Confinement Model Research Articles

Compression behavior of reinforced concrete columns jacketed with multi‐spiral transverse reinforcement

AbstractThe objective of this study was to investigate the compressive behavior of reinforced concrete (RC) columns jacketed by modified multi‐spiral transverse reinforcement, in which columns were jacketed by a large welded octagonal stirrup at the center and four small spiral stirrups at the corners of specimens. Sixteen large‐scale concrete columns were jacketed by the proposed method and subjected to axial compression tests. The investigated parameters included the axial compression ratio of existing column and the volumetric ratio of stirrups in jacket. The experimental results revealed that the jacketed columns failed by the formation of an inclined shear failure plane and specimens still kept rather high load‐bearing capacity after core concrete crushed, owing to the multiple confinement materials in jacket. The axial load‐strain curves of specimens could be divided into four phases, corresponding to failure modes. Furthermore, increasing the volumetric ratio of stirrups in jacket effectively improved ductility of jacketed RC columns compared to the load‐bearing capacity, while increasing the axial compression ratio of existing column decreased the enhancement of jacket. Six recent confinement models were selected to predict the peak strength of confined concrete and the corresponding strain. The predicted models performed well in the ascending branch of the analytical stress–strain curves, while the descending branch showed a lower rate of decrease than experimental values. The compression behavior of RC columns jacketed by modified multi‐spiral transverse reinforcement was analyzed, and the effects of axial compression ratios of existing columns and the volumetric ratio of stirrups of jacket on the compression behavior of columns were exhibited. Furthermore, the experimental results were evaluated by six existing models.

Handling and Physiological Aspects of the Dual-Purpose Water Buffalo Production System in the Mexican Humid Tropics.

Simple SummaryBuffalo is a domesticated large ruminant that can be raised for beef, dairy, and work. In some systems, these animals can be raised with a dual purpose (beef and dairy). The present review describes the characteristics of the dual-purpose water buffalo production system in Mexico’s humid wetlands. This article provides extensive information on the water buffalo and includes comparisons with other species to note similarities and differences. The aim is to describe the buffalo handling procedures used in this system, particularly during breeding, milking, confinement, and mobilization, relating them to the neurological processes involved and analyzing the productive results. Understanding these processes will allow us to obtain a more precise vision of the advantages that this species can offer, and the possible implications of the development of this type of livestock under tropical conditions.The purpose of this paper is to describe the characteristics of the dual-purpose water buffalo production based on the Mexican production system as a model in tropical wetlands. It includes a broad literature review emphasizing the most recent and specialized publications examining key findings to improve our understanding in the performance of the buffalo species (Bubalus bubalis). The complementary topics addressed include reproductive management, parturition, the dam–calf bond, milking routines, and models of confinement and management, in addition to aspects related to milk commercialization. This article summarizes the advances made to date in this production system and its current margins for improvement. The development of dual-purpose water buffalo production systems in Mexico’s tropical wetlands is a relatively recent phenomenon that has progressed and improved due to herd management. Buffaloes are an interesting alternative for dual purpose systems that offer several advantages. The lower milk production of this species compared to cattle is its main limitation. However, the properties of their milk allow one to obtain an added value and make this type of farms competitive. In synthesis, consolidating buffalo production in Mexico’s tropical wetlands will require broadening our knowledge of this species, and perfecting the most appropriate handling procedures. The activities of government agencies and processing enterprises will play vital roles in achieving the integral modernization of this potentially important economic activity.

Large-rupture-strain (LRS) FRP-confined concrete in square stub columns: Effects of specimen size and assessments of existing models

As an environmental-friendly material with high rupture strain capacity, polyethylene terephthalate (PET) fiber reinforced polymer (FRP) has promising industry applications. Previous studies mainly focused on the application of PET FRP-confined concrete in circular columns, while investigations on PET FRP-confined concrete in square columns are rather limited. The purpose of this study is to fundamentally understand the confinement mechanism of PET FRP-confinede concrete in square stub columns by conducting axial compression tests. Particularly, the influences of confinement thickness, corner radius and specimen size were investigated. Test results reveal that the specimen size is not significant for small- and medium-sized stub columns with a similar confinement level. The minimum confinement stiffness ratio and modified confinement ratio for achieving a sufficient confinement are 0.0036 and 0.13 respectively. Additionally, assessments of existing confinement models for PET FRP-confined concrete are conducted.

