beam188单元.docx

1、beam188单元BEAM188 3-D 2-Node Beam MP ME ST PR PRN DS DSS PP VT EME MFS Product Restrictions BEAM188 Element Description BEAM188 is suitable for analyzing slender to moderately stubby/thick beam structures. The element is based on Timoshenko beam theory which includes shear-deformation effects. The el

2、ement provides options for unrestrained warping and restrained warping of cross-sections. Beam188 单元适合于分析从细长到中等粗短的梁结构，该单元基于铁木辛哥梁结构理论，并考虑了剪切变形的影响。-The element is a linear, quadratic, or cubic two-node beam element in 3-D. BEAM188 has six or seven degrees of freedom at each node. These include transla

3、tions in the x, y, and z directions and rotations about the x, y, and z directions. A seventh degree of freedom (warping magnitude) is optional. This element is well-suited for linear, large rotation, and/or large strain nonlinear applications. Beam188 是三维线性（2 节点）或者二次梁单元。每个节点有六个或者七个自由度，自由度的个数取决于KEYO

4、PT(1)的值。当KEYOPT(1)0（缺省）时，每个节点有六个自由度；节点坐标系的x、y、z 方向的平动和绕x、y、z 轴的转动。当KEYOPT(1)=1 时，每个节点有七个自由度，这时引入了第七个自由度（横截面的翘曲）。这个单元非常适合线性、大角度转动和/并非线性大应变问题。-The element includes stress stiffness terms, by default, in any analysis with large deflection. The provided stress-stiffness terms enable the elements to anal

5、yze flexural, lateral, and torsional stability problems (using eigenvalue buckling, or collapse studies with arc length methods or nonlinear stabilization). Elasticity, plasticity, creep and other nonlinear material models are supported. A cross-section associated with this element type can be a bui

6、lt-up section referencing more than one material. Figure188.1:BEAM188 Geometry BEAM188 Element Technology and Usage Recommendations BEAM188 is based on Timoshenko beam theory, which is a first-order shear-deformation theory: transverse-shear strain is constant through the cross-section (that is, cro

7、ss-sections remain plane and undistorted after deformation). The element can be used for slender or stout beams. Due to the limitations of first-order shear-deformation theory, slender to moderately thick beams can be analyzed. Use the slenderness ratio of a beam structure (GAL2 / (EI) ) to judge th

8、e applicability of the element, where: G Shear modulus A Area of the cross-section L Length of the member (not the element length) EI Flexural rigidity Calculate the ratio using some global distance measures, rather than basing it upon individual element dimensions. The following illustration shows

9、an estimate of transverse-shear deformation in a cantilever beam subjected to a tip load. Although the results cannot be extrapolated to any other application, the example serves well as a general guideline. A slenderness ratio greater than 30 is recommended. Figure188.2:Transverse-Shear Deformation

10、 Estimation Slenderness Ratio (GAL2/(EI) Timoshenko / Euler-Bernoulli 25 1.120 50 1.060 100 1.030 1000 1.003 The element supports an elastic relationship between transverse-shear forces and transverse-shear strains. You can override default values of transverse-shear stiffnesses via the SECCONTROLS

11、command. BEAM188 does not use higher-order theories to account for variation in distribution of shear stresses. Use ANSYS solid elements if such effects must be considered. BEAM188 supports “restrained warping” analysis by making available a seventh degree of freedom at each beam node. By default, B

12、EAM188 elements assume that the warping of a cross-section is small enough that it can be neglected (KEYOPT(1) = 0). You can activate the warping degree of freedom by using KEYOPT(1) = 1. With the warping degree of freedom activated, each node has seven degrees of freedom: UX, UY, UZ, ROTX, ROTY, RO

13、TZ, and WARP. With KEYOPT(1) = 1, bimoment and bicurvature are output. When KEYOPT(3) = 0 (linear, default), BEAM188 is based on linear shape functions. It uses one point of integration along the length; therefore, all element solution quantities are constant along the length. For example, when SMIS

14、C quantities are requested at nodes I and J, the centroidal values are reported for both end nodes. This option is recommended if the element is used as stiffener and it is necessary to maintain compatibility with a first-order shell element (such as SHELL181). Only constant bending moments can be r

15、epresented exactly with this option. Mesh refinement is generally required in typical applications. When KEYOPT(3) = 2 (quadratic), BEAM188 has an internal node in the interpolation scheme, effectively making this a beam element based on quadratic shape functions. Two points of integration are used, resulting in linear variation of element solution quantities along the length. Linearly varying bending moments are represented exactly. When KEYOPT(3) = 3 (cubic), BEAM188 has two internal nodes and adopts cubic shape functions. Quadratically varying