Performance Limit States Research Articles

Modified fragility functions for offshore wind turbines considering soil-structure interaction subjected to wind, wave, and seismic loads

Investment allocation for offshore wind turbines (OWT) as an important class of structures is typically carried out through supporting decision-making approaches utilizing some fragility functions. This study attempts to deliver fragility functions for OWTs on monopile foundations accounting for soil-structure interaction (SSI) effects. Simultaneous wind, wave, and earthquake loads were considered probabilistically by adjusting their occurrence hazard levels for predefined damage states in diverse performance levels. The designated damage states in this study are defined based on collapse probability and some targeted performance levels which could be very straightforward to distinguish. The damage state detection is based on rotation in the connection section of the tower’s transition part to the foundation, which perceptibly reveals the effects of SSI on fragility functions. The expected results comprise modified fragility functions accounting for SSI effects contributing to less median spectral acceleration, more evidently rotational demands, further dispersions, and a subsequent dominant increase in the probability of exceeding performance limit states. Considering operational performance level, the most applied design performance level for turbines as an important class of structures, not considering the SSI effects could noticeably underestimate the demands and lead to high-risk decisions.

Probabilistic resilience assessment framework of structures considering the combined functionality-recovery-duration uncertainty

In the current stage, the risk-guided performance-based earthquake engineering (PBEE) has become the main direction in the earthquake community. As an important part of risk, seismic resilience indicators have been increasingly emphasized and elevated to new levels in recent years. Seismic resilience refers to the capacity of social entities to reduce disaster risks and to facilitate recovery efforts with the least social disruption in possible. Currently, the calculations of resilience indicators are commonly based on the deterministic approach. In fact, resilience indicators are also random variables, and the corresponding recovery time, recovery function or residual function in resilience calculation may vary within a range for different intensity levels and limit states. Therefore, characterizing resilience indicators through probabilistic models or confidence intervals can be a more practically valuable and meaningful strategy for future research. In this paper, a probabilistic resilience assessment framework of structures is proposed, and a sinusoidal-based continuous recovery function characterized by different limit states and recovery modes is given. The combined uncertainties of functionality, recovery and duration are incorporated into the framework, and an application example via the reinforced concrete frame is given to implement the framework. Besides, the sensitive analysis of different variables to the resilience assessment result is performed, and the comparison between the deterministic and probabilistic analysis is further discussed. In general, the framework consists of three parts, i.e., (1) Generating samples, fragility and damage states; (2) Calculating total stochastic recovery functions for resilience analyses; and (3) Performing probabilistic seismic resilience analyses. If deterministic analysis is used, the resilience index is only a value, while if probabilistic analysis is used, the resilience index will be a variable with a corresponding probability and distribution range. Compared with other variables, the amplitude and wavelength have a stronger influence in the result of resilience index. This is because these two parameters are function-dependent and will directly affect the envelope curve in the resilience calculation. Although the changes in coefficient of variation (COV) will affect the curve results, the macro characteristics are consistent when comparing different target resilience index. Moreover, as the intensity rises, there is a statistical decrease in both the average residual functionality and resilience indicators, along with a statistical increase in the average recovery durations. The annual exceeding probability decreases as the target resilience level increases, while the life-cycle exceeding probability increases when the target resilience level decreases for the same year. In a sense, the integrated probabilistic resilience framework realizes the decoupling of resilience indicators for different performance groups and limit states, and provides a reference for the further stochastic resilience assessment from a probabilistic perspective.

The probabilistic performance-based seismic assessment of concrete bridge piers with SMASC reinforcing bars: Effect of pulse-like ground motion and vertical load-to-capacity ratio

