#### Further Information

In addition to our technical support (e.g. via chat), you’ll find resources on our website that may help you with your design using Dlubal Software.

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• ### 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?

New

FAQ 004349 EN-US

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).
• ### Is it possible to perform a detailed analysis of connections, supports, or reinforcements of cross‑laminated timber plates in RF‑LAMINATE?

In principle, it is also possible to perform detailed analysis in RF‑LAMINATE. In the case of a very high shear distortion, for example, it can be reasonable to use orthotropic solids for modeling. The video shows a simple modeling and result evaluation of a layer structure by using solids.

A criterion, as of when is the modeling using solids useful, is the shear correction factor. Further information and other criteria can be found in the following FAQ:

• ### How can I consider the flexibility of a continuous beam with slotted dowel connections?

The easiest way to consider this is to use the RF-/JOINTS Timber Steel to Timber module. For this purpose, the module decomposes the original connection, and creates a new structural system that considers the flexibility accordingly. This is taken into account separately for load-bearing capacity, suitability for use, and exceptional.
• ### Where can I set the Poisson's ratio?

New

FAQ 004341 EN-US

The Poisson's ratio is set under the material by using the Edit Material dialog box.
• ### When displaying the result diagrams on a member (the "rib" type), there is the option to display the internal force VL. What is this value and how is it calculated?

New

FAQ 004340 EN-US

The force VL is the longitudinal shear force between the top surface and the member. It is calculated as an integrated shear flow between the plate and the member at a particular point on the member.

For the simplified example provided here, the resulting cross-section values for the integration width of 10 cm are as follows:

• $I_y=\frac{b\times h^3}{12}=\frac{10 cm\times20 cm^3}{12}=6,666.67 cm^4$
• $S_y=h_1\times b\times((h-e_z)-\frac{h_2}2)=10 cm\times10 cm\times((20 cm-10 cm)-\frac{10 cm}2)=500 cm^3$
• $\tau=V_L=\frac{V_z\times S_y}{I_y\times b}=\frac{5.53 kN\times500 cm^3}{6,666.67 cm^4}=0.415 kN/cm=41.5 kN/m$
The integration width has been set to the total of 10 cm.

Values:
• Iy second moment of area
• Sy statical moment
• h1 height of the upper cross-section part
• h2 height of the lower cross-section part
• ez centroidal distance
• h total height
The values can be adjusted for a T-beam.
• ### I design a combined structure made of timber materials with different creeping parameters. How can I perform the serviceability limit state design according to EN 1995‑1‑1?

New

FAQ 004325 EN-US

In RFEM and RSTAB, the simplified design from [1], Chapter 2.2.3, have been implemented for the automatic load combinations. This means that strictly speaking, only structures concerning the final deformation may be analyzed, in which materials with identical creep behavior occur since the creep deformations are considered in a simplified way on the load side. If the structure is a mixed structure made of wood with different creep properties or in combination with steel, the final deformations must be determined according to [2] Amendment to 2.2.3 as follows:

'(4) If a structure consists of structural components or components with different creep properties, the long-term deformations should be calculated according to 2.3.2.2 (1) due to the quasi-permanent combination of actions with the final values of the mean values of the corresponding elasticity, shear, and displacement modules. The final deformation ufin is then calculated by superposition of the initial deformation due to the difference of the characteristic and quasi-permanent combinations of actions with the long-term deformation.'

However, this requires a superposition of results from different load combinations, which cannot be implemented automatically in RFEM and RSTAB.

If the different creep properties are to be taken into account, the load combinations must be created manually, and the stiffness must be reduced according to the creep coefficient.
The procedure is described using the example of a timber-concrete composite floor presented on the Info Day 2017. Below this FAQ, you can find the link for this.

• ### Is the Gust-effect (G or Gf) from the ASCE 7-16 Sect. 26.11 considered in RWIND Simulation?

In the ASCE 7-16, the conservative value for the Gust-factor, G, is 0.85 for rigid buildings. The engineer can calculate an alternative and more accurate value. The Gust-effect, Gf, for flexible buildings accounts for size and gust size similar to rigid buildings but also considers dynamic amplification including wind speed, natural frequency, and damping ratio.

The Gust-factor G or Gf, is considered to be 1.0 in RWIND Simulation. The structure is rigidly simulated in the numerical wind tunnel. The loads which are transferred back into RFEM are applied to the elastic structure with true stiffness considered.

To account for any value other than 1.0 for this factor, the wind load case factor can be adjusted in RFEM under the applicable load combination.
• ### According to DIN EN 1995-1-1/NA, the crack factor kcr may be increased by 30% for softwood in areas at least 1.50 m from the end of the timber grain. How to implement it in RF-/TIMBER Pro?

New

FAQ 004298 EN-US

The increase of the crack factor kcr still has to be done manually because the program does not know where the end of the grain is defined. To do this, divide the member by 1.5 m from the end of the grain so that the affected areas can be designed as a separate member (see Figure 01).

Two design cases are now required (File → New Case ...). In case 1, members within the 1.5 m are selected for the design. In case 2, it is necessary to select the members where the 30% needs to be considered. Then, in case 2, the kcr value is adjusted manually in the settings for the National Annex. Thus, a kcr of 0.65 results for C24, which is entered as shown in Figure 02. The design is carried out this way with an increased kcr value.
• ### How to control an overpressed joint in the ridge?

An overpressed joint between two members can be controlled in RFEM by means of the member stress results. For members, this stress result represents the effective stress as a color gradient across the member surface depending on the assigned cross-section.

Figure 01 - Stresses on Members

Based on the local member axis, the member stress result gives the following stress components and reference stresses with an associated color palette:

• Stress
• σx
• τy
• τz
• Elastic stress component
• σN
• σMy
• σMz
• σN+My
• σN+Mz
• σM
• Elastic equivalent stresses
• σv,Mises
• σv,Tresce
• σv,Rankine
• σv,Tresca+Rankine
• σv,Bach

Using active displaying for the members connected to the joint, and displaying the σx stresses, it is possible to visualize the state of stress on and thus also between the members. If only negative stresses occur in the area between the members, the joint is overpressed.

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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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