Axial Force Loading Research Articles

Linear and non-linear analysis on two-dimensional steel frame under different temperatures

Purpose Progressive collapse because of high temperatures arising from an explosion, vehicle impact or fire is an important issue for structural failure in high-rise buildings. Design/methodology/approach The present study, using ABAQUS software for the analysis, investigated the progressive collapse of a two-dimensional, three-bay, four-storey steel frame structure from high-temperature stresses. Findings After structure reaches the temperature results like displacement, stress axial load and shear force are discussed. Research limitations/implications Different temperatures were applied to the columns at different heights of a structure framed with various materials. Progressive collapse load combinations were also applied as per general service administration guidelines. Originality/value This study covered both steady-state and transient-state conditions of a multistorey-frame building subjected to a rise in temperature in the corner columns and intermediate columns. The columns in the framed structure were subjected to high temperatures at different heights, and the resulting displacements, stresses and axial loads were obtained, analysed and discussed.

A biomechanical comparison of three fixation techniques in osteoporotic reverse oblique intertrochanteric femur fracture with fragmented lateral cortex.

The treatment of the reverse oblique osteoporotic femur fractures is still problematic and can be complicated especially that are accompanied by a fragmented lateral cortex. The aim of this study was to compare three different internal fixation methods in the osteosynthesis of osteoporotic reverse oblique intertrochanteric femur fracture models with a fragmented lateral cortex. Biomechanical experiment study. A total of 24 osteoporotic femur models were obtained and divided into three groups [Group A: Proximal femoral nail(PFN), Group B: 95° angled blade plate (ABP), and Group C: proximal femoral anatomic locking plate (PFLP)] with each group which include eight bones. A standard fracture configuration was created as a reverse oblique intertrochanteric fracture and fixed with these implants. After fixation, all femur constructs were tested with an Instron 5800R tester (Instron, Canton, MA) in the biomechanics laboratory with axial loading and bending forces to assess axial and rotational stiffness and failure load. Displacement over 10mm and angulation greater than 10° in the fracture line were considered as failure. In all tests, ABP had statistically poorer results in comparison to the PFN and PFLP group. PFLP fixation had better biomechanical fixation results in comparison to the PFN group, although the results were not statistically significant. Orthopaedic surgeons should keep in mind that lateral cortex comminution brings further instability to these reverse oblique intertrochanteric osteoporotic fractures and high rates of failure may be encountered due to this instability. PFLP fixation may be an alternative fixation method biomechanically for these instable fractures.

Classifications in Brief: Sanders Classification of Intraarticular Fractures of the Calcaneus.

Classifications in Brief: Sanders Classification of Intraarticular Fractures of the Calcaneus.

Drift capacity of high-strength concrete columns with mixed-grade longitudinal reinforcements

A unique reinforced concrete column design method which aims to improve the ductile behavior of reinforced concrete columns by utilizing various steel grades for longitudinal reinforcements is evaluated in this article. Six large-scale reinforced concrete columns were tested, with the columns subjected to axial load and cyclic forces under reversed bending. The parameters varied in the test program including the axial loading level and the ratio and strength of longitudinal steel reinforcement. It was found from the test results that utilizing longitudinal high-strength steel reinforcement by the ratio of 30%, 50%, and 100% of the total longitudinal reinforcement in a column section will increase the lateral loading drift capacity by 18%, 26%, and 55% on average, respectively. Parametric studies via nonlinear finite-element approach were performed to study the influence of various design parameters on the ultimate drift capacity of reinforced concrete columns. The correlation between the ultimate drift capacity and the confinement level, the axial loading level, and the ratio and grade of longitudinal high-strength reinforcing bars was investigated. Design charts for various ultimate drift levels in terms of other design parameters were developed.