Comparison of Helium Abundance between ICMEs and Solar Wind near 1 au

Abstract The helium abundance, defined as A He = n He/n H × 100, is ∼8.5 in the photosphere and seldom exceeds 5 in fast solar wind. Previous statistics have demonstrated that A He in slow solar wind correlates tightly with sunspot number. However, less attention is paid to the solar cycle dependence of A He within interplanetary coronal mass ejections (ICMEs) and comparing the A He characteristics of ICMEs and solar wind. In this paper we conduct a statistical comparison of helium abundance between ICMEs and solar wind near 1 au with observations of the Advanced Composition Explorer from 1998 to 2019 and find that the ICME A He also exhibits the obvious solar cycle dependence. Meanwhile, we find that the A He is obviously higher within ICMEs compared to solar wind, and the means within 37% and 12% of ICMEs exceed 5 and 8.5, respectively. It is interesting to answer where and how the high helium abundance originates. Our statistics demonstrate that 21% (3%) of ICME (slow wind) A He data points exceed 8.5 around solar maximum, which decreases dramatically near minimum, while no such high A He values appear in the fast wind throughout the whole solar cycle. This indicates that the high A He (e.g., >8.5) emanates from active regions as more ICMEs and slow wind originate from active regions around maximum, and it supports that both active regions and quiet-Sun regions are the sources of slow wind. We suggest that the high A He from active regions could be explained by means of the magnetic loop confinement model and/or photoionization effect.

On the regularity of optimal dynamic blocking strategies

The paper studies a dynamic blocking problem, motivated by a model of optimal fire confinement. While the fire can expand with unit speed in all directions, barriers are constructed in real time. An optimal strategy is sought, minimizing the total value of the burned region, plus a construction cost. It is well known that optimal barriers exists. In general, they are a countable union of compact, connected, rectifiable sets. The main result of the present paper shows that optimal barriers are nowhere dense. The proof relies on new estimates on the reachable sets and on optimal trajectories for the fire, solving a minimum time problem in the presence of obstacles.

Compressive Behavior and Analytical Model of Ultra-Early Strength Concrete-Filled FRP Tube With Zero Curing Time

Fiber-reinforced polymer (FRP) has been widely used in civil engineering due to its light weight, high strength, convenient construction, and strong corrosion resistance. One of the important applications of FRP composites is the concrete-filled FRP tube (CFFT), which can greatly improve the compressive strength and ductility of concrete as well as facilitate construction. In this article, the compressive performances of a normal concrete-filled FRP tube (N-CFFT) column with 5-hour curing time and an ultra-early strength concrete-filled FRP tube (UES–CFFT) column with zero curing time were studied by considering the characteristics of rapid early strength improvement of ultra-early strength concrete and the confinement effect of the FRP tube. Monotonic axial compression tests were carried out on 3 empty FRP tubes (FTs) without an internal filler and 6 CFFT (3 N-CFFTs and 3 UES-CFFTs) specimens. All specimens were cylinders of 200 mm in diameter and 600 mm in height, confined by glass fiber–reinforced polymer (GFRP). Test results indicated that the compressive bearing capacity of the specimens increased significantly by adopting the ultra-early strength concrete as the core concrete of the CFFT, although the curing time was zero. It was also shown that the compressive behavior of the UES–CFFT specimens with zero curing time increased significantly than that of the N-CFFT specimens with 5-hour curing time because the former was able to achieve rapid strength enhancement in a very short time than the latter. The ultimate compressive strength of UES–CFFT specimens with zero curing time reached 78.3 MPa, which was 66.2 and 97.2% higher than that of N-CFFT with 5-hour curing time and FT specimens, respectively. In addition, a simple confinement model to predict the strength of UES–CFFT with zero curing time in ultimate condition was introduced. Compared with the existing models, the proposed model could predict the ultimate strength of UES–CFFT specimens with zero curing time with better accuracy.

