ETFE气枕平面充气成形过程的非线性结构性能分析

对基于平面裁切的乙烯-四氟乙烯（ethylene-tetrafluoroethylene,ETFE）气枕进行充气成形试验,利用激光位移计测量气枕矢高,基于三维摄影测量得到的形状,分析了气枕膜面应力分布。采用Peirce模型模拟ETFE膜材的材料力学非线性并进行相同充气过程的数值模拟,对比分析数值模拟与实测的气枕矢高和应力分布。结果表明：Peirce模型仅在反映ETFE两个屈服点之间的应力-应变关系上有所偏差;气枕充气完成后矢高约为172mm,气枕膜面应力最大值集中于气枕中心与各边中点的连线区域;不同内压下的气枕矢高,膜面应力、应变的数值模拟结果与实测结果相对误差均在10%以内。此外,Peirce 模型数值模拟结果表明,内压为2kPa时气枕膜面出现塑性应变;膜面总应变与塑性应变最大值集中于气枕中心与各边中点连线区域。     

ETFE foil spring cushion structure and its analytical method

The traditional Ethylene Tetra Fluoro Ethylene (ETFE) foil cushion is in the form of air cushion, whose structural stiffness is offered by the inner air pressure. Because the air supply and control systems are needed, air cushion structures cost extra energy and need much maintenance. In order to overcome the shortcomings of air cushion, the ETFE foil spring cushion that uses a spring to take the place of air pressure is developed in this paper. At first, the analytical method for shape finding analysis and stress analysis of the spring cushion is described in the paper. A numerical example is shown by means of the software package ANSYS and the suggested method so as to verify the validity of the method. Then, a model experiment on the ETFE foil spring cushion is carried out. In the loading test, the compression of spring is recorded and the experimental results are compared with the analytical results. At the end of the paper, an experimental hall using both ETFE foil air cushion units and spring cushion units as its roof structure is introduced. Through the construction and daily use of the experimental hall, the spring cushion system shows advantages such as easier construction, needing no air supply and control equipments, no running energy and little maintenance compared with the air cushion system.     

An automatic system for pressure control and load simulation of inflatable membrane structure

Inflatable membrane structure employs flexible membranes as main constructive materials, as well as pressurized gas in the membrane envelope aiming to provide the bearing capacity and structural integrity. Therefore, the internal pressure control and load simulation method are very significant to estimate the structural behavior of inflatable membrane structure. This paper presents an automatic system for pressure control and load simulation of inflatable membrane structure, including a pressure control subsystem and a load simulation subsystem. For pressure control, internal pressure of inflatable membrane structure is controlled by switching the high-speed on/off valves which connect air compressor to the structure. For load simulation, wind pressure and wind suck loads, acting on membrane surface in the normal direction, are simulated by controlling the solenoid valves to allow the vacuum pumps to inflate air into or pump air out from the load simulation chamber which is closely connected to inflatable membrane structure with an airtight space. More importantly, the coupling control of two subsystems can be automatically carried out to simulate the inflatable membrane structure under resisting the varied wind loads. These above actions are automatically performed based on the control logic coded in software module. In order to estimate the proposed automatic system, the internal pressure control, load simulation and coupling control tests were performed on a square double-layer ETFE (ethylene tetrafluoroethylene) cushion model. Control performance and accuracy of the proposed system are proved by analyzing the measured pressures. It is thus demonstrated that the proposed automatic system is considerably automatic, accurate, efficient and reliable for pressure control and load simulation of inflatable membrane structures.     

