrete (RC) buildings for supporting essential mechanical/electrical equipment are encountered in almost all industrial plants. Hence, to ensure the undisrupted operation of an industrial facility, the integrity of such structural assets along with their nested nonstructural components should be verified against a spectrum of natural and man-made hazards. Focusing on the earthquake peril, this study presents an analytical seismic fragility assessment framework for two RC equipment-supporting buildings that are deemed typical to an oil refinery. The proposed fully-probabilistic fragility concept, utilises reduced-order building models for the evaluation of the induced seismic demands and accounts for both drift and acceleration-sensitive failure modes in the definition of the damage states. The findings can be exploited by designers and facility managers for developing efficient pre- and post-event risk-aware mitigation/response strategies and are delivered in a manner that can be readily integrated into the seismic performance assessment framework of an entire industrial facility.
[paper]
Melissianos V.E., Vamvatsikos D., Danciu L., Basili R. (2022). An engineering approach to fault displacement hazard for lifelines crossing active tectonic faults. Proceedings of the 3rd European Conference on Earthquake Engineering and Seismology (3ECEES), Bucharest, Romania.
Abstract | Lifelines, such as pipelines, tunnels, and bridges are vulnerable to seismic-induced ground displacements caused by the activation of active tectonic faults. Lifelines are forced to follow the ground movement in fault crossings and develop excessive deformation. Safeguarding the integrity of such critical infrastructure is of paramount importance. Contrary to typical deterministic design approaches that discount fault productivity, a performance-based approach can achieve a balance between safety and economy. Towards this goal, a set of simplified expressions is developed for determining fault displacement at given return periods, developed by analyzing the outcome of probabilistic fault displacement hazard analysis (PFDHA) for European faults. The proposed methodology allows the computation of the design fault displacement with data available to the engineer and has been adopted as an informative Annex in EN1998-4.
[paper]
Melissianos V.E., Karaferis N.D., Kazantzi A.K., Bakalis K., Vamvatsikos D. (2022). An integrated model for the seismic risk assessment of an oil refinery. Proceedings of the 3rd International Conference on Natural Hazards & Infrastructure ICONHIC 2022, Athens, Greece.
Abstract | Oil refineries play a key role in the energy supply chain. Safeguarding the integrity of such high-importance facilities against natural hazards is crucial because a potential failure may result in a sequence of unwanted events, spanning from business disruption to uncontrolled leakage and/or major accidents. Despite the strict criteria enforced during the design, construction, maintenance, and operation of an oil refinery, Natural-Technological events caused by earthquakes still occur.
Oil refining is a complex process that involves a variety of structural typologies, such as buildings, tanks, chimneys, pipe-racks, pressure vessels, and process towers. These structures have fundamentally different dynamic properties and seismic responses. A comprehensive seismic risk assessment framework is thus required to account for the refinery as an integrated system and provide information about both the structural and operational integrity of the individual assets and the system. In the present study, a virtual crude oil refinery is examined as a case study to demonstrate the steps of a preliminary seismic risk assessment framework, consisting of the seismic hazard calculation, the development of the exposure model, the analysis of the structures at risk, and the damage assessment of the facility. Scenario-based results are presented for the refinery and the critical assets are identified.
[paper]
Karaferi E.D., Melissianos V.E., Vamvatsikos D. (2022). Simplified Seismic Risk Assessment for the Water Supply Network of Rhodes, Greece. Proceedings of the 3rd International Conference on Natural Hazards & Infrastructure ICONHIC 2022, Athens, Greece.
Abstract | A methodology is developed for the risk assessment of the water supply network of the city of Rhodes under spatially distributed seismic loading. Graph theory is used to implement this methodology by creating in-house software in the object-oriented programming language Python. Multiple seismic events are employed that have been generated with a probabilistic approach for a 10,000 year period using the OpenQuake platform and the 2013 European Seismic Hazard Model. The intensity measure used is the peak ground velocity (PGV). Since a direct generation capability for ground motion fields with spatial correlation is not readily available for PGV, the spatial distribution of the spectral acceleration at a period of 1s was employed, which is strongly correlated
with the ground velocity. Results are obtained for the length of the pipes that will break for each event. The complex topology of the network is efficiently tackled via the graph theory to track which pipes cannot supply water and which need repair. The outcomes of the analysis indicate the percentage of the customers that are left without water in each building block of the city, to assess the population that has no access to water after a destructive event. Finally, curves of the mean annual frequency of exceeding given values of the damaged pipe length and the number of pipe breaks are produced, and the average annual losses are estimated.
