共查询到20条相似文献,搜索用时 15 毫秒
1.
Changes of the material fracture energy consumption with crack propagation can be described by a crack extension resistance curve, one of the fundamental fracture criteria in crack mechanics. Recently, experimental observation of the fracture behavior in concrete was used to develop a new fracture criterion, the crack extension GR resistance curve, to analyze crack propagation during the entire concrete fracture process. The variation of the crack extension resistance is mainly associated with the energy consumption in the fracture process zone ahead of the stress-free crack tip. The crack extension resistance is then a function of the softening curve, which is a basic mechanical property in the fracture process zone. The relationship between the softening curve and the crack extension GR resistance curve is then analyzed based on results of three-point bending beams tests. The results indicate that the characteristic points of the crack extension resistance GR curve is closely related to the characteristic point on used tension softening curve. 相似文献
2.
Fracture toughening exhibited in quasi-brittle materials such as concrete is often mainly related to the action of aggregate
bridging, which leads to the presence of a fracture process zone ahead of stress-free cracks in such materials. In this investigation,
the fracture resistance induced by aggregate bridging, denoted by G
I-bridging, in the primary focus. In order to quantitatively determine it, a general analytical formula is firstly developed, based
on the definition of fracture energy by Hillerborg. After this, we further present the calculated procedures of determining
this fracture resistance from the recorded load vs. crack opening displacement curve. Then, both numerical simulations and
fracture experiments are performed on concrete three-point bending beams. Utilizing the obtained load against crack opening
displacement curve, the value of G
I-bridging at any crack extension as well as the change of G
I-bridging with the crack extension is examined. It is found that G
I-bridging will firstly increase with the development of crack and then stay constant once the initial crack tip opening displacement
reaches the characteristic crack opening displacement w
0. The effects of material strength and specimen depth on this fracture resistance are also investigated. The results reveal
that the values of G
I-bridging of different specimens at any crack propagation are strongly associated with the values of fracture energy of specimens.
If the values of fracture energy between different specimens are comparable, the differences between G
I-bridging are ignored. Instead, if values of fracture energy are different, the G
I-bridging will be different. This shows that for specimens with different strengths, G
I-bridging will change greatly whereas for specimens that are different in depth, whether G
I-bridging exhibits size effect depends on whether the fracture energy of specimens considered in the calculation of G
I-bridging is assumed to be a size-dependent material parameter. 相似文献
3.
开展了橡胶混凝土三点弯曲梁断裂试验,获得了不同试件尺寸和橡胶掺量下的裂缝断裂全过程曲线,对橡胶混凝土断裂能GF及裂缝扩展K-R阻力曲线进行研究。基于数字图像相关方法,获得了橡胶混凝土试件垂直于裂缝扩展方向的全场位移和应变信息,对裂缝扩展的损伤断裂演化过程进行研究。结果表明:随试件尺寸增加和橡胶掺量提高,断裂能均呈现出上升趋势;K-R阻力曲线随试件尺寸变化表现出明显尺寸效应,橡胶掺量在0%~14%设计范围内时,K-R阻力曲线与橡胶掺量无关。 相似文献
4.
Zhang Xiufang Xu Shilang Zheng Shuang 《Frontiers of Architecture and Civil Engineering in China》2007,1(4):448-457
The double-K fracture model can well describe the development of cracks undergoing during the entire fracture process in concrete. Therefore,
it has been selected as the theoretical basis of the “Norm for fracture test of hydraulic concrete” (China) and the double-K fracture parameters proposed in this model are regarded as the essential fracture parameters needed to be measured. Therefore,
the primary objection of this paper is to present an overall report on the determination of the double-K fracture parameters of concrete involving the fundamental theory, calculation formulas, experimental arrangement and identification
of initial cracking load in order to provide a reference for the specification committee. The fracture tests are carried out
on the total of 43 concrete specimens where the small-size aggregates with the maximum size of 10 mm are chosen. Two typical
widely-used geometries, i.e. three-points bending beam and wedge splitting specimen are adopted. The initial cracking load
is determined by means of graph method or electrical resistance strain gauge method. Then, the initial fracture toughness
and unstable fracture toughness are measured. It is found that the ratio of initial cracking load to maximum load is 0.67–0.71
and the ratio of initial fracture toughness to unstable fracture toughness is 0.45–0.50. It is also found that, for the initial
fracture toughness and unstable fracture toughness, the values are approximately close to the constants when the depth of
specimens is large than 200 and 400 mm for three-points bending beams and wedge splitting specimens respectively. Besides,
the critical crack tip opening displacement of each specimen is calculated, too. The big difference between two geometries
is noticed.
