Large Axial Loads Research Articles

Airborne Boost-Phase Ballistic Missile Defense

Boost-phase ballistic missile defense is alluring because rocket boosters are easy to detect and track, they are relatively vulnerable due to the large axial loads on a missile under powered flight, the entire payload (single or multiple warheads and midcourse penetration aids) may be destroyed in a single shot, and countermeasures to defeat boost-phase defense are more difficult to devise than for midcourse ballistic missile defenses. Moreover, if intercepted several seconds before booster burnout, the debris will land well short of the target area, although collateral damage to other territory is a serious concern. On the other hand, boost-phase ballistic missile defense is technically challenging because the intercept timelines are very short (1–3 minutes for theater-range ballistic missiles and 3–5 minutes for intercontinental range missiles) and missile boosters are accelerating targets, thus complicating the design of homing kinetic-kill vehicles (KKVs). This article examines the technical feasibility and nominal capability of one type of boost-phase defense, namely, airborne boost-phase intercept (ABI). Airborne laser systems are not examined here.1 This article concludes that ABI should be technically achievable within the next decade and that airborne platforms offer some unique advantages, especially for theater ballistic missile defense, that warrant their serious consideration in future U.S. missile defense architectures.

Several phenomena in structural impact and structural crashworthiness

Abstract This article discusses the dynamic plastic instability of various basic structural members, subjected to large axial impact loads, which is relevant to the fields of structural impact and structural crashworthiness. In particular, studies on the dynamic axial response of idealised elastic–plastic models, rods, cylindrical shells and square tubes, is discussed in some detail. The analyses for some of the rods, shells and tubes retain the simultaneous influence of elastic and plastic stress waves (axial inertia) and the structural response (lateral inertia). The predictions reveal the profound influence of stress wave propagation phenomena which explain the characteristics of many of the experimental results obtained in laboratories over the years. These more complete analyses are vital for the higher velocity impact scenarios encountered increasingly in designs and for comparing properly the relative merits of different ductile materials in potential energy absorbing systems.

Return-to-play criteria in athletes with traumatic injuries to the cervical spine

Football, diving, gymnastics, and wrestling are among the sports associated most commonly with cervical spine injury. Defensive players and the head-forward position have been associated with an increased risk, and a significant decrease in cervical spine injury has resulted from rule changes banning spearing and other forms of head-first contact. The most frequent mechanism of injury in ice hockey involves a player being driven head-first into the boards, and rules have been instituted to move the action away from the boards. Diving is the recreational activity involved most commonly in cervical spine injury, with alcohol involved in 40% of cases. Stingers are traction or compression injuries to the cervical nerve root or brachial plexus and are typically considered benign injuries that should not prevent return to play once pain and weakness resolve. Bilateral symptoms should prompt evaluation for possible spinal cord injury. The relation between transient quadriparesis in football players and developmental stenosis remains controversial, but the presence of an abnormal Torg ratio does not appear to be predictive of future spinal cord injury. Athletes sustaining multiple episodes of transient quadriparesis or with magnetic resonance imaging evidence of cord injury should be advised to avoid collision sports. Quadriplegia is usually the result of cervical spine fracture–dislocation resulting from a large axial load delivered to the vertex of a player's head. Again, rules prohibiting head-first contact have reduced significantly the incidence of serious spinal cord injury. Cervical spine injury is a potentially catastrophic outcome of sports participation. Systematic data collection and analysis by independent sports and health care organizations have provided much insight into the risk factors and mechanism of injury associated with cervical spine trauma in many sports. This information has allowed a rational approach to injury prevention and has often led to dramatic declines in the incidence of cervical spinal cord injury. One of the most effective interventions has been the institution of specific rules prohibiting head-first contact in American football. Since these rules went into effect in 1976, the incidence of football-related quadriplegia has decreased from 13 cases per million players between 1976 and 1980 to 3 per million cases between 1991 and 1993. The number of basic science and clinical studies directly applicable to the issue of cervical spine injury in athletics has been sparse during the past year. As a result, this expanded review presents data and opinion that has appeared in the literature during the past 4 years.

CFT 3層骨組の弾塑性変形性状に関する実験的研究

Three story and one span CFT frames were tested under the constant vertical and alternately repeated horizontal loads in order to study the seismic performance of multi story CFT frames. In this paper, the effects of steel shear walls and beam-to-column connection types (an external diaphragm connection type and a new connection type) on the elastic-plastic behavior of CFT frames are discussed. CFT frames showed large ductile behavior, whereas 1st story columns were subjected to alternately large compressive and tensile axial load. In a steel tube frame, local buckling occurred at column top and column base on the 1st story at a drift angle R=2/100 rad, and after which the strength decreased rapidly.

