Effects of rotational components of earthquake on seismic response of arch concrete dams

The present study deals with dynamic analysis of arch concrete dams,taking rotational components of earthquakes into account.A modified methodology was used to evaluate the rotational components of the earthquake.The translational components of the earthquake have been used in to obtain the rotational components of the earthquake,based on the intersecting isotropic elastic wave propagation.Two rotational components of Taft,Tabas and San-Fernando earthquakes are evaluated based on the translational components of the earthquakes and considering frequency dependencies of incident angle and wave velocity.Finally,dynamic analyses of Morrow Point Dam are presented to evaluate the effects of combined translational and rotational components on the seismic response of the dam.Various conditions of reservoirs,including full and empty state,are considered in the analyses.Fluid–structure interaction was completely taken into account.It was realized that incorporating rotational components increased the maximum compressive and tensile stresses in both empty and full reservoir analyses.Distribution of maximum tensile stresses is very sensitive to the rotational components of the earthquake.Also,it can be concluded that the segregated effect of the rocking component on the response of concrete dams is more effective than the sole effect of the torsional component.

Performance index limits of high reinforced concrete shear wall components

The deformation performance index limits of high reinforced concrete （RC） shear wall components based on Chinese codes were discussed by the nonlinear finite element method. Two typical RC shear wall specimens in the previous work were first used to verify the correctness of the nonlinear finite element method. Then, the nonlinear finite element method was applied to study the deformability of a set of high RC shear wall components designed according to current Chinese codes and with shear span ratio λ≥2.0. Parametric studies were made on the influence of shear span ratio, axial compression ratio, ratio of flexural capacity to shear capacity and main flexural reinforcement ratio of confined botmdary members. Finally, the deformation performance index and its limits of high RC shear wall components under severe earthquakes were proposed by the finite element model results, which offers a reference in determining the performance status of RC shear wall components designed based on Chinese codes.

Effect of CSH Crystal Nucleus on Steam-Free Cured Fly Ash Precast Concrete Components

The measures of steam curing and early-strengthening agents to promote the precast components to reach the target strength quickly can bring different degrees of damage to the concrete.Based on this,the new nanomaterial CSH-the hydration product of cement effectively solves these measures’disadvantages,such as excessive energy consumption,thermal stress damage,and the introduction of external ions.In this paper,the effect of CSH on the early strength of precast fly ash concrete components was investigated in terms of setting time,workability,and mechanical properties and analyzed at the microscopic level using hydration temperature,XRD,and SEM.The results showed that under the same workability,CSH could significantly reduce the amount of admixture,shorten the final setting time,almost not affect the initial setting time,and accelerate the hydration of cement.At the optimum dose of 5%,the mechanical properties of the specimens were improved by more than 98%within 12 h of hydration,resulting in an earlier release time of 12 h and no risk of strength inversion later.The results of this paper give theoretical support to the behavior of precast components under steam-free curing.

Robust Virtual Network Embedding Based on Component Connectivity in Large-Scale Network

Virtual network embedding problem which is NP-hard is a key issue for implementing software-defined network which is brought about by network virtualization. Compared with other studies which focus on designing heuristic algorithms to reduce the hardness of the NP-hard problem we propose a robust VNE algorithm based on component connectivity in large-scale network. We distinguish the different components and embed VN requests onto them respectively. And k-core is applied to identify different VN topologies so that the VN request can be embedded onto its corresponding component. On the other hand, load balancing is also considered in this paper. It could avoid blocked or bottlenecked area of substrate network. Simulation experiments show that compared with other algorithms in large-scale network, acceptance ratio, average revenue and robustness can be obviously improved by our algorithm and average cost can be reduced. It also shows the relationship between the component connectivity including giant component and small components and the performance metrics.

