Influence Of Axial Load Research Articles

Influence of axial loading and carbonation age on the carbonation resistance of recycled aggregate concrete

This paper presents the results of research on the carbonation resistance of recycled aggregate concrete (RAC) and natural aggregate concrete (NAC) under loading. The correlation between axial stress/carbonation age and the carbonation depth was analyzed. Based on theoretical analysis and experiment results, a model to predict the carbonation depth of RAC under axial stress was established. The carbonation depths of NAC and RAC under the same experimental parameters were compared and results were discussed. The experimental results show that the carbonation depth of RAC first decreases and then increases with an increase in axial compressive-stress ratio, and consistently increases with a growing of axial tensile-stress ratio. The experimental data also demonstrate that the carbonation depth increases with the carbonation age, and that the carbonation resistance of RAC is lower than that of NAC under the same experimental conditions.

The influence of vertical load to the natural vibration of series isolation system

The influence of axial load to the natural vibration of series isolation system is analyzed. The natural frequency of series isolation system is solved by differential quadrature method. According to the vertical load which is the main factor of natural vibration characteristic on the series isolation system, the parameter analysis is carried out. It should provide the basis for the vibration characteristic analysis for the structure of bearing on the top of first story column, and it can also provide evidence for the overall stability analysis of series isolation structure.

Analysis of stress and fatigue life of ball screw with considering the dimension errors of balls

Ball screw is a kind of mechanism, it is widely used in machinery and may be loaded with axial and radial load in practice. In the past, people calculated the contact load of ball screw which only bear axial load and didn't take the influences of dimension errors of balls into consideration. The authors take ball screw with outer cycling device as the research object, establish a calculation model to calculate the contact stress and fatigue life of ball screw by mechanics analysis. With a concrete example, the authors study the contact stress and fatigue life of three situations, the first one is that every ball has no dimension error, the second one is that only one ball has dimension error, and the third one is all balls have random dimension errors. The results have been analyzed and explained. At the same time, the authors analyze the influences of axial load, radial load and size accuracy of balls on the fatigue life of ball screw.

The dynamic stiffness matrix (DSM) of axially loaded multi-cracked frames

The presence of axial load, due to mechanical loading or to temperature effects, represents a strong peculiarity of frame applications both in direct and inverse problems involving the presence of cracks. The lack of explicit formulations of the Dynamic Stiffness Matrix (DSM) for cracked beam elements accounting for the influence of axial loads inspired and motivated the present work and the calculations herein reported. In this paper, the transcendental, frequency dependent, exact explicit expression of the DSM of an Euler-Bernoulli beam-column in presence of an arbitrary number of open cracks is presented. The advantage of the derived expression consists in a fourth order DSM whose dimension stays consistent independently as the number of cracks along the beam increases. Assembling DSMs of single beam-column elements, according to any required frame layout, leads to a number of degrees of freedom of the overall damaged frame structure exactly the same as those of the equivalent undamaged structure. Among other recent achievements on the vibration of damaged frames, the presented formulation provides a further original contribution, in the context of the dynamic stiffness method, which, in conjunction with the Wittrick & Williams algorithm, allows the exact evaluation of the frequencies and vibration modes of damaged frame structures in presence of axially loaded elements.

Model tests on piled raft subjected to lateral soil movement

Passive loadings due to lateral soil movement-induced activities are highly influencing the serviceability and safety of constructions. This research aims to investigate the influence of axial loads, sand density and the depth of moving soil on the lateral behaviour of piled raft under progressively moving sand. In order to achieve this goal taking into account the complex interaction effects of piles, cap and subsoil, a laboratory apparatus and small scale models have been designed and fabricated carefully to ensure a reasonable simulation of this geotechnical problem. It is found that the above parameters play an important role in the response of piled foundations. The value of soil displacement at which the measured moment reaches its ultimate value decreases as axial loads increase. Peak displacement of the raft has been found to be a function of soil density.

