scholarly journals Experimental analysis and design strength models adopted by international guides for FRP-confined concrete columns subjected to axial compression

2021 ◽  
Vol 71 (344) ◽  
pp. e266
Author(s):  
J.P. Gutiérrez ◽  
S. Martínez ◽  
A. De Diego ◽  
V.J. Castro ◽  
L. Echevarría
Keyword(s):  
Carbon Fiber ◽  
Cross Sections ◽  
Rectangular Cross Section ◽  
Effective Strain ◽  
Plain Concrete ◽  
Experimental Program ◽  
Design Strength ◽  
Analysis And Design ◽  
Intermediate Size ◽  
Strength Models

Carbon fiber jacketing is an efficient technique for increasing the strength and strain capacity of concrete circular and square section columns subjected to axial load, although confinement efficiency decreases for rectangular cross-section members. The research project BIA 2016-80310-P includes an experimental program on intermediate-size plain concrete specimens strengthened with carbon fiber jackets, mostly with square and rectangular cross-sections. The results, alongside others with similar characteristics from two databases published, are compared to predictions of four international guides. The incidence of the key parameters in the experimental results is analyzed, such as the aspect ratio of the section, the effective strain in FRP jacket attained at failure or the rounded corner radius. As a result, two efficiency strain factors are proposed, one for circular and another for rectangular specimens. The predictions contained in certain guides, based on a simple linear design-model, are improved by using the proposed efficiency strain factor for rectangular sections.

EXPERIMENTAL INVESTIGATION ON STRENGTHENING OF REINFORCED CONCRETE COLUMNS WITH CARBON CONCRETE COMPOSITE

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Klaus Holschemacher ◽  
Dennis Messerer ◽  
Wladislaw Polienko
Keyword(s):  
Reinforced Concrete ◽  
Carbon Fiber ◽  
Bearing Capacity ◽  
Cross Sections ◽  
Concrete Columns ◽  
Experimental Program ◽  
Load Bearing Capacity ◽  
Reinforced Concrete Columns ◽  
Load Bearing ◽  
Concrete Members

The application of textile reinforced concrete is well-approved technique for strengthening of reinforced concrete members. When using carbon fiber meshes and carbon fiber reinforced polymer bars as reinforcement, this material is called carbon concrete composite. Based on the outstanding properties of carbon fibers, carbon concrete composite is characterized by high bending and tensile strength, and good durability. Therefore, carbon concrete composite is increasingly applied as replacement for ordinary steel bar or steel mesh reinforced concrete. It is favorable building material for production of new buildings and for strengthening of existing reinforced concrete members. In the context of strengthening of existing reinforced concrete columns, it is a usual procedure to cover the member’s surface with a thin layer of carbon concrete composite aiming on reduction of lateral strains of the core concrete when load is increasing. The result is an increased load-bearing capacity of the strengthened column. However, there is insufficient knowledge about the influence of curvature of the carbon meshes in circular cross-sections and in the corners of rectangular cross-sections on their load-bearing capacity. For this reason, an experimental program started to study the influence of curvature, number and type of mesh layers and specimen dimensions on structural behavior of strengthened columns under axial loading. As main outcome it can be stated that besides the curvature other parameters like yarn properties are of essential importance.

Determination of Creep Behavior of Concrete Beams Made with Rice Husk Ash

2021 ◽  
Vol 15 (1) ◽  
pp. 339-346
Author(s):  
Winfred Mutungi ◽  
Raphael N. Mutuku ◽  
Timothy Nyomboi
Keyword(s):  
Prediction Model ◽  
Rice Husk ◽  
Creep Behavior ◽  
Rice Husk Ash ◽  
Concrete Beams ◽  
Plain Concrete ◽  
Reinforced Concrete Beams ◽  
Partial Replacement ◽  
Design Strength ◽  
Concrete Production

