Search results for " Capa"
showing 10 items of 1248 documents
Analysis-oriented stress–strain model of CRFP-confined circular concrete columns with applied preload
2018
The compressive behavior of FRP-confined concrete is a current issue in the field of structural retrofitting. The available models well predict the stress–strain behavior under monotonic and cyclic loads. However, in the practical applications, columns that need an increasing of bearing capacity are often strengthened under serviceability load conditions, with a stress and strain state that could change the response of the reinforced systems with respect to the case of the unloaded state. In this paper, the compressive behavior of circular FRP-confined concrete columns with preload is analyzed with the introduction of a modified analysis-oriented model. Differently from the classical formul…
Azolylborates for Electrochemical Double Layer Capacitor Electrolytes
2017
Abstract Asymmetric tetraalkylammonium salts of azolylborates were synthesized and studied with respect to their suitability as supporting electrolytes in electrochemical double layer capacitors. In contrast to current conducting salts used in this device, azolylborates exhibit an excellent stability towards thermal load and moisture. In addition to good conductivity and stability towards cathodic reduction we found certain limitations when more positive potentials were applied.
Nanogoniometry with scanning force microscopy: a model study of CdTe thin films.
2007
In this paper scanning force microscopy is combined with simple but powerful data processing to determine quantitatively, on a sub-micrometer scale, the orientation of surface facets present on crystalline materials. A high-quality scanning force topography image is used to determine an angular histogram of the surface normal at each image point. In addition to the known method for the assignment of Miller indices to the facets appearing on the surface, a quantitative analysis is presented that allows the characterization of the relative population and morphological quality of each of these facets. Two different CdTe thin films are used as model systems to probe the capabilities of this met…
Strength and strain capacities of concrete compression members reinforced with FRP
2003
The analytical compressive behavior of concrete members reinforced with fiber-reinforced polymer (FRP) was examined. The variation in the shape of the transverse cross-section was analyzed. The bearing capacity and the increase in the maximum strain for members having a cross-section which was circular, square or square with round corners reinforced with FRP were determined. The proposed analytical model allows one to evaluate the confining pressure in ultimate conditions considering the effective confined cross-section and also allows one to determine the ultimate strain corresponding to FRP failure through a simplified energetic approach. Analytical results are then compared to experiment…
Compressive behavior of short fibrous reinforced concrete members with square cross-section
2011
In the present paper a mechanical model to predict the compressive response of high strength short concrete columns with square cross-section confined by transverse steel is presented. The model allows one to estimate the equivalent confinement pressures exercised by transverse steel during the loading process taking into account of the interaction of the stirrups with the inner core both in the plane of the stirrups and in the space between two successive stirrups. The lateral pressure distributions at hoop levels are obtained by using a simple model of elastic beam on elastic medium simulating the interaction between stirrups and concrete core, including yielding of steel stirrups and dam…
A new gas sensor electronic interface with generalized impedance converter
2008
A new gas sensor conditioning circuit that allows a direct resistance-to-frequency conversion, as well as the procedure for the design, is presented. The generalized impedance converter (GIC) proposed is configured as a variable capacitor connected with the capacitor timing terminal of an astable multivibrator implemented by a PSoC (programmable system on chip) microcontroller device. The GIC effective input impedance, which is controlled by the gas sensor resistance, controls the astable output frequency. Good correlation of the experimental output frequency, which depends on the gas concentration, is achieved. The circuit is a simple gas sensor digital interface with frequency output.
Imaging of photonic nanopatterns by scanning near-field optical microscopy
2002
We define photonic nanopatterns of a sample as images recorded by scanning near-field optical microscopy with a locally excited electric dipole as a probe. This photonic nanopattern can be calculated by use of the Green’s dyadic technique. Here, we show that scanning near-field optical microscopy images of well-defined gold triangles taken with the tetrahedral tip as a probe show a close similarity to the photonic nanopattern of this nanostructure with an electric dipole at a distance of 15 nm to the sample and tilted 45° with respect to the scanning plane.
Influence of FRP wrapping techniques on the compressive behavior of concrete prisms
2006
Abstract Results of an experimental investigation on the compressive behavior of concrete prisms with square cross-section, externally wrapped with carbon fiber reinforced plastic (CFRP) sheets are presented. The effects of the following parameters were analyzed: local reinforcement at the corners and continuous layers; horizontal and vertical discontinuous strips; number of continuous layers—length of specimens. An analytical model is proposed to determine the maximum bearing capacity of compressed concrete members with square cross-section and externally wrapped with FRP for the different configurations examined, and also able to consider the strength reduction with the length increase of…
Behaviour in compression of lightweight fiber reinforced concrete confined with transverse steel reinforcement
2004
Abstract The compressive behavior of lightweight fiber reinforced concrete confined with transverse reinforcement consisting of steel stirrups or spirals was analyzed. Pumice stone and expanded clay aggregates were utilized to decrease the weight of the composite; hooked steel fibers were also added. The investigation was carried out by testing cylindrical and prismatic specimens of different sizes in compression using an open-loop displacement control machine, recording the full load–deformation curves. The influence of the dimensions and shape on the bearing capacity and on the ductility of the specimens confined with transverse steel reinforcements was analyzed. The results show the poss…
Flexural response of FRC corbels
2009
Abstract A strut-and-tie macro-model is proposed to determine the flexural response of fiber reinforced concrete (FRC) corbels, reinforced with longitudinal bars and subjected to vertical load. The effects of the corbel geometry, the percentage of steel fibers, and grades of concrete and steel bars are also included. The model, which is specific for FRC corbels with hooked steel fibers, allows the determination of load levels, and corresponding displacements, associated with the first cracking, yielding of the main steel bars and crushing of the concrete strut. The sequential occurrence of these phenomena is established, depending on the amounts of steel fibers and reinforcing steel. The si…