High Bending Moments Research Articles

Loading Analysis of Composite Wind Turbine Blade for Fatigue Life Prediction of Adhesively Bonded Root Joint

Nowadays wind energy is widely used as a non-polluting cost-effective renewable energy resource. During the lifetime of a composite wind turbine which is about 20 years, the rotor blades are subjected to different cyclic loads such as aerodynamics, centrifugal and gravitational forces. These loading conditions, cause to fatigue failure of the blade at the adhesively bonded root joint, where the highest bending moments will occur and consequently, is the most critical zone of the blade. So it is important to estimate the fatigue life of the root joint. The cohesive zone model is one of the best methods for prediction of initiation and propagation of debonding at the root joint. The advantage of this method is the possibility of modeling the debonding without any requirement to the remeshing. However in order to use this approach, it is necessary to analyze the cyclic loading condition at the root joint. For this purpose after implementing a cohesive interface element in the Ansys finite element software, one blade of a horizontal axis wind turbine with 46 m rotor diameter was modelled in full scale. Then after applying loads on the blade under different condition of the blade in a full rotation, the critical condition of the blade is obtained based on the delamination index and also the load ratio on the root joint in fatigue cycles is calculated. These data are the inputs for fatigue damage growth analysis of the root joint by using CZM approach that will be investigated in future work.

Centrifuge Model Study of High Strength Piles Composite Foundation Settlement & Instability under Embankment in Different Kind Soils by Different Pile Spacing

A series of centrifuge model tests has been conduced to examine the behavior of high strength piles composite foundation stability under railway embankment in silt or clay or sand different kind of soils. The high strength composite foundation has a symmetrical plan layout consisting of 3×4, 4×6, and 5×8 piles with a center-to-center spacing of 6 or 4 or 3 times pile width. The piles are under the same height of railway embankment, with the same length, and on the same lying soil layer. The high strength composite foundation stability test results are expressed in terms of soils kinds-pile displacement response of the composite foundation, embankment load experienced by soil between piles and piles in the composite foundation, and bending moment profile along individual pile. It is established that the high strength composite foundation stability efficiency reduces significantly with decreasing of the strength of soil between piles in composite foundation. The tests reveal the shadowing effect phenomenon in which the marginal piles experienced larger laterally and bending moment than that of the central piles. The shadowing effect is most significant for the lead row piles and considerably less significant for subsequent rows of middle piles. The approach adopted by many researchers of taking the average performance of piles in the same row is found to be inappropriate for the middle rows, of piles for composite foundation as the outer piles in the row carrying significantly more laterally load and experience considerably higher bending moment than those of the inner piles.

Towards a Novel, Implantable Limb Lengthening Device1

Several surgical techniques and devices have been developed to help patients born with limb deformities, limb length inequalities, and extreme short stature. People with such ailments often experience pain, dysfunction, and joint degeneration. The primary method of treating such deformities is an osteotomy followed by callus distraction [1]. Commonplace lengthening devices are external fixators and intramedullary devices, but each has its drawbacks. Traditional external fixators, such as the Ilizarov device and Taylor spatial frame, are cumbersome, painful, and produce large residual scars [2]. Due to pin tract infection rates of 10–20%, lengthening with these methods requires careful surveillance [3]. Intramedullary lengthening devices can cause severe complications such as intramedullary infection [4]. Surgeons have recently experienced success with a motorized, intramedullary nail (Fitbone), but pediatric use of this device can be limited due to interference with open growth plates [5]. The investigators have designed an extramedullary device that retains the attractive qualities of an intramedullary nail, without the risk of deep infection or damage to growth plates. Additionally, the device can be equipped with a six-axis force-torque sensor capable of measuring forces and moments in real time.

Low-cycle fatigue analysis of a web frame corner in ship structures

Ship structures are subjected to cyclic loads which may lead to fatigue failures particularly at welded joints. In addition to loads induced by waves and structural vibrations, which contribute to high-cycle fatigue, various structural details are also subjected to a limited number of high-stress cycles caused by changing loading conditions, which may lead to low-cycle fatigue. Thus, appropriate procedures are required for the shipbuilding industry, which are missing in the existing design codes. Experimental investigations and numerical analyses were performed to validate a procedure for the design of ship structures in the low-cycle fatigue regime. Three large-scale fatigue tests were carried out with high bending moments on test models of web frame corners in order to initiate fatigue cracks after few hundred cycles. Different cracks occurred; however, a crack at the cruciform joint has shown to determine the failure of the connection. An extension of the effective notch stress approach was applied to this joint to assess the low-cycle fatigue life, considering the elastic–plastic strain, evaluated by nonlinear finite element analyses, in the notch of the weld toe. This practical method offers promising possibilities to assess the fatigue life of welded joints in the low-cycle fatigue regime.

