Large scale offshore wind farms are relatively new infrastructures and are being deployed in regions prone to earthquakes. Offshore wind farms comprise of both offshore wind turbines (OWTs) and ...balance of plants (BOP) facilities, such as inter-array and export cables, grid connection etc. An OWT structure can be either grounded systems (rigidly anchored to the seabed) or floating systems (with tension legs or catenary cables). OWTs are dynamically-sensitive structures made of a long slender tower with a top-heavy mass, known as Nacelle, to which a heavy rotating mass (hub and blades) is attached. These structures, apart from the variable environmental wind and wave loads, may also be subjected to earthquake related hazards in seismic zones. The earthquake hazards that can affect offshore wind farm are fault displacement, seismic shaking, subsurface liquefaction, submarine landslides, tsunami effects and a combination thereof. Procedures for seismic designing OWTs are not explicitly mentioned in current codes of practice. The aim of the paper is to discuss the seismic related challenges in the analysis and design of offshore wind farms and wind turbine structures. Different types of grounded and floating systems are considered to evaluate the seismic related effects. However, emphasis is provided on Tension Leg Platform (TLP) type floating wind turbine. Future research needs are also identified.
An increasing number of offshore wind farms are being constructed in seismic regions over liquefaction susceptible soils. This paper presents a methodology for the analysis and design of monopiles in ...seismically liquefiable soils by extending the established "10-step methodology" with an additional 7 steps. These additional steps include assimilation of seismic data, site response analysis, stability check of the structure (ULS check through the concept of load-utilization ratio), input motion selection, prediction of permanent tilt/rotation, and ground settlement post liquefaction. A flow chart, which shows the interdependence of the different disciplines, is presented and can be extended to routine design. This proposed method is validated using the observed performance of an offshore and nearshore turbine from the Kamisu wind farm during the 2011 Great East Japan earthquake. Predicted results based on the proposed methodology compare well with the field observation and demarcate the (i) good overall performance of the offshore turbines and (ii) limit state exceedance of the nearshore turbine. It is envisaged that the proposed method will be useful towards the design of monopiles-supported wind turbines in seismic areas.
•A comprehensive review of seismic loading on monopiles in liquefiable soils.•A framework to predict the permanent tilt for monopiles in seismically liquefiable soils.•Parametric studies to understand the influence of different parameters affecting the tilt.•Flowchart of the methodology which can be coded.•Validation of the method using Kamisu Wind Farm.
Corrosion-induced deterioration of material properties can noticeably affect the seismic performance of coastal reinforced concrete (RC) bridges in aggressive marine environments, causing significant ...adverse economic and environmental consequences post extreme events. This study systematically investigates the time-dependent seismic performance, resilience, and sustainability of coastal RC bridges. For that purpose, a three-dimensional (3D) nonlinear finite element (FE) framework is developed and combined with the formulation of performance-based earthquake engineering (PBEE) and an economic input-output life cycle assessment (LCA) approach. Seismic resilience and robustness of the coastal RC bridges are subsequently evaluated in terms of the post-earthquake repair cost, repair time, and carbon footprint quantified by CO2. Within this framework, additional analyses are conducted to explore possible retrofit measures, including the use of fiber-reinforced polymer (FRP) reinforcement on the sustainability and resilience of the retrofitted RC bridges. For the presented scenario, it is shown that wrapping bridge columns with FRP composites can effectively increase the moment capacity, thus improving resilience and sustainability by reducing as much as 650 Mg of CO2 for this specific bridge. Overall, the derived insights highlight the need for sustainability, resilience, and potential retrofit analysis of coastal RC bridges in seismically active regions affected by corrosion-induced deterioration.
•A nonlinear 3D FE framework for coastal RC bridges is developed and combined with the PBEE formulation and EIO-LCA approach.•Seismic resilience and sustainability of RC bridges under aggressive marine environments and earthquakes are investigated.•Effectiveness of FRP composites to potentially enhance the performance of bridge columns is thoroughly explored.•Wrapping coastal bridge columns with FRP composites can effectively improve seismic resilience and sustainability.
