External blast flow field evolution and response mechanism of single-layer reticulated dome structure

Single-layer reticulated dome structure are commonly high-profile building in the public and can be attractive targets for terrorist bombings,so the public can benefit from enhanced safety with a stronger understanding of the behavior of single-layer reticulated dome structure under explosion.This paper investigates the fluid-structure interaction process and the dynamic response performance of the singlelayer reticulated dome under external blast load.Both experimental and numerical results shown that structural deformation is remarkably delayed compared with the velocity of blast wave,which advises the dynamic response of large-span reticulated dome structure has a negligible effect on the blast wave propagation under explosion.Four failure modes are identified by comparing the plastic development of each ring and the residual spatial geometric of the structure,i.e.,minor vibration,local depression,severe damage,and overall collapse.The plastic deformation energy and the displacement potential energy of the structure are the main consumers of the blast energy.In addition,the stress performance of the vertex member and the deep plastic ratio of the whole structure can serve as qualitative indicators to distinguish different failure modes.

Sensitivity analysis and probability modelling of the structural response of a single-layer reticulated dome subjected to an external blast loading

The structural response of a single-layer reticulated dome to external explosions is shaped by many variables,and the associated uncertainties imply non-deterministic results.Existing deterministic methods for predicting the consequences of specific explosions do not account for these uncertainties.Therefore,the impact of the uncertainties associated with these input variables on the structures’response needs to be studied and quantified.In this study,a parametric uncertainty analysis was conducted first.Then,local and global sensitivity analyses were carried out to identify the drivers of the structural dynamic response.A probabilistic structural response model was established based on sensitive variables and a reasonable sample size.Furthermore,some deterministic empirical methods for explosion-resistance design,including the plane blast load model of CONWEP,the curved blast load model under the 50%assurance level,and the 20%mass-increased method,were used for evaluating their reliability.The results of the analyses revealed that the structural response of a single-layer reticulated dome to an external blast loading is lognormally distributed.Evidently,the MB0.5 method based on the curved reflector load model yielded results with a relatively stable assurance rate and reliability,but CONWEP did not;thus,the 1.2MB0.5 method can be used for making high-confidence simple predictions.In addition,the results indicated that the structural response is very sensitive to the explosion parameters.Based on these results,it is suggested that for explosion proofing,setting up a defensive barrier is more effective than structural strengthening.

External blast load factors for dome structures based on reliability

Dome structures have been used extensively for industrial,residential,and military infrastructure.Therefore,it is necessary to understand the damage risk potential for such structures for blast-resistant design considerations.This paper investigates the effect of blast load variability on the design value and the structural dynamic response.Therefore,the sources of uncertainty in the external blast load on dome structures were discussed firstly.Then based on the probabilistic blast load model for the dome,the rationality of a deterministic mass-increase safety method was assessed.It was found that previous deterministic design method cannot provide a consistent and sound assurance factor or reliability index on the entire dome roof.In addition,it was also proved that the assurance-based load method fails to ensure compliance with structural safety design standards on the dome roof when compared with the reliability-based blast method.A sensitivity analysis on the probabilistic blast load was conducted,and the results indicate that stand-off distance and explosive mass both act as dominant sources to influence the mean and variability of blast load.Therefore,based on the Latin hypercube sampling method,a reliability-based external blast load factor technique was proposed.This technique was further used to estimate structural damage levels of a single-layer reticulated dome under different reliability requirements,associated with a low,medium,and high level of protection grades for a specific explosion scenario,and it indicated that this technique can be useful in the building design to achieve a higher structural anti-explosion capacity.This study herein can serve as a reference for the calculation method of designed blast load.