双弹簧支撑ETFE枕式膜结构性能研究

利用压缩弹簧代替充气形成无需充气设备的ETFE薄膜结构,采用数值分析与模型试验方法对双弹簧支撑ETFE枕式膜结构的可行性及结构性能进行研究。数值分析结果表明：膜面形状由膜面初始应力和弹簧弹力之比决定;弹簧刚度对膜面应力影响较小,增大弹簧刚度可减小膜面位移但使荷载作用下弹簧弹力的变化增大;膜面矢跨比对膜面应力影响不大,但减小矢跨比使膜面变形增大。模型试验结果表明：膜面成形可通过调整弹簧弹力完成,方法简便可靠,膜面成形精度较高;加载试验中弹簧支撑系统工作可靠,可以较好地追随并张紧膜面;支撑点处膜面应力集中不明显,试验结果与数值分析结果吻合较好。     

ETFE气枕模型试验与有限元分析

通过2 m×2 m的ETFE气枕模型试验,进行了气枕形状测试、充气加压测试和气压一定的加载测试。通过在上下膜面画上一组刻线,测量膜面在充气过程中刻线长度的变化,进而求得膜面应力的变化。基于膜面应力和气枕矢高的试验测试值与几何非线性有限元分析结果比较,验证了ETFE气枕有限元模拟方法的正确性。研究表明：由于ETFE气枕充气过程中膜材伸展率较大,膜面粘贴应变传感器很难捕捉准确的膜面应力,采用膜面画刻线的方法可以用于测试ETFE充气结构的膜面应力;立体裁剪的ETFE气枕,充气成形过程中,膜面基本展开时零应力状态下,膜面角部区域已张紧,具有初始应力,因此,角部区域膜面应力测试时需给予初应力补偿;ETFE膜材热熔焊缝相当于膜材局部加强,顺焊缝及垂直焊缝的实测应力小于按均匀材料计算的应力,但对整体充气膜面应力的影响很小;膜面应力和气枕矢高的试验测试值与有限元分析值基本吻合。     

ETFE气枕力学性能分析及其蒙皮效应研究

利用ANSYS软件对ETFE气枕结构进行找形分析,考虑预应力和内压两个控制因素,给出了三角形、四边形和六边形气枕的找形结果,并推导了四边形和圆形气枕找形的解析式。编制了计算气枕体积的MATLAB程序,并与ANSYS软件联合应用,计算了矩形气枕结构在7种荷载工况下的变形和膜面的应力分布。通过参数分析,得到了膜面应力和矢高、膜厚、矢跨比之间的关系,提出了气枕合理的膜厚、矢跨比,并给出了不同跨度气枕充压建议值,最后对ETFE气枕结构的蒙皮效应进行了研究。研究结果表明：膜面初始预应力宜介于5~8MPa;ETFE膜厚可根据气枕跨度选择单层0.2 mm或双层0.4 mm,矢跨比0.1左右,成形后膜面最大、最小应力分别位于中心区、角点区;ETFE气枕充压的初始内压介于250~1 150 MPa,充压值随跨度增大而减小;初始内压500 Pa常用尺寸（4 m×5 m矩形）的气枕,可抵抗大小与内压相当的正负风压、均布和半跨雪荷载和偶然集中荷载,但在超载工况下,需对气枕充气加压方可继续工作;ETFE气枕具有明显的蒙皮效应。     

ETFE气囊膜形态、结构特性与材料性能试验

进行了聚偏四氟乙烯(ETFE)薄膜单向拉伸和反复荷载试验,分析了应力-应变曲线、滞回环曲线特征;根据受约束条件的力密度法找形分析方法,建立了充气膜设计分析理论,并介绍了EasyVol充气膜分析方法;通过数值算例分析,研究了ETFE气囊膜基本形态(菱形、六边形、矩形、圆形)、矢高、气压、初应力等对找形分析的影响及相互作用;进行了气囊膜在风压、风升作用下的荷载特性分析以及结构特性参数分析。该研究对ETFE气囊膜设计具有重要参考价值。     

ETFE薄膜结构积水试验与数值分析

膜结构是一种柔性结构,膜面容易发生雨水积留。针对ETFE(四氟乙烯)薄膜结构,利用ANSYS软件通过迭代计算分析了正方形平面膜面和正方形气枕膜面的积水极限承载力,考察不同跨度及矢跨比时的积水进展情况。计算结果显示,厚度为250μm的单层正方形平面膜面,跨度3m时就会发生积水破坏。对于气枕膜面,是否发生积水破坏由跨度与矢跨比决定。由两层厚度为250μm的ETFE薄膜叠合的正方形边界气枕膜面,当跨度达到5m时将发生积水破坏,跨度为4m、矢跨比达到1/8及以上时也将发生积水破坏。设计制作了3种矢跨比的ETFE薄膜气枕膜面,进行了积水承载试验,将试验结果与数值分析结果进行了对比。     

