Virtual Joist

 

15.2

SCIA Engineer v15.2 brought out integrated design checks for Open Web Steel Joists (OWSJ) in compliance with the specifications issued by the Steel Joist Institute (SJI). An OWSJ is a light-weight steel trust which normally consists of parallel chords and a triangulated web system.

The virtual joist element in SCIA Engineer allows for the joist stiffness to be correctly incorporated in the FE model. A library of virtual steel joists was added to the Section Library of SCIA Engineer. The user may now assign a joist section to beams in the 3D model, and design and optimise them based on the virtual joist method. The joist that fulfils all ULS and SLS requirements is determined via an optimisation routine and carries the standardised joist designation as used by the SJI.

Introduction

In structural engineering, the Open Web Steel Joist (OWSJ) is a lightweight steel truss consisting, in the standard form, of parallel chords and a triangulated web system, proportioned to span between bearing points. The main function of a steel joist is to provide direct support for roof or floor deck and to transfer the load imposed on the deck to the structural frame i.e. beam and column. A standard joist designation includes the value of the depth, chord size, and the joist series. The Steel Joist Institute (SJI) supplies tables to allow engineers to select a joist designation based on load and span requirements. This designation can then be given to a joist manufacturer who is responsible to produce a joist which is able to meet the design requirements. Because of this, structural engineers have historically not been able to incorporate joists with known realistic physical properties into their building models. To allow engineers to incorporate joists with physical properties into the building model, the Steel Joist Institute (from US) has developed a table of virtual joists which have “equivalent I-beam” cross sectional properties. The virtual joist component of SCIA Engineer allows the engineer to incorporate joist member stiffness in the overall model, making the analysis of the overall building system more accurate. The joist members can be checked and auto-designed and are given a realistic joist designation consistent with expectations from joist manufacturers and the SJI.

Highlights

Joist and joist girder member stiffness can be accounted for in the overall model, making the analysis of the overall building system more realistic and accurate.

Using virtual joists and joist girders provide a more accurate estimate of appropriate joist depth and weight when sizing joists for special loading.
In lateral load resisting frames that use joists, member end forces and member end moments can be realistically calculated in the model
SCIA Engineer has the unique ability to design special joists, consistent with expectations from steel joists manufacturers and the SJI. A joist determined to be special, is given a designation which includes the depth of the virtual joist and a diagram showing the actual loading on the joist member.
Checks are performed according with the American codes and a detailed calculation note includes all used formulas, tables and references.
Wide library of profile sections according with the standard load tables (joist: K, LH, and DLH joists or KCS). SCIA Engineer 15.2 includes the latest full libraries of Virtual Joist and Virtual Joist Girder cross-sections.
An automated optimisation procedure (AutoDesign) selects suitable profiles depending on load conditions, internal forces and the set of preferred profiles indicated by the user.
Mapping virtual joist with real joist.
SCIA Engineer utilizes its transparent Design Forms technology to assign a realistic designation to each joist and joist Girder member based on how the member is loaded. This designation can easily be included in the engineering report and given to the joist manufacturer.

Presentation of the design process

  • User selects an initial member from the virtual joist available in the profile library.

  • Linear calculation and unity check can be performed according with Steel Code Check
  • Auto-design functionality is available. The user will select the criteria for which they wish to optimize the joist – depth, weight, or moment of inertia. If weight is selected, a depth must be specified.

  • The user can update his model based upon the recommended optimal joist size and re-run the analysis.
  • The user must specify the design method they wish to use (ASD or LRFD). For joists with uniform load that receive a standard designation, the user may select a preference for which standard joist series to use as well as a preference on how to sort joists within the standard table.

Presentation of results

  • Checks according with steel code checks.
  • Final designation of the joist will consist of both the virtual joist name and a realistic designation to each joist and joist Girder member based on how the member is loaded.
  • Transparency of the result. This designation can easily be included in the engineering report and given to the joist manufacturer.

Conclusions

The virtual joist functionality within SCIA Engineer delivers capabilities that span the gap between traditional design procedures used by engineers and detailed analysis done by manufacturers. As a result, users can optimize structures with complex geometry and loading conditions, while also providing joist designations that are in line with today’s standards.

Required modules

esasd.01.05

19/10/2015