Background: Creep in concrete is a long-term deformation under sustained loading. It is influenced by many factors, including constituent materials, environmental conditions, among others. Whenever there is an alteration in the convectional concrete preparation process, the creep characteristics need to be realistically assessed. In the present construction, rice husk ash has been used for partial replacement of cement in concrete production. This is because its properties of both tensile and compressive strength in concrete have been tested and found comparable with plain concrete. However, durability characteristics such as creep, which take place in the long run, have not been realistically assessed. Therefore, it is important to study the creep of rice husk ash concrete, which will further help in the development of a creep prediction model for such concrete for use by design engineers. Objectives: Rice husk ash was used as supplementary cementitious material in concrete, and the creep behavior was studied with the aim of producing a creep prediction model for this concrete. Methods: The cement was replaced with 10% of rice husk ash in concrete with a design strength of 30MPA. Reinforced concrete beams were cast and loaded for flexural creep 35 days after casting. The loading level was 25% of the beam’s strength at the time of loading. The creep observation was done for 60 days. The rice husk used was obtained locally from Mwea irrigation scheme in Kenya. The experiments were carried out in our school laboratory at Jomo Kenyatta university of Agriculture and Technology. Results: The creep strain data of rice husk ash concrete beams was obtained with the highest value of 620 micro strain for 60 days. The results were used to develop a creep prediction model for this concrete. Conclusion: A creep prediction model for rice husk ash concrete has been developed, which can be adopted by engineers for class 30 of concrete containing rice husk ash at a 10% replacement level.

scholarly journals Experimental Investigation of a Rectangular Airlift Pump

2010 ◽  
Vol 2010 ◽  
pp. 1-5 ◽  
Author(s):  
I. I. Esen
Keyword(s):  
Experimental Investigation ◽  
Cross Section ◽  
Flow Rate ◽  
Liquid Flow ◽  
Liquid Flow Rate ◽  
Rectangular Cross Section ◽  
Hydraulic Performance ◽  
Experimental Program ◽  
Empirical Equations ◽  
Airlift Pump

Hydraulic performance of an airlift pump having a rectangular cross-section 20 mm × 80 mm was investigated through an experimental program. The pump was operated at six different submergence ratios and the liquid flow rate was measured at various flowrates of air injected. The effectiveness of the pump, defined as the ratio of the mass of liquid pumped to the mass of air injected, was determined as a function of the mass of air injected for different submergence ratios. Results obtained were compared with those for circular airlift pumps using an analytical model for circular pumps. Effectiveness of the rectangular airlift pump was observed to be comparable to that of the circular pumps. Hydraulic performance of the rectangular airlift pump investigated was then described by a set of semilogarithmic empirical equations.

scholarly journals Particle separation of a modified feed nozzle hydrocyclone under different operating parameters

2021 ◽  
Vol 11 (5) ◽  
pp. 159-170
Author(s):  
Zsolt Hegyes ◽  
Máté Petrik ◽  
L. Gábor Szepesi
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Rectangular Cross Section ◽  
Circular Cross Section ◽  
Particle Separation ◽  
Baffle Plate ◽  
Important Data ◽  
Preliminary Research ◽  
All Speeds ◽  
Plate Solution

During the operation of the hydrocyclone the cut size diameter is the most important data. This is connected to feed rate, which is closely related to the feed cross section. Preliminary research has revealed that square cross-section is more effective than circular cross-section. The research compared 2 types of feed cross sections at 5 different feed rates. One is a standard rectangular cross-section and the other is a square cross-section that narrows with a baffle plate. Preliminary calculations for cut size diameter have shown that better particle separation at all speeds can be achieved with the baffle plate solution. In both types, the increased velocity created decreased cut size diameter. During the simulation, the baffle plate did not cause any abnormalities in the internal pressure and velocity distributions. The simulation revealed that the particles did not behave as previously calculated.

scholarly journals Simplified and Accurate Stiffness of a Prismatic Anisotropic Thin-Walled Box

2018 ◽  
Vol 12 (1) ◽  
pp. 1-20 ◽  
Author(s):  
Giacomo Canale ◽  
Felice Rubino ◽  
Paul M. Weaver ◽  
Roberto Citarella ◽  
Angelo Maligno
Keyword(s):  
Cross Sections ◽  
Torsional Stiffness ◽  
Element Analysis ◽  
Cross Sectional ◽  
Analysis And Design ◽  
Proposed Model ◽  
Vertical Walls ◽  
Thin Walled ◽  
High Level ◽  
Realistic Geometries