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Translated from Journal of Hydraulic Engineering, 2006, 37(5): 543–553 [译自: 水利学报] 相似文献
5.
The process of propagation, kinking of microcracks in concrete and the interaction among cracks as well as the induced failure
were analyzed using the model that describes the wing type crack from the point of view of micromechanics. The pseudo-force
method is applied to calculate the compressive strength factor of kinky propagated crack taking into account the effect of
interaction among cracks. On the assumption that the micro fracture toughness of concrete does not vary with stain rate, the
static and dynamic strength of concrete under different confinements can be calculated. The comparison of calculation result
with experimental data indicates that a good agreement is achieved which implies that the model can be used to explain the
rate-dependent properties of concrete in multi-axial stress state.
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Translated from Shuili Xuebao, 2007, 38(5): 538–545 [译自: 水利学报] 相似文献
6.
Jinyang Jiang Wei Sun Yunsheng Zhang Cuicui Chen Jing Wang 《Frontiers of Architecture and Civil Engineering in China》2008,2(2):179-183
The mix ratio of steel fiber reinforced concrete (SFRC) was optimized using the principles that workability must meet the
pumping demand and anti-cracking performance should be optimal. The effect of SFRC on the initial cracking load, the ultimate
load and the crack width of the reinforced concrete (RC) member were analyzed in this paper. It was found that the admixture
had good preservation of moisture and adhesion and the fibers distributed homogeneously in one hour out of the machine. According
to the pumping results, the SFRC could be pumped vertically up to 306 m. Based on the standard computation formula of cracks,
the maximum crack width of an RC member with 0.8% steel fiber (by volume) is about 32% lower than that of standard RC member.
Through an experimental research on full-scale model tests for the steel and concrete composite anchorage zone on a pylon,
the SFRC not only remarkably increases the crack resistance and the ultimate load, but the initial load also improves 33%a
pproximately. It is also indicated that plastic shrinkage cracking of SFRC in which volume fraction of steel fibers is 0.8%
can be restrained obviously and the unrestrained drying shrinkage can be diminished by about 50% at early age. The results
confirmed that the SFRC can lessen the shrinkage crack of concrete and enhance markedly the direct tensile strength. Therefore,
the SFRC can solve the key question of crack resistance for the anchorage zone of a bridge tower.
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Translated from Journal of Southeast University (Natural Science Edition), 2007, 37(1): 123–127 [译自: 东南大学学报(自然科学版)] 相似文献
7.
Min Li Hongtao Kao Chunxiang Qian 《Frontiers of Architecture and Civil Engineering in China》2008,2(3):281-287
To evaluate the remaining durability of concrete materials after combustion, the permeability of high strength concrete (HSC)
after combustion was studied. The transport behavior of chloride ion, water and air in concrete after combustion and the effect
of temperature, strength grade, and aggregation on the permeability of HSC after combustion are investigated by chloride ion
permeability coefficient (D
c), water permeability coefficient (D
w) and air permeability coefficient (D
a). The experiment results show that all three permeability coefficients commendably reflect changes of permeability. The permeability
coefficient increases with the evaluation temperature. After the same temperature, the permeability coefficient of HSC is
lower than that of normal strength concrete (NSC). However, the degree of degradation of permeability coefficient of HSC is
greater than that of NSC. The permeability resistance of HSC containing limestone is better than that of HSC containing basalt.
Combining changes of compressive strength and permeability, the remaining durability of concrete materials after combustion
is appropriately evaluated.
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Translated from Journal of Southeast University (Natural Science Edition), 2006, 36(5): 825–830 [译自: 东南大学学报(自然科学版)] 相似文献
8.
