Reference Column Research Articles

Stability of Slender Masonry Columns with Circular Cross-Section under Their Own Weight and Eccentric Vertical Load

ABSTRACTThis work concerns the stability of unreinforced masonry slender circular cross-sectional columns subjected to their own weight and eccentric vertical load. Cantilever columns are examined, considering that the material has infinitely linear elastic behavior in compression and has no tensile strength. For the analysis, an existing numerical model and solution procedure developed for the stability analysis of masonry elements with rectangular cross-section are utilized and adapted to the circular columns. For the instability of the columns, an appropriate criterion that relates the top lateral deflection to the intensity of the applied eccentric vertical load is employed. By considering a reference column, critical buckling load is obtained, behavior of the column interpreted and efficiency of the numerical model emphasized. Performing a nonlinear buckling analysis using a general purpose software on this reference column, obtained results are compared with those of the adapted procedure of the present study. Implementing parametric analyses on reference column, effects of the column slenderness, eccentricity of vertical load, elastic modulus, and self-weight on the buckling load are investigated. Presented calculation procedure provides a useful tool in order to calculate the critical loads or to check the stability of masonry circular columns.

Behavior of reinforced concrete columns strenghtened by partial jacketing

This article presents the study of reinforced concrete columns strengthened using a partial jacket consisting of a 35mm self-compacting concrete layer added to its most compressed face and tested in combined compression and uniaxial bending until rupture. Wedge bolt connectors were used to increase bond at the interface between the two concrete layers of different ages. Seven 2000 mm long columns were tested. Two columns were cast monolithically and named PO (original column) e PR (reference column). The other five columns were strengthened using a new 35 mm thick self-compacting concrete layer attached to the column face subjected to highest compressive stresses. Column PO had a 120mm by 250 mm rectangular cross section and other columns had a 155 mm by 250mm cross section after the strengthening procedure. Results show that the ultimate resistance of the strengthened columns was more than three times the ultimate resistance of the original column PO, indicating the effectiveness of the strengthening procedure. Detachment of the new concrete layer with concrete crushing and steel yielding occurred in the strengthened columns.

Column Selection for Biomedical Analysis Supported by Column Classification Based on Four Test Parameters.

This article focuses on correlating the column classification obtained from the method created at the Katholieke Universiteit Leuven (KUL), with the chromatographic resolution attained in biomedical separation. In the KUL system, each column is described with four parameters, which enables estimation of the FKUL value characterising similarity of those parameters to the selected reference stationary phase. Thus, a ranking list based on the FKUL value can be calculated for the chosen reference column, then correlated with the results of the column performance test. In this study, the column performance test was based on analysis of moclobemide and its two metabolites in human plasma by liquid chromatography (LC), using 18 columns. The comparative study was performed using traditional correlation of the FKUL values with the retention parameters of the analytes describing the column performance test. In order to deepen the comparative assessment of both data sets, factor analysis (FA) was also used. The obtained results indicated that the stationary phase classes, closely related according to the KUL method, yielded comparable separation for the target substances. Therefore, the column ranking system based on the FKUL-values could be considered supportive in the choice of the appropriate column for biomedical analysis.

Behaviour of Reinforced Concrete Columns Strengthened with Ferrocement under Compression Conditions: Experimental Approach

This paper reports a study based upon experimental investigation which aims to assess the behaviour of reinforced concrete columns strengthened with a new configuration of steel wire mesh as part of ferrocement layer under the action of axial compression loads. Square and circular small scale columns with three different slenderness ratios of 5, 6.7 and 10 were adopted. A comprehensive experimental progarmme was then running to measure the load capacity and both lateral and vertical displacements. The failure mode was also monitored for each tested case. The results obtained was compared with the reference column samples (without wire mesh) and with some expressions suggested by ACI Code. The experimental results showed that the most influential parameter on the property of load carrying capacity is the slenderness of column. As the slenderness increases, the load capacity clearly decreases. The use of wire mesh enhanced the capability of column to resist the axial loads due to confinement role provided by such material. The maximum percentage increase in load carrying capacity for the modified columns compared with those for the reference samples was 53% for the circular column at slenderness ratio of 10. The critical path of the failure mode was similar for all of the tested columns and normally began from the top or bottom ends, then, in some cases, passed through the middle zone of the column. A suitable expression was suggested to be used for calculating the modulus of elasticity of the tested column based upon the value of load carrying capacity under compression loads.

