Analysis of Rolling Pressure in Asymmetrical Rolling Process by Slab Method

The plane strain asymmetrical rolling was analyzed using slab method.The contact arc was replaced by parabola,and the constant surface friction status was adopted during the analysis.The deformation area was divided into three zones according to the direction of the friction.Then,the three zones were studied,respectively.A rolling force model and a rolling torque model were developed based on the analysis,and they were used to analyze the influence of asymmetrical rolling factors on deformation area and unit pressure if they had good precision which was determined by comparing the calculated results with the measured ones.

ANALYSIS OF SLAB EDGING BY A 3-D RIGID VISCO-PLASTIC FINITE ELEMENT METHOD

Drigid visco-plastic finite element method(FEM) is used in the analysis of metal forming processes,including strip and plate rolling,shape rolling ,slab edging,special strip rolling.The shifted incomplete Cholesky decompositon of the stiffness matrix with the solution of the equations for velocity increment by the conjugate gradient method is combined,This technique,termed the shifted ICCG method,is then employed to solve the slab edging problem.The performance of this algorithm in terms of the number of iterations,friction variation,shifted parameterψand the results of simulation for processing parameters are analysed.Numerical tests and application of this technique verify the effciency and stability of the shifted ICCG method in the analysis of slad edging.

Longitudinal crack on slab surface at straightening stage during continuous casting using finite element method

Deformation behavior of slab at the straightening stage during continuous casting was simulated by the explicit dynamic finite element method,and the stress distribution along the width direction of the slab and its change regularity at slab center during continuous casting were obtained.The influence of distribution and change of stress on the propagation of longitudinal cracks on slab surface was discussed.The results show that the tensional stress appears on slab surface at the inner arc side and the compressive stress appears on slab surface at the outer arc side at stages 6-8 in straightening zone during continuous casting.Longitudinal cracks generally appear on slab top surface and do not appear on slab bottom surface,which are also observed in industry.

NONLINEAR ANALYSIS OF REINFORCED CONCRETE RECTANGULAR SLABS USING FINITE ELEMENT METHOD

The nonlinear analysis of reinforced concrete rectangular slabs undermonotonic transverse loads is performed by finite element method.The layered rectangu-lar element with 4 nodes and 20 degrees of freedom is developed,in whichbending-stretching coupling effect is taken into account.An orthotropic equivalentuniaxial stress-strain constitutive model of concrete is used.A program is worked out andused to calculate two reinforced concrete slabs.The results of calculation are in goodconformity with the corresponding test results.In addition,the influence of tension stif-fening effect of cracked concrete on the results of calculation is discussed.

Elastic one-return boundary element method and hybrid elastic thin-slab propagator for strong-contrast media with sharp boundaries

In this paper, we developed the theory and algorithm of an elastic one-way boundary element method(BEM) and a corresponding hybrid elastic thin-slab propagator for earth media with sharp boundaries between strong contrast media. This approach can takes the advantage of accurate boundary condition of BEM and completely overcomes the weak contrast limitation of the perturbationtheory based one-way operator approach. The one-way BEM is a smooth boundary approximation, which avoids huge matrix operations in exact full BEM. In addition, the one-way BEM can model the primary-only transmitted and reflected waves and therefore is a valuable tool in elastic imaging and inversion. Through numerical tests for some simple models,we proved the validity and efficiency of the proposed method.

Revised RPS Method for Complex Solution of Multimode Slab Waveguides with Metal layers

The RPS method,which integrates the real numerical solution, the perturbation solution and the shooting solution reasonably,can obtain the complex solution of a slab waveguide with small gain/loss regions without searching the root in the entire complex plan.A revision to the RPS method is presented so that it can deal with the waveguide including large gain/loss regions.The application indicated that the simulation results are precise.

Improved methods for decreasing stresses of concrete slab of large-span through tied-arch composite bridge

Mechanical behavior of concrete slab of large-span through tied-arch composite bridge was investigated by finite element analysis (FEA). Improved methods to decrease concrete stresses were discussed based on comparisons of different deck schemes, construction sequences and measures, and ratios of reinforcement. The results show that the mechanical behavior of concrete slab gets worse with the increase of composite regions between steel beams and concrete slab. The deck scheme with the minimum composite region is recommended on condition that both strength and stiffness of the bridge meet design demands under service loads. Adopting in-situ-place construction method, concrete is suggested to be cast after removing the full-supported frameworks under the bridge. Thus, the axial tensile force of concrete slab caused by the first stage dead load is eliminated. Preloading the bridge before concrete casting and removing the load after the concrete reaching its design strength, the stresses of concrete slab caused by the second stage dead load and live load are further reduced or even eliminated. At last, with a high ratio of reinforcement more than 3%, the concrete stresses decrease obviously.

