Introducing Multiframe 13
Multiframe Version 13 introduces a great new way to apply loads to structures. Our new automated load case for wind loads greatly simplifies and speeds up the application of wind loads to exposed members and planar cladding.
Also new with Multiframe 13 are new 64-bit versions of Multiframe and a new lifting analysis solver. The 64-bit versions run with the new 64-bit versions of Windows 7 and provide virtually unlimited memory access as well as improved performance.
64-bit Versions & Multi-Core Optimisation
This release introduces 64-bit versions of all programs for the first time. 64-bit applications allow you to use larger amounts of memory and are somewhat faster than 32-bit applications. On a 32-bit version of Windows, only a maximum of 2GB of memory is available to any programs running. Under 64-bit Windows, applications can theoretically utilise up to 128GB of memory. In practice if you get a 64-bit machine then you will want to get 8-12GB of RAM. For users with large designs, the 64-bit versions are highly recommended.
Please note that we have restricted our 64-bit versions to Windows 7 64-bit only to allow us to take advantage of some of the new features available in future.
This release of Multiframe also includes support for multicore processors. If your computer has multiple cores this feature will be enabled by default. Multi-core optimisation is used for the post-processing of member and plate results. We will continue to work on supporting more aspects of the solver in the future. If your model has a large number of plates you will see very good improvements in analysis performance.
Automated Wind Loads
It is now possible to add a new automated load case of type, Wind load case, which automates the addition of wind loads to the structure. You can enter details of the wind strength and direction and which variables you would like to be automatically calculated. Multiframe converts this information into member, panel and plate loads on the structure.
The key inputs are a wind velocity profile, wind direction, a choice of whether to apply loads to exposed members or to load panels, and the coefficients to use when loading members or panels. The wind velocity profile is defined as pairs of height and velocity values. A height of zero is equivalent to the global axis origin ie y = 0. The wind profile is shown graphically as you enter the values. The wind direction is entered as an angle relative to the global x-axis.
For loads which are to be applied to exposed members, member factors may be automatically calculated. The member factors are:
Kar – Aspect ratio factor. As defined by AS1170 Appendix E Table E1. Defaults to 1.0.
Ki – Inclination factor. As defined by AS1170 Appendix E2.1. Defaults to 1.0.
Cf – Drag force coefficients. As defined by AS1170 Appendix E3. Defaults to 1.5.
You can also specify shielding factors and a user factor to adjust the calculated loads by any desired factor. Shape factors for the orientation of the structural shape relative to the wind flow are automatically calculated for standard shapes and can also be user defined.
For wind pressure loads to be applied to plates and load panels, coefficients can be calculated based on Australian Standard AS1170.2.2002 or to a set of user defined values. The plate/load panel factors are:
Ka – Area reduction factor. As defined by AS1170 Table 5.4. Defaults to 1.0.
Cp – External pressure coefficient. As defined by AS1170 Chapter 5.4. Defaults to 0.8.
h – Average roof height. Defines the average roof height of the structure at which the
wind velocity for all patches/load panels will be taken.
All of these factors can be overridden by user factors if desired. In addition, Friction Drag can be included to include friction drag force to sidewalls and roofs that run parallel with the defined wind direction.
The Friction Drag Force is calculated by
P = 0.5*Rhoair*V^2*Cf*Cu
Where Cu is the user coefficient (default 1.0).
The default value of Cf, Friction Drag Coefficient, is taken to be 0.01.
A new type of analysis has been added for analysing frames which are used for lifting calculations. Typical examples would be lifting of baskets and skids with slings which are attached to a crane.
Such models are typified by a lack of restraint in the horizontal plane which allows the frame to either rotate or swing freely. If you model a frame like this you will often get the error message “Solution does not make sense”. The lifting analysis function automatically adds additional spring restraints to the model to provide sufficient horizontal restraint to allow the model to be analysed. This eliminates the need for you to apply your own manual spring restraints.
The stiffness of these restraints is automatically set by Multiframe so as to have a minimal effect on the actions within the frame. They are set at a small proportion of the other stiffnesses in the frame. While you are creating your structural model, you should review the location of the centre of mass and ensure that the lifting point is located as near as possible to a location directly above the centre of mass of the structure and its loads.
A lifting analysis is in fact a special type of linear analysis and as such the results of the lifting analysis are stored as the results of a linear analysis. If your sling members are set to Tension-Only, then a dialog will appear allowing you to take those effects into account during analysis.
Some care must be taken in performing a lifting analysis as the additional spring restraints added for the analysis will also help to suppress structural mechanisms. After analysis is complete, you will notice that all nodes in the model will have reactions. You should see normal reactions at any nodes where you have applied a restraint, and at other nodes where automatic springs have been applied, you should see reactions with a very small magnitude.