Load Distribution Function Research Articles

Study on load distributing function of square slab surface under the action of underwater close‐in blast loading

AbstractThe mode and magnitude of the blast load are the main cause of damage to the structure. Most current studies have simplified the blast load into a bilinear form that differs greatly from the actual time history curve and is applied directly to the structure, avoiding the fluid–solid coupling interaction between the water fluid and the structure. The simplified blast load for near‐explosion or internal explosion will bring a big error to the calculation results. To quickly determine the load on the structure surface under the action of underwater near the explosion, this study studies the interaction between water hammer wave and structure through the verified full coupling model, and puts forward the explosion load distribution function on the square plate surface under the action of underwater explosion, and establishes a simplified prediction formula for the explosion load parameters (peak pressure and positive reflection impulse) at the center of the plate surface, using these formulas, a general method for constructing the explosion load at any point on the structural surface is proposed, which lays a foundation for subsequent structural damage and failure analysis.

Biomechanical Comparison of Two Different Sutures for the Tensile Strength of the Pullout Repair of Posterior Meniscal Root Tear.

Background Medial meniscal posterior root tear has garnered attention because it causes increased joint contact pressure and loss of load distribution function. Currently, the common treatment for posterior meniscal root tears is transtibial pullout repair, and loop suture remains the gold standard procedure. Purpose The aim of this study is to validate whether the meniscus-suture complex exhibits better structural properties after loop stitch using a suture tape versus the conventional thread. Study design and methods This is a controlled laboratory study. In total, 20 menisci harvested from castrated male pigs were prepared and randomly assigned to two suturing techniques: loop stitch using ULTRATAPE (n = 10, tape group) or loop stitch using 2-0 UltraBraid (n = 10, control group). The single-loop stitch meniscus-suture technique was used. A single suture using ULTRATAPE or 2-0 UltraBraid was placed through the meniscus 5 mm medial from the resected edge of the posterior meniscus horn. The meniscus-suture complex specimens were mounted on a tensile tester to apply tensile load on the meniscus-suture complex parallel to the long axis of the stitched suture materials. Each specimen was stretched to failure at a crosshead speed of 50 mm/minute. The structural properties of the meniscus-suture complex (maximum load, linear stiffness, and elongation at failure) were determined. Results In the tape group, all the repaired complexes were torn at the ligature; conversely, in the control group, the threads were torn in three of 10 specimens, and the repaired complexes in the remaining seven specimens were torn at the ligature. No significant between-group differences were observed in linear stiffness (9.0 ± 4.1 vs 7.1 ± 2.9 N/mm) and elongation at failure (15.8 ± 6.1 vs 19.6 ± 20.1 mm); however, the tape group exhibited a significantly higher average maximum load than the control group (104.6 ± 41.2 vs 62.6 ± 32.1 N; P = 0.020). Conclusion Suture tape can be a potential alternative to the conventional thread for Medial meniscal posterior root tear repair. Clinical relevance Medial meniscal posterior root tear repair using tape rather than the conventional thread may be beneficial in obtaining better structural properties.

Measurement of bearing reaction force by distributed strain variation

Bearing is a crucial transmission component of aero-engines under high-speed and heavy-load conditions. To design a roller bearing with high loading capacity and reliability, it is essential to focus on the relationship between the external load state (reaction force) and the internal load distribution (load distribution). Therefore, a measurement method for bearing reaction force using load distribution and radial basis function neural network is presented in this study. Unlike conventional static reaction force measurement methods, both the direction and magnitude of the reaction force are considered in the proposed method without modifications to bearing. First, an experimental system is designed to investigate the load distribution in a roller bearing under different reaction forces using strain variation measurements. Then, a finite element analysis is conducted, and simulation results of the strain variations at three interested points match well with the experimental measurements. Finally, a radial basis function neural network with strong nonlinear fitting ability is applied to construct the mapping relationship between strain variation and reaction force. The results demonstrate that the proposed method can predict the reaction force with high accuracy based on the strain variation at three measuring points.

