Load Moment Research Articles

Finite-Element Analysis of Adjacent Concrete Box Girders Transversely Post-Tensioned at the Top Flanges Only

A three-dimensional non-linear finite-element model (FEM) was constructed using a commercial software (ATENA-Studio) to investigate the transverse load distribution behavior of adjacent precast prestressed concrete box-girder bridges. An innovative connection between box girders was used, where transverse post-tensioning was applied at the top flanges only eliminating the need for intermediate transverse diaphragms. The FEM was validated in terms of deflections, strains, cracking and ultimate loads against experimental results previously reported by the authors. The validated FEM was then used to perform a parametric study investigating the influence of adding concrete topping, load location, and bridge width on the transverse load distribution behavior of the newly developed connection. The results of the FEM demonstrated the efficiency of concrete topping in limiting mid-span deflections up to 25%. Additionally, the maximum live load moment distribution factors (LLMDFs) for different load locations and bridge widths were evaluated.

Scaled Modeled Tests and Finite Element Numerical Study on Lateral Responses of PRF System under V-H-M Loading

ABSTRACT Considerable research has been endeavoured to examine the responses of piled raft foundation (PRF) under gravity load. In reality, PRF often encounters combined vertical (V), horizontal (H) and moment (M) load simultaneously due to wind, earthquake and wave load along with dead load of the structure, and vertical soil pressure. Present study aims at a scaled-model test on the PRF subjected to V-H-M loads to investigate the lateral responses of PRF due to the interaction of loadings. The scaled model tests are conducted in Agartala sand with a relative density of 30%. Effects of relative stiffness raft with respect to soil, the length and spacing to diameter ratio of the pile, number of piles in a group and non-uniform pile length configuration on the lateral response of PRF are studied. Results indicate that the V load in V-H-M loading has a significant influence on the lateral response of PRF. Further, a substantial influence of other parametric variations on lateral response is also observed. Furthermore, a numerical model is also developed and validated based on experimental results that substantiate investigation on prototype foundation. Finally, the load-sharing behaviour of prototype PRF is also studied through the validated numerical model.

Comparison of Characteristics of Poultry Litter Pellets Obtained by the Processes of Dry and Wet Torrefaction

Torrefaction is a technology for the preliminary thermochemical treatment of biomass in order to improve its fuel characteristics. The aim of this work is to conduct comparative studies and select the optimal operating conditions of fluidized bed torrefaction for the processing of poultry litter (PL) into an environmentally friendly fuel. PL torrefaction was evaluated according to three different process configurations: (1) torrefaction of PL pellets in a fixed bed in a nitrogen medium at temperatures of 250 °C, 300 °C and 350 °C (NT1, NT2 and NT3); (2) torrefaction of PL pellets in a fluidized bed of quartz sand in a nitrogen medium at temperatures of 250 °C, 300 °C and 350 °C (NT4, NT5 and NT6); and (3) torrefaction of PL pellets in a fluidized bed of quartz sand in an environment of superheated steam at temperatures of 250 °C, 300 °C and 350 °C (ST1, ST2 and ST3). The duration of the torrefaction process in all experiments was determined by the time required for completion of CO2, CO, H2, and CH4 release from the treated biomass samples. The gas analyzer (Vario Plus Syngaz) was used to measure the concentration of these gases. The torrefaction process began from the moment of loading the PL sample into the reactor, which was heated to the required temperature. After the start of the torrefaction process, the concentration of CO2, CO, H2, and CH4 in the gases leaving the reactor initially increased and, subsequently, dropped sharply, indicating the completion of the torrefaction process. The chemical composition of the obtained biochar was studied, and it was found that the biochar contained approximately equal amounts of oxygen, carbon, nitrogen, hydrogen and ash, regardless of the torrefaction method. Furthermore, the biogas yield of the liquid condensate, obtained from the cooling of superheated steam used in the torrefaction process, was evaluated. The results highlight the efficiency of fluidized bed torrefaction, as well as the performance of superheated steam as a fluidization medium.

