Top Of Column Research Articles

Seasonal variation of floc population influenced by the presence of algae in the Changjiang (Yangtze River) Estuary

The variation of the floc population in the Changjiang Estuary has been studied for both winter and summer season as a function of the presence of living (micro)algae. The influence of algae has been characterized through the use of the chlorophyll-a concentration to suspended sediment concentration (CC/SSC) ratio. Two whole tidal cycle sampling campaigns were carried out and a full set of parameters (particle size distribution, particle concentration, salinity, velocities, chlorophyll-a concentration) was recorded as function of time for 6 vertical depths. It is found that the floc population can be described by three particle classes. The two most dynamic classes (microflocs and macroflocs) co-exist in the water column. It was nonetheless found, due to the correlation between CC/SSC and particle sizes that the system is at steady state, both in summer and in winter. This can be explained by the limited flocculation ability between the classes due to their segregation in the water column. In winter, macroflocs are found at the top of the water column but their amount and size are very reduced with a mean CC/SSC value of 13 ± 11 μg g−1. In summer, algae-rich macroflocs are abundant at the top of the water column with a mean CC/SSC value of 21 ± 18 μg g−1, especially at flood tide. Microflocs, on the other hand, have a higher density and are generally found deeper in the water column. At high water slack, both macroflocs and microflocs will settle but will never catch-up. The fact that the flocs are at steady-state in terms of flocculation is of importance for sediment transport modelling.

A resilient column with angular friction damper for seismic performance upgrading of underground structures

Underground structures can be vulnerable due to seismic-induced deformation. A resilient underground structure is preferable for seismic response mitigation and quick recovery. In this study, a resilient central column with angular friction damper (RC-AFD) was constructed for the seismic performance upgrading of underground structures, and a practical design procedure was developed for the RC-AFD to enable the two-state control for underground structures subject to seismic excitations with multi-intensity. The RC-AFD consists of a self-centering column characterized by relaxed constraints at the top and bottom column that is restricted by unbounded prestressed tendons, whereas a pair of angular friction dampers are placed at the top of the central column. The mechanical model and its physical realization are detailed, whereas the two-state control mechanism is proposed by following the enhanced demand of seismic performance upgrading. The effectiveness and robustness of the proposed RC-AFD for structural seismic response mitigation of typical underground structures were investigated in terms of structural displacement, shear force, bending moments, and energy-based responses. The obtained results show that the two flexible connection joints concentrated at the top and bottom of the RC-AFD produce a significant isolation effect, through which the multiple responses of the central column can be reduced significantly. Benefiting from the two-state design and the employed angular friction damper with a large radius plate, the RC-AFD exhibits an enhanced energy dissipation capacity, which robustly dissipates the intense plastic energy for multi-intensity excitations. As a consequence, the plastic energy dissipation burden of the primary structures can be significantly relieved and residual deformation can be avoided due to the excellent self-centering ability.

Identifying geometric configuration of earthquake-resistant buildings

Indonesia is an earthquake-prone area because it is located at the world's most active tectonic plates and hundreds of local faults. Obviously, there have been many earthquake victims caused by collapsed buildings, hence the need for earthquake-resistant construction. However, there is not much guidance for architects to design earthquake-resistant buildings. This research proposes guidance for architects on how to design building forms relatively able to resist earthquakes. The simulation experiment method involving 32 building models in various forms was employed. The experimental results were then analyzed with modal analysis in ETABS and SVA for architectural design. Based on the analysis report, some guidelines were proposed: 1). Avoid buildings that are too slender, use the slenderness ratio H/D ≤ 2, 2). Avoid soft stories where the ratio of the top column height (h) to the bottom column height (h1) ≤ 0.8, 3). Use symmetrical shapes with 1 or 2 axes and avoid shapes with random compositions, 4). Use the additive and subtractive mass transformation ≤ 15%, 5).Strengthen the structural elements, install shear walls, or use dilatation to minimize potential torsional irregularities and non-parallel system irregularities of L, T, U, +, and Z forms6). Avoid using non-axial asymmetrical forms.