Coastal bridges are particularly prone to damage caused by prior earthquakes, rendering them more vulnerable to subsequent hazards. The potential occurrence of a near-field tsunami can significantly ...exacerbate this damage, leading to detrimental environmental and economic impacts. Aiming to quantitatively assess these consequences, this study delves into the multihazard resilience and sustainability of a typical coastal Reinforced Concrete (RC) bridge under sequential earthquake-tsunami events. As such, a nonlinear three-dimensional (3D) finite element (FE) framework is established, seamlessly merging the economic input-output life cycle assessment (EIO-LCA) methodology with the principles of performance-based earthquake engineering (PBEE). To minimize the uncertainty in the probabilistic seismic demand model and the subsequent PBEE outcomes, an optimal intensity measure is chosen based on a comprehensive evaluation of efficiency, correlation, and coefficient of variation. Consequently, the multihazard resilience of the coastal RC bridge is assessed according to the repair time, repair cost, and carbon footprint. It is shown that bridges are more vulnerable under sequential earthquake-tsunami events compared to earthquake events alone, leading to notably increased carbon footprints and reduced resilience levels. Overall, the developed framework enhances the assessment of coastal RC bridge performance, providing valuable insights into the consequences for both the environment and socioeconomic aspects resulting from bridge damage during sequential earthquake and tsunami events.
•A framework for multihazard analysis of coastal RC bridges is developed by integrating FE modeling, PBEE, and EIO-LCA approach.•An optimal intensity measure is identified by considering correlation, efficiency, and coefficient of variation.•Multihazard resilience and sustainability of a coastal RC bridge during earthquake-tsunami sequential events is investigated.•Increased bridge susceptibility under earthquake-tsunami events causes increased carbon footprint and decreased resilience.
Shake table testing was conducted to document the seismic response of a bucket foundation offshore wind turbine (OWT) system. Salient response of the system's soil-structure interaction effects is ...presented and discussed. Among the observed response characteristics, excess pore pressure fluctuation within and around the soil-bucket domain is thoroughly addressed, including the strong tendency for the soil dilation excursions driven by the induced cyclic strains. The experimental data is used to calibrate a numerical model with dynamic soil response simulated by a coupled solid-fluid formulation. The calibrated model is extended to investigate seismic response of a prototype utility-scale OWT, with and without added wind loading effects. Overall, the research outcomes indicate that: i) excess pore pressure fluctuations in the vicinity of the bucket play an important role in dictating the extent of potential permanent base rotation, ii) consideration should be given to wind loading that might further exacerbate this base rotation, and iii) it is of importance to model the turbine tower as a system of discrete masses rather than the simplified proposed for practice equivalent top mass idealization.
•Shake table testing was conducted to document seismic response of bucket foundation offshore wind turbine (OWT) system.•The experimental data is used to calibrate a numerical model.•The calibrated model is extended to investigate seismic response of a prototype utility-scale OWT.•Excess pore pressure changes in the vicinity of the bucket play an important role in dictating the permanent base rotation.•Modeling the OWT as a system of discrete masses rather than the simplified single equivalent mass idealization is crucial.
Due to seismic response, accumulation of permanent ground deformation (lateral spreading) is an important mechanism of much practical significance. Such deformations typically occur near a ground ...slope, behind retaining structures such as sheet-pile and quay walls, and in mildly sloping ground. In conducting a shake table test, the generation of permanent deformations further elucidates the underlying mechanisms and allows for related ground–foundation–structure response insights. In this paper, an approach for development of accumulated ground deformations is presented, in which asymmetric inertial loading results in a biased dynamic one-dimensional shear state of stress. As such, the proposed approach allows for further insights into the soil cyclic response and pore pressure build-up, with deformations accumulating in a preferred direction. To permit a virtually unlimited number of such loading cycles, focus is placed on motions that do not cause the shake-table actuator to accumulate displacement, in view of its possible limited stroke. Using this approach, representative experimental response is outlined and discussed. This experimental response can be used for calibration of numerical models to emulate the observed permanent strain accumulation profile and associated mechanisms. In addition to liquefaction-induced lateral spreading, this asymmetric shaking approach might be beneficial for a wide class of earthquake engineering shake table testing applications.
This paper presents a three-dimensional (3D) multi-surface plasticity model to computationally simulate the behavior of coarse-grained granular soil during seismically-induced liquefaction. The model ...extends an existing multi-surface plasticity formulation and includes the Lade–Duncan failure criterion as the yield function to more closely capture salient characteristics of laboratory test data. Subsequently, flow rules are updated for modeling the essential shear response mechanisms associated with dilatancy, cyclic mobility, and post-liquefaction shear strain accumulation. The constitutive model is implemented into the OpenSees computational framework, and Finite Element (FE) calibrations are undertaken to match a set of laboratory test data, including drained monotonic/undrained stress-controlled cyclic triaxial tests, and a centrifuge test on a liquefiable sloping ground. It is demonstrated that the soil constitutive model and the employed computational framework can reasonably predict the seismic response of the liquefiable sloping ground under earthquake loading. On this basis, full 3D FE simulations of a typical bridge abutment seated on liquefiable sloping ground are conducted to further highlight underlying earthquake-induced liquefaction effects on the ground-structure system deformations. Overall, the developed constitutive model provides a useful tool for evaluating earthquake-induced soil liquefaction hazards and associated 3D ground seismic response scenarios.
