Pure Axial Loading Research Articles

Hybrid system of longitudinal CFRP laminates and GFRP wraps for strengthening of existing circular concrete columns

This paper presents an investigation on the behavior of a strengthening system of longitudinal premanufactured carbon fiber-reinforced polymer (CFRP) laminates and transverse glass FRP (GFRP) wrapping for strengthening of concrete columns (here after is called a hybrid system). The idea behind using the longitudinal CFRP strips was to enhance the system by increasing the flexural stiffness of the column which is effective for the strengthening of slender columns and eccentrically loaded columns where additional flexural stiffness is required for buckling control. The study was conducted experimentally in two phases under monotonic loads. Phase I was conducted on small-scale concrete specimens to characterize the hybrid system and phase II was conducted to verify the effectiveness of the hybrid system for the strengthening of large-scale slender concrete columns. In phase I, it was observed that by applying GFRP wraps on longitudinal CFRPs, the failure mode of CFRP laminates changed from buckling/debonding to crushing to achieve the full capacity of the system. However, as expected, test results in phase I showed that the usage of wrapping without longitudinal CFRP laminates was more effective than the proposed hybrid system for the strengthening of small scale concrete columns subjected to pure axial loading. For slender columns in phase II, the hybrid system enhanced the wrapping system by adding 52%, 105%, and 94% gain for axial capacity, flexural capacity, and lateral displacement at peak load, respectively, by altering the load–deflection curve of the slender columns to achieve a higher performance level.

Experimental Investigations on Strengthened Reinforced Concrete Columns under Monotonic Axial Loading

Strengthening of the existing reinforced concrete (RC) column is nessesary to enhance their axial load-carrying capacity or ductility. This paper presents the results of an experimental study relating to the performance of reinforced concrete columns strengthened with different techniques such as the steel angle, steel straps, and ferro-cement under pure axial load. A total of six square short reinforced concrete columns were constructed. The cross-section and height of tested columns are 150×150 mm and 1.2 m, respectively. Two specimens were set as the control columns (without strengthening). The other four reinforced concrete columns were strengthened with different techniques. Two columns are strengthened with four steel angles at each corner of the column confined with prestressed steel straps. Another two columns are also strengthened with four steel angles confined with prestressed steel straps and ferro-cement. The experimental results are reported in terms of the load-deformation curves as well as the failure modes. A significant enhancement of the maximum axial load-carrying capacity and the ductility is observed for the strengthened reinforced concrete columns. Finally, the discussion of the use of different strengthening techniques is also carried out in this paper.

Finite Element Analysis (FEA) of Palatal Coverage on Implant Retained Maxillary Overdentures

Purpose: The aim of this study was to determine stress levels on supporting structures of implant-retained overdentures as a function of varying degrees of palatal coverage using finite element analysis modeling at different loading angles. Materials and Methods: ABAQUS®-software was used to perform finite element analysis on eight overdenture models with three and four implants and with and without palatal coverage designs. Loads were applied perpendicular and 45º to the implants. Von Mises stress was measured to determine bone stress. A one-way ANOVA determined which model caused the most stress to the maxillary bone. Results: Palatal coverage increased stress to anterior implant in three implant (p = 0.08) models but decreased stress to all implants in four implant models (p = 0.43). Distal implants received more stress than anterior implants for all models. There was no significant difference between a full palate and no palate coverage overdenture prosthesis when a bar was added under axial loading (p = 0.954). Under non-axial loading, a decrease in stress was noted with the bar in all areas except the anterior implant site. Conclusions: Palatal coverage may not be necessary when applying a pure axial load. The addition of a bar decreased stress at loading.

Influence of angular misalignment on the tribological performance of high-speed micro ball bearings considering full multibody interactions

To study the angular misalignment effects on the high-speed micro ball bearing which is applied to the dental handpiece, an improved five-degree-of-freedom quasi-dynamic model considering full multibody interactions is established in this paper. Then the modified fatigue life model presented by Jones is adopted to further evaluate the influence of angular misalignment on the reliability of the bearing. The results show that the angular misalignment significantly influences the contact load and contact angle distributions as well as the skidding behavior under both pure axial load and combined axial and radial loads. After comprehensive comparison, it is found that the impacts of angular misalignment on total power loss and bearing fatigue life are different under the two types of loads. Under pure axial load, the total power loss increases consistently and the bearing fatigue life decreases significantly when the absolute value of angular misalignment becomes larger. However, under combined axial and radial loads, the effects of angular misalignment are rather complicated and the direction of angular misalignment turns out to be a key influencing factor.