Failure surface for shallow foundations in sand using a classical bearing capacity

Much effort has been made to elucidate the ultimate capacity of shallow foundations under the general cases of vertical (V), lateral (H), and moment (M) loads in soils. The nature of the dependency of the ultimate capacity of shallow foundations on the combination of V, H, and M loads, the ratio of embedment to diameter, and soil properties has has not yet been analytically revealed. In this paper, an analytical investigation into failure effect of V, H, and M loads applied to shallow foundations in nonhomogeneous sand is made using a classical bearing capacity theory. Of the bearing capacity equations proposed thus far, the most appropriate bearing capacity equation which can predict experimental results of shallow foundations in sand is presented. A no-tension interface between a foundation base and a soil and an effective diameter of the foundation are used to analyze the base failure produced by the vertical stress of the soil below the foundation base when vertical and moment loads are applied. For shallow foundations with various embedment ratios in sand under the two different loading ways, the displacement-load curves and failure envelopes in the H-M, H-V, and M−V planes and in the H-M−V space are presented. For failure envelopes in the H-M plane under a constant vertical load for shallow foundations in sand, the results obtained from experiments are well predicted by the present method.

DC Drive Adaptive Speed Controller Based on Hyperstability Theory

The scope of this research is to develop a hyperstable adaptive control system of a direct current (DC) drive speed for effective load torque attenuation. The proposed speed controller is based on the model reference adaptive control framework and integrated into the conventional DC drive cascade control system. Its main features are as follows: (1) the boundedness of the control action signal, as well as the armature current control loop non-stationarities, are taken into consideration with the help of the reference model hedging technique; (2) its inputs include only measurable signals, thus there is no need to use any kind of state estimators; (3) it attenuates the disturbances, which are matched with its control action signal, particularly, the inertia moment non-stationarity and load torque. The asymptotic hyperstability of the obtained DC drive control system is proven with the help of Lyapunov’s theorems and Popov’s criterion. The numerical experiments corroborate the obtained results. They include the demonstration of disadvantages of the conventional cascade control system under conditions of the drive parameters’ non-stationarity and advantages of the proposed solution for different disturbance types and amplitudes.

Trailing Edge Flap Effects on Dynamic Stall Vortex and Unsteady Aerodynamic Forces on a Pitching Airfoil

This study focuses on the effect of the upward deflection of trailing edge flap (TEF) on the strength and trajectory of dynamic stall vortex (DSV) around a pitching airfoil by means of numerical simulations based on unsteady Reynolds-averaged Navier-Stokes (URANS). The effect of the upward deflection of the TEF on the unsteady aerodynamic forces due to DSV is analyzed. The numerical simulation method for large mesh deformation is constructed. Radial basis function- (RBF-) based mesh deformation algorithm, as well as Laplacian and optimization-based mesh smoothing algorithm, is adopted to ensure the mesh quality in flow field simulations. The results reveal that the upward deflection of the TEF can reduce the peaks of drag and pitching moment coefficients. Although the maximum lift coefficient of the airfoil is slightly reduced, its maximum drag and pitching moment coefficients are significantly reduced by up to 34.8% and 31.8%, respectively. The vorticity transport behavior in a planar control region during the DSV formation and detachment is analyzed. It is found that the TEF can change the development process of the DSV. The upward deflection of the TEF reduces the vorticity flux from the leading edge shear layer, which causes the circulation of the DSV and the translational velocity of the vortex center to decline. The peaks of the unsteady aerodynamic forces on the airfoil induced by the DSV are reduced. The upward deflection of the TEF plays the role of alleviating the pitching moment load. The longer TEF can result in a better control effect. The bigger the upward deflection angle of the TEF, the better its control effect.

Undrained capacity of circular shallow foundations under combined VHMT loading

Wind turbine (WT) foundations are generally subjected to large combined vertical, horizontal, moment, and torsional (VHMT) loads. The available investigations of the ultimate limit states of WT foundations focus predominately on unlimited-tension soil-foundation interfaces that are more appropriate for offshore settings. However, the interfaces for onshore WT foundations are generally unable to resist tensile loads. To address this omission, a zero-tension interface is used to investigate the VHMT failure envelope of circular shallow foundations under undrained soil conditions using finite element analysis. The effects of soil strength heterogeneity and foundation embedment were investigated. The results show that torsional loads reduce the VHM bearing capacity of circular foundations. The foundation embedment is also found to significantly increase the foundation bearing capacity. A full 4-D analytical expression for the VHMT failure envelope has been proposed based on the calculated failure envelopes.