混凝土结构裂缝扩展全过程的新GR阻力曲线断裂判据 总被引:5,自引:0,他引:5
混凝土结构的受力特性与裂缝的发展密切相关。在对国际断裂力学领域里所提出的三种裂缝扩展阻力曲线理论加以总结的基础上,以能量为表征,基于裂缝黏聚力提出了描述混凝土结构裂缝扩展全过程的新GR阻力模型。在该模型中,裂缝扩展阻力分为三部分:一部分是基体水泥凝胶材料裂缝发展需克服的表面能,一部分是克服细骨料桥联作用的能量消耗,另一部分是粗骨料桥联闭合作用消耗的能量。文中对粗细骨料所消耗的能量进行了详细推导,得出了不同区段裂缝扩展阻力的解析计算公式。根据实测试验结果,得到了混凝土新GR阻力曲线。结果表明GR曲线是材料的基本参数,与试件尺寸无关,并建立了适用于混凝土结构裂缝扩展全过程的断裂判据。 相似文献
9.
Chen Changfu Xiao Shujun Yang Yu 《Frontiers of Architecture and Civil Engineering in China》2007,1(3):329-333
Based on the unified strength theory [1], a unified strength criterion for strain softening materials, such as concrete or
rock, was derived, and the elastic and plastic limit loads of a thick-walled cylinder made of these materials subject to external
pressure were also given. In addition, the influence of some factors on the limit loads of such cylinders as the ratio of
the external radius to internal radius, r
b/r
a, the coefficient b, which reflects the effect of medium principal stress and the normal stress of the relevant surface on the material destroy
degree, the ratio of tensile strength to compressed strength of the material, α, and the damage variable β were discussed
in detail. Some examples were given and some meaningful results were obtained.
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Translated from Journal of Hunan University (Natural Science), 2006, 33(2): 1–5 [译自: 湖南大学学报 (自然科学版)] 相似文献
10.
Hu Kexu He Guisheng Lu Fan 《Frontiers of Architecture and Civil Engineering in China》2007,1(4):399-404
In this paper, two reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP) and attached with
thick-painted fire resistant coating were tested for fire resistance following the standard fire testing procedures. The experimental
results show that the specimen pasted with the insulated layer of 50 mm in thickness could resist fire for 2.5 h. It is also
demonstrated that the steel wire mesh embedded in the insulated layer can effectively prevent it from cracking and eroding
under firing.
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Translated from Journal of Tongji University (Natural Sciences), 2006, 34(11): 1452–1456 [译自: 同济大学学报 (自然科学版)] 相似文献
11.
Hong Zhong Gao Lin Hongjun Li 《Frontiers of Architecture and Civil Engineering in China》2009,3(3):316-322
Based on the assumption that concrete is macroscopic homogeneous, the cracking evolution process and damage mode of high arch
dams are studied in consideration of the heterogeneity of concrete in mesoscale. The bilinear damage evolution model and the
damage evolution model expressed in power function with descending section are adopted to combine with the Mohr-Coulomb criterion
with tension cut-off to investigate the crack development and fracture mode of high arch dams under the action of an earthquake.
The analysis result of a high arch dam in China under design shows that cracks that take place in concrete are caused by excessive
tensile stress. The cracks initiate at the middle of the dam top and distribute at the upper half of the dam while the rest
of the parts remain intact. This conclusion agrees with the model test result.
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Translated from Shuili Xuebao, 2008, 39(7): 848–853 [译自: 水利学报] 相似文献
12.
Yiyi CHEN Ruoning BIAN Fangfang LIAO 《Frontiers of Architecture and Civil Engineering in China》2008,2(4):295-301
Impact effect of sudden fracture at steel frame connections under severe earthquake or other extreme loads is presented in
this paper. The relation of impulse caused by structural fracture to the release of inner force at the cracked location, the
magnitude of the response to impact on the basis of one degree of freedom model, and the ratio of the peak value of response
to natural period of the system are investigated. Two types of fracture tests were designed and carried out both on uniaxial
steel bar tensioned and moment resistant steel frame model. It is proven that the response during the fracture process can
be measured quite well using high-frequency data processing system. It is also revealed that the instant fracture of structural
connection is characterized by progressive and partial fracture. Numerical evaluation of the impact effect of connection fracture
is carried out.