Optimising column family for OLAP queries in HBase

Apache HBase is a column-oriented NoSQL key-value store built on top of the Hadoop distributed file-system. Logically, columns in HBase are grouped into column families. Physically, all columns in one column family are stored in the same set of files. Therefore the division of column families is closely related to the response time for a specific row query. In this paper, a new evolutionary algorithm is designed and applied to group columns and find the optimum column family schema for the given user queries. The reading performance of the optimised column family schema is evaluated on a real dataset provided by ZANOX. It is shown that by using the found optimised column family schema, the reading performance while executing OLAP queries is improved with a statistical significance. Queries from a test set show that the average response time is reduced by up to 72% compared to reference column family schemas.

Effect of thickness of inner carbon fibre reinforced polymer tubes on axial compressive behaviour of steel-concrete-carbon fibre reinforced polymer-concrete columns

Steel-concrete-carbon fibre reinforced polymer-concrete columns (SCCC columns) have been introduced as a new form of hybrid columns by first author. An SCCC column consists of an outer steel tube, an inner carbon fibre reinforced polymer tube, an annular concrete between two concentric tubes and a core concrete encased in carbon fibre reinforced polymer tube. This paper presents the results of a test study that was conducted to investigate the effect of thickness of inner carbon fibre reinforced polymer tube on the axial compressive behaviour of SCCC columns. Four SCCC columns with carbon fibre reinforced polymer tubes of two different thicknesses of 0·167 mm and 0·334 mm in addition to two reference columns without carbon fibre reinforced polymer tube were prepared. All the six short columns, each 260 mm in diameter, 780 mm in height, were manufactured and tested to failure under pure axial compression. Test results demonstrate that the circular hybrid SCCC columns are of excellent axial compression behaviour, and that increasing the thickness of inner carbon fibre reinforced polymer tube can increase the ultimate axial load capacity and ultimate axial strain of SCCC columns remarkably.

Experimental and numerical study of the behaviour of heat-damaged RC circular columns confined with CFRP fabric

This paper describes an experimental and numerical study of the behaviour of RC columns, damaged by heating and subsequently wrapped by CFRP. Twenty large-scale (Ø 204×750mm) nominally identical reinforced concrete (RC) columns were tested. Six columns were left as reference columns and 14 were heated and cooled down under 30% of maximum load at ambient temperature. Subsequently, 8 were confined with carbon fibre reinforced polymer (CFRP) fabrics. A photogrammetric method using the digital image correlation technique (DICT) was used to measure the strain variation over the surfaces of all columns. The experimental parameters included unheated and heat-damaged columns, level of heat exposure and number of CFRP fabric layers. Finite element analysis (FEA) was conducted using ATENA-GiD software, which is only applicable to RC elements. It was found that the CFRP can significantly increase the strength and ductility of unheated and heat-damaged columns. It was also noted that it is possible to repair or even restore the lost strength of columns damaged by elevated temperature, depending on the performance of the CFRP material. The finite element models (FEMs) were able to reasonably predict the experimental behaviour. The FEMs were used to undertake a parametric study to determine the influence of factors not directly considered by the experimental program.

Sum of ranking differences to rank stationary phases used in packed column supercritical fluid chromatography

The identification of a suitable stationary phase in supercritical fluid chromatography (SFC) is a major source of difficulty for those with little experience in this technique. Several protocols have been suggested for column classification in high-performance liquid chromatography (HPLC), gas chromatography (GC), and SFC. However, none of the proposed classification schemes received general acceptance. A fair way to compare columns was proposed with the sum of ranking differences (SRD). In this project, we used the retention data obtained for 86 test compounds with varied polarity and structure, analyzed on 71 different stationary phases encompassing the full range in polarity of commercial packed columns currently available to the SFC chromatographer, with a single set of mobile phase and operating conditions (carbon dioxide–methanol mobile phase, 25°C, 150bar outlet pressure, 3ml/min). First, a reference column was selected and the 70 remaining columns were ranked based on this reference column and the retention data obtained on the 86 analytes. As these analytes previously served for the calculation of linear solvation energy relationships (LSER) on the 71 columns, SRD ranks were compared to LSER methodology. Finally, an external comparison based on the analysis of 10 other analytes (UV filters) related the observed selectivity to SRD ranking. Comparison of elution orders of the UV filters to the SRD rankings is highly supportive of the adequacy of SRD methodology to select similar and dissimilar columns.

