Confinement Technique Research Articles

Confinement Effect of Geo-grid and Conventional Shear Reinforcement Bars Subjected to Corrosion

An experimental study was performed to examine the effects of polyester geo-grid as a shear reinforcement bar for corroded and uncorroded reinforced concrete beams. The main aim of this study was to investigate the effect of geo-grids on flexural strength, moment-curvature, bond–slip and crack patterns for uncorroded and corroded reinforced concrete beams. For each parameter, a geo-grid confinement technique was compared with conventional reinforced concrete beams as a function of corrosion level. The experimental program consisted of testing ten reinforced concrete beams for two different configurations of shear reinforcement bars at six different corrosion levels (0% and approximately 2, 3, 5, 6, and 9%). Test specimens were subjected to an accelerated corrosion method to corrode the reinforcement bars using a full-scale corrosion pool. Actual corrosion levels were obtained from fully extracted reinforcement bars by breaking the concrete. At the same overall corrosion levels which were differed at longitudinal and transverse reinforcement bars at the same applied corrosion current time for different RC beams. Obtained actual corrosion levels with the aid of fully extracted reinforcement bars from concrete provided to examine the effect of corrosion levels by considering the type of reinforcement bars. The results indicated that the performance of the polyester geo-grid was very poor compared to conventional steel stirrups, even at this stage of corrosion. It was found that the utility of a geo-grid as shear reinforcement bars in reinforced concrete beams is not proper.

Stress–strain evaluation of steel‐strapped high‐strength concrete with modified self‐regulating end clips

High‐strength concrete (HSC) is increasingly used in columns of building all over the world. Although it offers superior properties, it is relatively a brittle material. This study intends to improve the ductility of HSC using modified pretensioning confinement technique. It investigates the effects of the technique on the performance of the column and develops equations to predict the stress–strain. The basis of the technique is to apply a pretensioning force to relatively low‐cost steel straps wrapped around the specimens. A modified end clip which is able to be self‐regulated is used to secure the strap ends. The parameters studied include various spacing between straps and number of layers of straps. The confined specimens were tested in compression until failure under monotonic loading conditions, focusing particularly on the mode of failure, loads at peak and ultimate conditions and longitudinal and lateral strains in both concrete and straps. It was observed that the pretensioning technique using steel straps enhanced the ductility as well as the strength of the concrete as the confining ratio increases. Moreover, the layers of straps had also delayed the onset of volumetric expansion and therefore, the concrete failure. Based on the regression analysis, new equations of strength and strain for the confined HSC column have been developed to predict its stress–strain behavior.

Experimental analysis of rubble stone masonry walls strengthened by transverse confinement under compression and compression-shear loadings

ABSTRACTStone masonry walls of ancient buildings have reasonable resistance to vertical loads but lower resistance to shear forces and reduced tensile strength. However, to achieve such compressive strength the masonry must not disaggregate when subjected to loading. This can be achieved if during the construction of the walls larger stones, usually referred as “through stones”, are used, spanning the thickness of the wall, making it possible to improve the transverse confinement of the masonry. For rehabilitation projects and structural reinforcement of such buildings, the transverse confinement can be achieved by fixing steel elements perpendicular to the wall. This confinement technique is often part of a more comprehensive rehabilitation solution, which includes the application of mortar or concrete reinforced layers applied to the wall surface.This article presents results of an experimental research on material properties and mechanical characterisation of stone masonry specimens strengthened by two transverse confinement solutions (independent steel reinforcing rods and continuous steel ribbons wrapping the specimen). Specimens were tested under compression and compression and shear loadings.This experimental work is part of a major research project to study the mechanical behavior of URM and strengthened walls, and the characteristics of the building materials of such specimens.

Confinement of Full-Scale Masonry Columns with FRCM Systems

The effectiveness of FRP systems as a confinement technique to strengthen masonry columns has been widely investigated in the last decades. Recently, a new technique, Fabric Reinforced Cementitious Matrix (FRCM), based on the use of fibrous nets embedded in inorganic matrix, has been developed and investigated as a strengthening solution in masonry buildings. Actually, the number of experimental tests on masonry columns confined by using FRCM systems is very limited, especially for real scale specimens. To fill such gap an experimental program aimed at investigating the behaviour of full scale columns made of limestone masonry blocks confined with different FRCM systems has been carried out. The results of four uniaxial compression tests are illustrated and discussed. The used FRCM systems are made with glass and basalt dry nets embedded in a lime-based mortar. The influence of transverse confinement by using internal reinforcement in forms of pultruded GFRP bars has been also investigated. The mechanical properties of the confined specimens resulted increased in terms of load-carrying capacity and ultimate axial strain.