Characterization of closed-die forged AZ31B under pure axial and pure shear loading

Extruded AZ31B was closed-die forged at a relatively low temperature of 250 °C. Quasi-static axial and shear tests in addition to cyclic pure axial and cyclic pure shear tests were performed to characterize the uniaxial response of the forged parts. To examine the effect of forging on the mechanical behavior of the material, quasi-static and fatigue response of the starting extruded AZ31B was also studied under axial loading. The forging process refined the grain structure and modified the crystallographic texture of the extruded AZ31B. The intensity of texture and the orientation of c-axis in the forged part were found to be controlled by the extent and the direction of plastic deformation, respectively. The modified microstructure resulted in insignificant effect on yield strength, slight decrease in ultimate strength, and enhanced failure strain of the forged AZ31B under axial loading. However, the forged AZ31B exhibited superior yield strength, similar ultimate strength, and lower failure strain under shear loading. The cyclic axial strength of the forging was similar to the starting extruded material under high strain amplitudes, but slightly superior under lower strain amplitudes, due to the development of a smaller tensile mean stress. The half-life hysteresis response for the forged material was asymmetric under large axial strain amplitudes, but it was symmetric under cyclic shear loading. This difference is originated from activation of twinning/ detwinning deformation under cyclic axial loading, while dislocation slip is the dominant deformation mechanism during cyclic shear loading. Fatigue fracture surface of forged AZ31B depicts that fatigue cracks were initiated from multiple locations under both cyclic axial and shear loadings.

Assessing the biofidelity of in vitro biomechanical testing of the human cervical spine.

In vitro biomechanical studies of the osteoligamentous spine are widely used to characterize normal biomechanics, identify injury mechanisms, and assess the effects of degeneration and surgical instrumentation on spine mechanics. The objective of this study was to determine how well four standards in vitro loading paradigms replicate in vivo kinematics with regards to the instantaneous center of rotation and arthrokinematics in relation to disc deformation. In vivo data were previously collected from 20 asymptomatic participants (45.5 ± 5.8 years) who performed full range of motion neck flexion-extension (FE) within a biplane x-ray system. Intervertebral kinematics were determined with sub-millimeter precision using a validated model-based tracking process. Ten cadaveric spines (51.8 ± 7.3 years) were tested in FE within a robotic testing system. Each specimen was tested under four loading conditions: pure moment, axial loading, follower loading, and combined loading. The in vivo and in vitro bone motion data were directly compared. The average in vitro instant center of rotation was significantly more anterior in all four loading paradigms for all levels. In general, the anterior and posterior disc heights were larger in the in vitro models than in vivo. However, after adjusting for gender, the observed differences in disc height were not statistically significant. This data suggests that in vitro biomechanical testing alone may fail to replicate in vivo conditions, with significant implications for novel motion preservation devices such as cervical disc arthroplasty implants.

Analysis of high speed bearing based on virtual rods model

The traditional high-speed ball bearing analysis is based on the quasi-static model proposed by Jones-Harris (J-H). This study gives another bearing analysis model based on the relative position of the ball center and the centers of curvature of the raceway grooves, described by the virtual rods. Specifically, the load and deformation of the virtual rods are determined according to the principle of force transmissibility, the translation theorem of a force, and elastic-contact deformation between steel ball bearings and raceway grooves. And the iterative variables such as the axial, radial and angular deformations are gradually introduced into the calculation model to solve the force and kinematic parameters under pure axial load, bidirectional and tri-directional combined loads. The correctness of the virtual rods model is verified by the contact angle for axial and bidirectional load. The influence of gyroscopic moment and raceway grooves control parameter on the actual contact angle under tridirectional loading conditions are calculated and analyzed respectively. The proposed model uses fewer equations and lower-dimension parameters than those used by the traditional highspeed ball bearing analysis method, improves the solution rate of the equations.

Prediction on compressive strength concrete using modified pull-off testing method (MPTM)

The classical pull-off test indicates that the compressive strength of concrete increases with its tensile strength. But it is difficult to obtain the effective data due to the loading eccentricity, which could produce combined bending plus axial stress instead of the uniaxial tension. The objective of this study is to introduce a modified pull-off testing method (MPTM) and improve the classical method by using a cup-shaped loading probe, so that the tensile strength of concrete can measured under pure axial-load. Experimental results indicate that several influential factors upon the MPTM strength could be excluded. There is a good relationship between the MPTM strength and the concrete cube strength (10–80 MPa) both at early age and later age. The repeatability of the MPTM is slightly better than the classical pull-off test method. The verification investigation shows that the MPTM provides a more accurate estimate of in-place cube strength and is easier to perform than the core-drilling method.