Regeneration Using Adipose-Derived Stem Cell Sheets in a Rabbit Meniscal Defect Model Improves Tensile Strength and Load Distribution Function of the Meniscus at 12 Weeks

The purpose of this study was to evaluate the mechanical properties, such as the tensile strength and load distribution function, of the meniscus tissue regenerated using adipose-derived stem cell (ADSC) sheets in a rabbit meniscal defect model. ADSC sheets were prepared from adipose tissue of rabbits. The anterior half of the medial meniscus was removed from both knees. One knee was transplanted with an ADSC sheet; the contralateral knee was closed without transplantation. Mechanical tests were performed at 4 and 12 weeks posttransplantation. In the tensile test, tensile force was applied to the entire medial meniscus, including the normal area (n= 10/group). Compression tests were performed on the entire knee, with soft tissues other than the ligament removed. A pressure-sensitive film was inserted under the medial meniscus and a 40-N load was applied (n= 5/group). In the tensile test, the elastic modulus in ADSC-treated knees was higher at 12 weeks (ADSC: 70.30 ± 18.50 MPa, control: 43.71 ± 7.11 MPa, P= .009). The ultimate tensile strength (UTS) in ADSC-treated knees at 12 weeks was also higher (ADSC: 22.69 ± 5.87 N, control: 15.45 ± 4.08 N, P= .038). In the compression test, the contact area was larger in the ADSC group at 4 weeks (ADSC: 31.60 ± 8.17 mm2, control: 20.33 ± 2.86 mm2, P= .024) and 12 weeks (ADSC: 41.07 ± 6.09 mm2, control: 30.53 ± 5.47 mm2, P= .04). Peak pressure was significantly lower in ADSC-treated knees at 12 weeks (ADSC: 11.91 ± 1.03 MPa, control: 15.53 ± 2.3 MPa, P= .002). The regenerated meniscus tissue, 12 weeks after transplantation of the ADSC sheets into the meniscal defect area, had high elastic modulus and UTS. In the meniscus-tibia compartment, the contact area was large and the peak pressure was low. ADSC sheets promoted regeneration of meniscus. ADSC sheet transplantation for meniscal defects could be an effective regenerative therapy.

A narrative review of lateral meniscus root tears and extrusion: techniques and outcomes.

In this review, we performed a literature search and described the surgical procedure for a lateral meniscus posterior root tears (LMPRT) repair using a pull-out technique and an arthroscopic centralization for lateral meniscus (LM) extrusion. The menisci play a pivotal role in the shock-absorbing and load-dispersing functions of the knee joint. They also contribute to its stability. Meniscal root tears substantially affect meniscal hoop function and accelerate cartilage degeneration. Additionally, LMPRT have been shown to affect anterolateral knee laxity and tibiofemoral contact pressure in knees with anterior cruciate ligament (ACL) injury. Therefore, appropriate management of LMPRT is essential for restoring knee function. Meniscus extrusion has attracted attention due to its association with early osteoarthritis (OA). Recently, an arthroscopic centralization technique has been proposed to reduce meniscal extrusion. During this procedure the capsule attached to the meniscus is sutured to the edge of the tibial plateau using suture anchors. A narrative review of LMPRT repair and arthroscopic centralization of lateral meniscal extrusion was performed through a PubMed search. Specific magnetic resonance imaging (MRI) signs were useful for the diagnosis of LMPRT. Pull-out techniques can restore knee stability and load distribution function and result in favorable clinical outcomes. Arthroscopic centralization of the extruded LM caused by meniscectomy and lateral discoid meniscus achieved satisfactory clinical outcomes at the 2-year follow-up. Biomechanical studies demonstrated that this procedure reduced meniscus extrusion and had beneficial effects on load distribution and joint stability. In summary, to restore knee function, LMPRT should be repaired as much as possible. The centralization technique is a promising surgical treatment for extruded lateral menisci due to meniscectomy and discoid meniscus. However, due to the lack of high-level evidence studies such as randomized control trials (RCTs) in this field, it remains necessary to accumulate evidence to confirm the efficacy of LMPRT repair and the centralization technique.

Fault Tolerance in WSN Through Uniform Load Distribution Function

Aim: The existing cluster-based energy-efficient models such as Low Energy Adaptive Clustering Hierarchy (LEACH) and Stable Election Protocol (SEP) unable for the distribution of sensor nodes uniformly during cluster formation. The non-uniform cluster distribution structure leads to rapid energy depletion and high energy consumption. So, this paper aims to create uniform load-based cluster formation. Background: This proposed idea is generated from the famous saying "If a Fault is Handling Another Fault Then That's not a Fault". Designing of energy-efficient and fault-tolerant model is indeed wireless sensor network deployments. The involvement of WSN's is not only limited to domestic purposes but also applied in a harsh and hostile environment. Objective: In this paper, we focus on the energy depletion-based fault occurrence and its tolerance. Here, we propose a Uniform Load Distribution Function (ULDF) with two objectives. The first one is to form equilibrium energy level clusters, and the second one is to avoid the frequent involvement of SNs in cluster formation. The proposed function is compared against the performance of both homogeneous LEACH and heterogeneous SEP protocols. Methods: Efficient clustering through equal distribution of SNs based on their current residual energy. Results: Our analysis concludes with the results where the proposed ULDF perform better than LEACH and SEP and reduces SNs involvement in cluster formation, which indirectly implies minimum energy consumption. Conclusion: Energy saving through uniform load distribution.

