Variable Axial Load Research Articles

Effects of Variation of Axial Load and Bidirectional Loading on Seismic Performance of GFRP Retrofitted Reinforced Concrete Exterior Beam-Column Joints

Most of the experimental studies available in literature on the seismic assessment and retrofit of existing, poorly detailed, reinforced concrete (RC) beam-column joints, typical of pre-1970s construction practice, have concentrated on the two-dimensional (2D) response, using unidirectional cyclic loading testing protocol and constant axial load. Even more limited information is available on the performance of exterior (corner) three-dimensional (3D) RC beam-column joints with substandard detailing subjected to bidirectional loading regime. In this study, the results of a comprehensive experimental program is presented, aiming to show the effects of varying axial and bidirectional loading on the seismic performance of deficient exterior RC beam-column joints before and after retrofit. Ten exterior beam-column joint subassemblies are tested, including four as-built specimens and six retrofitted specimens using externally bonded glass fiber-reinforced polymer (GFRP) sheets. Test results are herein presented...

Parametric analysis of liquid storage tanks base isolated by curved surface sliding bearings

Curved surface sliding bearings, which are usually called as friction pendulum system (FPS) are commonly used for base isolation of liquid storage tanks since the period of the isolation system is independent of the storage level. However the restoring force and the damping at the isolation system are functions of axial load which changes during an earthquake excitation. This change might be in appreciable amounts especially for the tanks with high aspect ratios. The present paper focuses on earthquake performances of both broad and slender tanks base isolated by FPS bearings. The effects of overturning moment and vertical acceleration on axial load variation at the bearings are considered. The efficiency of the isolation system is investigated by analyzing the effects of various parameters such as; (i) isolation period, (ii) tank aspect ratio and (iii) coefficient of friction. The Haroun and Housner's three-degrees-of-freedom lumped mass model was used to solve the governing equations of motion in which convective, impulsive and rigid masses were included. A number of selected ground motions were considered and the results were compared to those of non-isolated cases. As a result, base isolation was found to be effective in reducing the base shear values for both broad and slender tanks without significantly affecting the sloshing displacements of the broad ones. The efficiency was even more pronounced for slender tanks subjected to near fault ground motions for isolation periods above 3 s. This specific value of isolation period also eliminated possible design problems arising from under-estimation of base shear values (up to 40%) due to ignoring the effects of axial load variation in lower isolation periods. Overturning effects should not be ignored especially for tanks with high aspect ratios ( S) and being subjected to near fault ground motion.

Exact Solutions for the Generalized Euler’s Problem

This paper is concerned with buckling analysis of a nonuniform column with classical∕nonclassical boundary conditions and subjected to a concentrated axial force and distributed variable axial loading, namely, the generalized Euler’s problem. Exact solutions are derived for the buckling problem of nonuniform columns with variable flexural stiffness and under distributed variable axial loading expressed in terms of polynomial functions. Then, more complicated buckling problems are considered such as that the distribution of flexural stiffness of a nonuniform column is an arbitrary function, and the distribution of axial loading acting on the column is expressed as a functional relation with the distribution of flexural stiffness and vice versa. The governing equation for such problems is reduced to Bessel equations and other solvable equations for seven cases by means of functional transformations. A class of exact solutions for the generalized Euler’s problem involved a nonuniform column subjected to an axial concentrated force and axially distributed variable loading is obtained herein for the first time in literature.