RC frame structures retrofitted by FRP-wrapping: A model for columns under axial loading and cyclic bending

Abstract In order to mitigate the seismic risk of existing RC frame structures not designed with seismic criteria, a widespread strengthening strategy is based on increasing strength and ductility of RC columns by means of Fiber Reinforced Polymer wrapping. The existing models for RC cross-sections wrapped by FRP sheets were developed principally considering pure axial loads with uniform confinement pressure. In seismic areas, RC columns are instead usually subjected to axial load and cyclic bending. In the present work, in order to consider the effective loading conditions, an iterative cyclic model for square RC cross-sections wrapped by composite FRP sheets subjected to axial force and cyclic bending is proposed. The model considers the strain gradient-effect over the cross-section due to the bending loads that change significantly the confinement level of RC cross-section. Moreover, the model has been validated by comparing the numerical outcomes with various cyclic experimental results. The model has been also implemented in an open-source software with distributed plasticity finite elements in order to perform pushover analyses of an existing RC frame structure with different retrofitting strategies to improve the ductility of the columns for lateral forces.

An innovative and inexpensive experimental setup for testing connections in gridshell structures

The design and manufacture of structural nodes for gridshell structures are complicated due to complex geometries and loading conditions. The validation of the design concepts of these nodes is even more challenging, because complex design loads are difficult to be applied in a laboratory test. In this paper, a testing rig is proposed and manufactured to test two different additively manufactured nodes. The two nodes are symmetrical and each connecting three members. These nodes are designed to sustain pure axial loads and pure out-of-plane bending moments, respectively. The results of the experiments show the importance of the bolt tolerance in the design of such a testing setup. Subsequently an innovative and inexpensive experimental setup is developed for testing nodes under dominant design loading conditions in gridshell structures. The proposed testing method is generalized, which can be applied to both individual and combined loading conditions, and the new testing rig can be easily fabricated at a low cost.

Comparison of Field Behavior with Results from Numerical Analysis of a Geosynthetic Reinforced Soil Integrated Bridge System Subjected to Thermal Effects

When subjected to ambient daily temperature fluctuations, a 109.5 ft-long geosynthetic reinforced soil integrated bridge system (GRS-IBS) was observed to undergo cyclic straining of the superstructure. The upper and lower reaches of the superstructure experienced the highest and lowest strain fluctuation, respectively. These non-uniform strains impose not only axial loading of the superstructure but also bending. Pure axial loading in a horizontal superstructure will cause the footings to slide. However, bending in the superstructure will cause the footings to rotate thereby inducing cyclic fluctuations of the vertical pressure beneath the footing and also lateral pressure behind the end walls. Measured vertical footing pressure closest to the stream experienced the greatest daily pressure fluctuation (≈ 2,500–3,000 psf), while that nearest the end wall experienced the least. The toe pressure fluctuations seem rather large. That these large vertical pressure fluctuations are observed in a tropical climate like Hawaii when no other GRS-IBS in temperate regions has reported the same (or perhaps higher fluctuation) is indeed surprising. The larger these pressures are, the greater the likelihood of inducing cyclic-induced deformations of the GRS abutment. A finite element analysis of the same GRS-IBS was performed by applying an equivalent temperature and gradient to the superstructure over the coldest and hottest periods of a day to see if the field measured values of pressures are reasonable and verifiable, which indeed they were. This methodology is novel in the sense that the effects of axial load and bending of the superstructure are simulated using measured strains rather than measured temperatures.

Analysis of Failure Effect of Cage Thickness on Spherical Roller Bearings

Spherical roller bearings are important parts of high-frequency crushers. Using the finite element analysis software to carry on the transient dynamics analysis to the bearing obtains the bearing deformation, the pressure and so on characteristis. Then, by contrasting and analysising, it is found that under pure radial load, radial load and axial load mixed force, influence of cage thickness on bearing performance. The results show that the thickness of the cage has little effect on the deformation of the bearing under pure radial load. Under the combined action of the radial load and the axial load, the radial deformation of the bearing decreases compared with the pure radial load. The deformation of the cage under the mixed load is increased than that under the radial load.

