Slab Designer as per IS 456-2000

SLAB DESIGNER ver 2.00 Name of author:Mofiz Ahmed Profession:B-Tech Civil Engineer (student IV year II sems) Software used: Slab Designer ver 2.00 Web site: www.mofizahmed.webs.com

An Example (For educational purpose only)

The given value that we have are: Grade of concrete used is Fck=25N/mm2 ( for M25 grade of concrete) Grade of steel used is Fy=415N/mm2 Shorter length of slab i.e slab in X direction lx=3000mm Longer length of slab i.e slab in Y direction ly=4000mm Given Live load is LL=4KN/m2 Given Dead load (beside the selfweight) is DL=0KN/m2 Given Floor finishing Load FL=0.65KN/m2 Now finding the ratio of ly and lx, ly/lx=1.33 Since the ratio (ly/lx)=1.33 is less than 2 so it is a Two way type of slab Selected type of slab i.e whether continuous or discontinuous= D kind of slab Effective depth of slab d=lx/30=100 Taking the value to nearest multiple of 5 or 10 then d=100 mm

Providing a nominal cover of 30 mm,therefor overall depth D=130 mm

/////////////// LOAD CALCULATION /////////////// Self weight per square unit=Volume*Unit weight of concrete=1*1*D*U concrete and is assumed as U=25 KN/m2

where U is the unit weight of

Self weight SL=3.25 KN/m2 Total load acting on the slab is W= DL+FL+LL+SL Total load acting on the slab W=7.90 KN/m2 Total factored load acting on the slab Wu=Factor of safety * W=1.50*7.90=11.85 KN/m2 Since d is less than support width so the effective spans are............................................... Lefx=lx+d=3100 mm Lefy=ly+d=4100 mm Ratio of effective spans in X and Y direction i.e Lefx/Lefy=1.32 For ratio of Lefy/Lefx=1.32,from Table 26 of IS-456,we get -ve alpha x i.e -ve ax=0.07 For ratio of Lefy/Lefx=1.32,from Table 26 of IS-456,we get -ve alpha y i.e -ve ay=0.05 For ratio of Lefy/Lefx=1.32,from Table 26 of IS-456,we get +ve alpha x i.e +ve ax=0.05 For ratio of Lefy/Lefx=1.32,from Table 26 of IS-456,we get +ve alpha y i.e +ve ay=0.03 As per ANNEX D of IS-456 Moment is calculated as : alpha value * load * square of effective length Positive moment in X direction(shorter span) for alpha positive i.e +ve ax M1=5.68 KN-m Negitive moment for alpha x negitive in X direction i.e -ve ax M2=7.56 KN-m Positive moment in Y direction (longer span) for alpha positive i.e +ve ay M3=3.99 KN-m Negitive moment in Y direction (longer span) for alpha negitive i.e -ve ay M4=5.35 KN-m Shear force as per IS-456 Vu=((Wu*Lefx*r)/2)(1+r)=13.84 KN,

where r=(Lefx/Lefy)^4=3.06

Design Moment is the maximum of all the above moment caculated. .'. Design moment=M=7.56 KN-m As per IS-456 for Fy=415 N/mm2 we have Xu=0.48*d=48.00

//////////// AREA OF STEEL REINFORCEMENT ///////////// From IS-456 we have ultimate moment as Mu=0.36*fck*1000*Xu*(d-(0.42*Xu)) Putting all the respective values in the above equation we get Mu=34.49 KN-m Since Mu is less than M therfor we can design the slab as singly reinforced From IS-456 we have M=0.87*Fy*Ast*d(1-((Fy*Ast)/(b*d*Fck))) where b=1000 mm, Ast=area of reinforcement steel required In this equation,we have all the values except Ast .'. Putting all the values we get Ast value Area of steel required for Moment=5.68 KN-m is calculated as = 161.74 mm2 Spacing required for this area of steel is given as..... (area of each bar*b)/total area of steel Spacing calculated or required spacing=485.59 mm Spacing provided=300 mm since it is less than 3d but more than 300 mm Converting it into lower multiple of 5 or 10 Spacing provided=300 mm Area of steel required for Moment=3.99 KN-m is calculated as = 112.49 mm2 Spacing required for this area of steel is given as..... (area of each bar*b)/total area of steel Spacing calculated or required spacing=698.17 mm Spacing provided=300 mm since it is less than 3d but more than 300 mm Converting it into lower multiple of 5 or 10 Spacing provided=300 mm Area of steel required for Moment=7.56 KN-m is calculated as = 217.11 mm2 Spacing required for this area of steel is given as..... (area of each bar*b)/total area of steel

Spacing calculated or required spacing=361.74 mm Spacing provided=300 mm since it is less than 3d but more than 300 mm Converting it into lower multiple of 5 or 10 Spacing provided=300 mm Area of steel required for Moment=5.35 KN-m is calculated as = 152.08 mm2 Spacing required for this area of steel is given as.... (area of each bar*b)/total area of steel Spacing calculated or required spacing=516.43 mm Spacing provided=300 mm since it is less than 3d but more than 300 mm Converting it into lower multiple of 5 or 10 Spacing provided=300 mm Minimum area of steel reinforcement required=0.12 % of b*d=120 mm2 Spacing required for minimum steel reinforcement =418.88 mm Spacing provided for minimum steel reinforcemen =300 mm since it was greater than 300mm and 5d is also more than 300 mm Finalyy spacing provided for minimum steel reinforcement after converting it into nearest multiple of 5 or 10 =300 mm For moment M2=7.56 KN-m we have reinforcement steel 112.49