Shear deformation effect in non-linear analysis of composite beams of variable cross section

In this paper the non-linear analysis of a composite Timoshenko beam with arbitrary variable cross section undergoing moderate large deflections under general boundary conditions is presented employing the analog equation method (AEM), a BEM-based method. The composite beam consists of materials in contact, each of which can surround a finite number of inclusions. The materials have different elasticity and shear moduli with same Poisson's ratio and are firmly bonded together. The beam is subjected in an arbitrarily concentrated or distributed variable axial loading, while the shear loading is applied at the shear center of the cross section, avoiding in this way the induction of a twisting moment. To account for shear deformations, the concept of shear deformation coefficients is used. Five boundary value problems are formulated with respect to the transverse displacements, the axial displacement and to two stress functions and solved using the AEM. Application of the boundary element technique yields a system of non-linear equations from which the transverse and axial displacements are computed by an iterative process. The evaluation of the shear deformation coefficients is accomplished from the aforementioned stress functions using only boundary integration. Numerical examples are worked out to illustrate the efficiency, the accuracy, the range of applications of the developed method and the influence of the shear deformation effect.

Biomechanical analysis of penile erections: penile buckling behaviour under axial loading and radial compression

To characterize the biomechanics of erectile function, as contrary reports have modelled the penis as an isotropic material and state that only axial buckling tests can effectively predict penile rigidity; that assumption is questioned and an alternative structure proposed and validated. Three experimental physical cylindrical models of diameters 1.9, 2.54 and 3.81 cm were fabricated and the relationship between axial loading and radial compression was measured for cylindrical pressures of 8-20 kPa. A finite element analysis (FEA) computer model of the penis was constructed to simulate the response of the corpora cavernosa to axial and radial loading for differing diameters and lengths of the penile shaft. The stresses developed in the tunica albuginea of the corporal bodies of the penis during buckling were assessed using a mathematical analysis. From the analysis of surface stresses under variable axial loading, as the angle of an applied load changes on an isotropic shaft, the magnitude of surface stresses varies up to 50 kPa, and for a pressure vessel the magnitude of surface stresses varies up to 100 kPa. The FEA model showed that nodal displacements were greatest around a ring under radial compression, and for the axially loaded model displacements were greatest at the vessel tip under the force gauge. All displacements were 0.1-1.0 mm. There was an exponential relationship between internal pressure and the axial force required to cause buckling in a thin-walled pressure vessel. There was a nearly constant relationship between circumferential displacement and internal pressure under uniform radial compression. The displacement values on the FEA analysis were approximately equal outside of the areas of high stress which were under the load of the external device (compressive ring or force gauge) in both cases. Physical modelling shows that when a pressurized vessel is under either axial or radial load the internal pressure increases. Vessels at high internal pressure require more force to cause buckling than vessels at lower internal pressure. The circumferential displacement of a vessel under radial compression is higher in vessels of lower internal pressure and less in vessels of high internal pressure. The size of a vessel also contributes to its ability to be buckled. Smaller vessels buckle under smaller load, but the ratio of force required to buckle vs. diameter of the cylinder remained constant. The computer simulations show that with slight deviations from perfectly aligned axial loading the stresses felt on the walls of cylindrical columns vary considerably, whether they are isotropic beams or pressurized vessels. The material properties of the tissues within the corpora cause it to behave as a thin-walled pressurized vessel, in which the hoop stress and axial stress have a constant relationship independent of the length to diameter ratio rather than as an isotropic beam where this relationship varies. Patient discomfort and high operator dependency further contribute to the inconsistencies of axial loading methods to determine penile buckling. Based on the constant relationship between hoop stress and axial stress in thin-walled pressurized vessels this study confirms the validity and desirability of using radial compression methods to assess penile rigidity in lieu of axial loading methods.

INELASTIC BEHAVIOR OF UNEMBEDDED TYPE COLUMN BASES IN SRC STRUCTURES SUBJECTED TO VARIABLE AXIAL AND CYCLIC FLEXURAL LOADING

We confirmed the mechanical behavior of unembedded type column bases subjected to variable axial and cyclic flexural load through the structural tests of two series. The structural tests of two series are composed of the experiment on the specimen of a real large size and the half reduction size. From the test result, it was shown that limit rotation angle of column bases subjected to variable axial loading decreases. The reason for this cause is that local bucking and fracturing of main reinforcement occurs at column bases subjected to cyclic flexural load under the variable axial load compared with column bases under the constant axial load. In addition, we carried out the elasto-plastic analysis, and verified the accuracy of the analysis.