Use of neural networks for the prediction of frictional drag and transmission of axial load in horizontal wellbores

AbstractThe use of mud motors and other tools to accomplish forward motion of the bit in extended reach and horizontal wells allows avoiding large amounts of torque caused by rotation of the whole drill string. The forward motion of the drill string, however, is resisted by excessive amount of friction. In the presence of large compressive axial loads, the drill pipe or coiled tubing tends to buckle into a helix in horizontal boreholes. This causes additional frictional drag resisting the transmission of axial load (resulting from surface slack‐off force) to the bit. As the magnitude of the frictional drag increases, a buckled pipe may become ‘locked‐up’ making it almost impossible to drill further. In case of packers, the frictional drag may inhibit the transmission of set‐up load to the packer. A prior knowledge of the magnitude of frictional drag for a given axial load and radial clearance can help avoid lock‐up conditions and costly failure of the tubular.In this study a neural network model, for the prediction of frictional drag and axial load transmission in horizontal wellbores, is presented. Several neural network architectures were designed and tested to obtain the most accurate prediction. After cross‐validation of the Back Propagation Neural Network (BPNN) algorithm, a two‐hidden layer model was chosen for simultaneous prediction of frictional drag and axial load transmission. A comparison of results obtained from BPNN and General Regression Neural Network (GRNN) algorithms is also presented. Copyright © 2002 John Wiley & Sons, Ltd.

Void-Filled Cold-Formed Rectangular Hollow Section Braces Subjected to Large Deformation Cyclic Axial Loading

This paper describes a series of tests on empty and void-filled rectangular hollow section (RHS) braces subjected to static and cyclic axial loading. The braces were made from cold-formed C450 (450 MPa nominal yield stress) RHS with two different plate slenderness ratios. The filler material used was normal concrete and light-weight concrete. Two loading protocols were applied, namely Cyclic-Direct (full axial displacement applied and load oscillated) and Cyclic-Incremental (load oscillated at several accumulating axial displacement increments). First-cycle buckling loads were compared with design loads predicted using various national standards. The effects of filler material and section slenderness on the load-deflection response, first cycle peak load, postpeak residual strength, ductility, and energy absorption of void-filled RHS braces are studied in the paper. The effect of the loading scheme is also discussed.

Stability of Elastomeric Seismic Isolation Bearings

Elastomeric seismic isolation bearings are subjected to large axial loads and lateral displacements during strong earthquakes. The existing Koh-Kelly model (1986, 1988, 1989) for elastomeric bearings accounts for axial load effects on horizontal stiffness. This linear model is based on small displacements and rotations and predicts stable postcritical behavior or increasing critical load with increasing horizontal displacement; however, unstable postcritical behavior is observed in the bearing test results presented in this study. The analytical model developed in this study, based on the Koh-Kelly model, includes large displacements, large rotations, and nonlinearity of rubber, and it predicts unstable postcritical behavior. The formulation of the analytical model, calibration, and verification using experimental results are presented. It is shown that the critical load reduces with increasing horizontal displacement and that the horizontal stiffness reduces with increasing horizontal displacement and axial load. It is also shown that the critical load capacity at a horizontal displacement equal to the width of the bearing is not equal to zero, as predicted by the approximate procedure used in design, but higher.

Inferring the effects of curvature of tubulars from pulse propagation tests

Drilling tubulars typically function under large static and dynamic axial loads. The axial load causes curvature in the tubing and when loads are excessive, sections of tubing are forced in contact with the borehole wall. This causes excessive wear and fatigue and leads to failure of the tubing. The feasibility of inferring the incidence of curvature in the tubing and the increase in the attenuation level due to wall contact was investigated with pulse propagation tests on sections of drill tubing. Propagation speed and attenuation as a function of frequency were estimated from impulse response data using a nonlinear least-squares inversion technique. The changes in dispersion of phase speed and attenuation levels were used to identify changes in wall contact condition. Further, attenuation levels were also used to identify the presence of tubing curvature through the resultant coupling between axial and bending waves.

Beam-Column Modeling

Two beam-column element models are compared for nonlinear planar problems in structural engineering using steel members. These problems deal with moment amplification in a slender column, hysteretic buckling and tensile yield of a brace, cyclic loading of a cantilever beam, and response of a frame to a harmonic ground motion of increasing amplitude. The models studied include one of the plastic-hinge type and one of the fiber type. The former is more computationally efficient than the latter, but the fiber element includes residual stresses and better represents features of the yielding process. These additional features of the fiber element proved to be most important when modeling collapse of a slender column, hysteretic brace behavior, and cyclic flexure under large axial load. Agreement between the two models for the frame problem was reasonably good, including the level of ground motion at which collapse occurred.