Spatial and Temporal Vertical Distribution of Chlorophyll in Relation to Submarine Wastewater Effluent Discharges

The vertical distribution of chlorophyll in coastal waters is influenced by a combination of the hydrodynamic environment and different biotic and abiotic processes. The spatial and temporal occurrences of chlorophyll profiles provide a good representation of the changes in the marine environment. The majority of studies in the Adriatic Sea have so far been conducted in areas unaffected by anthropogenic pressure. Our study site is located near two marine outfalls, which are part of the public sewage system. This study aims to characterize the chlorophyll vertical distribution and describe its variability based on the stratification conditions and the presence of a wastewater effluent plume. Based on these conditions, we identified three characteristic scenarios/types of chlorophyll profiles. The first one occurs when the vertical mixing of the water column creates the upwelling of chlorophyll and nutrients to the upper part of the water column. The second and third scenarios occur during stratified conditions and differ by the extent of the effluent plume intrusion. Using modern fluorescence techniques, we identified and described three different vertical chlorophyll profiles, characterizing them according to their physical and biological parameters and processes. For cases with a visible effluent intrusion, we confirmed the importance of the pycnocline formation in keeping the effluent below and maintaining the higher water quality status at the top of the water column.

Determination of the Minimum Catalyst Amount in the Design of Catalytic Distillation Columns

This paper presents a method to determine the minimum amount of a catalyst needed to operate a heterogeneously catalyzed reactive distillation column based on kinetic and VLE data only, avoiding rigorous column simulations. Good initial estimates for catalyst loadings are rarely discussed, and shortcut methods are lacking. The described method determines the highest possible reaction rate using known kinetics and column stage temperatures obtained from ternary diagrams of the column top and bottom sections, neglecting the highest or lowest boiler of the column, respectively. The method was validated against several literature cases. From these cases, it could be determined that a conservative estimate for the amount of the catalyst in the early design phase is six times the minimum catalyst found using the method described. Additionally, the presented method provides information regarding the operability of the column, for example, related to catalyst deactivation.

Stiffness of Rubber Bearings Considering Nonstandard Top and Bottom Boundary Conditions

AbstractTypical installations of seismic isolation assume flexurally rigid end conditions; however, in retrofit scenarios where bearings may be placed at the tops of columns or in bridges with tall...

Study on fire resistance of a prefabricated reinforced concrete frame structure

PurposeThis study aims to further study the fire resistance of prefabricated concrete beam-column joints with end-plate connection. This paper aims to analyze the fire resistance of this joint in prefabricated reinforced concrete frame structure (PRCS).Design/methodology/approachFirst, the accuracy of the model is verified by using the test data. Based on this, a refined finite element model of PRCS structure with two stories and two spans is established. The influence of four working conditions with different fire floors (positions) and different axial compression ratios on the deformation, failure and fire resistance of PRCS structure are analyzed.FindingsThe results show that under the four working conditions, the fire resistance of the PRCS structure under Condition 1 and Condition 2 is smaller. It shows that the beam deformation develops slowly in PRCS structure under four kinds of fire positions, and the large displacement emerges 60 min later, which is poles apart from that of prefabricated beam column members. With the increase of the fire time, the material is damaged and deteriorated, which leads to the eccentricity of the axial load, so that the column top appears large lateral displacement. Under the Conditions 1 and 3, the lateral displacement of the column gradually decreases as the axial compression ratio rises.Originality/valueIt is found that there is a distinct lack of researching on the fire resistance of prefabricated joints, and the existed research studies are limited to the fire resistance of members. Thus, it is necessary to strengthen the first floor and side column design of prefabricated frame structure.

Investigation of metal built-up columns Part II: Results

AbstractIn the frame of a large parametrical study metal built-up columns made from steel and made of aluminum alloy were investigated. The second order theory is used for the analysis of the battened and laced built-up columns under combined compression and bending. The bottom column ends are fixed and the upper ones are free in the case of in-plane buckling. At the column base the translation and the rotation are fixed, at the column top the translation and the rotation are free in the case of in-plane buckling. Translation is fixed and rotation is free at both column ends in out-of plane buckling. The built-up columns are considered as the columns with effective bending and smeared shear stiffness with a local bow imperfection amplitude e0 = L/500.

