Axial Force Levels Research Articles

Vibration of beams with multiple open cracks subjected to axial force

A new method is proposed to obtain the eigenfrequencies and mode shapes of beams containing multiple cracks and subjected to axial force. Cracks are assumed to introduce local flexibility changes and are modeled as rotational springs. The method uses one set of end conditions as initial parameters for determining the mode shape functions. Satisfying the continuity and jump conditions at crack locations, mode shape functions of the remaining parts are determined. Other set of boundary conditions yields a second-order determinant that needs to be solved for its roots. As the static case is approached, the roots of the characteristic equation give the buckling load of the structure. The proposed method is compared against the results predicted by finite element analysis. Good agreement is observed between the proposed approach and finite element results. A parametric study is conducted in order to investigate the effect of cracks and axial force levels on the eigenfrequencies. Both simply supported and cantilever beam-columns are considered. It is found that eigenfrequencies are strongly affected by crack locations, severities and axial force levels. Simple modifications to account for flexible intermediate supports are presented as well. The proposed method can efficiently be used in detecting crack locations, severities and axial forces in beam-columns. Furthermore it can be used to predict the critical load of damaged structures based on eigenfrequency measurements.

Component method extension to steel beam‐to‐beam and beam‐to‐column knee joints under bending and axial forces

Abstract This paper presents an analysis of semi‐rigid beam‐to‐beam end‐plate bolted and beam‐to‐column end‐plate bolted knee joints that are subjected to bending and tension or compression axial force. Usually the influence of axial force on joint rigidity is neglected. According to EC3, the axial load, which is less than 10 % of plastic resistance of the connected member under axial force, may be disregarded in the design of joint. Actually the level of axial forces in joints of structures may be significant and has a significant influence on joint rigidity. One of the most popular practical method permitting the determination of rigidity and strength of joint is the so‐called component method. The extension of the component method for evaluating the influence of bending moment and axial force on the rigidity and strength of the joint are presented in the paper. The numerical results of calculations of rigidity and strength of beam‐to‐beam and beam‐to‐column knee joints are presented in this paper as well.

Seismic performance evaluation of steel arch bridges against major earthquakes. Part 1: dynamic analysis approach

AbstractIn this study the inelastic behavior of steel arch bridges subjected to strong ground motions from major earthquakes is investigated by dynamic analyses of a typical steel arch bridge using a three‐dimensional (3D) analytical model, since checking seismic performance against severe earthquakes is not usually performed when designing such kinds of bridge. The bridge considered is an upper‐deck steel arch bridge having a reinforced concrete (RC) deck, steel I‐section girders and steel arch ribs. The input ground motions are accelerograms which are modified ground motions based on the records from the 1995 Hyogoken‐Nanbu earthquake. Both the longitudinal and transverse dynamic characteristics of the bridge are studied by investigation of time‐history responses of the main parameters. It is found that seismic responses are small when subjected to the longitudinal excitation, but significantly large under the transverse ground motion due to plasticization formed in some segments such as arch rib ends and side pier bases where axial force levels are very high. Finally, a seismic performance evaluation method based on the response strain index is proposed for such steel bridge structures. Copyright © 2004 John Wiley & Sons, Ltd.

Behaviour of flush end-plate beam-to-column joints under bending and axial force

Steel beam-to-column joints are often subjected to a combination of bending and axial forces. The level of axial forces in the joint may be significant, typical of pitched-roof portal frames, sway frames or frames with incomplete floors. Current specifications for steel joints do not take into account the presence of axial forces (tension and/or compression) in the joints. A single empirical limitation of 10% of the beam's plastic axial capacity is the only enforced provision in Annex J of Eurocode 3. The objective of the present paper is to describe some experimental and numerical work carried out at the University of Coimbra to try to extend the philosophy of the component method to deal with the combined action bending moment and axial force.

