Joints for releasing degrees of freedom between surfaces
Contents
1. of the surface features you are joining Page 2 You may assign the mesh by selecting one line with your mouse and adding it to the selection memory this will be the slave of the joints Then select the second line with your mouse and assign the joint mesh attribute by dragging and dropping it from the TreeView onto the model working pane this second line will be the master This is as described in the help menu item Help Topics gt Contents gt Modeller User Manual gt Building a Model gt Attributes gt Meshing and Element Selection gt Joint Interface Element Meshes When you assign the mesh attribute you are able to specify a local coordinate dataset if one is defined recommended You may check element axes using TreeView gt Layers tab gt Mesh gt check Show element axes oe ff ta ae A Dan f ee PPP A a p F Pia Pi anes ae ee z BS Ea Y 218 ioe ee a ye a a ale y Oa a PA B PA oo aw SS s Ns 7 a a ss ae ae ee 2 3 Geometric attributes As stated in the Element Reference Manual Geometric properties are not required for the 3 degree of freedom 3 dof JNT4 elements but are required for the 6 degree of freedom 6 dof JSH4 elements For JSH4 elements you should use Attributes gt Geometric gt Joint to define a geometric eccentricity which can of course just be zero 2 4 Material attributes Your surfaces should have an appropriate material attribute assigned2. CSN LUSAS 1017 CUSTOMER SUPPORT NOTE Joints for releasing degrees of freedom between surfaces Note Number CSN LUSAS 1017 This support note is issued as a guideline only Page 1 1 Introduction Interface joint elements can be used to connect surface elements e g shells without full fixity This mesh is assigned to the two line features on the edge of the two separate surfaces one line is designated master and one slave The gap between these surfaces could be zero The approach outlined below will enable the generation of for example moment release between surfaces meshed with shell elements 2 Description 2 1 Geometry Surface and Line Features You must have a model which includes two surface features arranged such that you can assign the joints between two parallel line features You may need to temporarily create a gap between the two lines e g copy a surface feature at an appropriate offset and delete the original surface The points and lines at the interface must be made unmergable so that they are not automatically merged by LUSAS Modeller if they share the same coordinate positions You can do this by selecting the features and using the menu items Geometry gt Point gt Make unmergable Geometry gt Line gt Make unmergable Joint elements have no length in a stiffness matrix and so any length given in the model will introduce an inaccuracy in the length of any substructure features and will
3. e g concrete steel etc The joint material attribute used in your model controls how the joint will behave when subjected to loading or displacements etc Materials appropriate to common uses of joints are described below full information on all available joint materials is given in the help menu Help topics gt Theory manual gt Chapter 4 Constitutive models gt 4 10 Joint Models For a simple hinge JNT4 joint you may use Attributes gt Material gt Joint gt drop down lists Joint type Spring stiffnesses Freedoms 3 The number of Freedoms specified in the material should match the DOF in joint mesh attribute selected You must enter a stiffness value for each DOF For JNT4 Freedom 3 should be used the DOF are in order local x y z For JSH4 Freedom 6 is appropriate the DOF are in order local x y z THx THy THz Page 3 The image below demonstrates the use of joint elements to create a hinge connection between two shell surfaces i Fan s ia i j i e i ee lt i J o jase a gy a if z pa mn Ri i ae Z ae fpr to M a aaa B eo ga Ri a gi For more information on the calculation of spring stiffnesses please see the following page on the password protected LUSAS User Area http www lusas com protected instruct joint_spring stiffness html The Username and Password for accessing the User Area are lusas and powerfulfe respectively Page 4
4. trigger a warning in the LUSAS Solver text output file OUT However moving the features at each end of joint elements to be coincident can make it difficult to be sure of the orientation of the joints element axes local x y z Therefore it is prudent always to use a local coordinate dataset to control the axes 2 2 Mesh attributes Your surfaces should be meshed in an appropriate manner usually using shell or plate elements The appropriate mesh to connect to all 6 degrees of freedom for thin shells QSI4 thick shells QTS4 QTS8 and 3D beam elements is joint for beams 3D JSH4 When no rotational stiffness is required however it may be more appropriate to use joint no rotational stiffness JNT4 This is simpler than using JSH4 as the rotational stiffnesses do not need to be calculated It is prudent always to use a local coordinate dataset to control the element axes for joints This should be defined before the joint mesh attribute is assigned More information on local coordinates may be found in the help menu item Help Topics gt Modeller user manual gt Building a model gt Attributes gt Local coordinate systems A JNT4 mesh for no rotational stiffness at all may be defined using the menu item Attributes gt Mesh gt Line gt drop down menus Generic element type Joint no rotational stiffness Number of dimensions 3d The mesh definition should include the number of divisions you want on the relevant side
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