Cyclic Loading Test of Unbonded and Bonded Posttensioned Precast Segmental Bridge Columns with Circular Section

Four 1/4-scale precast segmental bridge columns (PSBC) with different reinforcement types and arrangements and one monolithic reference column (MRC) were designed and tested under cyclic quasi-static loading. Both UPC (PSBC with unbonded tendons only) and UPCE (PSBC with unbonded tendons and bonded mild steel bars) use unbonded posttensioned (PT) strands to connect the segments. Bonded energy dissipation (ED) bars were added in UPCE to increase the ED ability of unbonded PSBC. Specimens BPC (PSBC with fewer bonded PT bars) and BPCII (PSBC with more bonded PT bars) use bonded PT bars to combine the segments together. The unbonded length was set in ED bars to delay the low-cycle fatigue damage. Test results showed PSBC only has minor concrete cracks or crushing at lower joints. The unbonded PT PSBC with ED bars had higher lateral strength, lower residual drift, and comparable ED with MRC. The bonded PT bar PSBC with appropriate bar arrangement also showed high lateral strength and medium energy-dissipation ability. However, bonded PT PSBC experienced large PT stress loss, which leads to a residual drift of 3% when unloading from 6% drift.

Design of C18 Organic Phases with Multiple Embedded Polar Groups for Ultraversatile Applications with Ultrahigh Selectivity.

For the first time, we synthesized multiple embedded polar groups (EPGs) containing linear C18 organic phases. The new materials were characterized by elemental analysis, IR spectroscopy, (1)H NMR, diffuse reflectance infrared Fourier transform (DRIFT), solid-state (13)C cross-polarization magic angle spinning (CP/MAS) NMR, suspended-state (1)H NMR, and differential scanning calorimetry (DSC). (29)Si CP/MAS NMR was carried out to investigate the degree of cross-linking of the silane and silane functionality of the modified silica. Solid-state (13)C CP/MAS NMR and suspended-state (1)H NMR spectroscopy indicated a higher alkyl chain order for the phase containing four EPGs than for the phase with three EPGs. To correlate the NMR results with temperature-dependent chromatographic studies, standard reference materials (SRM 869b and SRM 1647e), a column selectivity test mixture for liquid chromatography was employed. A single EPG containing the C18 phase was also prepared in a similar manner to be used as a reference column especially for the separation of basic and polar compounds in reversed-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC), respectively. Detailed chromatographic characterization of the new phases was performed in terms of their surface coverage, hydrophobic selectivity, shape selectivity, hydrogen bonding capacity, and ion-exchange capacity at pH 2.7 and 7.6 for RPLC as well as their hydrophilicity, the selectivity for hydrophilic-hydrophobic substituents, the selectivity for the region and configurational differences in hydrophilic substituents, the evaluation of electrostatic interactions, and the evaluation of the acidic-basic nature for HILIC-mode separation. Furthermore, peak shapes for the basic analytes propranolol and amitriptyline were studied as a function of the number of EPGs on the C18 phases in the RPLC. The chromatographic performance of multiple EPGs containing C18 HILIC phases is illustrated by the separation of sulfa drugs, β-blockers, xanthines, nucleic acid bases, nucleosides, and water-soluble vitamins. Both of the phases showed the best performance for the separation of shape-constrained isomers, nonpolar, polar, and basic compounds in RPLC- and HILIC-mode separation of sulfa drugs, and other polar and basic analytes compared to the conventional alkyl phases with and without embedded polar groups and HILIC phases. Surprisingly, one phase would be able to serve the performance of three different types of phases with very high selectivity, and we named this phase the "smart phase". Versatile applications with a single column will reduce the column purchasing cost for the analyst as well as achieve high separation, which is challenging with the commercially available columns.