Concrete bridge piers are critical components of bridge structures and their performance under seismic loading is of utmost importance. Traditional reinforced concrete bridge piers have shown limitations in terms of residual deformations and seismic resilience. This has led researchers to explore alternative reinforcement materials, such as Shape Memory Alloy (SMA) coupled with steel reinforcing bars, which have demonstrated promising attributes like energy dissipation as well as self-centering capacity. This study aims to fill this gap by evaluating the performance of concrete bridge piers with SMA-Steel coupled (SMASC) reinforcing bars under various intensities of vertical gravity loads and the action of pulse-like ground motion components, throughout a probabilistic framework. To this end, a group of bridge piers with different reinforcement types, including pure steel and SMASC are considered. These piers are subjected to 55 near-fault (NF) pulse-like records as well as 32 far-fault (FF) ground motions, throughout the Incremental Dynamic Analysis (IDA). The influence of distinct frequency components is analyzed by decomposing NF records into low-frequency pulses and high-frequency residual components. Also, the role of pulse to the 1st modal period of the piers (Tp/T1) is investigated by evaluating the piers’ response under the action of NF records, which were clustered into four groups. Results were assessed by evaluating the intensity measure and capacity of the studied piers at the desired performance objectives according to the FHWA manual. Moreover, the mean annual frequencies of exceeding performance limit states and the confidence levels of meeting performance objectives are studied. The results of the study indicate that the dominance of the component of NF ground motions depends on factors such as the intensity of gravity loads, ground motion characteristics, and the Tp/T1 ratio. The components of NF records within certain clusters of the Tp/T1 ratio are necessary for accurate response assessment, while FF records can be used for conservative design purposes, depending on the level of ground motion intensity and the intensity of applied gravity load. The SMASC-reinforced piers with specific λ factors (i.e. λ = 0.5 or λ = 1.0) and low intensity of gravity loads lead to a higher (1.6 times higher) mean annual frequency of exceeding a limit state, compared to pure steel rebars. Also, the confidence levels for meeting performance objectives vary depending on the ground motions, but, as gravity load intensity increases, confidence levels decrease, particularly for piers with a λ factor of 0.5.

Multi-hazard life-cycle consequence analysis of deteriorating engineering systems

Probabilistic life-cycle consequence (LCCon) analysis (e.g., assessment of repair costs, downtime, or casualties over an asset’s service life) can enable optimal life-cycle management of critical assets under uncertainties. This can lead to effective risk-informed decision-making for future disaster management (i.e., risk mitigation and/or resilience-enhancing strategies/policies) implementation. Nevertheless, despite recent advances in understanding, modeling, and quantifying multiple-hazard (or multi-hazard) interactions, most available LCCon analytical formulations fail to accurately compute the exacerbated consequences which may stem from incomplete or absent repair actions between different interacting hazard events. This paper introduces a discrete-time, discrete-state Markovian framework for efficient multi-hazard LCCon analysis of deteriorating engineering systems (e.g., buildings, infrastructure components) that appropriately accounts for complex interactions between natural hazard events and their effects on a system’s performance. The Markovian assumption is used to model the probability of a system being in any performance level (i.e., limit state) after multiple hazard events inducing either instantaneous and/or gradual deterioration and after potential repair actions through implementing stochastic (transition) matrices. LCCon estimates are then obtained by combining limit state probabilties with suitable system-level consequence models in a computationally efficient manner. The proposed framework is illustrated for two case studies subject to earthquake and flood events as well as environment-induced corrosion during their service life. The first is a reinforced concrete building and the second is a simple transportation road network with a reinforced concrete bridge.

Mode-{I, III} multiaxial fatigue of welded joints in steel maritime structures: Total stress based resistance incorporating strength and mechanism contributions

Arc-welded joints in steel maritime structures are typically identified as weakest links in terms of fatigue limit state performance. Multiaxiality can be involved, consisting of predominant mode-I and non-negligible mode-III components. Aiming to answer the question if a cracked geometry based fatigue strength parameter would outperform an intact geometry based one like the effective notch stress, the total stress is adopted. A von Mises type of criterion is defined at the critical fracture plane and includes mode specific and material characteristic strength and mechanism contributions. A lifetime dependent shear strength coefficient is introduced to cover the resistance curves intercepts and slopes, whereas the total stress parameter contains the mean stress contribution as well as the (mixed) mode dependent notch and crack tip elastoplasticity coefficients, reflecting an interaction mechanism. Cycle counting includes a cycle-by-cycle non-proportionality measure and damage accumulation is based on a linear model. Evaluating mid-cycle fatigue resistance data, the total stress and effective notch stress performance turns out to be similar. However, the total stress related elastoplasticity coefficients are an explicit and sensitive measure to incorporate the actual physics of the fatigue damage process, whereas the material characteristic lengths for the effective notch stress seem to be more implicit and less sensitive ones.