Influence of axial loads on the health monitoring of concrete structures using embedded piezoelectric transducers

Piezoceramic-based smart aggregate has been widely used to evaluate early-age concrete strength and to detect damage in concrete structures. In these structural health monitoring systems, they are generally verified and calibrated through experiments under load-free condition. However, the stress levels of actual concrete members are different. The microstructures of concrete will change with the variation of external load, and the high-frequency waves used in the monitoring system may be highly sensitive to these changes. In this study, the effects of axial compressive loading on the monitoring results are investigated. Specifically, three loading cases, that is, single cycle load, cyclic load, and step-by-step load, are employed to stress the concrete specimens embedded with smart aggregates. The amplitude and velocity of monitoring signals were measured before, during, and after each loading case. The test results show that the axial load lower than 30% of failure load still have a significant impact on the received signals. The amplitude attenuation is dependent on both frequency and load history, while the velocity is highly stress-dependent. The results indicate that the baselines of monitoring signals obtained from the same concrete structure in its healthy state can vary under different stress levels. The axial load variation should be carefully considered during the monitoring process. This study also provides a potential method to assess stress state in concrete structures using smart aggregates.

Deformation capacity of non-conforming r.c. columns under compressive axial load and biaxial bending

In a performance based approach, the knowledge of ultimate capacity of reinforced concrete (r.c.) columns subjected to simultaneous compressive axial load and biaxial bending becomes essential to correctly assess the seismic capacity of existing structures. In the present work, the reduction of ultimate deformation (i.e. rotational) capacity of r.c. members due to the two components of bending moment is analysed by using a specific simplified numerical model. The influence of axial load, geometry, amount of longitudinal reinforcement and mechanical properties on the ultimate chord rotation of r.c. columns is investigated on a dataset of 780 numerical tests on non-conforming columns with plain bars governed by flexural mode. Then, a practice-oriented formulation for the ultimate rotation domain, based on the Load Contour method extended to the chord rotations, is proposed and discussed.

The internal force relationship of rectangular and I-section for bi-linear hardening material with limit strain

Based on bilinear stress-strain constitutive law σ = f (e), the elastic to fully plastic analysis of bending of rectangular-section and bi-symmetrical I-section beams with the influence of axial load is presented for hardening material with limit strain. The variation of the applied bending moment with the axial force for the fully elastic, elastic-plastic, and fully plastic conditions is given in analytical form. The Internal force relationship of the elastic limit is the same for both hardening and non-hardening material and independent of the geometry of the beam section. However, for the elastic-plastic and plastic limits, the relationships are dependent of the hardening parameter β q, limit strain e lim and the geometry of the beam section for neutral axis (N.A) inside the cross section. When N.A outside the cross section, the relationships are dependent of hardening parameter β q and limit strain e lim but independent of the geometry of the beam section. The results given by the analytical expressions reduce to the ones for non-hardening material are in good agreement with the existing results.

Nonlocal vibration and stability of a multiple-nanobeam system coupled by the Winkler elastic medium

The nonlocal Euler–Bernoulli beam theory is proposed for the free vibration and stability analyses of a multiple-nanobeam system (MNBS) using the Eringen nonlocal continuum theory. It is assumed that every nanobeam in the system of multiple-nanobeams is simply supported and under the influence of axial load. The MNBS is embedded in the Winkler elastic medium. The motion of the system is described by a set of m homogeneous partial differential equations, which are derived by using D'Alembert's principle. Analytical solutions of free vibrations and buckling for a multiple-nanobeam system are obtained by using the classical Bernoulli–Fourier method and trigonometric method, for the case of the identical nanobeam. To validate the accuracy of application of trigonometric methods for a determined natural frequency and buckling load of MNBS, numerical solution of the characteristic polynomial are also conducted for a different number of nanobeams. Moreover, the finite difference method is employed to solve the system of partial differential equations of motion of MNBS, where good agreement with the analytical results is achieved. Numerical studies show the effect of the nonlocal parameter, stiffness of Winkler elastic medium and number of nanobeams for the free transversal vibration and buckling of MNBS. The presented analyses are very useful for the study and design of the nanoelectromechanical systems such as nano-resonators.

Influence of axial load on the lateral pile groups response in cohesionless and cohesive soil

The lateral response of single and group of piles under simultaneous vertical and lateral loads has been analyzed using a 3D finite element approach. The response in this assessment considered lateral pile displacement and lateral soil resistance and corresponding p-y curve. As a result, modified p-y curves for lateral single pile response were improved with respect to the influence of increasing axial load intensities. The improved plots can be used for lateral loaded pile design and to produce the group action design p-multiplier curves and equations. The effect of load combination on the lateral pile group response was performed on three pile group configurations (i.e., 2×1, 2×2 and 3×2) with four pile spacings (i.e., s = 2D, 4D, 6D and 8D). As a result, design curves were developed and applied on the actual case studies and similar expected cases for assessment of pile group behavior using improved p-multiplier. A design equation was derived from predicted design curves to be used in the evaluation of the lateral pile group action taking into account the effect of axial load intensities. It was found that the group interaction effect led to reduced lateral resistance for the pile in the group relative to that for the single pile in case of pure lateral load. While, in case of simultaneous combined loads, large axial load intensities (i.e., more than 6H, where H is lateral load values) will have an increase in p-multiplier by approximately 100% and will consequently contribute to greater group piles capacities.

