生态毯不同上层承载材料对土壤水分及植物生长的影响

生态毯是一种使用便捷的边坡修复材料,但因承载材料的限制,实际应用中植被恢复效果差。为提高生态毯的性能,比较纤维纸、薄无纺布、厚无纺布、针织布4种不同上层承载材料对边坡植物生长状况、水分入渗率以及土壤含水率等指标的作用差异。结果表明:种植30 d后,植物生长指标表现为针织布组>薄无纺布组>纤维纸组>厚无纺布组;坡面水分入渗量表现为针织布组(0.52 L)>纤维纸组(0.47 L)>薄无纺布(0.44 L)>厚无纺布(0.41 L);24 h内土壤含水率降低率表现为厚无纺布组(12.7%)<薄无纺布组(16.2%)<针织布组(17.2%)<纤维纸组(28.4%)。针织布在水分入渗、减少蒸发方面表现良好,也不会阻碍植物出苗,植被恢复情况最佳,是一种较为理想的上层承载材料,可以替代传统的无纺布,改善生态毯的性能。

承载结构聚氨酯硬泡材料的研究进展

评述了近十几年来聚氨酯硬泡作为承载结构材料的研究现状 ,着重举例介绍了高密度聚氨酯硬泡和增强聚氨酯硬泡两种材料 ,并展望了该领域的发展前景。

加氢反应器壁材料的氢损伤特性

研究了在模拟加氢反应器工况条件下 ,国产加氢反应器壁材料 [2 (1/ 4 )Cr - 1Mo及其上的 30 9L和 347L不锈钢堆焊层 ]的氢损伤特性 .结果表明 :热渗氢后 ,明显降低了它们的断裂应力 (σf)和塑性 .对于 30 9L和 347L堆焊层 ,未经热渗氢的原始试样 ,无论是光滑试样还是缺口试样 (除缺口位置在 30 9L区域试样外 )均断裂在 347L区域内 .而经热渗氢后 ,无论是起裂于 2 (1/ 4 )Cr - 1Mo和 30 9L的熔合线 ,还是 30 9L和 347L的熔合线处 ,最后都断在30 9L区域内 (除缺口位置在 347L区域试样外 ) .这是因为热渗氢使 30 9L和 347L的σf 分别从原始状态的 885MPa降至 4 78MPa和从原始状态的 799.9MPa降至 5 6 4MPa ;在对短裂纹的低周疲劳特性研究中 ,用da/dN =C(ΔJ) n计算了裂纹扩展速度 (da/dN)和门槛值 (ΔJth) .经热渗氢后 ,ΔJth有明显的下降 ,da/dN～ΔJ曲线也向左移 ,提高了da/dN .SEM断口分析结果与上述结论一致 .裂纹扩展以穿晶为主 ,热渗氢后有二次裂纹存在 .说明热渗氢降低了其力学性能 。

大开口高承载网格加筋壳的设计与工艺

本文采用有限元法计算了承受高轴压和外压作用下的大开口复合材料纵横密加筋壳的稳定性 ,得出不同铺层角度、不同受力工况下的大开口圆柱壳的临界载荷 ,并采用 1:1试验件进行试验验证 ,将计算值与实验值进行了比较 ;对大开口复合材料纵横密加筋壳的缠绕工艺进行了研究 ,解决了大开口网格加筋壳开口补强的一次成型技术和密筋及开口部分的多丝嘴、无增量、非线性机械化缠绕成型工艺技术。

秀印高速公路涵洞软基换填材料选择

换填垫层法是一种常用的涵洞地基处理方法。其目的是增大地基承载力、减少沉降及不均匀沉降。通过列举常见的换填材料,并以秀印高速公路涵洞换填设计为依托,对不同材料垫层的受力进行分析计算,结果表明:换填材料的选择应充分考虑材料的承载力、压应力扩散角的大小和经济性。

钢筋混凝土梁极限承载力分析

根据分层有限元的基本原理和计算假设,编制了钢筋混凝土梁极限承载力分析的有限元程序,并对两个钢筋混凝土模型梁进行了分析,结果表明:分层有限元法是一种很好的计算钢筋混凝土梁极限承载力的分析方法。

Ultimate flexural strength of normal section of FRP-confined RC circular columns

Numerical analysis is carried out to study the sectional properties of the fiber-reinforced polymer（FRP）-confined reinforced concrete（RC）circular columns. The axial load ratio, the FRP confinement ratio and the longitudinal reinforcement characteristic value are the three main parameters that can influence the neutral axis depth when concrete compression strain reaches an ultimate value. The formula for computing the central angle θ, corresponding to the compression zone, is established according to the data regression of the numerical analysis results. The numerical analysis results demonstrate that the concrete stress enhancement from transverse confinement and strain hardening of the longitudinal reinforcement can cause a much greater flexural strength than that defined by the design code. Based on the analytical studies and the test results of 36 large scale columns, the formula to calculate the flexural strength when columns fail under seismic loading is proposed, and the calculated results agree well with the test results. Finally, parametric studies are conducted on a typical column with different axial load ratios, longitudinal reinforcement characteristic value and FRP confinement ratios. Analysis of the results shows that the calculated flexural strength can be increased by 50% compared to that of unconfined columns defined by the code.

