Region Of Column Research Articles

Constraining calcification habitat using oxygen isotope measurements in tropical planktonic foraminiferal tests from surface sediments

Geochemical signals from planktonic foraminiferal tests provide a wide array of tools to investigate past hydrographic changes, but these techniques are limited by our understanding of the habitat at which these organisms form their shell. Quantitative constraints on the variability of the calcification habitat of these organisms can thus lead to better interpretations of these signals and more quantitative constraints on indirect properties related to these signals. We compiled oxygen isotope data from the Tropics to investigate global trends in the apparent calcification depth (ACD) of commonly used planktonic foraminifera. Using Globigerinoides ruber albus, Trilobatus sacculifer, Globorotalia tumida, Neogloboquadrina dutertrei and Pulleniatina obliquiloculata, we find that our ACD estimates for the global tropics largely match regional ACD estimates from other studies. G. ruber and T. sacculifer seem to calcify in the surface mixed layer with a mean ACD and 95% confidence interval of 17 [0,86] m and 48 [0,128] m, respectively, and G. tumida, N. dutertrei, and P. obliquiloculata seem to calcify below the mixed layer with a mean ACD of 210 [123,385] m, 114 [42,173] m, and 94 [0,169] m, respectively. The global data set enables the determination of calcification depths across locations with a wide range of thermocline depths. We find that G. tumida exhibits a calcification depth that is more spatially invariant, while N. dutertrei and P. obliquiloculata seem to calcify deeper in the water column in regions where the thermocline is deeper, as has been previously suggested.

Generalized Loading Protocols for Experimentally Simulating Multidirectional Earthquake Actions on Building Columns in Regions of Low-to-Moderate Seismicity

AbstractThis study aimed to quantitatively develop realistic quasi-static loading protocols for simulating bidirectional cyclic actions and axial load variation on building columns in a way that is...

Resetting response of precast segments with gently keyed interface under seismic action

SummaryIn an attempt to promote the use of precast segmental bridge columns in regions of moderate to high seismicity, sliding planar joints have been adopted to relieve the adverse effects of seismic action. However, despite the ability to survive an earthquake, the sliding segments often result in noticeable residual relative movements afterwards, which require costly repairs. To better understand the kinetic and self‐centering performance of sliding segments with W‐shaped gently keyed interface, the concept of sliding hysteresis center curve is put forward. A bidirectional asymmetrical pure sliding model is explored for better control of the self‐centering ability, where the downslope slip caused by the energy at the post‐peak stage of an earthquake may benefit the self‐centering performance of asymmetrical sliding systems. A series of parametric studies using real earthquake records are then conducted to evaluate the effects of inclination θ and coefficient of friction μ at the interface on the dynamic response. It is found that the seismic excitations, especially the post‐peak cycles, have profound influence on the residual displacement of an asymmetrical sliding system. With proper design, a W‐shaped gently keyed sliding system can provide superior self‐centering performance without affecting its seismic isolation ability during the peak stages of earthquakes.

Behaviour of Beam-Column Subjected to Reversed Lateral Loading

This paper presents an experimental investigation on the behaviour of Concrete Filled Double Skin Tubular (CFDST) column connected to Concrete Filled Steel Tubular (CFST) beam under reversed lateral loading. The CFDST column consists of two concentric cold-formed steel tubes with concrete sandwiched between them and the CFST member consist of cold-formed steel hollow section completely filled with concrete. The specimen in this study consists of a hollow square tube as the outer skin for both CFDST and CFST members. The inner skin of the CFDST column is a circular steel tube and M30 grade concrete having 40% cement replaced with fly ash was filled in between the tubes. The connection between the beams and the columns were provided using through bolts and angle plates. A pair of specimens considered as the control specimens having CFST members for both beam and column were also tested for comparison. All the four specimens were subjected to a constant axial load and reversed lateral loading which simulates the earthquake forces. The seismic characteristics like hysteretic behavior, peak load displacement, ductility, stiffness degradation and energy dissipation of CFDST beam-column were compared with that of the CFST beam-column. The beam-column specimens with CFDST columns exhibited favorable seismic behaviour with reduced self-weight and hence a better choice than CFST columns in regions of seismic risk.