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Translated from Journal of Tongji University (Natural Science), 2007, 35(3): 299–303, 314 [译自: 同济大学学报(自然科学版)] 相似文献
13.
Wang Yiqun Xu Yidong Zhao Yanjing Chen Yunxia 《Frontiers of Architecture and Civil Engineering in China》2007,1(2):176-181
Thousands of columns with special shape are analyzed by nonlinear numerical methods. The ductility is calculated to investigate
the limit of the axial force ratio and circumstantial requirement for stirrups of an reinforced concrete (RC) column with
special shape, in the point of view of the characteristic value for providing stirrup. The limit of the axial force ratio
of columns with special shape in relation to the characteristic value of the stirrup is obtained. Then, the effect of stirrup
arrangement on the ductility of the RC column is discussed in case of buckling of the longitudinal reinforcement and constraint
concrete columns. The complete requirement for stirrups of RC column with special shape is given.
Translated from Journal of Tianjin University (Natural Science Edition), 2006, 39(3): 295–300 [译自: 天津大学学报 (自然科学版)] 相似文献
14.
Yuedong SUN Jianzhuang XIAO Research 《Frontiers of Architecture and Civil Engineering in China》2008,2(4):302-308
A study is conducted on the seismic behavior of one natural concrete frame and two recycled concrete frames with 100% recycled
coarse aggregate whose scales are 1:2 entirely, and a comparative study is conducted under low-reversed cyclic lateral loading
and different vertical loading. This work aims to estimate the failure mechanism, hysteresis loops, displacement ductility,
deterioration of strength and stiffness and energy dissipation of recycled concrete frames under low-reversed cyclic loading
as well as the influence of different vertical loading. Analysis on the basis of the experiment proves that it is entirely
feasible to apply recycled concrete to practical engineering for the sake of its good seismic behaviors. Theoretical base
is provided for further study and practical application of recycled concrete structure.
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Translated from Journal of Tongji University (Natural Science), 2007, 35(8): 1013–1018 [译自: 同济大学学报(自然科学版)] 相似文献
15.
Song Yupu Zhang Zhong Qing Likun Yu Changjiang 《Frontiers of Architecture and Civil Engineering in China》2007,1(1):94-98
Biaxial tension-compression experiments of concrete of five stress ratios at high temperatures were carried out using the
large static-dynamic triaxial test system in the State Key Laboratory of Coastal and Offshore Engineering, Dalian University
of Technology. The stress ratios σ
1/σ
3 are 0, 0.1, 0.25, 0.50, and 0.75. The temperatures are 20°C, 200°C, 300°C, 500°C, 600°C. The mechanical behavior of concrete
under biaxial tension-compression at high temperatures is analyzed. It is found that both the tensile strength and strain
diminished with the increase in temperature under each stress ratio. Based on the test results, the relationship between tensile
strengths and stress ratios and temperature is proposed. In addition, the failure criterion of concrete under biaxial stress
state of tension-compression at high temperatures is established.
Translated from Journal Dalian University of Technology, 2006, 46 (1): 54–58 [译自: 大连理工大学学报] 相似文献
16.
Peiheng Long Xianting Du Weizhen Chen 《Frontiers of Architecture and Civil Engineering in China》2008,2(3):274-280
The formula for the contribution of prestressed reinforcement on embedded reinforcement element is derived according to the
mechanical behavior of PC bridges and the foundational principle of finite element method. Mechanical concept is definite
and examples validate the calculation results. Reinforcement element model allows generating a finite element mesh without
taking into consideration the layout of reinforcements. Furthermore, the prestressing tendon may pass through the concrete
elements in an arbitrary manner. It is an effective approach that the no-node loads are diverted from the tendons to the adjacent
concrete elements. A useful arithmetic analysis of the spatial curved tendon PC Bridges is provided.
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Translated from Journal of Tongji University (Natural Science), 2007, 35(4): 455–460 [译自: 同济大学学报(自然科学版)] 相似文献
17.