[paper]
Vamvatsikos, D., Fragiadakis, M., Georgopoulos, I.-O., Koumousis, V. K., Koutsoyiannis, S., Manetas, A. Melissianos, V. E., Papadopoulos, C., Papanikolopoulos, K. E., Toumpakari, E.-E. (2021). The ARCHYTAS intelligent decision-support system for the protection of monumental structures. Proceedings of the 4th International Conference on Protection of Historical Constructions (PROHITECH 2020), Athens, Greece
Abstract | The ARCHYTAS platform is based on using (i) reliable mechanical models and damage thresholds for assessing structural performance (ii) a network of sensors for updating the model parameters, (iii) detailed estimates of earthquake and flood hazard at the sites of interest and (iv) a state-of-art approach for multi-hazard risk assessment that can deliver accurate pre/trans/post-event evaluation of the risk at multiple geographically distributed cultural heritage sites. The core of the proposed system comprises a cloud-deployed computational platform, where data obtained from on-site measuring systems is processed, critical environmental actions are identified and flags are raised to provide alerts on the predicted monument structural condition. The decision-support system is fully uncertainty-aware, employing the concept of the mean annual frequency of limit-state exceedance under specified confidence levels to offer monument-specific courses of action based on the convolution of the current state of the monument (as determined by its best-estimate fragility, and updated by current or past measurements) and the predicted, recorded or evolving hazard. All-in-all, the platform can assist the relevant authorities to prioritize inspection, maintenance and rehabilitation actions be-fore or after events subject to limited available resources.
Lachanas, C. G., Melissianos, V. E., and Vamvatsikos, D. (2021). Spatial variability of ground motion hazard and preliminary regional damage assessment of ancient monuments. Proceedings of the 4th International Conference on Protection of Historical Constructions (PROHITECH 2020), Athens, Greece
Abstract | The seismic hazard is a spatial variable and its distribution depends on the site and soil conditions, the distance from the influencing faults, their geometric characteristics etc. To characterize a future seismic event, multiple correlated Intensity Measure (IM) fields are employed. In Greece and especially in the Attica region, there are numerous monuments of classical antiquity that are spread throughout the territory, e.g., the Temple of Poseidon in Sounio, the Ancient Walls of Piraeus etc., and not only in the center of the city of Athens, where the well-known Parthenon, the Temple of Olympian Zeus, etc. lie. To capture the ensemble risk of such widely distributed antiquities a regional risk assessment approach is adopted, based on the principles of the Performance-Based Earthquake Engineering. Event-Based Probabilistic Seismic Hazard Analysis (PSHA) is used as basis, where the distribution of the ΙΜ fields is evaluated for a stochastic event set, spanning thou-sands of realizations, allowing the estimation of damages over an entire region on an event-by-event basis. A basic application is offered by considering a typical single multi-drum column at each site of interest to assess its performance. Different fragility representation schemes are employed, and their consequences are compared for both the event-based and the classical approach of PSHA as a first decisive step towards the formulation of a comprehensive methodology for the assessment of seismic damages of ancient monuments within a region.
Melissianos, V. E., Lachanas, C. G., and Vamvatsikos, D. (2021). Preliminary seismic risk assessment of monolithic columns of the Aphaia Temple in Aegina. Proceedings of the 4th International Conference on Protection of Historical Constructions (PROHITECH 2020), Athens, Greece
Abstract | Studies on the seismic assessment of monumental structures of antiquity are mostly focused on the estimation of the structural behavior and do not involve the pertinent uncertainties. Towards filling this research gap, a preliminary seismic risk assessment of monolithic columns of the Aphaia Temple in Aegina island, Greece, is presented. A comprehensive application of the framework of Performance-Based Earthquake Engineering is carried out. Site-specific seismic hazard estimation is performed at first by employing Probabilistic Seismic Hazard Analysis. The rocking column is analyzed under seismic excitation by numerically solving the equation of motion in order to extract the fragility curves. Finally, the convolving of seismic hazard and structural response yields the seismic risk of the column that is used to estimate the mean annual rate of exceeding predefined limit states that are associated with damage and collapse of the column.
