Columns Of Square Cross-section Research Articles

Experimental studies of non-centrally compressed corrosion-damaged reinforced concrete elements under dynamic loading

In the scientific literature, there is practically no analysis of the effect of corrosion damage on the operation of compressed reinforced concrete elements, especially on the stress-strain state of such structures under dynamic loading. For experimental studies, 37 reinforced concrete samples were made – columns of square cross-section with dimensions of 100×100mm, height of 700mm, extensions of 100×200mm were made in the supporting parts to create off-center compression. In the manufactured samples of reinforced concrete, local corrosion damage of concrete and reinforcement was created for accelerated corrosion of elements, a concentrated solution (37%) of hydrochloric acid (HCl) was used as an aggressor. The article describes experimental studies of non-centrally compressed reinforced concrete elements damaged by corrosion under dynamic loading. According to the load cell readings, it was recorded that corrosion damage leads to a decrease in the height of the compressed concrete zone, due to a decrease in the cross-section of the stretched reinforcement, as well as the lack of joint reinforcement with concrete. The obtained deformation diagrams of transverse, non-centrally compressed, corroded and undamaged samples based on glued strain gages on concrete and stretched reinforcement showed that these deformation diagrams fundamentally differ in shape. The deformations of reinforcement and concrete obtained as a result of a full-scale study made it possible to assess the stress-strain state of damaged and uncorroded structures according to the parameter Ne-1/r (curvature). The effect of corrosion damage on the nature of destruction of non-centrally compressed elements has been established.

Compressive behavior of concrete-filled steel tubular columns with internal high-strength steel spiral confinement

Concrete-filled steel tubular (CFST) columns have been extensively studied and widely used in practice. Existing research has shown that non-circular CFST columns is much less ductile than their circular counterparts, particularly when thin/high strength steel (HSS) tubes and high-strength concrete are used. To address this problem, a new form of CFST columns has recently been proposed by the first author. The new column consists of a steel tube filled with concrete that is confined with HSS spiral reinforcement typically with a yield stress exceeding 1000 MPa. These columns, referred to as confined concrete-filled steel tubular (CCFST) columns, also maintain the ease for connection to CFST or steel beams. This paper presents the results of a series of concentric axial compression tests on such columns of square cross-section to demonstrate their advantages. The experimental program included 13 CCFST columns, four CFST columns without internal spiral confinement, two hollow steel tube (HST) columns, and 11 circular HSS spiral-confined concrete columns. Three different compressive strengths and three HSS spiral pitches were examined in the experimental program. The CFST columns, HST columns, and HSS spiral-confined concrete columns were all tested under axial compression to gain a good understanding of the confinement mechanism in a CCFST column. The test results show that the new columns possess much greater ductility than those without internal spiral confinement, although the use of HSS spirals increases the steel volume by only a small percentage. It is also shown that the axial load-axial strain curve of a CCFST column can be conservatively predicted by summing the axial load-axial strain curves of the hollow steel tube without local buckling, the HSS spiral-confined concrete core, and the sandwiched concrete between the two.

Reliability Analysis of a Solid Timber Column Subjected to Axial and Lateral Loading

In this paper, a reliability analysis of a solid timber column of square cross section subjected to axial and lateral loading in accordance with the design requirements of Eurocode 5 is carried out. Compression and bending were the two failure criteria considered in the reliability investigation. The First Order Reliability method was employed to solve the limit state functions formed from the two failure criteria and was coded in MATLAB for quick estimation of the reliability indices. The results obtained showed that both the load and slenderness ratios have effects on the reliability of a solid timber column. The results of the sensitivity analysis carried out on the stochastic variables showed that the reliability indices decreased with increase in slenderness ratio for 3m, 4m and 5m length of column considering both the compression and bending failure modes and decreased with increase in load ratio for 3m, 4m and 5m length of column considering both the compression and bending failure modes. The reliability indices also decreased with increase in length of column mode and decreased with increase in ratio considering bending failure mode. The reliability indices were also found to decrease with increase in load ratio for varying values of axial and lateral loads at constant slenderness ratio and length of column considering compression and bending failure modes. The choice of adequate and suitable dimensions having a lower slenderness ratio will enhance the reliability of the column. Keywords- Reliability analysis, solid timber column, Eurocode 5, failure criteria, slenderness ratio

Experimental investigation of substandard RC columns confined with SRG jackets under compression

This paper aims to explore the behaviour of substandard reinforced concrete (RC) columns confined with Steel-Reinforced Grout (SRG) jackets under monotonically increasing uniaxial compression. A total of 24 specimens of short RC columns of square cross section were designed to fail due to longitudinal reinforcement buckling. Single-layered SRG jackets were applied to 18 of these specimens, whereas the rest served for control without SRG jackets. Parameters of this investigation were the type and density of the steel fabric as well as the corner radius of the cross section. The employed SRG jacketing managed to increase the strength and strain capacity and postpone the buckling of the longitudinal steel bars to occur at higher compressive strain level. Confinement effectiveness with respect to the lateral confining pressure exerted by the used SRG jacketing is discussed along with the observed mode of failure.