Increasing the efficiency of the partial oil removal column

The operation of the primary oil refining unit is considered. An analysis of the operation of the operating column K-1 showed that there are noticeable fluctuations in the operating mode of the apparatus in the summer and cold season, as a result, a change in the temperature of the column top and a deterioration in the clarity of fraction rectification were observed. To study the methods of adjusting the parameters of the K-1 topping column, a computational experiment was carried out using the UniSim Design modeling system, in which the models of the apparatus and the installation model as a whole were formed. The Peng-Robinson method was used as a mathematical package for calculating the thermodynamic properties of the mixture components. Comparison of the calculated performance of the two options for the equipment of the column K-1. According to the first version, the operation of the K-1 column was simulated, in which the raw material enters the 19 tray, the hot stream is fed to the bottom of the column to the 24 tray, oil reflux to the 5 tray, acute irrigation and a partial condenser are used. Unstable technological regimes of the column top were observed in this variant in industrial conditions. To assess the fundamental possibility of changing the hardware design of the K-1 column, another option was chosen, in which there is no acute irrigation and oil irrigation, at the same time, upper circulating irrigation was introduced from the 5th to the 1st tray with cooling the flow and the technological scheme of forming and feeding the hot jet was preserved. Comparison of the fractional compositions of the topped oil showed that for the considered options, there are practically similar calculated estimates, while the use of upper circulating irrigation allows not only to unload the upper part of the distillation column from the heat load, but also to use a significant heat flow of the cooler of the upper circulating irrigation for preheating oil , which will also reduce the consumption of liquid fuel for furnaces.

Modelling of a continuous distillation process with finite reflux ratio using the hydrodynamic analogy approach

The hydrodynamic analogy (HA) approach offers an alternative to stage models describing packed distillation columns. So far, HA models have been successfully applied to separation processes, in which the properties of fluid streams entering the packing bed are pre-set as input parameters. However, in a continuous distillation process, the internal fluid streams are coupled via a reboiler and a condenser, thus making the inlet compositions a part of the solution.In the present work, an extension of the HA approach for the description of a continuous distillation process with finite reflux ratio is presented. Equations describing the relationships between the inlet and outlet streams at the column top and bottom are incorporated in the model. Furthermore, changes in compositions and flow rates induced by the feed stream are considered. The model is verified by comparison with experimental data on distillation of a methanol/ethanol/water mixture in a column of 2.3m height and 210mm diameter. The simulated composition profiles are in good agreement with the experiments.

Consolidation theory for the stone column reinforced ground with time-dependent drainage boundary considering the foundation stiffness

Considering the foundation stiffness, this paper presents a new theory for consolidation of the stone column reinforced ground with time-dependent drainage boundary. The differential settlement between the soil the and column is obtained by using an improved equal-strain assumption. And the drainage capacity at the top of column is described by a time-decaying exponential function. Based on the above assumptions, a general solution for the differential governing equation is derived using the method of variables separation. A parametric study is carried out to evaluate the effects of the stiffness and the drainage boundary on the average degree of consolidation, the differential settlement and the stress concentration ratio. Finally, the settlement predicted by the present solution is compared with the measured settlement from a previous case study, and the value of the parameter in time-dependent boundary is discussed.

Dynamic Response of Wooden Columns in Traditional Timber Structures Under Horizontal Earthquake

Accurately predicting the structure’s response under external loads is a prerequisite for scientific protection of traditional timber structures. Wooden columns are the key components for transmitting the vertical loads and resisting the lateral loads in traditional timber structures. The dynamic response characteristics of wooden columns eccentrically overlain by top column component under horizontal earthquakes are investigated in this paper. The critical triggering conditions for different phases of the dynamic response are derived. The factors that determine the transition between various phases of the dynamic response are obtained. Based on the trigger conditions, the trigger sensitivity of each phase of the dynamic responses is studied. The results show that there are four phases of dynamic response that can be triggered on the wooden column, i.e. the static, uplift, uplift followed by slipping, and simultaneous uplift and slipping. Uplift is most likely to be triggered. Uplift with rocking is the main form of wooden columns. The results of theoretical analysis are verified by numerical simulation. This study provides the necessary theoretical basis for the phase assessment and protection of the traditional timber structures.