Predicting the Strength of Rectangular Reinforced Concrete Columns Confined with FRP Sheets

A complete reorganization about the behavior of rectangular RC columns confined with FRP sheet is very important to predict the axial compressive strength values of the strengthened rectangular RC columns. That is because the process of strengthening RC rectangular column depending on several parameters that role this type of strengthening. These parameters include the characteristics of the used fiber, the grade of concrete and the geometry of the cross section including the rectangularity aspect ratio, corner radius, and size of specimens. Besides that, using a wide scope of experimental data may affect positively to generalize a model that considers the whole parameters affect the value of the axial strength. So, in this paper a review about parameters that affect the axial compressive strength values of rectangular RC columns was conducted. After that, based on the test results regarding FRP-confined rectangular RC columns available in the literature or conducted by the author, some existing confinement models for rectangular RC columns were assessed. Further, a new model is proposed through regression analysis of the database. A new model is proposed through regression analysis of the database. The proposed model was found to be in good agreement with the test results in the database. Finally, based on the results conclusions were drawn.

Finite element modeling and regression analysis of concrete filled – Glass fibre reinforced polymer tubes

This exploratory research narrates the axial compressive behavior of concrete filled circular GFRP (Glass Fibre Reinforced Polymer) tubes under concentric compression using FEA software ANSYS15.0, followed by optimizing the confinement models using Number Cruncher Statistical System (NCSS11). In this study about 40 specimens having (H/D ratio confined to 2) 150 mm diameter and 300 mm height were considered with tube thicknesses being 3, 4, 5 and 6 mm. The unconfined concrete strength was varied between 30 MPa and 120 MPa. Newer simplified linear confinement models were arrived for the short unreinforced CFFT columns which encourages optimality followed by acceptable correlation with the available codal equations of ACI 440.2R08.

Dual Superconductor Model of Confinement: Quantum-String Representation of the 4D Yang–Mills Theory on a Torus and the Correlation Length away from the London Limit

This paper is devoted to the dual superconductor model of confinement in the 4D Yang–Mills theory. In the first part, we consider the latter theory compactified on a torus, and use the dual superconductor model in order to obtain the Polchinski–Strominger term in the string representation of a Wilson loop. For a certain realistic critical value of the product of circumferences of the compactification circles, which is expressed in terms of the gluon condensate and the vacuum correlation length, the coupling of the Polchinski–Strominger term turns out to be such that the string conformal anomaly cancels out, making the string representation fully quantum. In the second part, we use the analogy between the London limit of the dual superconductor and the low-energy limit of the 4D compact QED, to obtain the partition function of the dual superconductor model away from the London limit. There, we find a decrease of the vacuum correlation length, and derive the corresponding potential of monopole currents.

RETRACTED: A correlation study between size and etching time in Ge mesoporous toward the incorporation of phonon dispersion effect in PCM

In this work, a new correlation study based on the phonon confinement model (PCM) and some advanced characterization tools was performed to extract the size of germanium (Ge) nanocrystals (NCs) fabricated by bipolar electrochemical etching. The PCM was established by incorporating simultaneously the size distribution and phonon dispersion effects. A correlation study of Raman spectroscopy with Atomic force microscopy (AFM), and High-resolution scanning transmission electron microscope (HRSTEM) was confirmed the presence of a spherical core with an average size of 8 nm and very small crystallites of 3 nm. This study confirms that the phonon dispersion has an excellent contribution to the broadness and the shifting of the Raman lines of Ge NCs. In addition, an observation of the breaking down and deviation of the PCM model due to the presence of crystallites in the range of [1–5 nm] is confirmed. • Strong contribution of phonon dispersion effect to quantum confinement effect in Ge nanocrystals. • AFM and Raman spectroscopy as powerful probing tools for tuning the synthesis parameters of Ge porous layers. • Limitations of phonon confinement model (PCM) is confirmed in the size range of [2–5 nm].

