Abstract:
Beam less floor directly resting on support (column and/ wall) is known as flat slab. Because of this, Story height can be maintained uniform throughout. This provides us an ease of installation of mechanic and electric services. This also helps us in reducing the cost of formwork. Flat slab reduces the loads on foundation because of less height of structure. It gives us plain ceiling which gives an attractive appearance.
Flat slabs are subjected to gravity and lateral loads. Gravity load analysis of flat slab is carried out by Direct Design Method (DDM) and Equivalent Frame Method (EFM) as prescribed by different standards. On site some times because of site conditions or the owners requirements the column orientation may not get in an alignment this is known as staggered column conditions. In those conditions we have to use Equivalent Frame Method for analysis and design of flat slab.
IS 456-2000, BS 8110-1997 prescribed the coefficients for analysis of prestressed concrete flat slab as per DDM and EFM. Analysis and design of prestressed concrete flat slab is carried out with respective to the coefficients prescribed by different standards for distribution of moments along longitudinal and transverse directions. Slab is divided into column strip and middle strip. IS 456-2000, BS 8110-1997 specifying the fixed value of column strip and middle strip irrespective of interior span and mid-span.
The present study also incorporates the comparison of distribution of width of column strip and middle strip as per IS 456, BS 8110-1997 and as per Equivalent frame method for the staggered columns and the without the staggered column. And a comparison is made. The positive moment increases and negative moment decreases with Equivalent Frame Method. The negative and positive moments at exterior support increases for IS 456 compared to other.
Excel worksheet is also prepared for analysis and design of prestressed concrete flat slab (with staggered and without staggered columns) as per EFM. EFM includes analysis as per IS 456-2000 & BS 8110-1997 and using the distribution coefficients along longitudinal and transverse directions.
Keywords: Prestressed concrete, flat slab Moment.