Melissianos V.E., Dasiou M.E., Vamvatsikos D. (2021). Seismic risk assessment of the ancient temple of Aphaia in Greece. Proceedings of the 17th World Conference on Earthquake Engineering (17WCEE), Sendai, Japan
Abstract | The protection of cultural heritage against natural hazards has attracted significant research efforts and funding during the last decades, recognizing its importance in humanity’s history and raising public awareness on this issue. In Greece, there are numerous monuments that have been exposed to environmental actions, and, consequently, many are classified as deteriorating structures. In addition, earthquakes pose a significant threat to their structural integrity and contribute to the accumulation of damage. The evaluation of the seismic performance of such heritage assets is a complex computational problem, especially as their structural elements are either not rigidly connected, or connected by weak mortar, and thus prone to rocking due to the seismic excitation.
Research on the seismic assessment of monuments is quite limited to the estimation of the structural behavior, thus excluding the incorporation of pertinent uncertainties. The aim of the study is to contribute to the seismic risk assessment of monuments. The framework of Performance-Based Earthquake Engineering is applied, comprising of four successive and interconnected steps: (1) the European seismic source model is used to estimate the seismic hazard in terms of a scalar intensity measure, (2) the structure is modeled with a discrete element approach. The rocking and/or sliding of the individual stone blocks are accurately addressed by the software since, during the calculation, it locates each contact and computes the motion of each block from the forces that are developed at the joints. Results in terms of maximum displacements are obtained from the analysis and related to damage states. (3) The limit-state and the aleatory and epistemic uncertainties are defined for the determination of discrete damage states and the associated fragility curves, and (4) the seismic risk is calculated in terms of the mean annual frequency of exceeding each limit state. The aforementioned methodology is applied to a free-standing column and a colonnade of two columns with an architrave at the ancient Temple of Aphaia, located on the Greek island of Aegina and built between 510 and 470 BC, comprising a significant example of the Archaic architecture.
Vamvatsikos D., Melissianos V., Kostaridis A., Kazantzi A.K, Karaferis N., Chatzidaki A., Diagourtas D., Bakalis K. (2021). The PANOPTIS-INFRASTRESS framework for infrastructure risk assessment. Proceedings of the 8th International Conference on Civil Protection & New Technologies (SafeGreece 2021), Athens, Greece.
Melissianos V., Karaferis N., Vamvatsikos D., Kazantzi A., Bakalis K. (2021). An integrated model for the seismic risk assessment of an oil refinery. Proceedings of the ICONHIC2022 – Preparatory Workshop 2021, Athens, Greece.
Abstract |
Melissianos V.E., Vamvatsikos D. (2020). Simplified estimation of design fault displacement for buried pipelines at fault crossing. Proceedings of the 11th European Conference on Structural Dynamics (EURODYN 2020), Athens, Greece
Melissianos V., Vamvatsikos D., Gantes C. (2019). Empirical expressions for predicting the buckling failure of buried pipelines under reverse faulting. Proceedings of the 4th Panhellenic Conference on Earthquake Engineering and Engineering Seismology, Athens, Greece (in greek)
Περίληψη | Οι υπόγειοι αγωγοί μεταφοράς καυσίμων αποτελούν κρίσιμο τμήμα της ενεργειακής υποδομής μιας χώρας καθώς εξασφαλίζουν τη μεταφορά και διανομή καυσίμων με οικονομικό τρόπο και ασφάλεια. Στην περίπτωση διέλευσης αγωγών από σεισμογενείς περιοχές, η ενεργοποίηση ενός διασταυρούμενου σεισμικού ρήγματος είναι πιθανό να προκαλέσει βλάβη του αγωγού με κοινωνικές, περιβαλλοντικές και οικονομικές επιπτώσεις. Στην περίπτωση ανάστροφης διάρρηξης, ο αγωγός υπόκειται σε σημαντική θλιπτική καταπόνηση, λόγω της κίνησης του ανερχόμενου τεμάχους του ρήγματος. Οι πιθανές μορφές αστοχίας σε αυτήν την περίπτωση είναι ο τοπικός ή καθολικός λυγισμός και η εφελκυστική θραύση σε θέσεις συγκολλήσεων. Καθοριστικές παράμετροι για το ποιά μορφή αστοχίας θα
είναι κυρίαρχη είναι η τοπική λυγηρότητα του αγωγού (λόγος διαμέτρου προς πάχος D/t) και το βάθος ταφής. Σκοπός της μελέτης είναι η διατύπωση μιας εμπειρικής σχέσης πρόβλεψης της μορφής αστοχίας. Συγκεκριμένα, μέσω παραμετρικών αριθμητικών αναλύσεων και στατιστικής επεξεργασίας των αποτελεσμάτων με τη μέθοδο της γραμμικής διακριτικής ανάλυσης, προτείνεται μια εμπειρική σχέση που διαχωρίζει της περιοχές εμφάνισης των διαφορετικών μορφών αστοχίας στο χωρίο «βάθος ταφής – λόγος D/t» συναρτήσει της γεωμετρίας διασταύρωσης αγωγού – ρήγματος.
