Finite Element Modeling for Static Bending Behaviors of Rotating FGM Porous Beams with Geometrical Imperfections Resting on Elastic Foundation and Subjected to Axial Compression

The static bending analysis of the FG porous beam resting on the two-parameter elastic foundation is initially carried out using a combination of Reddy’s high-order shear deformation theory and the finite element technique, where the initial geometrical imperfection and rotation movement in one fixed axis are calculated. Through the power-law distribution function with porosities, material characteristics vary constantly from one surface to the next in the direction of thickness, and the beam is concurrently impacted by an acting force perpendicular to the beam axis and an axial compressive force. The stiffness matrix of the beam element changes as a result, and the static bending response of this beam is significantly different from that of ordinary beams. Comparison cases with published findings are used to verify the computational theory. The calculations clearly reveal many innovations for rotating beams that are influenced by many different kinds of loads, which may be used to the designing, manufacturing, and usage of these structures in reality.

Buckling Knockdown Factors of Composite Cylinders under Both Compression and Internal Pressure

The internal pressure of a thin-walled cylindrical structure under axial compression may improve the buckling stability by relieving loads and reducing initial imperfections. In this study, the effect of internal pressure on the buckling knockdown factor is investigated for axially compressed thin-walled composite cylinders with different shell thickness ratios and slenderness ratios. Various shell thickness ratios and slenderness ratios are considered when the buckling knockdown factor is derived for the thin-walled composite cylinders under both axial compression and internal pressure. Nonlinear post-buckling analyses are conducted using the nonlinear finite element analysis program, ABAQUS. The single perturbation load approach is used to represent the geometric initial imperfection of thin-walled composite cylinders. For cases with the axial compressive force only, the buckling knockdown factor decreases as the shell thickness ratio increases or as the slenderness ratio increases. When the internal pressure is considered simultaneously with the axial compressive force, the buckling knockdown factor decreases as the slenderness ratio increases but increases as the shell thickness ratio increases. The buckling knockdown factors considering the internal pressure and axial compressions are higher by 2.67% to 38.98% compared with the knockdown factors considering the axial compressive force only. The results show the significant effect of the internal pressure, particularly for thinner composite cylinders, and that the buckling knockdown factors may be enhanced for all the shell thickness ratios and slenderness ratios considered in this study when the internal pressure is applied to the cylinder.

On the Flexural-Torsional Vibration and Stability of Beams Subjected to Axial Load and End Moment

The free vibration of beams, subjected to a constant axial load and end moment and various boundary conditions, is examined. Based on the Euler-Bernoulli bending and St. Venant torsion beam theories, the differential equations governing coupled flexural-torsional vibrations and stability of a uniform, slender, isotropic, homogeneous, and linearly elastic beam, undergoing linear harmonic vibration, are first reviewed. The existing formulations are then briefly discussed and a conventional finite element method (FEM) is developed. Exploiting the MAT LAB-based code, the resulting linear Eigenvalue problem is then solved to determine the Eigensolutions (i.e., natural frequencies and modes) of illustrative examples, exhibiting geometric bending-torsion coupling. Various classical boundary conditions are considered and the FEM frequency results are validated against those obtained from a commercial software (ANSYS) and the data available in the literature. Tensile axial force is found to increase natural frequencies, indicating beam stiffening. However, when a force and an end moment are acting in combination, the moment reduces the stiffness of the beam and the stiffness of the beam is found to be more sensitive to the changes in the magnitude of the axial force compared to the moment. A buckling analysis of the beam is also carried out to determine the critical buckling end moment and axial compressive force.

On the Flexural-Torsional Vibration and Stability of Beams Subjected to Axial Load and End Moment

The free vibration of beams, subjected to a constant axial load and end moment and various boundary conditions, is examined. Based on the Euler-Bernoulli bending and St. Venant torsion beam theories, the differential equations governing coupled flexural-torsional vibrations and stability of a uniform, slender, isotropic, homogeneous, and linearly elastic beam, undergoing linear harmonic vibration, are first reviewed. The existing formulations are then briefly discussed and a conventional finite element method (FEM) is developed. Exploiting the MAT LAB-based code, the resulting linear Eigenvalue problem is then solved to determine the Eigensolutions (i.e., natural frequencies and modes) of illustrative examples, exhibiting geometric bending-torsion coupling. Various classical boundary conditions are considered and the FEM frequency results are validated against those obtained from a commercial software (ANSYS) and the data available in the literature. Tensile axial force is found to increase natural frequencies, indicating beam stiffening. However, when a force and an end moment are acting in combination, the moment reduces the stiffness of the beam and the stiffness of the beam is found to be more sensitive to the changes in the magnitude of the axial force compared to the moment. A buckling analysis of the beam is also carried out to determine the critical buckling end moment and axial compressive force.

