共查询到20条相似文献,搜索用时 31 毫秒
1.
The paper presents results of an experimental investigations carried out to estimate the cooperation between a steel bar reinforcement
and round concrete cylinders confined by a carbon-epoxy composite, concerning the increase in the concrete compression strength
due the composite wrapping. The steel bar reinforcement with its yield stress considerably increases the bearing capacity
of concrete. This also happens above the unconfined concrete strength of specimens. The onset of reinforcement yielding roughly
coincides with reaching of the unconfined concrete strength at a compressive strain of ≈0.20%, and therefore it does not produce
a change in the tangent modulus of the stress-strain relationships above the limit of linearity.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 3, pp. 293–308, May–June, 2007. 相似文献
2.
This paper presents the results of an experimental investigation of concrete columns confined by wound pretensioned epoxy-impregnated
carbon filament yarns. The yarn winding equipment, with the ability to set the desired pretension force and thereby to produce
confined concrete specimens with different initial lateral pressure, was developed at the Institute of Polymer Mechanics.
It is shown that the pressure in creases the axial stress at which intense internal cracking of concrete develops. 相似文献
3.
External confinement by the wrapping of fiber-reinforced polymer (FRP) sheets is a very effective method for the strengthening
and retrofit of round concrete columns. The stability and strength of concrete columns confined by carbon FRP jackets in which
the fibers are oriented in the hoop direction was studied. Stability tests were conducted on hinged plain and confined concrete
columns of different slenderness. The theoretically predicted critical stress at the on set of in stability was compared with
that obtained experimentally, and a good agreement between them was observed.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 5, pp. 657–666, September–October, 2007. 相似文献
4.
Results of an experimental investigation into the mechanical properties of concrete cylinders confined by a carbon-epoxy composite
wrapping are presented. It is shown that, for all the con fined con crete spec i mens tested, the loading paths in the normalized
stress space follow a single master curve, what ever the concrete strength and confinement intensity. At stresses in the confined
concrete exceeding the strength of plain concrete, the tangent modulus was found to depend on the slope angle of the master
curve and the asymptotic value of the differential Poisson ratio (the first derivative of the lateral strain with respect
to the axial one). Formulas for predicting the ultimate axial strain and the tangent modulus are derived and compared with
the corresponding fib (fédération internationale du béton) recommendations.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 4, pp. 433–448, July–Au gust, 2006. 相似文献
5.
The mechanical behavior of round concrete cylinders confined by a carbon-epoxy composite wrapping is analyzed concerning the
increased concrete compression strength due the wrapping. It is shown that the loading trajectories in the normalized stress
space fit into a single master curve for all the concrete batches and jacket thicknesses investigated. The loading paths ended
at failure of the composite wrapping from the increased internal lateral pressure. The strength of the composite was determined
by split-disc tests of composite rings, but the strength of composite jackets realized on concrete specimens did not reach
the strength of the rings. Therefore, a coefficient of composite strength reduction was introduced. A simple formula for predicting
the strength of confined concrete is derived, and a comparison with fib (fédération internationale du béton) recommendations
for strength predictions is given.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 165–178, April–May, 2006. 相似文献
6.
The external confinement by CFRP wrappings is a very efficient method to increase the load-carrying capacity of round concrete
columns. Nevertheless, the serviceability of such columns under loads exceeding the strength of unconfined concrete is limited
by different factors. One of them is the reduced stability of the columns due to the significantly reduced tangent elastic
modulus inactive loading. To increase the critical load of buckling instability of concrete columns, an additional longitudinal
composite reinforcement can be used. In this paper, the stability and strength of concrete columns confined by circumferential
wrappings and strengthened with a longitudinal external CFRP reinforcement are studied. Plain and confined columns of length
300 and 1500 mm were tested. Theoretical predictions show that the additional longitudinal reinforcement is efficient in improving
the stability of confined columns in the region of moderate slenderness. The prediction for the ultimate strength and stability
of the columns coincides rather well with experimental results.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 3, pp. 295–308, May–June, 2005. 相似文献
7.
A detailed finite-element analysis of the stress-strain state in the load transfer zone of uneasily tensioned flat test specimens
made of a high-strength unidirectional carbon fiber-epoxy composite is carried out with account of the elastoplastic behavior
of a structural polyurethane adhesive. Various schemes of introduction of external loads into the specimens are considered.
A numerical finite-element analysis of different configurations of specimen tabs allowed us to put forward a technique for
significantly reducing the dangerous concentration of operating stresses.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 1, pp. 43–58, January–February, 2007. 相似文献
8.
S. B. Sapozhnikov A. N. Aniskevich V. A. Tsarevskii 《Mechanics of Composite Materials》2006,42(6):571-576
A numerical method for predicting the deformational and strength characteristics of a calcite-quartzitic polymer concrete
from the known properties of its components is developed based on the finite-element method. Components of the material are
assumed elastic and isotropic, and the filler particles are modeled by round inclusions perfectly bonded to the polymer matrix.