Initial pre-stress finding procedure and structural performance research for Levy cable dome based on linear adjustment theory

The cable-strut structural system is statically and kinematically indeterminate. The initial pre-stress is a key factor for determining the shape and load carrying capacity. A new numerical algorithm is presented herein for the initial pre-stress finding procedure of complete cable-strut assembly. This method is based on the linear adjustment theory and does not take into account the material behavior. By using this method,the initial pre-stress of the multi self-stress modes can be found easily and the cal-culation process is simplified and efficient also. Finally,the initial pre-stress and structural performances of a particular Levy cable dome are analyzed comprehensively. The algorithm has proven to be efficient and correct,and the numerical results are valuable for practical design of Levy cable dome.

New Superconductivity Dome in LaFeAsO1-xFx Accompanied by Structural Transition

High-temperature superconductivity is often found in the vicinity of antiferromagnetism. This is also true in LaFeAsOl-xFx （x ≤ 0.2,） and many other iron-based superconductors, which leads to proposals that supercon- ductivity is mediated by fluctuations associated with the nearby magnetism. Here we report the discovery of a new superconductivity dome without low-energy magnetic fluctuations in LaFeAsO1-xFx with 0.25 ≤ x ≤ 0.75, where the maximal critical temperature Tc at Xopt =0.5-0.55 is even higher than that at x ≤0.2. By nuclear magnetic resonance and transmission electron microscopy, we show that a C4 rotation symmetry-breaking struc- tural transition takes place for x 〉 0.5 above To. Our results point to a new paradigm of high temperature superconductivity.

ON SOME PROBLEMS IN DYNAMIC COMPUTATION FOR THIN-WALLED STRUCTURES

This article discusses the problems of the dynamic computation for thin-walled structures such as thin plates and thin shells under impact load to find the dynamic factor mainly. In calculation we take into account the effect of the mass of the striking object and the system of thin-walled structures to be struck and transform the distributed mass of thin-walled structures into only one concentrated 'equivalent mass' by the method of reduced mass. Accordingly we derive the dynamic factor for the system of thin-walled structures under impact load.

Structural Systems Composed of Concentric Hoops and Designed for Lightweight Domes of Large Spans

The paper presents a selected group of tension-strut structural systems designed for the construction of lightweight dome covers of large spans, which can be comparatively easy to assembly and have rises of which can be relatively small. This will allow significant decrease costs of erection and maintenance of objects covered by these roof structures. The proposed systems have been obtained from the results of suitable transformations of a chosen type of double-layer space frame and an appropriate arrangement of tetrahedron modules in the space of each of the newly designed type of the structural system. All these systems are built by means of concentric hoops having their own integral spatial stiffness obtained after an appropriate pre-stressing. Particular hoops can be mounted on the ground level and then one by one will be hoisted to the designed positions where they will be connected by means of special sets of the tension members. Due to these structural features, the assembly process of each system should be relatively simple, fast and not expensive. The whole tension-strut structure has to be connected to the compression perimeter ring and suitably pre-stressed. There are presented visualizations of the proposed systems prepared on the basis of the appropriate numerical models especially defined for each particular structure.

Design of Roof Cover Structures by Help of Numerical Models Defined in Formian

Numerical models defined by means of a suitably assumed set of parameters make it possible to select the optimal structural solution for the given or assumed conditions. The paper presents examples of applications of numerical models defined in the programming language Formian during the shaping processes of various types of spatial structural systems designed for roof covers. These types of numerical models can be relatively easily adapted to the requirements, which can be frequently changed during the investment process, what makes possible a considerable reducing of costs and time of design of the space structures having even the very complex shapes. The advantageous features of application of numerical models defined in Formian are presented in models determined for selected forms of the roof covers designed also by means of a simple type of a space frame. In the paper, there are some presented visualizations made on bases of these models defining mainly for structural systems developed recently by the author for certain types of the dome covers. The proposed structural systems are built by means of the successive spatial hoops or they are created as unique forms of the geodesic dome structures.