An acoustic estimate of methane concentration in a water column in regions of methane bubble release

A remote acoustic method is presented for estimating the methane flux into water from rising bubbles. With the proposed method and data of hydroacoustic measurements in the Sea of Okhotsk, the dissolved methane concentration profile that forms in the water column in regions of methane bubble release is estimated. Comparison of the aforementioned methane concentration profile with results of direct measurements shows good quantitative and qualitative agreement. This testifies to the fair accuracy of the proposed acoustic method and is indicative of the dominant role of bubble transport in the formation of the concentration of dissolved methane in the water column in such regions.

Plastic Hinge Length of RC Columns under the Combined Effect of Near-Fault Vertical and Horizontal Ground Motions

Plastic hinges are an extension of the ductile design concept used in building seismically resistant structures. The formation of a plastic hinge in an RC column in regions that experience inelastic actions depends on the characteristics of the earthquakes as well as the column details. Recordings from recent earthquakes have proved that in the near-fault region of large earthquakes, the vertical component of the near-fault ground motion has exceeded the horizontal, and damage to the structures has been predominantly by these motions. Therefore, this paper focuses on near-fault ground motions that have been recorded within rather 20 km of the causative fault and 936 inelastic time-history analyses have been performed to predict the nonlinear behavior of RC columns subjected to combined effect of near-fault vertical and horizontal ground motions. The effects of some parameters are evaluated analytically by finite element methods and the results are compared with corresponding experimental data. Findings from this study provide a simple expression to estimate plastic hinge length of RC columns subjected to the combined effect of near-fault vertical and horizontal ground motions.

Plastic hinge length of RC columns considering soil-structure interaction

During an earthquake, soils filter and send out the shaking to the building and simultaneously it has the role of bearing the building vibrations and transmitting them back to the ground. In other words, the ground and the building interact with each other. Hence, soil-structure interaction (SSI) is a key parameter that affects the performance of buildings during the earthquakes and is worth to be taken into consideration. Columns are one of the most crucial elements in RC buildings that play an important role in stability of the building and must be able to dissipate energy under seismic loads. Recent earthquakes showed that formation of plastic hinges in columns is still possible as a result of strong ground motion, despite the application of strong column-weak beam concept, as recommended by various design codes. Energy is dissipated through the plastic deformation of specific zones at the end of a member without affecting the rest of the structure. The formation of a plastic hinge in an RC column in regions that experience inelastic actions depends on the column details as well as soil-structure interaction (SSI). In this paper, 854 different scenarios have been analyzed by inelastic time-history analyses to predict the nonlinear behavior of RC columns considering soil-structure interaction (SSI). The effects of axial load, height over depth ratio, main period of soil and structure as well as different characteristics of earthquakes, are evaluated analytically by finite element methods and the results are compared with corresponding experimental data. Findings from this study provide a simple expression to estimate plastic hinge length of RC columns including soil-structure interaction.

Plastic hinge length of reinforced concrete columns subjected to both far‐fault and near‐fault ground motions having forward directivity

SUMMARYIn a strong earthquake, a standard reinforced concrete (RC) column may develop plastic deformations in regions often termed as plastic hinge regions. A plastic hinge is basically an energy dampening device that dampens energy through the plastic rotation of a rigid column connection, which triggers redistribution of bending moments. The formation of a plastic hinge in an RC column in regions that experience inelastic actions depends on the characteristics of the earthquakes as well as the column details. Recordings from recent earthquakes have provided evidence that ground motions in the near field of a rupturing fault can contain a large energy or ‘directivity’ pulse. A directivity pulse occurs when the propagation of the fault proceeds at nearly the same rate as the shear wave velocity. This pulse is seen in the forward direction of the rupture and can cause considerable damage during an earthquake, especially to structures with natural periods that are close to those of the pulse. In the present paper, 1316 inelastic time‐history analyses have been performed to predict the nonlinear behaviour of RC columns under both far‐fault and near‐fault ground motions. The effects of axial load, height over depth ratio and amount of longitudinal reinforcement, as well as different characteristics of earthquakes, were evaluated analytically by finite element methods and the results were compared with corresponding experimental data. Based on the results, simple expressions were proposed that can be used to estimate plastic hinge length of RC columns subjected to both far‐fault and near‐fault earthquakes that contain a forward‐directivity effect. Copyright © 2011 John Wiley & Sons, Ltd.