Seismic fragility curves for concrete gravity retaining wall

Seismic fragility analysis plays a crucial role in performance-based seismic design (PBSD). The seismic fragility analyses for the concrete gravity retaining walls were performed in this study. Numerical models were developed for two concrete gravity retaining walls using OpenSees, considering two different backfill slope angles (0° and 12°). According to the probabilistic seismic demand models and comprehensive evaluation of intensity measures (IMs), the most suitable IM for concrete gravity retaining walls was determined. An approach for quantifying the limit state performance of concrete gravity retaining walls based on IDA was also proposed, and its reliability was verified based on observed damage during the 2008 Wenchuan earthquake. Seismic fragility curves for concrete gravity retaining walls were established under two backfill slope angles using three IMs. It is demonstrated to what extent a backfill slope angle can influence the damage probability under a specific seismic intensity level.

Seismic fragility analysis of high‐strength concrete frame structures reinforced with high‐strength steel bars

SummaryTo investigate the influence of using high‐strength steel bars in columns on the seismic resistance capacity and seismic resilience of frame structures, seismic fragility evaluation of three 8‐story reinforced concrete (RC) frame structures was conducted based on the incremental dynamic analysis (IDA) using 11 ground motion records. The main parameter is the longitudinal reinforcement configuration in the frame columns, where the first structure is reinforced with HRB 600 grade steel bars in the columns, the second structure is replaced with equal area ultra‐high‐strength (UHS) steel bars (i.e., with a yield strength of approximately 1425 MPa), and the third structure is replaced with equal strength UHS steel bars. A numerical model of the RC frame structure was developed and then validated using previous experimental results. The exceeding probabilities at various performance limit states were calculated based on two typical engineering demand parameters (EDPs) of maximum interstory drift and residual interstory drift. The results showed that using UHS longitudinal steel bars instead of HRB 600 grade steel bars in frame columns could reduce the energy dissipation capacity of the structure, inevitably leading to an increase in the maximum interstory response of the frame. However, much lower exceedance probability was observed in the UHS‐enhanced frame under the repair available limit state based on the residual interstory drift, indicating that the UHS‐enhanced RC frame had higher seismic resilience. In addition, compared to equal area substitution, equal strength substitution is a more ideal design method that can use fewer UHS steel bars to achieve comparable reparability and a smaller increase in maximum interstory drift.

Probabilistic analysis of FRP efficacy in seismic risk reduction

Engineers are tasked with the challenging task of evaluating the performance and analyzing the risk of systems in the context of performance-based seismic design. All sources of random uncertainty must be taken into account during the design phase in order to complete this assignment. The performance limit states for a structure must be defined using appropriate procedures that take into consideration the system characteristics describing the structure, the soil, and the loads applied to the structural reactions. The main objective of this study is to conduct an in-depth analysis, both linear and non-linear (Pushover), of seismic vulnerability for a reinforced concrete (RC) structure. This aims to probabilistically evaluate the effectiveness of composite materials, particularly those reinforced with glass and carbon fibers, in reducing seismic risk when used to reinforce structural columns. The outcomes of this study will provide valuable insights into the efficacy of FRP reinforcements in enhancing seismic resistance, regardless of the analytical approach adopted (linear or non-linear). They reveal a seismic risk reduction of 48 % for structures equipped with glass fiber-reinforced columns and 67 % for those with carbon fiber-reinforced columns.

An advanced assessment framework for seismic resilience of railway continuous girder bridge with multiple spans considering 72h golden rescue requirements

Given the common sense that people in danger could survive with high probability in the golden rescue time of 72 h after earthquakes, railway bridges that are important transportation hubs and the lifelines for earthquake relief have been required to satisfy the necessities of safe passage and fast traffic for emergency response personnel in this critical period. To ensure the post-earthquake temporary functionality of the railway bridges to a sufficient safety level in golden rescue scenario, an advanced resilience assessment framework, including seismic resilience determinations for individual bridge components based on residual responses with respect to the plastic capacities originated from performance limit state definitions, definitions of three recovery levels considering repair efficiency for different recovery phases, and the series-parallel and parallel-serial system resilience models developed in temporal and spatial domains, was established. A commonly constructed irregular railway multi-span continuous girder bridge was chosen to verify the practicability of the aforementioned framework. The finite-element model of the illustrative bridge was developed taking abutment-girder interaction effects and nonlinear seismic behaviors of girder into account. Average spectral acceleration was taken as the intensity measure (IM) to consider the response variations originated from higher modes and natural period extension during earthquakes, and the site-matched and IM-based scaled ground records were adopted in the multiple stripe analysis to obtain instantaneous peak and residual seismic responses. Based on the framework, post-event resilience characteristics of bridge components were discussed, four recovery strategies were proposed for bridge system, and the seismic resilience of the illustrated bridge was assessed at system level. The research shows that the response contribution of fundamental dominant mode is only 64.37 %, indicating the dynamic response contributions from higher modes are considerable and the case bridge can show a strong irregularity during seismic events. Obvious nonlinear seismic behaviors occur to the superstructure where material strain in girder critical sections can increase to 0.00422 during earthquakes, which illustrates the inaccuracy of girder modeling only taking elastic behavior into consideration. Also, the prestress loss after earthquakes can reach 31.14 % and attention should be paid to the prestress recovery in subsequent repair works. Most components can satisfy the easy recovery resilience level, and the resilience is closely related to ground intensities and repair-waiting time; earthquake-induced functionality reduction can be 46.57 %, and resilience can increase by 25.35 % if the waiting time is shortened by 5 h. System resilience is influenced by the similar factors with component and varies in cases of different repair sequences due to the accumulation effect of repair-waiting time for various subsystems.