A liquid spring–magnetorheological damper system under combined axial and shear loading for three-dimensional seismic isolation of structures

This study focuses on experimental investigation of a fail-safe, bi-linear, liquid spring magnetorheological damper system for a three-dimensional earthquake isolation system. The device combines the controllable magnetorheological damping, fail-safe viscous damping, and liquid spring features in a single unit serving as the vertical component of a building isolation system. The bi-linear liquid spring feature provides two different stiffnesses in compression and rebound modes. The higher stiffness in the rebound mode prevents a possible overturning of the structure during rocking mode. For practical application, the device is to be stacked together along with the traditional elastomeric bearings that are currently used to absorb the horizontal ground excitations. An experimental setup is designed to reflect the real-life loading conditions. The 1/4th-scale device is exposed to combined dynamic axial loading (reflecting vertical seismic excitation) and constant shear force that are up to 245 and 28 kN, respectively. The results demonstrate that the device performs successfully under the combined axial and shear loadings and compare well with the theoretical calculations.

Experimental study on axially preloaded circular steel tubes subjected to low-velocity transverse impact

Steel circular hollow section tubes are widely used as tubular structural members, and impact accidents usually occur while these tubes are in their working states. This paper presents experimental studies on axially preloaded circular steel tubes subjected to transverse low-velocity mass impact. A total of 32 impact tests, representing four types of scenarios, are conducted to investigate the influences of preloading and the boundary condition on the structural responses of tubes. An axial force loading system is designed, and a bladder accumulator is adopted in the system to compensate for the axial compressive loading. The test processes of the tubes under transverse impact are described in detail, and four failure modes are identified. All specimens of the four scenario types deformed according to the three-hinge mechanism. Based on the test results, the influence and mechanism of axial force are proposed. The effects of axial tension, axial compression and the boundary condition on the structural behaviour of tubes are discussed. The results show that the axial tension can enhance the bending resistance and lateral collapse capacity of tubes, while the axial compression reduces the collapse capacity significantly. By comparing the responses of tubes under different boundary conditions, the lateral resistance of tubes and the structural response are shown to have a strong correlation with the axial constraint.

Analytical bounds for the electromechanical buckling of a compressed nanocantilever

• We obtain novel and accurate analytical bounds for the pull-in parameters of a compressed nanocantilever. • The interaction between electrostatic, surface, and axial forces is investigated. • The analytical predictions closely agree with numerical results obtained by shooting method. • The analytical bounds are very useful for validating numerical and approximated methods. • The approach may also include the effects of surface elasticity and residual stresses. An analytical approach is presented for the accurate definition of lower and upper bounds for the pull-in voltage and tip displacement of a micro- or nanocantilever beam subject to compressive axial load, electrostatic actuation and intermolecular surface forces. The problem is formulated as a nonlinear two-point boundary value problem and has been transformed into an equivalent nonlinear integral equation. Initially, new analytical estimates are found for the beam deflection, which are then employed for assessing novel and accurate bounds from both sides for the pull-in parameters, taking into account for the effects of the compressive axial load. The analytical predictions are found to closely agree with the numerical results provided by the shooting method. The effects of surface elasticity and residual stresses, which are of significant importance when the physical dimensions of structures descend to nanosize, are also included in the proposed approach.

Investigating Seismic Behavior of Reinforced Concrete Columns with SFRP Using Finite Element Method

Currently, various methods have been used for repairing and retrofitting reinforced concrete columns including Steel Fiber Reinforced Polymer (SFRP) jackets in order to improve load bearing capacity. However, the enclosure mechanism is less known by consideration of the effects of slender columns which needs much more studies. Avoiding the buckling of a slender Reinforced Concrete (RC) column against the compressive axial force using SFRP is the main aim of this research. One of the parametrical studies in this paper is the influence of the number of layers that is investigated by Finite Element Method (FEM). Accordingly, in this paper, several RC columns are modeled under the Manjil earthquake record and the force-displacement curves of each model are numerically calculated. The columns are divided into three groups: the first group is non-SFRP and the subsequent groups are reinforced by one and two layers of SFRP. At first, three-dimensional models of the columns were prepared by ABAQUS finite element software and then by applying axial load and seismic forces, the parametric effect on behavior of the columns has been investigated. The results show that the retrofitting of the column with SFRP increases the flexural and stiffness, which plays a significant role in reducing the buckling of the RC columns.