Intensification of mass transfer in a pulsed bubble column

The application of liquid pulsations to a classic bubble column substantially changes the hydrodynamics of bubble flow and the process of mass transfer. The paper presents a wide range of experimental results concerning the intensification of mass transfer in a pulsed bubble column of square cross section with side D=0.135m and slenderness ratio Hp/D ranging from 3 to 14.5. Experimental measurements were carried out at a frequency ranging from 1 to 70Hz and the amplitude of a disk vibration exciter from 0.25 to 2mm.The effect of liquid pulsation and volumetric gas flow rate on gas hold-up εG, mass transfer coefficient kLa and free liquid surface deflection Yi was investigated. It was shown that the application of pulsations to a bubble column caused a significant increase of gas hold-up and mass transfer coefficients. Based on the experimental results correlation equations for gas hold-up and mass transfer coefficient in a bubble column (with and without pulsations) were proposed and confirmed experimentally with an accuracy of ±15% and ±25%, respectively. A simple method in the form of a diagram has been proposed to determine optimal operating conditions of a pulsed bubble column.

Intensification of bubble column performance by introduction pulsation of liquid

The application of pulsations at determined parameters to a bubble column can significantly modify the process of mass transfer. However, determination of these parameters is so difficult that it has not been done so far in a satisfactory way even for technical purposes. Hydrodynamics of pulsed-bubble columns has been a subject of a few research works published so far. This paper presents results of studies on flow hydrodynamics of gas bubbles in a glass pulsed-bubble column of square cross section with side D=0.14 m and height H=2.25 m, filled with water. Experiments were carried out at air superficial velocity UG ranging from 1.6 to 13.9mm/s. Operating parameters of the pulsed-bubble column were measured in the frequency range f from 0 to 100Hz and the amplitude of vibration exciter Xp from 0.25 to 2mm. On the basis of results obtained so far it was shown that the application of pulsations at determined parameters to a bubble column caused a significant increase in the gas holdup. Based on the analysis of results of the measurements, model equations were developed to determine the Sauter diameters of bubbles and gas holdup during the pulsed-bubble column operation.

CFRP-Based Strengthening Technique to Increase the Flexural and Energy Dissipation Capacities of RC Columns

A strengthening technique, combining carbon fiber-reinforced polymer (CFRP) laminates and strips of wet layup CFRP sheet, is used to increase both the flexural and the energy dissipation capacities of reinforced concrete (RC) columns of square cross section of low to moderate concrete strength class, subjected to constant axial compressive load and increasing lateral cyclic loading. The laminates were applied according to the near surface mounted technique to increase the flexural resistance of the columns, while the strips of CFRP sheet were installed according to the externally bonded reinforcement technique to enhance the concrete confinement, particularly in the plastic hinge zone where they also offer resistance to the buckling and debonding of the laminates and longitudinal steel bars. The performance of this strengthening technique is assessed in undamaged RC columns and in columns that were subjected to intense damage. The influence of the concrete strength and percentage of longitudinal steel bars on the strengthening effectiveness is assessed. In the groups of RC columns of 8 MPa concrete compressive strength, this technique provided an increase of about 67% and 46% in terms of column’s load carrying capacity, when applied to undamaged and damaged columns, respectively. In terms of energy dissipation capacity, the increase ranged from 40%–87% in the undamaged columns, while a significant increase of about 39% was only observed in one of the damaged columns. In the column of moderate concrete compressive strength (29 MPa), the technique was even much more effective, since, when compared to the maximum load and energy dissipation capacity of the corresponding strengthened column of 8 MPa of average compressive strength, it provided an increase of 39% and 109%, respectively, showing its appropriateness for RC columns of buildings requiring upgrading against seismic events.

Ordered packings of bubbles in columns of square cross-section

The introduction of bubbles of equal size into a confined space with dimensions comparable to the bubble diameter generally leads to the formation of ordered foam structures. We present experimental data and computer simulations of the four simplest observed structures in columns of square cross-section. The topology of the ordered structure is dependent upon the ratio of bubble size to cross-sectional area of the enclosing tube. Ordered foam structures are observed to form over a smaller range of this parameter than in the cylindrical case.

