# Design of Retaining Wall and Water Tank

### Contents

**Define the term Retaining wall**1**Classify Retaining wall**1**Recall the stability of the Retaining wall**2**Recall the general design requirements**2**Describe the design procedure of Retaining wall.**3**Classify Water Tank**4**Recall the Permissible Stresses in Concrete: i. For resistance to cracking ii. For strength calculations**5**Recall the Permissible Stress in Steel**5**Recall Stresses during Temperature change**6**Classify Joints**6**Describe Spacing of Joints**7**Describe the following components of a Water Tank: i. Floors ii. Roofs iii. Walls**7**Recall the Minimum Reinforcement in the Water Tank**8**Describe the analysis of members subjected to Axial tension only.**9**Describe the analysis of members subjected to Bending moment only**10**Describe the analysis of members subjected to combined Axial, Tension, and Bending moments.**11**Describe the design procedure for Circular water tanks**12**Describe the design procedure for Rectangular water tanks**13

Define the term Retaining wall

A retaining wall is a structure designed to hold back soil, rock, or other materials that are behind it, preventing them from sliding or eroding away. The purpose of a retaining wall is to provide stability to slopes, prevent soil erosion, and protect adjacent structures and properties. Retaining walls can be made of various materials, including concrete, masonry, wood, and other materials, and they can be designed in various shapes and sizes to fit the specific needs of a site. The design of a retaining wall must take into account factors such as the type of soil being held back, the height of the wall, the angle of the slope, and other factors that may affect the stability of the wall. The design procedure for retaining walls involves calculating the forces acting on the wall and ensuring that the wall is strong enough to resist these forces.

Classify Retaining wall

Retaining walls can be classified into various categories based on various factors, including the following:

- Material used: Retaining walls can be made of various materials such as concrete, masonry, wood, steel, etc.
- Purpose: Retaining walls can be used for various purposes such as providing stability to slopes, preventing soil erosion, and protecting adjacent structures and properties.
- Load-bearing capacity: Retaining walls can be designed to support different loads, including earth pressure, water pressure, and seismic forces.
- Height: Retaining walls can vary in height, from short retaining walls used to hold back small amounts of soil to tall retaining walls used to support large amounts of soil or rock.
- Shape: Retaining walls can be designed in various shapes, including straight, curved, stepped, and tiered.
- Type of backfill: Retaining walls can be designed to hold back different types of backfill, including soil, rock, and other materials.
- Type of foundation: Retaining walls can be designed with different types of foundations, including deep foundations, shallow foundations, and gravity foundations.

These classifications help engineers and designers to determine the most appropriate type of retaining wall for a given site, based on its specific needs and requirements.

Recall the stability of the Retaining wall

The stability of a retaining wall refers to its ability to resist the forces acting on it and maintain its position without collapsing. This stability is achieved by ensuring the proper design and construction of the retaining wall, taking into account factors such as the height of the wall, the weight of the soil behind it, the type of soil, and the type of wall being used. The stability of the retaining wall is dependent on several factors, including the material properties, the geometry of the wall, and the loads acting on the wall. It is important to assess the stability of the retaining wall to ensure its safety and prevent failures that could result in damage to property or injury to people. The stability of the retaining wall is typically assessed through calculations and analysis using design codes and standards, such as the Indian Standard Code of Practice for Concrete Structures (IS:456).

Recall the general design requirements

Recall the general design requirements for Retaining walls refers to the necessary considerations and guidelines that must be taken into account when designing a retaining wall. These requirements are essential to ensure the safety, stability, and functionality of the retaining wall.

The following are some of the general design requirements for a retaining wall:

- Loads: The retaining wall must be able to withstand the loads it will encounter, including the weight of the soil, water pressure, seismic forces, and wind loads.
- Stability: The retaining wall must have adequate stability to resist overturning, sliding, or collapsing.
- Drainage: The retaining wall must have proper drainage to prevent water build-up and damage to the structure.
- Foundation: The retaining wall must have a strong foundation that can support the loads and resist settling.
- Material selection: The retaining wall must be constructed using materials that are suitable for the local conditions and are durable, strong, and resistant to weathering.
- Reinforcement: The retaining wall may require reinforcement, such as steel bars, to increase its strength and stability.
- Height: The height of the retaining wall must be limited to what is necessary to support the soil and prevent instability.
- Structural Integrity: The retaining wall must be designed to ensure its structural integrity and stability over its expected lifetime.

These design requirements should be considered in conjunction with the relevant building codes, regulations, and standards to ensure that the retaining wall is safe, stable, and functional.

Describe the design procedure of Retaining wall.