Testing of concrete elements with internal shape memory alloy spirals

In recent years, an innovative concrete confinement technique using shape memory alloys (SMAs) has emerged. The new technique utilises active confinement, which is proven to be more effective than traditional passive confinement in improving the strength and ductility of concrete. However, most of the previous research on this technique has focused on retrofit/repair applications of circular concrete elements by applying external SMA spirals or ties. This paper presents an experimental study on implementing this new confinement technique using SMA spirals as internal transverse reinforcement in newly constructed square columns. In this study, short, square, concrete columns are designed and constructed with internal longitudinal steel rebars and internal transverse reinforcement. One of the concrete columns is designed with internal SMA transverse spirals, while two other columns are constructed using traditional transverse steel reinforcement for comparison. Experimental results demonstrate that, compared to the traditional steel transverse reinforcement, SMA spirals effectively delay the longitudinal rebar buckling and significantly reduce strength degradation.

Plasticity Modeling of Concrete Confined With NiTiNb Shape Memory Alloy Spirals

Concrete confinement is proved to be an effective method to improve concrete strength and ductility. In recent years, a novel confinement technique using NiTiNb shape memory alloy (SMA) spirals was proposed and proved to be promising for seismic retrofit of concrete structures. Despite the experimental work that has been done in this area, there is few computational tools available that are capable of describing the three-dimensional constitutive behavior of NiTiNb-SMA confined concrete. This paper proposes a plasticity-based NiTiNb-SMA confined concrete constitutive model, which is capable of predicting and simulating three-dimensional stress-strain behavior of NiTiNb-SMA confined concrete under both monotonic and cyclic loading. New hardening/softening function, dilation rate function and damage parameter are derived and validated based on experimental results. The proposed model is able to closely simulate the axial and lateral stress-strain behaviors of NiTiNb-SMA confined concrete when compared to experimental results.

Mechanical activation-assisted electro-thermal explosion synthesis of the Ti2AlC phase

ABSTRACTThis study deals with the synthesis of the Ti2AlC phase using the Electro-Thermal Explosion under Pressure with Confinement (ETEPC) technique. The effects of the ETEPC technique and the milling process parameters on the TiCx phase content and the formation mechanism of the Ti2AlC phase were investigated. The latter is mainly affected by the morphology of the powder mixture and aluminum melted amount. The optimization of the above parameters allowed the achievement of the desired reaction, leading to the formation of the Ti2AlC phase with a purity of about 97 wt%. The results clearly demonstrate that the ETEPC process enables one to control both time and material synthesis temperature.

Strengthening of Circular RC Column through External Confinement using Ferrocement

Objectives: The present study investigates the effect of confinement using ferrocement as wrapping material on the circular RC columns under concentric loading condition. Methods: Experimental studies were carried out on the confining effect using external confinement technique with one layer and two layers of GI wire mesh under concentrically loaded condition. All columns were tested by uniform concentric compressive load from top with a hydraulic compression testing machine of capacity 1000 KN. Findings: Most of the researches have done on confining effect of either long column or short column (slenderness ratio more than 3). This paper demonstrates the confining effect on short column having slenderness ratio is less than 3, such a column is called pedestal. Pedestal is a form of short column which is used as a base support for steel structure, statue or vase. To protect the column of steel structure from corrosion that is in direct contact of soil, pedestal is provided. During earthquake such a structure can collapse or even cracks can develop. Hence, ferrocement structures are highly ductile and energy dissipating material that can undergoes large deformations without collapsing during earthquakes. Even the deformed structures can be strengthened at very low cost after deformation. Steel jacketing has proved to be an effective measure for strengthening or retrofitting and has been widely used in practice, but the engineering community is currently looking for alternatives. Applications/Improvements: Material like ferrocement is oldest, cost effective method emerges an alternative solution for strengthening of reinforced concrete column. External confinement or encasing of column with ferrocement enhances the strength and ductility of concrete column.

