Moving loads

The "Moving load" tool is mentioned to specify traffic loads on different types of structures: stylobate pavement, floor slabs of parking, bridge structures, motorways, etc. With this command, it is possible to model the trajectory of transport movement with standing points. That is, you can use it in modelling, for example, the loads from a fire truck on the pavement of a stylobate. This article describes the algorithm for modelling the moving load as an example of generating the moving load from a fire truck.

1. In LIRA-CAD libraries, in the "Loads" section (Fig. 1), various types of moving loads are available, but not all of them. There is a certain algorithm that allows you to add any load to the libraries; this load can then be used in the modelling of moving loads in accordance with any implemented building code. For this example, the algorithm for adding a fire truck load will be described.

   

   Figure 1. Loads available in LIRA-CAD libraries

2. To add a custom load to LIRA-CAD libraries, it is necessary to create an imaginary object, for example, the lines that indicate the axes of the truck (Fig. 2a), and the load (Fig. 2b).

   a	b

   
   
   Fig. 2. a - Imaginary lines that indicate the axes of the fire truck; b - Load collected from the fire truck
   
   

   Sel ect the created objects and unite them into a block. Then, sel ect the block, and on the "Libraries" tab, sel ect the "Load" section, and click "Add to library" . In the dialog box that appears (Fig. 3), enter the name "Fire truck", sel ect the model type "Parametric model" and set the base point. Click "Save"

   

   Figure 3. Adding an object to the library

3. Activate the "Moving load" command (on the Create tab, on the Loads panel). Double-click to sel ect the load "Fire truck" in the list. Then define the trajectory of movement by standard method. The trajectory is selected based on the general layout (passages between buildings, etc.).

4. Standing points should also be selected based on the general layout. The most unfavourable locations for standing, e.g. in the middle of a span, above a support, etc., should also be considered. The number and spacing between the standing points can be changed in tabular form. To do this, just click the "Parameters" button (Fig. 4). Location can be also changed graphically along the trajectory.

   

   Figure 4. Parameters of moving load

5. If there is a ramp, car park entrance, etc. in the model, you can design the trajectory so that it takes into account the features of the site. To do this, sel ect the movement trajectory and click the "Projection on trafficway" button (Fig. 5).

   
   Figure 5. The "Projection on trafficway" command

6. Once the meshed model is created, each standing point will correspond to a different load (Fig. 6). In the "Load cases" dialog box, you can create your own combinations for the moving load.

   
   Figure 6. Loads that correspond to standing points
   
   
   
   Stresses from standing points