框式ETFE膜结构幕墙的性能分析

ETFE材料重量轻、透光率高、自洁性好、具有阻燃性,是一种可用于建筑围护系统中的新型建筑薄膜材料。根据支撑结构的不同,ETFE幕墙可分为框式薄膜幕墙和点支式薄膜幕墙。运用ANSYS软件对5个框式幕墙模型进行找形和荷载分析,结果表明:幕墙受荷膜面最大应力与荷载值基本呈线性变化关系;跨度为2m的ETFE幕墙的可用高度可以达到100m。     

ETFE薄膜气枕模型试验研究

设计制作了2个不同矢跨比的ETFE薄膜气枕模型,进行了气枕形状测试、加压以及铺砂加压试验,得到了气枕形状坐标以及膜面随气压的变形量。对ETFE薄膜进行单向拉伸试验,测得材料的屈服强度、切线弹性模量和割线弹性模量。利用几何非线性有限元进行了数值分析,将数值结果与试验值进行了比较分析。结果表明:ETFE薄膜可按各向同性材料分析,数值计算结果与试验值吻合较好;在同样内压作用下,气枕矢高较高时膜面位移与膜面应力较小;ETFE薄膜采用割线弹性模量计算得到的膜面位移与试验值比较吻合,采用切线弹性模量计算得到的变形小于试验值。     

ETFE膜结构屋面刍议

建筑外围护的膜结构有骨架式、张拉索膜式以及充气式三种,所用ETFE膜材化学稳定性好,不需其他面层保护,透光性强。国家体育场“鸟巢”的膜材外围护结构,创造性地将钢索复合在膜材背面,既抗风揭,又保持其自然外观。这一使建筑造型多样化的全新的建筑技术表现形式,将获得广泛应用。     

“水立方”围护结构声学性能研究

国家游泳中心“水立方”采用大面积ETFE膜气枕作为围护结构，ETFE膜气枕的声学性能将直接影响比赛大厅的室内声学设计效果与室内装饰效果。在比赛大厅声学设计过程中，建立了声学测试专项实验室，对ETFE膜气枕的声学性能进行测试，获得了真实详尽的数据。本文对声学实验室的建立、声学性能的测试过程做了较为详细的介绍，对测试结果进行了分析与总结，希望对类似材料构造的声学性能测试提供一些参考资料。     

ETFE薄膜的材料性能及其工程应用综述

就ETFE薄膜的材料性能、在膜结构工程中的应用形式、ETFE气垫的工作原理、膜材连接方法、典型工程等进行综述     

天津华侨城水公园大馆大跨度网壳结构研究与设计

天津华侨城生态欢乐岛水公园大馆网壳结构长向跨度195.5米,短向跨度115米,高32.5米,是由一个直径140米,两个直径80米的空间曲线旋转相交形成的空间"球面"双层网壳,网壳上弦为六边形网格,下弦为三角形和六边形网格,类似蜂窝型三角锥网格,屋面材料为ETFE气枕,该结构形式在国内尚属首次采用。为实现建筑创意,提出了基于六边形蜂窝异型曲面网壳结构三维模型的构建方法,采用3D3S、SAP2000和ANSYS等多种软件,对网壳结构进行了静力计算和线性、几何非线性稳定分析,解决了大跨度异型曲面网壳结构建模、计算与分析、设计难题,为中国的"伊甸园"工程信息化加工、制作、施工、管理提供了基础模型。     