Analytical modeling of subband quantization and quantum transport in very Low-dimensional dual metal double gate TFET

We present a novel and comprehensive quantum analytical modeling of a sub-20 nm Dual Metal Double Gate (DMDG) Tunnel Field Effect Transistor (TFET) for the first time in literature. Owing to structural confinement at sub-20 nm regime, the energy states at channel are quantized and carrier propagation is regulated by quantum transport . We address such quantization aspects (viz. subband quantization, bandgap shifting, tunneling through barrier etc.) and incorporate them in analytical modeling using self-consistent solution of Schrödinger-Poisson's equation. As a result of work function difference at gate, we observe creation of quantum well , followed by a tunneling barrier, along the channel. Energy states in the quantum well are derived from Schrodinger equation, whereas, transmission coefficients are derived for each tunneling barrier. Finally, current density is obtained using ‘Landauer formula for quantum transport’. We methodically study the effects of structural confinement on device performances and observe significant shift from classical counterpart. Moreover, we note that quantization in DMDG TFET can be optimized that will lead to superior device performance. The results are verified with simulation data in each occasion to substantiate analytical models. • In this work, compact analytical model of quantum confinement in low-dimensional Dual Metal Double Gate TFET is presented. • Formation of quantum well, quantum tunneling, band gap widening effect and density of states correction are analysed. • Modelling is done based upon self-consistent Schrödinger-Poisson's solution and ‘Landauer formula for quantum transport’. • Device performances are explored in light of quantum confinement and results are validated through device simulation. • Comparative performance analysis is presented between semi-classical and quantum approach..

Interfacial Confinement in Semi-Crystalline Shape Memory Polymer Towards Sequentially Dynamic Relaxations

Sequential glass and melting transitions in semi-crystalline shape memory polymers (SMPs) provide great opportunities to design and generate multiple shape-memory effects (SMEs) for practical applications. However, the complexly dynamic confinements of coexisting amorphous and crystalline phases within the semi-crystalline SMPs are yet fully understood. In this study, an interfacial confinement model is formulated to describe dynamic relaxation and shape memory behavior in the semi-crystalline SMPs undergoing sequential phase/state transitions. A confinement entropy model is first established to describe the glass transition behavior of amorphous phase within the SMPs based on the free volume theory, where the free volume is critically confined by the crystalline phase. An extended Avrami model is then formulated using the frozen volume theory to characterize the melting and crystallization transitions of the crystalline phase in the SMPs, whose interfacial confinement with the amorphous phase has been identified as the driving force for the supercooled regime. Furthermore, an extended Maxwell model is formulated to describe the effect of dynamic confinement of two phases on the multiple SMEs and shape recovery behaviors in the semi-crystalline SMPs. Finally, the effectiveness of the newly proposed model is verified using the experimental data reported in the literature. This study aims to provide a new methodology for the dynamic confinements and cooperative principles in the semi-crystalline SMP towards multiple SMEs.

On non-monotonic temperature dependence of linear contact probability in atomic chains

In this paper, we theoretically investigate the temperature T dependence of linear contact probability in atomic chains. In these chains, the transverse motion of the electrons is assumed to be confined in the harmonic oscillator confinement model. The intra-chain electron correlations are treated within both Hartree–Fock Approximation (HFA) and Random Phase Approximation (RPA). As artifact HFA correlation functions are used in the RPA perturbative calculations. Results are presented for numerically computed pair-correlation functions at different temperatures and electron densities. An enhanced singlet-state is observed in these chains at zero inter-electronic spacing which remains independent of T. At non zero inter-electronic spacing, shrinking of Pauli’s hole is observed with increasing T. Using the RPA, the short-range pair-correlation functions are found to be considerably modified at finite-T and contact probability shows non-monotonic dependence on T. Smearing of exchange-correlation hole is also observed above a critical value of T in the diffusion zone. We also estimate the strength of the coupling parameter up to what the RPA is capable of dealing with carrier correlations in atomic chains. This work may prove useful for density functional theory calculations as estimation of the exchange-correlation hole is imperative for exchange-correlation functionals.