Analysis of the behavior of reinforced concrete columns strengthened with sleeve wedge bolts and a self compacting concrete layer

Strengthening of reinforced concrete columns by jacketing is one of the most common structural rehabilitation techniques in Brazil. For adequate performance, it is necessary, among others, to avoid detachment of the new concrete layer (strengthening material) from the old concrete substrate when the strengthened member is again in service conditions. This paper describes the test results of eight reinforced concrete rectangular columns subjected to combined compression and one-axis bending to evaluate the efficiency of using sleeve wedge bolts across the new concrete/old concrete interface to avoid detachment. The strengthening technique, in this case, consists of adding a layer of self-compacting concrete to one face of the column. Two columns tested were monolithic and named PO (original column) e PR (reference column). The other six columns were strengthened using a new 35 mm thick self-compacting concrete layer attached to the column face subjected to highest compressive stresses. Column PO had a 120mm by 250 mm rectangular cross section and its results gave information about column behavior without the use of strengthening. Column PR had a 155mm by 250 mm rectangular cross section and its cross section dimensions matched the strengthened columns but it was cast monolithically. To improve bond conditions between the existing concrete and the new concrete, the concrete surface was roughened and the outermost aggregate was exposed using hydro jetting. Holes along the concrete surface were made to insert the wedge bolts responsible for increasing the bond between the two concrete surfaces. The difference among the six strengthened columns was the position and amount of bolts used. Results indicate that the position and amount of the bolts alters significantly the strength capacity of the columns, since premature rupture by concrete detachment was delayed.

Axial compressive behaviour of GFRP tube reinforced concrete columns

This paper presents an innovative reinforcing scheme for concrete columns using glass fibre reinforced polymer (GFRP) tubes. GFRP tubes (solid and perforated) have been placed into concrete columns to provide reinforcement in both longitudinal and transverse directions. In this study, 14 columns with 150mm diameter and 300mm height have been cast and tested under axial compression. The columns have been divided into seven groups; each group contains two columns. The first group of columns are the reference columns without any reinforcement. The other six groups of columns are reinforced with solid and perforated (axially and diagonally) GFRP tubes. The test results show that GFRP tubes are effective in improving the strength and the ductility capacity of FRP (fibre reinforced polymer) tube reinforced concrete (FTRC) columns. Also, perforated GFRP tubes have been found effective in integrating concrete core with concrete cover. However, axially perforated FTRC columns have been found most effective considering the strength and the ductility capacity of the concrete columns. In addition to the experimental investigations, numerical simulations have been carried out to assess the influence of tube perforations on the behaviour of FTRC columns. The simulation results show that reduction in the hole diameter, rather than increase in the vertical hole spacing, is the most effective in increasing the strength and the ductility capacity of FTRC columns.

Performance Analysis of CFRP Composite Strips Confined RC Columns under Axial Compression

In an attempt to mitigate the high cost of FRP composite strengthening, an experimental investigation was carried out that sought to achieve efficient and most favorable FRP strengthening using CFRP composite strips. 50 mm wide CFRP composite strips were used in two different spacings (20 mm and 40 mm) to confine columns. The test results of the column confined with smaller spacing (20 mm) showed significant restraint of axial deformation of the column and enhanced the strength capacity to a maximum of 99.20% compared to that of reference column. In contrast, the column confined by strips with larger spacing (40 mm) failed by crushing of concrete alone, which occurred even before the CFRP strips reached their ultimate strain. In addition, the embodied energy that exists in the CFRP strips could not be utilized effectively. The stress and strength enhancement ratio of this present study was compared with the previous research that has been conducted on columns confined with full wrapping. From the obtained results, it is recommended that CFRP strips with a spacing of 20 mm be used to improve the strength capacity of the RC column; in addition, this wrapping technique provides economic benefits compared to a column confined with full wrapping.

Considerations regarding autologus blood injection for tennis elbow tendinopathy.