Formatting and ligating biopolymers using adjustable nanoconfinement

Sensitive visualization and conformational control of long, delicate biopolymers present critical challenges to emerging biotechnologies and biophysical studies. Next-generation nanofluidic manipulation platforms strive to maintain the structural integrity of genomic DNA prior to analysis but can face challenges in device clogging, molecular breakage, and single-label detection. We address these challenges by integrating the Convex Lens-induced Confinement (CLiC) technique with a suite of nanotopographies embedded within thin-glass nanofluidic chambers. We gently load DNA polymers into open-face nanogrooves in linear, concentric circular, and ring array formats and perform imaging with single-fluorophore sensitivity. We use ring-shaped nanogrooves to access and visualize confinement-enhanced self-ligation of long DNA polymers. We use concentric circular nanogrooves to enable hour-long observations of polymers at constant confinement in a geometry which eliminates the confinement gradient which causes drift and can alter molecular conformations and interactions. Taken together, this work opens doors to myriad biophysical studies and biotechnologies which operate on the nanoscale.

SHORT TERM DURABILITY OF STEEL-STRAP CONFINED CONCRETE

Steel strapping tensioning technique (SSTT) confinement has been proven as a type of external confinement to retrofit and upgrade concrete structures. Their remarkable enhancement to concrete mechanical properties, practicing active lateral confinement, low cost, easy to operate, time saving and no structure interruption during application have brought this technique as of the most affordable technique for column confinement, especially for high strength concrete (HSC) which naturally behaves insufficient in ductility. Although a great number of previous studies have demonstrated the performance of SSTT confinement, there are several anxieties related to the long term behaviour of SSTT confined columns which have yet been implemented especially in real hostile condition. Environmental effects, such as ultraviolet radiation exposure and saline solution (sea water) may affect the confining material properties, and therefore decrease the performance of the confined columns. In this study a total of twenty HSC specimens with dimension of 100 mm and 200 mm in diameter and height respectively were prepared, volumetric-identically pre-tensioned with steel strap and exposed to three conditions: indoor, outdoor and saline water for three months. The exposed specimens were monotonically tested and their performance was studied through the stress-strain relationship, mode of failure and degree of corrosion. The results show that none of the forenamed environmental conditions have exaggerating influence on the performance of the SSTT confined concrete specimens even some material has been severely corroded. It is then parallel compared with existing FRP confinement studies and the result proves that SSTT confinement able to possess the highest strength performance under similar environmental exposure.

STRENGTHENING AND REHABILITATION OF REINFORCEMENT CONCRETE SQUARE COLUMNS CONFINED WITH EXTERNAL STEEL COLLARS

Strengthening and rehabilitation by confinement technique of reinforced concrete columns was investigated. The columns were confined by external steel collars. Behavior and failure load of columns were experimentally investigated. Results show thatConfinement in concrete column has improved its strength and ductility. Effect of confined area, size of collar and compressive strength of concrete on strengthening was investigated .Confined areahad significanteffect on the failure loadfor strengthened specimens and had more effective on the failure load for repaired specimens. The confinment hadclearer effect with low compressive strength of concrete.The result show an increase in ultimate axial load reach to (12.36 –56.04%)for strengthening columns and (47.5 –96.7%)for reaparingcolumns

Analytical compressive stress–strain model for high-strength concrete confined with cross-spirals

The behavior of high-strength concrete members subjected to seismic loads is mainly based on the ultimate strength of concrete and its ductility. The ductility of reinforced concrete is defined by both axial stresses and strains, which could be represented by the total amount of energy that concrete can absorb before failure. Conventional spiral confinement increases the nominal compressive axial capacity of concrete due to the confinement action of the concrete core, which consequently provides increase in the crushing (failure) strain. The pitch (spacing) of spiral reinforcement has a significant effect on increasing the amount of energy that concrete can absorb. This paper presents a stress–strain model for the prediction of the confined compressive strength of high-strength concrete subjected to axial stress. The stress–strain model is based on confining concrete using cross-spirals. The main parameters were the spiral spacing, and the confinement technique either conventional or cross spirals. The model is based on the results of twenty-one high-strength reduced scale concrete columns that were tested under concentric compressive axial load. The proposed model was compared with two existing models where showed good agreement with the experimental results.

