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ST7-1.50 Modelling

ST7-1.50.20 Modelling / Manual Meshing

1.3 MB
ST7- Interfacing Different Element Types
This Webnote examines the modelling considerations required to connect different element types - beams, plates, and bricks. In a mesh connecting different element types, simple element-to-element connection at the node may not transfer all load components correctly. Additional interface entities can be introduced to ensure compatibility of all degrees of freedom at the interface.
ST7-1.50.30 Modelling / Loading

0.5 MB
ST7- Wind Loads on Shell Elements
Wind loads are often expressed in terms of force per unit length, and often vary with respect to height. It is quite easy to apply this sort of loading to a beam element using a distributed force, but applying equivalent wind loading to a shell element mesh takes some additional consideration. This document outlines how to apply an equivalent varying wind load to both beam and shell elements. A 1.5 m diameter tower is considered.  Given a wind load of 30 kgf/m at a height of 4 m, and 100 kgf/m...

0.8 MB
ST7- Applying Moments to a Brick Mesh
3D solid elements (otherwise referred to as brick elements) do not contain rotational degrees of freedom in the element formulations. Each node in a brick element has only three translational degrees of freedom, meaning that the displacements DX, DY and DZ are calculated, while the rotations RX, RY and RZ (and corresponding moments) are not considered. If one were to apply a point moment directly to a brick mesh, it would be ignored as reflected in the solver log file Warning 6.

5.2 MB
ST7- Load Patches for Area Load
Area Load (or Floor Load), as referred to by some other engineering software packages, is equivalent to Load Patches in Strand7. In this Webnote we look at how load patches can be applied to model these situations. However, since the patch plates in Strand7 are very flexible, they can also be applied to non-planar meshes in 3D space; some examples are illustrated in this Webnote.  The following structure is provided: A floor live load of 30 kPa is to be applied to the structure. Open the...

1.6 MB
ST7- Using the Moving Load Module
This Webnote outlines the use of the Strand7 Moving Load module for the modelling of transient loads moving along a path, the generation of load cases relevant to the possible positions of loads moving along a path, and to create static combination of loads moving along a path that minimises or maximises a specified response variable. Whilst each of these capabilities addresses different analysis types, central to them all is the definition of moving loads in a Load Path Template. In Strand7,...

0.7 MB
ST7- Using Normal Pressure to Fold a Box
The plate normal pressure attribute updates the direction of applied load as the structure deforms in a geometric nonlinear analysis. This means it can be used to apply load which causes structure to fold or wrap around other structure. In this Webnote we examine the folding of a box from a flat creased aluminium plate. The load is then released and the spring-back effect is measured.  The starting planform shape of the box is shown at right. The model needs to have contact elements defined...

0.5 MB
ST7- Global Pressure Attribute Projection Options
This Webnote examines the load projection options for Global Distributed Force and Face Pressure attributes. The projection options dictate whether the total surface area or only the projected area of the element is used to calculate the total applied load. For area projection two methods are considered, namely projection in the direction of each load component, and projection in the direction of the load resultant.

9.3 MB
ST7- Balancing Load in Pressure Vessels with Openings
When modelling contained pressure loads that act on the structure, it is important that the load be balanced to model the physical reality accurately. That is, if there is an opening in the pressurised body, the lack of applied pressure on the opening (due to lack of finite elements that cover up these openings) will result in a large force imbalance. This effect is analogous to that of a propelling nozzle.
ST7-1.50.40 Modelling / Contact

0.6 MB
ST7- Multi-Body Contact of a Rubber Bushing Assembly
There are several ways to connect multiple bodies to form contact surfaces. We will cover the case where the bodies are completely separate and have meshes which do not necessarily line up across the gaps between them. A rubber bushing used to restrain a window pane is analysed. It consists of 5 parts, one of which is a co-moulded steel-rubber bushing. The analysis we will perform on the bushing assembly is Axisymmetric. Create a new file. Set the units to Nmm. Import the file Bushing...

2.4 MB
ST7- 3D Solid Multi-Body Contact
A sliding joint model is built by extrusion and automeshing methods. Contact is defined between the two bodies to determine the response of the multi-body system. Open ST7- Sliding Joint.st7. Note that there are two groups defined (Global/Groups). Turn off the group Stub and Base. Select the face which defines the cross-section of the track. Automesh the face with an edge length of about 2.4 mm using Tools/Automeshing/Surface Mesh. Extrude this mesh to 120 mm length in...

1.0 MB
ST7- Defining Contact Interfaces
Contact between multiple bodies in Strand7 is achieved using contact elements, which are a type of beam element. Whenever possible, it is best to use node to node contact, which is simply a contact beam element connecting two nodes. This is generally done in situations where there is a regular mesh, or the mesh on either side of the gap is the same, facilitating extrusion of contact beam elements between them.  In the model shown at right, contact has been defined between the nodes on the two...