Shrinkage and creep response of slender reinforced concrete columns under moment gradient: theory and test results

Slender structural members experience geometric non-linearities under eccentric axial compression. Reinforced concrete columns under sustained compression also experience material non-linearities owing to the viscoelastic effects attributable to shrinkage and creep. This paper presents a technique based on expanding the deflected shape of an eccentrically loaded column as a Fourier series to study the response of rectangular reinforced concrete columns under a sustained compressive force applied at each end with unequal eccentricities. The technique allows for the coupling of geometric non-linearity and viscoelasticity, and includes cracking of the concrete. Test results are reported on five slender columns of square cross-section (with L/D ratios of 33·3) under sustained axial compression applied eccentrically, and it is shown that the numerical scheme predicts the experimental results with good accuracy. These test results also add to the smallish pool of accurately conducted experiments on slender columns under sustained loading, and especially provide benchmark test data for unequal end eccentric loading for which test results seem somewhat scarce.

Shrinkage and creep response of slender reinforced concrete columns under moment gradient: theory and test results

Slender structural members experience geometric non-linearities under eccentric axial compression. Reinforced concrete columns under sustained compression also experience material non-linearities owing to the viscoelastic effects attributable to shrinkage and creep. This paper presents a technique based on expanding the deflected shape of an eccentrically loaded column as a Fourier series to study the response of rectangular reinforced concrete columns under a sustained compressive force applied at each end with unequal eccentricities. The technique allows for the coupling of geometric non-linearity and viscoelasticity, and includes cracking of the concrete. Test results are reported on five slender columns of square cross-section (with L/D ratios of 33·3) under sustained axial compression applied eccentrically, and it is shown that the numerical scheme predicts the experimental results with good accuracy. These test results also add to the smallish pool of accurately conducted experiments on slender columns under sustained loading, and especially provide benchmark test data for unequal end eccentric loading for which test results seem somewhat scarce.

Experimental study on convective coefficients in a slurry bubble column

The main objective of this work was to determine the influence of gas and slurry velocities and solid load concentration on experimental convective heat transfer coefficients (h), for a three-phase suspension in cross flow around a square in-line tube array. Experiments were performed in a pilot scale equipment conformed by a column of square cross section. In the central part of this equipment there is a bank of 49 tubes with a S T =S L =4.4 cm. The system used was air, tap water and sieved sand at average particle diameter of 505 μm. The velocities of liquid and gas phases were varied from 0.28 to 0.60 cm/s and from 1.36 to 2.45 cm/s, respectively; and the solid load concentration from 0 to 30% w/w. The results allow to conclude that h for a three-phase system is larger than either for a two-phase or one-phase system. The presence of solid phase enhances the heat transfer, however, this increase is less evident for high values of solid Concentration.

Electronic states and optical properties of silicon nanocrystals

Photoluminescence properties of nanometer Si-based materials have motivated a great deal of experimental and theoretical research effort because they exhibit favourable applications in opto-electronic devices. The quantum confinement effect of photoexcited carriers within nanocrystallites was mainly proposed to be responsible for the visible luminescence from these materials. In this work, the electronic states and optical transition properties of Si nanocrystals are studied by means of an sp3s* semiempirical tight-binding approximation and supercell model, in which the silicon nanocrystals are columns of square cross-section with width from a to 7a, where a is the lattice constant. The calculations have been carried out for light polarized in the [100] direction, i.e., perpendicular to the wire alignment. We present the dependence of the imaginary part of the dielectric function on the quantum confinement within two different schemes, which are applied and compared.

Band-Gap Structure of Spectra of Periodic Dielectric and Acoustic Media. II. Two-Dimensional Photonic Crystals

We consider the two-component dielectric medium consisting of a periodic array of parallel air columns of square cross section embedded into a lossless optically dense host material with the dielectric constant $\zeta > 1$. We show that if$\zeta $ is large enough and the relative distance $\delta $ between the air columns is such that $\zeta \delta \gg 1$ and $\zeta \delta ^2 \ll 1$, then the corresponding Maxwell operator has a series of gaps in the spectrum. We also provide some analytic formulas that enable one to detect location of bands and gaps in the spectrum. In particular, the typical wavelength exhibiting a photonic band gap is $2\pi L\sqrt {\zeta \delta } $ where L is the distance between the axes of adjacent air columns. We also give some estimates on the space distribution of electric field energy for different eigenmodes.