Tests were conducted on 3 specimens to study the flexural behavior of fiber reinforced polymer (FRP)-concrete-steel double-skin
tubular members (DSTMs). The strip method was used to calculate the section momentcurvature curves of the 3 specimens and
12 models. A theoretical formula is presented for the flexural strength of DSTMs. The test results show that the tension zone
of the specimen FRP tubes was in hoop compression while the compression zone was in hoop tension. The load-carrying capacity
did not decrease even when the mid-span deflection reached about 1/24 of the span length. The tests, simulation and theoretical
analysis resulted in a simplified formula for the flexural strength of DSTMs and a tri-linear moment-curvature model was expressed
as a function of the section bending stiffness for DSTMs.
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Translated from Journal of Tsinghua University (Science and Technology), 2008, 47(12): 2105–2110 [译自: 清华大学学报(自然科学版)] 相似文献
18.
Liu Qijian Yang Linde Wu Jun 《Frontiers of Architecture and Civil Engineering in China》2007,1(4):443-447
Based on the disturbed state concept (DSC), a new model of load transfer function for pile analysis is established by the
idea that the deformed material between pile and soil can be treated as a mixture of two constituent parts, which are in intact
or critical state and assumed to obey random distribution. Starting from the homogenization theory of heterogeneous materials
and statistics method, a parameter D to describe the disturbance degree is proposed, and a formula to determine the parameter has been derived by using the plastic
displacement of a pile as distribution variable. In the model, shear intensity of elements in an intact state are simulated
by Duncan-Zhang model and that in a critical state by Mohr-Coulomb criterion. The model of this paper has few parameters,
which can reflect the aspects of load transfer function, such as hardening, softening and the effects of confining pressure.
The well agreement between the in-situ data and the predicted shows that the validity of the model herein. So the proposed
model in this paper is easy to be used in engineering practice.
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Translated from Journal of Tongji University (Natural Science Edition), 2006, 34(2): 165–169 [译自: 同济大学学报 (自然科学版)] 相似文献
19.
Shudong CHEN Wei SUN Yunsheng ZHANG Fei GUO 《Frontiers of Architecture and Civil Engineering in China》2008,2(4):395-400
Based on accelerated carbonation test, 1D, 2D and 3D carbonation of high performance concrete with different fly ash contents
(0%, 15%, 20%, 40%, 60%) were studied. The interaction coefficients of 2D and 3D carbonation are defined. The time-dependent
coefficient n of carbon dioxide diffusion and the interaction coefficients K of 2D and 3D carbonation are analyzed. The mathematical model which includes n and K is deduced. The experiments indicate that 2D and 3D carbonation have obvious interaction. Interaction coefficients obey the
attenuation function through time t. The mathematical model of 2D and 3D carbonation life prediction based on Fick scattering law can be solved by Fourier expansion.
The life prediction of concrete of Sutong Bridge beam shows that the 1D, 2D, 3D carbonation prediction life are 1595 a, 882
a and 758 a, respectively, 2D and 3D carbonation life predicted are reduced clearly.
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Translated from Journal of Southeast University (Natural Science Edition), 2007, 37(4): 645–650 [译自: 东南大学学报(自然科学版)] 相似文献
20.
Pusheng Shen Hui Fang Xinhong Xia 《Frontiers of Architecture and Civil Engineering in China》2009,3(2):234-239
This paper aims to study the different vertical displacements in tall hybrid-structures and the corresponding engineering
measures. First, the method to calculate the different vertical displacements in tall hybrid-structures is presented. This
method takes into account the effects of construction process by applying loads sequentially story by story. Based on the
concrete creep and shrinkage calculation formula in American Concrete Institute (ACI) code, with the assumption that loads
are increased linearly in members, the creep and shrinkage effects of members are analyzed by adopting two parameters named
average load-aged coefficient and average age-last coefficient. The effects of steel ratio on members creep are analyzed by
age-adjusted module method (AEMM). The effects that core-tube were constructed in advance to outer steel frame were also considered.
Then, based on the sample calculation, the measures to effectively reduce the different vertical displacements in hybrid-structures
are proposed. This method is simple and practical in the calculation of different vertical displacements in tall and super-tall
hybrid-structures.
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Translated from Journal of Hunan University (Natural Sciences), 2008, 35(1): 1–5 [译自: 湖南大学学报 (自然科学版)] 相似文献