EN 1994 composite design extensions in SCIA Engineer 16.1
Version 16.0 of SCIA Engineer saw the release of an integrated composite design module (esacbd.01.01) according to EN 1994-1-1:2004. The unique about the released functionality was the integration of code-based member verifications into advanced design workflows, such as slab based finite element analysis including nonlinearities. The consequence was that the user could now use the same platform for the creation of sophisticated models in an advanced 3D analysis environment while, in that same platform, run design checks and code-compliant optimisation on all or selected members from the 3D model.
The functionality that translates advanced finite element analysis (FEA) into output that can be streamlined for code-specific checks is known as the Composite Analysis Model (CAM). The CAM ensures that:
- the stages of construction (and exploitation) are reflected in the analysis;
- the influence of creep is taken into account for long-term loads;
- the composite deck is represented in the 3D model by realistic stiffness in all directions;
- the composite deck and supporting beams are (partially) connected, resulting in additional stiffness against bending in the beams;
- sheeting contributes to the stiffness of the structure in both construction and final composite stages, also keeping sheeting orientation in mind;
- primary and secondary beams are recognised and treated differently during, e.g., the determination and layout of studs;
- the composite deck and beams are modelled in such a way that no axial forces exist due to eccentricities (because the code only describes the verification of bending moment and shear force);
- beam effective widths are automatically calculated such that the internal forces in the beams contain the integrated stresses in the slab within the effective width.
When composite decks are present in your model, the software knows that a staged analysis should be performed. Different load cases are calculated with different stiffness, based on when these loads are first applied on the structure (in construction or final stage) and (2) what the duration of these loads is (short or long term). From a modelling perspective, the composite slab consists of a shell with partially connected rib elements. Additional modelling tricks are put in place to take into account the specific detailing and behaviour of composite structures.
In an effort to continually expand the software’s functionality, the latest version of SCIA Engineer brings further extensions to the composite workflow. The following sections outline the extensions to the module for composite design (esacbd.01.01) in version 16.1.
Provision for the weight of fresh concrete
Fresh concrete weighs more due to its high water content; it is estimated that the density of concrete is around 4% higher in the fresh state than in the dry state. In addition to that, the dead weight of fresh concrete should be considered as a variable load (with corresponding load factors in limit state design) due to the delivery methods and the fact that liquid concrete can heap on top of an individual sheet of deck or beam.
In version 16.1 of SCIA Engineer, the following functionality is added in order to properly account for the weight of fresh concrete:
- The material properties of concrete have been extended with an additional (editable) property "Density in fresh state." By editing this value, the user may specify how much the nominal concrete density should be increased during the construction stage;
- The increased self-weight of fresh concrete is taken into account in the construction stage. The weight of all other load-bearing elements and materials remains unchanged in both construction and final stage.
- The necessary load cases pertaining to the self-weight of the structure are created automatically and assigned to the correct stage (construction or final).
- The weight of fresh concrete is, by default, considered as a variable load on the structure due to the possibility of heaping during pouring; however, the user may edit this and consider the weight of fresh concrete as a permanent load;
- Precautions are taken to ensure that the user cannot, by mistake, include both concrete weights (fresh and final) in the same result class (and thus account for the concrete twice).
NCCI PN001a-GB alongside the BS NA
The SCI publication “NCCI: Resistance of headed stud shear connectors in transverse sheeting” is used in the UK in addition to the NA of EN 1994-1-1. It prescribes a modification to the shear resistance of welded studs in a composite slab, taking into account the geometry and behaviour of more modern steel sheeting.
NCCI PN001a-GB has been written based on test data from the period between 2006 and 2008. At the time, the need arose to investigate the behaviour of composite decks made with modern steel sheets (whose geometry is much more sophisticated, with various stiffeners on walls that are as a rule more slender). It was found that the Eurocode 4 calculation of shear stud resistance may be unsafe in the case when two studs are welded to the troughs of commonly-used modern profiles.
SCIA Engineer now takes into account the reduction factor prescribed in this publication when the NA of the ESA project is set to the United Kingdom. By supporting NCCI PN001a-GB, the composite module esacbd.01.01 complies to both the international code and the common engineering practice in the region.
This development is in line with SCIA strive to react to new tendencies in design practice and modern construction.