Composite analysis and design extensions
Composite analysis extensions in SCIA Engineer v17.0 focus on two main steps in the design process:
- the creation of code-compliant load combinations;
- the use of rigid diaphragms on the level of the FE analysis.
Creating load combinations is a necessary task in the design workflow. The question is whether this task should not be fully automated, considering that it is pretty straightforward and very well-defined in the relevant design norms. In the context of composite design, such automation is needed even more, because different construction stages need to be considered, and even self-weight varies between the stages of construction and exploitation.
Diaphragms provide clearer results and faster calculation, because they simplify the analysis model. This simplification lies on a few reasonable assumptions, all of which are based on decades of engineering experience. The choice to use diaphragms lies with the design engineer. Using diaphragms in your model is like automating engineering judgement in CAE computation routines.
In addition, composite cellular beams can now be analysed. Support for cellular beams is important in the context of composite design, because without the web openings, composite floors cannot accommodate all the needed services while remaining cost-effective.
Code-based load combinations can now be managed in the background: based on the loads defined on the structure, SCIA Engineer creates, tracks, and dynamically updates a set of necessary load combinations for composite design.
Construction stages and the increased weight of fresh concrete are taken into account, thus eliminating the need for the user to figure out, create and keep up-to-date load combinations.
Rigid in-plane diaphragms combined with tributary-area distribution for gravity loads offer a good approximation of the actual behaviour of composite slabs. These two analysis extensions offer the user a way to obtain clear and verifiable results while reducing computation time.
Composite cellular beams are now supported on analysis level; these can also be designed according to the British and Irish NA via a bi-directional link to the CellBeam* design tool provided by the British fabricator Westok.
Automatic load combination generation
For a structure with composite floors, there is practically only one correct set of code-based load combinations that should be defined. But the possible mistakes are many. This is why we decided to offer full automation on the level of load combination generation for composite projects. This makes composite design in SCIA Engineer clearer and easier for the user.
The user can now specify if he would like for combinations to be managed by the software. Based on the load cases that exist in the model, a set of combinations will be generated and load cases will be assigned according to their stage.
Automatic generation of (staged) combinations is supported according to the ASCE 07 and to the EN 1990 code. Four code combinations will be created in the case of IBC design (ultimate and serviceability for both construction and final stages), whereas five are needed for EuroCode design (an accidental combination for fire design is generated in addition).
Once created, combinations are automatically updated. If the user adds more loads or new load cases, these will also be included without any action on the user side. The user may disable the update. He can also edit the generated combinations manually, if needed. This will prevent any future updates of the edited combinations.
Automatically generated and manual combinations can coexist in one model without any limitations.
FE analysis extended with diaphragms
Flexible diaphragms have also been provided; these are useful for the modelling of steel decking roofs. Such roofs are often found in buildings where the floors are composite, but the pouring of a concrete slab for the roof is, in most cases, not financially justified.
The user can actually choose between three diaphragm types:
- a rigid diaphragm behaves as an infinitely stiff body for in-plane loads;
- a semi-rigid diaphragm uses the actual physical properties of the slab to derive the response for in-plane loads;
- a flexible diaphragm distributes in-plane loads as a load panel, disregarding the stiffness of vertical load bearing elements.
Diaphragms distribute gravity loads as a load panel. By default, the method of gravity load distribution is set to tributary area; however, a more accurate FEM approach is available as well.
In addition, the new development allows for the type of slab to be switched easily between a diaphragm with load-panel action, a standard FE-meshed slab, and a simple load panel (without stiffness of weight). This gives more flexibility to the user to perform different types of analytical verifications while still using the same model.
FE analysis extended with cellular beams
The user can now model and analyse composite slabs that are supported on cellular steel beams.
The stiffness of composite beams in SCIA Engineer already takes into account the contribution of a partially-connected concrete slab; in the case of cellular composite beams, this stiffness is now also reduced to take into account the presence and geometry of openings in the web.
Composite cellular beams can also be used in combination with diaphragms.
Design extensions within SCIA Engineercomposite functionalities include the following:
- A bi-directional link with the software CellBeam from the British manufacturer Westok;
Deflection limits can now be overwritten per a beam; this is often necessary for façade beams, where stricter deflection requirements may apply.
- Descriptions (notes and images) were attached to composite settings in the Setup. The user can consult these if he is not sure what a particular setting is intended for.
* Westok production limitations apply.