Multiframe allows you to automatically include the self weight of the structure as a separate load case.
§ Choose Self Weight… from the Load menu or the short cut menu
A dialog will be displayed which allows you to enter the acceleration to be applied to the mass of the structure to convert it into a load.
You will usually use the default setting which applies a standard gravity acceleration to the structure. However if you are investigating inertial or seismic effects, you may wish to apply accelerations in the x or z directions.
After clicking OK, a new load case named Self Weight will be created. You can create any number of self weight load cases with different acceleration factors. You should make sure that you have set all of the section types for the structure before you use the self weight command. If any of the sections used in the structure have zero mass, Multiframe will prompt you with a dialog to go ahead with or cancel the use of self weight. If you wish to use self weight with custom sections, make sure you enter an appropriate value for the mass when adding the section to the library.
If you add a self weight case, you can specify whether or not a member's weight is to be included by using the Member Self Weight command from the Load menu.
To specify whether a member's weight should be included in self weight
§ Make sure a self weight load case is the current load case
§ Select the member(s) to be changed in the Load window
§ Choose Member Self Weight from the Load menu
§ Click the Ignore or Include radio button as appropriate
§ Click OK
If you have more than one self weight load case, you can turn on the check box to have the same self weight settings used for all self weight cases, otherwise the settings may be different for each self weight load case.
The Member Self Weight command only affects the self weight for static analysis. If you are doing a dynamic analysis in 4D, the member's weight is controlled by the Member Masses command from the Frame menu. The default setting is that the mass is included.
A self weight load case can be combined with other load cases in the usual way. The numerical values of the self weight loads are not displayed in the Data window. These values will be updated just prior to analysis to ensure that the weight for any members you have changed are included correctly.
The loads for self weight are included in two ways. Members which are vertical are loaded with an axially distributed load, Wz', acting in the vertical direction, from joint 2 to joint 1. You will see values for this load in printouts or in factored load cases that are made up from a self weight load case. Members that are not vertical, are loaded with a vertical distributed load scaled to take into account the horizontal projected length of the member (see Global Distributed Load above). Because global distributed loads are applied in units of force/horizontal length, the magnitude of the distributed load must be scaled to take into account.
For example, a 10ft long member weighing 100 pounds with a horizontal projected length of 1 foot would require a distributed load of 100lb/ft to apply the correct self weight. The same 10 foot long member with projected length of 5 feet would only require a distributed load of 20lb/ft to correctly apply the self weight. For this reason, if you have members that are very nearly vertical and therefore have a very small projected length, you will see very high values for the distributed load applied due to self weight.