To determine the number of piles factored or unfactored load of column should be used?
which load to be used for the design of pilecap ?
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Pile capacity is like the Soil bearing capacity of soil with respect to your questions.
We use unfactored load for sizing the footing.However once we finish sizing,then the design is based on the factored pressure.
The reason for doing this is simple.The SBC provided by soil consultants are infact downfactored. That is, the geotechnical code asks you to adopt a factor of safety of 3. This means if a soil report shows a SBC of 200, then with out down factoring it is 600
If your column load is 1200kN then the size of footing needed with out a safety factor is 1200/600 = 2m2. However code wants you to consider only 200kN/m2 and hence area needed is 1200/200 =6m2 .This is the reason that we take unfactored load for the sizing so that an additional safety factor is not needed for loads.Once the sizing is complete, the design shall be based on factored forces.
It is same with pile design. The number of piles are based on the unfactored loads. Pilecapacity will have the necessary down facotring generally.You can always check with the soil consultant once to confirm.
The design of pile will be based on factored loads.Same is the case with pile cap design.You have to use the factored loads.You have 2 methods to design pile caps - The truss theory based design and the beam theory based design.
Our courses on Foundation design covers all these topics comprehensively.You can see the course page here.
You can see our other blogs related to soils below
Blog 1 - 4 tips for Foundation design
Blog 2 - Number of bore holes for buildings