Dear Editor, We read with interest the article by Karimi Mobarakeh et al. (1) titled as “Autologous Blood Injection for Treatment of Tennis Elbow”. We would like to congratulate the authors for taking up such a study. However, we have several considerations regarding this manuscript: What was the number of patients who received the local steroid injections before being in the study and also, what was the duration from the last steroid injection before patients were given the autologous blood injection. After injection, the authors state that “Immobilization via a long arm cast was done for 3 weeks”. Unfortunately, the authors have omitted to mention the reasons leading to cast immobilization. Also, there is no information concerning the occurrence of post injection stiffness of elbow when a 3 weeks long arm cast immobilization was maintained. In the Results column, the manuscript states that “The mean duration of symptoms was 7.9 ± 1.3 months. Table 1 shows results of NPS and VAS before and 1, 3 and 6 months after ABI”. However, there is no table available to support the results. Furthermore, in the results column, the authors say that “The level of patient satisfaction on Verhaar scale is shown in Figure 1; 84% of patients showed a high level of satisfaction at the end of the study. None required a second injection, although some of them were obliged to change their activities”. However, no Figure is shown to justify such data. The authors have mentioned that their results were comparable to other studies. However, the studies mentioned in the reference column had used ultrasound guided autologous blood injection for tennis elbow (2). Only one study from the references has used autologous blood injection similar to the present study (3). We would rather suggest the authors to compare their results with comparable studies to justify their implication for the healthcare policy making. We hope our suggestions will be taken with a positive note and the revised manuscript with all missing Figures and Tables will be made available.

Possible resolution gain in enantioseparations afforded by core–shell particle technology

Whether columns packed with core–shell particles may outperform those packed with fully porous particles for chiral separations is controversial. The potential advantages of such columns are investigated from a theoretical viewpoint. The height equivalent to a theoretical plate (HETP) associated to the slow adsorption-desorption process typical of chiral chromatography was derived from the Laplace transform of the general rate model of chromatography for core–shell particles. The relationship between the resolution factor and the core-to-particle diameter ratio is predicted at constant selectivity. The calculations are based on a complete set of actual kinetic parameters (longitudinal diffusion, eddy dispersion, intra-particle diffusivity, and adsorption-desorption constant) measured for a reference column packed with Lux Cellulose-1 fully porous particles. If we compare columns packed with the best procedure available in either case, the results demonstrate that those packed with core–shell particles may outperform to a degree those packed with fully porous particles. The minimum reduced HETP could decrease from 2.0 to 1.7. The maximum relative gain in resolution is about 10%, which is not negligible for critical enantioselective-separations. This gain is observed only if the packing uniformity of the core–shell particles is achieved.

Comparison of core–shell and totally porous ultra high performance liquid chromatographic stationary phases based on their selectivity towards alfuzosin compounds

This paper focuses on the application of a column classification system based on the Katholieke Universiteit Leuven for the characterization of physicochemical properties of core–shell and ultra-high performance liquid chromatographic stationary phases, followed by the verification of the reliability of the obtained column classification in pharmaceutical practice. In the study, 7 stationary phases produced in core–shell technology and 18 ultra-high performance liquid chromatographic columns were chromatographically tested, and ranking lists were built on the FKUL-values calculated against two selected reference columns. In the column performance test, an analysis of alfuzosin in the presence of related substances was carried out using the brands of the stationary phases with the highest ranking positions. Next, a system suitability test as described by the European Pharmacopoeia monograph was performed. Moreover, a study was also performed to achieve a purposeful shortening of the analysis time of the compounds of interest using the selected stationary phases. Finally, it was checked whether methods using core–shell and ultra-high performance liquid chromatographic columns can be an interesting alternative to the high-performance liquid chromatographic method for the analysis of alfuzosin in pharmaceutical practice.

Copolymer-grafted silica phase from a cation–anion monomer pair for enhanced separation in reversed-phase liquid chromatography

This work reports a new imidazolium and L-alanine derived copolymer-grafted silica stationary phase for ready separation of complex isomers using high-performance liquid chromatography (HPLC). For this purpose, 1-allyl-3-octadecylimidazolium bromide ([AyImC18]Br) and N-acryloyl-L-alanine sodium salt ([AAL]Na) ionic liquids (IL) monomers were synthesized. Subsequently, the bromide counteranion was exchanged with the 2-(acrylamido)propanoate organic counteranion by reacting the [AyImC18]Br with excess [AAL]Na in water. The obtained IL cation-anion monomer pair was then copolymerized on mercaptopropyl-modified silica (Sil-MPS) via a surface-initiated radical chain-transfer reaction. The selective retention behaviors of polycyclic aromatic hydrocarbons (PAHs), including some positional isomers, steroids, and nucleobases were investigated using the newly obtained Sil-poly(ImC18-AAL), and octadecyl silylated silica (ODS) was used as the reference column. Interesting results were obtained for the separation of PAHs, steroids, and nucleobases with the new organic phase. The results showed that the Sil-poly(ImC18-AAL) presented multiple noncovalent interactions, including hydrophobic, π-π, carbonyl-π, and ion-dipole interactions for the separation of PAHs and dipolar compounds. Only pure water was sufficient as the mobile phase for the separation of the nucleobases. Ten nucleosides and bases were separated, using only water as the mobile phase, within a very short time using the Sil-poly(ImC18-AAL), which is otherwise difficult to achieve using conventional hydrophobic columns such as ODS. The combination of electrostatic and hydrophobic interactions are important for the effective separation of such basic compounds without the use of any organic additive as the eluent on the Sil-poly(ImC18-AAL) column.

