If you work with moving loads and want to automate your work as much as possible, RFEM 6 is just what you need! Our program allows you to apply moving loads and generate associated load cases quickly and easily - and all this without having to buy additional products. Hence, if you have purchased an RFEM 6 license, are using a student license, or have a 45-day free trial version, you can create and apply moving loads, such as vehicles on bridges, completely free of charge.
As you may already know, the input of member and surface loads in RFEM 6 is greatly facilitated by load wizards. One of them is the Moving Load Wizard, which is directly integrated into RFEM 6 and enables the application of single load, or load models consisting of several loads, to surfaces, as well as the generation of load cases resulting from these loads’ different positions. The step-by-step procedure in the wizard for defining such loads and generating the corresponding load cases is explained in the Knowledge Base:
This article shows you, using a practical example, how to use the Moving Load Wizard to create a load that moves along a bridge. The goal is to represent the loads P as two surface loads p at the distance defined by the gauge, each of them acting on the specified width and length (these are shown in the wheel contact area, for example). The loading scheme is shown in Image 1; the corresponding bridge can be seen directly below, and is also available for download.
The surface loads shown in Image 1 should be applied on the bridge along a trajectory, which must be defined as one of the parameters in the Moving Load Wizard. If you have read the above-mentioned article, you know that the trajectory is defined using a line set. Although the line set can be created by calling the New Line Set dialog box directly from the Moving Load Wizard, we recommend defining the line set representing the trajectory in advance, in the RFEM model. In this example, you want to represent the load as moving along the vertical center of the bridge; therefore, lines 46, 49, 50, and 51 are grouped in Line Set 1 – Trajectory (Image 2).
Although it is just a matter of preference, the load model can also be defined in advance. As you probably already know from the KB article on moving loads mentioned above, the load model manages the load parameters of the moving loads and defines the set of loads that move along the trajectory. This can be done by opening the New Load Model window from the Navigator, as shown in Image 3. For this example, it is enough to specify a load component defined as a force acting in the global Z direction. The load distribution should be assigned as Axle – Free Rectangular Load, since you want to apply two surface loads (p) with magnitude of 240 kN/m2 acting on a width and length of 0.250 m. The free rectangular loads are then applied at the distance defined by the gauge, which in this case is 1.5 m.
Now you can open the Moving Load Wizard dialog box and continue by entering the other parameters of the moving load (Image 4). The first input is to specify the surfaces on which the moving loads are to be generated. For the bridge in question, you can simply check the "All" box, since there are no other surfaces in the model than those of the bridge to which you want to apply the load (that is, surfaces 1-8).
Next, you should define the geometrical parameters of the moving load by defining the trajectory and the lane(s). For the former, the Line Set 1-Trajectory has already been predefined so that you can directly select it from the drop-down list. For the latter, you only need to define one lane and a moving step ∆ of 0.250 m (that is, the length of the load itself), since you want to represent a load that moves continuously along the bridge (Image 4). No eccentricity, offsets, or bumpers are required for this specific load representation.
After defining the geometric parameters of the load and the load model, the Movements tab allows you to link the two into a set of movements (Image 5). Since only one lane was defined in the previous tab, you only need to select Lane 1 and the load model 1-Basic that you created earlier. The load factor, which is used to scale the load effect, is automatically set to 1, and that is the value you want to keep, since in this example there is no need to amplify the load. Given that there are no multiple loads on the same lane, the “Distance from Previous Load” entry and the “Independently Related to Previous Load” option are also not applicable in this case.
The last step of the Moving Load Wizard is to generate the load cases associated with the different positions of the moving load. To do this, you need to select the action category to which each load case should be assigned. As you probably know, this is important because the action categories control the superposition of the load cases, as well as the partial safety factors and combination coefficients. For this example, you can assign the load cases to the action category “Imposed loads – category F: traffic area – vehicle weight <= 30 kN". Once you do this and the “Generated load cases” checkbox is activated, you will see a load case list consisting of separate load cases for each step of the moving load (Image 6).
The load cases associated with the moving load can now be found alongside all other load cases on the Load Cases tab of the Load Cases and Combinations window, under the Load Cases entry in the Navigator, as well as in the toolbar. This allows you to select a load case from the drop-down list in the toolbar or in the Navigator and view the load generated in that particular load case, as shown in Image 7.