Melissianos, V. E., and Gantes, C. J. (2019). Protection Measures for Buried Steel Pipelines Subjected to Fault rupture. Proceedings of the 2nd International Conference on Natural Hazards & Infrastructure, Chania, Greece
Abstract | Buried steel pipelines are critical lifelines that supply necessary energy resources for the economy and society. Pipelines are hazardous structures and any potential failure caused by fault rupture has to be eliminated. Various alternative protection measures are applied in practice or have been studied by researchers against the consequences of faulting on buried pipes. A comprehensive evaluation of the effectiveness of protection measures is presented in the paper for pipes subjected to normal and reverse fault rupture. The analysis is carried out numerically by employing the beam-on-Winkler-foundation model. The effectiveness of protection measures is compared to extract conclusions regarding their applicability. Results indicate that the most effective protection measure among the conventional ones examined is the trench backfilling with pumice, while steel grade upgrade and wall thickness increase provide little protection. Trench widening was found to be ineffective, while maximum strain reduction is achieved in the case of the introduction of flexible joints.
Karvelis, A. C., Melissianos, V. E., and Gantes, C. J. (2017). Numerical Investigation of Local Buckling of Steel Pipelines under Seismic Fault Rupture. Proceedings of the 9th Hellenic National Conference on Steel Structures, Larisa, Greece (in greek)
Summary | Onshore buried pipelines are the main mean for fuel transportation in order to meet the increasing energy demands of the economy and extend over long distance. When seismic areas are attempted, eventual pipe – fault crossing is increased. A fault activation leads to imposed large permanent ground displacements on the pipe, which the latter has to follow. The main failure modes in this case are tensile fracture of the girth welds between the adjacent pipe parts and local buckling of the pipe wall. Pertinent safety checks are carried out in terms of tensile and compressive strains, respectively. The occurrence of local buckling is numerically investigated in the present study and the pertinent code-based strain limits are evaluated. Firstly, a numerical model is formulated that is calibrated based on experimental results from four-point bending tests. Then, a simplified numerical model is developed in order on the one hand to investigate the main parameters affecting the local buckling occurrence and on the other hand to formulate the basis for the next step of the research, where the surrounding soil will be taken into account. The evaluation of the numerical results reveals the unstable post-buckling behavior of the pipe. Moreover, the effect of the diameter over thickness ratio on the ultimate load and the critical buckling strain is investigated.
Melissianos, V.E., Gantes, C.J. (2017). Numerical Modeling Aspects of Buried Pipeline—Fault Crossing. In: Papadrakakis, M., Plevris, V., Lagaros, N. (eds) Computational Methods in Earthquake Engineering. Computational Methods in Applied Sciences, vol 44. Springer, Cham.
Abstract | Onshore buried steel pipelines transporting oil and gas play a major role in the energy supply chain. Hence, when seismic areas are transversed, fault crossing might be inevitable, which may heavily endanger the pipeline integrity. Thus, the design of buried pipelines at fault crossing remains a research topic of great interest both for the industry and the academia. Experimental, analytical and numerical approaches are used for that purpose. In this chapter, the numerical modeling of pipelines subjected to faulting is addressed and the advantages and disadvantages of the available numerical approaches are highlighted. The impact of fault type on the pipeline mechanical behavior is investigated and numerical considerations, such as the geometrical nonlinearity, the ovalization and the internal pressure are evaluated using a simple, well-established and reliable numerical approach. The outcome of this study provides useful information and guidelines to practicing engineers for the analysis and design of buried pipelines at fault crossings.