Liquefied soils may induce widespread permanent ground deformation in the vicinity of abutments and cause extensive damage to bridge foundations during earthquakes. As such, it is essential to ...systematically assess the performance of bridges susceptible to earthquake hazards and associated soil liquefaction. Motivated by details of an actual 18-span bridge system, a three-dimensional (3D) nonlinear Finite Element (FE) framework is presented to quantify the damage exceedance probability conditioned on various earthquake intensity levels. An optimal intensity measure is identified by overall consideration of correlation, efficiency, and coefficient of variation to reduce the degree of uncertainty in the probabilistic seismic demand model, thus enhancing the confidence in the corresponding fragility results. To capture the salient mechanisms associated with soil liquefaction, this study focuses on the longitudinal seismic performance of bridge-ground as an integral system exposed to earthquake hazards. Within the developed 3D FE framework, the potential of geotechnical and structural mitigation measures is explored to reduce the vulnerability of the bridge structure. It is shown that the vulnerability of the bridge at some locations of interest is noticeably reduced by employing these measures. Overall, the 3D FE analysis technique and derived insights are of significance for the seismic response and fragility assessment of integral bridge-ground systems in liquefaction-induced lateral spreads.
•Longitudinal seismic fragility of an integral bridge-ground system under liquefaction-induced lateral spreading is studied.•An optimal intensity measure is identified by overall consideration of correlation, efficiency, and coefficient of variation.•Effects of sand permeability and retrofit options to potentially reduce the seismic vulnerability of the bridge are examined.•Bridge's global connectivity and the abutment-to-abutment interaction may significantly affect the vulnerability.
This study evaluates the application of helical piles to reduce liquefaction-induced foundation settlement and investigates their seismic performance in liquefiable grounds. Two large-scale shake ...table test series, one without mitigation and one using helical piles, were conducted using the shake table facility at the University of California, San Diego. Each model was extensively instrumented and subjected to two consistently applied shaking sequences. The experimental results indicated reduced excess pore-water pressure generation around the helical pile group, attributed mainly to the densification around the piles during installation. The foundation supported on helical piles underwent almost no foundation differential settlement and tilt. The post-shaking liquefaction-induced settlement mechanisms did not affect the helical pile foundation settlement. Although this study introduced helical piles as a reliable and highly efficient measure to mitigate liquefaction-induced foundation tilt and settlement, the proper design and application of helical piles still need thorough investigation due to possible amplified superstructure response.
•Evaluated the performance of helical piles in liquefiable grounds.•First of its kind large-scale shake table test on helical piles in liquefiable soils.•Improved performance of shallow foundations underpinned by helical piles.•Introduced helical piles as an effective foundation settlement mitigation measure.
A practical yet realistic three‐dimensional (3D) constitutive model is presented for modeling the cyclic degradation behavior of soil. Such response can be attributed to pore pressure build‐up and ...loss of cementation, among other stiffness and strength degradation mechanisms. Extending an existing multi‐yield surface (MYS) plasticity formulation, the cyclic degradation model (CDM) is developed by incorporating a novel degradation logic in terms of accumulated plastic strain or as prescribed by the user. Thereafter, the CDM is implemented into a computational framework (OpenSees), and Finite Element (FE) calibrations are undertaken to match the available experimental data at the element and system levels. A generally good agreement between the FE simulations and centrifuge test data demonstrates the CDM's capabilities to simulate the seismic response of sloping sites. Using the calibrated model properties, full 3D FE simulations of a large‐scale multi‐span bridge configuration, motivated by details of an actual bridge system in sloping ground, are conducted to highlight the underlying response mechanisms. In addition, computed results including and precluding the effects of cyclic degradation are directly compared and discussed. It is shown that loss of soil strength and stiffness play a noticeable role in the resulting ground and bridge response. Overall, the newly developed constitutive model and findings are of importance for a wide range of soil formations where cyclic degradation occurs under earthquake loading.
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