Recent research and development on forming for large magnesium alloy components with high mechanical properties

The lightweight of high-end equipment relies on high mechanical properties magnesium(Mg) alloy structural components, because it is the best way to improve equipment service performance and reduce energy consumption. This article summarizes the current progress and characteristics of large-scale high-performance Mg alloy components by analyzing the strengthening-toughening mechanisms, characteristics of plastic forming, and the preparation of large high mechanical properties forging blanks. Due to the lack of breakthroughs in the key technologies for forming large-scale Mg alloy components, their uniformity of mechanical properties and consistency are poor, the forming accuracy of components is low, and the production cost is high, which limit their engineering application and restrict the lightweight level of high-end equipment. In view of the above problems, the forming trends and research directions of large-scale and high mechanical properties Mg alloy components are proposed in this paper. It can provide help for the breakthrough of the key technology of large-scale Mg alloy components with high mechanical properties and expand the application of Mg alloy in high-end products.

Scaling of motion and governing equations for baroclinic large-scale motions in equatorial ocean

An obvious characteristic of the baroclinic large-scale motions in the equatorial ocean is that the meridional scale H of motion is far smaller than the zonal scale L. The scaling of motion carefully with this striking characteristic in this paper results in two conclusions, i. e., the Coriolis terms associated with the horizontal component of the rotation vector cannot be neglected in the governing equations; and the use of the absence of heating is not suitable to the equatorial region. In this paper the equatorial β-plane nondimensional governing equations with the small parametersδ_0 andδ_1 have been Obtained.

Corrosion Processes in the Concrete of the Dams

During the whole operation life of Bratsk and Ust-Ilimsk hydroelectric plants, chemical analysis of water filtering through the pressure front of the concrete dams was under systematic monitoring by sampling in places of concemrated outcome in the inspection galleries of a dam. Long-term cumulative observations made up a basis for study of the indicated dams concrete corrosion caused by the Angara water in the process of its filtration through the cracks formed in the period of the dam erection, through construction joims and other defects. Mathematical-statistical analysis allowed the classification the processes of corrosion from the point of view of their time dynamics and divided them correspondingly into stationary （stable） and non-stationary. On the basis of a calculation of the cement stone componem removal along with the ideas of the process dynamics the pressure from filtration developmem forecast has been made and their danger level has been estimated. The developed conception is of rather a general character and can be used when analyzing the state of concrete dams of the Angara cascade and other similar cases.

基于激光诱导击穿光谱的混凝土氯元素分布测量方法

氯元素会对混凝土结构产生侵蚀,引起结构内部的钢筋锈蚀,导致混凝土开裂,破坏结构的完整性。化学滴定等常规的混凝土中氯元素含量测量方法存在操作复杂、检测速度慢等问题。激光诱导击穿光谱(LIBS)具有无须样品预处理、二维扫描检测和原位定点分析等优势,但其用于混凝土中的氯元素含量测量仍存在氯元素定量限难以降低、非水泥成分对氯元素二维分布测量结果的影响等问题。面向核电站混凝土构筑物中氯元素含量现场快速检测的需求,研究了氯元素含量分布的双脉冲激光诱导击穿光谱检测方法,进一步评估了核电站混凝土模拟样品渗透面中氯离子的侵蚀状况。首先,分别采用内标法、主成分回归和支持向量回归建立氯元素定标模型,基于内标法得到的氯元素检测限为0.006 02 wt%、定量限为0.018 06 wt%,并采用留一法交叉验证法来评估三种模型的预测性能。其次,为了排除非水泥基质对氯元素检测的影响,分别建立了结合主成分分析的逻辑回归分类和支持向量机分类模型对混凝土中的水泥和骨料进行精确识别。同时选取Si、 Ca、 O三种元素组合的支持向量机模型的分类效果最优,其对总体组分识别的准确率达到了98.20%,其中骨料识别准确率97.84%、水泥识别准确率为98.33%。最后,基于主成分回归定标模型针对侵蚀15和30 d的混凝土渗透面的氯含量进行二维分布测量,两种样品的平均预测Cl含量均在约2 mm处达到最大值分别为0.890 wt%和0.599 wt%,结果与电位滴定法一致。综上,基于双脉冲激光诱导击穿光谱检测方法,在30 mJ的总能量下实现了氯元素检测限达0.006 02 wt%,实现了混凝土中骨料和水泥的精确识别,获得了混凝土侵蚀渗透面的氯元素含量二维分布,为核电站混凝土构筑物氯元素含量快速检测的现场应用提供了工程化解决方案。

