Force Profile

The Force Profile area allows for the input of multiple time varying loadings, which can be input as forces or as moments, applied in the global axis directions and acting on selected nodes within the model. Loads can be varied over input time intervals and the dynamic response of the structure analysed and displayed as an animation. The Force Profile analysis outputs includes the nodal deflections, velocity or accelerations. it is also possible to observe the results over the analysis time for particular nodes, with the results for a particular node being displayed in a graph for simpler interpretation. Snaps shots of the model displacement and member forces can also be created, which can then be combined with loading cases in Masterframe to than incorporate the effects of time varying loading within the static load cases.

As noted in the previous section, the mode shape analysis is the necessary first step for any of the dynamic or seismic analyses. Therefore, the mode shape analysis is required prior to doing a Force Profile analysis. If mode shapes have not been calculated, the other tabs will be greyed out and inactive.

On first selecting the Force Profile tab, the screen layout is as shown below.

The input forces are defined in the table at the bottom left hand side of the screen. The results are is contained in the right hand pane. Forces are defined by the time and intensity along with the force direction and the nodes to which the forces are applied. Changes in forces are taken to be linear within the times defined. When a force is input, the graph to the right of the force definition will display the force profile in the selected force direction.

An example of a load varying over a one second interval from 0 to 10kN and back to zero is shown below, along with the force profile graph.

The above force is linearly varying from 0 to 10kN from 1 to 1.5 seconds. For more irregular time varying loads, these will require more definitions of the load values and times.

When defining forces, the inputs do not need to be in strict time sequence. Thus it is possible to define time varying loads for loads which overlap in time, but define each load separately. An example of 'overlapping' loads is shown below.

By defining multiple time varying loads in this way it is possible to built up complicated time dependant loadings and apply them to a range of nodes within a model.

To apply loads to nodes, the nodes can be select either by typing in the node number, or by using the mouse and selecting the individual nodes from the frame graphical display. The loads associated with the selected line in the force input table will be displayed graphically at the selected node. The scale of the displayed nodal loading can be altered by selecting the required scale from the  icon.

Adding a Snapshot to a Masterframe Loadcase

When snap shots have been created, either directly in the Snapshot results or as part of the Min/Max displacement and member forces results, these can be added to a loadcase within Masterframe, such that the effects of the Force Profile loading can be included within a load case. Snapshots can be added to a Masterframe load case by going to Loads>Dynamic and Seismic Loads>Dynamic Snap Shot Loads. This opens a pane on the right hand side of the screen. The required load case is selected from the drop down at the top of this pane. To attach a snap shot, check the "Attach Dynamic Snapshot" checkbox. The snap shot to be added to a loadcase is selected from the "Select a force snapshot" drop down. Snap shots are labelled with the time stamp. Therefore to add a particular snap shot, the time of the appropriate snap shot needs to be noted in the Dynamic results area. The factor to be applied to the snap shot is entered in the "Apply a factor" input.