立铣刀优化设计

在满足立铣刀强度下,以尽可能发挥材料承载能力、刀具排屑性能好和后刀面的磨损小为目标,选取前角、后角和螺旋角为设计变量,构建优化模型,确定最优的立铣刀几何参数,提高刀具综合铣削性能。

力对开孔型频率选择表面电磁性能的影响(英文)

频率选择表面(FSS)被广泛用于各个领域。很多情况下,频率选择表面会受到外力的作用,例如:嵌在集成桅杆外壳或者雷达吸波-承载复合材料结构中的频率选择表面。文章研究了在力的作用下,频率选择表面的电磁性能是否会改变、如何改变。首先,分析了力影响频率选择表面电磁性能的机理;然后,使用力学有限元法和电磁学有限元法分析了不同大小、不同方向的力作用下,频率选择表面电磁性能改变的模式和大小。计算获得的电磁性能-力关系曲线显示:电磁性能的改变主要表现为电磁波响应频率的偏移和透射带宽的改变;在不同方向的力作用下,电磁性能的改变程度不一样。为了降低力对频率选择表面电磁性能的影响,在布置频率选择表面时,应使受力的方向避开频率选择表面的最敏感方向,同时带圆角的开孔型频率选择表面值得研究。

PDSWJ系列皮带熟化喂料机

将拌合后的湿面团放入该设备，进行短暂的静置熟化，同时间隙性的将湿面团输送至面片压延设备等下一道工序。 该机采用无菌输送带作为承载材料，具有面团静置熟化和湿面团先进、先出的工艺效果；能使面筋网络得到较好的形成。该机具有变频调速、光控喂料的特点。

浅谈汽车式起重机倾翻事故的防范措施

当前，我国汽车式起重机大量吸取了国际上的先进设计。并在广泛的市场调研和技术论证的基础上，结合国内市场的实际情况，采用新材料和新工艺，在主要关键液压元件和承载材料上引进国际化配套，并大量应用电比例操纵系统、双变量液压系统、具有专利技术的冷暖空调、椭圆形吊臂等新技术，

Flexural behaviors of double-reinforced ECC beams

In order to investigate the flexural behaviors of engineered cementitious composites （ECC）, theoretical and experimental researches are done on flexural doublereinforced ECC beams. Based on the assumption of the plane section remaining plane in bending and simplified constitutive models of materials, the calculation methods of load carrying capacities for different critical stages are obtained. Then, these calculation methods are demonstrated by comparing the test results with the calculation results. Finally, based on the proposed theoretical formulae, the effects of the compression strength, compression strain and tension strength of ECC, and the reinforcement ratio on the flexural behaviors of double-reinforced ECC beams are analyzed. The calculated and measured results are in good agreement, which indicates that the theoretical model can be used to predict the momentcurvature response of steel reinforced ECC beams. And the results of parametric studies show that the increase in the compression strength of ECC can greatly improve the flexural performance of beams; the increase in the ultimate compression strain can significantly improve the ultimate curvature and ductility, but has little effect on the load bearing capacity of beams. little effect on the flexural The tensile strength of ECC has behaviors of ECC beams. The increase in the steel reinforcement ratio can lead to significant improvement of the load bearing capacity and the stiffness of beams, but a degradation of the ductility of beams. The theoretical model and parameter analysis results in this paper are instructive for the design of steel reinforced ECC beams.

Lateral load-carrying capacity analyses of composite shear walls with double steel plates and filled concrete with binding bars

A method is developed to predict the lateral load-carrying capacity of composite shear walls with double steel plates and filled concrete with binding bars(SCBs). Nonlinear finite element models of SCBs were established by using the finite element tool, Abaqus. Tie constraints were used to connect the binding bars and the steel plates. Surface-to-surface contact provided by the Abaqus was used to simulate the interaction between the steel plate and the core concrete. The established models could predict the lateral load-carrying capacity of SCBs with a reasonable degree of accuracy. A calculation method was developed by superposition principle to predict the lateral load-carrying capacity of SCBs for the engineering application. The concrete confined by steel plates and binding bars is under multi-axial compression; therefore, its shear strength was calculated by using the Guo-Wang concrete failure criterion. The shear strength of the steel plates of SCBs was calculated by using the von Mises yielding criterion without considering buckling. Results of the developed method are in good agreement with the testing and finite element results.