Maximal strengths of dielectric elastomer fingers for a passive grip

Dielectric elastomer minimum energy structures (DEMESs) are useful as low-force robotic grippers; they can sweep a large angle but carry not much load. It was a design dilemma to reinforce the benders without compromising the stroke angle. As a stronger variant of DEMES, a dielectric elastomer (DE) finger can unbend the ‘phalanges’ of a load beam upon activation of the ‘intrinsic muscles’ of the dielectric elastomer actuator (DEA). The DE finger used a uniform tendon hood that raises the tension center of a single-layered DEA and thus enhances the moment generation and load capacity. In this work, we further optimize the structural design of a slender DE finger by mimicking the human thumb profile. This thumb-inspired DE finger has a tapered load beam for hood shaping of multi-layered DEAs with a blunter fingertip. This thumb-up profile greatly enhances the passive lift strength (against a tip weight) by 54% as compared to the earlier rectangular design, at the cost of a 13% reduction in the active stroke. Further, it exploited the axial stiffness to achieve an order-greater pull strength as compared to the lift strength. Finally, the optimized DEMES grippers carried a payload well exceeding the lift strength; they managed to pick an apple of nearly ten times the gripper weight. In addition, a foot of three DE toes hung upside-down to a branch of a horizontal tube while supporting a payload of close to ten times the foot’s weight.

Athree-dimensional method to calculate mechanical advantage in mandibular function : Intra- and interexaminer reliability study.

Masticatory muscles are physically affected by several skeletal features. The muscle performance depends on muscle size, intrinsic strength, fiber direction, moment arm, and neuromuscular control. To date, for the masticatory apparatus, only atwo-dimensional cephalometric method for assessing the mechanical advantage, which is ameasure for the ratio of the output force to the input force in asystem, is available. This study determined the reliability and errors of athree-dimensional (3D) mechanical advantage calculation for the masticatory system. Using cone-beam computed tomography images from teenage patients undergoing orthodontic treatments, 36craniofacial landmarks were identified, and the moment arms for seven muscles and their load moment arms (biomechanical variables) were determined. The 3D mechanical advantage for each muscle was calculated. This procedure was repeated by three examiners. Reliability was verified using the intraclass correlation coefficient (ICC) and the errors by calculating the absolute differences, variance estimator and coefficient of variation (CV). Landmark coordinates demonstrated excellent intra- and interexaminer reliability (ICC 0.998-1.000; p < 0.0001). Intraexaminer data showed errors < 1.5 mm. Unsatisfactory interexaminer errors ranged from 1.51-5.83 mm. All biomechanical variables presented excellent intraexaminer reliability (ICC 0.919-1.000, p < 0.0001; CV < 7%). Interexaminer results were almost excellent, but with lower values (ICC 0.750-1.000, p < 0.0001; CV < 10%). However, the muscle moment arm and 3D mechanical advantage of the lateral pterygoid muscles had ICCs < 0.500 (p < 0.05) and CV < 30%. Intra- and interexaminer errors were ≤ 0.01 and ≤ 0.05, respectively. Both landmarks and biomechanical variables showed high reliability and acceptable errors. The proposed method is viable for the 3D mechanical advantage measure.

Inelastic response of two-pile group under moment loading

Shallow foundations are mostly used in transmitting loads from the superstructure to the supporting soils. In several cases, these footings are subjected to moment loading such as vertical load and bending moment due to wind and earthquake. The main objective of the present investigation is to find out the load-displacement response of group of two piles subjected to pure moment loading in sand bed without any reinforcement. The advantage of model study is that the pertinent parameters influencing the behaviour of 2-pile group embedded in sand can be controlled easily as per the requirement. In addition, the cost of carrying out model investigations is quite less and convenience is more compared to field tests. Therefore, model study is adopted in the present investigation. The relevant parameters considered for the study are (a) dimensions of the pile models (l/d ratios), (b) Relative density conditions, (c) spacing between piles (s/d ratios).