STRUCTURAL PERFORMANCE OF EXTERIOR BEAM-COLUMN JOINTS FOR COMPOSITE CES STRUCTURAL SYSTEMS

Two exterior CES beam-column joints with different failure mode, the beam yielding type and the joint shear failure type, were tested under lateral load reversals and variable axial load to investigate the structural performance. The test results indicated that the CES beam-column joins had the stable hysteresis behavior until large story drift angle of 1/20 radian. In addition, the use of the FRC facilitates to control the crack width of the joints. The development of stresses in the joint panel was clarified by the rosette analysis and non-linear FEM analysis. It is shown that the joint shear strength of exterior CES beam-column joints cloud be evaluated by the method based on AIJ design standard for SRC structures.

Nonlinear analysis of beams of variable cross section, including shear deformation effect

In this paper the analog equation method (AEM), a BEM-based method, is employed for the nonlinear analysis of a Timoshenko beam with simply or multiply connected variable cross section undergoing large deflections under general boundary conditions. The beam is subjected in an arbitrarily concentrated or distributed variable axial loading, while the shear loading is applied at the shear center of the cross section, avoiding in this way the induction of a twisting moment. To account for shear deformations, the concept of shear deformation coefficients is used. Five boundary value problems are formulated with respect to the transverse displacements, the axial displacement and to two stress functions and solved using the AEM. Application of the boundary element technique yields a system of nonlinear equations from which the transverse and axial displacements are computed by an iterative process. The evaluation of the shear deformation coefficients is accomplished from the aforementioned stress functions using only boundary integration. Numerical examples with great practical interest are worked out to illustrate the efficiency, the accuracy and the range of applications of the developed method. The influence of the shear deformation effect is remarkable.

Shear deformation effect in second-order analysis of frames subjected to variable axial loading

In this paper a boundary element method is developed for the second-order analysis of frames consisting of beams of arbitrary simply or multiply connected constant cross section, taking into account shear deformation effect. Each beam is subjected to an arbitrarily concentrated or distributed variable axial loading, while the shear loading is applied at the shear center of the cross section, avoiding in this way the induction of a twisting moment. To account for shear deformations, the concept of shear deformation coefficients is used. Three boundary value problems are formulated with respect to the beam deflection, the axial displacement and to a stress function and solved employing a BEM approach. The evaluation of the shear deformation coefficients is accomplished from the aforementioned stress function using only boundary integration. Numerical examples with great practical interest are worked out to illustrate the efficiency, the accuracy and the range of applications of the developed method. The influence of both the shear deformation effect and the variableness of the axial loading are remarkable.

Shear deformation effect in nonlinear analysis of spatial beams

In this paper a boundary element method is developed for the nonlinear analysis of beams of arbitrary doubly symmetrical simply or multiply connected constant cross-section, taking into account shear deformation effect. The beam is subjected in an arbitrarily concentrated or distributed variable axial loading, while the shear loading is applied at the shear centre of the cross-section, avoiding in this way the induction of a twisting moment. To account for shear deformations, the concept of shear deformation coefficients is used. Five boundary value problems are formulated with respect to the transverse displacements, the axial displacement and to two stress functions and solved using the analogue equation method, a BEM-based method. Application of the boundary element technique yields a system of nonlinear equations from which the transverse and axial displacements are computed by an iterative process. The evaluation of the shear deformation coefficients is accomplished from the aforementioned stress functions using only boundary integration. Numerical examples are worked out to illustrate the efficiency, the accuracy and the range of applications of the developed method. The influence of both the shear deformation effect and the variability of the axial loading are remarkable.