Melissianos, V. E., and Gantes, C. J. (2015). Failure Mode Evaluation of Onshore Buried Steel Pipelines with Flexible Joints due to Faulting. Proceedings of the SECED 2015 Conference: Earthquake Risk and Engineering towards a Resilient World, Cambridge, UK
Abstract | Oil and gas onshore steel buried pipelines are hazardous structures, thus mitigating their potential failure due to faulting is a research topic of significant interest. Conventional preventive measures that are currently used in practice aim at reducing pipe-soil friction, so that the pipeline is more free to deform within the soil and occurring tensile and compressive strains do not exceed certain limits. In the present study a different approach is examined, namely the introduction of flexible joints between adjacent pipeline steel parts in the vicinity of fault crossing, in order to concentrate strains at these joints and drastically reduce developing strains on steel pipe parts. Advanced numerical models are adopted to investigate the behavior of continuous pipelines and pipelines with flexible joints under strike-slip fault offset. Numerical results highlight the effectiveness of flexible joints in terms of reducing resulting strains, while a parametric study on pipe-fault crossing angle indicates the angle range within which flexible joints are effective.
Melissianos V.E., Vamvatsikos D., Gantes C.J. (2015). Probabilistic assessment of pipeline – fault crossing. Proceedings of the COMPDYN2015 Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Crete, Greece
Abstract | Buried steel pipelines transporting oil and oil products play a vital role in the energy supply chain. Pipelines extend to long distances and thus intercepting tectonic faults, when a seismic area is crossed, is often inevitable and may heavily threat the pipeline integrity. Earthquakes and the associated fault displacements are naturally random events and therefore the imposed large ground displacements on the pipeline have to be considered through a probabilistic perspective. In the present study, a comprehensive seismic risk analysis of buried pipeline – fault crossing is presented, consisting of two steps. The first step is the probabilistic assessment of the fault displacement accounting also for the pertinent uncertainties. The second step is the pipeline structural analysis. The transition from the seismological data to the structural analysis is realized through the fault displacement components as the selected vector intensity measure. The outcome of the proposed methodology is the strain hazard curves for both tensile and compressive longitudinal strains. The resulting strain capacities are compared to strain demands from structural codes in order to assess the potential of pipeline failure due to local buckling or tensile fracture. Furthermore, uncertainty and disaggregation results from the fault displacement hazard analysis are presented for the selection of the appropriate deterministic design scenario and the evaluation of the fault displacement hazard parameters. Lastly, the proposed process is a reliable estimation tool for seismic risk assessment of pipeline – fault crossing and a decision making tool for route selection and application of preventive measures against the consequences of faulting on pipelines.
Melissianos V.E., Vamvatsikos D., Gantes C.J. (2015). Probabilistic assessment of innovative mitigating measures for buried steel pipeline – fault crossing. Proceedings of the ASME 2015 Pressure Vessels & Piping Conference PVP2015, Boston, MA
Abstract | A methodology is presented on assessing the effectiveness of flexible joints in mitigating the consequences of faulting on buried steel pipelines through a comprehensive analysis that incorporates the uncertainty of fault displacement magnitude and the response of the pipeline itself. The proposed methodology is a two-step process. In the first step the probabilistic nature of the fault displacement magnitude is evaluated by applying the Probabilistic Fault Displacement Hazard Analysis, considering also all pertinent uncertainties. The second step is the “transition” from seismological data to the pipeline structural response through the fault displacement components as the adopted vector intensity measure. To mitigate the consequences of faulting on pipelines, flexible joints between pipeline parts are proposed as innovative measure for reducing the deformation of pipeline walls. Thus, the mechanical behavior of continuous pipelines and pipelines with flexible joints is numerically assessed and strains are extracted in order to develop the corresponding strain hazard curves. The latter are a useful engineering tool for pipeline – fault crossing risk assessment and for the effectiveness evaluation of flexible joints as innovative mitigating measures against the consequences of faulting on pipelines.
Melissianos, V. E., and Gantes, C. J. (2014). On the Efficiency of Flexible Joints in Mitigating the Consequences of Seismic Fault Activation on Buried Pipelines. Proceedings of the Qatar Foundation Annual Research Conference 2014, Doha, Qatar
Abstract | Attempts to meet rising worldwide energ y demands, often leads to the construction of hydrocarbonate pipelines over ver y long distances. Crossing seismic areas is often inevitable for such pipeline routes even though the design of new pipelines takes place within a stringent framework of regulations to protect the environment and avoid populated areas. In such cases, the potential for large ground differential movement due to fault activation often becomes the primar y cause of pipeline failure.
