Carbonation depth prediction of fly ash concrete subjected to 2- and 3-dimensional CO attack

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.     

荷载作用下粉煤灰混凝土一维、二维碳化研究

对不同粉煤灰掺量(0%,20%,40%,60%)、不同应力比(0.20,0.35,0.50,0.65,0.80)下高性能混凝土一维和二维碳化规律展开研究;建立了荷载作用下二维碳化测试方法;定义了二维碳化交互系数;研究了不同应力比对交互系数的影响规律。试验表明:一维、二维碳化深度随着应力比的提高而增加,碳化28 d时(相当于自然碳化50 a),应力比为0.8时的一维、二维碳化深度分别是应力比为0时的1.61倍、1.39倍;同时,碳化深度服从应力比的指数函数关系;混凝土二维碳化具有显著的交互作用,荷载作用下的二维交互系数明显小于不受力时的交互系数,并且随着应力比的增加,其数值有变小的趋势。混凝土加载状态下的一维和二维碳化研究对混凝土结构耐久性和寿命预测具有现实意义。     

混凝土二维、三维碳化的研究

研究了不同水灰比（0．3、0．35和0．4）,不同粉煤灰掺量（0,15％,20％,40％,60％）下混凝土二维和三维碳化深度;建立了二维和三维碳化的测试方法;提出了二维和三维碳化的数学模型。试验表明。混凝土的二维、三维碳化深度和一维碳化相似．也服从时间t的指数函数;水灰比对二维碳化的影响最大,一维其次,三维最小;粉煤灰掺量小于15％时,其对三维的影响最大,二维其次。一维最小;粉煤灰掺量大于15％时,掺量对二维、三维碳化的影响和一维碳化影响相近。混凝土二维和三维碳化研究对混凝土结构耐久性和寿命预测具有现实意义。     

粉煤灰混凝土二维和三维碳化研究

本文首先建立了2D和3D碳化测试方法,在此基础上系统研究了粉煤灰混凝土在加速碳化试验中2D和3D碳化深度的依时变化规律,探讨了粉煤灰掺量(0%、10%、20%、40%、60%)、粉煤灰种类(Ⅰ级、Ⅱ级)、水胶质量比(0.3,0.35,0.4)、胶凝材料用量(458,380kg/m3)、养护龄期(28,90d)5个重要因素对粉煤灰混凝土2D和3D碳化深度的影响规律。另外,还将2D和3D碳化试验结果与同条件下1D碳化进行了定量比较,发现2D和3D碳化明显存在交互作用,为量化该交互作用提出了2D和3D碳化交互系数概念,并给出了2D和3D碳化交互系数随时间变化的数学表达式。以期为准确预测实际混凝土结构在真实状态下碳化寿命提供科学依据。     

Degradation of permeability resistance of high strength concrete after combustion

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. __________ 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)]     

Limit of axial force ratio and requirement for stirrups of RC columns with special shape

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)]     

Experimental research on seismic behavior of recycled concrete frame under varying cyclic loading

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. __________ 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)]     

Experimental study of aerodynamic interference effects on aerostatic coefficients of twin deck bridges

The aerodynamic interference effects on aerostatic coefficients of twin deck bridges with large span were investigated in detail by means of wind tunnel test. The distances between the twin decks and wind attack angles were changed during the wind tunnel test to study the effects on aerodynamic interferences of aerostatic coefficients of twin decks. The research results have shown that the drag coefficients of the leeward deck are much smaller than that of a single leeward deck. The drag coefficients of a windward deck decrease slightly compared with that of a single deck. The lift and torque coefficients of windward and leeward decks are also affected slightly by the aerodynamic interference of twin decks. And the aerodynamic interference effects on lift and torque coefficients of twin decks can be neglected. __________ Translated from Journal of Hunan University (Natural Science), 2008, 35(1): 16–20 [译自: 湖南大学学报(自然科学版)]     

General framework for bridge life cycle design

Based on a detailed illustration for bridge life cycle design which comprises the processes of service life design, aesthetics design, performance design, environmental and ecological design, inspection, maintenance and repair design as well as cost analysis, this paper presented a general framework for bridge life cycle design comprising three design phases and six design processes. __________ Translated from Journal of Tongji University (Natural Science), 2007, 35 (8): 1003–1007 [译自: 同济大学学报(自然科学版)]     

Behavior of steel fiber-reinforced high-strength concrete at medium strain rate

Impact compression experiments for the steel fiber-reinforced high-strength concrete (SFRHSC) at medium strain rate were conducted using the split Hopkinson press bar (SHPB) testing method. The volume fractions of steel fibers of SFRHSC were between 0 and 3%. The experimental results showed that, when the strain rate increased from threshold value to 90 s⁻¹, the maximum stress of SFRHSC increased about 30%, the elastic modulus of SFRHSC increased about 50%, and the increase in the peak strain of SFRHSC was 2–3 times of that in the matrix specimen. The strength and toughness of the matrix were improved remarkably because of the superposition effect of the aggregate high-strength matrix and steel fiber high-strength matrix. As a result, under impact loading, cracks developed in the SFRHSC specimen, but the overall shape of the specimen remained virtually unchanged. However, under similar impact loading, the matrix specimens were almost broken into small pieces. __________ Translated from Journal of Southeast University (Natural Science Edition), 2007, 37(5): 892–897 [译自: 东南大学学报(自然科学版)]     