Background:Beam models have been proven effective in the preliminary analysis and design of aerospace structures. Accurate cross sectional stiffness constants are however needed, especially when dealing with bending, torsion and bend-twist coupling deformations. Several models have been proposed in the literature, even recently, but a lack of precision may be found when dealing with a high level of anisotropy and different lay-ups.Objective:A simplified analytical model is proposed to evaluate bending and torsional stiffness of a prismatic, anisotropic, thin-walled box. The proposed model is an extension of the model proposed by Lemanski and Weaver for the evaluation of the bend-twist coupling constant.Methods:Bending and torsional stiffness are derived analytically by using physical reasoning and by applying bending and torsional stiffness mathematic definition. Unitary deformations have been applied when evaluation forces and moments arising on the cross section.Results:Good accuracy has been obtained for structures with different geometries and lay-ups. The model has been validated with respect to finite element analysis. Numerical results are commented upon and compared with other models presented in literature.Conclusion:For cross sections with a high level of anisotropy, the accuracy of the proposed formulation is within 2% for bending stiffness and 6% for torsional stiffness. The percentage of error is further reduced for more realistic geometries and lay-ups.The proposed formulation gives accurate results for different dimensions and length rations of horizontal and vertical walls.

scholarly journals Electrodeposited Platinum Iridium Enables Microstimulation With Carbon Fiber Electrodes

2021 ◽  
Vol 3 ◽  
Author(s):  
Elena della Valle ◽  
Beomseo Koo ◽  
Paras R. Patel ◽  
Quentin Whitsitt ◽  
Erin K. Purcell ◽  
...  
Keyword(s):  
Carbon Fiber ◽  
Cross Sections ◽  
Minimal Scarring ◽  
Pulse Testing ◽  
Implant Tests ◽  
Before And After ◽  
Voltage Transients ◽  
Scanning Electron

Ultrasmall microelectrode arrays have the potential to improve the spatial resolution of microstimulation. Carbon fiber (CF) microelectrodes with cross-sections of less than 8 μm have been demonstrated to penetrate cortical tissue and evoke minimal scarring in chronic implant tests. In this study, we investigate the stability and performance of neural stimulation electrodes comprised of electrodeposited platinum-iridium (PtIr) on carbon fibers. We conducted pulse testing and characterized charge injection in vitro and recorded voltage transients in vitro and in vivo. Standard electrochemical measurements (impedance spectroscopy and cyclic voltammetry) and visual inspection (scanning electron microscopy) were used to assess changes due to pulsing. Similar to other studies, the application of pulses caused a decrease in impedance and a reduction in voltage transients, but analysis of the impedance data suggests that these changes are due to surface modification and not permanent changes to the electrode. Comparison of scanning electron microscope images before and after pulse testing confirmed electrode stability.

scholarly journals Self-Inductance of the Circular Coils of the Rectangular Cross-Section with the Radial and Azimuthal Current Densities

Physics ◽  
2020 ◽  
Vol 2 (3) ◽  
pp. 352-367
Author(s):  
Slobodan Babic ◽  
Cevdet Akyel
Keyword(s):  
Cross Sections ◽  
Special Functions ◽  
Rectangular Cross Section ◽  
The Self ◽  
Thin Wall ◽  
Elementary Functions ◽  
Special Cases ◽  
Current Densities ◽  
New Formula ◽  
Azimuthal Current

In this paper, we give new formulas for calculating the self-inductance for circular coils of the rectangular cross-sections with the radial and the azimuthal current densities. These formulas are given by the single integration of the elementary functions which are integrable on the interval of the integration. From these new expressions, we can obtain the special cases for the self-inductance of the thin-disk pancake and the thin-wall solenoids that confirm the validity of this approach. For the asymptotic cases, the new formula for the self-inductance of the thin-wall solenoid is obtained for the first time in the literature. In this paper, we do not use special functions such as the elliptical integrals of the first, second and third kind, nor Struve and Bessel functions because that is very tedious work. The results of this work are compared with already different known methods and all results are in excellent agreement. We consider this approach novel because of its simplicity in the self-inductance calculation of the previously-mentioned configurations.