基于spike-and-slab先验的贝叶斯时间序列模型

贝叶斯方法通过引入先验信息并结合似然的方法进行参数估计和变量选择,使模型估计和预测结果更为精确。在贝叶斯框架下考虑时间序列之间的相关性,将偏自相关系数融合先验信息,提出基于spike-and-slab先验的贝叶斯层次时间序列模型(Spike-and-slab Prior with Partial Autocorrelation Coefficients,SS-PAC)。SS-PAC模型采用spike-and-slab先验并结合偏自相关系数,实现时间序列滞后阶数的选择、参数估计和预测。基于模拟数据和真实数据的实证研究表明,该模型相较于以往模型在变量选择和预测结果上表现更优。

钢纤维细石混凝土-钢组合板抗弯性能试验研究

钢纤维细石混凝土是一种具有优异力学性能和良好工作性的高性能混凝土复合材料。本试验针对正交异性钢桥面铺装层裂缝病害问题,对4组采用不同钢筋配筋率和保护层厚度的横桥向钢纤维细石混凝土-钢组合桥面板进行了抗弯破坏试验,研究了组合板的荷载-挠度关系与裂缝开展特征;用等效截面法计算了开裂应力、裂缝宽度和钢筋应力,验证了钢纤维细石混凝土-钢组合板的抗裂性能。结果表明:60 mm厚钢纤维细石混凝土铺装层在小配筋率(2.6%)和低于规范要求的保护层厚度(15 mm)条件下呈现出多缝开裂的破坏形态,具备较高的延性和开裂应力,满足规范和工程应用的要求。

双向受力的开槽混凝土叠合板力学性能试验研究

为了解决双向受力的叠合板拼缝处外伸的胡子筋容易与其他部件产生冲突从而影响施工的问题,采用了一种双向受力的开槽混凝土叠合板,在板件拼缝位置预留槽口,并在槽口处放置附加钢筋进行预制板之间的连接,共设置了3个试件对其力学性能进行试验研究.试验结果表明,双向受力的开槽混凝土叠合板与现浇混凝土板的承载力、刚度比分别达到0.99和1.08,延性系数达到9.59,且二者破坏形态一致,增加槽口数量对试件弹性刚度、开裂荷载、极限承载力的影响有限,但是可以提升叠合板的延性.双向受力的开槽混凝土叠合板可以实现拼缝处的有效传力,具有与现浇混凝土板一致的力学性能,在应用于实际工程时,可以提高施工效率、降低钢筋用量、提升经济效益,具有广阔的应用前景.

SCC灌注过程中轨道板变形与扣压装置受力特性分析

针对自密实混凝土(Self-Compacting Concrete,SCC)灌注过程中出现的轨道板上浮以及扣压装置受力过大的问题,基于耦合的欧拉-拉格朗日(Coupled Eulerian-Lagrangian, CEL)方法,建立直线地段CRTSⅢ型板式无砟轨道自密实混凝土灌注过程的流固耦合模型,从理论上研究不同施工参数对自密实混凝土灌注过程的影响规律和机理,重点分析漏斗高度、漏斗数量等参数对填充率、轨道板垂向和横向位移以及扣压装置受力等关键指标的影响.研究结果表明:漏斗高度与数量的增加均会减少灌注时间、提高施工效率,且增加漏斗数量的效果更明显;单孔灌注时的轨道板最大垂向位移出现在板边中部,双孔灌注时出现在观察孔附近,而最大横向位移仅出现在扣压装置附近;增加漏斗高度导致自密实混凝土对轨道板的压强增大,因而轨道板垂向与横向位移增加,扣压装置的垂向和横向力均增大;与单孔灌注相比,双孔灌注时轨道板上浮量、横向位移以及扣压装置受力明显增大.

铰缝损伤及铺装层对空心板桥横向刚度的影响

铰缝损伤是空心板桥梁较易出现的病害。为研究铺装层在铰缝损伤后对空心板桥梁横向刚度的影响,根据铰接板法理论,采用梁格法和Midas civil软件建立其有限元模型,对铰缝损伤后空心板桥梁的横向受力性能进行计算分析。研究结果表明:铺装层在空心板桥梁铰缝损伤后可起荷载横向传递的作用,提高了桥梁的横向受力性能,并且在多铰缝出现损伤时,提升效果更为明显;同时当铺装层厚度为10~20 cm时,铺装层厚度越大,桥梁的横向刚度越大,但对结构横向刚度的提升效果并不明显。

预应力先张法板梁裂缝防控

先张法预应力板梁裂缝是一种较为普遍的质量通病,其形成的主要原因是由于施工过程中施工操作不当、工艺控制欠佳等。通过对预制板梁施工工艺进行改进,采取控制芯模上浮、合理设计混凝土配合比、规范浇筑工艺、控制保护层厚度、严格张力程序等措施,裂缝得到了有效控制。