Buried steel pipelines deform to adapt to movement of the surrounding soil, so possible failure modes are tensile fracture of girth welds between adjacent pipeline parts, local buckling of the pipeline wall due to compressive strains, and upheaval buckling due to high compressive forces in the case of reversetype faults. The latter is the dominant failure mode for relatively shallowly buried pipelines with low diameter-to-thickness ratio, but is not usually relevant for the relatively thin-walled pipelines used to transport fuel.
Minimizing the consequences of induced large ground displacements on pipeline integrity is both an industrial and academic research topic of high priority. Among conventional mitigating measures, such as constructing a wider trench and backfilling with loose granular soil to reduce soil-pipeline friction, research is directed towards integrating flexible joints between adjacent steel parts in buried pipelines crossing areas prone to large ground displacements. This approach aims at concentrating strains at the joints, leaving the steel pipe virtually undeformed. Thus, the failure modes caused by high strain concentrations, i.e. tensile fracture of the welds and local shell buckling, are avoided.
However, the introduction of flexible joints – acting as internal hinges and transforming the continuous pipeline to a segmented one – tends to decrease pipeline global stiffness and render them more susceptible to upheaval buckling, to the extent that it may become the dominant failure mode, even for deeply-buried pressurized pipelines with relatively high diameter-to-thickness ratios crossing reverse faults. This issue is investigated numerically by modeling the pipeline with beam-type finite elements, and the surrounding soil with nonlinear translational springs. The numerical models are calibrated by comparison to experimental tests. Numerical analyses incorporating geometrical nonlinearities as well as pipeline steel and soil nonlinearities are carried out in order to investigate upheaval buckling and postbuckling global behavior of pipelines with flexible joints at reverse fault crossings, and compare it to the aforementioned local – compressive or tensile – failure modes. Results indicate that during pipeline design a balance has to be struck between the advantages of using flexible joints to reduce strains and the limitation of hazard against failure due to upheaval buckling.
Melissianos, V. E., Gantes, C. J., and Kalfantis P. P. (2014). Upheaval Buckling Risk Assessment of Buried Pipelines due to Reverse Seismic Fault Activation. Proceedings of the 8th Hellenic National Conference on Steel Structures, Tripoli, Greece (in greek)
Summary | Buried pipelines are classified as hazardous structures as among others due to their extended length crossing areas prone to large ground deformations due to seismic fault activation is usually inevitable. In this case a potential failure mode is upheaval buckling under acting compressive forces, due to reverse fault activation. In the present study the risk of upheaval buckling of buried steel pipelines is numerically investigated against other failure modes by also accounting for geometrical and pipeline steel and soil nonlinearities. Obtained results indicate that upheaval buckling is not the critical failure mode. Instead inelastic local buckling is the critical failure mode for the relatively deeply buried pipeline under investigation characterized by high diameter to thickness ratio.
Melissianos, V. E., and Gantes, C. J. (2014). Upheaval Buckling of Onshore Buried Steel Pipelines with Flexible Joints. Proceedings of the International Association for Shell and Spatial Structures 2014 Symposium – IASS 2014 Symposium, Brasilia, Brazil
Abstract | Buckling and post-buckling behavior of beams resting on nonlinear foundation is addressed in the present study, as a decisive step towards investigating upheaval buckling of onshore buried pipelines. The adopted mechanical model is that of a beam with fixed boundary conditions supported laterally by uniformly distributed uniaxial springs that model vertical downward and upward pipeline movement in the trench. An internal hinge equipped with an elastic rotational spring in the beam middle span models the introduced flexible joint. The beam under investigation is subjected to constant compressive axial force over its length. Linear Buckling Analyses (LBAs) are initially conducted to obtain eigenmodes that are then adopted as imperfection shapes. Then, geometrically and materially nonlinear analyses with imperfections (GMNIAs), incorporating soil nonlinearity, are carried out, indicating unstable post-buckling behavior. Obtained results are of importance regarding the use of flexible joints in pipelines crossing areas prone to large ground differential movement.