The Surface Evolver and the stability of liquid surfaces

The Surface Evolver is an interactive program for studying the shapes of liquid surfaces. Recently added features permit the calculation of the Hessian matrix of second derivatives of the energy. The Hessian can be used for fast convergence to an equilibrium, and eigenvalue analysis of the stability of that equilibrium. This paper describes the use of the Hessian by the Surface Evolver, presents some sample stability analyses, and gives some numerical results on the accuracy and convergence of the methods. It is also shown how one can evolve unstable surfaces.

The negative wake in a second-order fluid

To investigate the origin of negative wakes in viscoelastic fluids, we used a perturbation method to calculate the flow induced by a solid sphere falling slowly through a viscoelastic fluid in a vertical column of square cross-section. The effects of normal stresses and inertia were determined by solving the perturbation problems numerically using a finite element method. The normal stresses give rise to a negative wake behind the sphere and a reversed flow at the front stagnation point.

Flow characteristics in a rectangular spout-fluid bed

Hydrodynamic studies are reported on six different materials, spouted and spout-fluidised with air in a column of square cross-section, using nozzles of five different sizes. Correlations for minimum spout-fluidised flow rate in cylindrical columns were investigated for this geometry. New correlations for predicting the minimum spouting velocity and the minimum spout-fluidising velocity are developed. The velocity profile in the bed agreed well with the observations of Lim and Grace [1], and Mamuro and Hattori [2].

Gas hold-up and liquid circulation in internal loop reactors containing highly viscous newtonian and non-newtonian liquids

When highly viscous liquids are used in bubble columns, the bubble population is bimodal; most of the gas passes through as large bubbles, but there is a substantial hold-up of small bubbles whose contribution to the gas flow is small. This paper describes flows of this nature for internal loop reactors (ILRs): an ILR is simply a bubble column containing an internal draught tube to promote liquid circulation. The gas flow enters at the bottom of the draught tube, which contains large and small bubbles: the large bubbles disengage at the top; the small bubbles recirculate with the downflowing liquid outside the draught tube. Two ILRs were used for measurements of gas hold-up, large bubble rise velocity and liquid circulation velocity: (i) a column of diameter 0.15 m containing a draught tube of diameter 0.09 m; (ii) a column of square cross section, 0.6 × 0.6 m, containing a square draught tube, 0.3 × 0.3 m. The rising velocity of single injected bubbles was also measured in clear liquid with no distributor gas flow in a 0.08 m diameter cylindrical column. The results show that the large bubble rising velocity is, to a first approximation, governed by equations appropriate for inviscid motion, notwithstanding the high viscosities of the liquids used: evidently inertial effects are dominant. The small bubbles receive only about 0.3–0.5% of the gas flow. The balance between this input and the rate of coalescence determines the small bubble hold-up. The mean residence time of small bubbles may well be comparable with the “half-life” for oxygen transfer from these bubbles. Hence the common assumption made in mass transfer calculations, that the oxygen concentration in these bubbles is always in equilibrium with the liquid, may not be valid. The liquid circulation velocities in the ILRs were measured by neutrally buoyant flow followers, and calculated from a pressure balance round the circulation loop: the expression used to calculate the pressure loss in the riser had to be modified to take account of liquid carried up by each large bubble; apparently this liquid flow did not contribute to the pressure loss.

Strength of Thin‐Walled Square Steel Box Columns

The present study is concerned with the strength of thin-walled steel box columns of square cross section that are pinned and subjected to axial load and equal moment at the ends. The local buckling in the component plates is allowed for by using piecewise linear stress-strain curves that are approximations of previous research findings. Due allowance is made to account for the effect of residual stresses due to welding and overall column imperfections upon the ultimate strength. The column analysis is carried out by integrating numerically along the length the moment-curvature-thrust relationships. This method of column analysis is free from iteration and could predict the ultimate strength accurately. The results are presented in the form of column curves and interaction diagrams for typical values of plate slenderness ratios, residual stress levels, and initial column imperfections. Comparisons are made between the proposed column curves and multiple column curves of ECCS and SSRC.

Design of beneficial geometric imperfections for elastic collapse of thin-walled box columns

This paper deals with the design of beneficial geometric imperfections for elastic collapse of thin-walled box columns of square cross-section under axial compression. From the point of view of high elastic post-collapse stiffness, it is desirable to force the column to collapse with a larger number of axial half-waves than with the preferred wave number which is approximately equal to the aspect ratio. By introducing a beneficial geometric imperfection with such a larger wave number and if the magnitude of such imperfection exceeds the transitional value, it is found that the column will collapse in the beneficial mode in the initial postbuckling (assume to be elastic) finite-deflection regime. Equilibrium paths of typical box columns are plotted and analyzed. The two-mode potential energy is found to fall into the category of a double-cusp catastrophe.