双块式无砟轨道轨枕与道床板界面脱空损伤识别

为准确识别双块式无砟轨道轨枕与道床板连接面脱空损伤,建立了双块式无砟轨道冲击回波有限元模型,分析界面损伤对弹性波传播规律的影响。在室内浇筑含有不同损伤位置和不同损伤程度的混凝土复合试件,采用冲击回波法进行损伤识别。研究结果表明:脱空损伤会显著影响弹性波在界面处的传播,基于回波信号分析可识别损伤;弹性波频率主要受激振锤大小的影响,应结合结构易损位置和理论计算选取合适的激振锤;混凝土复合试件的试验厚度值与理论厚度值相差仅为1 cm,测试结果合理,可用于判断脱空损伤程度,但不能确定损伤区域;利用平面成像技术可准确识别轨枕与道床板界面脱空范围,为双块式无砟轨道结构养护维修提供一定参考,试验结果验证了冲击回波法用于双块式轨道层间脱空识别的可行性和合理性。

预应力T梁预制阶段裂缝产生的原因及补救措施

裂缝是梁板典型病害之一,其对桥梁的耐久性影响较大,由于预应力桥梁制作工序较多,人为干扰因素大,导致裂缝产生根本原因时常难以发现,本文通过对某高速项目桥梁预制阶段裂缝产生原因进行研究分析,找出了该项目预应力T梁预制阶段裂缝产生原因,并通过调整拆模后梁体静置时间,解决了T梁腹板预制阶段的裂缝,并在此基础上介绍了裂缝补救方法,使后续梁板生产质量得到了保证。

地铁工程减振垫浮置板无砟道床施工技术研究

随着当今社会经济的发展,人们对在市区内安全且高效的出行方式需求逐渐增大,为缓解城市交通压力,满足人们日常出行,各大城市在地铁建设方面加大了建设力度。为更好打造舒适环保型地铁,广大设计人员在减振降噪方面做出较大努力,将地铁对居民生活影响降到最低。结合青岛地铁4号线减振垫整体道床施工,从施工工法流程方面着手,采用轨排架轨法施工,是目前应用较广泛,减振等级高的减振道床之一,总结一套行之有效的工艺流程,解决关键控制技术,是广大建设人员共同的目标。

超高曲线梁双层屋盖板施工技术的应用研究

为打造21世纪新海丝文化新传播中心,厦门海沧区政府特邀国际普利兹克建筑奖获得者-王澍大师以五代董源的《潇湘图卷》为蓝本,设计了具有重峦叠嶂屋面、造型独特的金沙书院项目。项目屋盖结构复杂,施工质量要求高,采用的新技术,新工艺较多。为了达到隐藏通风管道美观的设计效果以及满足建筑使用功能,局部屋盖采用2.2 m超高曲线梁双层板楼盖,形状为双曲线,施工难度大。通过双层楼盖结构2.2 m超高曲线梁钢筋模板砼工程的制作安装施工,探讨总结特殊施工工艺的做法.该施工技术得以应用,行之有效,具有较广的应用前景,可为类似工程提供理论指导与技术借鉴。

Effects of the width and thickness of slabs on broadening in continuous casting

A 3D viscoelastic-plastic thermal-mechanical coupled finite element model was built on the basis of the secondary development of the commercial software MSC.Marc. Numerical simulations were performed to study slab broadening in the secondary cooling zone. The effects of slab width and thickness on slab broadening were considered. The obtained results reveal that the width broadening is noticeable, and the ratio of ultimate broadening slightly increases with the increase of slab width. This agrees well with the measured data in practice. There is no obvious increase in ultimate broadening when the thickness of slabs increases.

分离电荷在碱金属过渡金属吸附中的影响——Jellium球/Slab模型

在计算中发现,Jellium/slab模型中Jellium减小了吸附原子对价电子的吸引能力,使得φ—θ曲线在极小处大大低于实验值,特别是Cs/Ir系统。本文提出了Jellium球/slab模型,以模拟实际分离电荷对电子的吸引作用,检验结果表明,分离电荷对功函数将给出大约0.4eV到0.8eV的贡献,这使得Cs/W及Cs/Ir吸附系统的计算φ—θ曲线和结果与实验趋于一致,但更重要的是使我们认识到了分离电荷影响的重要性。

Optical properties of the two-port resonant tunneling filters in two-dimensional photonic crystal slabs

We have designed and fabricated two types of two-port resonant tunneling filters with a triangular air-hole lattice in two-dimensional photonic crystal slabs.In order to improve the filtering efficiency,a feedback method is introduced by closing the waveguide.It is found that the relative position between the closed waveguide boundary and the resonator has an important impact on the dropping efficiency.Based on our analyses,two different types of filters are designed.The transmission spectra and scattering-light far-field patterns are measured,which agree well with theoretical prediction.In addition,the resonant filters are highly sensitive to the size of the resonant cavities,which are useful for practical applications.