A pure boundary element analysis of Reissner's shear deformable plates subjected to higher-order polynomial loading

In this paper, a direct Boundary Element Method (BEM) solution without load domain integrals for Reissner's plates subjected to higher-order polynomial loads is derived. To this end, the Multiple Reciprocity Method (MRM), which consists to transform original domain integrals into a series of equivalent boundary integrals using Green's second identity in a recursive way, is used. Moreover, higher-order fundamental solutions of thick plates in bending, which are essential in MRM technique, are also derived and presented in an explicit form for all terms of the series. Despite this present approach deals directly with higher-order polynomial distribution load, this boundary element solution can be also applied to other load distribution functions, since it is possible to expand them in a polynomial series. Numerical results are presented for differing cases of boundary conditions and load functions, such as linear, double quadratic, exponential, and double sinusoidal distributions. The BEM results are compared to analytical solutions showing good agreement among them.

Distributed Dynamic Load Identification on Irregular Planar Structures Using Subregion Interpolation

Spatially distributed load on aircraft structures is difficult to obtain due to the limitation of measurement technology, the complexity of load and the external environment of the aircraft during flight, etc. A load identification method based on a subregion interpolation technique is proposed to indirectly estimate the distributed dynamic load from measured strain data on planar structures. The load distribution area is discretized into several subregions and the load distribution function in each subregion is represented by a set of local interpolation functions multiplied by their corresponding coefficients. A modified Green’s function matrix is formulated to establish the relationship between the local distributed dynamic load in the domain composed of the subregions sharing the same node and the structural response data. Hence, both the load’s distribution and time histories can be identified from structural response by solving the new formulated inverse problem. Numerical simulations on a flat cantilever plate and a planar structure with irregular geometry are conducted to show the effectiveness of the proposed method. Results show that the proposed method has better adaptability on the types of load distribution and structural configurations than the existing methods.

Sparse identification of time-space coupled distributed dynamic load

A novel and efficient method utilizing blind source separation and orthogonal matching pursuit is proposed in this paper to identify the time-space coupled distributed dynamic loads. By using proper orthogonal decomposition, the time-space coupled distributed dynamic load can be decomposed into the form of series of independent spatial distribution functions and time history functions. Considering the influences of the load distribution functions and time history functions on the structural responses are different, the non-uniqueness of distributed dynamic load identification is analyzed. The modal loads can be regarded as the weighted mixtures of the unknown independent time history functions and are identified by Green’s kernel function method and regularization. Then, the blind source separation technique is introduced to realize the identification of load time history functions, and the orthogonal matching pursuit algorithm is adopted to achieve the unique sparse solutions for load distribution functions. Finally, the distributed dynamic load is sparsely identified and equivalently represented as several concentrated dynamic loads acting on the appropriate positions. This proposed method is capable to deal with the time-space coupled distributed dynamic load on complicated structures, and to realize its spatial distribution representation and time history reconstruction separately. The results of the numerical examples demonstrate the reasonability and effectiveness of the method.

Deriving formulas of loading distribution on underground arch structure surface under close-in explosion

Arch structure is one of the basic structural form used in underground engineering. Its load distribution under blasting load directly affects/determines its failure mode and damage grade. However, the experimental studies on this issue are currently limited, owing to the complexity and difficulty of the blasting experiments of underground structures. Therefore, in order to explore the propagation and distribution of blasting stress waves in concrete, comparative analyses, which are based on model test results of concrete target implosion, in view of fluid–solid coupling algorithm were firstly adopted. The reliability of numerical simulation algorithms was also verified. Then, the close-in blasting simulation calculations of the underground arch structure were performed using the verified numerical algorithm. The distribution law of the surface load of the underground arch structure was analyzed, and the time-history curves of overpressure and impulse at various points on the surface were obtained. Through the data normalization and fitting method, the load distribution function of structure surface is obtained, and a simplified prediction formula for predicting the vault point blast load parameters was established. Utilizing these formulas, a general method for determining the blast load at any point on the structure surface is proposed.