MAAT – Promising innovative design and green propulsive concept for future airship's transport

Airships were the first air vehicles, which had the ability to generate lift without the use of aerodynamic flow around wings, also to enable controlled, powered flight, providing long endurance at low energy consumption. They were widely used before the 1940s, but their use decreased as their capabilities were exceeded by those of the airplanes. Their decline continued with a series of several accidents, including the burning of the hydrogen-filled Hindenburg, and the destruction of the USS Akron. Nowadays, airships are used in certain applications: cargo transportation, tourism, aerial observations and many others, where the ability to hover in one place for an extended period of time is important. In Europe the reborn of airships is being supported by the European Union, recently providing financing for Project MAAT – Multibody Advanced Airship for Transportation, supported by 7 FP Program. This project, comprises twelve research institutions, introduces the concept of feeder–cruiser airship for transportation of people and goods. The main idea is to use a cruiser (PTAH)–feeder (ATEH) concept to allow transport of people and goods [9], [10], [47]. For this novel airship concept a new envelope and propulsion concept design is envisaged. The present study deals with the methodology and results for numerical modeling and research on airship with an innovative shape and implementation of its unconventional propulsion system. Attention has been paid to the logical sequence and obtained results for modeling and research of an airship with innovative shapes. The innovative design concept is analyzed and comprised with classic airship shape in point of aerodynamic and energetic needs. It was found that the classic airship shape provokes many problems, which are mainly referred to as high bending moments, in case of given buoyancy volume and optimal fineness ratio. The newly proposed shape needs an extensive research, which cannot rely on classic approach for drag coefficient calculations. Furthermore, based on the research results and conclusions for the airship shape, aerodynamic features at given altitudes and the propulsion needs, a feasible and innovative propulsion concept air-jets, is analyzed. Attention was focused on the performance of the air-jets working with high mass flow rates and low jet flow speeds. The outcome of the research highlights the opportunities for future developments of the propulsion concepts for airships with innovative shape as it is a very important and promising area in nowadays air-vehicles technology.

Experimental studies of hollow flange channel beams subject to combined bending and shear actions

This paper presents the details of an experimental study of a cold-formed steel hollow flange channel beam known as LiteSteel beam (LSB) subject to combined bending and shear actions. The LSB sections are produced by a patented manufacturing process involving simultaneous cold-forming and electric resistance welding. Due to the geometry of the LSB, as well as its unique residual stress characteristics and initial geometric imperfections resultant of manufacturing processes, much of the existing research for common cold-formed steel sections is not directly applicable to LSB. Experimental and numerical studies have been carried out to evaluate the behaviour and design of LSBs subject to pure bending actions and predominant shear actions. To date, however, no investigation has been conducted into the strength of LSB sections under combined bending and shear actions. Combined bending and shear is especially prevalent at the supports of continuous span and cantilever beams, where the interaction of high shear force and bending moment can reduce the capacity of a section to well below that for the same section subject only to pure shear or moment. Hence experimental studies were conducted to assess the combined bending and shear behaviour and strengths of LSBs. Eighteen tests were conducted and the results were compared with current AS/NZS 4600 and AS 4100 design rules. AS/NZS 4600 design rule based on circular interaction equation was shown to grossly underestimate the combined bending and shear capacities of LSBs and hence two lower bound design equations were proposed based on experimental results. Use of these equations will significantly improve the confidence and cost-effectiveness of designing LSBs for combined bending and shear actions.

Computational studies of horizontally curved, longitudinally stiffened, plate girder webs in flexure

Abstract Summarized herein is a study that explored single span, horizontally curved, plate girders having a yield stress of 50 ksi (345 MPa) to investigate their flexural behavior as a function of the position of a single longitudinal stiffener at various locations along the depth of the web. The studies were conducted using ABAQUS [1] with the girder cross-sections under high vertical bending moment and low shear. As a result of these studies, recommendations are made for positioning longitudinal stiffeners on horizontally curved webs that complement existing criteria for straight plate girders in bending. The study shows that, for the high flexure situations and girder specimens that were examined: (1) the optimal position for longitudinal stiffeners on a horizontally curved web does not appear to differ appreciably from that for a straight web as recommended in the AASHTO LRFD Bridge Design Specifications [2]; and (2) horizontal curvature can contribute to enhancing web stability, and, in certain instances, curvature may mitigate the need to use longitudinal stiffeners to help increase cross-section flexural strength.

