Support structure for hdpe
- 1. INSTALLATION 8.11 8.6. SUPPORT STRUCTURES FOR PRESSURE PIPES Pipes under pressure need support at fittings, valves and ends to avoid stress peaks. The support blocks are made of reinforced concrete. The calculations and design should be based on a pressure 1,5 times the design pressure. The design should be done in a way so that the strength values of the soil and concrete are not exceeded. Butt-welded bends, T-pieces and other fittings are completely surrounded by concrete. The pipe should be supported before the pressure test in site. Horizontal bend Vertical bend up Vertical bend down T-Branch End of pipe At least Be1 = De+de/2 Be1 = 200 mm+de/2 OR Be2 = de+De/2 Be2 = 200mm+De/2
- 2. INSTALLATION 8.12 Reaction Force in a Pipe Bend P = p A = p p D2 / 4 R = 2 P sin a / 2 where p = pressure D = pipe diameter under water pressure a = pipe bend
- 3. INSTALLATION 8.13 Support length (l) mm h b Reinforcement Bend = mm mm Steel A 40 H Pipe 100 (300) 400 500 300 150 ø 8 k/k 200 # 150 (500) 600 800 450 150 ø 8 k/k 200 # I.D. 200 (400) 600 700 1000 600 200 ø 8 k/k 200 # 250 (500) 800 1000 1400 700 200 ø 10 k/k 200 # mm 300 700 1000 1200 1800 800 250 ø 10 k/k 180 # 400 900 1400 1800 2500 1000 300 ø 10 k/k 150 # 500 1100 1600 2100 3000 1300 350 ø 12 k/k 200 # 600 1300 1900 2400 3400 1600 400 ø 12 k/k 190 #
- 4. INSTALLATION 8.14 Design of support 1. Basic table in frictional soil. Friction angle = 28°. Density 17 kN / m3 (1.7 t / m3 ). Depth of the pipe - center line Z = 2 m. Pressure in the pipe 10 bar, 1 MPa. 2. If the friction angle > 35° (ex. gravel) the support slab can be decreased by 30% (factor 0.7). In cohesive and intermediate soils the slab must be increased by 50% (factor 1.5), if the shear strength is higher than 1.5 kPa (1.5 t / m2 ), and 100% (factor 2.0) if the shear strength is higher than 10 kPa (1.0 t / m2 ) and smaller than 15 kPa (1.5 t / m2 ). 3. The depth of the pipe is paid attention to by using a correction factor 2 / Z. Z is the depth of the center line of the pipe. EXAMPLE 1. D = 300 mm = 68°, frictional soil = 40° Z = 2,5 m A = 2 / Z x 0.7 (1.4 x 0.2) = 0.63 m2 , take 800 mm x 800 mm = 0.64 m2 EXAMPLE 2. T-piece = 90° Soil clay, shear strength 12 kPa Z = 1.8 m A = 2 / 1.8 x 2.0 x (1.0 x 0.6) m2 = 1.33 m2 , take 2250 mm x 600 mm