BIOMECHANICAL COMPARISON OF MEDIAL VERSUS LATERAL SIDED PLATING IN FEMORAL FRACTURES.

ABSTRACTObjective:The aim of the present study was to determine whether the side of application of the plate itself affects the mechanical stability of the fixation. The specific question addressed is whether or not a lateral or medial plate application is biomechanically better, for the treatment of distal diaphysis fractures of the femur.Methods:Stability and stiffness of medial sided plating relative to the conventional lateral sided plating in distal diaphysis of the femur were measured by analyzing axial loading forces leading to implant failure. Sixty synthetic femurs were tested in physiological bending, to calculate the yield and ultimate load to displacement following fixation of distal diaphysis fractures of the femur by either medial or lateral sided plating. Axial loading was applied to samples using a uniaxial testing machine.Results:There was more implant deformation in the lateral sided plating group – a difference with statistical significance.Conclusion:Medial sided plating was found to be as stiff as lateral plating. Medial plating may be a reasonable treatment option that can be used safely in selected cases. Level of Evidence I, Therapeutic Studies Investigating the Results of Treatment

Tibiofemoral Contact Mechanics with Horizontal CleavageTears and Resection of the Lateral Meniscus in the Human Knee

Objectives:Knee menisci are known to increase contact area, reduce contact pressure and absorb shocks. Meniscectomy is considered likely to lead to arthritic changes to the knee. The effects of a horizontal cleavage meniscus tear, repair and meniscectomy are still not clear for the lateral meniscus. The purpose of this study was to explore the impact of these conditions on tibiofemoral contact mechanics.Methods:Eleven fresh frozen human cadaveric knees were used in this study. Testing conditions included the intact meniscus, horizontal cleavage tear, inferior leaf resection and resection of both inferior and superior leaves of the lateral meniscus. The test was performed at 0° and 60° of knee flexion under 800 N axial loading force. Tekscan® pressure sensors were used to measure the tibiofemoral contact area and pressure.Results:Horizontal cleavage tears and subsequent repair of the lateral meniscus resulted in no significant changes in contact area and peak contact pressure compared to the intact condition. Resection of the inferior leaf resulted in a significant drop in contact area (34.6 ± 14.1% at 0° and 23.9%[Office1] ±14.8% at 60° knee flexion; p < 0.05). Peak contact pressure after resection of the inferior leaf significantly increased by 27.0 ± 22.1%at 0° and 37.9 ±33.6% at 60° knee flexion (p<0.05). Additional resection of the superior leaf resulted in a further decrease in contact area (49.5 ±7.2% at 0° and 47.9± 16.7% at 60° knee flexion compared to the intact condition; p < 0.05). Peak contact pressure increased correspondingly (by 38.6% ± 24.3 at 0° and 55.5 ±34.7%at 60° knee flexion compared to intact; p < 0.05).Conclusion:Resection of the inferior leaf or resection of both leaves of the lateral meniscus after horizontal cleavage tear resulted in decreased contact area and increased peak contact pressure at both knee flexion and extension.

Research on seismic behavior and shear strength of SRHC frame columns

The seismic behavior of steel reinforced high strength and high performance concrete (SRHC) frame columns was investigated through pseudo-static experiments of 16 frame columns with various shear span ratios, axial compression ratios, concrete strengths, steel ratios and stirrup ratios. Three kinds of failure mechanisms are presented and the characteristics of experimental hysteretic curves and skeleton curves with different design parameters are discussed. The columns’ ductility and energy dissipation were quantitatively evaluated based on seismic resistance. The research results indicate that SRHC frame columns can withstand extreme bearing capacity, but the abilities of ductility and energy dissipation are inferior because of SRHC’s natural brittleness. As a result, the axial load ratio should be restricted and some construction measures adopted, such as increasing the stirrup ratio. This research established effect factors on the bearing capacity of SPHC columns. Finally, an algorithm for obtaining ultimate bearing capacity using the flexural failure mode is established based on a modified plane-section assumption. The authors also established equations to determine shearing baroclinic failure and shear bond failure based on the accumulation of the axial load force distribution ratio. The calculated results of shear bearing capacity for different failure modes were in good agreement with the experimental results.

