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Frequently Asked Questions (FAQ)
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AnswerThe most convenient and fastest solution is to copy a load case to the next load case. If already generated loads have been created for several load areas in a load case (see Figure 1), all loads are transferred to the next load case during copying (see Figure 2). Subsequently, only the load values of the generated loads have to be adapted to the respective load case.This method is particularly useful for plane structures whose load type remains the same.
When selecting the nodes for basic geometry and roof geometry, always make sure that the nodes have the same layout as in the graphic (see Figure 1), that is:
- Node A via node I
- Node B over node J
- Node C over node K
- Node D via node L
AnswerWith the load generator it is not yet possible to generate the loads for open buildings.You could generate the loads for a closed hall and then manually fill in the missing loads.For free-standing roofs there are other assumptions according to the standard, which are not yet covered in the load generator. There is already an interesting article on the wind load on a freestanding roof on our website.
For example, if you have a grid with different grid spacing in areas, it is not suitable to apply the load generator with the defined area load plane only. The load would otherwise be determined according to the size of the area load plane and applied to all members (except the boundary members) with the same load value (see Figure, the top part).
However, if the area load is divided into several sections (dialog box section "Boundary of the Area Load Plane"), the load is distributed correctly. This is shown on the bottom part of the figure.
If the load generator is used for simple and fast generation of wind loads, for example, for a hall with roof overhangs, it is possible to consider the load on the roof overhang. The data are entered separately for the base geometry of the building (without the roof overhang) and the roof geometry (with the roof overhang). The input dialog box is shown in Figure 01.
The program determines the roof overhang from the difference and applies the load accordingly (see Figure 02).
The load generators create a rectangular building shape. The following roof shapes are available for the roof geometry:
- Flat roof
- Monopitch roof
- Duopitch roof
In the case of different building or roof shapes, you can apply the loads manually using the tool "Generate Loads → From Area Load on Members via Plane." The load value must be determined manually.
The prerequisite for using both generators for wind and snow load are that you are working with the 3D model type. For a 2D model type, the program does not have the corresponding geometrical parameters.
The model type is set in the general data of the model. The corresponding dialog box can be opened by right-clicking "Model Data" and selecting the "General Data" shortcut menu option in Project Navigator - Data (see Figure).
If changing the model type, it may be necessary to adjust the modeling (supports, joints).
AnswerIn both cases shown in Figure 1, the total load is 51 kN in global X. The problem is the different distributions in both cases. In variant A, the green loads are larger and the red smaller and in variant B it is the other way round. The biggest problem in variant A is that the red loads are strangely the same size as in the area above, but where there are still the intermediate bars (green load). The problem here is the yellow bordered area. Internally, the load of the entire surface is first calculated (51 kN) and then the closed cells (plane completely framed by bars) are subtracted from it. Since the yellow framed surface does not represent a cell (the limiting rod between nodes 20 and 36 is missing), there is a special case here. The generator proceeds as follows. Removing the horizontal bars creates a large fictitious cell between nodes 23,760,36 and 20. By the already mentioned missing cell it is assumed that the outer bars all have a constant load (here 1.6 and 1.0 kN / m) and the remaining load is distributed to the inner rods. As a result, in variant A the green load is higher and the red loads smaller. To modify this distribution, the load generator has the following option "Apply all bars", as shown in Figure 2. This option creates the missing cell internally and distributes the loads according to Variant B. In our blog, there is one more interesting post: http: //www.dlubal.com/blog/9034/dlubal-rfem-5-rstab-8-behandlung-von-unbelasteten-staben-bei-derlastlastierung
The reason is that the "Correction of Generated Loads" is inactive and thus, only intermediate values are determined. To change that, select the "According to moment equilibrium of total loads and generated member loads" option in detail settings of the load generator (see Figure).
You can find more information about the load correction in Chapter 11.8.1 of the RFEM or RSTAB manual.
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