DESIGN OF RC ELEMENTS

1.Design a rectangular footing for a column 300*550mm.the column is subjected to a axial (factored) load 1750 kn. the SBC of soil is 200 kn/m2.sketch detail. Step no:01 Given dataColumn size =300*550mmFactored load=1750 knSBC =200kn/m2 self wt 10%= 175 knM20 & Fe 415 steel.

Step no:02Area of footingAf = = =6.42 M2Assume 7m2 as area of footing

By size of columnSide can be calculated(s.s*l.s) i.e(3:5.5)(3x)*(5.5x) =7m2X2 (16.5) =7m2X = 0.65

Step no:03 Soil pressure @ basePu = = = 250 kn/m2SBC =200*1.5 =300kn/m2 Hence section provided is safe.Step no:04 Cantilever projection on footingShorter side = 3.5/2 -0.55/2 =1.475 mLonger side =2/2 -0.3/2 =0.85 m

Bending moment on shorter side B.Ms = =250*1.4752/2 =271.95 knm B.M on longer side.B.ML =pu.LL2/2 =250*0.852/2 = 90.31 knm

Step no:05 Depth calculation (1) Mu = 0.138 fck bd2

d = = =313.89 mm (2)from shear stress calculation SF will be @ d from of column VUL = Pu (L-d) here L-larger length of section SF actedPu = 250 kn/m 250 N/mm. VUL =250 (1475-d).As per code IS 456-2000 table No:19

c = VUL/bd .

0.36 =

360d = 368.75*103 - 250d

510d = 36.75*103

D = 723 mm

Adopt eff.depth (d) = 750 mm.D = 50 mmOverall depth (D) = 800 mm

Step no:06 Ast calculation

Mu = 0.87 fy Ast d [1-]

For shorter side.

Mu = 271.95*106 Nmm. Fy = 415 N/mm2 fck = 20 N/mm2 D = 750 mm b = 1000 mm

271.95*106 = 0.87*415*Ast*750[1-]

7.49 Ast2 - 270.79*103 + 271.95*106 = 0

Ast = 1033.85 mm2

Used as longer span Provide 16 mm dia bar.

Spacing = = 194 mmProvide 16 mm @ 175 mm c/c.

Ast1p = 1149 mm2.

For longer side:

90.31*106 = 0.87*415*Ast*750[1-]

7.49 Ast2 270.79*103 + 90.31*106 =0

Ast = 336.64 mm2

Used as shorter span

Revised shorter span Ast:-Ast = . = 3.5/2. = 1.75Ast = 244.83 mm2

Provide 12 mmSv =

Sv = 461.94 mmCheck for min. % of steel0.12% c/s area= 0.12 *1000*800/100= 960 mm2

Shorter span spacing (Sv)

Provide 12 mm dia Sv = = = 117.81 mm.Provide 12 mm dia @ 100mm c/c Ast,p = 1131 mm2

Step no:07

Check for shear stress v = Vu/bdMax. shear will be @ a distance d from face of column. v = = 0.24 N/mm2.

Pt = 100Ast/bd = (100*1149)/(1000*750) =0.21 %.

c value is o.33 N/mm2 & k value

Clause 40.2.1.1 k =1 k.c = 0.33 N/mm2 v < k.c

Hence safe.