Experimental study on fire protection methods of reinforced concrete beams strengthened with carbon fiber reinforced polymer

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. __________ 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)]     

Correlation between tension softening relation and crack extension resistance in concrete

Changes of the material fracture toughness 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 G _R 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 G _R 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 G _R curve is closely related to the characteristic point on used tension softening curve. __________ Translated from Journal of Tsinghua University (Science and Technology), 2008, 48(3): 316–320 [译自: 清华大学学报(自然科学版)]     

Spatial embedded reinforcement of 20-node block element for analysis PC bridges

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. __________ 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)]     

Unified solution of limit loads of thick wall cylinder subject to external pressure considering strain softening

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. __________ 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)]     

Calculation of prestressed anchor segment by 3D infinite element

Based on 1D infinite element theory, the coordinate transformation and shape function of 3D point-radiation 4-node infinite elements were derived. They were coupled with 8-node finite elements to compute the compressive deformation of the prestressed anchor segment. The results indicate that when the prestressed force acts on the anchor segment, the stresses and displacements in the rock around the anchor segment are concentrated in the zone center with the anchor axis and are subjected to exponential decay. Therefore, the stresses and the displacement spindles are formed. The calculation results of the infinite element are close to the theoretical results. __________ Translated from Journal of Huazhong University of Science and Technology (Nature Science Edition), 2007, 35(9): 28 30 [译自: 华中科技大学学报自然科学版]     

Micromechanics model for static and dynamic strength of concrete under confinement

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. __________ Translated from Shuili Xuebao, 2007, 38(5): 538–545 [译自: 水利学报]     

Consumption of carbon fiber plates in the reinforced concrete beams strengthened with CFPs

Four-point bending flexural tests were conducted to one full-size reinforced concrete (RC) beam and three full-size RC beams strengthened with carbon fiber plates (CFPs). The experimental results showed that the consumption of CFP had significant effects on failure modes and the flexural capacity. An analytical procedure, based on the limit failure mode and ductility, was presented to predict the applied area of CFP. An analytical program, based on Smith-Teng model and Cheng-Teng model, was provided to calculate the bonding length of CFP. The test results are used to validate the proposed procedure. The results are also applied to the design and construction of RC beam strengthened with CFP. __________ Translated from Journal of Hunan University (Natural Sciences), 2006, 33(6): 16–20 [译自: 湖南大学学报 (自然科学版)]     

Vibration analysis of medium and small span bridges subjected to mixed marshalling freight trains

It has been reported several times that train derailment occurs when mixed marshalling freight trains traverse bridges at high speeds in China. This study aims to explain this phenomenon numerically based on the train-bridge coupling vibration theory and its associated computer program. The train-bridge vibration characteristic is analyzed by a computer program when mixed marshalling freight trains traverse 32-meter-span prestressed concrete simple beam bridges. The mechanism that dynamic responses of the bridges are prominent and that empty trains are inclined to derail are derived from the dynamic responses analysis. The analysis indicates that the significant differences of axle loads between heavy vehicles and empty vehicles produce periodic forced loadings of large amplitudes. These periodic loadings cause severe vibration of bridges. In turn, severe vibration of the bridges produces intensive counteraction to empty vehicles. __________ Translated from Journal of Tongji University (Natural Science), 2007, 35(2): 171–175 [译自: 同济大学学报(自然科学版)]     

Numerical simulation of flood inundation processes by 2D shallow water equations

In order to strengthen flood risk management in a river basin, to upgrade the capability of flood control, and to reduce the loss of lives and properties in urban areas, a numerical simulation model using 2D shallow water equations was proposed in this study. A satisfactory result has been obtained by applying the model in the Fuji River basin in central Japan. The result indicates that the numerical simulation model proposed can be adopted not only in the risk management of a river basin, but also in the study of real-time operations of rescue jobs and evacuation routes in a municipal region suffering from a serious flooding event. Translated from Journal of Sichuan University (Engineering Science Edition), 2006, 38(1): 20–25 [译自: 四川大学学报 (工程科学版)]     

Meshless numerical method based on tensor product

A normalized space constructed by tensor product is used in field function approach to give a special case of moving least squares (MLS) interpolation scheme. In the regular domain, the field function which meets homogenous boundary conditions is constructed by spanning base space to make the MLS interpolation scheme simpler and more efficient. Owing to expanded basis functions selection, some drawbacks in general MLS method, for example repeated inversion, low calculation efficiency, and complex criterions, can be avoided completely. Numerical examples illustrate that the proposed method is characterized by simple mathematical concept, convenient repeat calculations with high accuracy, good continuity, less computation and rapid convergence. __________ Translated from Journal of Huazhong University of Science and Technology (Nature Science), 2007, 35(2): 8–11 [译自: 华中科技大学学 报(自然科学版)]