Different effects of the lateral meniscus complete radial tear on the load distribution and transmission functions depending on the tear site.

To compare the effect of the lateral meniscus (LM) complete radial tear at different tear sites on the load distribution and transmission functions. A compressive load of 300N was applied to the intact porcine knees (n = 30) at 15°, 30°, 60°, 90°, and 120° of flexion. The LM complete radial tears were created at the middle portion (group M), the posterior portion (group P), or the posterior root (group R) (n = 10, each group), and the same loading procedure was followed. Finally, the recorded three-dimensional paths were reproduced on the LM-removed knees. The peak contact pressure (contact area) in the lateral compartment and the calculated in situ force of the LM under the principle of superposition were compared among the four groups (intact, group M, group P, and group R). At all the flexion angles, the peak contact pressure (contact area) was significantly higher (lower) after creating the LM complete radial tear as compared to that in the intact state (p < 0.01). At 120° of flexion, group R represented the highest peak contact pressure (lowest contact area), followed by group P and group M (p < 0.05). The results of the in situ force carried by the LM were similar to those of the tibiofemoral contact mechanics. The detrimental effect of the LM complete radial tear on the load distribution and transmission functions was greatest in the posterior root tear, followed by the posterior portion tear and the middle portion tear in the deep-flexed position. Complete radial tars of the meniscus, especially at the posterior root, should be repaired to restore the biomechanical function.

Nonlinear vibration signatures for localized fault of rolling element bearing in rotor-bearing-casing system

Fault signatures in the vibration signal are an important basis for diagnosis of localized defects in a rolling element bearing. Normally the defect-induced impulses will result in harmonics of the fault characteristic frequency and sidebands in the demodulated spectrum. But there will be obvious difference for fault signatures of different bearings with different surroundings, especially the shape of the modulation sidebands. This paper gives an explanation on the causes and influencing factors of bearing fault signatures using an impulse sequence model and a nonlinear multi-body dynamic bearing model in the rotor-bearing-casing system. The frequency components of the load force function on the defect will affect the amplitude of the impulses due to contact loss, becoming the modulation sidebands of the fault characteristic frequency. The extend of the load distribution on rolling elements are controlled by the initial bearing clearance, while the load force function on the defect is given by substituting the estimation of the load force on the bearing and the motion of the defect into the load distribution function. The influence of the defect position and random fluctuations are also analyzed in the simulation, as well as multiple localized defects of the same or different types. The numerical and experimental results show that this modeling and analysis method could be applied to explain and estimate fault signatures of localized bearing faults in a typical rotor-bearing-casing system.

Reliability of Steel Truss Roof Systems Under Variable Snow Load Profiles

The probabilistic safety analysis of steel truss roof systems under variable snow load profiles is investigated. The roofs of structures such as industrial buildings or sports halls, which require wide areas, are frequently subjected to unexpectedly high loads. Therefore, compared to the residential buildings, that type of buildings often comes across failure or prohibition of usage. Probabilistic techniques are utilized for the analysis of the problem. Thirty-six steel roof structures with different structural dimensions and load variations are modelled and their failure probabilities are calculated. In this paper, a complicated stochastic analysis is reduced to the solution of a load–resistance (S–R) problem by utilizing sensitivity analyses. Firstly, the structures were designed through structural analyses, and then the sensitivity analyses were conducted to understand the response of the structure to the load and to the span-length parameters. In this paper, a reliability study which gradually monitors the effect of geometrical parameters on the failure trend is presented. Three different snow load distribution functions were used. The relation between failure, and load or structural dimension variations was investigated. The results obtained in this study are discussed and compared with the results from the literature for similar structures subjected to snow loads. It is observed that for the snow load distributions with high standard deviations the structural reliability indices may give results below the target safety levels of the design codes. Finally, the assessment of the results shows that the effect of the standard deviation of the snow load on failure probability is much more than the effect of intensity of the nominal snow load.

Complementary Function of the Meniscofemoral Ligament and Lateral Meniscus Posterior Root to Stabilize the Lateral Meniscus Posterior Horn: A Biomechanical Study in a Porcine Knee Model.