Biomechanical Study of Lumbar Spine (L2-L4) Using Hybrid Stabilization Device - A Finite Element Analysis

Spinal instrumentations have been designed to alleviate lower back pain and stabilize the spinal segments. The present work aims to evaluate the biomechanical effect of the proposed Hybrid Stabilization Device (HSD). Non-linear finite element model of lumbar segment L2-L4 were developed to compare the intact spine (IS) with rigid implant (RI) and hybrid stabilization device. To restrict all directional motion vertebra L4 bottom surface were kept fixed and axial compressive force of 500N with a moment of 10Nm were applied to the top surface of L2 vertebrae. The results of range of motion (ROM), intervertebral disc (IVD) pressure and strains for IVD-23 and IVD-34 were determined for flexion, extension, lateral bending and axial twist. Results demonstrated that ROM of HSD model is higher than RI and lower as compared to IS model. The predicted biomechanical parameters of the present work may be considered before clinical implementations of any implants.

ON THE NUMERICAL SOLUTION TO A NON-CLASSICAL PROBLEM OF BENDING AND STABILITY FOR AN ORTHOTROPIC BEAM OF VARIABLE THICKNESS

The mathematical model of the problem of bending of an elastically clamped beam is constructed on the basis of the refined theory of orthotropic plates of variable thickness. To solve the problem in the case of simultaneous action of its own weight and compressive axial forces, a system of differential equations with variable coefficients is obtained. The effects of transverse shear and the effect of reducing compressive force of the support are also taken into account. Passing on to dimensionless quantities, the specific problem for a beam of linearly varying thickness is solved by the collocation method. The stability of the beam is discussed. The critical values of forces are obtained by varying the axial compressive force. Results are presented in both tabular and graphical styles. Based on the results obtained, appropriate conclusions are drawn.

The Effect of Non-Conservative Compressive Force on the Vibration of Rotating Composite Blades

This paper investigates the effectiveness of a resonance avoidance concept for composite rotor blades featuring extension–twist elastic coupling. The concept uses a tendon, attached to the tip of the blade, to apply a proper amount of compressive force to tune the vibration behavior of the blade actively. The tendon is simulated by applying a non-conservative axial compressive force applied to the blade tip. The main load carrying part of the structure is the composite spar box, which has an antisymmetric layup configuration. The nonlinear dynamic behavior of the composite blade is modelled by using the geometrically exact fully intrinsic beam equations. The resulting nonlinear differential equations are discretized using a time–space scheme, and the stationary and rotating frequencies of the blade are obtained. It is observed that the proposed resonance avoidance mechanism is effective for tuning the vibration behavior of composite blades. The applied compressive force can shift the frequencies and the location at which the frequency veering take place. Furthermore, the compressive force can also cause the composite blade to get unstable depending on the layup ply angle. Finally, the results, highlighting the importance of compressive force and ply angle on the dynamic behavior of composite blades, are presented and discussed.

Biomechanical Evaluation of Suture Button Spread with and without Deltoid Repair in Combined Syndesmosis and Deltoid Injury

Category: Sports; Basic Sciences/Biologics Introduction/Purpose: Syndesmosis injuries are common and frequently occur with deltoid injuries but optimal repair remains controversial. Prior biomechanical studies have demonstrated that 1 and 2 suture buttons are equivalent to screw fixation and that parallel or divergent suture buttons are equivalent to single suture button. Prior studies, however, created constructs with suture buttons within 1cm from each other (2-3cm from joint surface). Additionally, the role of deltoid injury and repair have not been evaluated in conjunction with syndesmosis injury and repair. The purpose of this study was to biomechanically compare a narrow vs spread 2-suture button construct with and without a deltoid repair. Methods: Four matched lower leg specimens (8 total specimens) aged mean 60.2 years (range 57-66 years; 6 females and 2 males; mean BMI 21.1) were tested. Ankle motion under cyclic loading was measured in multiple planes: first in the intact state, following simulated syndesmosis and deltoid injury, then following fixation with 1 of 2 randomly assigned constructs: 2 parallel suture buttons at 2 and 3cm from joint line (narrow); and 2 parallel suture buttons at 1 and 4cm from joint line (spread), and then finally following a deltoid repair with each construct. Each state was tested at a constant 750 N axial compressive force and 5N internal/external torque. Rotation position (degrees) and anterior-posterior displacement (mm) were collected throughout the testing to characterize relative spatial relationships of the tibiofibular articulation using 3D video capture technology. Results: Narrow and spread 2-suture button constructs improved rotation and translation compared to cut state (p<0.05) but not to intact state (p>0.05). There were no significant differences in rotation or translation between Narrow and Spread constructs (p>0.05). The addition of a deltoid repair did not improve rotation or translation compared to syndesmosis repair with either construct alone (p>0.05). Conclusion: The preliminary results of this study suggest that constructs with suture button placed close together or spread apart during fixation of combined syndesmosis and deltoid injury could improve rotation and translation equally. Additionally, in a combined syndesmosis and deltoid injury, the addition of a deltoid repair to a syndesmosis repair did not strengthen the construct. These findings suggest that repair of syndesmosis alone may be sufficient in combined syndesmosis and deltoid injuries. Additional matched samples will be tested to validate preliminary findings.