戈壁集料混凝土物理性能及抗压强度研究

为资源化利用西北地区工程建设开挖的弃方材料——戈壁集料,基于西北某机场扩建工程的戈壁集料,首先对戈壁集料基本物理性能及矿物成分进行分析,随后以水灰比、戈壁砂率、戈壁细集料种类及水泥浆量为变化参数,先后对戈壁集料混凝土的工作性能、破坏形态以及抗压强度进行研究。试验结果表明:戈壁集料含泥量高,其黏土矿物含量约20%且以吸水能力强的蒙皂石和伊利石为主;随水灰比减小,戈壁粗集料混凝土的坍落度减少,而抗压强度近似线性增大,与普通混凝土规律一致;同配合比下,全戈壁集料混凝土抗压强度高于戈壁粗集料混凝土,但前者的拌合物表现更黏稠;筛除粒径小于0.15 mm的戈壁细集料虽可小幅提高全戈壁集料混凝土的坍落度,但对抗压强度不利;随砂率增加,戈壁集料混凝土的坍落度增大,其抗压强度先增后减。最后,通过回归分析为戈壁集料混凝土配合比提供参考。

基于BIM的PC构件排样优化设计

针对PC构件排样与上游装配式建筑设计模型的协同效用问题,进行了基于BIM的PC构件排样优化设计研究。分析了装配式BIM中PC构件的组成元素,完成PC构件信息的提取;结合改进蚁群算法与动态剩余矩形算法对PC构件排样进行优化,采用遗传变异策略与路径选择机制改进算法后期易陷入局部最优的不足,经过多次优化迭代得出最优排样。某PC构件企业的生产排样实例验证了基于BIM的PC构件排样优化方案可实现上游装配式建筑设计模型与PC构件排样的协同效用,提高了排样效率。

装配式混凝土PC构件施工技术及力学性能分析

为高效而精确地完成装配式混凝土结构的施工,以中建东湖锦城项目为载体对装配式混凝土PC构件的施工技术进行了分析,尤其是装配式混凝土PC构件起吊安装定位和标高等施工控制,同时进行了力学计算分析。工程实践表明,装配式混凝土PC构件的应用可提高施工效率和节约施工时间。

基于构件性能的SRC框架结构抗震性能评估研究

针对位移抗震性能设计的不足,现行规范采用构件损伤程度补充评估结构的抗震性能,但对于型钢混凝土(steel reinforced concrete,SRC)框架结构,其在各性能水平下的损伤构件比例未有明确规定。在此背景下,提出了SRC框架的构件性能状态与结构性能水准的对应关系,建立了基于构件性能的SRC框架结构抗震性能评估方法。对不同高度和抗震设防烈度的SRC框架结构模型进行增量动力分析(incremental dynamic analysis,IDA),明确了结构的层间位移角和构件损伤分布,通过统计多条地震波下结构不同极限状态的构件破坏比例,建立用于体型规则SRC框架结构抗震评估的构件性能指标,并进一步采用地震易损性分析对结构抗震性能进行了评估。

6.4级漾濞地震某RC框架及其非结构部件震害分析

2021年云南漾濞6.4级地震造成了较大范围的建筑破坏,在漾濞县城记录到的地震加速峰值(PGA)高达720.2 gal。在强震作用下,大量土木结构的民居发生了破坏,而约束砌体和钢筋混凝土(RC)结构的震害则相对较轻。现场震害调查发现,部分框架结构的震害明显重于同一区域的其他同类型结构,呈现明显、多样的非结构部件破坏特征。因此,该文对某震害较重的框架进行详细调查,分类分析结构及其非结构部件地震破坏细节;依据图纸及现场考察信息建立精细有限元分析模型,对此次地震的地震动破坏力特征以及该框架结构及其非结构部件的地震破坏机理进行了量化分析。分析结果表明:带填充墙框架仿真模型的分析结果与实际震害现象更接近;框架结构局部大空间、框架底部的约束形式和填充墙的布置形式的综合作用导致结构产生局部过大变形与各类非结构部件的严重破坏。在考虑填充墙对框架结构的作用效应后,结构的不规则性大幅增加,导致结构薄弱层的最大层间位移角相较纯框架模型增加127%,并且明显加剧非结构部件的震害。该文对该建筑震害现象的详细调查与仿真分析,可为结构抗震设计与应急救援决策提供参考。

