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Example 6 1 Rectangular Water Tank Design – Free download as PDF File .pdf), Text File .txt) or read online for free. leakage. This project gives in brief, the theory behind the design of liquid retaining structure (Elevated circular water tank with domed roof and conical base). and further guidance on seismic design methods for storage tanks larger tanks, and as such the seismic design for these larger storage tanks.

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Skip to main content. Log In Sign Up. The tanks resting on ground like clear water reservoirs, settling tanks, aeration tanks etc.

The walls of these tanks are subjected to pressure and the base is subjected to weight of water and pressure of soil. The tanks may be covered on top. The tanks like purification r.c.x.overhead, Imhoff tanks, septic tanks, and gas holders are built underground.

The walls of these tanks are subjected to water pressure from inside and the earth pressure from outside. The base is subjected to weight of water and soil pressure. These tanks may be covered at the top. Elevated tanks are supported on staging which may consist of masonry walls, R. The walls are subjected to water pressure.

The base has to carry the load of water and tank load. The staging has to carry load of water and tank. The staging is also designed for wind forces. From design point of view the tanks may be classified as per their shape-rectangular tanks, circular tanks, intze type tanks. Design requirement of concrete I. I In water retaining structures a dense impermeable concrete is required therefore, proportion of fine and course aggregates to cement should be such as to give high quality concrete.

Concrete mix weaker than M is not used. The design of the concrete mix shall be such that the resultant concrete is sufficiently impervious. Efficient compaction preferably by vibration is essential. The permeability of the thoroughly compacted concrete is dependent on water cement ratio. Increase in water cement ratio increases permeability, while concrete with low water cement ratio is difficult to compact.

Other causes of leakage in concrete are defects such as segregation and honey combing. All joints should be made water-tight as these are potential sources of leakage. Design of liquid retaining structures is different from ordinary R.

C, structures as it requires that concrete should not crack and hence tensile stresses in concrete should be within permissible limits.

A reinforced concrete member of liquid retaining structures is designed on the usual principles ignoring tensile resistance of concrete in bending. Additionally it should be ensured that tensile stress on the liquid retaining face tajk the equivalent concrete section does not exceed the permissible tensile strength of concrete as given in table 1.

For calculation purposes the cover is also taken into concrete area. Such restraint may be caused by — i the interaction between reinforcement and concrete during shrinkage due to drying. Use of small size bars placed properly, leads to closer cracks but of smaller width.

The risk of dexign due to temperature and shrinkage effects may be minimised by limiting the changes in moisture content and temperature to which the structure as a whole is subjected. The risk of cracking can also be minimised by reducing the restraint on the free expansion of the structure with long walls or slab founded at or below ground level, restraint can be minimised by the provision of a sliding layer.

water tank design example | Ravindra Ranatunga Ranatunga –

This can be provided by founding the structure on a flat layer of concrete with interposition of some material to break the bond and facilitate movement. In case length of structure is large it should be subdivided into suitable lengths separated by movement joints, specially where sections are changed the movement joints should be provided. Where structures have to store hot liquids, stresses caused by difference in temperature between inside and outside of the reservoir should be taken into account.


Joints in Liquid Retaining Structures. Joints are classified as given below. There are three types of movement joints. It is a movement joint with deliberate discontinuity without initial gap between the concrete on either side of the joint.

The purpose of this joint is to accommodate contraction of the concrete.

The joint is shown in Fig. A complete contraction joint is one in which both steel and concrete are interrupted and a partial contraction joint is one in which only the concrete is interrupted, the reinforcing steel running through as shown in Fig. It is a joint with complete discontinuity in both reinforcing steel and concrete and it is to accommodate either expansion or contraction of the structure. Taank typical expansion joint is shown in Fig. It is a joint with complete discontinuity in both reinforcement and concrete and with special provision to facilitate movement in plane of the joint.

A typical joint is shown in Fig.

This type of joint is watfr between wall and floor in some r.c.c.overheav tank designs. This type of joint is provided for convenience in construction. Arrangement is made to achieve subsequent continuity without relative movement.

One application of these joints is between successive lifts in a reservoir wall. A gap is sometimes left temporarily between the concrete of adjoining parts of a structure which Fig.

In the first case width of the gap should be sufficient r.c.c.ovverhead allow the sides to be prepared before filling. Unless alternative effective means are taken to avoid cracks by allowing for the additional stresses r.c.c.overhhead may be induced by temperature or shrinkage changes or by unequal settlement, movement joints should be provided at the following spacings: The wall and floor joints should be in line except where sliding joints occur at the base of the wall in which correspondence is not so important.