A new numerical method for determining collapse load-carrying capacity of structure made of elasto-plastic material

Determination of collapse load-carrying capacity of elasto-plastic material is very important in designing structure. The problem is commonly solved by elasto-plastic finite element method （FEM）. In order to deal with material nonlinear problem involving strain softening problem effectively, a new numerical method-damped Newton method was proposed. The iterative schemes are discussed in detail for pure equilibrium models. In the equilibrium model, the plasticity criterion and the compatibility of the strains are verified, and the strain increment and plastic factor are treated as independent unknowns. To avoid the stiffness matrix being singularity or condition of matrix being ill, a damping factor a was introduced to adjust the value of plastic consistent parameter automatically during the iterations. According to the algorithm, the nonlinear finite element program was complied and its numerical example was calculated. The numerical results indicate that this method converges very fast for both small load steps and large load steps. Compared with those results obtained by analysis and experiment, the predicted ultimate bearing capacity from the proposed method is identical.

Mechanical Behavior of Rectangular Steel-Reinforced ECC/Concrete Composite Column under Eccentric Compression

In order to improve the seismic performance, deformation ability and ultimate load-carrying capacity of columns with rectangular cross section, engineered cementitious composite （ECC） is introduced to partially substitute concrete in the edge zone of reinforced concrete columns and form reinforced ECC/concrete composite columns. Firstly, based on the assumption of plane remaining plane and the simplified constitutive models, the calculation method of the load-carrying capacity of reinforced ECC/concrete columns is proposed. The stress and strain distribu- tions and crack propagation of the composite columns in different states of eccentric compressive loading are ana- lyzed. Then, nonlinear finite element analysis is conducted to study the mechanical performance of reinforced ECC/concrete composite columns with rectangular cross section. It is found that the simulation results are in good agreement with the theoretical results, indicating that the proposed method for calculating the load-carrying capacity of concrete/ECC composite columns is valid. Finally, based on the proposed method, the effects of ECC thickness, com- pressive strength of concrete and longitudinal reinforcement ratio on the mechanical performance of reinforced ECC/ concrete composite columns are analyzed. Calculation results indicate that increasing the thickness of ECC layer or longitudinal reinforcement ratio can effectively increase the ultimate load-carrying capacity of the composite column with both small and large eccentricity, but increasing the strength of concrete can only increase the ultimate Ioad- carrying capacity of the composite column with small eccentricity.

Bearing capacity and settlement of strip footing on geosynthetic reinforced clayey slopes

The effect of geosynthetic reinforcing on bearing capacity of a strip footing resting on georeinforced clayey slopes was investigated.The results of a series of numerical study using finite element analyses on strip footing upon both reinforced and unreinforced clayey slopes were presented.The objectives of this work are to:1) determine the influence of reinforcement on the bearing-capacity of the strip footings adjacent slopes,2) suggest an optimum number of reinforcement and 3) survey the effect of friction angle in clayey soils reinforced by geogrids.The investigations were carried out by varying the edge distance of the footing from slope.Also different numbers of geosynthetic layers were applied to obtaining the maximum bearing capacity and minimum settlement.To achieve the third objective,two different friction angles were used.The results show that the load?settlement behavior and ultimate bearing capacity of footing can be considerably improved by the inclusion of reinforcing layer.But using more than one layer reinforcement,the ultimate bearing capacity does not change considerably.It is also shown that for both reinforced and unreinforced slopes,the bearing capacity increases with an increase in edge distance.In addition,as the soil friction angle is increased,the efficiency of reinforcing reduces.

Numerical Analysis of the Composite Connection of Steel Joist Embedded in Concrete Girder

So far, numerous numerical studies have been conducted on the behavior of Composite Reinforced Concrete-Steel （RCS） beam-to-column connections. However, the lack of studies regarding the steel joist-concrete girder connection has yet to be addressed through comprehensive finite element methods to get an understanding of influential parameters. Hence, in this paper, composite connection of embedded steel joist in concrete girder is investigated with an appropriate finite element software, namely, ABAQUS. The validity of the proposed model is examined by the comparison made with the test data in literature. Results indicate that maximum bending capacity of the connection is achieved when embedment ratio is 1.78. Moreover, double web angles in the embedment region significantly reduce the embedment length required to achieve the maximum bending capacity. Finally, damage analyses show that bending capacity of concrete girder is slightly reduced in the connection zone.