Effect of a vertical guide plate on the wind loading of an inclined flat plate

Wind tunnel experiments were performed to study the wind loads on an inclined flat plate with and without a guide plate. Highly turbulent flow, which corresponded to free-stream turbulence intensity on the flat roof of low-rise buildings, was produced by a turbulence generation grid at the inlet of the test section. The test model could represent a typical solar collector panel of a solar water heater. There are up-stream movements of the separation bubble and side-edge vortices, more intense fluctuating pressure and a higher bending moment in the turbulent flow. A guide plate would result in higher lift coefficient, particularly with an increased projected area ratio of a guide plate to an inclined flat plate. The value of lift coefficient is considerably lower with increased free-stream turbulent intensity.

Finite Element Analysis and Investigation of Double-Row Piles Supporting Structure<sup></sup>

The double-row piles supporting structure is a new type of supporting and protecting for deep foundation excavation. It is widely used to in design of deep foundation pit. Now how to simply and effectively design the structure of double-row piles is in a research and discuss stage. Using the Midas GTS finite element method, the displacement and stress distribution of double-row piles in the different stages of excavation are obtained, and the horizontal displacement and stress distribution of double-row piles in the different stages of excavation are calculated. The results of Midas GTS finite element analysis as follows: (1) after the excavation of foundation pit, the horizontal displacement of pile-top is maximum. The horizontal displacement decreases gradually with depth increases. And the displacement of front row piles is larger than that of back row piles; (2) the maximum shear stress is at the distance 5m to the foundation basement. The higher bending moment at the pile-top and the distance 10m to the foundation basement are consistent with the actual monitoring date. (3) the results of finite element analysis is close to the Richard software and actual monitoring data. It is show that using the finite element analysis to analyze the double-row piles supporting structure with is veritable and credible.

Moment–shear interaction of stiffened plate girders—Tests and numerical model verification

Abstract Results of four full-scale tests on plate girders stiffened with transverse and longitudinal stiffeners subjected to interaction of high bending moment and shear force are presented and discussed. In longitudinal direction the web was stiffened with open or closed stiffeners positioned in the compression zone. Detailed information on initial geometric imperfection and residual stresses is given. The experimental results were used to verify numerical model. The resistance is compared against reduced stress method and effective width method given in EN 1993-1-5.

Experimental research on concrete filled steel tube columns under combined compression-bending-torsion cyclic load

Based on the force–displacement mixed control quasi-static test on eight CFST columns subjected to combined compression, bending and torsion cyclic load, the mechanical behavior of CFST columns with various section types, bending moment to torsion moment ratios and axial load levels was studied. The test results showed that the hysteretic curves of CFST columns under combined compression, flexure and torsion are plump due to the good seismic behavior and the ductility was also good. But for rectangular CFST columns with high bending moment to torsion moment ratio, the strength degradation was observed due to the local buckling of the steel plate at the bottom. The torsion capacity of CFST columns would be reduced by the bending moment. The plane section assumption of axial strain of CFST columns could be satisfied. The shear strain of the steel tube has good linear relationship with the rotation angle of the section when CFST columns subjected to combined compression, flexure and torsion. Based on the test results and literatures available, the mechanism of CFST columns was qualitatively analyzed. ► The test on CFST under compression-bending-torsion cyclic load was carried out. ► The failure modes and strain state of CFST columns under cyclic torsion were found. ► The torsion mechanism of CFST columns was analyzed based on the test results.