Influence of data sampling on confidence in the calculation of reliability index for simple performance functions

The mean (point) estimate of reliability index (β) for simple limit state performance functions is most often based on load and resistance model bias statistics taken from bias data of limited size. The paper shows how the confidence in the point estimate of β can be computed using the bootstrap method and a closed-form solution for the special case of lognormally distributed nominal and bias random variables. Bias data collected for the pullout limit state for steel strip mechanically stabilized earth walls are used to demonstrate the approach but the method is general. Mean and confidence intervals on β are computed using the entire available bias data sets and smaller sample sizes located in the tails of the original populations, or smaller sample sizes that result in upper and lower extreme point estimates of β. The closed-form solution for β varies linearly with the logarithm of the nominal factor of safety for the example pullout limit state. Depending on the load and resistance bias sample sizes and where they are taken from in the original larger population, results in a wide range of nominal factors of safety to satisfy a target β at time of design.

The Influence of Slope Angle Variation on Structures Resting on Hilly Region Considering Soil–Structure Interaction Under Earthquake Loadings Using Capacity Curves and Probabilistic Approach

ABSTRACT A five story (G + 4) residential structure is positioned on 15°, 30°, and 45° slopes to be explored in this study in terms of vulnegrability and compared to the same structure resting on flat ground 0°. The RC frame models were constructed in accordance with Eurocode 8 and then subjected through a series of 10 ground motion records. In accordance with Vision 2000 performance limit states (PLS), this research provided the use of nonlinear static analysis (NL-SA) and nonlinear dynamic analysis (NL-DA) methodologies to assess seismic risk performance and vulnerability of structures resting on various slope angles. Incremental Dynamic Analysis (IDA) and Pushover Analysis (POA) capacity curves, as well as the fragility curve and the collapse margin ratio, are generated for the four selected models (M0, M15, M30, M45). The results show that the RC frame model M45, located on a 45°-degree incline, is the most vulnerable to damage. The risk of damage to the RC frame M0 is minimal because it is not elevated off the ground. To this end, the relative degrees of vulnerability among the frames were determined to be as follows: M45 > M30 > M15 > M0.

Lateral load resistance of reinforced concrete columns with brittle details

AbstractAnalytical models for shear strength and deformation capacity estimation of reinforced concrete members are essential for the practical implementation of performance‐based seismic evaluation of existing structures and form a key part of current seismic assessment codes (e.g., EN 1998‐3 (2005), (2022), ASCE/SEI 41‐17). Although these models have been derived from regression or calibration of large datasets collected from experimental literature, discrepancy persists between experimental and analytical estimates, especially in cases of members with old‐type detailing. The evident uncertainty about parametric dependencies of the underlying mechanistic problem motivated the present work, where a set of benchmark columns that represent older structural detailing are studied parametrically through advanced finite element simulation. Parameters considered were, the axial load ratio, transverse reinforcement amount and spacing, longitudinal reinforcement ratio, and anchorage/lap splice detailing; results were gauged in terms of the resulting drift ratio (deformation capacity) at the performance limit states and were compared with the Code estimates to evaluate their limits and conservatism. The simulation results were used to vet the assumptions that underlie the simple mechanistic models used in deriving seismic design expressions for yield and ultimate deformation capacities, shear strength, and the rate of its degradation with increasing ductility.

