节点柔度对导管架海洋平台结构Pushover分析的影响及简化计算模型

发布时间：2018-06-25 03:23

本文选题：导管架海洋平台 + 节点局部柔度　；参考：《烟台大学》2017年硕士论文

【摘要】：空心圆钢管结构由于其受力性能的优越性、施工的简单快捷性以及外观的美观性被广泛的应用在日常的大型空间钢结构建筑以及导管架海洋平台结构中。钢管结构的管件之间一般使用焊接连接进而形成相贯节点,由于节点处弦管的径向刚度远小于支管的轴向刚度,因此当荷载由支管传递到主管时,节点相贯线处的主管壁会发生局部变形,节点出现半刚性的特性,而在实际工程中,钢管桁架结构常被简化为普通梁单元模型,这种方法建模简单,分析速度快,但忽略了节点柔度的影响,因此不能确保分析结果的准确性,对结构的安全设计造成影响。在计算中如果想准确的模拟节点的局部柔度就需要使用实体单元或壳单元建立整个结构的有限元模型,而这种方法对于大型的管桁架结构来说建模过程极为复杂,占用大量电脑内存,且分析效率低。为了解决这个问题,本文提出了在普通梁单元模型中引入虚拟梁单元(FBE,Fictitious Beam Element)的方法,在结构的弹性变形阶段,通过定义虚拟梁单元的轴向刚度和抗弯刚度来实现节点处的局部轴向变形和弯曲变形,虚拟梁单元的轴向刚度和抗弯刚度可使用相关文献给出的节点局部柔度计算公式进行等效。共设计12组不同几何参数的T/Y型节点管桁架模型,并用ABAQUS软件构建各组模型的壳单元模型,同时用Fortran编写刚架程序构建刚架模型和简化模型。通过对比三种不同建模方法的计算结果,验证了简化模型在管桁架结构弹性变形阶段的精确性,并直观地反映了节点局部柔度在钢管结构静力分析中的显著影响。在结构的弹塑性变形阶段,对虚拟梁单元的材料属性进行了等效定义,其方法为:首先用有限元软件对管节点单独建模并计算其荷载-位移曲线,然后将求出的曲线通过公式转换为虚拟梁单元的应力-应变曲线。建立简化模型时,将这种等效的本构关系应用到虚拟梁单元的弹塑性材料属性中,以虚拟梁单元模拟管节点进入塑性阶段后的局部变形。对设计的12组T/Y型节点管桁架进行弹塑性分析,通过对比壳单元模型、简化模型和刚架模型计算出的荷载-位移曲线,验证了简化模型在结构的弹塑性变形阶段受力分析中的精确性。为了研究节点柔度对导管架海洋平台Pushover分析的影响,本文取一导管架海洋平台结构实例进行静力弹塑性分析,借助SAP2000结构设计软件用能力谱的方法求解出结构在8度罕遇地震作用下的目标位移,然后用ABAQUS有限元分析软件对结构分别建立壳单元模型、简化模型和刚架模型,并进行推覆分析得出Pushover曲线,发现刚架模型会过高估计结构的侧向刚度,造成Pushover分析结果有很大偏差,不利于结构的安全抗震评估,而简化模型计算出的Pushover曲线与壳单元模型计算出的曲线有很高的吻合度,可以在实际工程的静力弹塑性分析中推广采用。
[Abstract]:The hollow circular steel pipe structure is widely used in large space steel structure and jacket offshore platform structure because of its superiority of mechanical performance, simplicity of construction and beauty of appearance. Welded joints are usually used to form intersecting joints between pipe fittings of steel pipe. Because the radial stiffness of chord at the joint is much smaller than the axial stiffness of the branch pipe, when the load is transferred from the branch tube to the supervisor, The superstructure of the joint intersecting line will be partially deformed and the joint will be semi-rigid. However, in practical engineering, the steel tube truss structure is often simplified as a common beam element model. This method is simple in modeling and fast in analysis. However, the influence of node flexibility is ignored, so the accuracy of the analysis results can not be ensured, which will affect the safety design of the structure. In order to simulate the local flexibility of nodes accurately, the finite element model of the whole structure needs to be established by using solid element or shell element, and this method is very complicated for large tubular truss structures. Takes up a lot of computer memory, and the analysis efficiency is low. In order to solve this problem, a method of introducing FBE-Based beam element into the ordinary beam element model is proposed in this paper, which is used in the elastic deformation stage of the structure. By defining the axial stiffness and bending stiffness of the virtual beam element, the local axial deformation and bending deformation are realized. The axial stiffness and flexural stiffness of the virtual beam element can be equivalent by using the local flexibility formula given in the relevant literature. Twelve groups of T / Y node tube truss models with different geometric parameters are designed. The shell element models of each model are constructed by Abaqus software. Fortran is used to program the rigid frame model and simplify the model. By comparing the results of three different modeling methods, the accuracy of the simplified model in the elastic deformation stage of the tubular truss structure is verified, and the obvious influence of the local flexibility of the joints on the static analysis of the steel tube structure is reflected intuitively. In the elastic-plastic deformation stage of the structure, the material properties of the virtual beam element are defined equivalent. The method is as follows: firstly, the pipe joints are modeled separately by finite element software and the load-displacement curves are calculated. Then the obtained curve is converted into the stress-strain curve of the virtual beam element through the formula. When the simplified model is established, the equivalent constitutive relation is applied to the elastic-plastic material properties of the virtual beam element, and the virtual beam element is used to simulate the local deformation of the pipe joint after it enters the plastic stage. The elastoplastic analysis of 12 groups of T / Y type tubular truss is carried out. The load-displacement curves calculated by comparing the shell element model with the rigid frame model are simplified. The accuracy of the simplified model in the stress analysis of the elastoplastic deformation stage of the structure is verified. In order to study the effect of node flexibility on pushover analysis of jacket offshore platform, the static elastic-plastic analysis of a jacket offshore platform is carried out in this paper. With the help of SAP2000 structural design software, the target displacement of the structure under the action of 8 degrees rare earthquake is calculated by the method of capability spectrum, and then the shell element model, simplified model and rigid frame model of the structure are established by Abaqus finite element analysis software. The pushover curve is obtained by push-over analysis. It is found that the rigid frame model can overestimate the lateral stiffness of the structure, which results in a great deviation of the pushover analysis results, which is not conducive to the seismic assessment of the safety of the structure. The pushover curve calculated by the simplified model has a high coincidence with the curve calculated by the shell element model, which can be widely used in the static elastoplastic analysis of practical engineering.
【学位授予单位】：烟台大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P75

【参考文献】