Design of composite members according to AISC 360-10 in SCIA Engineer 15
The new release 15 of SCIA Engineer features a comprehensive solution for the 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 the 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 concrete slabs.
The AISC 360-10 stipulates which parts of a composite slab can be considered to contribute to the strength and stiffness of a composite beam. In SCIA Engineer 15, the effective width of a composite beam is automatically calculated. This includes an 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 the 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 the beams. As a result, normal forces are generated in both beam and deck as a result of the actual eccentricity of the 1D member. The latter approach is useful if horizontal loads could lead to additional bending in the composite beams.
No limitations are stipulated 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 the slab – composite beams are analysed accurately without any additional user input.
Finally, a shear stud library, as well as a steel decks library with common profiles from US manufacturers are also provided.
The design of composite beams is performed according to AISC 360-10 standard and includes the following features:
- Ultimate limit states (ULS) design checks are performed for both construction and composite stages.
- Both the Load and Resistance Factor Design (LRFD) and Allowable Strength Design (ASD) methods are supported for checks in the ULS.
- Positive & negative flexural strength is evaluated per AISC 360-10, Chapter I2.
- The contribution of concrete slabs to the resistance of steel beams in the final composite stage is taken into account via calculated effective width;
- Shear strength (including shear buckling) is evaluated per AISC 360-10, Chapters I4 & G2.
- The strength of shear connectors is evaluated per AISC 360-10 Chapters I3b & I8.
- Other detailing provisions (related to concrete slab, steel deck and shear studs) are taken into account as per AISC 360-10 Chapter I.
- Serviceability limit state (SLS) checks are performed for both the construction and final (composite) stages.
- Camber can be set as an absolute value or as a value relative to the span length.
- All unity checks values may be plotted along the beams in the 3D view, or listed in tables.
Main advantages of the composite module
- The multi-model approach of the Composite Analysis Model allows for parallel checks for construction and composite stages to be performed without modifications to the model.
- A 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 the 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.
- Support for both longitudinal and transverse alignment of the steel sheeting
- 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 be listed in tables.
- A brief calculation output in table form.
- A detailed calculation output with rendered formulas and intermediate calculation steps.