Confinement model for concrete wrapped with fiber reinforced cementitious mortar

Fiber reinforced cementitious mortar (FRCM) improves the performance of fiber-reinforce polymer (FRP) by replacing the organic matrix (e.g., epoxy) with inorganic one, resulting in a more sustainable alternative with a much improved fire resistance. While numerous models have been developed for FRP-confined concrete, FRCM-confined concrete have not received nearly as much attention. This study introduces a design-oriented model for FRCM-confined concrete. The model is the first to be derived from a very large database comprising 139 experimental specimens with various geometric and material properties, complemented with additional 144 numerical specimens obtained from finite element (FE) analysis. A nonlinear three-dimensional FE model was developed and verified with experimental results. It was used to examine the effects of mortar compressive strength (fm) and thickness (tm), type of FRP fabric, number of FRCM layers (n), compressive strength of unconfined concrete (fco), and height-to-diameter ratio (H/D). Results showed that the confined concrete strength (fcc) increases linearly as fm and tm increase, for all examined n, fco, and (H/D) values. fcc also varies almost linearly with n for all fabric types. A statistical analysis was performed on the combined database and a semi-empirical confinement model was developed to predict the peak strength and corresponding strain. It provided much better statistical performance and correlation with results than existing models and included a special coefficient for the effects of mortar properties.

Behavior and design of thin-walled double-skin concrete-filled rectangular steel tubular short and slender columns with external stainless-steel tube incorporating local buckling effects

Rectangular concrete-filled double-skin steel tubular (CFDST) columns consisting of stainless-carbon steel tubes are high-performance composite columns that offer high corrosion resistance in harsh environments and have a wide range of applications in the construction industry. However, the buckling resistance of CFDST short and slender columns has not been properly investigated and design models for such columns need to be developed. In this paper, an extensive study on their performance is undertaken by employing the cost-effective fiber-based computation model. An accurate new confinement model for the confined concrete is suggested and implemented in the numerical modeling. The computational analysis procedures, which simulate the complete load-axial strain (P−ɛ) curves, load-lateral deflection (P−um) curves, and interaction diagrams of CFDST columns, are presented. The experimental data available is employed to validate the numerical predictions. The fundamental behavior of CFDST columns is then studied to investigate the influences of a wide range of column parameters. On the setback of the lack of design specifications, design models for such columns are suggested and validated against the test and numerical results. The mathematical model developed is found to be a computationally efficient simulator that can simulate the responses of CFDST short and slender columns loaded either concentrically or eccentrically and the design models suggested can be used in the absence of the proper guidelines from the international design codes.

Assessment of Confinement Models and Minimum Volumetric Ratio for Glass Fiber-Reinforced Polymer-Reinforced Concrete Circular Columns

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Computational analysis of axially loaded thin-walled rectangular concrete-filled stainless steel tubular short columns incorporating local buckling effects

This paper investigates the structural performance of concrete-filled stainless steel tubular (CFSST) columns composed of rectangular and square sections. A fiber-based mathematical model is developed to simulate the nonlinear performance of such columns loaded concentrically accounting for the local buckling of steel tube. An accurate lateral pressure model, as well as a strength degradation parameter are proposed based on the existing test results and incorporated in the mathematical modeling developed. A large test dataset is used to validate the accuracy of the numerical prediction. The mathematical model is employed to study the sensitivities of important column parameters on their axial behavior. The accuracy of the existing confinement model of rectangular CFST columns is evaluated in predicting the performance of CFSST short columns. Furthermore, the accuracy of the existing codified design models as well as and the simplified design model proposed in this study to quantify the ultimate compressive strength of such columns is investigated. An accurate artificial neural network (ANN) model along with the GUI feature is developed for the design engineers as a tool to predict their ultimate axial strengths.