0.5 MB
ST7- Determining Appropriate Contact Stiffness
Contact is modelled in Strand7 using a special type of beam element. These beam elements react load nonlinearly, and in proportion to axial compression. The stiffness of these contact elements can affect the solution results accuracy and convergence. There are many physical situations that may be modelled with various configurations of contact elements. This Webnote aims to provide a guideline of what the axial stiffness value should be. Refer to ST7- Contact Element Fundamental...

1.2 MB
ST7- Sliding Contact
This Webnote introduces a technique that can be used to model sliding contact with pre-strained cutoff bar elements. Examples including pedestrian step loading, sliding of an interference fit, and reeling of a cable onto a spool are presented. We will use the following example to introduce the idea: A person of mass of 70 kg walks across a simply-supported steel beam 8 m long with 1000x100x10 mm rectangular hollow section. Create a new model and choose Nmm as the unit system. Create...
ST7-1.50.50 Modelling / Details

1.9 MB
ST7- Bolted Joints
Bolted joints can be modelled using Strand7 with varying levels of detail depending on the level of accuracy and local detail required in the analysis. Five options are presented, each with increasing levels of complexity.

0.6 MB
ST7- Beam End Releases
Beam end releases are provided as a beam element attribute in Strand7. These attributes can be applied to one or both ends of a beam element. Both translations and rotations can be independently released to model a variety of joint configurations. Where no end release is applied, two beam elements that share a node are modelled as being welded together. Using end release attributes, ends of beam elements can be fixed (no end release), partially released (where a connection stiffness is specified),...

0.6 MB
ST7- Tapered Beams
It is common to use beams which are tapered in engineering structures. One approach for modelling a continuous tapered beam is to use a sequence of untapered beam elements of varying size as shown below. This modelling approach could take considerable time for models with many tapered beams, as the accuracy of the solution may require many stepped beams. However, to reduce modelling time and solution time, and to improve accuracy, the beam Taper attribute may be applied to beam elements....

0.9 MB
ST7- Modelling with Cables
This Webnote examines different modelling approaches for cables and slender members with only axial capacity. The modelling consideration of tension-only capacity is also examined. Such cables and slender members can be modelled using Cable, Truss and Cutoff Bar type Beam elements in Strand7.

0.7 MB
ST7- Using String Groups
The Beam String Group attribute is used to model a continuous chain of truss type beam elements sliding through frictionless connections at nodes. The attribute ensures that a constant axial force develops in all the elements in the same string group. A common application of the attribute is to model massless cables (or strings) such as pulley systems, lifting sling cables, and pre-stressed steel tendons in reinforced concrete. This Webnote examines the Beam String Group attribute and its modelling applications.

1.5 MB
ST7- Simplified Spline Contact and Fatigue Analysis
In this Webnote we model the end of a winch drum which has a 60 mm diameter spline with 50 teeth. The effect of the spline is all that is needed the local stress in the teeth of the spline are not of interest. Fatigue analysis of the hub is the primary concern. Thus, we can use a simplified approach which gives an accurate coupling of the input shaft and winch, while maintaining a reasonably small model size. The interface between the male and female parts of a spline is complex. The gap...

0.7 MB
ST7- Beam Element Orientation
This Webnote discusses how beam elements are orientated in Strand7, together with methods for changing the orientation. The orientation of both Beam2 and Beam3 elements is presented. By default, Strand7 beam elements are aligned according to the principal axes of the cross section. Principal axes for an I-section, as shown in the Geometry tab of the Beam Property dialog, are illustrated at right. The orientation of the Beam2 element is fully specified by the definition of two non-coincident...
ST7-1.50.60 Modelling / Links

0.4 MB
ST7- Link Types
The various link types available in Strand7 are summarized below, including example uses.  ...

0.5 MB
ST7- Link Forces
Links do not produce output like other FEA entity types (e.g. plate elements). We must instead extract the forces from links using one of two techniques, which are outlined below. The first involves Element Node Force, which is used to create free body diagrams at the link interface. The second makes use of Node Reaction output, which holds the forces due to restraints and can be modified to extract link forces as well.  Consider the plane stress model below, which is included as ST7-

1.5 MB
ST7- Using Attachment Links
Although it is generally preferable to have full mesh compatibility between connected parts, in practice this is sometimes very difficult, if not impossible. Attachment attributes offer a versatile way of joining dissimilar meshes so that displacement compatibility is enforced by multi-point constraint equations that are automatically generated.

0.6 MB
ST7- Using Master-Slave Links
Master-Slave links are often misused, which can lead to non-physical behaviour. This Webnote outlines typical valid uses of the Master-Slave link, illustrates how the Master-Slave link differs from the Rigid Link, and summarises some of the common pitfalls of using Master-Slave links.