An improved transfer matrix technique as applied to BHA lateral vibration analysis

In previous work on BHA (bottomhole assembly) lateral vibration, the effects of axial loads have often been neglected. In this paper an improved transfer matrix technique is applied to study the dynamics of a BHA system which is always subject to a large axial load. The transfer matrix developed, which is derived directly from the consistent equations of motion of rotating Timoshenko shafts subject to axial loads, includes the effects of rotary inertia, gyroscopic moments, transverse shear and axial load. The mud-drillstring interaction is represented by an added mass coefficient. The influences of rotation speed, weight on bit and added mass coefficient on the lateral vibration are investigated. The buckling loads of horizontal BHA’s are calculated by observing the disappearance of the corresponding eigenfrequencies.

Stability optimization of beams conveying fluid or carrying other axially moving materials

Optimal designs, and sensitivities of such designs, are calculated for transversely vibrating structures carrying an axially moving material. The structures studied consist of piecewise uniform and initially straight beam elements conveying a piecewise constant-speed plug flow of material along their deflected axes. The beams can be supported by a distributed Winkler-type ambient medium. Viscous damping in the beam material and the ambient medium is considered. Large static axial loads may act on the beam and on the moving material. The beams are modelled with a generalized second-order Rayleigh-Timoshenko theory including the Euler-Bernoulli theory as a special case. The structures investigated may also contain taut strings and rigid bodies. Considering a given subcritical material speed, the aim of the present study is to modify the initial design of a given beam structure in such a way that the transient vibrational motion following a transverse disturbance will die out as quickly as possible. To this end, complex eigenfrequencies pertaining to transverse vibration are calculated, and design parameters are changed so as to maximally raise the imaginary part of that eigenfrequency which has the smallest such part. In one of the examples, the objective is to maximally raise the product of the real and imaginary parts of the eigenfrequency which has the smallest such product.

Second‐Order Refined Plastic‐Hinge Analysis for Frame Design. Part I

This paper discusses the issues involved in using simplified second‐order inelastic analysis for design of steel‐frame structures. In particular the elastic‐plastic hinge method is examined and the assumptions inherent in its use are outlined. It is shown that this method does not always lead to an accurate representation of inelastic behavior, and that it does not furnish enough information for assessment of the ultimate strength of individual members. An alternative approach called the refined plastic‐hinge method is introduced, and its design implications are discussed. The refined plastic‐hinge approach accounts for inelastic stiffness degradation, and a column tangent‐modulus expression is utilized to represent the effective stiffness of the element when it is loaded with large axial loads. This paper highlights and illustrates the qualities and limitations of these two inelastic analysis methods with regard to their acceptability for use in predicting the ultimate strengths of steel frames and their members. Case studies and recommendations for use of inelastic analysis for direct frame design are presented in a companion paper.

Helical Buckling of Pipes in Extended Reach and Horizontal Wells—Part 2: Frictional Drag Analysis

Abstract This paper studies the frictional drag of helically buckled pipes (drillstring and tubing) in extended reach and horizontal wells to correctly predict the actual bit weight or packer load, in cases where helical buckling of pipes may have occurred. Helical buckling of pipes in such wells may occur, since large axial loads are often required. The differential equation of axial force balance with consideration of the axial friction for helically buckled pipes is resolved, and the solution shows that when the pipes are helically buckled, the frictional drag will become very large. The actual bit weight for drilling or packer load for well completion may therefore become much smaller than estimated under the unbuckled pipe conditions. The analytical solution is also shown to agree with the results from laboratory experiments, which simulate the real wellbore-pipe conditions. An example is provided to show the calculation procedure and the importance of the results.

Fluid-Conveying Damped Rayleigh-Timoshenko Beams in Transient Transverse Vibration Studied by Use of Complex Modal Synthesis

Complex modal synthesis is used for studying transient transverse vibration of piecewise uniform straight beams conveying a piecewise constant-speed plug flow of material along the deflected beam axis. The beams can be supported by a distributed Winkler-type ambient medium. Viscous damping in the beam material and the ambient medium is included. Large static axial loads may act on the beam and on the moving material. The time-dependence of the prescribed transient loads support accelerations is given by a temporal sequence of products of polynomial, exponential and cosine functions. The beams are modelled with a generalized second-order Rayleigh-Timoshenko theory including the Euler-Bernouli theory as a special case. The structures studied may also contain taut strings and rigid bodies.

Compression of a Cord

Cord is a structural element that is generally used to resist relatively large axial loads in tension in comparison to bending and torsional loads. However, in certain cases, a cord may be called upon to resist a compressive load such as occurs when a cord is placed in a composite. When a cord is subjected to compression, the individual filaments lose contact with each other. This results in a considerable reduction in the axial stiffness of the cord. Generally, most cord composites are fabricated at elevated temperatures and cooled to room temperatures. Some remarks are made concerning the buckling of these cords since the coefficients of thermal expansion are different for the matrix and the cord.