兰州奥体综合馆弦支穹顶结构模型预应力张拉试验研究及模拟分析

为了研究弦支穹顶结构预应力的分布特性,基于兰州奥体综合馆弦支穹顶屋盖按照1∶20制作了缩尺模型,对该模型分3级进行预应力施工张拉试验,测试了2种不同张拉顺序下模型的杆件内力及节点竖向位移变化规律,并将试验结果和MIDAS Gen数值模拟结果进行了对比分析。研究表明:对于肋环型小矢跨比弦支穹顶结构,在张拉时环索相互影响较大,张拉初期环索内力变化更明显;张拉过程中预应力的施加对环杆的影响大于对径杆的影响,最外圈环杆在张拉过程中承力占比最大,节点竖向位移在第4圈达到最大;不同张拉顺序会改变外圈杆件内力及节点位移变化趋势,从外到内分级循环张拉下部索对结构更有利。

悬浮物对三亚珊瑚礁区浮游动物群落结构及其摄食的影响

随着人类活动对珊瑚礁的影响日益加剧,输入到近岸珊瑚礁区的悬浮物日益增多,不仅影响珊瑚的生理,也会对珊瑚礁生态系统基础生物生产过程产生影响。为了解悬浮物对珊瑚礁区浮游动物组成及摄食的影响,于2015年4月在三亚典型岸礁区设置了昼夜连续观测站点(W4为悬浮物浓度高的站位,W5为对照站位),分析了悬浮物波动对浮游动物群落结构的影响,并用分子生物学方法结合室内实验,研究了悬浮物对优势桡足类现场食物组成和摄食选择的影响。结果显示:两个站位叶绿素a浓度偏低,昼夜波动较大;W4站的悬浮物和叶绿素a浓度均高于W5站,但W5站悬浮物中有机颗粒物组分比例(73.69%)高于W4站(46.09%);W5站浮游动物种类多样性和丰度均高于W4站。进一步摄食分析表明,两个站位桡足类均以后生动物来源的有机碎屑为主要食物,在W4站桡足类食物组成中浮游植物的比例也相对较高,而在W5站桡足类还摄食较多的微型浮游动物。在摄食实验中,高浓度的悬浮颗粒物显著提高了红纺锤水蚤(Acartia erythraea)的滤水率和摄食率,但其食物组成却由以浮游植物为主转而以陆生植物碎屑为主,说明浓缩海水中较高的悬浮颗粒物含量限制了桡足类的摄食选择,使其摄食大部分有机碎屑作为补偿营养来源。研究结果表明,高悬浮物浓度会影响浮游动物的摄食选择,但悬浮物中高比例的有机碎屑可为浮游动物提供重要的补充食物来源,支持其维持较高的生物量。

江西彭山穹隆构造成因及地质意义

为探讨彭山穹隆成因及时代,在彭山地区开展了野外地质调查、构造解析和年代学等研究工作。结果表明,彭山穹隆为构造穹隆,形态为短轴背斜,其及周边存在稳定的印支期近SN向古构造应力场,伴生NNE向走滑断层,其东侧发育东倾的逆断层。切穿穹隆的断层被霏细斑岩脉贯入,霏细斑岩脉的锆石U-Pb年龄为(123.0±1.0) Ma,隐伏黑云母花岗岩的U-Pb年龄为(123.0±1.4) Ma,古应力场同期断层中断层泥的伊利石K-Ar年龄为(228.1±10.3)~(233.2±6.5) Ma,因此认为彭山穹隆形成时间为印支期或更早。