Design of composite tidal turbine blades

Tidal turbine blades are subjected to significant thrust and torsional loadings due to the high density of the seawater in which they operate. These thrust loadings lead to high bending moments at the blade root, which can prove to be a serious design constraint for these devices and can have implications with respect to cost-effectiveness and scalability. This work presents a combined hydrodynamic-structural design methodology for a commercial scale (1.5 MW) tidal turbine. A hydrodynamic analysis of the blade is carried out to determine force distributions along the blade span under normal and extreme operating conditions. Using output from the hydrodynamic model, a pre-processor for computing blade structural properties is used to determine the strain distribution along the blade spar caps. The strain distributions from this analysis are then compared with a finite element model of the blade which is then used to compare the structural performance of glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP) as spar cap materials. ► Combined hydrodynamic-structural design methodology for a tidal turbine blade is presented. ► Comparison of glass fibre and carbon fibre as blade construction materials. ► High bending moments are likely to restrict up-scaling of composite designs. ► Predicted spar cap thickness has significant cost implications for production.

Are there any differences in various polyaxial locking systems? A mechanical study of different locking screws in multidirectional angular stable distal radius plates

Numerous angular stable plates for the distal radius exist, and technically based comparisons of the polyaxial locking interfaces are lacking. The aim of this mechanical study was to investigate three different locking interfaces of angular stable volar plates by cantilever bending: VA-LCP Two-Column Distal Radius Plates 2.4 mm (Synthes® GmbH, Oberdorf, Switzerland), IXOS® P4 (Martin, Tuttlingen, Germany) and VariAX™ (Stryker®, Duisburg, Germany). We assessed the strength of 0°, 5°, 10° and 15° screw locking angles and tested the bending strength from 10° to 5° angles by cyclic loading until breakage. The final setup repeated the above assessments by inclusion of four locking screws. The single screw-plate interfaces of the VA-LCP showed the highest bending moment at an angle of 0° and 5°, the IXOS® P4 at an angle of 10° and 15° and the VariAX™ when changing the insertion angle from 10° into 5°. The strength of polyaxial locking interfaces and mechanism of failure proved to be different among the examined plates.

The Simulation and Sensitivity Analysis of S-Lay Installation in Deep Water

Pipelines being laying is subjected the high external water pressure, axial tension and bending moment, influencing the large deformation and the stability of pipelines. It is a key problem about the pipeline deformation and stress analysis under installation. The paper is focused on the analysis of the S-Lay method in deep water, modeling the deepwater S-lay installations considering interactions among the pipeline and stinger and the barge, which make the simulations more realistic. The large work of the paper issues the sensitivity analysis in the installation procedure, several examples are presented to calculate the pipeline configuration and mechanical analysis for different laying water depth, pipe diameter, thickness of wall and concrete weighted coating layer and stinger radius. Some results are presented as well.

Transient Loads Control of a Variable Speed Rotor During Lagwise Resonance Crossing

Varying rotor speed during operation is a potential way to improve rotorcraft performance. The transient aeroelastic response of a stiff in-plane rotor system undergoing variable speed operation in forward flight is considered. During crossing of the fundamental lag mode near 2/rev, high transient lag bending moments are observed. The flapping amplitude and duration of the resonance crossing event have a strong influence on the peak lagwise root bending moment. Embedded chordwise fluidlastic dampers are explored as a way to reduce the peak bending moments. Determination of the fluidlastic damper properties is based on the analysis of a two degree-of-freedom blade-damper system. Parametric studies show that tuning port area ratios, loss factors, and device mass can be modified to enhance damper performance, and control the stroke. Results indicate that more than 6% critical lag damping can be provided around the resonance rotor speed, and that approximately 65% peak-to-peak moment reduction can be achieved with those devices. The stroke of the damper is limited to less than 2.5% blade chord length in the worst-case scenarios. Embedded chordwise fluidlastic dampers can successfully control the lagwise transient loads during the lagwise resonance crossing for the variable speed stiff in-plane rotors studied.

Bending moment resistance of corner joints constructed with spline under diagonal tension and compression

We determined the effects of the penetration depth and spline material and composite material type as well as joining method on bending moment resistance under diagonal compression and tension in common wood panel structures. Composite materials were laminated medium density fiberboard (MDF) and particleboard. Joining methods were butt and miter types. Spline materials were high density fiberboard (HDF). The penetration depths of plywood, wood (Carpinus betolus) and spline were 8, 11 and 14 mm. The results showed that in both diagonal compression and tension, MDF joints are stronger than particleboard joints, and the bending moment resistance under compression is higher compared with that in tension. The highest bending moment resistance under tension was shown in MDF, butt joined using plywood spline with 8 mm penetration depth, whereas under compression bending moment resistance was seen in MDF, miter joined with the HDF spline of 14 mm penetration depth.

