Design of composite members according to EN 1994 in SCIA Engineer 15
The new release 15 of SCIA Engineer features a comprehensive solution for modelling, analysis and design of composite-beam floor systems. This new development meets the two principle demands that engineers put forward when working with composite structures:
- the accurate structural analysis in a 3D FEM environment,
- the code-based design of individual structural entities (ULS and SLS checks).
Accurate FEM-based calculation
The Composite Analysis Model (CAM) in SCIA Engineer analyses the entire structure during stages of construction, service, and maintenance. Deformations and load effects obtained from different stages are superimposed, taking into account the presence or lack of composite action and creep in the concrete slabs.
The EN 1994-1-1 standard stipulates which parts of a composite slab can be considered to contribute to the strength and stiffness of the composite beam. In SCIA Engineer 15, the effective width of the composite beam is calculated automatically. This includes the automatic detection of:
- span length;
- distance to neighbouring elements in the 3D model (i.e., other beams, openings),
- distance to slab edges;
The Composite Analysis Model calculates the exact orthotropic properties of corrugated steel decks and composite slabs (corrugated steel deck & concrete topping). These orthotropic properties, as well as the augmented contribution of the steel beams (depending on the degree of composite action), are used in the FEM calculations.
Internally, the calculation distinguishes between three FEM submodels (with different stiffness of the composite slabs) – one for the construction stage and two for the final (composite) stage. The stage-based model evaluates rheological effects (i.e., creep) by distinguishing between long and short-term load cases in the final (service) phase.
The functionality supports two possible ways of modelling of steel ribs in a composite slab. The first one (a "standard composite action") overrules any parasitic normal forces that may arise from eccentricity between the slab and beam in the FEM model. This idealisation is suitable for majority of composite floors. The second one (an "advanced composite action") uses the actual cross-section properties and alignment of beams. As a result, normal forces will be generated in both beam and deck as a result of the actual eccentricity of the 1D member, also taking into account the degree of composite action). The latter approach is useful if horizontal loads could lead to additional bending of the composite beams.
No limitations are imposed on the structural system, span type, or arrangement of beams in the slab. Composite beams may be simply supported, continuous, or cantilevers. Regardless if these are parallel or with arbitrary orientation within a slab – composite beams will be analysed accurately without any additional user input.
Finally, a shear stud library, as well as steel decks libraries with common profiles from European and North American manufacturers are also provided.
The design of composite beams is performed according to the EN 1994-1-1 standard and includes the following features:
- Ultimate limit states (ULS) design checks for both the construction and composite stages;
- Positive and negative flexural capacity of the composite beams (evaluated as per EN 1994-1-1, Chapter 6);
- Contribution of concrete slabs to the resistance of steel beams in the final, composite stage (taken into account via calculated effective width);
- Shear lag taken into account at multiple locations along the beam (in effective-width calculations for the composite stage as per EN 1994-1-1, 22.214.171.124);
- Section classification of the steel beam in the composite stage (as per EN 1993-1-1, 5.5.2);
- Shear connector capacity and effect of number and strength of connectors on the overall beam resistance (evaluated per EN 1994-1-1, 6.6.4);
- Verification of longitudinal shear (as per EN 1994-1-1, 126.96.36.199);
- Verification of crushing of concrete flange (as per EN 1992-1-1, 6.2.2 (6));
- Shear capacity and shear buckling of composite beams (evaluated per EN 1993-1-1, 6.2.8 based on the steel section);
- Serviceability limit state (SLS) checks for the final (composite) stage.
Main advantages of the module for design of composite members
- The multi-model approach of Composite Analysis Model allows for parallel checks for construction and composite stages to be performed without modifications to the model.
- The partial connection between composite slab and steel beams will be taken into account both during the FEM analysis and in the design checks.
- Creep in concrete slabs is taken into account during the FEM analysis (using a modular ratio for the concrete Young's modulus).
- Calculated resistances are based on a plastic distribution of stresses in the section.
- Section classification takes into account the actual position of the neutral axis in the composite cross-section.
- Support for both longitudinal and transverse alignment of the steel sheeting
- Additional checks control minimal degree of shear connection, minimum area of longitudinal reinforcement as per EN 1994-1-1 5.5.1(5), etc.
- National annex support.
- Detailing provisions, e.g., on the spacing and diameter of shear connectors, are taken into account.
- All unity checks values may be plotted along the beams in the 3D window, or listed in tables.
- Brief & summary calculation outputs in table form.
- A detailed calculation output with rendered formulas, intermediate calculation steps, realistic dynamic drawings of the composite system, of the derivation of plastic moment resistance and location of plastic neutral axis.
The composite functionality benefits from a number of already existing functionalities in SCIA Engineer:
Limit state design based on partial safety factors in accordance with EN 1990;
- Actions in accordance with EN 1991; combination of actions in accordance with EN 1990;
- Action effects calculated in an elastic global analysis (in the Composite Analysis Model environment).
- Negative flexural strength can only be evaluated for beams with full composite action (as specified in EN 1994-1-1).
- Beams of section classes 1 and 2 are supported.