orion flat slab design training

Orion Training

Flat Slabs

Copyright CSC(UK) Ltd. 2006

Flat Slabs

CONTENTIntroduction Model Generation

Suggested Modelling SequenceTips for meshing & punching perimeter modelling

Building AnalysisFE Analysis

Adjusting model properties for deflections

Design and DetailingComparison with the Code Approach

Flat Slabs - Introduction

Why Flat Slab and why FE?Perhaps you can tell us, is it:

For flat slab:Reduced Structural Zones?Potential for Fast Formwork Erection and Construction?Un-obstructed service zones?

For FE:A potential to accommodate more irregular column positioning?Only way to deal confidently with more complex isolated load conditions?Only way to deal confidently with significant openings?

Flat Slabs - Introduction

Why Flat Slab and why FE?

Whatever the reasons, we are certainly seeing more and more demand for an FE based flat slab solution within the context of a building modelling environment.

Flat Slabs Flowchart

1. Build the Model

2. Run the general building analysis to generate column & wall forces for lateral loads only. *

3b. Slab Design and Detailing

3a. Use sequential FE floor analyses to chase gravity loads down through the structure & generate slab design forces.

4a. Merge FE column results for gravity loads with building analysis results for lateral loads.

4b. Column/Wall Design and Detailing

3c. Punching Shear Checks

* If FE Floor Analysis for Beam Loads has been used to decompose slab loads at each floor level, then building analysis generates valid design forces for lateral and gravity load cases in the walls.

Orion Training

Orion Training

Flat SlabModel Generation

Copyright CSC(UK) Ltd. 2006

Flat Slabs Flowchart

1. Build the Model

2. Run the general building analysis to generate column & wall forces for lateral loads only. *

3b. Slab Design and Detailing

3a. Use sequential FE floor analyses to chase gravity loads down through the structure & generate slab design forces.

4a. Merge FE column results for gravity loads with building analysis results for lateral loads.

4b. Column/Wall Design and Detailing

3c. Punching Shear Checks

* If FE Floor Analysis for Beam Loads has been used to decompose slab loads at each floor level, then building analysis generates valid design forces for lateral and gravity load cases in the walls.

We would suggest that by using the following sequence you will ultimately save time.

Flat Slab Model Generation

1. Make slab insertion easy by being organised with grids

Avoid multiple closely spaced parallel grids use one rather than two where possible.If intention is to include column/wall sections, avoid short distances from the slab edge to the column face. (Introduces short length meshing problems).Consider shrinking grids before placing slabs.

Flat Slab Model Generation

2. Create larger regular slab panels, avoid multiple slab panels between columns and especially around columns.

Flat Slab Model Generation

3. As you insert slabs, (and before adding holes and concentrated loads) occasionally check the following:

Run Punching Checks and use hatch option to see that punching perimeters can be found.Generate an FE mesh to see that meshing works (using column section modelling if it is your intention to do so).

Flat Slab Model Generation

4. Repeat the previous step after adding holes and concentrated loads.

Flat Slab Model Generation

5. You should now have one floor that you know is going to work in both FE and punching. Other floors may be completely different, in which case the above procedure should be repeated. If other floors are partial duplicates you are now sure that the copied model works before editing starts.

Flat Slab Model Generation

6. Duplicate Floors It is not essential to model every floor genuine duplicates can be dealt with as such hence avoiding repetitive meshing etc take full advantage of his.

Flat Slab Model Generation

There are 2 primary difficulties with FE models of flat slabs

Meshing fails to workPunching perimeters cannot be found

Flat Slab Model Generation

Meshing difficulties can be caused by:Short slab edgesShort slab spans between openings/edgesLoads within a column boundary

(Using the column/wall section modelling option inherently introduces short edges and can cause meshing difficulties)

Flat Slab Model Generation

Flat Slab Model GenerationExample 1: Short slab edge

Because walls not meeting at 90 degrees, Short slab edges created at corner of wall.