The size distribution of the inclusions correspond to that of actual fillers. The destruction process of the components is
simulated by sequentially excluding the particles in which the maximum principal stress has achieved the ultimate value for
this component. A comparison of calculated and experimental characteristics of the polymer concrete showed errors of 2–4%
for the elastic modulus and about 10% for the ultimate strength if the finite-element cell included not less than 20–30 average-size
particles and 2–5 large ones.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 817–824, November–December, 2006 相似文献
9.
I. J. Gnip S. A. Veyelis V. I. Kersulis S. I. Vaitkus 《Mechanics of Composite Materials》2007,43(1):85-94
Data obtained in investigating the ultimate strength and deformability of expanded polystyrene under short-term shear loading
according to EN 12090 are discussed. Linear regression equations are used for describing the ultimate shear strength and modulus
in relation to the density of EPS. A correlation is found to exist between the ultimate strength of EPS and its density and
specimen thickness. An empirical dependence between the shear modulus and density of EPS is established. The strains corresponding
to the conditional limit of proportionality and to the ultimate shear strength of EPS in short-term loading are determined.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 1, pp. 121–134, January–February, 2007. 相似文献
10.
The paper deals with evaluation of the bond performance between a CFRP plate and concrete with respect to various compressive
strengths of concrete and bond lengths of the CFRP plate as parameters. To consider stress conditions in the tensile zone
of reinforced concrete (RC) structures, double-lap axial tension tests were conducted for eight specimens with CFRP plates
bonded to concrete prisms. In addition, a simple linear bond-slip model for the CFRP plate/concrete joints, developed from
the bond tests, was used. To verify the model proposed, a total of seven RC beams were strengthened with CFRP plates and tested
in flexure employing various bond lengths, strengthening methods, and numbers of CFRP plates. A nonlinear finite-element analysis,
with the bond–slip model incorporated in the DIANA program, was performed for the strengthened RC beams. Also, the results
of flexural test and analytical predictions are found to be in close agreement in terms of yield and ultimate loads and ductility. 相似文献
11.
The prediction of the high-cycle fatigue strength of polymeric and composite materials in asymmetric loading is considered.
The problem is solved on the basis of a nonlinear model of ultimate state allowing us to describe all typical forms of the
diagrams of ultimate stresses. The material constants of the model are determined from the results of fatigue tests in symmetric
reversed cycling, in a single fatigue test with the minimum stress equal to zero, and in a short-term strength test. The fatigue
strength characteristics of some polymers, glass-fiber laminates, glass-fiber-reinforced plastics, organic-fiber-reinforced
plastics, and wood laminates in asymmetric tension-compression, bending, and torsion have been calculated and approved experimentally.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 1, pp. 87–102, January–February, 2008. 相似文献
12.
A. B. Mitkevich 《Mechanics of Composite Materials》2006,42(4):297-302
The deformation of pressure vessel domes in asymmetric winding with the use of two families of yarns is accompanied by shear
deformations and torsion. For the case of large deformations, a system of equations for describing the stress-strain state
of an asymmetrically reinforced netlike shell of revolution loaded with an internal pressure is obtained. It is shown that
the shear deformations depend on the deformations of both the yarn families and the deformations of meridians and parallels
of the shell. As an example, the dome of a pressure vessel in a deformed state is calculated for an initial equilibrium shape
determined on the assumption that the yarns are inextensible.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 4, pp. 425–432, July–August, 2006. 相似文献
13.
D. Pizele V. Kalkis R. Merijs Meri T. Ivanova J. Zicans 《Mechanics of Composite Materials》2008,44(2):191-196
Blends of low-density polyethylene (LDPE) and ethylene-octene copolymer (EOC) were obtained. The effect of EOC content and
absorbed radiation dose on the mechanical and thermomechanical properties of LDPE/EOC blends are investigated. Particular
attention is given to a tensile stress-strain analysis and the “form-memory” effect of the blends. With growing LDPE content,
the elastic modulus, the yield stress, and the thermorelaxation and residual stresses of the blends increase, but the ultimate
elongation at break decreases, which is caused by the higher crystallinity of polyethylene. As a result of radiation-induced
cross-linking, the elastic modulus, the yield stress (at a 1% strain), the ultimate yield strength, and the thermorelaxation
and residual stresses increase, while the ultimate elongation at break and the melt flow-behavior index decrease, which is
confirmed by the growing gel fraction in the blend.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 2, pp. 279–286, March–April, 2008. 相似文献
14.