0.4 MB
ST7- Master-Slave Link Considerations
Master-Slave links provide a method of directly relating the degrees of freedom of two nodes in the mesh. These link types are normally intended to connect small gaps. Since the length of the link is not considered, usage over large gaps can lead to some non-intuitive results. This Webnote outlines the behaviour of Master-Slave links in some specific situations.  From the point of view of moment calculations Master-Slave links are effectively of zero length. Consider the top mechanism shown...

1.0 MB
ST7- Using Links to Model Rigid Diaphragms
Certain structural members can be modelled as having infinite in-plane stiffness, and zero out-of-plane stiffness. This is typically done in the analysis of buildings, in which the floors are assumed to act in this way during seismic events. To achieve this, Strand7 provides a special type of planar rigid link cluster, in which the plane with infinite stiffness is specified by the user.  A simple example is developed in which the floors of the six storey building from ST7- AS 1170.4-2007...
ST7-1.50.70 Modelling / Attributes

0.4 MB
ST7- Beam End Release and Node Displacement in GNL Analysis
This Webnote describes the relationship between the beam end release results and nodal displacement for linear and geometric nonlinear (GNL) solution cases. The focus here is on the rotational end release attribute, but the discussion is also applicable to the translational end release attribute. The default joint condition for a beam element in Strand7 is that of a welded joint. Strand7 has two Beam End Release attributes: one is the translational end release and the other is the rotational...

0.6 MB
ST7- Beam Bending and Nodal Rotational Stiffness
This Webnote illustrates the changing bending moment at the ends of beams subjected to uniformly distributed loads due to the effect of nodal restraints and joint connections. Consider a beam subjected to a uniformly distributed load as shown in the illustration. If the ends of the beam are pinned (nodes assigned zero rotational stiffness) then the bending moment at these ends is zero.  If the ends of the beam are fully fixed (nodes assigned infinite rotational stiffness) then the bending...

0.7 MB
ST7- Modelling Soil with Support Attributes
When modelling a structure which is supported by soil, it is often simpler to model the soil with a support attribute. These attributes model the linear elastic response of a supporting medium. This Webnote outlines the basic procedure to apply supports equivalent to that of the surrounding grade. Support attributes only represent normal support; shear stiffness is not possible using support attributes alone.  Support attributes can be applied to all element types. When applying brick face...

0.5 MB
ST7- Contouring Nodal Attributes
Strand7 allows the automatic contouring of element attributes, but not nodal attributes. However, there is a way to contour nodal attribute values on elements by using the Online Editor, Excel and a user defined nodal contour file.  A complex nodal loading is applied to the nodes of some plate elements shown at right for the purpose of demonstrating nodal attribute contours. This method applies to any other nodal attribute, and also to brick or beam elements.  The following general procedure...

1.1 MB
ST7- Assigning Attributes using Equations
Strand7 attributes can be applied using an equation which references the currently active coordinate system directions. Any UCS type (cartesian, cylindrical, toroidal or spherical) can be used. This functionality can be used to define non-uniform attributes on nodes and elements. Attributes which are applied with an equation only reference the equation at time of application. If the UCS is changed or the entity is moved the attributes will remain unchanged.  Create a cylindrical UCS centred...

0.7 MB
ST7- Modelling Supporting Structure with Support Attributes
Support attributes can be used to represent supporting structure which is not of interest aside from the stiffness contribution. Take for example a plate of glass resting on a rubber pad supported by a beam. Instead of modelling the beams with contact beneath the glass, a plate support attribute can be applied with an equivalent stiffness. This simplifies modelling and also allows the contouring of bearing stresses at the support points.  A cross-section of a patch fitting holding two panes...
ST7-1.50.80 Modelling / Model Manipulation

1.0 MB
ST7- Importing and Exporting Strand7 Model Data with Spreadsheets
This Webnote examines the exchange of Strand7 finite element model data with a spreadsheet. This method is useful for exchanging model information between Strand7 and other structural analysis software packages for which Strand7 does not offer import/export functionality. The Online Editor is used for this purpose. This discussion focusses on the import of finite element model data into Strand7, although the discussion is also applicable to the export of models from Strand7.

0.9 MB
ST7- Aligning Beam Elements
This Webnote examines the beam alignment tools. The beam axis system is used to define section properties, beam attributes, and beam result quantities such as force, moment, stress and strain results. The alignment of beams in a certain direction or in a consistent manner is a common modelling requirement. Strand7 provides several tools for changing the orientation of beam elements and alignment of their cross section.
ST7-1.50.90 Modelling / Restraints

2.7 MB
ST7- Modelling Symmetry
Many structures exhibit some degree of symmetry. This can sometimes be exploited such that only a portion of the model need be represented in FEA, reducing the time to get solutions or freeing up resources for a more refined mesh. In order to exploit this symmetry, both the geometry and loading must be symmetric.  Symmetry can be expressed as a fraction of the structure which remains once all redundant sectors are removed. / / / The resulting sector shown below is obviously much...
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