The biomechanical and histological effects of posterior cruciate ligament rupture on the medial tibial plateau

BackgroundThe objective of this study was to investigate the biomechanical and histological effects of the posterior cruciate ligament (PCL) on the medial tibial plateau.MethodsA total of 12 cadaveric human knee specimens were collected and grouped as follows: the PCL intact group (n = 12), the anterolateral bundle rupture group (n = 6), the postmedial bundle rupture group (n = 6), and the PCL rupture group (n = 12). The strain on the anterior, middle, and posterior parts of the medial tibial plateau with an axial loading force at different flexion angles was measured and analyzed, respectively. Forty-eight rabbits were chosen for animal study: surgery was performed on the one side of each rabbit randomly (experimental group), while the other side was taken as control (control group). Every 12 rabbits were culled at each of the four selected time points to collect the medial tibial plateau for morphological and histological observation.ResultsThe PCL rupture, either partial or complete, may generate an abnormal load on all the parts of the medial tibial plateau with axial loading at all positions. Noticeable time-dependent degenerative histological changes of the medial tibial plateau were observed in the rabbit models of PCL rupture. Compared with the control group, all the PCL rupture groups exhibited a higher expression of the matrix metalloproteinase-7 (MMP-7) and the tissue inhibitors of metalloproteinase-1 (TIMP-1) at all the time points.ConclusionsEither partial or complete PCL rupture may generate an abnormal load on all the parts of the medial tibial plateau with axial loading at all the positions and may cause cartilage degeneration on the medial tibial plateau.

Introducing the \u201cBone-Screw-Fastener\u201d for improved screw fixation in orthopedic surgery: a revolutionary paradigm shift?

BackgroundConventional screws used for fracture fixation in orthopedic surgery continue to rely on the historic buttress thread design. While buttress screws generally provide solid resistance against unidirectional axial loading forces, their design suffers from several limitations, as the buttress thread does not adequately resist multiaxial forces. Furthermore, the buttress screw is prone to stripping at the bone-screw interface and can cause microfracturing of the surrounding bone due to its thread design. Standard buttress screws are therefore at risk of adverse postoperative outcomes secondary to failure of bone fixation. A new patented Bone-Screw-Fastener was recently designed that is based on an interlocking thread technology. This new fastener provides distributive forces from the threads onto the bone and therefore resists loads in multiple directions. The underlying concept is represented by a “female thread” bone cutting technology designed to maximize bone volume, preserve bone architecture, and create a circumferential interlocking interface between the implant and bone that protects the thread from stripping and from failing to multiaxial forces.Presentation of the hypothesisWe hypothesize that the new Bone-Screw-Fastener overcomes the classic shortcomings of conventional orthopedic screws with buttress threads by ease of insertion, improved bone preservation, increased resistance to off-axis multidirectional loading forces and to stripping of the threads. These advanced biomechanical and biological properties can potentially mitigate the classic limitations of conventional buttress screws by providing better resistance to implant failure under physiological loads, preserving bone biology, and thus potentially improving patient outcomes in the future.Testing the hypothesisThe presumed superiority of the new fastener will require testing and validation in well-designed prospective multicenter randomized controlled trials (RCTs), using the conventional buttress screw as control.Implications of the hypothesisOnce validated in multicenter RCTs, the new Bone-Screw-Fastener may drive a change in paradigm with regard to its innovative biomechanical principles and biologic bone preservation for surgical applications requiring screw fixation.

