5.0 DESIGN CALCULATIONS

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1 5.0 DESIGN CALCULATIONS Load Data Reference Drawing No Foundation loading for steel chimney Boiler foundation plan sketch : Figure 1 Quantity Unit Dia of Stack, d 6.00 m Dia. of Raft, D m Area of Raft, A = 3.14 xdxd/ m^2 Section Modulus, z = 3.14xDxDxD/ m^3 Height of soil above Raft, h 4.00 m Thickness of the Raft, t 2.00 m Height of pedestal, h m Thickness of pedestal t m Load from chimney Mimimun Dead Load, W ton Maximun Dead Load and Live Load, W ton Wind Load Shear due to wind on main stack, H ton Moment due to wind on main stack, M ton-m Hence Addition Moment due to shear at founding level, M2 = H1 x (h1+t) ton-m Load from Boiler Foundation Dead Load and live(hrsg Foundation) Dead Load + Live Load + Vertical wind Load, W3 = ton Hence moment, M3 = W3 x a ton-m where 'a' = 5.1, distance from center line of the stack to central line of HRSG pedestal Wind shear and Thermal Shear = Additional Moment, M4 = (6.5+16)xb ton-m where 'b' = 3.5, distance from the founding level of HRSG to top of HRSG Pedestal Net Safe Bearing Pressure = S.B.C ton/m^2 Gross Bearing Pressure (DL+LL) = S.B.C. + (1.8x(h+t)) ton/m^2 Gross Bearing Pressure (in DL+LL+WL) = S.B.C. + (1.8x(h+t)) ton/m^2 No increase in stresses as chimney is a critical structure Weight of pedestal, W5 = 3.14xdxt1xh ton Weight of soil above the raft, W6 = ((3.14x(D^2)/4)-(Area of pedestal)) Xhx unit wt of soil ton =(3.14x13^2/4-(3.14x6x1))x4x1.8 Weight of raft, W7 =3.14xD^2/4 x H X uint wt of concrete ton W self = W5+W6+W ton 5

2 Case 1 : Check for Bearing Pressure in Pure Dead Load Live load Total Axial Weight (gross) Wg = W2+W3+W self ton Total Moment = Mg1 = M ton-m Maximum Base Pressure, q1 = Wg/A + Mg1/z ton/m^2< 50 ok Minimum Base Pressure, q2 = Wg/A-Mg1/z ton/m^2 > 0 Ok Case 2 : Check for Bearing Pressure in Dead Load+Live Load+Wind Load Total Gross Weight Wg = W2+W3+Wself Total Moment = Mg2 = M1+M2+M3+M ton ton-m Maximum Base Pressure, q3 = Wg/A + Mg2/z Minimum Base Pressure, q4 = Wg/A-Mg2/z ton/m^2 <60.8 OK ton/m^2 Modified Base Pressure e = Mg2 / Wg 3.27 m e/ D = 3.28 / 13 = 0.25 Crossponding to e/d, C2 = 3.55 (refer Mark Fintel, Fig 5-14) q5 = Wg / A ton/m^2 Modified Base Pressure, q p = C2xq <60.8 ton/m^2 ok Check for overturning : Vertical load V = W1 + W self ton lever arm = D/ Moment of Rsistance, MR = 0.9x(V)xD/ Overturning Moment, MO = Mg Factor of safety F.O.S <1.5 Check for sliding ( µ = 0.5) sliding =(V)xµ/ Η <1.5 Analysis and Design of Raft: Case A : Full Raft with axial laod condition For Bending Moment Calculation in raft, Selfweight and weight above soil not considered Axial load without soil and weight of raft ton Kn p = P / A Kn/m^2 a= 6.5 β =(c/c of chimney rad,r)/(radius of raft,a) =3/ Refer table 6.9, Tall chimneys by S.N. Manohar Y2 =-2.52-(8Xln β)-(2.96xβxβ) 3.13 Y3 = Y Y6 = xβxβ 4.74 Y Y7 =-8XβXβ