ETFE膜结构主要形式及ETFE工程难点

ETFE膜结构具有不同的结构形式,包括单层ETFE、单层ETFE加单向钢索、单层ETFE加双向钢索、单层ETFE加含跨中支座的单向钢索以及ETFE气枕等。结构选型时,应结合边界尺寸、荷载条件、膜材厚度、变形控制等要求综合决定。ETFE做为一种新型的建筑材料,尚未被建筑师普遍熟悉,易造成某些方案不符合ETFE的加工和安装条件。ETFE对钢结构的制作精度以及ETFE自身的安装工艺要求都很高。节点防水处理以及温度的影响是ETFE膜结构需要重视的问题。     

Deflections of inflatable fabric panels at high pressure

Inflatable structures made of modern textile materials with important mechanical characteristics can be inflated at high pressure (up to a several hundreds of kPa). They can be used as strong building elements thanks to their mechanical strength. The aim of the paper is to present experimental and analytical studies on the behaviour of inflated fabric panels at high pressure and submitted to bending loads. It is shown that inflatable structures cannot be viewed as ordinary plates or beams, because their deformation pattern is quite different. Experiments show that their behaviour depends on the applied load, the inflation pressure, and the constitutive law of the fabrics. Equilibrium equations are written in the deformed state to take into account the influence of geometrical stiffness and the following forces. A Timoshenko’s beam theory must be used because sections of the panels do not satisfy the usual Bernoulli’s beam theory. A new inflatable beam theory is developed. Wrinkling loads are derived from equilibrium equations. Deflections satisfy the fact that the compliance of the inflatable panel is the sum of the beam compliance and of the yarn compliance. Comparisons between the results of our modelling and experimental results are shown and prove the accuracy of this theory on the mechanical strength of inflatable structures at high pressure.     

Deflections of highly inflated fabric tubes

Inflatable beams made of modern textile materials with important mechanical characteristics can be inflated at high pressure. The aim of the paper is to present experimental, analytical and numerical results on the deflections of highly inflated fabric tubes submitted to bending loads. Experiments are displayed and we show that tube behaviour looks like that of inflatable panels (Thin-Walled Struct. 40 (2002) 523–536). Equilibrium equations are once again written in the deformed state to take into account the geometrical stiffness and the following forces. The influence of the shear stress cannot be neglected and Timoshenko’s beam theory is used. A new inflatable tube theory is established and simple analytical formulas are given for a cantilever-inflated tube. Comparisons between analytical and experimental results are shown. A new inflatable finite tube element is constructed by use of algebraic operations, because the compliance matrix of the cantilever beam is not symmetric. Comparisons between experimental, analytical and numerical results prove the accuracy of this beam theory and on this new finite element for solving problems on the deflections of highly inflated tubes.     

Free vibration analysis of inflatable beam made of orthotropic woven fabric

The free vibration of inflatable beams was studied using the dynamic stiffness method. A 3D Timoshenko beam with a homogeneous orthotropic woven fabric (OWF) was considered. Using the usual total Lagrangian form of the virtual work principle, the model took the geometric nonlinearities and the inflation pressure follower force effect into account. The nonlinear equilibrium equations were then linearized around the prestressed reference configuration. The exact dynamic stiffness matrix was developed by directly solving the governing differential equations of a 3D loaded inflatable beam in a free vibration. The effects of the inflation pressure, fabric mechanical properties and the boundary conditions on the natural frequencies and mode shapes of the inflatable beams were demonstrated. The proposed model was validated favorably through its comparison with a 3D thin shell finite element model and an isotropic fabric model found in the literature.     

高性能ETFE膜气枕成套技术在国家游泳中心的应用

介绍了国家游泳中心ETFE充气膜结构系统的设计,高性能膜气枕的加工制作和安装施工,系统的电子监控和工程技术、施工质量的验收标准;指出这一成套技术已达国际先进水平,它的成功实践带动了该系统在我国的应用和发展.     

ETFE薄膜材料

ETFE薄膜材料是一种新型的建筑膜材,具有透光率高、耐久性好、自洁性能优异等特点,在植物园、游泳馆、体育场等大跨度建筑中得到越来越多的应用。本文对ETFE薄膜材料性能作了简单的介绍,对材料特点作了描述,为ETFE薄膜建筑提供材料方面的基本信息。