AISC 360 & AISI S100 design



Year 2016 saw the update of two very important design codes for steel and composite structures: the ANSI/AISC 360-16 Specification for Structural Steel Buildings, and the AISI S100-16: NA Specification for the Design of Cold-Formed Steel Structural Members. We took care to react to these code updates timely, and v17.0 of SCIA Engineer now includes the modifications published in these latest code editions.

Related to the analysis of composite floors, 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 to automatic load combinations and support for diaphragms, a number of small improvements were made in composite design functionalities with two main objectives:

  • to speed up the use of this design module in terms of learning and daily use;
  • to give more options to the user to customise his composite structure.
The steel design specifications AISC 360-16 and AISI S100-16 are now supported in SCIA Engineer.
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.
More possibilities for the FE analysis of composite floors are provided, with focus on rigid and flexible diaphragms and support for cellular composite beams.
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.
A clearer and more customisable composite design workflow simplifies learning and the daily software use and provides more flexibility to the designer.

New versions of North American steel design codes

SCIA Engineer now supports AISC 360-16 and AISI S100-16. Adapted formulas and coefficients were taken into account in the Steel code check; also references, notation and terminology were changed to correspond to the current versions of the two design publications.

An advantage of using the latest code version is, for example, that one can make use of the inelastic reserve for distortional buckling failures when designing cold-formed steel members. This leads to more economic designs and optimised material use.

Composite design extensions

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.

Composite design workflow improvements

Design-related settings for the whole structure (Composite Setup) and for individual members (Composite Beam Data) were extended:

  • The type of stud and reinforcement grade can now be set for all composite floors in the structure with a single click.
  • The user can overwrite the minimal and maximal spacing of studs, both on the level of the whole structure or per a beam; this is important when the contractor wants to set custom requirements for the execution on site.
  • 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 all composite settings. The user can consult these if he is not sure what a particular setting is intended for.
  • Check-boxes were introduced in the Composite Setup for settings that previously used YES/NO drop-down lists.

Other small improvements include:

  • At the creation of a composite beam, the effective width is set to 'calculated' by default. This saves the user the additional click and prevents mistakes of the sort of using a hard-coded value of the effective width that does not depend on the beam span.
  • Composite beams are now skipped when running the Steel Code Check. This ensures that the optimisation of steel-only members will never overwrite the results of composite optimisation.