Enlarged View of Wall Corner

Flat Slab Model GenerationNo problem if column/wall sections notincluded.

But fails to mesh when column/wall sections included.

Solution:Edit grids to ensure walls are orthogonal.

Flat Slab Model GenerationExample 2: Another Short slab edge

Flat Slab Model GenerationNo problem if column/wall sections not included.

Flat Slab Model GenerationBut problem when column/wall sections included

Flat Slab Model Generation

Solution: Move column down to remove gap

Short slab edge problem sometimes indicated in the mesh generator by slabs being incorrectly displayed as triangular.

Flat Slab Model Generation

Example 3: Slab load within column perimeter

Flat Slab Model Generation

Meshes OK if column/wall sections not included

Flat Slab Model Generation

Error if column/wall sections included

Flat Slab Model Generation

Solution: Move the load outside the column perimeter

Flat Slab Model Generation

Punching Perimeters

As geometry becomes more complex, it becomes increasingly difficult to find the punching perimeter.Potentially very frustrating if you have meshed and analysed lots of floors and then cannot do punching checks.

Flat Slab Model Generation

However

This frustration is completely avoidable.You can check the perimeters can be found before even attempting meshing.

Flat Slab Model Generation

This is done as follows:

Display the Punching Shear dialogClick Hatch Floor Area (Initially with Inc. Col, Wall, Beam Edges Unchecked).

Flat Slab Model Generation

If entire floor area is hatched then punching perimeters can generally be determined for all columns.

Flat Slab Model Generation

If entire floor area is NOT hatched then punching perimeters can not be determined in the un-hatched areas

Flat Slab Model Generation

But, there is a tool that may resolve this:

Check the box to Inc. Col, Wall, Beam Edges, and then click Hatch Floor Area again.If entire floor area is hatched then perimeters are OK

Flat Slab Model Generation

Orion Training

Orion Training

Flat SlabBuilding Analysis

Copyright CSC(UK) Ltd. 2006

Flat Slabs Flowchart

1. Build the Model

2. Run the general building analysis to generate column & wall forces for lateral loads only. *

3b. Slab Design and Detailing

3a. Use sequential FE floor analyses to chase gravity loads down through the structure & generate slab design forces.

4a. Merge FE column results for gravity loads with building analysis results for lateral loads.

4b. Column/Wall Design and Detailing

3c. Punching Shear Checks

* If FE Floor Analysis for Beam Loads has been used to decompose slab loads at each floor level, then building analysis generates valid design forces for lateral and gravity load cases in the walls.

Flat Slabs Building Analysis

Building Analysis has to be run in order to generate lateral design forces for columns and walls.After running a building analysis, the gravity design forces will not be correct unless the FE column/wall results are merged.

Flat Slabs Building Analysis

It should be emphasized that FE analysis only deals with gravity loads, and in building analysis sway load will not be resisted by any framing action between slabs and columns. Sway loads should therefore be resisted by walls (ie braced flat slab construction).Unbraced flat slab construction remains beyond the current scope of Orion.

Flat Slabs Building Analysis

The building analysis will only be valid provided steps are taken to ensure the notional load calculation is correct use the un-decomposed loads option for calculation of storey weight.

Orion Training

Orion Training

Flat SlabsFE Floor Analysis

Copyright CSC(UK) Ltd. 2006

Flat Slabs Flowchart

1. Build the Model

2. Run the general building analysis to generate column & wall forces for lateral loads only. *

3b. Slab Design and Detailing

3a. Use sequential FE floor analyses to chase gravity loads down through the structure & generate slab design forces.

4a. Merge FE column results for gravity loads with building analysis results for lateral loads.

4b. Column/Wall Design and Detailing

3c. Punching Shear Checks

* If FE Floor Analysis for Beam Loads has been used to decompose slab loads at each floor level, then building analysis generates valid design forces for lateral and gravity load cases in the walls.

Flat Slabs FE Analysis

Sequential finite element analysis in general is covered el