EFFECTS OF AXIAL FORCE VARIATION IN THE SEISMIC RESPONSE OF BRIDGES ISOLATED WITH FRICTION PENDULUM SYSTEMS

The effects of the axial load variations on the seismic response of bridges isolated with friction pendulum systems (FPS) are investigated. A series of parametric time history non-linear analyses are performed for different bridge configurations, defined after an extensive investigation on typical existing cases. The influence of both horizontal and vertical components of the ground motion is considered. The behaviour of the pier-isolator-deck system is predicted using two analytical models characterised by hysteretic loops sensitive or insensitive to axial force variations, in order to compare the different responses. Level of axial force, maximum displacements and induced bending moment are investigated, as well as shear and torsion demand, caused by different shear actions acting on the isolator devices. A comparison between demand and resistance capacity of the bridge piers is performed, in order to investigate possible non-conservative approaches in the current design methods and to raise controversial issues on the subject.

Steel-reinforced concrete joints under reversal cyclic load

The performance of structural joints comprising built-up steel-reinforced concrete (SRC) columns connecting to reinforced concrete (RC) beams under reversal cyclic loads is described in this paper. Eight composite joint specimens were tested to failure. Three modes of failure, namely, bending failure in beam, bending–shear failure in beam and shear failure in beam and joint were observed. Test results indicated that energy dissipation capacity of the SRC joint depends on the modes of failure and the levels of axial load imposed on the column. The higher the level of axial force imposed on the column, the lower the energy dissipation capability but the larger shear capacity of the joint. An analytical model for the evaluation of the shear capacity of SRC joint taking into account the effects of the presence of steel section, stirrups, axial force in column and ductility demand is proposed. Analytical and experimental results show good agreement.

Steel-reinforced concrete joints under reversal cyclic load

The performance of structural joints comprising built-up steel-reinforced concrete (SRC) columns connecting to reinforced concrete (RC) beams under reversal cyclic loads is described in this paper. Eight composite joint specimens were tested to failure. Three modes of failure, namely, bending failure in beam, bending–shear failure in beam and shear failure in beam and joint were observed. Test results indicated that energy dissipation capacity of the SRC joint depends on the modes of failure and the levels of axial load imposed on the column. The higher the level of axial force imposed on the column, the lower the energy dissipation capability but the larger shear capacity of the joint. An analytical model for the evaluation of the shear capacity of SRC joint taking into account the effects of the presence of steel section, stirrups, axial force in column and ductility demand is proposed. Analytical and experimental results show good agreement.

Assessment of seismic performance of extended pile‐shafts

AbstractThe seismic performance of extended pile‐shafts subjected to the current level of displacement ductility demand is assessed for different soil conditions. Local curvature ductility demand is compared with the curvature ductility capacity provided by the current level of confining steel. Parameters in the assessment of extended pile‐shafts include the undrained shear strength of cohesive soils, relative density of cohesionless soils, aboveground height, longitudinal reinforcement ratio, axial force level and pile diameter. Results indicate that the curvature ductility demand in the pile decreases with increased soil stiffness but increases with increased aboveground height. The curvature ductility demand however is not sensitive to the longitudinal reinforcement ratio or axial force level, and is independent of the pile diameter. Results further indicate that the curvature ductility capacity available from the current level of confining steel may not be adequate for tall extended pile‐shafts, especially for piles with large longitudinal reinforcement ratio and embedded in soft or loose soils. Limits on the maximum longitudinal reinforcement ratio are suggested in the paper. Copyright © 2003 John Wiley & Sons, Ltd.

曲げ降伏後にせん断破壊するRC柱の靭性評価に関する実験研究

In this study, the effect of lateral reinforcement and ductility of reinforced concrete columns subjected to shear failure after flexural yielding is examined. The major parameters for the specimen used in the study include the yield strength and quantity of lateral reinforcement, strength of concrete and axial force level. This paper describes the results of quantitative evaluation of relationship between the shear deformation and effect of lateral reinforcement after flexural yielding. It is also found that the ductility (plastic deformation capacity and energy absorption capacity) of the columns in the case of shear failure after flexural yielding can be evaluated by the shear strength safety margin.