Evaluation of the Collection Length and Optical Path Enhancement in a-Si:H Solar Cells

The characterization of the electrical parameters of solar cells is fundamental to improve their performance. In the case of a-Si:H thin film solar cells, the degrading effect of light has to be mitigated, among others, with thin absorber layers and light confinement techniques. The novelty of this paper is the development of method that evaluates both, the light trapping enhancement and the collection length of the carriers in these and other field-driven devices. In this research we compared experimental results of a-Si:H cells with our simulation model, obtaining good agreement.

Indium-Tin-Oxide for High-performance Electro-optic Modulation

Abstract:Advances in opto-electronics are often led by discovery and development of materials featuring unique properties. Recently, the material class of transparent conductive oxides (TCO) has attracted attention for active photonic devices on-chip. In particular, indium tin oxide (ITO) is found to have refractive index changes on the order of unity. This property makes it possible to achieve electrooptic modulation of sub-wavelength device scales, when thin ITO films are interfaced with optical light confinement techniques such as found in plasmonics; optical modes are compressed to nanometer scale to create strong light-matter interactions. Here we review efforts towards utilizing this novel material for high performance and ultra-compact modulation. While high performance metrics are achieved experimentally, there are open questions pertaining to the permittivity modulation mechanism of ITO. Finally, we review a variety of optical and electrical properties of ITO for different processing conditions, and show that ITO-based plasmonic electro-optic modulators have the potential to significantly outperform diffractionlimited devices.

Nuclear fusion: bringing a star down to Earth

Nuclear fusion offers the potential for being a near limitless energy source by fusing together deuterium and tritium nuclei to form helium inside a plasma burning at 100 million K. However, scientific and engineering challenges remain. This paper describes how such a plasma can be confined on Earth, and discusses the similarities and differences with fusion in stars. It focuses on the magnetic confinement technique and, in particular, the method used in a tokamak. The confinement achieved in the equilibrium state is reviewed and it is shown how the confinement can be too good, leading to explosive instabilities at the plasma edge called edge localised modes (ELMs). It is shown how the impact of ELMs can be minimised by the application of magnetic perturbations and discusses the physics behind the penetration of these perturbations into what is ideally a perfect conducting plasma.

(Invited) Monolithic Integration of III-V Semiconductors by Selective Area Growth on Si(001) Substrate: Epitaxy Challenges & Applications

Driven by fabrication cost reduction and device performance improvement, the Silicon semiconductor industry continues its never-ending pursuit of new approaches for fabricating integrated circuits. Monolithic integration of III-V semiconductors epitaxially grown on Si substrate have been attracting much attention as building blocks for next-generation electronics and photonics due to their potential intrinsic properties. Direct heteroepitaxy of III-V compound semiconductors on Si has traditionally represented a formidable challenge, due to the extensive lattice mismatch of 8% between the Si substrate and high mobility III-V compounds, such as In0.53Ga0.47As/InP heterostructure. The defect confinement technique has recently attracted great interest due to the possibility of obtaining high quality III-V based active layers on Si. Using this approach we integrate III-V materials monolithically on Si through the epitaxial growth of III-V materials into a pre-patterned structure by Selective Area Metal-Organic Vapor Phase Epitaxy. We report here on the growth of InP on STI patterned Si wafers using the defect confinement technique while focusing on scaled trench widths (W < 50 nm). We demonstrate the impact of the crystalline alignment of the InP layer with the underlying substrate by exploring as starting geometry at the bottom in between the STI either a rounded etch pit covered with a Ge buffer layer versus a crystalline <111> V-groove structure in Si. We show the large impact of the main layer growth temperature and the growth pressure on the trench filling, the growth uniformity and the crystal quality which we could correlate with changes in resistivity and the presence of impurity diffusion in the III-V layer. Moreover, we derived a fundamental understanding and theoretical modeling of the growth mechanisms in STI trenches and the determining role of the nucleation layer. This lead to a strong enhancement of the crystalline quality and growth uniformity of the InP semiconductor. As a conclusion, this study of III-V selective area growth brings some elements for the optimization of the heteroepitaxy of III-V compounds on (001) oriented Si substrates. The demonstration of a clear reduction in defect density along the trench orientation is original and obviously confirm the potential of this heterogeneous integration option for high mobility logic devices, and photonic applications on a common Si platform.