Piezoelectric control of columns prone to instabilities and nonlinear modal interaction

This paper attempts to unravel the issues of piezoelectric control of structures prone tononlinear static and dynamic instabilities. A simple yet typical example is considered,namely the problem of a simply supported axially compressed imperfect column on anelastic softening foundation. Here the significant nonlinearity arises from the softeningfoundation. The column is so designed as to have coincident critical loads for thefirst two modes of buckling. Piezoelectric actuators/sensors are deemed to beattached to a column in regions of maximum strain at several locations along thelength of the column. The issues involved in (i) enhancing the static bucklingload, (ii) suppression of vibrations as the column is compressed to a load close toits dynamic instability load and (iii) enhancing the dynamic instability load areinvestigated and discussed. It is shown that there is a premium price to pay forenhancing the buckling capacity of the column, be it static or dynamic. The paperconcludes by alluding to the possibility of a failure of patch control if a higher-ordershortwave mode happens to be the governing principal mode of the structure.

Drift-Dependent Confinement Requirements for Reinforced Concrete Columns Under Cyclic Loading

This paper examines the influence of transverse reinforcement and axial load on the drift limit of rectangular columns using test results from 184 specimens subjected to cyclic loading. Columns within the set were selected to have shear span-to-depth ratios of at least equal to 2.5 so that truss action would be the main mechanism of shear resistance and the deformation component related to shear would be small compared with that related to flexure. Expressions relating the limiting drift ratio to the axial load ratio and the amount of confining reinforcement were evaluated. Equations indicating the amount of confining reinforcement required to achieve a given limiting drift ratio for reinforced concrete columns in regions of moderate and high seismicity are proposed.

Reliability of atom column positions in a ternary system determined by quantitative high‐resolution transmission electron microscopy

Employing an iterative structure refinement procedure, we have determined the atomistic structure of the Σ3 (111) grain boundary in strontium titanate (SrTiO3) from high‐resolution transmission electron microscopy (HRTEM) images. This grain boundary serves as a model system to study the effect of column occupancies on the reliability of the column positions. In this paper we introduce a method to derive confidence regions for the positions of individual atom columns at crystal defects. Based on a statistical approach we first determine the reliabilities of different types of atom columns in regions of unfaulted crystal. Next we extrapolate these reliabilities to obtain the reliabilities of individual atom columns at the grain boundary. The method accounts correctly for random errors and promises to be generally applicable provided that repetitive units of unfaulted crystal structure are contained in the HRTEM image. Under the conditions of the present study, the reliability of a column position correlates with the projected electrostatic potential of the column. Accordingly, the reliabilities of the column positions at the boundary vary with the column type: 0.008 nm for Sr–O columns, 0.014 nm for Ti columns, and 0.018 nm for O–O columns.

Optimum Design of Columns Supported by Tension Ties

A rational procedure for the optimization, on a weight basis, of columns supported by tension ties is developed. The tension ties provide a degree of intermediate elastic support which renders these systems more efficient than simple tubular columns in regions of low structural index P/L2. Two different configurations are considered. The first has one intermediate support-plane, and is stable up to a compressive load at which the second buckling mode occurs. The second has three intermediate support-planes and remains stable up to a compressive load corresponding to the fourth mode shape. Results are presented in such a fashion that conditions under which tie supported columns are more efficient than simple columns are readily apparent, and such that all design parameters are obtainable with a minimum of computational effort. Examples are included. Results indicate that, in favorable circumstances, columns supported by tension ties may be constructed with approximately half the weight required for a simple column capable of transmitting the same load over the same distance.