Shear deformation effect in nonlinear analysis of spatial composite beams subjected to variable axial loading by bem

In this paper a boundary element method is developed for the nonlinear analysis of composite beams of arbitrary doubly symmetric constant cross section, taking into account the shear deformation effect. The composite beam consists of materials in contact, each of which can surround a finite number of inclusions. The materials have different elasticity and shear moduli with same Poisson's ratio and are firmly bonded together. The beam is subjected in an arbitrarily concentrated or distributed variable axial loading, while the shear loading is applied at the shear center of the cross section, avoiding in this way the induction of a twisting moment. To account for shear deformations, the concept of shear deformation coefficients is used. Five boundary value problems are formulated with respect to the transverse displacements, the axial displacement and to two stress functions and solved using the Analog Equation Method, a BEM based method. Application of the boundary element technique yields a system of nonlinear equations from which the transverse and axial displacements are computed by an iterative process. The evaluation of the shear deformation coefficients is accomplished from the aforementioned stress functions using only boundary integration. Numerical examples with great practical interest are worked out to illustrate the efficiency and the range of applications of the developed method. The influence of both the shear deformation effect and the variableness of the axial loading are remarkable.

Seismic performance assessment of reinforced concrete bridge columns under variable axial load

The current paper aims to assess analytically the seismic performance of reinforced concrete bridge columns under variable axial load. Variable axial load is very important to the ductility, strength, stiffness and energy dissipation of reinforced concrete bridge columns. The effects of variable axial loads on bridge columns are analysed to obtain a more realistic characterisation of the actual performance and capacity of bridge columns. A computer program, RCAHEST (reinforced concrete analysis in higher evaluation system technology), for the analysis of reinforced concrete structures was used. Models for material nonlinearity include tensile, compressive and shear models for cracked concrete and a model of reinforcing steel incorporating the smeared crack approach. The proposed numerical method for the seismic performance assessment of reinforced concrete bridge columns under variable axial load is verified by comparison of its results with reliable experimental results.

Experimental Investigation on Friction Performance of Mechanical Seals with a Laser-Textured Seal Face

Regular micro-surface structure in the form of micro-pores produced on the face of mechanical seals by laser technology can be used to improve the friction performance of the seal mating rings. A test rig with variable axial load was used to test laser-textured seal rings with micro-pores of various pore depth and pore ratio to study the effect of the laser-textured seal face structure parameters on the friction performance of mechanical seals. It is found that there are optimum texturing face parameters at which the friction torque and the face temperature rise of seal rings are minimum. Results of these tests show that the micro-pores on one of the seal mating faces can generate substantial hydrodynamic effect. Heat generation due to frictional contact on seal-ring surfaces is a major factor that causes deterioration of face seals and shortens their service life[1,2]. Excessive temperature rise can be avoided by improving structure of a seal surface. By means of laser technology return-flow structure, oblique line groove and spherical micro-pores are engraved on the seal face[3-5]. The research shows that substantial hydrodynamic effect can be generated between the seal faces with micro-pores[6-8]. In this study experiments are performed on laser-textured micro-pores seal faces at various axial loads to investigate the effect of the face structure and operating parameters on friction torque and face temperature rise.

변동 축하중을 받는 중공 철근콘크리트 교각의 비탄성거동에 관한 해석적 연구

이 연구의 목적은 변동 축하중을 받는 중공 철근콘크리트 교각의 비탄성 거동을 파악하는데 있다. 변동 축하중은 연성도, 강도, 강성, 에너지 소산 등에 큰 영향을 미친다. 사용된 프로그램은 철근콘크리트 구조물의 해석을 위한 RCAHEST이다. 재료적 비선형성에 대해서는 균열콘크리트에 대한 인장, 압축, 전단모델과 콘크리트 속에 있는 철근모델을 조합하여 고려하였다. 이 연구에서는 변동 축하중을 받는 중공 철근콘크리트 교각의 비탄성 거동의 파악을 위해 제안한 해석기법을 신뢰성 있는 연구자의 실험결과와 비교하여 그 타당성을 검증하였다. The purpose of this study is to investigate the inelastic behavior of hollow reinforced concrete bridge columns under varying axial load. The role of the variable axial load is very important in the ductility, strength, stiffness, and energy dissipation. A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The proposed numerical method for the inelastic behavior of hollow reinforced concrete bridge columns under varying axial load is verified by comparison with reliable experimental results.

