Structural Engineers' eBook

Floor Analysis & Design

 
RCC slabs, beams and columns of a floor are analyzed as sub-frames for gravity loads by the stiffness method. Flexural and shear reinforcement in slabs and beams is calculated per various codes of practice. 

User input is greatly simplified as there is no need to number elements and nodes or to specify member connectivity and section properties. Uniform loads on slabs are automatically converted to trapezoidal or triangular loads on beams.

Entire input is entered in one web page consisting of  two forms - one for framing plan and another for element types. Parts of the two forms are shown below.

Framing Plan

The first form defines floor layout. Far left column and bottom row are used for entering distances between grid-lines in millimeters. Cells marked C, B and S  represent columns, beams and slabs respectively. Choose appropriate identifier in each cell from those marked in the next form. 

Depending on the floor layout, some cells may not have any column, beam or slab. Leave such cells as they are. However, make sure that all slabs have peripheral beams along gridlines. When there are two columns at a location, one above and another below the floor, use two column identifiers separated by a slash e.g. C3/C9. 

Column Data

Beam Data

Slab Data

  
Mark Cx
mm
Cy
mm
H
mm
Mark bw
mm
D
mm
Load
kN/m
Mark t
mm
Load
kN/m2

Details of various element types viz. column, beam and slab are entered in this second form. An element mark has at least two characters : the first character represents element type C, B or S  followed by an alpha or numeric element identifier. Thus CA, B11 and Sz are all valid examples of element marks. 

Other entries in the form are more or less self-explanatory. Cx and Cy are the dimensions of column parallel to x (horizontal) and y (vertical) axes, H is column height, bw and D are beam width and depth respectively and t is slab thickness. Enter factored uniform loads on beams and slabs inclusive of self weight. The software does not apply any load factors nor does it calculate self-weight of elements.

Let us take an example of a floor slab S1 5m x 6m, 200 mm thick with a load of 5 kN/m2 supported on beams B1, 300 mm wide x 600 mm deep which in turn rest on 3m tall columns C1, 400 mm x 500 mm above and below the floor as shown below:

The framing plan and element types for this case are entered as follows:

 

Framing Plan

Column Data

Beam Data

Slab Data

  
Mark Cx
mm
Cy
mm
H
mm
Mark bw
mm
D
mm
Load
kN/m
Mark t
mm
Load
kN/m2

And here is the resulting output :

 
 
   Slab      Type     -Mx1--   -Mxm--   -Mx2--   -My1--   -Mym--   -My2--
kN-m/m kN-m/m kN-m/m kN-m/m kN-m/m kN-m/m
 
A1B2 S1 0.00  7.00  0.00  0.00  9.00  0.00 
 
 
---Beam---   Type   ---Shear---- -------Moment------
End1   End2    End1     End2     End1    Middle    End2  
    kN       kN      kN-m     kN-m     kN-m  
A1 A2 B1 25.62   25.63   -15.31   23.23   -15.31  
B1 B2 B1 25.63   25.62   -15.31   23.23   -15.31  
A1 B1 B1 33.87   33.88   -29.60   31.63   -29.60  
A2 B2 B1 33.88   33.88   -29.60   31.63   -29.60  
 
 
  Column    -Type-  Axial -----Mx----- -----My-----
1 2 Type1 Type2 Type1 Type2 
    kN      kN-m     kN-m     kN-m     kN-m  
 
A1 C1 C1 59.50   -14.80   -14.80   7.65   7.65  
A2 C1 C1 59.50   -14.80   -14.80   -7.65   -7.65  
B1 C1 C1 59.50   14.80   14.80   7.65   7.65  
B2 C1 C1 59.50   14.80   14.80   -7.65   -7.65  
 
Nomenclature used in output requires some explanation: 

For slabs and columns Mx and My values are moments about x and y axis respectively. Suffix 1 and 2 on Mx represent moments at lower and upper edge while those on My represent left and right edges of slab respectively. Suffix m denotes moment at mid-span of slab.

You may try variations of the example by changing values in the two forms. Pressing will get you another set of results.

Design of flexural and shear reinforcement is calculated using the following default values:

 

Characteristic strength of concrete : 25 MPa
Yield strength of steel : 415 MPa
Effective cover to slab reinforcement :   25 mm
Effective cover to beam reinforcement :   50 mm

Flexural reinforcement values preceded by '<' and '>' signs indicate minimum values required by code.