Comparison of two internal fixation systems in lumbar spondylolysis by finite element methods

Background and purposeInternal fixation surgeries are currently the most effective treatments for lumbar spondylolysis, but the optimal fixation method is still on debate. This study was designed to compare the biomechanical characteristics of two fixation methods for lumbar spondylolysis, the pedicle screw-U shape rod (PSUSR) internal fixation system, and the pedicle screw-vertebral plate hook (PSVPH) internal fixation system, through three-dimensional finite element analysis, expecting to provide clinical guidance. MethodsFour finite element models (A, B, C, D) of L4-S1 vertebral body of a female patient were reconstructed by CT image segmentation. (A: intact model. B: spondylolysis model. C: spondylolysis model with PSUSR internal fixation. D: spondylolysis model with PSVPH internal fixation). Six physiological motion states were simulated by applying 500N concentrated force and 10Nm moment load to four models. The biomechanical advantages of the two internal fixation systems were evaluated by comparing the range of motion (ROM), maximum stress, maximum strain, and maximum displacement of the models. ResultsCompared to model B, the ROM decreased by 35.7%-57.1% in model C and 39.7%-64.8% in model D. The maximum displacements of model C and D both decreased. The maximum stresses in both vertebral and the internal fixation system are greater in model C than those in model D. The maximum stress and strain reduction of L5-S1 intervertebral disc in model D was greater than that in model C. Model D restores the articular cartilage stresses to the normal levels of model A. The maximum stress and maximum displacement of the bone graft in model C are greater than those in model D. ConclusionsThe PSVPH internal fixation system has better biomechanical properties than PSUSR internal fixation system in several mechanical comparisons. Experimental results suggest that PSVPH internal fixation system can effectively treat lumbar spondylolysis while preserving segmental mobility, and can be the treatment of choice.

On the Free Vibration and the Buckling Analysis of Laminated Composite Beams Subjected to Axial Force and End Moment: A Dynamic Finite Element Analysis

This work presents the bending–torsion coupled free vibration analysis of prestressed, layered composite beams subjected to axial force and end moment using the traditional finite element method (FEM) and dynamic finite element (DFE) techniques. Current trends in the literature, in terms of different types of modeling techniques and constraints, were briefly examined. The Galerkin-type weighted residual method was applied to convert the coupled differential equations of motion into a discrete problem using a polynomial interpolation function in the finite element method. In the dynamic finite element method, trigonometric shape functions were implemented to describe the equations in terms of nodal displacements. The eigenvalue problem resulting from the discretization along the length of the beam was solved in order to determine the system’s natural frequencies and modes. The results, showing the effects of axial load, end moment, and combined loading on natural frequencies, are discussed and are followed by some concluding remarks.

Prestressed stayed beam–columns under eccentric compression: Behaviour and prestress optimization

For prestressed stayed beam–columns, the structural behaviour and optimization method under eccentric compression are investigated numerically. The eccentric compression usually occurs when there exist installation errors, or when the member takes both the axial load and end moment. The indicators to quantify structural efficiency and failure mode are defined, and they together with load-carrying capacity of the stayed member with different structural configurations and prestress distributions are studied. The results reveal, for the first time, that when the short crossarm and eccentricity are located on the same side of the main member, the behaviour of the prestressed stayed beam–column under eccentric compression can be divided into small and large eccentricity zones owing to the different failure modes, such as compression dominant and bending dominant modes. Moreover, different optimization methods for the structural configuration and prestress distribution in the different zones are determined by striking a balance between maximizing load-carrying capacity and structural efficiency. This work would provide suggestions for the design of the prestressed stayed beam–columns under eccentric compression and the eccentric tolerance in installation.