The fatigue failure of reinforced plastics and unoriented polymers under a joint action of static and high-cycle loadings is considered. The fatigue failure strength is estimated from stress range diagrams with a static tensile component. The models of ultimate state are constructed based on the hypothesis of existence of a unified ultimate diagram invariant with respect to the number of cycles to failure. The unified diagram is given by a transcendental power function whose exponent characterizes the sensitivity of the material to the stress-cycle asymmetry. The models of ultimate state make it possible to span practically all forms of ultimate diagrams of composite and polymer materials, including concave, rectilinear, S-shaped, and convex ones. 相似文献
15.
The results of a theoretical and experimental research project on the use of an innovative technique for strengthening concrete
beams are presented. A spacer element is inserted between the tension side of a beam and the composite material to increase
its lever arm and to enhance the over all stiffness of the strengthened beam. The main aim of this exploratory project was
to increase the ultimate failure load of strengthened beam specimens, whilst guaranteeing acceptable over all deflections
at the serviceability limit states. This resulted into a significant reduction in the amount of FPR required and in a better
utilization of the materials employed. A preliminary theoretical study was carried out to investigate the effect of Young’s
modulus, failure strain, and thickness of the element to be used as a spacer in order to determine the best possible candidate
material. Three tests on 2.5-m-long beams were carried out, and different anchorage techniques were used to try and prevent
the debonding of the strengthening system. The results from this pilot study are very promising, as the strengthening system
ensures an adequate initial stiffness along with an improved ultimate flexural capacity.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 3, pp. 403–416, May–June, 2008. 相似文献
16.
为了分析及深入探讨混凝土在受拉加载及卸载情况下的力学特性,基于随机损伤本构关系提出了一种混凝土轴拉加卸载模型,推导出了混凝土加卸载的应力 应变关系表达式.为了印证理论表达式,进行了混凝土轴向拉伸及加卸载的试验研究,测得了混凝土的材料参数及其相应的轴拉加卸载应力-应变曲线.结合模型的计算结果,对混凝土的轴拉加卸载试验结果进行了对比分析,结果表明:混凝土轴拉加卸载模型能够预测混凝土的极限强度,同时能描述混凝土的强度软化、加载过程中的弹模折减及卸载后的塑性变形. 相似文献
17.
Yu. M. Pleskachevskii A. O. Shimanovskii G. M. Kuzemkina 《Mechanics of Composite Materials》2008,44(3):209-214
A finite-element model of a reinforced concrete beam with rebars modeled by a 3-D deformable body has been developed. An analysis
of the stress-strain state of the beam allowed us to determine the stress distribution on cross sections of the rebars and
the location of zones with cracks in concrete. It is found that the break of bond between the reinforcement and concrete goes
outside the areas of intensely cracked concrete matrix.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 3, pp. 309–316, May–June, 2008. 相似文献
18.
R. D. Maksimov S. Gaidukovs J. Zicans M. Kalnins E. Plume V. Spacek P. Sviglerova 《Mechanics of Composite Materials》2006,42(3):263-272
The preparation of polymer nanocomposites by mixing a solution of a styrene-acrylate copolymer with a suspension of organically
modified montmorillonite in dimethyl formamide is described. Seven different compositions with organomontmorillonite content
from 0 to 7 wt.% were prepared and tested. Results of their X-ray diffraction analysis are presented. Data on the influence
of organomontmorillonite content on the tensile stress-strain curves, elastic modulus, strength, and ultimate elongation of
the nanocomposites are obtained. The concentration dependences of elastic properties of materials with differently oriented
platelike nanoparticles is analyzed by using an algorithm elaborated for stepwise calculations of elastic constants with account
of the features of structural hierarchy of intercalated and exfoliated nanocomposites.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 3, pp. 375–388, May–June, 2006. 相似文献
19.
We introduce and study a family of Markov processes on partitions. The processes preserve the so-called z-measures on partitions
previously studied in connection with harmonic analysis on the infinite symmetric group. We show that the dynamical correlation
functions of these processes have determinantal structure and we explicitly compute their correlation kernels. We also compute
the scaling limits of the kernels in two different regimes. The limit kernels describe the asymptotic behavior of large rows
and columns of the corresponding random Young diagrams, and the behavior of the Young diagrams near the diagonal.
Our results show that recently discovered analogy between random partitions arising in representation theory and spectra of
random matrices extends to the associated time– dependent models. 相似文献
20.
Maksimov R. D. Jirgens L. A. Plume E. Z. Jansons J. O. 《Mechanics of Composite Materials》2003,39(2):99-110
The results of experimental investigation of polyester resin and polymer concrete at a long-term (four-year) exposure to water and air with 98% RH are presented. The polymer concrete was composed of a polyester resin as a binder, lime flour, quartz sand, and granite chips. The resin content in concrete was 20 wt.%. The features of sorption properties of the materials investigated are discussed. Data on the water effect on the compressive strength in short-term loading are reported. The creep tests of virgin polymer-concrete specimens were carried out for five years at different stress levels from 0.11 to 0.44 of the short-term prismatic strength. The effect of moisture on the creep behavior was also studied. 相似文献