Small-sized Columns Research Articles

Effects of structural size and corner radius on eccentric failure of rectangular CFRP-wrapped RC columns: Meso-scale modellings

The strengthening and retrofitting technique with fiber-reinforced polymer (FRP) composites on reinforced concrete (RC) columns has been widely popular. Compared with concentric compression behaviors of rectangular FRP-confined concrete columns, there are only limited investigations on their eccentric behaviors. Additionally, the applicability of existing design codes obtained from tested small-size columns in calculating load capacity of large-size columns has not been reasonably explained. In view of this, this paper developed a meso-scale numerical analysis method using a random aggregate model based on consideration of concrete heterogeneity. A series of rectangular carbon FRP (CFRP)-confined RC columns having different cross-sectional heights were modelled to investigate the influences of corner radius and size effect on their eccentric compression behaviors. Simulated results showed that there was a transformation of failure mode from brittle compression failure to ductile tensile failure with the increasing load eccentricity. An identical globally failure mode for rectangular columns having different cross-sectional heights was observed whereas crack widths became larger obviously with the increasing cross-sectional height. Regarding the axial load versus mid-height deflection relationship, the corner radius had a significant influence on maximum axial load and softening stage, especially at smaller load eccentricities. One can see that from nominal interaction diagrams, small-eccentrically-loaded columns exhibited more obvious size effect than large-eccentrically-loaded columns. The safety factor of load capacity decreased with the increasing cross-sectional height compared with existing design codes of ACI 440.2R-17 and GB 50608, illustrating that design codes appear to be not conservative for large-size specimens. Taking the influence of size effect into account, the design equations suggested by ACI 440.2R-17 were modified in this study, and the rationality of this correction methodology was verified against simulated data and results of tested large-size rectangular columns.

Enhancement of Quercetin Oral Bioavailability by Self-Nanoemulsifying Drug Delivery System and their Quantification Through Ultra High Performance Liquid Chromatography and Mass Spectrometry in Cerebral Ischemia.

Background Quercetin (Qur) and its major in vivo bioactive metabolites i. e., 3'-O-methyl quercetin, 4'-O-methyl quercetin and quercetin 7-O-β-D-glucuronide, may be used to treat cerebral ischemia however the poor aqueous solubility and less intestinal absorption of Qur results low bioavailability. Purpose To improve Qur bioavailability through preparation of nanoformulation and to develop and validate a sensitive quantification method for Qur detection in brain homogenate. Methods Qur-containing self-nanoemulsifying drug delivery system (Qur-SNEDDS) was developed to form oil-in-water nanoemulsions in situ. Ultra-high performance liquid chromatography electrospray ionization-synapt mass spectrometric method (UHPLC/ESI-QTOF-MS/MS) was developed and validated for quantification whereas for optimal recovery of analyte, a liquid-liquid extraction method (LLE) was used. Results A droplet size of 94.63±3.17 nm and zeta potential of -17.91±1.02 mV for nanoemuslion, elution time for Qur and internal standard (IS) Rutin as 1.21 and 1.50 min alongwith a transition at m/z 301.04/151.03 and 609.21/299.21, were observed respectively. Similarly, linear dynamic range (1.00 ng/mL-2 000.0 ng/mL), intra and inter-assay i. e., %CV of 0.26-2.04, lower limit of detection (LOD) 0.08 ng/mL as well as lower limit of quantitation (LOQ) as 0.131 ng/mL were also observed. Conclusion The developed method have advantage over previous all methods i. e., less time consuming (<3.0), low consumption of solvents (flow rate 0.20 mL/min.) via small size column, more accuracy and specificity as well as use of acetonitrile as compared to hazardous solvents. This certainly adds advantages for green chromatography technique and supports application of current developed method for quantification and evaluation of Qur-SNEDDS.