Geiger型索穹顶冲击动力响应与失效机理研究

针对当前索穹顶结构缺乏冲击荷载作用下结构动力响应和失效机理的研究现状,该文基于ANSYS/LS-DYNA分析软件,提出了Geiger型索穹顶结构冲击动力分析模型,详细分析了冲击作用下结构的节点位移和杆件内力响应,并进一步结合美国规范UFC4-023-03的倒塌准则,对结构的失效模式进行评价,提出了三种失效模式,即结构轻微损伤、结构局部损伤和结构整体失效。随后,基于冲击破坏杆件数和杆件内力损伤程度,提出了结构整体损伤指数的概念,通过参数分析,探索了索穹顶结构在不同冲击物参数下整体损伤指数的变化特点及不同设计参数下的抗冲击性能。研究发现了整体损伤指数与三种失效模式之间的关系:当失效模式为结构轻微损伤时,其整体损伤指数小于0.3;当失效模式为结构局部损伤时,其整体损伤指数位于0.3~0.8之间;当失效模式为结构整体失效时,其整体损伤指数大于0.8。基于此提出了失效模式控制方程。冲击荷载越靠近结构中心,结构发生整体失效概率越大,反之则局部损伤和轻微损伤概率越大。提高初始预应力水平和杆件截面面积能有效提高结构的抗冲击性能。

冲击荷载作用下Levy型索穹顶结构动力响应分析

建立Levy型索穹顶结构有限元分析模型,给出有限元结果合理性的判定准则,提出冲击失效准则。进行大量冲击工况下的动力响应全过程分析,给出杆件破坏分布规律和失效模式,揭示结构在竖向冲击荷载作用下的失效机理。依据冲击失效机理及参数分析,提出抗冲击措施。研究结果表明:所有冲击工况均符合冲击判定准则,在所选竖向冲击荷载范围内,Levy型索穹顶结构的失效模式可分为4种,即结构轻度损伤、结构局部1级失效、结构局部2级失效和结构整体破坏。随着冲击动能的增加,结构的动力响应模式逐渐呈模式1→模式2→模式3→模式4的发展趋势。通过分析可知,结构的动力响应模式由结构的能量吸收值及构件两端速度差决定。

天津中医药大学体育馆不连续支承弦支穹顶结构抗火分析

以天津中医药大学体育馆为背景,对大跨度不连续支承弦支穹顶结构进行抗火性能分析。利用高大空间火灾升温公式对结构进行火灾温度场模拟。采用ANSYS软件对不连续支承弦支穹顶结构进行火灾响应分析,得到火灾下该结构变形规律、节点位移及构件预应力损失规律;改变火源位置和火源释热功率,探究火源参数变化对结构抗火性能的影响。结果表明:中心火源工况下,不连续支承弦支穹顶结构变形呈“部分微上凸,局部桁架处下陷明显”;该结构对偏心火灾敏感,偏心火灾下结构最大正、负向位移及环索预应力损失较中心火灾显著增大,且第1、2圈部分环索预应力降为0;局部桁架处压杆及第1、2圈环索为抗火设计重点。火源释热功率越大对不连续支承弦支穹顶结构抗火越不利,但火源释热功率改变对结构火灾响应的影响较小。

斜入射地震波下单层球面网壳土-结构相互作用及其地震响应分析

为分析斜入射地震波下单层球面网壳土-结构相互作用及其地震响应,采用等效节点力实现地震波输入,通过黏弹性人工边界处理无穷远辐射条件,分析了地震波类型、土体参数、入射角度等因素对单层球面网壳结构的土-结构相互作用及其地震响应影响。结果表明:单层球面网壳结构在地震波入射一侧出现翘起,网壳总体沿入射方向发生旋转,当P波斜入射时支座位移差最大达0.514 m,为网壳跨度的1/250。当P波斜入射时,软弱土情况下网壳顶点位移比中硬土和中软土大,顶点位移随入射角增大呈现先增大后减小的趋势;当SV波入射时,中软土情况下网壳顶点位移比中硬土和软弱土大,顶点位移随入射角增大而增大。斜入射地震波下,考虑土-结构相互作用后网壳顶点位移增幅最大达5.5倍,网壳外圈位移增幅大于网壳跨中增幅。