The magnetized white dwarf + helium star binary evolution with accretion-induced collapse

ABSTRACT Accretion-induced collapse (AIC) from oxygen/neon/magnesium composition white dwarf (ONeMg WD) + stripped helium (He) star binaries is one promising channel to form peculiar neutron star objects. It has been discussed that the WD’s magnetic field may alter the accretion phase in the WD binary evolution. By considering non-magnetic and sufficiently magnetized WDs, we investigate the evolution of ONeMg WD + He star binaries with detailed stellar evolution and binary population synthesis simulations. The role of the magnetically confined accretion in the possible formation pathway for like millisecond pulsars (MSPs) and magnetars is also studied. Comparing with the case of spherically symmetric accretion, the mass accumulation efficiency of the WDs is enhanced at low mass-transfer rate under the magnetic confinement model. The initial parameter space of the potential AIC progenitor systems moves toward shorter orbital period and lower donor mass (but not so significantly) due to the effect of the magnetic confinement. This also allows final MSPs to have lower mass WD companions and shorter orbital periods. There is no significant difference between the Galactic birth rates of the AIC derived with and without the magnetic confinement, which implies that the magnetic field of the WD does not dramatically change the number of ONeMg WD + He star binaries which can produce AIC. It is worth noting that these conclusions can be applied for the carbon/oxgen (CO) WD + He star binaries as progenitors of type Ia supernovae, because the accretion phases of ONeMg WDs and CO WDs are similar. The Galactic rate of magnetars possibly formed via AIC of highly magnetized WDs is $0.34\times 10^{-4}\, {\rm yr}^{-1}$.

Strength models for uPVC-confined concrete

In the present study, an experimental program was executed to investigate the performance of a composite structural system under direct compression load. The system consists of a uPVC tube as the mold for pouring the fresh concrete and a confining device for structural concrete. Three thicknesses of plastic tubes (4, 5, 7 mm) were investigated using four sets of three stub columns. Rice husk ash (RHA) was used as a cement replacement material to improve the strength and other mechanical properties of concrete core with target compressive strengths of 30 MPa for sets one and two and 60 MPa for sets three and four, respectively. The load capacity of uPVC strengthened blended concrete improved, and the ultimate failure is ductile due to the elongation capacity of the polymeric tube. To examine the post-peak behavior of the confining device at near-collapse conditions, two stub columns were subjected to five repeated loading that almost produced full collapse conditions in each cycle of loading after the first cycle. The tubes effectively dissipated energy by plastic yielding, which could be considered a partial progressive failure. Several analytical expressions have been proposed, in total twenty-four, for predicting the strength capacity of the composite system. However, most of these empirical expressions have been derived based on limited experimental tests. Therefore, to assess the performance of the existing strength models in predicting the capacity of PVC-confined concrete (PCC) and uPVC-confined concrete (uPCC); a comprehensive database of 389 test results was assembled from the published literature that covers the studies published in the period 1979–2021 combined with the twelve data from the present study. To account for the height/diameter ratio (H/D), three cases were examined; case one (3 ≤ H/D >3), case two (H/D ≤ 3), and case three (H/D >3). Based on the compiled database, two strength-based confinement models were proposed for circular concrete specimens confined externally with PVC or uPVC tube. The two models include several parameters that influence the properties of the concrete core and the confining device. The proposed models are the most accurate among all the models yielding lower values of absolute average error for the three cases examined.

Confinement model for LRS FRP-confined concrete using conventional regression and artificial neural network techniques

Concrete confined using fiber-reinforced polymer (FRP) composites experience significant enhancements in strength and strain. For the seismic retrofitting of existing reinforced concrete (RC) structures, a large rupture strain (LRS) FRP (i.e., polyethylene terephthalate and naphthalate, denoted as PET and PEN respectively), with a larger rupture strain of more than 5%, is a promising alternative to conventional FRPs with a rupture strain of less than 3%. The majority of analytical models on the stress–strain behavior of FRP-confined concrete under axial compression have focused largely on concrete confined with the traditional FRP material. Analytical research on LRS FRP-confined concrete is, however, limited. Moreover, all existed stress–strain models were determined based on theoretical analysis and test data fitting. In this paper, the artificial neural networks (ANN) method is employed to build a confinement model directly from experimental data to predict the different components of the stress–strain response. A test database consisting of 226 axial compression tests on LRS FRP-confined concrete specimens is used. The test results, in terms of full confined stress–strain response, strength, strain, FRP rupture strain, and dilation response were investigated. Predictive expressions and practical ANN models for the strength, strain, and shape of an axial stress–strain response are provided. Existing models for LRS FRP-confined concrete were also evaluated. The results of the existing and proposed models report that the proposed methods achieve significantly better results.