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Unformatted text preview: 5 mm is in between 50 mm and 6 mm. Hence, the area of spiral (A,) considered is correct. H-3.2 Initial Compressive 1000 — X (3.45)2 = 6.89 x 0.7854 Stress Induced in Core (Q 1000 =— 76.89 = 13.oomm &i =1114.75X Centre to centre spacing of spiral wire 0.7188 ~ = 11.4468 N/mm2 H-3.3 For futher design, the procedure as given in Annex G shall be adopted. ANNEX J (Clause 7.8) DESIGN OF PRESTRESSED CONCRETE PIPES FOR DRAINAGE, SEWERAGE AND CULVERT d=tC+t~=60+22=82mm J-1 Explanation of various symbols used in subsequent clauses is given in Annex K. Z=+x1000x82 =112066.7mm3 J-2 DATA Diameter of pipe, D Core thickness of pipe, t, Coat thickness of pipe, t~ Three edge bearing load, P =looomm =60mm =22mm = 72.6 kN/m =72 600 N/m Stress – M _ 12489959 112066.7 z = 11.14 N/mm2 (Stress due to three edge bearing load) - (Flexural strength of concrete) Final prestress = required Flexural strength of spun concrete = 6.87 N/mm2 ~,= 11.14-6.87 J-3 ASSUMPTIONS : Counter weightlBreak Process of winding =4mm Diameter of circumferential wire, d = 1 715 N/mm2 IJltimate t~nsile strength of circumferential wire = 4.27 N/mm* J-4.2 Design of Circumferential Prestressing J-4.2.1 Spacing of Circumferential Wire (see 8.4.5) Allowable clear spacing Maximum clear spacing of wire = 50 mm Minimum clear spacing of wire = 6 mm Area of spiral considered in design (A,) = 0.240 mm2/mm Number of turns per meter length Area of circumferential wire, A,= 0.240 mm2/mm J-4 DESIGN J-4.1 Calculation of Final Prestress Required 1000 x (4)* = 19.09 = 0.240 x — 19.09 Calculation of moment at bottom = M A4=0.159x PxD~ Where, D~ = Mean diameter of pipe = D + tc+ tb =1000 +60+22 =1082mm A4=0.159x 72600 X 1082 1000 Centre to centre spacing of spiral wire= — 19.09 = 52.38 mm = 12489959 Nmm Calculation of section modulus of pipe, Z Clear spacing of spiral wire = 52.38 – 4 = 48.38 mm 48.38 mm is in between 50 mm and 6 mm Hence, the Area of spiral (A,) considered is correct. Z=~xbxd2 6 24 IS 784:2001 Initial Stress in wire during winding (fi) (see 8.3.2) Total losses 16.46 + 102.90+ 12.86+ 20.00= 152.22 N/mm* Losses at factory test (3.9 x Total loss 0.9 x 152.22 .f~i= 0.75 x 1715 = 1286.25 N/mmz Initial Compressive stress induced in core ~Ci) = 137.00 N/mm2 Stress in wire at factory test ~,f) J-4.2.2 Calculation of Prestressin Core in Circumferential Direction &f= 1286.25-137.00 = 1149.25 N/mm2 Stress in wire at Site test ~) & = 1286.25-152.22 = 1134.03 N/mm2 Compressive stress in core at site test 0.240 f;, = 1286.25 x ~ = 5.1450 N/mm* J-4.2.2.1 Loss of stress in wire (see Annex F) a) Elastic deformation 0.240 &,= 1134.03 x ~ = +4.5361 N/mm2 3.2 X~i = 3.2 x 5.1450 = 16.46 N/mm2 b) Relaxation of wire 0.08 x f,i = 0.08 x 1286.25 = 102.90 N/mm2 c) Deformation due to creep 2.5 x 5.1450 = 12.86 N/mm2 d) Deformation due to creep and shrinkage 0.0001 x E,= 0.0001 x 20 x 104 . 20.00 N/mm2 As final prestress (4.536 1) is more than final prestress required (4.270 O), the design is safe. J...
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This document was uploaded on 10/01/2013.

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