功能梯度混凝土管片的设计及材性研究

引入功能梯度材料设计原理,对盾构隧道衬砌管片进行分层设计,制备出功能梯度混凝土管片。并针对影响混凝土管片性能的关键性指标如抗渗性能、体积稳定性以及力学性能等进行了试验研究。结果表明,混凝土管片保护层材料抗渗性优良,氯离子扩散系数相比普通混凝土管片降低1个数量级;保护层材料与结构层材料体积稳定性良好,且具有较好的体积变形匹配性能;同时保护层及结构层混凝土力学性能均完全满足工程需要,有效保证了混凝土管片的高耐久、长寿命。     

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]     

Limit span of self-anchored cable-stayed suspension cooperation system bridge based on strength

The limit span of self-anchored cable-stayed suspension bridge is deduced. The relations among the geometrical parameters, loads and material characteristics are also analyzed. Based on the material strength and commonly used materials, the limit spans of self-anchored cable-stayed suspension bridges with concrete girder or steel girder under vertical static load are discussed in detail. The corresponding upper limit spans and the effect of the factors on the span are given. The results indicate that increasing rise-span ratio, height-span ratio and cable-stayed segment length or reducing the second dead load could increase the cooperation system span. __________ Translated from Journal of Dalian University of Technology, 2008, 48(3): 387–391 [译自: 大连理工大学学报]     

混凝土耐久性破坏经时模型在HILS服役寿命预测中的应用

采用混凝土耐久性破坏经时模型(CDFTModel)对不同体系设计下的武汉长江隧道管片进行服役寿命预测。结论表明:考虑各种潜在影响因素,按实际应用过程的最保守估计,高抗渗长寿命大直径盾构管片(HILS)功能梯度层体系的使用寿命可达到150年以上。采用有限元法分别对各体系进行Cl-离子渗透浓度分布模拟,结果显示,功能梯度体系管片的抗Cl-离子渗透性能远远优于复合胶凝材料体系。     

Endochronic damage constitutive model for fully-graded aggregate mass concrete

The behavior of deformation and strength of a fully-graded aggregate concrete under complex stress state is the basis of the nonlinear analysis and design for mass concrete structures such as concrete dams. In this paper, based on the combined endochronic theory with damage mechanics and on the quantities of experimental data, an endochronic damage constitutive model suitable for various aggregate grade concrete is proposed. This model takes into consideration the scale effect and the effect of wet screen sieve of aggregate in which the concept of yield surface is not needed and the difference of damage evolution rule of various graded aggregate concrete is a concern. The proposed model is used to analyze the deformation and strength of fully-graded aggregate mass concrete and the wet screened aggregate concrete specimens. The calculated results are in good agreement with experimental data, which can be used as a guide for the design of arch dams and other mass concrete structures. __________ Translated from Journal of Hydraulic Engineering, 2006, 37(7): 769–778 [译自: 水利学报]     

Exploring the potential of functionally graded materials concept for the development of fiber cement

In this study we establish the concept of functionally graded fiber cement. We discuss the use of statistical mixture designs to choose formulations and present ideas for the production of functionally graded fiber cement components for Hatschek machines. The feasibility of producing functionally graded fiber cement by grading PVA fiber content has been experimentally evaluated. Thermogravimetric analysis (TG) was employed to assess fiber distribution profiles and four-point bending tests were applied to evaluate the mechanical performance of both conventional and graded composites. The results show that grading PVA fiber content is an effective way to produce functionally graded fiber cement, which allows for a reduction of the total fiber volume without a significant reduction on modulus of rupture of composite. TG tests were found adequate to assess the fiber content at different points in functionally graded fiber cements.     

Application of cable-supported spatial grid in dry coal shed

This paper presented a new structural style cable-supported spatial grid, which was applied in large span dry coal sheds. The influence of configuration of cable on the force of cable and beam, the ratio of beam force to cable force and the deflection of span was investigated, and a rational configuration of cable was obtained. The results show that the cable-supported spatial grid can maximize the use of material strength, and have the advantages of low usage of steel, large span and sufficient headroom. __________ Translated from Journal of Hunan University (Natural Sciences), 2007, 34(2): 29–32 [译自: 湖南大学学报 (自然科学版)]     

Tolerance modelling of vibrations of thin functionally graded plates

A problem of a modelling of vibrations of thin plates with a functionally graded macrostructure and a tolerance-periodic microstructure in planes parallel to the plate midplane is analysed. The proposed model, based on the Kirchhoff plate theory assumptions and additional hypothesis of the tolerance averaging technique [Wo?niak et al., editors. Thermomechanics of heterogeneous solids and structures. Tolerance averaging approach. ?ód?, University Press, Technical University of ?ód?; 2008], describes the effect of the microstructure size on dynamic behaviour of the plate. In this paper, as an example there are analysed free vibration frequencies of a functionally graded plate band. These frequencies are obtained in the framework of two proposed models—the tolerance model and the asymptotic model, using the known Ritz method.     