LOAD-BEARING CAPACITY OF CONCRETE-FILLED STEEL COLUMNS

2009 ◽  
Vol 15 (1) ◽  
pp. 21-33 ◽  
Author(s):  
Artiomas Kuranovas ◽  
Douglas Goode ◽  
Audronis Kazimieras Kvedaras ◽  
Shantong Zhong
Keyword(s):  
Bearing Capacity ◽  
Cross Section ◽  
Cross Sections ◽  
Rectangular Cross Section ◽  
Circular Cross Section ◽  
Steel Tube ◽  
Sustained Load ◽  
Load Bearing Capacity ◽  
Concrete Core ◽  
Load Bearing

This paper represents the analysis of 1303 specimens of CFST experimental data. Test results are compared with EC4 provided method for determining the load‐bearing capacity of these composite elements. Several types of CFSTs were tested: both circular and rectangular cross‐sections with solid and hollow concrete core with axial load applied without and with moment, with sustained load and preloading. For circular cross‐section columns there is a good agreement between the test failure load and the EC4 calculation for both short and long columns with and without moment. For rectangular cross‐section columns the agreement is good except when the concrete cylinder strength was greater than 75 MPa, when many tests failed below the strength predicted by EC4. Preloading the steel tube before filling with concrete seems to have no effect on the strength. This paper also presents the stress distribution, confinement distribution and complete average longitudinal stress‐strain curves for concrete‐filled steel tubular elements. Based on the definition of the “Unified Theory”, the CFST is looked upon as an entity of a new composite material. In this paper, the research achievement of the strength and stability for centrifugal‐hollow and solid concrete filled steel tube are introduced. These behaviours relate to the hollowness ratio and the confining indexes of corresponding solid CFST. If the hollow ratio equals to 0,4–0,5 and over, the N‐ϵ relationship exists in steady descending stage. The critical stress of CFST elements stability is determined as an eccentric member with the initial eccentricity by use of finite element method. Santrauka Straipsnyje analizuojami 1303 betonšerdžių plieninių strypų bandinių eksperimentiniai duomenys. Duomenys lyginami su eurokode 4 pateiktais kompozitinių elementų laikomosios galios nustatymo metodais. Analizuojami šie betonšerdžių plieninių strypų bandinių tipai: pilnaviduriai ir tuščiaviduriai, apskrito ir stačiakampio skerspjūvio kolonos, kurių galuose veikia arba neveikia momentas, su iš anksto pridėta arba ilgalaike apkrova. Apskrito skerspjūvio kolonų laikomosios galios bandymų rezultatai atitinka skaičiavimų reikšmes, apskaičiuotas pagal eurokode 4 pateiktu metodu. Stačiakampio skerspjūvio elementų laikomosios galios reikšmių bandymo rezultatai puikiai atitinka teorines reikšmes, kai betono ritininis stipris nesiekia 75 MPa. Išankstinis elementų apkrovimas poveikio elementų laikomajai galiai beveik neturi. Taip pat nagrinėjami betonšerdžių elementų įtempių būvių pasiskirstymas, betono apspaudimo poveikis ir išilginių deformacijų ir įtempių kreivės. Pateikiama S. T. Zhong „Unifikuota teorija“, kuri nagrinėja kompozitinį elementą kaip visumą. Straipsnyje nagrinėjamos kompozitinio plieninio ir betoninio elemento stiprumo ir pastovumo sąlygos. Tokių elementų reikšmėmis. Jeigu tuštumos santykis lygus 0,4–0,5 ir daugiau, N-ε sąryšis yra kritimo stadijoje. Elgsenos stadijos keičiasi pagal tuštumos koeficientą.

A spectroscopic examination of carbon fiber cross sections using XPS and ISS

Carbon ◽  
1996 ◽  
Vol 34 (10) ◽  
pp. 1221-1228 ◽  
Author(s):  
S.D. Gardner ◽  
G. He ◽  
C.U. Pittman
Keyword(s):  
Carbon Fiber ◽  
Cross Sections ◽  
Spectroscopic Examination
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