Experimental Investigation for Horizontal Ultimate Bearing Capacity and Target Ductility Factor Improvement Results of the RC Column Reinforced by AFL with Damages

Deem test results from the low reversed cyclic loading quasi-static test with 2 RC columns as the basic information of secant stiffness damage of the reference column and take use of the TMS instrument in the test to artificially make the damage percentage of secant stiffness of the RC column as 33%, 50% and 66%, 6 damaged columns in total; reinforce the 6 damaged columns and 2 undamaged ones under the same conditions with AFL, through quasi-static contrast test. Test results show that it is able to effectively boost horizontal ultimate bearing capacity and ductility deformability of the RC columns with AFL for reinforcement; besides, there is a linear function relationship between horizontal ultimate bearing capacity, target ductility factor, and damage percentage of secant stiffness.

Compressive Behaviour of RC Column with Fibre Reinforced Concrete Confined by CFRP Strips

The structural application of synthetic fibre reinforced concrete (FRC) has become widespread in the construction industry in order to satisfy the requirement of the earthquake resistant structures. Research conducted so far are focused on the structural behaviour of RC column externally confined with FRP composites, while studies are needed to address the behaviour of FRP strengthened RC column fabricated using fibre reinforced concrete. With the intention that the experimental investigation was carried out to evaluate the feasibility use of CFRP composite strips in strengthening of RC column made with fibre reinforced concrete. Circular synthetic Polypropylene fibre was used in the rate of 0.50% in the volume of concrete. CFRP strips having a width of 50 mm were used to confine the column and the experimental parameters were effective spacing between the CFRP strips (20 mm and 30 mm) and the number of CFRP layers (one, two and three). The externally bonded CFRP strips counteract the lateral expansion of the concrete significantly by providing restraining effect and thus effect enhanced the stiffness of the column. The column strengthened with CFRP strips showed a maximum of 198.87% and 91.75% enhancement in axial deformation control and ultimate strength, respectively, compared to that of reference column. From the test results obtained, it is suggested that CFRP strips with the spacing of 20 mm and 30 mm can be used in strengthening of RC column made with FRC; however the column confined with 30 mm spacing provides an economical advantage compared to that of 20 mm spacing.

Experimental Research on Seismic Behavior of Seismically Damaged RC Frame Column Strengthened with Sprayed Hybrid BF/CFRP

This experimental program was designed for investigating the seismic behaviors and strengthening effect of pre-damaged RC frame columns retrofitted with sprayed BFRP and hybrid BF/CFRP. Four RC frame column specimens, among which one was unstrengthened and three was pre-damaged and strengthened with sprayed FRP, were tested under an incremental loading procedure of the pseudo-static, cyclic shear loads combined with constant gravity loads. The test results including the failure mode, ultimate bearing load capacity, load-displacement hysteresis curves and ductility of specimens were obtained and analyzed. It indicates that spraying hybrid BF/CFRP strengthening scheme can effectively improve the ductility and energy dissipation ability of pre-damaged concrete frame columns. Although the improvement of the peak loads and ultimate lateral deformation of damaged frame columns were not obvious compared with those of the reference column, but it should be pointed out that the strengthened columns were pre-damaged seriously with yielded steel bars and the recover of load bearing ability resulted from spraying FRP retrofit can not be neglected. It also shows that increasing the thickness of spraying overcoat can effectively improve the energy dissipation ability of damaged frame columns.