Effects of axial-shear-flexure interaction in static and dynamic responses of steel beams

This paper proposes analytical model for axial-shear-flexure interaction, with inelastic shear stress and strain distributions, for 2D beam elements with AISC flanged and hollow box cross-sections. The shear stress and shear strain distributions within the beam section, for an applied shear force, are developed considering both elastic and inelastic ranges. Standard shear stress distribution is adopted for the elastic range. The distribution of the plastic component of the shear stress is assumed to have a quadratic variation. The shear stress and strain distributions are verified adequately with the finite element software ABAQUS/CAE with 3D brick elements. Further, incremental axial load (P), bending moment (M), and shear force (V) are applied to the section, along the various direction vectors in the PVM space, up until the section attained a certain level of plasticization according to the von-Mises material model, to generate the (P, V, M) points. Using these (P, V, M) data points, a quadratic PVM surface equation is proposed by combining an elliptical and a planar surface with a smoothening function. The PVM interaction is then integrated with an existing force based beam formulation with full geometric nonlinearity. Force-displacement responses obtained with the PVM interaction for 2D beams agreed well with the ABAQUS models simulated with 3D inelastic brick elements. Static responses with P-M interaction predicted higher yield force and lower displacement demand, for lower span to depth ratios and heavier flanged sections. Dynamic responses with the PVM interaction predicted higher displacement demand than that with the P-M interaction.

初期不整が軸方向圧縮力と単調逆対称曲げモーメントを受ける角形鋼管柱の弾塑性挙動に与える影響

It is well know that initial imperfections (e.g. bow-shaped imperfection of member, bow-shaped imperfection of plate and residual stress) have an influence on the performance of the columns. Most studies regarding this issue are investigated under single axial load or single shear force. In reality, the columns of steel structures are subjected to axial load and bending moment. Therefore, it is necessary to clarify the influence of the initial imperfections under combined loading. The influences of initial imperfections on the performance of square steel tubular columns under compressive axial force with one end monotonic bending moment were investigated by means of FEM in our previous study. As mentioned before, the columns of steel structures are subjected to axial load and bending moment, and the moment diagram is antisymmetric bending moment distribution or bending moment distribution close to antisymmetric. Therefore, it is not enough to clarify one end bending moment distribution. Also, in the previous study, the influence of the residual stress in the circumferential direction was not considered despite it exists in the member. In this study, the influences of initial imperfection on the performance of the square steel tubular column which is subjected to a compressive axial force with monotonic antisymmetric bending moment are investigated. The bow-shaped imperfection of the member (global imperfection) and continuous bow-shaped of the plate (local imperfection) are selected as geometrical initial imperfections and these imperfections are described by trigonometric function to reproduce easily. The residual stress in the longitudinal direction and the residual stress in the circumferential direction are selected as material initial imperfections. Firstly, the influence of initial imperfection on the performance and on the elastic-plastic behavor is investigated individually. Secondly, the influence of combined initial imperfections on the performance of the columns and on the elasto-plastic behavor is investigated; comparison between the experimental results are shown. Firstly, followings were found from the analysis results where initial imperfection is introduced in the member individually. 1) When the ultimate state was determined by local buckling, the global initial imperfection had a small impact on the performance. When the ultimate state was determined by bending deformation in in-plane, the direction of global imperfection had an impact on the performance as well its amplitude. 2) The amplitude of the local imperfection had a great impact on the performance of the columns. The maximum bending moment and the deformation capacity significantly decreased when its maximum amplitude exceeded 10% of permissible deviation. 3) When the ultimate state was determined by bending deformation, the plastic deformation capacity decreased with the increase of the amplitude of the residual stress in the longitudinal direction; initial stiffiness gradually decreased with the increace of its magnitude. 4) Regardless of the ultimate states, with the increase of the amplitude of the residual stress in the circumferential direction, the maximum bending moment and plastic deformation capacity decreased. Secondly, followings were found from the analysis results, where combined initial imperfections are introduced in the member. 5) In comparison with analysis results which were introduced the initial imperfection individually, the influence of the combination of initial imperfections on the variation trend of the performance was not confirmed. The local imperfection had the most significant influence on the perfomance in the imperfections that are considered in this study. 6) Validation of the numerical simulation was also performed; initial imperfections that could simulate test results in reasonable accuracy was shown.

Isolated Fracture of the Trapezoid. A Rare Injury.

