EXAMPLE 2.4.3. VOLUME METHOD: ESTIMATING CONCRETE FOR A COLUMN-FOOTING STRUCTURE

Estimate the quantity of concrete components for six 1.0m x 1.10m x 0.40m footing with 0.35m x 0.35m columns. Footing is embedded at 1.5m from the ground. 

There are two ways to work on this problem.

1. You can separately determine the quantities needed for the footings separate from the columns. This method is applicable usually when bill of materials require detailed values per structural member.
2. Take the volume of all members, that is, the footings and the columns, then take the material proportions. Most often, columns and footings require same concrete grade or strength, thereby, the total volume can be considered.

Let's show the two methods in this example:

METHOD 1: SEPARATE FOOTING FROM COLUMNS

       FOOTING:

                  
                         

                          

• For cement, using class A (1:2:4)

                   

                           

• For sand:

                    

                    Consider sand bulking:

                            

• For gravel:

                     Gravel bedding with 50mm thickness:

                    
                            

                            

                           

                       Total volume:

                            


          COLUMN: 

Assuming the height of column will be until the ground level. Footing embedment is usually measured from the bottom, so the height of column is:

                  

                         

                       

• For cement:                   

                         

                         

• For Sand:          

                          

                  Considering sand bulking:

                         

• For gravel:

                

      Summary of materials:

           Footings:        24 bags 40-kg cement (19 bags 50-kg cement)
                                1.65 cubic meters sand
                                3.00 cubic meters gravel

            Columns:       8  bags 40-kg cement (6 bags 50-kg cement)
                                0.50 cubic meters sand
                                1.00 cubic meters gravel


METHOD 2: TOTAL VOLUME

Take volumes for footing:

                   
                         

                          

and column:

                           

                           

Total volume is then computed:
                   

                           

• For cement:                         

                          

                         

• For sand:                

                          

                 Considering sand bulking: 

                         

• For gravel:

                       
                          

                          
               

                          

Summary of materials:

                                32 bags 40-kg cement (25 bags 50-kg cement)
                                2.50 cubic meters sand
                                4.00 cubic meters gravel


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