基于BP-PCA-WCA-SVM的混凝土大坝变形预测方法

传统基于单一模型的混凝土大坝变形预测方法预测精度低,噪声稳健性差,泛化能力弱。为解决该问题,提出一种基于贝塔先验主成分分析(BP-PCA)与水循环算法(WCA)优化支撑向量机(SVM)相结合的混凝土大坝变形组合预测方法。首先利用所提BP-PCA模型对变形数据进行多尺度降噪分解,将复杂非线性、非平稳随机过程分解为一系列结构简单的主分量;然后利用WCA优化的SVM(WCA-SVM)对每个主分量分别建立预测模型;最后将多个主分量的预测结果综合叠加得到最终预测结果。以我国中部地区某混凝土大坝变形监测数据开展试验,结果表明,所提BP-PCA模型能够有效挖掘数据中隐含的趋势性和规律性信息,BP-PCA-WCA-SVM模型能够获得较高的预测精度,预测结果的相对误差为1.07%,误差均方根为0.065。相对于Kalman滤液、SVM、CNN 3种方法,所提模型预测性能提升均超过62%,并且具有更强的噪声稳健性和泛化能力。

建筑混凝土轻钢结构损伤可靠检测仿真研究

建筑混凝土轻钢结构强度高、整体刚性好、变形能力强,但由于其构件断面偏小,发生开裂损伤后极限承载能力下降,严重影响建筑整体质量,所以应研究建筑混凝土轻钢结构损伤检测方法。先构建轻钢结构实体并自动生成三维轻钢结构有限元模型,利用模态分析模块求解轻钢结构模态参数。采用希尔伯特振动分解算法,获取轻钢结构损伤检测的最大幅值分量信号,并将其输入至全连接神经网络,检测损伤情况,并输出损伤结果。测试结果显示:获取的一阶和二阶频率结果与实际结果之间最大差值分别为0.75Hz和1.2Hz,说明上述方法可准确得出轻钢结构的相关模态参数,能够完成建筑混凝土轻钢结构损伤的可靠检测。

考虑约束作用的混凝土柱耐火试验加载方式研究

为找到一种在构件耐火试验中能有效考虑整体结构对受火构件约束作用的加载方式,建立了2层2跨的钢筋混凝土框架和受火单柱的有限元模型,对比分析荷载比为0.2、0.4和0.6时,恒载、变位移加载、变力加载和交互加载方式下受火单柱与整体结构的内力、变形和耐火极限的差异。研究结果表明:恒载单柱不能准确反映整体结构受火柱的变形、轴力和耐火极限;变位移加载和变力加载在荷载比为0.2时能较好考虑整体结构中的约束作用,在荷载比为0.4和0.6时误差增大也不能准确反映整体结构的抗火性能;交互加载的相对误差随荷载比增大而增大,且最大误差小于20%。恒载、变位移加载、变力加载和交互加载中,交互加载可以较好考虑整体结构中的约束作用,近似达到整体结构试验的效果。

