Prestressed concrete tanks have been widely used for storage of fluids, such as water, oil, gas, sewage, granular materials like cement, process liquids and chemicals, slurries and more recently cryogens water storage tanks of large capacity are invariably made of prestressed concrete recent applications include special forms of prestressed concrete tanks, which are triaxially prestressed and serve as containment vessels and biological shields for nuclear reactors.

The tension in wire is produced by pulling it through a die which reduces its section, consequently developing required amount of tensile stress in steel and wrapped wires are generally protected against corrosion by a coating of cement mortar recent developments reported by dandies include use of picovex mortar which consists of a proprietary epoxy resin formulation containing coal tar used as binder of a sand filled mortar.

Clean and neat in appearance and requiring negligible maintenance for a number of years, thus ideally suited for urban installation and have increased crack resistance, rigidity and can resist dynamic loads better than reinforced concrete poles, lighter because of reduced cross section when compared with reinforced concrete poles and fire resistant, particularly to grass and brush fires near ground line.

The manufacturing process consists of pouring concrete under high frequency vibration in a vertically placed steel mould consisting of an inner and outer shell and outer shell consisting of longitudinal sections held toger by spring assembles, permits mould to expand while inner steel mould is covered with an expansible rubber membrane.

The Indian standard code stipulates floor slabs of tanks resting on ground should be provided with a nominal reinforcement of not less than 0.15 percent and floor slabs should be cast in panels of area not more than 4.5m² with contraction or expansion joints and se slabs are to be cast over a layer of concrete not less than 75mm thick with a sliding layer of bitumen paper provided to prevent bond between screed and floor slab.

In case of tapered poles with a reduced cross section towards top, effective prestressing force should be reduced in proportion to cross section by techniques of de bonding or by dead ending or looping some of tendons at mid height and according to Gerwick a constant cross section proves to be better solution in many cases since top must be as strong as base for resisting torsion with added advantage of effective use of prestressing and easier connections.

Prestressed concrete slabs systems are ideally suited for floor and roof construction of industrial buildings where live loads to base supported are of a higher order and uninterrupted floor space is desirable for which reason longer span between supporting elements are required.

The compressive state of stress in shell membrane results in which construction water tight construction and according to Haas prestressing has a favorable influence in providing adequate safety against limit state of collapse by inelastic bulking India in 1941 over spans of 36m, with a chord width of 10.5m, thickness of shell being 63mm and prestressed shell roof of aircraft hangar at Karachi was built in 1942 over spans of 40m and as se shells gave satisfactory performance and were also economical in France, U.K, Germany and or countries.

The folded plate is also analyzed for transverse moment by considering plate as a continuous slab with imaginary supports at junctions and transverse reinforcement are designed to resist se moments and according to IS:224 nominal reinforcements consisting of 10mm bars are to be provided in compression zones at 200mm centers and maximum spacing of reinforcements in any direction is limited to five times thickness of member and minimum reinforcement in section should conform to provisions in various national codes.

N_d = 720, f_min.w = 1, ? = 0.75, t = 120mm
F_c = N_d/ ?_t+ f_min.w/ ? = 720/0.75 x 120+1/0.75 = 9.4n/mm².