Hot Bitumen Pipeline Valve Replacement: Pipe Prop Anchoring Design With Mechanical Tensioning

An NPS 24 inline gate valve on a buried hot bitumen pipeline operating at temperatures up to 149°C failed open. The valve is on the north bank of the Steepbank River in northern Alberta and is equipped with an actuator that can automatically close the valve to protect the river in case of an emergency. It was therefore important to replace the valve as soon as practical. Worley was engaged to provide detailed engineering services for replacing the valve. Engineering objectives covered safety concerns associated with high operating temperatures and large axial compressive force in the pipeline, minimization of downtime, development of the best long-term valve replacement solution, and return of the pipeline to service with the same resistance to upheaval buckling it had when it was originally designed and constructed. Because the pipeline is buried and therefore restrained by the surrounding soil, an important goal of the original design was to prevent upheaval buckling and possible loss of containment by controlling thermal expansion forces due to its high operating temperature. Control was achieved during the original construction in two ways. Firstly, thermal compressive forces were reduced by heating the line to 90°C with forced air and locking it into the surrounding soil in its expanded state, and secondly, restraint was increased by using good backfill compaction, increased depth of burial, and imported fill wherever necessary. The high axial compressive force on the inline buried valve was identified as a possible cause of failure, and an early decision was made to replace it using an aboveground valve with sufficiently flexible aboveground piping to minimize or eliminate compressive forces on the valve. When the pipeline was cooled and cut to install the new valve, the original prestress was released, and the cut ends of the pipe pulled back on either side of the valve. The lost prestress was reinstated to the level specified in the original design using an innovative custom designed load bearing strut and tensioning system, referred to here as a Pipe Prop, that was installed between the cut ends of the buried mainline after the failed valve and fittings had been removed. The Pipe Prop also prevented differential axial movement between the cut ends of the buried pipeline due to changes in the operating pressure and temperature. This reduced the need for flexibility in the aboveground piping and allowed a short offset to be used between the new valve and the buried mainline, which reduced the footprint of the aboveground piping enough to fit within the restrictive boundaries of the site. Strain gauges were installed on the pipeline adjacent to the failed valve and upstream and downstream of the valve site. The gauges measured changes in stress when the buried pipeline was first cut, and allowed the stress state of the buried pipeline to be calculated to find if the cause of failure had been large axial loads imposed on the valve by the pipeline. The strain gauges also measured strain in the buried pipeline while using the tensioning system built into the Pipe Prop to re-establish the design level of prestress. Permanent strain gauges were also installed on the new aboveground piping adjacent to the replacement valve. The pipeline was returned to hotbit service in August 2019 and has operated continuously since that time without further problems at the valve station.

Arching followed by catenary response of steel shear connections in disproportionate collapse

Steel shear connections are mainly designed to sustain shear forces. There is limited research assessing the axial response of shear connections, which is important in the evaluation of robustness of steel structures. Structural collapse can be arrested following localized damage if an alternative load path with sufficient capacity is available. In this study, the formation of compressive arching action followed by tensile catenary action is investigated. It is shown that in a column loss scenario, connections may develop significant axial compressive force before catenary action begins; this phenomenon has often been neglected in assessments of connection robustness in the sense that axial force is reported as a tensile action only. The presence of arching action has been confirmed in two experimental programs, and one set is selected for further study using a numerical approach. A simplified analytical model is then presented and compared with the observed axial response of these connections. It is concluded that vertical eccentricity between the centres of rotation of the connections at the two ends of a beam is the principal factor causing the development of a compressive arching force. Another influential parameter that affects the formation of arching action is the stiffness of the surrounding structure.