Evaluation on influences of inertial mass on seismic responses and structure-soil interactions of pile-soil-piers

This research is to assess the influences of the inertial mass from the girder on the dynamic characteristic, dynamic response, and structure-soil interaction of a pile-soil-pier subsystem in a scale-model of a cable-stayed bridge. Therefore, both connection configurations between the pile-soil-pier and girder, including the sliding and fixed connections, were designed to present various inertial mass from the superstructure delivered to the pile-soil-pier. The pile-soil-pier supported by a 3 × 3 pile-group in mixed soil placed in a shear box was tested using shaking tables. The dynamic characteristics, seismic responses, inertial interactions, and pile group effects of the pile-soil-pier between the sliding and fixed connections were analyzed under three input motions with different shaking amplitudes. These results showed that more inertial mass from the girder significantly increased the reinforcement strain and bending moment at the column bottom and pile top, displacement at the column top, inertial interaction effects, and pile group effects of the pile-soil-pier due to the sliding connection changing to the fixed connection. The inertial mass increment from the girder noticeably decreased the peak accelerations of the column of the pile-soil-pier when subjected to three input motions with different amplitudes. However, the inertial mass insignificantly affected the accelerations of the pile and free-soil. Therefore, the corresponding kinematic interaction effects were almost unaffected by the inertial mass. Additionally, the evident pile group effects were observed in the sliding and fixed connections between the pile-soil-pier and girder. The numerical model could approximately reproduce the macroscopic seismic responses of the pile-soil-piers with sliding and fixed connections and capture the typical response variations induced by the connection configuration change.

Damage control of a twin-column pier with a replaceable steel shear link in a cap beam under transverse seismic motion

This paper proposes a novel twin-column pier with a steel shear link (SSL) installed in the cap beam to reduce seismic damage in the transverse direction. The SSL interrupts the rigid cap beam and relieves the coupled deformation of the two columns. Benefits of the yieldable SSL in the event of a strong earthquake are the longer effective deformation of a column and limited axial compressive load. A benchmark reinforced-concrete bridge is employed in a seismic performance evaluation to verify the damage reduction performance of the novel twin-column pier with an SSL. Five numerical models, calibrated in a physical component test, are built in ABAQUS; that is, one original bridge and four novel bridges with different SSLs and accompanying configurations. Modal analysis shows that introducing the SSL does not change the overall structural dynamic characteristics. The nonlinear dynamic analysis results indicate that adopting the SSL effectively reduces the peak compressive strain of the reinforced-concrete column, but energy dissipation from the SSL is negligible compared with the total inputted seismic energy. There is no evident change in the macro seismic response of the twin-column pier when using the SSL, such as overall drift and structural damping ratio. Moreover, a transverse continuous main girder is suggested for realizing an additional restoring moment at the column top, which further reduces compressive strain.

Shake table experimental study of cable-stayed bridges with two different design strategies of H-shaped towers

As one of the main load-carrying components of cable-stayed bridges, bridge towers are typically required to remain elastic even when subjected to severe ground motions with a 2%–3% probability of exceedance in 50 years. To fulfill this special requirement imposed by current seismic design codes, reinforcement ratios in the bridge towers have to be kept significantly higher than if limited ductility behavior of the tower is allowed. In addition, since the foundation capacity is closely related to the moment and shear capacities of the bridge tower, a large increase in bridge construction cost for elastically designed cable-stayed bridge is inevitable. To further investigate the possibility of limited ductility bridge tower design strategies, a new 1/20-scale cable-stayed bridge model with H-shaped bridge towers designed according to strong strut-weak tower column design was tested. The shake table experimental results are compared with a previous strong tower column-weak strut designed full bridge model. A comparison of the results show that ductility design with plastic hinges located on tower columns, i.e., strong strut-weak tower column design, is another effective seismic design strategy that results in only small residual displacement at the top of the tower column, even under very severe earthquake excitations.

