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Author
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Dalel Daleyev
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University
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Vienna University of Technology, Austria
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I-Joists in Timber - Discussion of Current Design Practice and Implementation in Structural Analysis Software
Finnjoists or I-joists are optimized composite beams with an I-section made of timber materials, where the flanges are made of laminated veneer lumber (LVL) and the web of OSB. The cross-section elements are glued together. The components can be used as a beam or a column. In this bachelor thesis, the simplified design practice of the European Technical Approval ETA 02/0026, based on the limit internal forces, is compared with the more general design practice according to ÖNORM B 1995‑1‑1:2019, based on the limit stresses, and checked for consistency of the results.
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Using the Timber Design add-on, timber column design is possible according to the 2018 NDS standard ASD method. Accurately calculating timber member compressive capacity and adjustment factors is important for safety considerations and design. The following article will verify the maximum critical buckling strength calculated by the Timber Design add-on using step-by-step analytical equations as per the NDS 2018 standard including the compressive adjustment factors, adjusted compressive design value, and final design ratio.
The three types of moment frames (Ordinary, Intermediate, Special) are available in the Steel Design add-on of RFEM 6. The seismic design result according to AISC 341-22 is categorized into two sections: member requirements and connection requirements.
To evaluate whether it is also necessary to consider the second-order analysis in a dynamic calculation, the sensitivity coefficient of interstory drift θ is provided in EN 1998‑1, Sections 2.2.2 and 4.4.2.2. It can be calculated and analyzed using RFEM 6 and RSTAB 9.
The coefficient θ is calculated as follows:$$\mathrm\theta\;=\;\frac{\displaystyle{\mathrm P}_\mathrm{tot}\;\cdot\;{\mathrm d}_\mathrm r}{{\mathrm V}_\mathrm{tot}\;\cdot\;\mathrm h}\;$$
The coefficient θ is calculated as follows:$$\mathrm\theta\;=\;\frac{\displaystyle{\mathrm P}_\mathrm{tot}\;\cdot\;{\mathrm d}_\mathrm r}{{\mathrm V}_\mathrm{tot}\;\cdot\;\mathrm h}\;$$
The Steel Design add-on in RFEM 6 now offers the ability to perform seismic design according to AISC 341-16 and AISC 341-22. Five types of seismic force-resisting systems (SFRS) are currently available.
Using the "Beam Panel" thickness type, you can model timber panel elements in 3D space. You just specify the surface geometry and the timber panel elements are generated using an internal member-surface construct, including the simulation of the connection flexibility.
The building model is calculated in two phases:
- Global 3D calculation of the global model, where the slabs are modeled as a rigid plane (diaphragm) or as a bending plate
- Local 2D calculation of the individual floors
After the calculation, the results of the columns and walls from the 3D calculation and the results of the slabs from the 2D calculation are combined in a single model. This means that there is no need to switch between the 3D model and the individual 2D models of the slabs. The user only works with one model, saves valuable time, and avoids possible errors in the manual data exchange between the 3D model and the individual 2D ceiling models.
The vertical surfaces in the model can be divided into shear walls and opening lintels. The program automatically generates internal result members from these wall objects, so they can be designed as members according to any standard in the Concrete Design add-on.
You have the option to perform the fire resistance design of surfaces using the reduced cross-section method. The reduction is applied over the surface thickness. It is possible to perform the design checks for all timber materials allowed for the design.
For cross-laminated timber, depending on the type of adhesive, you can select whether it is possible for individual carbonized layer parts to fall off, and whether you can expect increased charring in certain layer areas.
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Among others, the following cross-laminated timber manufacturers are available in the layer structure library:
- Binderholz (USA)
- KLH (USA, CAN)
- Kalesnikoff (USA, CAN)
- Nordic Structures (USA, CAN)
- Mercer Mass Timber
- SmartLam
- Sterling Structural
- Superstructures listed in Lignatec Edition 32 "Cross-Laminated Timber of Swiss Production"
By importing a structure from the layer structure library, all relevant parameters are adopted automatically. The library is continually updated.
What does each option do under the "Calculation of Torsion" section under the Strength Configuration settings?
Which Dlubal software products do you recommend for the structural analysis and design of timber structures in particular?
What is the difference between the RANS, URANS, and DDES turbulence models?
How can I model a timber beam with stiffening on both sides? (splice)
How can I generate an area load on members via cells in RFEM 6 or RSTAB 9?
What is the most accurate CFD method for the wind simulation of parapets?
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