Revised Iain A MacLeod

Transcription

1 LUSAS User Guidelines Revised Iain A MacLeod Contents 1 Geometrical features and meshes Toolbars Inserting points Inserting a line between two points Creating a dataset Assigning a dataset to features on the model Reviewing the information about a mesh feature Information needed to achieve a run Axes Local Axes To initiate a run Beam Elements Creating Mesh Features Loadcases Creating a mesh of plate or shell elements Defining a local co-ordinate set Geometrical features and meshes 'Points', 'lines', 'surfaces' and 'volumes' are geometrical features: A point is defined by its co-ordinates A line is defined between two points A surface is defined by a set of lines A volume is defined to be within a set of surfaces A mesh is a set of elements. A set of geometric features is converted to a mesh by adding information such as element type, geometric properties, material properties etc. 2 Toolbars Clicking on the View menu button and selecting toolbars gives a list of options. The most used toolbars are Main, Define and View tools. It is best to keep all these toolbars active. 3 Inserting points Click on Geometry, Point. A dialog box opens up into which co-ordinate values of points are keyed. Use the 'tab' key to move forward in the table. Either a single column with coordinate values separated by commas or a three column x,y,z table can be used - see tick box. 4 Inserting a line between two points Select a point with the cursor. Hold down the 'control' key and select another point. both points are now selected. Click on the 'line' icon on the Define toolbar (mauve line). A line is inserted between the points 1

2 5 Creating a dataset A dataset is a set of information that can be repeated in different parts of the model. For example the cross sectional properties of an element is defined by a dataset. Most of the needed datasets are listed in the Attributes part of the Treeview (defined by three spheres). Each dataset is assigned a name in the dialog box in which values are defined. If the user neglects to do this, the system assigns a name. Selecting features There are icons on the View tools toolbar (click on the view View menu and select Toolbars and View tools ) with arrows sloping up to the left. The left one of these is for selecting features. Clicking on this 'select' icon gives a general select cursor which will select any feature. If it is difficult to select a specific feature right click on the right of the 'select' icon and a pull-down menu appear of buttons which will allow selection of types of feature. For example if you click on the point icon, clicking will only select points. To select more than one feature at a time, hold down the 'control' key and click on all the required features consecutively. There is other select functionality - see the Edit menu. There are also special selection function on the Edit menu - Associate downwards, Selection memory, Advanced selection. See LUSAS Help. 6 Assigning a dataset to features on the model Select the relevant features on the model view, click on the dataset icon in the Attributes part of the Treeview and drag to the model view. The dataset is assigned to the features. A description of this action is shown in the Status bar which is blow the main windows and is opened from the View menu. 7 Reviewing the information about a mesh feature Select the feature and right click the mouse. Clicking on the 'Properties' command at the bottom of the resulting menu opens up a box with information about the feature. 8 Information needed to achieve a run The geometry needs to be defined, i.e. points and lines (and surfaces) Each element needs to have assigned: Element type e.g. thick beam Geometric properties (i.e. cross sectional properties) Material properties The supports need to be defined At least one loadcase needs to be defined. 9 Axes In LUSAS the x axis has a double arrow, the Y axis has a single arrow and the Z axis has no arrow. Directions of the axes are according to the right hand rule and moments are according to the right hand screw rule as below: 2

