局部火灾下凯威特—联方型弦支穹顶结构破坏模式分析

发布时间：2018-04-17 20:44

本文选题：局部火灾 + 弦支穹顶结构　；参考：《南京工业大学》2015年硕士论文

【摘要】：弦支穹顶结构是将单层网壳结构和索撑体系相结合形成的一种大跨度预应力空间钢结构,具有受力合理、充分发挥刚柔两种材料优势的特点,在实际工程中得到越来越多的应用。目前国内外对于弦支穹顶结构的研究主要是常温下结构的设计和施工方法,针对高温下结构力学性能的研究并不全面,而弦支穹顶结构中高强度预应力拉索的引入使得结构对于火灾的危害更为敏感,因此亟待对其抗火性能开展深入研究。本文以工程中常用的凯威特—联方型弦支穹顶结构为研究对象,主要进行了以下研究工作：(1)采用基于非线性有限元理论开发的ANSYS数值模拟软件,参照实际工程中常用的几何尺寸,采用初始应变法张拉径索对下部索撑体系施加预应力,建立凯威特-联方型弦支穹顶结构数值分析模型,对比已有工程实例确定所建立的结构数值分析模型的可靠性,明确矢跨比、预应力水平和外荷载对弦支穹顶结构力学特征的影响规律。(2)采用ANSYS数值模拟软件,考虑结构的几何非线性和材料非线性,以CECS200：2006中规定的压弯构件或拉弯构件高温承载力作为网壳杆件受火承载极限状态,以轴心压杆高温承载力作为撑杆受火承载极限状态,以高温抗拉强度极限作为钢拉索受火承载极限状态,按温度增量法,模拟高温下弦支穹顶结构的受火反应,分析均匀升温与非均匀升温时结构的力学响应及其破坏模式。(3)制定弦支穹顶结构局部火灾下受火反应分析的参数方案,以温度场非均匀性、荷载比、火源特性、矢跨比和预应力水平作为关键参数对弦支穹顶结构的受火反应进行数值分析,深入了解关键参数对凯威特—联方型弦支穹项结构在局部火灾下变形特征、应力历程和临界温度的影响规律,定性得出弦支穹顶高温下的破坏模式,为进一步研究弦支穹顶结构的受火工作机理提供参考。研究表明,火灾历程中,弦支穹顶结构的变形规律为整体先向上起拱然后向下塌落。火源半径对弦支穹顶结构的临界温度影响较小,温度场的非均匀性、荷载比、火源位置、矢跨比、预应力对结构临界温度影响较大。局部火灾中温度场的非均性越大,结构的临界温度越高;弦支穹顶结构的荷载比越大,临界温度越低；火源距结构跨中位置越近,临界温度越高；随着弦支穹顶结构矢跨比的增大,临界温度增大；随着弦支穹顶结构常温下预应力的增大,临界温度越高。局部火灾下弦支穹顶结构的破坏模式主要有两种：外圈环索的受火极限承载力明显下降而成批发生受拉破坏或最外圈环杆的应力增长较大而产生较多环杆单元的破坏,最终导致整体结构失效。
[Abstract]:The chord dome structure is a kind of large span prestressed space steel structure which is formed by combining the single-layer reticulated shell structure with the cable bracing system. It has the characteristics of reasonable force and full play of the advantages of rigid and flexible materials.It has been applied more and more in practical engineering.At present, the research of the dome structure at home and abroad is mainly about the design and construction method of the structure at room temperature, but the research on the mechanical properties of the structure under high temperature is not comprehensive.The introduction of high-strength prestressed cables in the domes makes the structure more sensitive to fire hazards, so it is urgent to conduct a deep study on its anti-fire performance.In this paper, the Kewitt-Coupling Dome structure, which is commonly used in engineering, is taken as the research object. The following research work is carried out: 1) the ANSYS numerical simulation software is developed based on nonlinear finite element theory.Referring to the geometric dimensions commonly used in practical engineering, the initial strain method is used to apply prestress to the lower cable-braced system, and a numerical analysis model of Cavette-United square domes is established.The reliability of the established numerical analysis model is determined by comparing the existing engineering examples, and the influence of the rise-span ratio, the level of prestress and the external load on the mechanical characteristics of the dome structure is determined. (2) the numerical simulation software ANSYS is used to simulate the reliability of the established numerical analysis model.Considering the geometric nonlinearity and material nonlinearity of the structure, the high temperature bearing capacity of the bending member or the tension bending member specified in CECS200:2006 is taken as the ultimate state of the fire bearing capacity of the latticed shell member, and the high temperature bearing capacity of the axial compression rod is taken as the ultimate state of the fire bearing capacity of the bracing member.Taking the high temperature tensile strength limit as the ultimate state of the steel cable fire bearing capacity, according to the temperature increment method, the fire response of the chord dome structure under high temperature is simulated.The mechanical response of the structure under uniform and non-uniform heating and its failure mode are analyzed. The parameter scheme of local fire response analysis of the domes under local fire is formulated. The temperature field inhomogeneity, load ratio and fire source characteristics are used.As the key parameters, the rise-span ratio and the prestress level are used to numerically analyze the fire response of the chordal dome structure, and the deformation characteristics of the key parameters to the Keweitt-Coupling string supporting Dome structure under local fire are deeply understood.The influence of stress history and critical temperature on the failure mode of the suspending dome at high temperature is obtained qualitatively, which provides a reference for further study on the mechanism of the chordal dome structure being subjected to fire.The results show that the deformation law of the domes is that the whole arch starts up first and then collapses down.The influence of the radius of the fire source on the critical temperature of the chord dome is small, and the inhomogeneity of the temperature field, the load ratio, the location of the fire source, the rise-span ratio and the prestress have a great influence on the critical temperature of the structure.The greater the inhomogeneity of temperature field in local fire, the higher the critical temperature of the structure; the higher the load ratio of the domes is, the lower the critical temperature is, the closer the fire source is to the central span of the structure, the higher the critical temperature is.With the increase of the rise-span ratio of the dome, the critical temperature increases, and the critical temperature increases with the increase of prestress at normal temperature.There are two main failure modes of the dome structure under local fire: the ultimate bearing capacity of the outer ring cable decreases obviously, resulting in the wholesale tensile failure or the stress increase of the outer-ring ring rod, which results in more damage of the ring bar element.Finally, the whole structure fails.
【学位授予单位】：南京工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU399

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