Moment-curvature relationship of FRP-concrete-steel double-skin tubular members

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. __________ 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)]     

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)]     

Field test on temperature field and thermal stress for prestressed concrete box-girder bridge

A field test was conducted to investigate the distribution of temperature field and the variation of thermal stress for a prestressed concrete (PC) box-girder bridge. The change of hydration heat temperature consists of four periods: temperature rising period, constant temperature period, rapid temperature fall period and slow temperature fall period. The peak value of hydration heat temperature increases with the increasing casting temperature of concrete; the relation between them is approximately linear. According to field tests, the thermal stress incurred by hydration heat may induce temperature cracks on the PC box-girder. Furthermore, the nonlinear distribution of temperature gradient and the fluctuation of thermal stress induced by exposure to sunlight were also obtained based on continuous in-situ monitoring. Such results show that the prevailing Chinese Code (2004) is insufficient since it does not take into account the temperature gradient of the bottom slab. Finally, some preventive measures against temperature cracks were proposed based on related studies. The conclusions can provide valuable reference for the design and construction of PC box-girder bridges. __________ Translated from Journal of Huazhong University of Science and Technology (Urban Science Edition), 2007, 24(4): 83–97 [译自: 华中科技大学学报 (城市科学版)]     

New form of geodetic coordinate system taking two length quantity as coordinate parameters

A new form of geodetic coordinate system based on geodesic coordinates instead of geodetic longitude and latitude was proposed. The vertical and horizontal geodesic coordinates measured with length were defined as coordinate parameters, but the two families of coordinate curves were still meridians and parallel circles. The first fundamental form on the ellipsoidal surface and its three coefficients were deduced by the geodesic coordinate. The formula for the latitudinal scale factor of length for geodetic parallel lines was derived, by which the obtained result conformed to that standard value calculated from geodetic latitude, and it is applicable in the range of 400 km from north to south. Therefore, it lays the foundation for establishing the differential equation and differential relationship based on this type of coordinate parameters; and consequently, it is convenient and accurate enough to operate on the ellipsoidal surface in this new form of geodetic coordinate system. __________ Translated from Journal of University (Natural Science), 2005, 33(11): 1537–1540 [译自: 同济大学学报(自然科学版)]     

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)]     

Improving existing “reaching law” for better discrete control of seismically-excited building structures

In this paper, a novel “composite reaching law” was explained in details: 1) the equation of discrete motion for a control system; 2) the design of discrete-time variable structure control. In addition, the model of a three-storey shear-type building structure was used to verify the effectiveness of the discrete variable structure control method. The results of numerical example analysis of the model show that the control law can effectively reduce the peak value of seismic response of the building structure and the chattering effect of the control system. __________ Translated from Journal of Northwestern Polytechnical University, 2007, 25(6): 869-873 [译自: 西北工业大学学报]     

Calculation method on shape finding of self-anchored suspension bridge with spatial cables

Based on the spatial model, a reliable and accurate calculation method on the shape finding of self-anchored suspension bridge with spatial cables was studied in this paper. On the principle that the shape of the main cables between hangers is catenary, the iteration method of calculating the shapes of the spatial main cables under the load of hanger forces was deduced. The reasonable position of the saddle was determined according to the shape and the theoretical joint point of the main cables. The shapes of the main cables at completed cable stage were calculated based on the unchanging principle of the zero-stress lengths of the main cables. By using a numerical method combining with the finite element method, one self-anchored suspension bridge with spatial cables was analyzed. The zero-stress length of the main cables, the position of the saddle, and the pre-offsetting of the saddle of the self-anchored suspension bridge were given. The reasonable shapes of the main cables at bridge completion stage and completed cable stage were presented. The results show that the shape-finding calculation method is effective and reliable. __________ Translated from Journal of Hunan University (Natural Sciences), 2007, 34(12): 20–25 [译自: 湖南大学学报(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)]     

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)]     

Analysis of behavior of melted dark green silty soil

The behavior of dark green silty soil of the 6th storey is studied by means of scanning electron microscopy (SEM). The shape, size and contact condition of the basic elements of the soil microstructure, and the shape and the size of the pore are further studied. In addition, a comparative study is made to analyze the experiment results of Cu and dynamic test. The mechanic characteristics of common soil and those of melted soil are presented and their influences on dark silty soil after being frozen are theoretically illustrated from a microscopic perspective. __________ Translated from Journal of Tongji University (Natural Science), 2007, 35(1): 6–9 [译自: 同济大学学报(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)]     

Centrifuge model test and field measurement analysis for foundation pit with confined water

The similarity law of centrifuge test was developed for the seepage field and stress field of a foundation pit with confined water by analyzing control equations, and a similarity index and a similarity coefficient of centrifuge test were obtained. Based on the deep foundation pit of the Huangxing Road Station of the Shanghai metro line M8, the deformation stability of the pit was tested. Finally, a comparative study was conducted on the test results of the pit deformation and the field measurement results. Comparison results show that the pit deformation regularity of the test is basically identical with that of the field measurement, and the difference in pit deformation between the test and the field measurement is within 50%. The centrifuge model test can effectively simulate the displacement response of the ground and retaining structure during dewatering and excavation for the pit with confined water, which provides a reliable basis for the design and construction of the pit with confined water. __________ Translated from Journal of Tongji University (Natural Science), 2008, 36(1): 23–26 [译自: 同济大学学报(自然科学版)]