Fatigue life prediction method for subsea wellhead welds based on the nonlinear fatigue accumulation model

In drilling and completion conditions, subsea wellheads are exposed to enormous alternating bending moment loads from the riser due to complex environmental conditions, causing fatigue damage. The joint weld between the high-pressure (HP) wellhead and the casing is especially vulnerable to fatigue, creating the risk of operational failure and accidents. Although fatigue analysis is vital, the traditional S–N curve method is often not accurate enough. This paper proposed an analytical technique to examine subsea wellhead fatigue by combining subsea wellhead fatigue decoupled analysis with a nonlinear fatigue accumulation theoretical model. This method was used to assess subsea wellhead weld fatigue in a gas field in China's Bohai Sea during drilling and completion. The bending moment load spectrum at the top of the HP wellhead was obtained via global dynamic analysis. The bending moment-stress and bending moment-strain response curves of the welds were extracted using local quasi-static analysis. Finally, the theoretical nonlinear fatigue accumulation model and traditional S–N curve method were used to evaluate subsea wellhead weld fatigue, respectively. The results indicated that the fatigue damage caused by drilling was more significant than completion, while the fatigue damage at the weld between the HP wellhead and the 16″ casing exceeded that of the weld between the low-pressure (LP) housing and the 30″ conductor. Furthermore, the technique proposed in this paper could be used to assess more extensive fatigue damage than when employing the S–N curve method, indicating that the results were more conservative and more suitable for practical engineering applications.

Buckling behaviour of cold-formed steel sigma and lipped channel beam–column members

To determine the load-bearing capacity of cold-formed steel (CFS) beam–column members, closed formed interaction formulas are generally used in most current design guidelines by linearly combining axial load and biaxial bending moment effects. However, this approach ignores the nonlinear interactions between these actions. To evaluate this issue, in this research the structural behaviour of eccentrically loaded beam–column CFS lipped and sigma channel profiles are investigated experimentally and analytically under simultaneous effects of axial loads and biaxial bending moments. Detailed Finite Element (FE) models are developed using ABAQUS software by considering geometric imperfections and actual material properties obtained from coupon tests, and validated against experimental data to estimate the strength and buckling behaviour of CFS beam–column elements. A total of 4480 FE analyses are then performed on 500 mm and 2000 mm long CFS members with different lipped and sigma channel sections subjected to a wide range of eccentricity values in various directions. The results of the analyses indicate that the failure modes are mainly dependent on the stress distribution of the cross-section generated by the combined actions. It is also demonstrated that regardless of the selected load combination, using sigma sections for the short beam–column members generally results in higher strength by up to 42% compared to those with lipped channel sections. It is shown that AISI and Eurocode underestimate the capacity of CFS beam–column members, on average, by around %50 and %25, respectively. However, the recently proposed extended Direct Strength Method (DSM) can generally provide more accurate strength predictions, especially in the case of short beam–column elements.

Design of cold-formed steel built-up open section members under combined compression and bending

The numerical investigation on cold-formed steel built-up open section members under combined compression and minor axis bending is described in this paper. Through validating against experimental results in the literature, a rational finite element model of built-up section beam–column members was developed. The verified numerical model was employed for a comprehensive parametric study to obtain the results of 280 eccentrically loaded built-up section members. Furthermore, the applicability of the design formulae provided in the AISI Specification, AISC Specification, AS/NZS Standard and European Code was examined by comparing nominal strengths with loading capacities of the 280 numerical data produced in this study and 33 existing test data. Overall, the strength predictions determined by the codified interaction formulae based on the nominal compressive and flexural resistances calculated by the current direct strength method (DSM) were found to be highly scattered and underestimated by average of 17% – 27% for the built-up open section components experiencing combined loading. Hence, the modified DSM was recommended to determine the nominal resistances of the members under isolated compression or bending for more accurate endpoints of the load–moment interaction curve. In addition, a bi-linear interaction expression was proposed in this study for the design of the cold-formed steel built-up section beam–columns, which offered better strength predictions in accuracy and consistency compared to the codified interaction formulae.

