A load case applied to a frame is represented within the Multiframe object model using the Loadcase object. This object contains the attributes of a load case such as its name, type, etc. It also contains several collections containing the loads applied in the load case. All the load cases applied to a structure are stored in a Loadcases collection that is contained within the Frame object. A new load case is added to a frame using the AddCase method of this collection. This method takes two parameters that specify the type and name of the load case.
The following code fragment is used in the portal frame script to define three load cases, a self weight case, a live load case and a factored case that combines the first two cases.
Dim myLC as Multiframe.Loadcase
'Add load cases to frame
With mfApp.Frame.LoadCases
Call .Item(1).Delete
Set myLC = .AddCase(mflcSelfWeight,
"Self Weight")
Set myLC = .AddCase(mflcStatic,
"Live Load")
Set myLC = .AddCase(mflcCombined,
"DL + 1.25*LL")
End With
Loads applied to elements within a model are represented by an ElementLoad object. This object has properties representing the magnitude of the load and its position along the element. All the element loads applied in a load case are contained in an ElementLoads collection that is stored in the Loadcase object. New loads are added to a load case by adding an item to this collection using the AddLoad method.
Dim myLoad as Multiframe.ElementLoad
'Define live loads
With mfApp.Frame.LoadCases(2) .ElementLoads
Set
myload=.AddLoad(2,mfDOFy,mfLoadshapeUniform,-3.5,0,-3.5,0,False)
Set
myload=.AddLoad(3,mfDOFy,mfLoadshapeLinear,-3.5,0,-1.5,0, False)
End With
A similar syntax is used to add other loads such as thermal, joint loads or prescribed displacements.
The load case factors used to define a combined load case are also stored as properties of the Loadcase object. They can be set using the Factor property of this object which, unlike many properties, takes a single parameter that identifies the index of the load case for which the load case factor is being set. In our portal frame example, this property is used as follows.
'Set factors for combined load case
With mfApp.Frame.LoadCases(3)
.Factor(1) = 1#
.Factor(2) = 1.25
End With
This snippet of code defines the factors for the 3rd load case that is a combination of the 1st load case and 1.25 time the 2nd load case.