Basic civil engineering 21

The minimum grades of concrete for prestressed applications are as follows. 
• 30 MPa for post-tensioned members (Ex:slabs)
• 40 MPa for pre-tensioned members. (Ex:sleepers)

Deflection of a simply supported beam for udl is 5 times more than the deflection of a fixed beam for the same loading and beam properties and dimensions.

REINFORCEMENT REQUIREMENT IN SLABS:-

-0.15% for Fe 250 grade of steel 
-0.12% for Fe 415 grade of steel.

REINFORCEMENT REQUIREMENT IN COLUMNS

--Minimum % of steel=0.8% of gross cross section area.
--Maximum % of steel=4% of gross cross section area and should not exceed 6%.
--Minimum number of rods in circular and rectangular/square columns are 6 and 4 respectively.
--Minimum diameter of bar=12 mm.
--Bars spacing shall exceed 300 mm along periphery.
--For pedestals minimum area of reinforcement=0.15% of gross cross sectional area.

-Minimum Grade of Concrete for Liquid storage structures is M30.(as per IS 3370(Part 1):2009-Code of practice for storage of liquids)
-Minimum cement content is 320 kg/m3.
-Maximum cement content is 400 kg/m3.

PINNED SUPPORT- The beam rods terminate at the end of the beam and are not anchored into the columns.

SAFETY CURVE 

ACCELERATORS

->Accelerators are admixtures used in cold weather to increase the rate of hardening and thereby reduce the failure of concrete.
->They accelerate the hardening of cement & increase the rate of evolution of heat;hence the temperature of concrete is raised.
->CaCl2 is the most commonly used and reliable accelerator.
->Used upto a maximum of 2% by weight of cement.