Composite design in SCIA Engineer 15.3
SCIA Engineer 15.3 includes new development in the composite beam design modules for EUROCODE 4 (esacbd.01.01) and AISC 360 (esacbd.01.05). The newly-added improvements broaden the scope of these verification tools and ensure a reliable building design that covers domains such as fire safety and lateral-torsional buckling.
Steel decking in the spotlight
The composite functionality is now seamlessly integrated with a universal steel decking library in SCIA Engineer. As a result:
- Steel sheeting assigned to a composite slab can now also be taken into account when running SCIA Engineer's steel design modules (such as esasd.01.01). In the construction stage (when the concrete does not contribute as a load-bearing element), the presence of decking will result in an increased torsional stiffness of the steel section. This will be taken into account in the lateral-torsional buckling verification of the steel beam (as described in Stahlbau nach DIN 18800, E. Kahlmeyer).
- Integration with the steel design modules ensures that the overall building stability in the construction stage can be verified and that diaphragms will contribute to the overall load-bearing capacity during this verification.
Usability improvements in the steel decking library make it quicker and easier for the user to:
- Select suitable decking from a catalogue of European, British and North American manufacturers. When the user first opens the steel sheeting library, he/she is directly prompted to select a sheet from an extensive database of products from established steel decking suppliers.
- Filter according to manufacturer or according to other criteria (a wildcard filter is also available). Filtering is possible in the main database as well as in the local set of sheets that are saved inside the model.
- Further extend the decking library with sheets of arbitrary geometry.
SCIA Engineer offers a unique solution for the analysis of composite floors which takes into account, on the level of finite element model:
- the stiffness of the composite slab and
- the (partial) shear connection between steel beams and concrete slab.
As a result, some numerical effects can be expected. Bending moments may occur in hinged locations on the beams if no hinges are defined in the concrete slab. In addition, floor loads can be transferred from the slab directly to the supporting columns, thus slightly reducing the internal forces in the beams (up to 10 %).
To tackle these issues, version 15.3 of SCIA Engineer brought a special "one-way" finite plate element for the modelling of composite slabs. A one-way deck ensures:
- that parasitic bending moments at the ends of, e.g., simple beams are avoided;
- that all loads are first transferred to the secondary beams, which in turn transfer load to the primary beams as concentrated forces;
- that results from SCIA Engineer's Composite Analysis Model are closer to hand calculations based on simplified load paths.
- Stiffness in the weakened direction of the slab is compensated by increased stiffness of the beams in order to obtain a realistic behaviour of the floor as a whole.
- The user may adapt the reduction factor that is used to modify the stiffness in the weak direction or he/she can switch the "one-deck" option off.
Lateral torsional buckling
Previously provided for composite design according to AISC 360 only, lateral-torsional buckling (LTB) checks are now performed in verifications according to EN 1994-1 also. The following methods are used:
- For LTB in construction stage: a relative LTB slenderness is calculated according to ECCS 119, Annex C;
- For LTB in exploitation stage: a relative LTB slenderness is calculated according to a simplified method in the Designers' guide to EN 1994-1-1 (Article 6.4.3).
- LTB checks are also performed under fire conditions.
Structural fire design
SCIA Engineer 15.3 includes a comprehensive fire safety verification according to EN 1993-1-2 & EN 1994-1-2 for both construction and final (exploitation) stages.
- Structural design at elevated temperatures is accessible from the Composite service along with the analogical checks at ambient temperature.
- Additional data for fire design (fire duration, fire protection, and type of fire exposure in the section and along the length) can be defined per composite beam.
- The air temperature development over time is considered as described in ISO 834.
- The temperature evolution in steel and concrete, as well as the corresponding temperature-dependent material properties are evaluated at an interval equal to 5 seconds for unprotected beams and 25 seconds for insulated ones.
- Heat insulation (paint) can be assigned to the steel surface.
- To determine the temperature gradient in the steel cross-section, the steel profile is split into flanges and a web; if a reduction of the compressive strength of concrete is required (in regions where the temperature exceeds 250° C), heat-affected zones in the slab are determined by dividing to layers of 10 mm, with each layer having different strength parameters as a function of the temperature in it;
- Verifications of bending and shear capacity are performed according to EN 1993-1-2 and EN 1994-1-2. LTB checks are performed in both construction and final stages, although these are not strictly required by the code.
- Checks of failure in longitudinal shear in the slab or in crushing of the concrete flange are performed in the composite stage.
- A detailed theoretical background document is also provided
SCIA Engineer now supports the simplified approach for limitation of crack widths in composite slabs described in EN 1994-1-1, §7.4. 2 and §7.4. 3.
- The method ensures that the cracks are limited to an acceptable width if a minimum reinforcement is provided, and either a bar diameter or the bar spacing is limited.
- A calculated minimal reinforcement is compared to the one provided by the user and a warning is sent if both the bar diameter and bar spacing do not comply with the recommendations of EN 1994-1-1, §7.4. 3..
- This new verification extends the scope of the offered SLS limit state verification for composite structures.