Background:It has been demonstrated that the load distribution function of the lateral meniscus (LM) is compromised by resecting both the meniscofemoral ligament (MFL) and LM posterior root (LMPR). However, the effect of resecting these fibers on load transmission through the LM needs to be investigated.Purpose:To evaluate using a porcine knee model (1) the in situ forces of the MFL and LMPR and (2) the effect of resecting these fibers on the in situ force of the LM under a compressive load and valgus torque to the lateral knee compartment.Study Design:Controlled laboratory study.Methods:Twenty fresh-frozen porcine knees and a 6 degrees of freedom robotic system were utilized. An axial compressive load of 250 N and 5 N·m of valgus torque were applied to intact, MFL-deficient, LMPR-deficient, and MFL/LMPR-deficient knees at 30°, 60°, and 90° of flexion. The valgus angles under the applied loads were compared among the 4 states. The in situ forces of the MFL and LMPR under the applied loads were calculated under the principle of superposition. The in situ forces of the LM under the applied loads were also calculated and compared among the 4 conditions (intact, without the MFL, without LMPR, and without the MFL/LMPR).Results:The valgus angles significantly increased after resecting both the MFL and LMPR at all the flexion angles. The in situ forces of the MFL and LMPR changed reciprocally as the knee flexed. The in situ forces of the LM significantly decreased after resecting both the MFL and LMPR, although resecting only the MFL or LMPR represented no significant effect.Conclusion:The MFL and LMPR functioned complementarily as the posterior attachments of the LM against a compressive load and valgus torque to the lateral knee compartment in porcine knee joints.Clinical Relevance:If the LMPR is completely detached and needs to be repaired, the MFL should be preserved because it may provide some stability to the LM posterior horn and protect the repaired LMPR.

Capacity and load-aware software-defined network controller placement in heterogeneous environments

Relying upon a single centralized controller in Software-Defined Networks may lead to scalability problems. To make the network scalable and keep latency low for wide area networks, using multiple controllers is proposed. The network is partitioned into some domains, each one is monitored by a controller. However, the number of required controllers, their location and load balancing among them, to prevent controller overloading, have become major challenges in the distributed control plane. Controller Placement Problem (CPP) is widely known as a solution to tackle these issues. Nonetheless, different costs and capacities of controllers should also be considered in solving CPP. In this paper, the problem is formulated as a location-allocation model and our proposed framework solves it in two phases. Regarding the different costs of deployment, types and capacities of controllers in the market, the first phase focuses on determining the required number of controllers while minimizing the total cost. Using the result, the second phase is to solve the location-allocation problem to balance the controller load with our introduced fair load distribution function and to reduce inter-controller latency. Two greedy procedures for location and also allocation are designed for our proposed framework algorithms to solve the models and numerical results show their efficiency.

Reliability-based design of stiffened plates in ship structures subject to wheel patch loading

Reliability-based design methods are among the engineering tools for design of structures considering uncertainties in the design variables such as loads, material properties, manufacturing tolerances, etc. In design of stiffened plates of ship structures, there are some sources for uncertainties regarding the loads due to the highly nonlinear environment of the ocean. In addition to the environmental uncertainties, internal forces decrease the reliability of design due to the vagueness of items, which are included in the deadweight. Cargos with patch loading pattern like wheel and steel coil are common type of loading in some ships. These cargos are usually transferred by ferries, general cargo ships and bulk carriers. The application of reliability method in design of such structures against this local loading pattern has not been studied so far. Therefore, in this paper, the stochastic method and plastic formulas have been explained in designing steel panels subject to the patch loading. As a case study, stiffened plate structure of the ships subject to the truck wheel was investigated considering all design parameters as random variables. Bound theorem model for the patch loads is used to calculate the plastic load carrying capacity of the plate. First Order Second Moment (FOSM), First Order Reliability Method (FORM) and Importance Sampling method have been employed in the analyses. Both probability of failure and reliability index are calculated for different axel load distribution functions. The total failure probability was determined based on the rule of total probability. Sensitivity analyses for all parameters were carried out and the effects of coefficient of the variation of dominant variables were studied.