3 The system coordinates are shown at Point 1. To hide this, right click on the structure window, select Properties then View Axes and untick the Visualise coordinate system tick box 10 Local Axes For lines the local Xaxis is in the direction of node 1 to node 2 where node 1 is the first node used to define the line For plane frames with the Y axis up, the local z axis is in the direction of the global Z axis i.e. towards the observer. The Y axis then is in the direction defined by the right hand rule. If a horizontal beam is numbered from left to right then the local axes will correspond to the global axes For space frames, LUSAS assigns default values to the local directions. These can be shown on the elements going to the Layers Treeview, right clicking on mesh and then selecting Properties. The tick box Show element axes should then be selected. 11 To initiate a run Click on the Solve Now button on the Main toolbar (it has a green = icon on it). The system will prompt you to save the file. It is good practice to save different versions of the model as you go along so that if you mess it up you can go back to the previous stage and not the beginning. This is especially important for bigger runs 12 Beam Elements It is recommended to use the 'thick beam' element. The 'thin beam' element is more complicated. The thick beam needs the following non-standard geometrical properties: Shear areas A y, A z To include shear deformation multiply the cross-sectional area - A x - by the relevant 'shear area factor' - (see Data Tables on website). To neglect shear deformation use values of A y and A z which are large compared with A x - e.g. use A y = A z = A x x 100. End eccentricities. These are offsets used if the beam is to act compositely with a slab. If the beam is to act non-compositely then set the eccentricities to zero. 13 Creating Mesh Features To define a line mesh, for example, click on the Menu button for Attributes and select Mesh and Line. A Line Mesh box opens up with a number of options in it. The Number of divisions box allows the line to be divided into several divisions. The lengths of the divisions can be uniform or varied. When the mesh feature is assigned to a line, the system creates nodes at each of the ends and at the junctions between the divisions and creates a separate element for each division. The elements which comprise the line feature thus created will all have the same element type, geometrical properties and material properties 14 Loadcases Open the Loadcases panel on the Treeview window by clicking on the icon with the L in it. In a new model it will show one loadcase - Loadcase 1. To create further loadcases right 3

4 click on Structural Analysis in the Loadcases panel and select New and then Loadcase. This will be called Loadcase 2. To rename a loadcase, right click on its name in the Loadcases panel and select rename. Active Loadcase When LUSAS carries out a solution it does it for each loadcase separately but while the model is being established and when the results are being accessed by the post processor, only one loadcase is active. Activate a loadcase by right clicking on its name in the Loadcases panel and select Set Active. When you drag loads on to the model they will be assigned to the active loadcase. Likewise when viewing results, select the loadcase you want to consider by setting it active (as above) from the Results file in the Loadcases panel. 15 Sign conventions for internal force actions Local y axis End 1 Shear force - Positive in the negative direction of the local y axis at End 2 Local x axis Axial force - Tension positive Positive bending moment give compression on the side of the beam in the positive direction of the local y axis LUSAS sign conventions for internal force actions 16 Creating a mesh of plate or shell elements To create, for example, a mesh of shell elements with 6 elements in one direction and 5 elements in the other follow the following process: 1. First create a surface : create 4 points to represent the vertices of the surface. 2. Select the 4 points. The local x axis for the surface will be from the first point to the second point selected 3. On the define toolbar click on the New Surface icon. This creates the surface 4. Create a 6 x 5 mesh of, for example, shell elements by clicking on the Attributes menu icon in the main toolbar and selecting Mesh and then Surface. This opens a Surface Mesh dialog box. In the top right hand panel remove the tick for Automatic Divisions and define a surface mesh with Local X divisions - 6 and Local Y divisions - 5. Call it, say, quad 5. Select the surface on the model (use the surface selection arrow) and drag the quad surface mesh over to it 6. An important issue is to make sure that the lines which form the sides of the surface in the local X direction are the ones that have six divisions. If you have forgotten which line order you chose the points to define the surface go to the Layers Pane in the Treeview window. Right click on Geometry then Properties and check the Surface axes tick box. The surface axes now show somewhere within the surface on the screen. 7. Define geometrical and material attributes for the surface, select the surface and drag the attributes to it. 4

5 17 Defining a local co-ordinate set. The simplest way to do this is as follows: 1. Select three points (by holding control ) in order P1, P2, P3. P1 is the origin, P1-P2 is the direction of the local x axis and P3 lies in the local y plane (positive on the side on which P3 lies) of the local axes. 2. From the Attributes menu select Local co-ordinates. A dialog box opens. About 1/3 up from the bottom of the box it says: Co-ordinate set generated from selection - click on Use, define a name for the dataset and click OK. 3. Select an element to which the new co-ordinate set will apply. 4. Drag a mesh dataset to the main window. A dialog box asks for Element Orientation. To use a non-default set, click on By Local Co-ordinates and select the required local coordinate dataset the select OK. 5. The element now has a new set of local axes. 5