Influence of axial load and loading path on the performance of R.C. bridge piers

Piers are the most vulnerable part of a bridge structure during an earthquake event. During Kobe earthquake in 1995, several bridge piers of the Hanshin Expressway collapsed for more than 600m of the bridge length. In this paper, the most important results of an experimental and analytical investigation of ten reinforced concrete bridge piers specimens with the same cross section subjected to constant axial (or variable) load and reversed (or one direction) cycling loading are presented. The objective was to investigate the main parameters influencing the seismic performance of reinforced concrete bridge piers. It was found that loading history and axial load intensity had a great influence on the performance of piers, especially concerning strength and stiffness degradation as well as the energy dissipation. Controlling these parameters is one of the keys for an ideal seismic performance for a given structure during an eventual seismic event. Numerical models for the tested specimens were developed and analyzed using SeismoStruct software. The analytical results show reasonable agreement with the experimental ones. The analysis not only correctly predicted the stiffness, load, and deformation at the peak, but also captured the post-peak softening as well. The analytical results showed that, in all cases, the ratio, experimental peak strength to the analytical one, was greater than 0.95.

改良9Cr-1Mo鋼周溶接継手管の内圧クリープ破断に及ぼす軸引張力の影響

改良9Cr-1Mo鋼周溶接継手管の内圧クリープ破断に及ぼす軸引張力の影響

Accelerated corrosion investigation of axially loaded reinforced concrete elements

Purpose – This paper aims to present results of an experimental investigation on a series of scaled reinforced concrete column elements which were subjected to chloride exposure under accelerated conditions under a concurrent service axial load, over a period. In the presence of an axial load, directed microcracks of increasing density and width are introduced in the concrete mass, depending on the axial load level. Such cracks are believed to enhance the intrusion rate of chlorides in the concrete, relative to what is obtained in the normally performed unloaded specimen tests. Design/methodology/approach – Eighteen column specimens were tested over two chloride exposure periods, of duration up to a maximum of six months. Three different service axial load levels were considered, namely, none, 22 per cent and 43 per cent of the normalized axial load capacity of the columns. Findings – The results indicate that the specimens loaded to the higher axial load, which closely resembles actual service situation of such type of elements, exhibited up to ten times faster rates of induced current flow under a constant applied voltage of 500 mV, compared to the unloaded and less loaded specimens. Practical implications – It is proven that the presence of axial load influences the rate of chloride ingress in columns and, therefore, should be taken into account in estimating the concrete cover of such elements in durability design. Originality/value – The influence of axial loading on corrosion rate has not been considered in published experimental and analytical studies of chloride ingression. These studies have typically so far considered the accelerated corrosion of unloaded column specimens.

Effect of axial loads in the seismic behavior of reinforced concrete walls with unconfined wall boundaries

About 2% of Reinforced Concrete (RC) buildings taller than nine stories suffered serious damage in structural walls during the 2010 Chile earthquake. The observed damage involved mostly crushing of concrete, buckling of vertical reinforcement, and opening of the horizontal reinforcement. This damage is attributed to poor concrete confinement in the web and boundaries, inadequate horizontal reinforcement detailing, and high axial loads. This research aims to reproduce the observed damage and evaluate the influence of axial loads in the seismic behavior of RC walls with unconfined boundaries. To achieve these objectives, three identical wall specimens were tested. The wall specimens were designed with characteristic wall detailing obtained from data of five damaged buildings. These wall specimens were tested under equal lateral displacement cycles and subjected to different axial load ratios. The flexural-compressive failure mode exhibited by damaged walls during the earthquake was reproduced in these tests. Experimental results indicate that high axial load has a significant effect on the seismic performance and failure mode of RC walls. Indeed, it triggers a dangerous brittle concrete crushing failure which occurs immediately after spalling of the concrete cover.