超深基坑吊脚桩局部稳定性分析

目前基坑设计中对于吊脚桩预留岩肩的宽度和支护桩的嵌固深度取值大多从对上部支护结构内力及变形的影响角度出发,往往忽略了支护结构底部附近的局部稳定性问题。依托珠江三角洲水资源配置工程超深竖井项目,提出了外倾结构面下或破碎岩体吊脚桩基坑可能存在的3种破坏模式,采用极限平衡法分别给出了不同破坏模式下稳定安全系数的计算方法。同时针对不同破坏模式下,影响稳定安全系数的参数如岩层的埋深、结构面的倾角和力学参数、岩肩宽度、岩肩深度等进行了分析,结果表明外倾结构面倾角、结构面或岩体的力学参数对稳定安全系数影响较大。研究成果可为类似工程提供参考。

我国建筑索结构的发展与工程实践

索结构已经成为现代大跨度建筑结构的首选体系之一。梳理了七十年以来我国索结构的发展历程,将其分为起步、缓慢发展和快速发展三个阶段,并对每个阶段进行了详细分类和阐述。对建筑索结构中的拉索构件和节点构件进行了归纳和总结,系统地列举了各类构件的主要形式。此外,综述了悬索结构、索膜结构、张弦(弦支)结构及索穹顶结构等典型结构形式的特点、受力机理及代表性工程,进一步展示了索结构在实际工程中的广泛应用和显著优势。这些结构形式不仅体现了索结构的创新性和灵活性,也证明了其在满足大跨度建筑需求方面的卓越性能。在可持续绿色发展的要求下,随着科技的不断进步,索结构在建筑领域的应用前景愈发广阔。我国的索结构将继续在大跨度建筑领域中扮演重要角色,为实现更加高效、环保和创新的建筑设计提供有力支持。

海上无人平台悬挂式巡检机器人行走机构设计与性能分析

针对海上无人值守平台智能化巡检的现实需求,设计一种悬挂式机器人行走机构,并对行走机构的驱动轮机构、承重轮机构、压紧轮机构、导向轮机构、防抖轮机构进行整体设计和性能分析。结合机器人本体及检测、算法系统,所设计的行走机构可用于海上无人平台日常巡检。

基于短周期密集台阵接收函数揭示的藏南错那洞穹窿地壳结构

位于印度-欧亚板块碰撞前缘的北喜马拉雅构造带,是研究陆陆碰撞过程中地壳增厚和深部岩浆活动的典型区域之一。北喜马拉雅穹窿带作为其中重要的伸展构造,其形成过程与造山运动引起的地壳增厚以及地壳深熔作用引起的地壳流动密切相关。本文以近年新发现的错那洞穹窿为例,利用短周期密集台阵观测,通过远震P波接收函数共转换叠加成像方法获取了错那洞穹窿区域地壳结构。结果表明:错那洞穹窿区域的地壳结构在东西方向上存在差异,壳内速度间断面存在多处不连续现象,局部区域甚至发生界面错断;而在错那裂谷和错那洞穹窿中、上地壳内存在低速区。综合前人研究,本文认为印度-欧亚板块持续碰撞使喜马拉雅东南缘岩石圈经历过地壳尺度拉伸变形。在地壳增厚及持续的高温变质作用下,中、上地壳随藏南拆离系伸展减压发生部分熔融,而熔融岩浆沿着藏南拆离系薄弱处不断上涌并在错那洞穹窿下方聚集,并使错那洞穹窿及错那裂谷中、上地壳弱化,促进区域东西向伸展,进而发生岩浆底辟形成错那洞穹窿。

光谷空轨高新大道站钢结构顶棚设计与分析

为了实现光谷空轨高新大道站钢结构顶棚外侧悬挑和中央抬高天窗的建筑造型,提出了叠级自平衡结构体系,即第一级弦支穹顶自平衡结构形式和第二级双侧悬挑梁柱框架自平衡结构形式,实现了建筑和结构功能形态的统一融合,解决了细柱受压问题并消除对基础的影响。采用SAP2000对结构进行了静力和非线性稳定分析,补充了ABAQUS梁柱节点应力分析,按上部结构受力特点采用了内侧桩基外围独基结合的基础形式。结果表明,上部结构和基础设计合理,整体稳定性较好,梁柱节点受力良好。