Impact Damage Characteristics of Quartz Fiber and NOMEX Paper Honeycomb Sandwich Panel composite materials

To provide a reference for practical engineering application of fiber composite materials, this work researches on the impact resistance of type-B quartz fiber/modified cyanate ester composite material laminates and NOMEX paper honeycomb sandwich panels. Firstly, low-speed impact tests are carried out on the quartz fiber laminates and the NOMEX paper honeycomb sandwich panels by setting different parameters to analyze the impact energy and punch mass on impact damage; secondly, based on the experimental results, impact responses are analyzed; and the damage morphology of the two composite materials is observed through visual inspection and with the aid of the CT scanning technology. The results show that according to time-load curves, the NOMEX paper honeycomb sandwich panels have two peak load moments, respectively corresponding to the moments when the upper and lower panels are penetrated; the quartz fiber laminates show three different types of failures, namely substrate cracking, fiber fracture and delamination. As for the NOMEX paper honeycomb sandwich panels, two types of damage are found: fiber fracture and honeycomb core extrusion fracture. When the punch mass is constant, the greater the impact energy is, the more serious the damage is; and when the impact energy is constant, the greater the punch mass is, the more serious the damage is.

Finite element analysis of punching shear behavior of reinforced concrete slabs supported on walls

AbstractDue to the low lateral stiffness of slabs supported on columns alone, reinforced concrete flat plates are typically combined with other structural elements, such as shear walls. In these structures, the slab–column connections are designed to carry gravity loads only, and the shear walls are required to resist both gravity and lateral forces. Therefore, the slab–wall connections are essential for the performance of both the gravity and lateral force resisting systems. However, most punching shear research and design provisions are focused on slab–column connections, even though punching failures around slab–wall connections have occurred experimentally. Empirical testing of slab–wall connections is difficult due to the specimen size. This paper investigates the punching shear behavior of interior slab–wall connections subjected to concentric vertical loading, and combined concentric vertical loading and uniaxial unbalanced moment using a plasticity‐based nonlinear finite element model (FEM) in ABAQUS. The analysis of isolated slab–wall connections demonstrates that punching failures can occur before one‐way shear failures. Since the overall connection capacity is much higher than the expected loads in most structures, if these punching failures happen they would be localized to the region around the wall end and are not expected to lead to structural collapse.

Arbitrary Prestrain Values for Ligaments Cause Numerical Issues in a Multibody Model of an Ankle Joint

Experimental studies report that ligaments of the ankle joint are prestrained. The prestrain is an important aspect of modern biomechanical analysis, which can be included in the models by: applying symmetrical, arbitrary prestrains to the ligaments, assuming a strain-free location for the joint or by using experimental prestrain data. The aim of the study was to comparatively analyze these approaches. In total, 4 prestraining methods were considered. In order to do so, a symmetrical model of the ankle with six nonlinear cables and two sphere–sphere contact pairs was assumed. The model was solved in statics under moment loads up to 5 Nm. The obtained results showed that the arbitrary prestrains caused an unbalanced load for the model at rest, and in turn modified its rest location in an unpredictable way. Due to the imbalance, it was impossible to enforce the assumed prestrains and thus cartilage prestrain was required to stabilize the model. The prestraining had a significant effect on the angular displacements and the load state of the model. The findings suggest that the prestrain values are patient specific and arbitrary prestrains will not be valid for most models.

A simplified formula for calculating the limit load of cracked offshore wind turbine monopile under bending

A simplified methodology is proposed for calculating the plastic collapse (limit) bending moment load of a pipe with a circumferential flaw with an emphasis on its application for use in the assessment of cracked offshore wind turbine monopile using failure assessment diagrams. The proposed methodology is based on the theory of net section collapse (NSC) but differs from existing approaches in that it does not need idealisation and categorisation of the crack before assessment. The proposed methodology is validated against results presented in literature and also finite element analysis results. Although it is possible to obtain limit loads using FE analysis, this is computationally expensive and time consuming. The proposed approach allows for near-instantaneous calculation of limit load for any arbitrary crack configuration and loading direction. This is a significant development for the analysis of offshore wind turbine monopiles as it allows the suitability of the cracked structure to be assessed in pseudo-real time.