Assessment of non-prismatic beams having symmetrical parabolic haunches with constant haunch length ratio of 0.5

Single span historic bridges often contain non-prismatic members identified with a varying depth along their span lengths. Commonly, the symmetric parabolic height variations having the constant haunch length ratio of 0.5 have been selected to lower the stresses at the high bending moment points and to maintain the deflections within the acceptable limits. Due to their non-prismatic geometrical configuration, their assessment, particularly the computation of fixed-end horizontal forces (FEFs) and fixed-end moments (FEMs) becomes a complex problem. Therefore, this study aimed to investigate the behavior of non-prismatic beams with symmetrical parabolic haunches (NBSPH) having the constant haunch length ratio of 0.5 using finite element analyses (FEA). FEFs and FEMs due to vertical loadings as well as the stiffness coefficients and the carry-over factors were computed through a comprehensive parametric study using FEA. It was demonstrated that the conventional methods using frame elements can lead to significant errors, and the deviations can reach to unacceptable levels for these types of structures. Despite the robustness of FEA, the generation of FEFs and FEMs using the nodal outputs of the detailed finite element mesh still remains an intricate task. Therefore, this study advances to propose effective formulas and dimensionless estimation coefficients to predict the FEFs, FEMs, stiffness coefficients and carry-over factors with reasonable accuracy for the analysis and re-evaluation of the NBSPH. Using the proposed approach, the fixed-end reactions due to vertical loads, and also the stiffness coefficients and the carry-over factors of the NBSPH can be determined without necessitating the detailed FEA.

In vivo measurement of shoulder joint loads during walking with crutches

Following surgery or injury of the lower limbs, the use of walking aids like crutches can cause high loads on the shoulder joint. These loads have been calculated so far with computer models but with strongly varying results. Shoulder joint forces and moments were measured during crutch-assisted walking with complete and partial unloading of the lower limbs. Using telemeterized implants in 6 subjects axillary crutches and forearm crutches were compared. A force direction was more in the direction of the long humeral axis, and slightly lower forces were assumed using axillary crutches. Similar force magnitudes as those experienced during previously measured wheelchair weight relief tasks were expected for complete unloading. The friction-induced moment was hypothesized to act mainly around the medio-lateral axis during the swing phase of the body. Maximum loads of up 170% of the bodyweight and 0.8% of the bodyweight times meter were measured with large variations among the patients. Higher forces were found in most of the patients using forearm crutches. The hypothesized predominant moment around the medio-lateral axis was only found in some patients. More often, the other two moments had larger magnitudes with the highest values in female patients. The assumed different load direction could only be found during partial unloading. In general the force magnitudes were in the range of activities of daily living. However, the number of repetitions during long-lasting crutch use could lead to shoulder problems as a long-term consequence. The slightly lower forces with axillary crutches could be caused by loads acting directly from the crutch on the scapula, thus bypassing the glenohumeral joint. The higher bending moments in the female patients could be a sign of lacking muscle strength for centring the humeral head on the glenoid.

Experimental Studies on the Bonding Failure between CFRP and Concrete in RC Two-Way Slabs Strengthened with CFRP Strips

It is well known that the bonding failure between concrete and externally bonded CFRP strips sets in where high shear forces and high bending moments occur. Despite this knowledge, experimental and theoretical studies had been exclusively focused on the bonding failure modes at the end of the CFRP-strip. This paper deals with strengthening of RC two-way slabs with CFRP strips bonded to the tensile face. It focuses on the bonding failure by dealing with an experimental study. The CFRP-strips strengthened slab test presents a failure mode with debonding of the external CFRP strips from the slab.

Buckling interaction of slender plates—Experimental and numerical investigations

Abstract In this paper the bending-shear interaction of slender plates is studied. Six large tests were performed on longitudinally and transversally stiffened girders in the range of high bending moment and shear force. In longitudinal direction the web was stiffened with a trapezoidal stiffener positioned at the mid web depth for two girders and in the compression zone for the other four girders. The test procedure and test results are presented in details from the point of global behaviour and web buckling. The girders were divided in three groups; within each group one of the parameters was varied. Furthermore, a numerical model built in the general-purpose code ABAQUS is presented and verified against test results regarding initial stiffness, resistance and failure mode. In the last part of this paper the maximum load and the design resistance according to EN 1993-1-5 are compared and discussed. The design resistance was calculated with both options, according to the effective width method and the reduced stress method.