Dear Sir, Trauma to the wrist can result in carpal bone fractures that are not always apparent on initial radiographic examination. Fractures of the trapezoid bone are the rarest of carpal fractures, with only a few reported cases in the published literature. We present a case of isolated fracture of the trapezoid that was managed conservatively and had a full functional recovery. A 20 year old male presented to the Emergency Department reporting having a car door accidentally close against the back of his wrist a few hours prior. The patient presented with localized edema and tenderness proximal to the base of the 2nd metacarpal. Radiographic evaluation was normal. Nonetheless some suspicion remained that an occult fracture of either a carpal bone or the base of the 2nd metacarpal was present. A CT scan of the wrist was obtained, which revealed a minimally displaced fracture of the trapezoid extending in the axial plane (Fig. 1). The patient was placed in a short arm splint for 6 weeks. At the follow – up visit, the pain had subsided and the edema had completely resolved, albeit some wrist stiffness was present. A new CT scan was obtained at that time, which demonstrated near complete union of the fractured parts. After a 2 week self-exercise program for the stiffness the patient was completely symptom free. At 1 year, he remains symptom free and reports being entirely satisfied with the outcome. Fig. 1 Axial thin slice (1 mm) CT demonstrating the fracture line through the trapezoid bone The trapezoid is the least commonly fractured carpal bone, with the literature containing only a few case reports and case series. These fractures can occur in isolation or in combination with other injuries to the carpus or metacarpals. Most authors describe the mechanism of injury to be either an axial loading or bending force through the 2nd metacarpal [1, 2] or a direct blow to the wrist [2]. The presentation is typically that of pain and tenderness at the base of the 2nd metacarpal. Initial radiography is invariably normal, and diagnosis was made through the use of CT [1, 2], MRI [3] or even technetium bone scan [3]. The ease and availability of CT scans and other advanced imaging modalities is probably the reason that these injuries are identified more frequently in recent years. The limited number of published cases prevents the recommendations regarding treatment of trapezoid fractures from carrying much power or weight. Nonetheless, the literature thus far suggests that for isolated fractures with minimal displacement, cast immobilization results in satisfactory outcomes [1]. Surgical treatment was performed for displaced fractures or for complex injuries [3]. Still, there are differences regarding type of casting (whether short -arm cast or thumb spica), length of time of immobilization, and so forth. Similarly, operative treatments were individualized based on the pattern and complexity of osseo –ligamentous injuries. Not much is known about the long –term outcomes of trapezoid fractures. Adverse outcomes of other carpal bone fractures, especially the scaphoid, such as non- union, avascular necrosis and development of arthritis are well known. In some of the cases reported in the literature so far, delayed union and non-union resulted in persistent pain [3, 4] and diminished grasp power [4]. Thus, a missed fracture could very well result in loss of function and diminished quality of life. It is only proper that in any patient with trauma to the base of the 2nd metacarpal, the appropriate mechanism of injury, or persistent pain after a period of rest and splinting that this fracture be suspected and sought after.

Uniaxial Compressive Constitutive Relationship of Concrete Confined by Special-Shaped Steel Tube Coupled with Multiple Cavities

A method is presented to predict the complete stress-strain curves of concrete subjected to triaxial stresses, which were caused by axial load and lateral force. The stress can be induced due to the confinement action inside a special-shaped steel tube having multiple cavities. The existing reinforced confined concrete formulas have been improved to determine the confinement action. The influence of cross-sectional shape, of cavity construction, of stiffening ribs and of reinforcement in cavities has been considered in the model. The parameters of the model are determined on the basis of experimental results of an axial compression test for two different kinds of special-shaped concrete filled steel tube (CFT) columns with multiple cavities. The complete load-strain curves of the special-shaped CFT columns are estimated. The predicted concrete strength and the post-peak behavior are found to show good agreement within the accepted limits, compared with the experimental results. In addition, the parameters of proposed model are taken from two kinds of totally different CFT columns, so that it can be concluded that this model is also applicable to concrete confined by other special-shaped steel tubes.

Spinal cord concussion: studying the potential risks of repetitive injury.