3 Moment calcluation due to axial laod f<b f<b f<b f>b f>b f>b Case B : Full Raft with Moment laod condition Y2 =3/β^ β^ Y3 = Y Y6 = xβxβ Y Y7 =3XβXβ 0.64 Refer : Tall chimney by S.N.Manohar TABLE 6.10 Moment calcluation due to Moment laod. When θ is 0 cos 0 = 1 Sin 0 = 0.00 r f Mr Mt Mtor Qr Qt Qtor=1.6 xmtor/b m - Kn-m Kn-m Kn-m Kn Kn Kn f<b f<b f<b f>b f>b f>b q = M / Z Kn/m^2 Total (max at f=β ) Radial Moment Mr Total (max at f=β ) Tengantial Moment Mt Kn-m Kn-m When θ is 45 cos 45 = sin 45 = 0.71 Qtor=1.6 r f Mr Mt Mtor Qr Qt xmtor/b m - Kn-m Kn-m Kn-m Kn Kn Kn f<b f<b f<b f>b f>b f>b 7

4 When θ is 90 cos 90 = 0 sin 90 = 1.00 r f Mr Mt Mtor Qr Qt Qtor=1.6 xmtor/b m - Kn-m Kn-m Kn-m Kn Kn Kn f<b f<b f<b f>b f>b f>b Summery at different angle When θ is When θ is When θ is Sample calculation Grade of concrete = M25 Grade Of steel = Fe415 Design Moment and Reinforcment Calculation Dia of bar to be used = 25 r Mr Mu/bd^2 pt min pt ast spacing Provided m Kn-m SP-16 (TABLE 1) mm^2 required

5 Reinforcment Due to Radial Moment (max at f= 0.5) Mr Kn-m Factored Moment Kn-m Depth of Raft D mm Effective Depth d mm Mu/bd For the Mu/bd2 and fck pt 0.23 Using SP-16 (table-1) Pt Min 0.12 Ast = ptxbxd mm^2 Dia of bar to be used Spacing required mm Provide 25 mm dia 100 mm C/C Reinforcment Due to Radial Moment (at f = 0.67) Mr Kn-m Factored Moment Kn-m Depth of Raft D mm Effective Depth d mm Mu/bd For the Mu/bd2 and fck pt 0.09 Using SP-16 Pt Min 0.12 Ast = ptxbxd mm^2 Dia of bar to be used Spacing required mm Provide 25 mm dia 200 mm C/C Design Moment and Reinforcment Calculation Dia of bar to be used = 25 r Mt Mu/bd^2 pt min pt ast spacing Provided m Kn-m SP-16 (TABLE 1) mm^2 required Reinforcment Due to (Max) Tangential Moment Mt Kn-m Factored Moment Kn-m Depth of Raft D mm Effective Depth d mm Mu/bd For the Mu/bd2 and fck pt 0.09 Using SP-16 Pt Min 0.12 Ast = ptxbxd mm^2 Dia of bar to be used Spacing required mm Provide 25 mm dia 200 mm C/C 9

6 Check for One Way Shear :: Shear Force (max at d at any angle ), KN per m length Factored shear force, Vu 1500 KN per m length Calculated Shear Stress N/mm2 Min % Of Steel provide Shear strength of conc N/mm2 Enhancement of shear strength,2xdxtc/av As per clause Of IS-456 Hence Safe Check for Two-Way Shear :: Max. vertical load on Raft = W2 + W3 Shear Sress Permissible stress KN N/mm2.t c 0.25 X fck N/mm N/mm 2 ok Design of Pedestal Mg Kn-m Wg kn e = M / W m r 7 m e / r β 0 µ 0 value of φ 150 ο from chart 7.1 value of C Assume % of reinforcment 3 % Fc= (CW)/( r t (1-p)) 0.84 N/mm^2 <0.38xfck 9.5 ok Fs = (SxmxW)/(r t (1-p) S = C ((cos F) + cos m))/((cos b) - cos f)) Maximum steel stress, Fs Provide 20 mm dia 150 mm C/C 0.64 N/mm^2 <0.57fy ok 10