Numerical and experimental validation of residual stresses of laser‐welded joints and their influence on the fatigue behaviour

AbstractIn this work laser‐welded tube‐tube specimens made of aluminium alloys AlMg3.5Mn and AlSi1MgMn T6 were experimentally tested under constant and variable amplitude loading, under pure axial and pure torsion loading. In order to evaluate the influence on fatigue behaviour of the residual stresses, because of the welding process, some specimens were subjected to postweld heat treatment and then were tested. The numerical analyses, using finite element (FE), were carried out to obtain a reliable estimation of the residual stress in the specimen. The numerical results were in a good agreement with experimental ones obtained by means of hole‐drilling method. Finally, the residual stress distribution was superimposed to stress distribution because of fatigue loads obtained by FE analyses applying local concept, to calculate the stresses in the crack initiation zone and to understand the different types of failure that occurred in as‐welded and relieved specimens.

107. Internal deformations in human intervertebral discs under axial compression: a 9.4T MRI study

BACKGROUND CONTEXT Back pain will be experienced by 70-85% of all people at some point in their lives, and is linked with intervertebral disc (IVD) degeneration. However, few studies have attempted to quantify changes in the internal deformations within IVDs as they degenerate without disrupting the disc continuity. Recent advances in MRI technology provide the opportunity to observe 3D deformations within intact IVDs in unprecedented detail. PURPOSE The aim of this study was to quantify human IVD deformations under axial compression. STUDY DESIGN/SETTING 9.4T MRI images were obtained of human cadaveric motion segments under pure axial loading. PATIENT SAMPLE Four human vertebral body–IVD–vertebral body specimens (L4-L5) were used for this study. Two were classed as degenerate (age = 55.5 ± 3.5 years (average ± SD), Pfirrmann rank = 3.5 ± 0.4) and two were classified as nondegenerate (age = 24.0 ± 2.8 years, Pfirrmann rank = 2.0 ± 0.3). OUTCOME MEASURES Digital volume correlation (DVC) was used to calculate the 3D strains within the IVDs. METHODS Specimens were aligned with the transverse plane of the disc parallel to the base of the mounting pots of a custom-made compression rig, and fixed in place using polymethylmethacrylate (PMMA). MR Images were acquired before, and after 2 mm of compression using a T2-weighted RARE sequence (coronal plane, resolution = (90 × 90) µm2, slice thickness = 800 µm, 17 min scan time). RESULTS High lateral strains were seen in the AF regions of the nondegenerate discs, while high lateral strains were seen in both the AF and the NP of the degenerate discs, particularly close to the end plates. The axial strain in both the NP and AF of the degenerate specimens was significantly higher (two tailed, unpaired t-test, p CONCLUSIONS This is the first study to use high field MRI to obtain images with in plane resolution as high as (90 × 90) µm2 to investigate internal deformations within degenerate and nondegenerate human discs. The 3D strain maps are useful for designers of partial or total disc replacement technologies who aim to restore the mechanical behavior of degenerate discs back to their nondegenerate state. Future investigations into 3D strains under different modes of loading will inform physical activities to mitigate high IVD strains, and the optimization of rigid instrumentation for fusion surgery by ensuring that modes of loading associated with the highest IVD strains are minimized. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

On the Eccentrically Loaded Socket Footings With Cut - Off Pyramid Shaped Socket

Abstract In this work considerations concerning eccentrically loaded socket footing with cut-off pyramid shaped socket were presented. As an object of study sloped footing with 1.40 m height, corresponding to the maximum frost depth has been adopted. Knowing that in practice there are no perfect pure axial loads, load applied on the eccentricity has been taken into considerations. Eccentric loads result in footing rotation in the direction of eccentricity and acting load, hence one footing end is imbedding into the ground, whereas second end tries to rise up. To observe that phenomenon, elastic type of support under the foundation was introduced corresponding to the naturally humid sand with medium compaction. Presented in this paper considerations of innovative connection technology between footing and column were based on performed numerical studies. Advantages and disadvantages of presented footing in comparison to normal socket footings solutions were widely discussed. Numerical analyses were performed with the utilization Finite Element Method based SolidWorks software.

