SOLVERS: Paths

Description

Selects load paths for analysis in the Quasi-static, Linear Transient Dynamic, Nonlinear Transient Dynamic and Transient Heat solvers.

The Paths sub-tab becomes available when there are load paths in the model. Each row in the grid lists a load path and enables the selection of a Factor vs Time table. Load paths can be used in these solvers to apply loads whose position varies as a function of time. By associating a Factor vs Time table with the path, the load can also be scaled as a function of time. If the table is not defined for a path, the load position will still vary with time, but its magnitude remains unscaled, and equal to the vehicle loads defined in the load path template (see LAYOUTS: Paths). The analysis of footfall loading on a footbridge can be modelled with a load path and a Factor vs Time table.

Auto Divisions

The moving effect of a load on a path is implemented by dividing the path into a number of segments lengthwise, positioning the load on each of these segments, and then scaling the magnitude of the load on each segment based on the vehicle start time and velocity as defined in the load path template (see LAYOUTS: Paths), for each time step of the analysis. For example, at vehicle start time, only the load on the first segment is active, with the load on all other segments scaled by zero. As solution time marches on, the segment loads are appropriately scaled to achieve the moving effect. The solvers perform this procedure automatically.

The resolution, or smoothness, of the moving load depends on the number of path divisions with respect to the time step used in the analysis. Although the total load applied will always be exact, no matter how many divisions are used, if the time step is too small for the number of divisions, the load will not transition smoothly. Conversely, if the number of divisions is too large compared with the time step, the solution will be unnecessarily slowed.

When a load path is first inserted into the model (Insert: Path), the number of divisions is specified. This can be subsequently changed by Path Attributes: Divisions. However, to avoid an inappropriate number of divisions for analysis on any path, the Auto Divisions option can be used. If set, the load path divisions are automatically calculated for the path based on the solution time step.