The maximum length desirable between vertical movement joints will depend upon the tensile strength of the walls, and may be increased by suitable reinforcement. When a sliding layer is placed at the foundation of a wall, the length of the wall that can be kept free of cracks depends on the capacity of wall section to resist the friction induced at the plane of sliding.

Overhead RCC Water Tanks Construction

Approximately the wall has to stand the effect of a force at the place of sliding equal to weight of half the length of wall multiplied by the co-efficient of friction. When the range of temperature is small, for example, in certain covered structures, or where restraint is small, for example, in certain elevated structures none of the movement joints provided in small structures up to 45m.

Where sliding joints are provided between the walls and either the floor or roof, the provision of movement joints in each element can be considered independently. General Design for Requirements I. Plain concrete member of reinforced concrete liquid retaining structures may be designed against structural failure by allowing tension in plain concrete as per the permissible limits for tension in bending.

This will automatically take care of failure due to cracking. However, nominal reinforcement shall be provided, for plain concrete structural members. Permissible Stresses in Concrete.

For calculations relating to the resistance of members to cracking, the permissible stresses in tension direct and due to bending and shear shall confirm to the values specified in Table 1. The permissible tensile stresses due to bending apply to the face of the member in contact with the liquid. In members less than mm. In strength calculations the permissible concrete stresses shall be in accordance with Table 1.

Where the calculated shear stress in concrete alone exceeds the permissible value, reinforcement acting in conjunction with diagonal compression in the concrete shall be provided to take the whole of the shear. Permissible Stresses in Steel a For resistance to cracking. When steel and concrete are assumed to act together for checking the tensile stress in concrete for avoidance of crack, the tensile stress in steel will be limited by the requirement that the permissible tensile stress in the concrete is not exceeded so the tensile stress in steel shall be equal to the product of modular ratio of steel and concrete, and the corresponding allowable tensile stress in concrete.


In strength calculations the permissible stress shall be as follows: Stress limitations for liquid retaining faces shall also apply to: Stresses due to drying Shrinkage or Temperature Change. Floors i Provision of movement joints. Movement joints should be provided as discussed in article 3. If the tank is resting directly over ground, floor may be constructed of concrete with norminal percentage of reinforcement provided that it is certain that the ground will carry the load without appreciable subsidence in any part and that the concrete floor is cast in panels with sides not more than 4.

In such cases a screed or concrete layer less than 75 mm thick shall first be placed on the ground and covered with a sliding layer of bitumen paper or other suitable material to destroy the bond between the screed and floor concrete. In normal circumstances the screed layer shall be of grade not weaker than Mwhere injurious soils or aggressive water are expected, the screed layer shall be of grade not weaker than M and if necessary a sulphate resisting or other special cement should be used.

The width of the slab shall be determined in usual manner for calculation of the resistance to cracking of T-beam, L-beam sections at supports. In such cases no separate beam curved or straight is necessary under the wall, provided the wall of the tank itself is designed to act as a beam over the supports under it.

In such cases the dome shall be designed for the vertical loads of the liquid over it and the ratio of its rise to its diameter shall be so adjusted that the stresses in the dome are, as far as possible, wholly compressive. The dome shall be supported at its bottom on the ring beam which shall be designed for resultant circumferential tension in addition to vertical loads. Walls i Provision of Joints a Sliding joints at the base of the wall.

Where it is desired to allow the walls to expand or contract separately from the floor, or to prevent moments at the base of the wall owing to fixity to the floor, sliding joints may be employed.

While designing the walls of rectangular or polygonal concrete tanks, the following points should be borne in mind.

An estimate should be made of the proportion of the pressure resisted by bending moments in the vertical and horizontal planes. The direct horizontal tension caused by the direct pull due to water pressure on the end walls, should be added to that resulting from horizontal bending moments. On liquid retaining faces, the tensile stresses due to the combination of direct horizontal tension and bending action shall satisfy the following condition: The walls thus act as thin plates subjected triangular loading and with boundary conditions varying between full restraint and free edge.

The analysis of moment and forces may be made on the basis of any recognized method. While designing walls of cylindrical tanks the following points should be borne in mind: In either case deformation of wall under influence of liquid pressure is restricted at and above the base. Consequently, only part of the triangular hydrostatic load will be carried by ring tension and part of the load at bottom will be supported by cantilever action.

Roofs i Provision of Movement Joints. To avoid the possibility of sympathetic cracking it is important to ensure that movement joints in the roof correspond with those in the walls, if roof and walls are monolithic.

It, however, provision is made by means of a sliding joint for movement between the roof and the wall correspondence of joints is not so important. Field covers of liquid retaining structures should be designed for r.c.c.oveerhead loads, such as the weight of roof slab, earth cover if any, live loads and mechanical equipment.


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