Analysis of crack geometry and location in notched bars by means of a three-probe potential drop technique

It is often necessary to define the crack initiation life of a fatigue tested component, generally at a given (short) crack length. The size of an initiated crack can be estimated by employing different experimental methods, one of which is the direct current potential drop (DCPD) technique. In the case of notched bars subjected to fatigue loadings, the crack configuration (i.e. circumferential or semi-elliptical) and location cannot be singled out by means of the potential drop method (PDM) operating with a single potential probe. In the present contribution, three potential probes are adopted to overcome this issue. The calibration curves reporting the three potential drops as a function of the crack size are derived by means of 3-dimensional electrical FE analyses. Two different crack configurations are analyzed: (i) circumferential and (ii) semi-elliptical surface cracks. The calibration curves have been validated by systematic comparison with experimental results, generated by fatigue testing of sharp as well as blunt notched specimens made of steel and a titanium alloy under pure axial loading. Finally, a procedure to assess the area, the configuration and the location of the initiated fatigue crack starting from the experimentally measured potential drops is discussed.

A comprehensive study on the speed-varying stiffness of ball bearing under different load conditions

The stiffness as one of the most important dynamic characteristics of ball bearing, has a great influence on the service performance of bearing and rotor systems. To obtain and analyze the stiffness matrix of ball bearing under arbitrary load conditions, this paper proposed a novel mathematical method for ball bearing modeling and stiffness matrix calculation based on a new initial condition assumption. Based on this, a comprehensive and systematical study to investigate the effect of rotating speed on the stiffness for ball bearing under three typical load conditions has been presented (the pure axial load condition, the pure radial load condition and the combined loads condition). And the influences of bearing basis structure parameters including the internal clearance, ball diameter, inner and outer raceway curvature coefficients on the change rule of the stiffness along with speed of ball bearing under three typical load conditions have been given. The results show that the proposed model has a high versatility, and the change rules of the stiffness along with rotating speed are greatly influenced by the load conditions, bearing structural parameters. Therefore, this paper not only presents a complete algorithm for the modeling and stiffness calculation of ball bearing under arbitrary load conditions, but also provides important guidance for the design of bearing and rotor systems.

Optimisation and validation of full and half foam filled double circular tube under multiple load cases

In this study, numerical results are conducted to determine the deformation mode of foam filled double circular tubes, namely; half foam filled double circular tube (FD), and full foam filled double circular tube (DD) under oblique loading. To validate the simulation and experimental results, two-parameter Weibull probability distribution was used. The proposed function of the multi-objective optimisation design (MOD) process was based on the Finite Element Analysis results. The metamodels in were constructed to predict the crashworthiness criteria of specific energy absorption and peak crushing force under oblique impact loading. Also examined in the study were the MOD problems of the two structure types under multiple impact angles using the NSGA II algorithm. The findings from the study determined that the optimal full foam filled double circular tube had better crashworthiness under pure axial loading. While the optimal half foam filled, double circular tube had more space to enhance the crashworthiness under an oblique impact.

Field and numerical analysis on effect of axial load on the lateral response of a pile

Purpose Piles often carry combination of axial and lateral. Currently, piles are designed separately for axial and lateral load. In the literature, few information is available on the influence of axial load on lateral behaviour of the pile. This paper aims to present the results of load deformation of a pile under pure lateral load and combined axial and lateral load. Design/methodology/approach The field load tests were carried out on four different pile diameters at two different bridge sites. Moreover, the paper addresses the numerical simulation of filed load test carried out on the pile under the combination of axial and horizontal load. Findings After field load tests and numerical simulation, it was found that the vertical load had a remarkable effect on the lateral load response of a pile. The lateral deflection of the pile was decreased about 25% under the effect of vertical load. In addition to this, the results from field and numerical simulation are quite comparable. Originality/value Typical field load tests were simulated numerically. This research adds a value in the areas of pile foundation subjected to vertical and lateral load particularly for structure such as transmission line tower and jetty.

Torque variations of ball bearings based on dynamic model with geometrical imperfections and operating conditions

Abstract A friction torque model of ball bearings with geometrical imperfections is proposed, integrating developed models of friction, raceway waviness, and multi-body dynamics. Torque variations consisting of average and fluctuation values for angular contact ball bearings due to waviness including linear, nonlinear and multi-orders situation are analyzed in time and frequency domains. The influences of waviness amplitude, load and speed are evaluated. Additionally, the correlation between axial displacement and torque fluctuation of ball bearings is discussed, and their spectrum similarity under pure axial load and the relative low-frequency amplitude enhancement of the torque spectrum under combined load are observed. Finally, a torque experiment is carried out on a bearing test apparatus, and the effectiveness of the present model is verified.