An analytical evaluation of the response of steel joints under bending and axial force

This paper presents an equivalent elastic model where each bi-linear spring is replaced by two equivalent elastic springs using an energy formulation and in the context of a post-buckling stability analysis. Such a model yields analytical solutions for the evaluation of the behaviour of steel joints under compressive forces, combined axial force and bending moment, which enables the reproduction of their full non-linear behaviour. The resulting formulation is applied to a simple beam-to-column welded connection initially loaded in pure compression. Subsequent loading of the joint in combined bending and various levels of axial force clearly shows the reduction in moment capacity.

Physical instability and geometric effects in frames

The interaction between physical instability and geometric (2nd-order) effects in plane frames is investigated herein within a finite element based mathematical programming framework, under the assumptions of quasistatic loading and lumped plasticity. The sources of physical instability consist of inelastic bending hinges characterized by softening nonholonomic (irreversible) moment versus rotation constitutive laws. The complex and insightful response spectrum which can arise is illustrated with the aid of simple, albeit instructive, reference examples. Stability domains are obtained for these examples in the space of the parameters characterizing the level of member axial force and the amount of hinge softening. Such domains highlight various key features, which are briefly commented upon, of the interplay between physical and geometric effects.

THE FORCES WHICH DEVELOP IN THE TISSUES DURING LEG LENGTHENING. A CLINICAL STUDY

Axial forces were measured during limb lengthening in a series of ten patients with varying pathologies in order to assess the mechanical characteristics of the distracted tissues and the levels of axial force to which soft tissues are subjected during leg lengthening. The pattern of force was found to vary according to the underlying pathology. For post-traumatic shortening in adults both the peak and the resting forces rose steadily during lengthening reaching maximum forces of the order of 300 N. Patients with congenitally short limbs developed very high peak forces (in some cases over 1000 N) and also showed large amounts of force relaxation (typically 400 to 500 N). When very high levels of force were recorded, there was a higher complication rate. In particular, there was a high instance of angular deformity. This occurred because the loads encountered resulted in failure of some of the external fixation frames.

Improved Frame Stability Analysis with Effective Lengths

Approximate methods for determination of effective lengths of compression members in frame systems are normally based on rotational restraints defined through so-called joint stiffness ratios or G -factors. These approaches allow the member to be considered in isolation from the rest of the frame. However, they are known to be inaccurate in many cases. A method is proposed that involves postprocessing of effective lengths from isolated column analyses to arrive at improved, weighted mean values. The approach, termed the method of means, satisfies general system instability principles, is attractively simple, and yields in general effective length predictions in excellent agreement with exact results for a wide variation of parameters. The errors are normally within a few percent of exact solutions. The method is applicable to braced and to a range of unbraced frames. It is particularly suitable for cases where drastic changes of beam or column stiffness occur, such as in the top or bottom stories of a frame, or where column stiffness, axial force level, and story height change at certain floor levels.

THE FORCES WHICH DEVELOP IN THE TISSUES DURING LEG LENGTHENING

Axial forces were measured during limb lengthening in a series of ten patients with varying pathologies in order to assess the mechanical characteristics of the distracted tissues and the levels of axial force to which soft tissues are subjected during leg lengthening. The pattern of force was found to vary according to the underlying pathology. For post-traumatic shortening in adults both the peak and the resting forces rose steadily during lengthening reaching maximum forces of the order of 300 N. Patients with congenitally short limbs developed very high peak forces (in some cases over 1000 N) and also showed large amounts of force relaxation (typically 400 to 500 N). When very high levels of force were recorded, there was a higher complication rate. In particular, there was a high instance of angular deformity. This occurred because the loads encountered resulted in failure of some of the external fixation frames.