Resonantly loaded apertures for sub‐diffraction near‐field imaging and surface probing

It is demonstrated that electromagnetic (EM) transmission through a subwavelength or non-resonant aperture in a conductive screen can be significantly enhanced by loading it with folded metallic strips exhibiting resonant properties. When illuminated by an EM plane wave, these loaded apertures enable very tight, subwavelength, collimation of the EM power in the near-field zone. The authors propose quasi-planar resonant insertion geometries that should allow, for the first time, simultaneous subwavelength near field focusing of both electric and magnetic fields. The proposed technique for resonance transmission enhancement and near-field confinement forms a basis for a new class of microwave near-field imaging probe with subwavelength resolution capable of operating over a wide range of imaging distances (0.01–0.25λ). Measurement results demonstrate the possibility of high-contrast (more than 3 dB in amplitude and 40° in phase) near-field subwavelength imaging of active sources as well as the characterisation of planar subwavelength non-resonant dielectric targets located in free space and at the interface of moderately lossy layered media.

Behavior of Confined Concrete Beam by Induced Compression Process

In order to provide higher mechanical effectiveness of confined concrete beam, the new technique proposed in this work consists to design at the ends of the steel reinforcements two opposing half cylindrical plates, creating an induced compression applied in the tended zone of the concrete beam element, when the steel reinforcement is subjected to tensile forces developed by the bending load. This technique ensures the concrete rigidity within the structure, avoids the problem of cracking and ruptures of the element and allows the transformation of the tensile force of the steel reinforcements into compressive force of the tended concrete inside the two half cylindrical plates. The confinement is induced by the displacement of the tended steel reinforcement, on all the transverse surface of the half-cylinder plates. This design avoids the penetration of the steel reinforcement in the concrete which generates a shear force of the section. Thus, the concrete of tended zone of the beam finds in position to take part in the resumption of the flexural efforts. The nonlinear finite element modeling shows that the proposed technique of confinement increases the strength and ductility of reinforced concrete beam. The numerical modelling analysis is completed by preliminary experimental work in order to allow for a better understanding of the behavior of this new confinement proposed technology.

General incorporation of diverse components inside metal-organic framework thin films at room temperature.

Porous metal-organic frameworks (MOFs) demonstrate great potential for numerous applications. Although hetero-functional components have been encapsulated within MOF crystalline particles, the uniform incorporation of functional species with different sizes, shapes and functions in MOF thin films with dual properties, especially at room temperature and without the degradation of the MOF framework, remains a significant challenge towards further enriching their functions for various purposes. Here we report a general method that can rapidly encapsulate diverse functional components, including small ions, micrometre-sized particles, inorganic nanoparticles and bioactive proteins, in MOF thin films at room temperature via a metal-hydroxide-nanostrand-assisted confinement technique. These functional component-encapsulated MOF composite thin films exhibit synergistic and size-selective catalytic, bio-electrochemical, conductive and flexible functionalities that are desirable for thin film devices, including catalytic membrane reactors, biosensors and flexible electronic devices.

Effect of Active versus Passive Confinement on Seismic Response of Wide RC Columns with Lap Splices

AbstractThe results of an experimental study on seismic bond strengthening of spliced reinforcement in wide RC columns using external confinement are presented. Two types of confinement techniques were evaluated and compared, as follows: (1) a combination of external carbon fiber-reinforced polymer (CFRP) jacket and CFRP anchors, and (2) active confinement by means of pretensioned steel anchor rods. The effectiveness of the different strengthening techniques was evaluated by comparing with test results of companion as-built columns, and earthquake-designed columns which were detailed in accordance with the seismic provisions of a national building code. The columns were subjected to a quasi-static cyclic loading, simulating regions of high seismic hazard. In addition to the type of the strengthening system used, the test variables included area and diameter of the column longitudinal reinforcement. The as-built columns suffered bond and load degradation immediately after yielding of the spliced reinforcem...