Earthquake Economic Loss Assessment of Reinforced Concrete Structures Using Multiple Response Variables

For buildings that meet the requirements of current seismic design codes, damage to nonstructural components and the internal objects of buildings often become the main source of the seismic economic losses of these buildings. However, the current specifications only consider the safety of ‘no collapse under strong earthquake’ and do not consider ‘functional recoverability’. In this paper, a six-story frame building was taken as an example. Four joint performance limit states were proposed, as per FEMA 273, to establish a two-dimensional probabilistic seismic demand model that considers parameter correlations. The limit state function was established, and the two-dimensional seismic vulnerability curve was calculated. The seismic intensity–economic loss curve and the annual average economic loss established by one-dimensional and two-dimensional seismic vulnerability curves were compared. The results showed that the seismic performance of the structure was lower than expected when using only a one-dimensional seismic vulnerability curve. However, the situation was more serious under high-intensity earthquake and high-performance levels.

Seismic Fragility Curves for Reinforced Concrete Dual System Buildings

A seismic fragility curve is a visual representation that illustrates the likelihood of a structure surpassing a particular damage or performance limit state caused by an earthquake with a specific intensity or ground motion level. This curve is typically generated using probabilistic seismic hazard analysis and structural reliability analysis methods. It is based on statistical models that rely on past earthquake data and simulations of future earthquake scenarios to predict the structure or system’s behavior under seismic forces. In this study, the seismic performance of 30 stories of 95 m height dual system reinforced concrete buildings located in Erbil is evaluated by analyzing three distinct ground motions. A non-linear platform is used to simulate and analyze data, followed by the generation of seismic inter-story drift fragility curves using Incremental Dynamic Analysis. The buildings’ seismic structural performance is assessed based on five different performance levels, including operational phase, immediate occupancy, damage control, life safety, and collapse prevention (CP). Each level is associated with different levels of damage and corresponding degrees of functionality and safety. The fragility curves show that the building has a 50% chance of achieving or exceeding the (CP) level with highly intense ground vibrations with peak ground acceleration = 1.6 g. In addition, these curves can be beneficial in creating future local design codes and provide significant support in evaluating the seismic performance of existing buildings.

The multi-dimensional fragility analysis of the underground large-scale frame structure based on the internal relationships of different seismic performance evaluating indexes

In this paper, the seismic performance of the underground large-scale frame structure (ULSFS) is thoroughly investigated aiming at the drift deformation and rotation deformation of vulnerable positions, and the multi-dimensional fragility analysis of the ULSFS is further developed based on the internal relationship of different seismic performance evaluating indexes. Employing the increment dynamic analysis (IDA) method, the seismic performance of the ULSFS is investigated during diverse earthquakes. The interlayer deformation ratio (IDR) and interlayer rotation angle (IRA) are adopted as Damage measures (DM) to assess the drift deformation and rotation deformation, respectively. The internal relationships of two DMs are revealed, and the correlation coefficients are proposed by the correlation analysis. Assuming the DMs subordinated to the joint lognormal distribution, the generalized equations are established to describe performance states of the ULSFS aiming at different seismic failure modes. Considering the seismic thresholds and correlation coefficients of two DMs in different performance limit states, the 2-D fragility curves of the ULSFS are achieved. The results shows that the correlation of seismic evaluating indexes would decrease with the increase seismic intensities due to the structural inelastic damage; and the 2-D fragility curves with considering the reasonable internal relationships of two DMs would be more accurate and conservative. This paper provides the theoretical basis and technical support for the seismic performance assessment of large underground frame structures with complicate seismic failure modes.

Performance-Based Characterization and Quantification of Uncertainty in Damage Plasticity Model for Seismic Fragility Assessment of Concrete Structures

Seismic probabilistic risk assessment requires explicit consideration and quantification of all sources of uncertainty. Although uncertainties in earthquakes and basic material properties, such as nominal concrete compressive strength, strain at maximum stress, and modulus of elasticity of concrete, have been considered in some studies, uncertainties in parameters used to model the nonlinear behavior of concrete are often not considered. Recent recommendations in design standards have incorporated performance-based limit states in the design and risk assessment of nuclear power plants. These recommendations have implicitly mandated that the uncertainty in the nonlinear behavior of concrete needs to be characterized and quantified in accordance with different performance limit states. This study focused on nonlinear model parameters in the concrete damage plasticity model (CDPM) and their characterization in terms of material strength parameters. Furthermore, a performance-based characterization and quantification of uncertainties in nonlinear model parameters was also conducted. Data from existing experimental studies were used to study the uncertainties in CDPM and were used as a basis for the proposed quantification.