What is spinal concussion? Spinal cord concussion is a variant of mild spinal cord injury, clinically designated as transient paraplegia or neurapraxia, and characterized by variable degrees of sensory impairment and motor weakness that typically resolve within 24–72 hours without permanent deficits (Del Bigio and Johnson, 1989; Zwimpfer and Bernstein, 1990; Torg et al., 1997). Accordingly, a grading system was developed based on the duration of symptoms, ranging from Grade I ( 24 hours) (Zwimpfer and Bernstein, 1990; Torg et al., 1997). Spinal cord concussion is predominantly a sport-related injury occurring in a wide variety of contact sports in adult and pediatric athletes including wrestling, hockey, gymnastics, and diving, but most commonly in American football, although spinal concussions can also occur after minor car accidents as “whiplash injuries” and falls (Zwimpfer and Bernstein, 1990). In contact sports, the cervical spine is particularly susceptible to injury because of axial loading forces to the head with the neck in flexion or extension. In these circumstances, injury may occur due to disc herniation, buckling of the ligamentum flavum or the posterior longitudinal ligament, or by compression of the spinal cord between vertebral bodies. There appears to be a mechanistic difference in the injury between adult and pediatric age groups. In the adult, a stenotic spinal canal or a diminished spinal canal to vertebral body diameter predispose patients to cervical concussion at the level of stenosis after hyperextension, hyperflexion, or axial loading. The pediatric spine, in contrast, has increased mobility, predisposing the spinal cord to contact with bony elements even in absence of focal stenosis (Clark et al., 2011). Guidelines regarding return to play have been developed based upon the duration of neurological symptoms, neurapraxia, and MRI analysis, but they are based on a limited number of small-scale retrospective studies (Tempel et al., 2015). Given the lack of randomized trials, medical clearance of athletes for resumption of activities is a highly controversial topic without consensus opinion (Cantu, 1998; Morganti, 2003; Mayers, 2008; Harmon et al., 2013). Furthermore, many individuals may experience multiple episodes of spinal cord concussion with recurrence of symptoms (Zwimpfer and Bernstein, 1990; Torreman et al., 1996; Clark et al., 2011). It has therefore been important to develop animal models of spinal cord concussion to elucidate the histological and functional deficits of single and repeated injuries. This perspective presents our recent efforts in developing such a model and the consequences of repetitive injury (Jin et al., 2014, 2015).

Load sequence effects on the fatigue crack growth in a cylinder subjected to combined rotary bending moment and axial force loads

This study used a fatigue crack growth model of a semi-elliptical external surface crack in a hollow cylinder subjected to a combination of rotary bending moment and axial force. In the literature, several authors have explored the problem of crack growth in a hollow cylinder but only for each loading case separately: cyclic tension, rotary bending and cyclic bending. Furthermore, no one has studied the effect of load sequence for this case of structure and loading. In this paper, the study shows the evolution of crack geometry during loading cycles seemingly depends only on accumulated life fraction of the already applied cycles (life fraction is the ratio of the number of load cycles N and the crack growth life NR corresponding to the constant cyclic loading). Therefore, the fatigue crack growth is independent of the load level and the load sequence. This remark can be used to explain the damage accumulation models in fatigue based on life fraction.

Analytical model end plate bolted joint under bending moment and axial force load

In typical buildings with steel-concrete composite floors, joints are designed to transmit only hogging bending moment. In case of the large horizontal loads due to wind, earthquake or accidental events, sagging bending moments in the joint and not to neglect axial force can also occur. Additionally, large deformations of the structure cause tying and prying effects. The joints loaded in this way are changing their characteristics, and their strength for the bending moment is decreased. In global analysis of the structures, the accurate knowledge of the characteristics of the joints allows for determine accurate internal forces in the structural elements. Procedures presented in literature and standards [1] allow for appointing of characteristics of the joint only for bending moment without taking into account axial loads. In the paper, a mechanical model based on “component method” for evaluation of characteristics of the composite joint under bending and axial loads is presented. The influence of tying and prying actions on distribution of the internal forces in a joint is also analyzed. The procedure for calculation of the characteristics of the composite joint with bolted end-plate connection is elaborated too.