#### Further Information

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• ### When entering the geometry of a ribbed timber plate, I always get the error message 30343: "The computed stiffness matrix is not positive definite." How can I define the surface?

In the case of using timber materials in RFEM, a message appears when creating the material, saying that the "isotropic linear elastic" material model is only correct for the calculation with members because the Poisson's ratio is very large. For surfaces, it is necessary to select a different material model.

If you have assigned the material with the orthotropic material model to the surface, it is not possible to use certain orthotropy types. This material cannot be used for ribbed plates.

However, if you have assigned the material to the surface with an isotropic linear elastic material model, you can access all types of orthotropy.

When entering the geometry for the ribbed plate, Error No. 30343 appears due to the incorrectly assigned timber material for the surface: "The computed stiffness matrix is not positive definite."

• ### Can I change the cutting angle for the "Main member only" joint type?

In the case of the "Main member only" joint type, the member can be cut at any angle. The cutting angle δ can be adjusted under the geometry properties (see the figure).
• ### In RF-/TIMBER AWC and RF-/TIMBER CSA, I receive the Error 49927 and Error 54089 respectively which says the cross-section is not permitted. Why can I not design this section in the module?

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In the add-on modules RF-/TIMBER AWC and RF-/TIMBER CSA, only rectangular and round cross-sections can be designed at this time.

We are looking to expand the cross-section design capabilities in a future release similar to what the add-on module RF-/TIMBER Pro allows according to Eurocode.

Therefore, design should be done manually for these types of cross-sections according to the NDS or CSA standards.

• ### When creating a material, there are no nonlinear material models available for surfaces or solids. Why?

The nonlinear material models are only available in the 3D environment. Please make sure that the model type is set to "3D" (see Figure 02).
• ### What is the formula used to calculate the ASCE 7 wind velocity profile?

The wind velocity profile in RWIND Simulation according to the ASCE 7-16 standard [1] is calculated based on Eq. 26.10-1. The coefficients and basic wind speed in this equation below are incorporated in the wind pressure equation.

Velocity wind pressure (imperial): qz = 0.00256 Kz Kzt Kd Ke V2

We must reference this equation to calculate the inlet velocity relative to elevation for the RWIND Simulation CFD wind tunnel. To consider only velocity rather than pressure from this equation, the basic wind speed is multiplied by the square-root of each coefficient. Notice the velocity variable in Eq. 26.10-1 is squared which requires the square root of the coefficients to be considered.

$Inlet\;velocity\;=\;V\sqrt{K_e\;\cdot\;K_{d\;}\cdot\;K_z\;\cdot\;K_{zt}}$

Because the ASCE 7-16 standard does not address wind CFD analysis and magnitude of the required inlet velocity, it is difficult to draw comparisons. Therefore, this is the closest estimate for calculating the RWIND Simulation inlet wind velocity per the code.

• ### I have manually defined a snow load of 5 kN/m² in the RX‑TIMBER program. However, the calculation uses a load of 4 kN/m². Why is the defined snow load not applied?

According to EN 1991‑1‑3, the snow load must be multiplied by the factor of 0.8 for the snow load on a roof. Therefore, the following load results:

sk = 5 kN/m² × 0.8 = 4 kN/m²

If the load has already been calculated for the roof, you can enter the load completely under the user-defined loads. This is shown in Figure 01 and in the video.

• ### When trying to import a model from AutoCAD into RFEM, I am getting the error message "3DSOLID or REGION entity detected. Those entities are written in binary format, so import is not possible."What does this mean?

The reason this warning appears is because it is not possible to import 3D solids into RFEM from AutoCAD. Only 1D and 2D members can be imported in from AutoCAD to RFEM. The reason for this is because only line elements can be imported so with 3D solids they could not be automatically generated.

• ### How do I create a user-defined material in the RX‑TIMBER program?

In RX‑TIMBER, you can create a user-defined material as a new material in the material library (see the figure), similar to the programs RFEM/RSTAB.

In contrast to RFEM/RSTAB, the category is set to "timber" in this case.
• ### Is it possible to perform automatic live load reduction in RFEM or RSTAB per the ASCE, IBC, or NBCC?

Live load reduction is not considered automatically in RFEM. RFEM and RSTAB are general FEA and framework programs. The program does not understand what is a floor element vs wall element. Only a general plate element is defined. It is not possible for the program to determine the area of a floor for live load reduction.

A user must manually consider the reduction by modifying the live load magnitude directly in the load application.

• ### Is it possible to perform fire resistance design of cross-laminated timber panels in RF‑LAMINATE?

Fire resistance design is not implemented in the RF‑LAMINATE add-on module by default.

However, you can calculate the charring rates yourself and consider them accordingly in the module. In the following example, this is explained on a simple plate.

Structural system (Figure 01):

• Span 5 m
• Plate width 2 m
• LC2 (medium) 2.5 kN/m²
• 3 layers
• S1 35 mm C24
• S2 20 mm C24
• S3 35 mm C24
The information regarding the correction factors and stiffnesses can be found in the attached file.

Factors for fire resistance:

• Charring rate ß0 = 0.65 mm/min
• Pyrolysis zone k0d0 = 7 mm
• Charring time t = 30 min
• Effective thickness def=t ß0+k0d0=30 min × 0.65 mm/min+7 mm = 26.5 mm
Remaining thickness of Layer 3 = 35 − 26.5 = 8.5 mm > 3 mm → thickness may be applied. (Figure 02)

Because of the modified layer thicknesses, a new stiffness matrix results, which is applied in RFEM for accidental combinations with the characteristic stiffness values. For the ultimate limit state, the design values are calculated here (Figure 03).

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#### First Steps

We provide hints and tips to help you get started with the main programs RFEM and RSTAB.

#### 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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