Experimental and Numerical Studies on the Seismic Performance of RC Interior Beam-Column Joints

This paper presents the results from Finite Element (FE) simulation on six Reinforced Concrete (RC) beam-column jointsand experimental study. The joints investigate dhave additional, vertically distributed reinforcement along the beams and lateral cyclic loading is applied, with constant axial force. Experimental results provide insight into the joint behaviour under conventional and unconventional displacement histories in terms of hysteresis loop, crack pattern and joint shear stress. The FE numerical models are validated by comparing the numerical results with experimental results obtained from six tested specimens and two specimens from previous studies. Parametric studies are performed to investigate the complex behaviour of the joints under the influence of axial loads as well as the numbers of vertically distributed reinforcement layers.

Influence of Axial Load on the Seismic Behavior of RC Beam-Column Joints with Wide Beam

Beam-column joints can play a key role on the seismic behavior of reinforced concrete buildings. Until now studies and experimental investigations on this topic have been mainly focused on beam-column joints with stiff beams, i.e. beams with height larger than the thickness of the adjacent floor slab. However, especially in the European residential building stock, frame structures are often equipped with wide - therefore rather flexible - beams. However, not many studies have been devoted so far to this type of connection, therefore an experimental investigation on full scale beam-column joints with wide beam was planned at the University of Basilicata and is currently in progress. In the present paper the main results of two cyclic tests are reported and discussed specifically analyzing the role of the axial load applied to the column on the joint performances and damage mechanisms. Test results highlights that the axial load value has a significant influence of on deformation capacity and ductility behavior.

Seismic assessment of existing RC shear walls non-compliant with current code provisions

This work forms part of a research programme to assess and strengthen existing reinforced concrete (RC) walls that were designed using older seismic codes. The main object of the present paper is to examine the behaviour of concrete shear walls that do not comply with modern seismic codes (Eurocode 2 (EC2) and Eurocode 8 (EC8)) and compare their experimental performance with the provisions for assessment of RC members included in EC8 Part 3. For this purpose, a series of six shear walls (height h = 1·40 m, length l = 0·74 m, thickness b = 0·10 m) was designed and tested under static cyclic loading. The wall specimens were characterised by various types of reinforcement arrangement, focusing on different amounts of shear reinforcement. The issues investigated are the failure modes, ductility level, the absence of confined boundary elements, the low amount of shear reinforcement, the influence of diagonal reinforcement and the influence of axial load. The experimental results are compared with the provisions included in EC8 Part 3, which predict the shear strength, the chord rotation ductility and the effective stiffness of RC shear walls.

Nonlinear behavior of reinforced concrete (RC) and steel fiber added RC (WS-SFRC) model piles in medium dense sand

Behavior of laterally loaded reinforced concrete (RC) model piles in medium dense sand was investigated in this study. Influence of steel fibers on nonlinear RC pile response was especially studied. Five types of model piles were tested under lateral loading and lateral+axial loading. RC-with bending reinforcement pile tests involved testing of model piles with and without shear reinforcement. Tests were performed also on concrete and steel fiber reinforced concrete piles in order to observe the influence of steel fibers by isolating them from bending and shear reinforcement. The steel fiber ratio by volume was decided as 1% based on previous experience. Prior to the model pile tests, bending tests were made on flexural elements to obtain the moment–curvature relationship. The study also enabled observation of loading rate effects and influence of axial load and steel fiber on reinforced pile response. Test results show that the RC-with steel fiber pile behavior is superior to the conventional RC pile under axial loading and different rate of loadings. It is concluded that steel fibers can be utilized to replace shear reinforcement to produce concrete piles with only bending reinforcement.

Three-dimensional analyses of concrete piles in clayey soils

The behaviour of solid circular concrete piles in clayey soils under a combination of lateral and vertical loading was investigated by numerical analysis. Piles with different lengths were considered, and ultimate lateral bearing capacity was calculated. The model was verified on the basis of data obtained from a previously published full-scale pile load test. The effect of axial loading on the ultimate lateral bearing capacity has been previously investigated in only a few studies. In this paper, particular attention was devoted to the influence of axial loading on lateral bearing capacity. In addition, a comparison between Flac three-dimensional results and both Allpile and Broms approaches was performed.

Influence of Axial Loads on the Nonplanar Vibrations of Cantilever Beams

Influence of Axial Loads on the Nonplanar Vibrations of Cantilever Beams