面向制造与装配的设计的装配式竖向预制混凝土构件参数化设计与应用

装配式建筑设计、生产过程存在标准化程度低、数据联系较差等诸多问题。引入了制造业中面向制造与装配的设计(design for manufacturing and assembly,DFMA)的产品设计理念,研究了装配式建筑竖向预制混凝土(precast concrete,PC)构件的快速建模与深化设计应用,通过对建筑企业大量装配式建筑项目PC构件深化设计图纸的梳理分析,分析了图纸中构件组成规律,创新性地将PC构件二次拆分为模块。分析模块的种类、组合规律、数据架构等,形成模块的设计标准。将设计标准融入建筑信息模型(building information modeling,BIM)软件中,并开发相应的工具软件实现模块的快速建模。以软件创建的参数化标准模块为基础,以关联、匹配、调取、组合、拆解的关键技术实现PC构件的深化设计与工厂的制造联系。最后,通过实际工程案例进行测试对比。结果表明,竖向PC构件的建模速度提升70%、深化设计效率提升约80%,深化设计费用节省约80%,实现最小制造成本。研究结果有助于构建装配式建筑标准化的设计和生产体系,推广少规格多组合的设计方法,强化数据联系,提高装配式建筑的综合效益。

隧道中的全预制装配式混凝土楼梯施工技术研究

针对传统市政领域用混凝土现浇楼梯结构施工时需进行外围脚手架搭设,现场人工、模板、支撑构件等消耗量大,混凝土浇筑和振捣困难,施工周期较长的问题,基于一项设计优化后的全预制混凝土楼梯方案,将楼梯结构中的预制梯段板、梯柱、梯梁和平台板构件全部预制,仅部分节点和拉结梁采用现浇,大大减少了现场脚手架搭设和支模板支设工作。通过研究和编制专项构件预制方案、装配式楼梯施工方案,利用装配式施工优势提升了构件质量,改进了现场施工条件,缩减了施工周期,总体应用效果良好。总结的经验可供类似工程参考。

巷道防冲吸能钢管混凝土拱架支护性能研究

针对目前巷道支护中钢管混凝土拱架缺乏可缩让压性能的问题,从吸能让位角度设计了一种防冲吸能钢管混凝土拱架结构。通过Abaqus建立新型钢管混凝土拱架与围岩组合模型,在静载与动载两种荷载状态下,对比分析新型拱架对巷道的支护效果与抗冲击能力。结论如下:①根据合理的让位阻力特性设计吸能构件壁厚与尺寸,在拱架上部连接处和底弧段中部设置吸能构件,可避免弯曲过大发生失稳。套管形状依据U型钢拱架卡揽结构设置为折纹型,与拱架摩擦实现缩动让压;②在竖向与侧向冲击下,优化后拱架支护巷道各点位移量呈减少趋势,降低了拱架顶弧段下沉与底弧段上拱,支护效果更强;③静载作用下,优化后拱架与吸能构件接触后,拱架各点处塑性应变不再增加,吸能构件代替拱架发生形变。在受到动载后,吸能构件能快速响应,同时拱架两帮拐角发生弯曲变形,其余部分仍未发生明显变形。吸能构件压溃后,拱架整体塑性应变开始增加,最终优化后拱架各点等效塑性应变竖向与侧向冲击下分别降低了10%~50%和13%~78%。

预制混凝土构件碳排放因子全因素计算研究

文中基于京津冀地区25家企业37个工厂的统计数据,系统研究了装配式建筑预制构件中建筑材料的隐含碳排放、能源消耗和运输的直接碳排放规律;建立了预制构件全因素碳排放计算模型;依托某大型企业百余万立方米预制构件供应数据,计算了典型预制构件的碳排放因子,并分析了其碳排放规律:与能源消耗和运输直接碳排放相比,预制构件中建筑材料产生的隐含碳排放更为突出,平均占比约85%,且混凝土强度越高,碳排放越大;能源消耗直接碳排放平均占比略大于9%;运输直接碳排放平均占比接近5%。建筑材料碳排放量中钢筋、水泥和钢模具的碳排放之和占总量的80%~90%。热养护环节能源碳排放量占生产阶段能源碳排放总量的60%左右。基于运输碳排放模型,计算得到京津冀地区为北京市供应预制构件的企业平均运距约134 km。建议各企业应从选用减碳建材、深化设计和优化生产工艺、改用绿色能源新型运输车等多方面综合研究减碳措施。文中研究成果可为装配式建筑碳排放计算提供典型数据与理论基础,有力促进装配式建筑绿色低碳可持续发展。