Melissianos, V. E., and Gantes, C. J. (2014). Earthquake Induced Upheaval Buckling of Buried Pipelines with Flexible Joints. Proceedings of the Second European Conference on Earthquake Engineering and Seismology – 2ECEES, Istanbul, Turkey
Abstract | Buckling and post-buckling behaviour of beams resting on elastic foundation with an internal hinge is addressed in the present study, as a first step towards modeling upheaval buckling of buried pipelines with flexible joints, induced by a reverse fault activation during a seismic event. The mathematical model used is that of a simply-supported Winkler beam supported laterally by uniformly distributed transverse springs, with an internal hinge stiffened by a rotational spring, and subjected to constant axial force over its length. Linear Buckling Analysis (LBA) is firstly carried out to illustrate the effect of internal rotational stiffness on critical buckling load with respect to a continuous beam. Additionally, through LBAs the interaction of elastic soil stiffness and elastic rotational stiffness is presented in terms of critical buckling load and eigenmode transition. Then, geometrically nonlinear analyses with imperfections (GNIA) are performed, indicating descending post-buckling paths, thus unstable post-buckling behaviour, as well as buckling mode interaction for certain ranges of values of soil stiffness.
Gantes, C. J., and Melissianos, V. E. (2014). Buckling and Post-Buckling Behavior of Beams on Elastic Foundation Modeling Buried Pipelines. Proceedings of the Civil Engineering for Sustainability and Resilience International Conference – CESARE ’14, Amman, Jordan
Abstract | Buckling and post-buckling behavior of beams resting on elastic foundation is addressed in the present study, as a first step towards modeling upheaval buckling of buried pipelines. The mathematical model used is that of a simply-supported Winkler beam supported laterally by uniformly distributed transverse springs, which is subjected to constant axial force over its length. Elastic critical buckling loads and corresponding eigenmodes are first obtained analytically, by formulating equilibrium equations in the deformed configuration and deriving and solving the corresponding buckling equation. The results are compared with results from linear buckling analyses of finite element models and indicate buckling mode cross-over with respect to soil stiffness. Then, geometrically nonlinear analyses with imperfections (GNIA) are performed, indicating descending post-buckling paths, thus unstable post-buckling behavior as well as buckling mode interaction for certain ranges of values of soil stiffness.
Melissianos V.E., Vamvatsikos D., Gantes C.J. (2014). Seismic risk assessment of buried pipelines at active fault crossings. Proceedings of the 2nd European Conference on Earthquake Engineering and Seismology (2ECEES), Istanbul, Turkey
Abstract | A methodology is presented on assessing the seismic risk of buried steel pipelines crossing active tectonic faults through a comprehensive analysis by incorporating the uncertainty of the loading resulting from fault movement, soil response and the response of the pipeline itself. The proposed methodology is a two-step process. In the first step Probabilistic Fault Displacement Hazard analysis is implemented to quantify the probabilistic nature of the load, namely the imposed differential displacement on the pipeline due to large permanent fault displacements, incorporating all pertinent uncertainties regarding, for example, seismicity rate, maximum moment magnitude, etc. The second step is the “transition” from seismological data to pipeline structural response through a vector intensity measure represented by the fault displacement components in 3D. Advanced pipeline numerical simulations are then carried out in order to form pipeline strain hazard curves as a useful engineering tool for pipeline fault crossing seismic risk assessment.
Gantes, C. J., and Melissianos, V. E. (2013). Numerical Analysis of Buried Steel Pipelines. Proceedings of the BCCCE 2013: 2nd International Balkans Conference on Challenges of Civil Engineering, Tirana, Albania
Abstract | Various alternative numerical analysis methods that are used to simulate the response of buried steel pipelines subjected to large imposed displacements triggered by seismic fault activation are presented. Due to the grave financial, social and environmental consequences of a potential pipeline leakage, damage or failure is a problem deserving special attention. Advanced nonlinear numerical simulations are the only way to handle with sufficient accuracy the complexity of the physical problem associated with the surrounding soil and the relevant pipeline-soil interaction. During preliminary design, however, reliable numerical models are required that demand minimum computational effort.
In this paper alternative simulations of the problem making use of beam-type finite elements are presented and compared in terms of accuracy and computational cost. Comparisons are carried out regarding the types of finite elements, whether geometric nonlinearity is included or not.