Experimental Study on Distillation Column Parameters for Liquefaction Device of Low Concentration Coalbed Methane

The input-output ratio and comprehensive energy consumption of low concentration coalbed methane cryogenic liquefaction devices are determined by the process parameters in control of the distillation column. In order to accurately control the actual operation process of the distillation column, the effect of the operating temperature of the distillation column on the liquefaction performance of a cold box was studied experimentally, and the optimal control parameters of the distillation column were obtained. The results show that the recovery rate of methane decreases with the increase in temperature at the top of the distillation column, and when this temperature is higher than −178 °C, the methane recovery rate drops sharply to below 90%. When the temperature at the bottom of the distillation column rises from −154 °C to −142.7 °C, the purity of LNG products is improved, and when this temperature is increased to −143.5 °C, the purity of products at the bottom of the distillation column reaches the standard, and can be stored safely. In actual operation, the evaporation temperature at the bottom of the column should not be higher than −140 °C. In the process of industrial plant design, measures should be taken to reduce the interaction of the temperature regulation at the top and bottom of the distillation column. When selecting the refrigerant circulation compressor, the leakage of the refrigerant should be considered to maintain the operating pressure of the refrigeration cycle.

Study on shear capacity of prestressed composite joints with concrete-encased CFST columns

Through assuming reasonable constitutive relation of materials, finite element analysis (FEA) models of joints consisting of prestressed concrete-encased steel beams and concrete-encased concrete filled steel tube (CFST) columns were established by soft ABAQUS, and the simulated results were compared with tested ones. On this basis, the nonlinear analysis on the total loading process was conducted, and the stress variation of concrete, profile steel skeleton, steel bar skeleton, and prestressing tendons were observed at yield, peak, and ultimate loads; the influence of axial compressive ratio, steel tube ratio, stirrup ratio, and prestressing level on lateral load-displacement curves at column top and shear force-shear angle in joint core were investigated, and the shear capacity formulae of joint core were developed. It could be concluded that, the lateral peak loads and shear capacity could be improved with the increase of axial compressive ratio, steel tube ratio, stirrup ratio, and prestressing levels in varying degrees, and the ductility of joints will reduce with the increase of axial compressive ratio. Additionally, the shear capacity calculated by proposed practical formula was a little lower than FEA results, which could keep the joints safety and could be used in engineering design.

Experimental Study on the Damage of Bridge Pier under the Impact of Rockfall

In this paper, a discussion is presented about the impact-induced damage suffered by bridge pier columns during rockfall events through model tests and impact force, column top displacement, stress-strain response, and other parameters in relation to the process of impact. On this basis, the following conclusions are drawn. Firstly, the impact force, as well as the displacement and strain of the column top, increases rapidly after taking a hit, while the displacement is reduced after reaching its maximum. Secondly, at the same falling height, the higher the impact position, the smaller the peak of impact force and the longer the attenuation period. Thirdly, at the same impact height, the impact energy, the displacement of the column top, and the peak of the impact force increase as the falling height of the pendulum ball is on the rise, but the attenuation period remains unchanged. Fourthly, the failure mode of column impacted by the swing ball conforms to shear-flexural failure. Fifthly, it is recommended to strengthen the preventative measures for those weak positions like 1/2 height and 1/4 height of bridge pier, so as to minimize the potential damage caused by rockfalls. Besides, a theoretical formula used to estimate the maximum impact force is proposed. Lastly, under the axial load of bridge deck, the performance of the pier in impact resistance under rockfall is better and the damage is less severe than in the experimental impact test. The axial load applied by the deck imposes some constraints on the pier, thus reducing concrete damage. The research results can contribute to the research on addressing the rockfall-bridge pier collision problem. The experimental research demonstrates its theoretical significance to engineering for the prevention of rockfall.

