Having reviewed the example above this is a question you might ask. The main point to bear in mind is that the example is unusual/extreme. Concentrated loads and dominant openings are not the norm.
The main disadvantage of the FE method is speed. When there are a large number of slabs, there are a correspondingly large number of plates required and the analytical models (even though it is one floor at a time) get big and hence slow.
Comparisons of uniformly loaded slabs have shown excellent correlation between the traditional (yield line) and FE methods, so you may find it easier to continue using the traditional method for much of your work.
If you think about the differences the FE method makes, you will be able to decide when it might be more appropriate - clearly the FE method is better if you have to deal with significant holes and/or isolated loading.
Ultimately, neither method is going to suit everybody all of the time. For this reason you can pick and choose on a beam by beam basis if you wish, or you can design all the beams using one method and then check them using the other. When checking you can use the option to select new steel when previous bars are insufficient so that you end up with all beams designed for the worst case from either load decomposition method.
Note In the FE method beams are replaced by a line of fully fixed supports. As a consequence, in ordinary regular slabs both the yield line and FE method will share loads equally to internal and edge beams. In other words continuity is not being considered. This is a simplification that has long been accepted in hand calculations.
A more extreme example of the above would be a cantilever slab. The beam adjacent to the cantilever takes the entire cantilever slab load, plus half of the internal slab load, for long cantilevers that can be a significant under estimate.
The only way to account for continuity in such a case would be to run an FE chasedown analysis and then merge the resulting beam loads. This method deals with the continuity, a higher load is put on the beam adjacent to the cantilever and correspondingly less load is put on the next internal beam - some engineers may prefer this. For details of how to perform an FE chasedown analysis refer to the chapter "Overview of Analysis and Design Using FE".
Orion Documentation page 66 Chapter 4 : Analysis Methods
Chapter 4 Analysis Methods
Introduction
Having constructed and loaded your model, an analysis will be required before member design1 can commence. The analysis method(s) used will depend on a number of factors; for certain structures (eg flat slabs) two or more analyses may be required.
A brief summary of the analysis methods available within Orion is given below, these are then discussed in more detail in the next four chapters:
General Building Analysis
A full 3D analysis is performed for all load cases and combinations, (vertical and lateral). The analysis model consists primarily of frame elements with an option to use FE meshing of shear/core walls. It does not include FE meshed floor elements.
General Building Analysis can be used to determine:
• Frame deflections/sway sensitivity
• Beam design forces (from both vertical and lateral combinations)
• Column and wall design forces (from both vertical and lateral combinations)
• Foundation forces (from both vertical and lateral combinations)
• In flat slab structures - the beam, column and wall design forces from lateral combinations.
A full description of this method is provided in the chapter General Building Analysis.
Eigenvalue Analysis
An Eigenvalue Analysis can (optionally) be performed as part of General Building Analysis to determine natural frequencies and mode shapes.
A full description of this method is provided in the chapter Eigenvalue Analysis.
Staged Construction Analysis
This is a sophisticated method of solution which takes account of time dependant effects. It is used in place of general building analysis where it is felt necessary to model the time
dependant properties of concrete.
Staged Construction Analysis can be used to determine:
• Frame deflections/sway sensitivity
• Beam design forces (from both vertical and lateral combinations)
• Column and Wall design forces (from both vertical and lateral combinations)
• Foundation Forces (from both vertical and lateral combinations)
• In flat slab structures - the beam, column and wall design forces from lateral combinations.
A full description of this method is provided in the chapter Staged Construction Analysis.
Footnotes
1. the exception being slabs, which can be designed directly using tabulated code coefficients, where applicable.
Finite Element Floor Analysis
Analysis is performed for vertical load cases and combinations on a single floor at a time extracted from the 3D building. In the analysis model, slabs are represented by horizontal FE meshed floor elements and beams by horizontal frame elements. Supporting columns and walls are also modelled (optionally) as frame elements as are the columns and walls connecting with the slab from floors above.
Sequential FE floor analyses can be performed to chase gravity loads down through the structure. The resulting column, wall and beam forces can be merged with those of the General Building Analysis.
FE floor analysis is required for the solution of flat slab (or flat plate) structures.
Finite Element Floor Analysis can be used to determine:
• Floor deflections
• Slab design forces
• Beam design forces (for vertical combinations)
• Column and wall design forces (for vertical combinations)
• Foundation forces (for vertical combinations)
A full description of this method is provided in the chapter Analysis and Design using FE.
Orion Documentation page 68 Chapter 5 : General Building Analysis
Chapter 5 General Building Analysis
Introduction
This chapter is split into two sections:
• The Structural Model section below describes various modelling considerations and analysis options that have a significant impact on the building analysis result.
• The Building Analysis Problems – Reviewing/Understanding section discusses the error and warning messages you might encounter when running a building analysis. It also describes how you can perform a model validity check and how you can further cross check the analysis result using the Axial Load Comparison Report.