Evaluation of the Performance Limit States in Codes for RC Columns Under Different Axial Loads

Evaluation of the Performance Limit States in Codes for RC Columns Under Different Axial Loads

Annular fiber-reinforced elastomeric bearings for seismic isolation of lightweight structures

The conventional laminated elastomeric bearing isolators, as a mature technology, have found significant application in earthquake protection of civil structures, which are typically large in size, heavy, and expensive in cost. The technology is not as effective in the seismic isolation of lightweight structures due to the challenges in providing effective period-shift while accommodating large isolator displacement demands. Further horizontal flexibility may yet be required in the elastomeric isolators concerning the Seismic isolation of lightweight structures. A novel hollow circular (HC, also called the annular) type of fiber-reinforced elastomeric isolators (FREIs) is introduced and examined in this study. To demonstrate the validity of the concept, the dynamic response characteristics of two similar full-scale HC-FREIs were evaluated experimentally and compared with those of a corresponding solid circular (SC)-FREI as the control specimen. The response parameters, performance limit states, and failure modes of the two isolator types were evaluated and compared in detail. In addition, the performance of the two isolator types in the base isolation of a lightweight structure was investigated. Given the significantly increased horizontal flexibility and superior damping properties, the unbonded HC-FREIs offer a feasible solution for the effective earthquake mitigation of many lightweight structures. Additionally, the comparatively lower volume of materials and the lighter weight of the isolator provide economic advantages for HC-FREIs over their SC-FREI counterparts.

Progressive collapse fragility of substandard and earthquake-resistant precast RC buildings

Several natural and man-made disasters have highlighted that precast reinforced concrete (RC) buildings often have insufficient levels of structural robustness, which is the last line of defence under extreme events. Even though robustness studies were originated by the progressive collapse of the Ronan Point precast RC building in 1968, such a structural feature of disaster resilience has been partially investigated in case of precast RC buildings to date. In this study, a precast RC frame structure representative of low-rise commercial buildings is analysed under different column loss scenarios, which can produce the partial or total collapse of the structural system. Two building classes are considered, namely, buildings designed only to gravity loads and buildings designed for earthquake resistance. Structural robustness is probabilistically assessed through a fragility analysis procedure, using three-dimensional fibre-based finite element models with nonlinear links simulating connections, large-displacement incremental dynamic analysis, and multiple performance limit states for damage assessment. The output of the study is threefold: (i) a detailed assessment of the effects of column loss on precast RC frame buildings, quantifying the major role of structural detailing and beam-column connections; (ii) a fragility-informed evaluation of beneficial effects of seismic detailing on structural robustness, which can drive designers in retrofitting of existing precast RC buildings and decision-makers towards prioritization-related issues; and (iii) the generation of typological fragility curves for progressive collapse risk assessment in both single- and multi-hazard environments. Progressive collapse fragility curves can be convolved with more classical fragility models describing the failure of single components (under, e.g., flow-type landslide impact, vehicle collision or blast) and hazard, to assess systemic structural risk.

Comparative dynamic analysis of two-rotor wind turbine on spar-type, semi-submersible, and tension-leg floating platforms

Multi-rotor floating offshore wind turbines have been recently proposed as an innovative technology to further reduce the cost of offshore wind energy. Even though examples of commercial prototypes are present, the literature lacks studies on the dynamic performance of such systems. This work presents a comparative analysis of a two-rotor wind turbine concept mounted on spar-type, semi-submersible, and tension-leg platforms. Their short-term performance is assessed by considering six different load cases considering directionally congruent turbulent wind profiles and irregular sea states. The analysis is carried out through an in-house fully-coupled code developed in Modelica. AeroDyn v15 within FAST v8 by NREL is coupled to the Modelica code to achieve blade-element momentum capabilities. Results indicate that platform yaw motion is an important dynamic mode of the systems, particularly for the spar configuration. Stiffer station-keeping lines and longer fairlead distance to the platform centerline reduce significantly yaw motion, as in the case of the semi-submersible and tension-leg configurations. Large tower base bending moment standard deviations and the associated concentration of energy at the platform heave and pitch motion frequencies indicate an increased risk for fatigue damage for the TLP configuration, especially at above-rated wind speeds. Moreover, large tendon loads can pose concerns in terms of fatigue and limit state performance. Large mean platform pitch angle and yaw standard deviation contribute to the reduction of electric power output quality. Extreme storm conditions greatly increase the response standard deviation, especially for the semi-submersible configuration.