Eigenfrequencies and eigenmodes of beam structures on an elastic foundation

A method for determining the eigenfrequencies of continuous structures containing beams in plane bending-shearing vibration is presented. Each beam member may rest on a general Winkler-type elastic foundation (including the Pasternak foundation as a special case) and may carry a large static axial load calling for use of a second order theory. The method could preferably be implemented in the Wittrick-Williams bisection algorithm. A numerical verification is given for a repetitive structure where an alternative solution is available through the use of exact difference equations. Practical applications to a rail/pad/sleeper system on its ballast and roadbed are foreseen.

Fluid-conveying damped Rayleigh-Timoshenko beams in transverse vibration analyzed by use of an exact finite element part I: Theory

Free and forced nonsynchronous harmonic linear vibrations of piecewise uniform straight beam structures supported by a Winkler-type ambient medium and conveying a piecewise constant-speed plug flow of material along the deflected beam axis are studied by means of finite elements. Hysteretic and viscous damping in the beam material and ambient medium are considered. Large static axial loads may act on the beam and fluid calling for use of a second-order theory. In a companion paper, exact complex-valued nonsymmetric transcendentally frequency-dependent member stiffness matrices have been established for uniform Rayleigh-Timoshenko beams, uniform Euler-Bernoulli beams (with infinite shear stiffness), and also for uniform strings (with zero bending stiffness). In the present paper, the corresponding approximate member stiffness matrices based on standard polynomial shape functions are given. Fluid-conveying rigid bodies are treated. Six numerical examples are presented for beam structures. Comparisons between results found by use of exact and approximate finite elements are performed. Forced and free harmonic vibrations are studied including the calculation of critical fluid velocities and mechanical power flows.

Casing Deformation in Ekofisk

Casing deformation resulting from reservoir compaction occurred in the Ekofisk field operated by Phillips Petroleum Co. Norway and is a serious problem in three of the fields. This study established a relationship between reservoir compaction and casing failure by statistical analyses, finite-element modeling (FEM), and the analyses of deformed casing and logs run through collapsed casings. Ekofisk casing deformation is related primarily to the near well incremental strain, well inclination, and casing diameter. Useful correlations to estimate future probabilities of casing deformation as a function of reservoir variables and well parameters were also obtained. The authors concluded that casing failure induced by reservoir compaction can be minimized through a pressure-maintenance program to reduce strain by drilling with the highest practical angle and by using the largest possible casing in the well.

高強度鉄筋SD50を用いた鉄筋コンクリート梁・柱断面の曲げ解析

The load-flexural deflection and the moment-flexural deflection relationships in test length of concrete beams and columns reinforced with high strength steel Grade SD 50 bars were studied analytically and compared with past test results. The analytical stress-strain curves for steel have been proposed on the experimental results of Grade SD 50 bars under alternatedly repeated loading. In this study, following conclusions were obtained. (1) The stress-strain curve proposed for steel seems to express experimental results of Grade SD 50 bars under alternatedly repeated loading. (2) For analysis of beam and column sections under monotonic loading, the overall strength and the stiffness, up to the maximum load seem to pursue the experimental results very well. But the analyses of column sections under large axial loading after maximum load were not in agreement with experimental results. (3) For analysis of beam and column sections under alternatedly repeated loading, the moment-flexural deflection relationships seem to pursue overall experimental results. Particulary, the assumptions of stress-strain curve for steel, that is, stiffness of strain hardening is E_s/50 and stiffness of unloading is E_s, seemed to be reasonable.

Experience with Use of Heavy W Shapes in Tension

During the last five years, a few cracking and fracture problems have been observed with welded, large rolled jumbo sections. This type of rolled section is classified as a group IV or V shape in the 8th Edition AISC Manual of Steel Construction. They include W12 and W14 rolled steel sections equal or exceeding 210 lbs./ft. The cracking has been observed in sections equal or exceeding 370 lbs./ft. They have been observed in sections produced without special metallurgical requirements as well as in sections produced with killed fine grain practice. This paper reviews the characteristics of these steel sections, the conditions that led to the cracking and provides recommendations for splicing and use of these members in tension applications. In addition, there are suggestions for weld splices in compression. When first introduced in the 1960s, these sections were intended as columns in structures resisting large axial loads. However, with passage of time the sections were gradually introduced in large trusses as tension members. This provided a means to develop the large forces in the chords and diagonals of long-span trusses or shorter spans carrying heavier loads. Figure 1 shows the fractured chord of a large truss fabricated from these rolled sections.