Size effect on axial stress-strain behavior of CFRP-confined square concrete columns

Research published on the axial compressive behavior of fibre-reinforced polymer (FRP)-confined concrete columns has been generally based on small-sized specimens. There have been limited studies published on large-sized columns and there have also been limited studies on the validity of upscaling results obtained from small-sized specimens. On account of such knowledge gap, this paper presents the test results of 23 carbon FRP-confined square concrete columns of varying sizes subjected to monotonic axial compression. The specimens were sorted into 10 groups based on (i) specimen size, (ii) theoretical lateral FRP confining pressure, (iii) number of layers of FRP wrap, and (iv) inclusion and exclusion of internal steel reinforcement. In each group, the specimens consisted of different cross-sectional sizes but the same theoretical lateral confining pressure. The experimental results showed that specimen size had no significant effect on the axial stress-strain behavior of FRP-confined medium- and small-sized columns (i.e. sections defined herein equal to and less than 300mm in width). The axial stress-strain responses exhibited differences as the specimen size increased. This was especially the case for FRP-confined large-sized columns (i.e. sections defined herein equal to and larger than 350mm in width). The rupture strain of the FRP wrap at the corner regions is proposed to be defined as the effective lateral rupture strain of FRP, and this strain was shown to decrease with an increase of specimen size. Based on the test results, a modified FRP effective strain factor model considering the influence of size effect is proposed.

Efficiency of short, small-diameter columns for reversed-phase liquid chromatography under practical operating conditions

Prototype small-size (1.0mm I.D., 5cm long) columns for reversed-phase HPLC were evaluated in relation to instrument requirements. The performance of three types of columns, monolithic silica and particulate silica (2μm, totally porous and 2.6μm, core–shell particles) was studied in the presence of considerable or minimal extra-column effects, while the detector contribution to band broadening was minimized by employing a small size UV-detector cell (6- or 90nL). A micro-LC instrument having small system volume (<1μL) provided extra-column band variance of only 0.01–0.02μL2. The three columns generated about 8500 theoretical plates for solutes with retention factor, k>1–3 (depending on the column), in acetonitrile/water mobile phase (65/35=vol/vol) at 0.05mL/min, with the instrument specified above. The column efficiency was lower by up to 30% than that observed with a 2.1mm I.D. commercial column. The small-size columns also provided 8000–8500 theoretical plates for well retained solutes with a commercial ultrahigh-pressure liquid chromatography (UHPLC) instrument when extra-column contributions were minimized. While a significant extra-column effect was observed for early eluting solutes (k<2–4, depending on column) with methanol/water (20/80=vol/vol) as weak-wash solvent, the use of methanol/water=50/50 as wash solvent affected the column efficiency for most analytes. The results suggest that the band compression effect by the weak-wash solvent associated with partial-loop injection may provide a practical means to reducing the extra-column effect for small-size columns, while the use of an instrument with minimum extra-column effect is highly desirable.

小型活性炭カラムにおける有機ガス破過曲線の近似計算の検討

小型活性炭カラムにおける有機ガス破過曲線の近似計算の検討

Simultaneous Determination of Nickel and Cobalt as Chelates with 1-(2-Pyridylazo)-2-naphthol Using an LC Switching Column Method

A simple liquid chromatographic method was developed for the separation and simultaneous determination of cobalt and nickel as chelates with 1-(2-pyridylazo)-2-naphthol (PAN). The method, using a switching column technique for the on-line purification and separation, enables to reach the sub-microgram per litre concentration level excluding off-line sample treatment with the exception of the derivatization reaction. Two small-sized columns packed with CN- and C4-bonded stationary phases were selected and used considering their complementary behaviour with respect to chelated Co and Ni ions. The analysis was performed within 10 min using an optimised eluent (water–acetonitrile–methanol–tetrahydrofuran, 40:45:10:5, v/v/v/v) containing Tween 40 (10−3 M) and acetate buffer (5 × 10−3 M, pH 4.8). Detection was performed by UV-vis spectrophotometry (λ = 565 nm) permitting to reach quantification limits of 0.9 and 0.5 μg L−1 for Co and Ni, respectively.