A Study on the Stiffness Characteristics according to the Body Pressure on the Seat Cushion for Vehicle

Objectives: Since the riding comfort upon seating is determined according to the driving environment or the driver’s preference, objective evaluations are accompanied by many constraints. Methods/Statistical Analysis: Variations in stiffness distribution of the seat cushion were analyzed by using body pressure distribution. First, to identify loaddeflection characteristics of the seat cushion, static load tests were conducted and stiffness characteristics as a function of load were affirmed by application of quadratic spline interpolation method. And, body pressure distribution of the male subject produced upon seating in the cushion was measured under actual vehicle conditions. Findings: Variations in stiffness distribution of the seat cushion produced when a driver comes aboard a vehicle, and the following conclusions could be obtained. First, by conducting static load tests for the seat cushion to obtain load-deflection curves, deflection characteristics per load point were identified. Second, through quadratic function for the load-deflection curves derived from static load tests, stiffness distributions were derived. Stiffness characteristics were continuously varied as a function of load distribution applied to the seat cushion, which was analyzed to have an effect on stiffness distribution as a function of body pressure distribution for the driver. Third, based on body pressure distribution data for the male subject and load-deflection curves for the seat cushion, variations in stiffness of the seat cushion were analyzed as a function of body pressure distribution. As a result, the extent of hardness felt by the human body was greater for the right side even if body pressure of the male subject was shown to be larger in the left-side region. Application/Improvements: Characteristics of seat stiffness distribution as a function of body pressure distribution which were derived in the present study are considered to be utilized for pad development of car seat.

Distributed dynamic load identification based on shape function method and polynomial selection technique

A new approach based on shape function method of moving least square fitting (SFM_MLSF) and polynomial selection technique is proposed in this paper for distributed dynamic load identification. The distributed dynamic load is represented as a product of spatial distribution function and time history, and the two parts are assumed to be independent. The modal transformation of structural dynamic equation throws light on the fact that all modal loads share the same form with the distributed dynamic load in time domain. As the structural modal parameters are known, the time history of dynamic load can be precisely identified through SFM_MLSF method which approximates the local dynamic load with shape functions in the moving supporting time domain. Then, the spatial distribution function of the load is substituted as a series of basic functions, and the identification of distribution function is transformed into a linear fitting problem. Through polynomial selection technique based on error reduction ratio, the significant components are picked out from the basis function responses, which greatly improves stability and precision of the load distribution function. During the inverse analyses of both the time history and distribution function, appropriate regularization methods are still applied to overcome the unavoidable ill-conditioned problem. Numerical examples demonstrate the validity and accuracy of the proposed method.

Gradation and Packing Characteristics Affecting Stability of Granular Materials: Aggregate Imaging-Based Discrete Element Modeling Approach

AbstractUnbound aggregate base and subbase in layered pavement structures provide an essential function of wheel load distribution through proper angular or crushed particle interlocking of coarse aggregate particles in the granular matrix. This paper used a validated model utilizing a particle image-aided discrete element method (DEM) to evaluate aggregate gradation and shape/morphological properties on pavement granular layer packing characteristics and load-carrying performance. The DEM packing simulations for different granular material gradations and particle shape categories were first performed to investigate the influence of the No. 4 (4.75-mm) sieve, separator of sand-sized and gravel-sized particles according to the Unified Soil Classification System (USCS), for typical dense-graded aggregates specified by the Minnesota Department of Transportation (MnDOT). Aggregate particles were modeled in the DEM as three-dimensional (3D) polyhedral discrete elements with both low and high angularity categor...

Influence of the control system on wind turbine loads during power production in extreme turbulence: Structural reliability

The wind energy industry is continuously researching better computational models of wind inflow and turbulence to predict extreme loading (the nature of randomness) and their corresponding probability of occurrence. Sophisticated load alleviation control systems are increasingly being designed and deployed to specifically reduce the adverse effects of extreme load events resulting in lighter structures. The main objective herein is to show that despite large uncertainty in the extreme turbulence models, advanced load alleviation control systems yield both a reduction in magnitude and scatter of the extreme loads which in turn translates in a change in the shape of the annual maximum load distribution function resulting in improved structural reliability. Using a probabilistic loads extrapolation approach and the first order reliability method, a large multi-megawatt wind turbine blade and tower structural reliability are assessed when the extreme turbulence model is uncertain. The structural reliability is assessed for the wind turbine when three configurations of an industrial grade load alleviation control system of increasing complexity and performance are used. The load alleviation features include a cyclic pitch, individual pitch, static thrust limiter, condition based thrust limiter and an active tower vibration damper. We show that large uncertainties in the extreme turbulence model can be mitigated and significantly reduced while maintaining an acceptable structural reliability level when advanced load alleviation control systems are used. We end by providing a rational comparison between the long term loads extrapolation method and the environmental contour method for the three control configurations.