Micro-vibrational erythrocyte sedimentation rate (ESR) for sensitive measurement of erythrocyte aggregation

The erythrocyte sedimentation rate (ESR) can act as a useful index of nonspecific disease activity in the diagnosis of inflammatory conditions. However, there are several drawbacks, including long time measurement. To promote ESR tendency, a micro-vibrational erythrocyte sedimentation rate (MV-ESR) was proposed. By controlling the profile of injecting flow rate into blood sample, air between the syringe pump and bottom of blood column was compressed and released. Micro-vibration (MV) is simple reciprocating flow including motion in both positive and negative directions in a line. It is determined as the edge of the interface between top of blood column and air is pinned under the pressure wave. From that, shear rate generated by determined MV is from 0 to 10–2 (s−1) in this study. Extremely low shear conditions may enhance the probability of erythrocyte aggregation formation. During measurement, a meniscus of separated plasma and sedimented erythrocytes was recorded using a camera. For validation of the proposed MV-ESR method, the effects of hematocrit as well as the frequency and amplitude of flow in the sedimentation tube were investigated. To quantify the enhancement of MV-ESR, the area of relative gradient (ARG) based on a relative gradient of 1 was used. When MV with a maximum flow rate of 1 mL/min and a period of 100 ms was produced until 15 min, MV-ESR exhibited the best performance. Then, the proposed technique was used to diagnose the ESR difference between a normal and periodontitis patient. The characteristic time (λESR), indicating the degree completion of the erythrocyte sedimentation, of the periodontitis patients was lower than that of the control. Based on the experimental demonstrations, λESR of the MV-ESR method has significant potential in the diagnosis of inflammatory conditions and prognosis of non-inflammatory conditions.

Effect of Phosphate and Hydrogen Peroxide on Bacterial Community and Removal Efficiency of Biological Activated Carbon (BAC) Process for Enhanced Biofiltration

Objectives:The correlation between the organic material removal ability of the enhanced BAC process injected by the phosphate (PO4-P) and/or hydrogen peroxide (H2O2) and attached bacterial community was evaluated.Methods:As pilot plant for the purification of raw water downstream of Nakdong river, 4 acrylic columns with an inner diameter of 20 cm and a height of 250 cm were operated at an empty bed contact time of 20 minutes. The four BAC columns are as followed; conventional BAC (control-BAC), enhanced BAC with phosphorus (PO4-P+BAC), enhanced BAC with hydrogen peroxide (H2O2+BAC), and enhanced BAC with phosphorus and hydrogen peroxide (PO4-P+H2O2+BAC). 0.01 mg/L of PO4-P and 1 mg/L of H2O2 were added in influent in the enhanced BAC, respectively. After 18 months of operation, activated carbon was collected from the top of each BAC column and 16S rRNA amplicon sequence analysis was performed.Results and Discussion:The long-term addition of PO4-P and H2O2 contributes the increase of biomass and activity of attached bacteria, respectively. In the attached bacterial community of conventional and enhanced process, Proteobacteria phylum is the most dominant specie and both α-Proteobacteria class and β-Proteobacteria class are also highly present. Each enhanced BAC exhibits very high bacterial community similarity based on the composition of various genera but it is completely different with conventional BAC. In particular, Bradyrhizobium, Sphingomonas, Methylobacterium, Sphingobium, Belnapia, Burkholderia, Polaromonas, and Desulfuromonas, which have excellent metabolism functions for a wide range of organic substrates, are highly dominated in the enhanced BAC process. The concentration of Biodegradable Dissolved Organic Carbon (BDOC) is obtained close to 0.15 mg/L for conventional BAC and less than 0.15 mg/L for enhanced BAC process, respectively. In general, the higher BDOC concentration can result in reducing biostability in water supply and distribution system when the residual chlorine concentration does not meet requirements. As result, less than 0.15 mg/L BDOC accomplished by PO4-P and H2O2 enhances the biostability.Conclusions:Compared to the conventional BAC process, the biomass and activity of attached bacteria and the ratio of the organization composition of the bacteria insides (genus) are considerably higher in the enhanced BAC process. These results achieve higher water quality and improve biostability.