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Frequently Asked Questions (FAQ)
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The RF-/DYNAM Pro - Equivalent Loads add-on module only contains a linear analysis of structures. If you now apply a nonlinear model for the calculation, RF‑/DYNAM Pro - Equivalent Loads will modify it internally and treat it as a linear model. The nonlinearity in your model is the masonry, which cannot absorb any tensile forces.
The problem is as follows: RF-/DYNAM Pro - Equivalent Loads calculates the equivalent loads linearly and exports the load cases from them. However, the load cases are subsequently calculated nonlinearly on the basis of the material model, which is not entirely correct. Furthermore, the results are superimposed according to the SRSS or CQC method, which results in tensile and compressive forces being present in the model.
In this case, you could change the masonry to isotropic linear and work with linear properties of the material model, for example. Additionally, it is possible to insert line hinges at this location, which could be used to avoid the moment restraint, for example.
AnswerIf the load-bearing capacity of the wall surface is neglected and only applied to the ceiling as a load by using a line load, it would result in very large deformations.
If the nonlinear property of the masonry is not considered, it would result in very small deformations.
In principle, there are three options available in RFEM.
- Line release: Vertical compression forces are only transferred. In this case, the nonlinear property is only applied for the force transmission directly to the connection line of both surfaces.
- Nonlinear material "Isotropic Masonry": In this case, the tension stresses in the x- and y-direction (that is, vertical and horizontal) are reduced iteratively to the specified limit values by reducing the stiffness. Using this model, it is possible to represent the behavior of a masonry wall that is closest to reality, because the tension stresses are reduced in the direction of the mortar joints. This requires the RF‑MAT‑NL add-on module.
- Nonlinear surface stiffness type "Membrane without tension": In this case, the tension stresses in the principal stress direction are reduced iteratively by reducing the stiffness.
Depending on the geometric requirements of bricks, these are integrated into Class 1 to Class 4. All geometric requirements for the brick classes are listed in Table 3.1 of EN 1996‑1‑1. An example of assigning the classes according to the total percentage of the brick holes (% of the gross volume) is as follows:Class 1 (all bricks)≤ 25Class 2vertical hole ratio> 25; ≤ 55Class 3vertical hole ratio ≥ 25; ≤ 70Class 4horizontal hole ratio> 25; ≤ 70
A mortar joint is available when the bricks of a wall are not laid on one but on two mortar strips. In this case, the mortar has to be applied to the outer edges of the support surfaces of the bricks. By using a mortar joint, it is necessary to take into account the restrictions in the ultimate limit state as the unfavorable stress diagrams occur in the wall.
Whether to apply the mortar joint in a European country is governed by the respective National Annex. The German National Annex does not alllow to use the mortar joint for the masonry construction. Therefore, in Germany, bed joints must always be mortared over the entire surface.
AnswerThe add-on module RF-MAT NL is already integrated in RFEM 5. It is assumed that the following material models can be used:Isotropic Plastic 1DIsotropic Plastic 2D/3DIsotropic Nonlinear Elastic 1DIsotropic Nonlinear Elastic 2D/3DOrthotropic Plastic 2DOrthotropic 3D PlasticIsotropic Masonry 2DIsotropic Damage 2D/3D
AnswerThe stiffness type "free of membrane tension" describes the plate and plate stiffness of surfaces.The plate stiffness including the shear stiffness perpendicular to the surface plane is linearly elastic and the plate stiffness in the surface plane is defined nonlinearly elastic with the material model according to "Drucker-Prague" depending on the defined thickness and the assigned material.In order to ensure that the surface behaves "draft-free" in the pane direction, the nonlinear material model reacts with tensile direct tensile stress fy, t that approaches zero for tensile-stressed elements in combination with a relatively small solidification modulus Ep. For compression forces, however, the elements remain linearly elastic due to a relatively high compression set tension stress fy, c, and react with an unrestricted compression force transmission.Since the "membrane-free" stiffness type fundamentally modifies the slice degrees of freedom of surfaces, it is only offered for surfaces in the relevant model types 3D, 2D-XZ (uX / uZ / φY) and 2D-XY (uX / uY / φZ).To better describe the partial nonlinearity of this surface stiffness type, the release "RFEM 5.06.1103" on 4.02.2016 renames the type from "Without Tension" to "Without Design".
AnswerThe ratio g/t is the ratio between the total width of the mortar strip and the thickness of the masonry wall. The ratio of mortaring of the vertical joints should not be selected smaller than 0.4 in accordance with the standard specification.
AnswerThe property of the material masonry depends on a large number of input parameters. It would be very extensive to list all possible combinations. To create a material, click the "Create new masonry material ..." button. Once created, the material remains in the library for repeated use.
The easiest case is the door lintel modeled directly on the line of the door opening without an offset. It is then necessary to generate extensions on the wall sides. In the end, the lintel thus consists of three members, as shown in Figure 01.
AnswerIn order to use the "Isotropic Masonry 2D" material, the RF‑MAT NL add-on module has to be licensed. Without the RF‑MAT NL license, only the material models "Isotropic linear elastic" and "Orthotropic elastic 2D/3D" are available.
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Wind Simulation & Wind Load Generation
With the stand-alone program RWIND Simulation, wind flows around simple or complex structures can be simulated by means of a digital wind tunnel.
The generated wind loads acting on these objects can be imported to RFEM or RSTAB.
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