Inertia-friction welding of SiC-reinforced 8009 aluminium

Inertia-drive friction welding (IFRW) of an 8009 Al alloy (Al-8.5 Fe-1.7 Si-1.3 V, wt%) reinforced with 11 volume per cent SiC particles (8009/SiC/11p) has been investigated. Inertia-drive friction welds were made with constant energy at two levels of axial force. The microstructures of the base material and the welds were characterized using optical and scanning electron microscopy, while the mechanical properties were evaluated using microhardness and tensile testing. Examination of weld sections revealed that the hot deformation experienced during welding produced a homogenized microstructure with a uniform distribution of SiC particles along the bond line. No evidence of a chemical reaction between the SiC and the matrix was found in any of the welds, but cracking of some of the larger SiC particles was observed in the base material as well as in the IFR welds. The average microhardness of the various heat-and-deformation affected zones (HDZs) of the welds did not vary greatly from that of the base material, and no weld induced weak regions were discerned. The room-temperature (RT) tensile strength of the IFR welds exceeded 90 per cent of the base material. The weld tensile specimens failed at the outer edge of the HDZ for all of the welds tested. The fracture surface of the 8009 matrix of tensile samples for both the base material and the welds exhibited a dimpled appearance indicating a ductile failure, while fracture through the SiC appeared to occur in a brittle fashion. IFRW has proven effective in joining 8009/SiC/11p with little loss in RT hardness and tensile properties.

Study of Human Operation of a Power Drill

This research investigated human operation of a hand-held power drill by analyzing patterns in upper limb posture for various drilling conditions: drilling height, drill length and level of axial force exerted on the drill handle. Subjects used similar postures for drilling locations with similar kinematics. In addition, posture was not statistically different for the range of axial forces and drill lengths studied. Results suggest that human do not try to obtain isotropy or maximum manipulability conditions at the hand while executing the task. Minimization of joint torques appears more plausible.

Analysis of Circular RC Columns for Short‐ and Long‐Term Deformations

The paper presents a method of analysis for the short‐term and timedependent response of slender reinforced concrete columns of circular cross section. The columns are assumed to be pin‐ended and loaded with equal end eccentricity. Creep and shrinkage effects are modeled using the age‐adjusted effective modulus method, coupled with a relaxation procedure described elsewhere. Although the analysis assumes linear short‐term material behavior, it is applicable to calculating the nonlinear behavior due to changes in geometry and the effective design strength of circular columns, since the concrete stresses are significantly lower than the cylinder strength at the axial force and moment levels corresponding to the design load‐moment envelope. Based on the computer solutions, a simplified design procedure is proposed that is suitable for routine office application.

軸方向引張り力を受けるRC梁のせん断耐力に関する実験的研究

The problems of the shear strength of the reinforced concrete members have been studied by manyresearchers. However there are few studies on the shear strength of reinforced concrete beam under the axial tensileforce. In this paper the effects of the axial tension on the shear strength and the failure status of the beams areanalyzed experimentally. In experimental studies, 78 simply supported beams having rectangular cross section aretested under axial tension and bending. The parameters adopted herein are the axial tensile force levels and the shearspan lengths. Considering the insufficient definitions of the Specification for Concrete the adequate regressiveequations are defined based on the experimental results.

P‐Delta Effect Under Repeated Loading

Recently, a novel P‐Delta method for the design of sway frames was introduced by the writer and demonstrated in conjunction with static proportional loading conditions. The method incorporates the rigid‐plastic collapse load and the elastic buckling load of the structure as the two boundary conditions and does not require iterations or a precise trace of the load history. In this paper it is argued and verified by experiments that the P‐Delta effect for sway frames can also be predicted by the same method if loadings vary independently. Such loadings can lead to a reduced failure load compared with the static load case due to premature incremental collapse if the so‐called shakedown load is exceeded. The presented approach is a simple alternative to much more complex analysis procedures which would have to follow repeatedly the loading and unloading paths until failure is indicated. This has to be done under changing axial forces which requires iterations until the structure stiffness and the axial force level match.

Olduvai Hominid 7 trapezial metacarpal 1 articular morphology: contrasts with recent humans.

A consideration of the metacarpal 1 articulation of the Olduvai Hominid 7 trapezium shows that, although it is generally similar to those of recent humans, it is considerably flatter radioulnarly and dorsopalmarly than those of modern humans and similar in its degree of dorsopalmar flattening to those of Upper Pleistocene late archaic humans. Even though this flattening may have slightly limited flexion-extension at the pollical carpometacarpal joint, it is most likely related to the apparently elevated levels of axial joint reaction force through the thumbs of archaic members of the genus Homo. It also documents the continuation of human carpometacarpal articular evolution through the Pleistocene.