Seismic Performance of Rectangular-Shaped Steel Piers under Cyclic Loading

The purpose of this experimental work is to investigate the seismic resistance characteristics of rectangular-shaped steel bridge piers commonly found in rigid frames, concerning the cross-sectional aspect ratios. To this end, seven specimens were tested under cyclic lateral loads. Six of them were under constant compressive axial load and one was under variable axial load. At first, the effects of web to flange aspect ratio ( W∕F ratio) on the differences between actual and estimated yield displacements, yield loads and flexural stiffness were examined. W∕F ratio of around 2.0 was found to offer minimum difference between those values. Secondly, the effects of W∕F ratio on ultimate strength, ductility, and energy dissipation capacity were determined. The highest strength was observed in columns with a W∕F ratio of about 2.0 while the highest ductility and cumulative energy dissipation capacity were in those with a W∕F ratio of around 1.60. Also, the effect of varying axial load on the strength was examin...

Improvement of the earthquake resistance of R/C beam-column joints under the influence of P-△ effect and axial force variations using inclined bars

In this study, theoretical and experimental results are presented which were obtained during an investigation of the influence of the <TEX>$P-{\Delta}$</TEX> effect that was caused by the simultaneous changing of the axial load P of the column and the lateral displacement <TEX>${\Delta}$</TEX> in the external beam-column joints. The increase or decrease of <TEX>${\Delta}$</TEX> was simultaneous with the increase or decrease of the axial compression load P and caused an additional influence on the aseismic mechanical properties of the joint. A total of 12 reinforced concrete exterior beam-column subassemblies were examined. A new model, which predicts the beam-column joint ultimate shear strength, was used in order to predict the seismic behaviour of beam-column joints subjected to earthquake-type loading plus variable axial load and <TEX>$P-{\Delta}$</TEX> effect. Test data and analytical research demonstrated that axial load changes and <TEX>$P-{\Delta}$</TEX> effect during an earthquake cause significant deterioration in the earthquake-resistance of these structural elements. It was demonstrated that inclined bars in the joint region were effective for reducing the unfavourable impact of the <TEX>$P-{\Delta}$</TEX> effect and axial load changes in these structural elements.

Controllability properties of a vibrating string with variable axial load

Controllability properties of a vibrating string with variable axial load

Behavior of Concrete-Filled Steel Tube Beam Columns

The behavior of concrete-filled circular and square steel tubular (CFT) beam columns with a variety of material strengths was investigated experimentally. The main test parameters are steel strength (400, 590, and 780 MPa), diameter- (width-) to-thickness ratio of steel tube, and concrete strength (40 and 90 MPa). The interior beam-column models were tested under constant axial compression and cyclic horizontal load with incrementally increasing lateral deformation to clarify the effects of the test parameters on the behavior. The exterior beam-column models were laterally loaded under variable axial load, including axial tension. The behavior of square beam columns subjected to biaxial bending was also investigated. The test results show that higher strength and thicker steel tubes give better overall behavior of the beam column, while higher strength concrete has an adverse effect on the behavior. Furthermore, computer simulations for the hysteretic behavior of CFT beam-column specimens are presented here. The analytical results show excellent agreement with the test results except for a few cases.

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.

Flexural and shear hysteretic behaviour of reinforced concrete columns with variable axial load

The importance of non-linear biaxial models that are applicable to the analysis of reinforced concrete members under cyclic and dynamic loads has been recognized. Variations in the axially applied force can influence strength, stiffness and deformation capacity of such members. In this study, an inelastic biaxial model based on plasticity theory, is proposed. This quadri-linear degrading model takes into account the effect of axial load variation on lateral deformation. The model predictions are examined against available experimental results. Using the developed model, the effect of various axial loading patterns on the lateral deformation of reinforced concrete columns is investigated.