Carbon fibre reinforced polymer wrapping for the rehabilitation of masonry columns

The use of carbon fibre reinforced polymer (CFRP) wrapping to strengthen existing cracked masonry columns was investigated experimentally. The study was aimed at quantifying the increase in strength that can be achieved and assessing the effect of column size on the strength increase. Eighteen columns were tested, with three different square cross-sectional sizes (290 mm × 290 mm, 390 mm × 390 mm, 490 mm × 490 mm) and two different types of clay masonry unit. Six columns were constructed in each size, two columns using unit type 1 and four columns using unit type 2. Strengthening was achieved by wrapping the square section columns directly with a single-layer CFRP laminate or by wrapping the columns after first casting a circular concrete jacket around the column. The latter treatment was applied to two of the small-sized columns and two of the intermediate-sized columns. All other square section columns were wrapped directly. Significant strength increases were achieved, particularly when the columns were provided with the cylindrical concrete jacket. These preliminary tests indicate that the use of CFRP wrapping is an effective technique for rehabilitating damaged masonry columns. Decisive conclusions could not be made regarding the effect of column size (cross-sectional area) on the strength increase achieved. Further tests together with nonlinear finite element modelling aimed at duplicating the experimental observations would greatly enhance the information provided by the current tests.Key words: masonry, columns, rehabilitation, strengthening, fibre reinforced polymer, experimental.

Removal of 137Cs from aqueous solutions using different cationic forms of a natural zeolite: clinoptilolite

Abstract Distribution coefficients of cesium on natural and cation-enriched (Na+, K+, NH4+ and Ca+2) forms of clinoptilolite were measured by batch, radioactive tracer technique. The measurements were carried out for an initial cesium concentration range of 10−6–10−1 mol/dm3 and at temperatures of 25, 40, 60 and 80 °C. Experimental isotherms evaluated from distribution coefficients were fit to Langmuir, Freundlich and Dubinin-Radushkevich (D-R)models. Of the models tested, D-R model was found to represent the isotherms better in a wider range of concentrations than either Langmuir or Freundlich model. Breakthrough behavior of cesium on natural and cation-enriched forms of clinoptilolite for a particular set of conditions were also determined in a small size column. Column parameters were evaluated using mass transfer zone concept.

Specific sorbent to remove solvent-detergent mixtures from virus-inactivated biological fluids.

A method involving a sorbent designed to capture specifically virus-inactivating solvent-detergent mixtures is described. Its specificity allows the adsorption of these undesirable chemicals with a high capacity in order to treat large amounts of inactivated biological fluids in small-sized columns. Typically, the volume of sorbent that can be used repeatedly is between one quarter and one tenth of the sample volume to be treated. Cleaning and sanitization can be done by classical methods while strong oxidizing agents can also be used to sterilize the sorbent.

Analysis of corticosteroids in mixtures by gradient elution liquid chromatography

A method is described for the fractionation of corticosteroids in mixtures by means of column chromatography with small size columns, reduced elution times and continous monitoring of the eflluent with data recording. As a test mixture, eight natural corticosteroids were chosen in order to reproduce extracts from glands or biological fluids: corticosterone , 11-dehydrocorticosterone, 11-deoxycortisol, cortisone, cortisol, aldosterone, tetrahydrocortisone and tetrahydrocortisol. Firstly, the influence of the activation of the adsorbent on the separation was studied and the shape and the extent of the gradient considered. The adsorbents were silicic acids of different structural types, and the gradient components were methanol and chloroform. Monitoring of the effluent was performed by means of two detectors, acting in parallel: the first was a UV detector and the second was a hydrogen flame ionization detector, part of the effluent being continously drawn off to the detector. Conditions for the optimization of the separations are reported and possible analytical applications are discussed.