The design procedure of a retaining wall involves the following steps:

- Determination of Loads: The loads acting on the retaining wall need to be determined, including the weight of the soil, water pressure, and lateral earth pressure.
- Selecting the Type of Retaining Wall: The type of retaining wall suitable for the particular situation must be selected, taking into account the type of soil, the height of the wall, and the loads acting on it.
- Dimensioning: The dimensions of the retaining wall need to be determined based on the height of the wall, the width of the base, and the thickness of the wall.
- Reinforcement: The reinforcement requirements for the retaining wall need to be calculated based on the loads acting on the wall, the height of the wall, and the type of soil.
- Footing Design: The design of the footing of the retaining wall needs to be done, taking into account the loads acting on the wall and the type of soil.
- Seepage Analysis: The seepage analysis of the retaining wall must be done to determine the potential for water to penetrate through the wall and cause damage.
- Stability Analysis: The stability of the retaining wall must be analyzed, taking into account the loads acting on the wall, the height of the wall, and the type of soil. The analysis must be done to ensure that the wall does not collapse or tip over.
- Detailing: The details of the retaining wall must be prepared, including the type and size of reinforcement, the spacing of reinforcement, and the type of concrete to be used.

These are the general steps involved in the design of a retaining wall. The design must be done in accordance with the relevant codes and standards, taking into account the specific conditions and requirements of each particular project.

Classify Water Tank

Water tanks can be classified based on various criteria, such as construction materials, size, shape, location, and purpose. Some common classifications include:

- Overhead/Underground Tanks: These are tanks that are built either above or below the ground.
- Concrete/Steel Tanks: These tanks are constructed using concrete or steel as the main building material.
- Rectangular/Circular Tanks: These tanks can be either rectangular or circular in shape.
- Small/Large Tanks: Tanks can be classified based on their size, with smaller tanks typically used for domestic purposes and larger tanks for industrial or agricultural applications.
- Elevated/Ground-Level Tanks: These tanks can be built either at an elevated level or at ground level.
- Potable/Non-Potable Tanks: These tanks are used to store either drinking water (potable) or non-drinking water (non-potable).

Recall the Permissible Stresses in Concrete: i. For resistance to cracking ii. For strength calculations

The permissible stresses in concrete are the stresses that can be safely sustained by the concrete without causing cracking or other permanent damage to the structure.

i. For resistance to cracking: The permissible stress for resistance to cracking is determined based on the tensile strength of concrete, which is typically between 1/10 and 1/15 of the compressive strength. It is generally recommended that the maximum tensile stress in concrete should not exceed 0.5 N/mm².

ii. For strength calculations: The permissible stress for strength calculations is determined based on the compressive strength of concrete. The IS code provides guidelines for determining the permissible stresses for different grades of concrete, with the permissible stress being directly proportional to the compressive strength of the concrete. The maximum permissible stress for concrete of strength 30 N/mm² is taken as 6 N/mm², while the maximum permissible stress for concrete of strength 40 N/mm² is taken as 8 N/mm².

Recall the Permissible Stress in Steel

- In Reinforced Cement Concrete (RCC) design, the permissible stress in steel refers to the maximum stress that can be allowed in the steel reinforcement used in the structure. The permissible stress is determined based on the yield strength of the steel and the factor of safety considered for the structure.
- The permissible stress in steel is an important factor in the design of RCC structures as it helps to ensure that the structure is safe and has adequate strength.

The permissible stress in steel is determined by dividing the yield strength of the steel by the factor of safety. In general, a factor of safety of 1.5 to 2 is used for steel reinforcement in RCC structures, resulting in a permissible stress of approximately 50-67% of the yield strength of the steel. - It is important to ensure that the permissible stress in steel is not exceeded during the design and construction of the structure to prevent any failure or collapse.

Recall Stresses during Temperature change

Stresses during temperature change in a water tank can be caused by temperature variations which cause the concrete to expand and contract. This can result in stresses developing within the tank walls and floor. The magnitude of these stresses depends on the magnitude of temperature change, the cross-sectional area of the tank, and the coefficient of thermal expansion of the concrete. In order to minimize the risk of cracking, it is important to control the temperature changes experienced by the tank, such as ensuring the concrete is properly cured and insulated. It is also necessary to consider these temperature stresses when designing the tank to ensure that it is able to withstand them and maintain its structural integrity.

Classify Joints

Joints are the spaces between two adjacent concrete members where movement or relative displacement can occur due to various reasons such as temperature, moisture, shrinkage, etc. Joints are classified into the following categories:

- Construction Joints: They are the joints that are deliberately introduced during the construction process to facilitate the construction.
- Contraction Joints: They are the joints that are introduced to control cracking due to the contraction of concrete during the curing process.
- Expansion Joints: They are the joints that are introduced to control cracking due to the expansion of concrete due to temperature change.

Describe Spacing of Joints

Spacing of joints in a concrete structure refers to the distance between two consecutive joints. Proper spacing of joints is crucial for the durability and longevity of the structure. If the spacing is too large, the concrete may crack due to excessive shrinkage or temperature changes. If the spacing is too small, the structure may become weaker and less resistant to loading.

The IS Code recommends a maximum spacing of 6m for plain concrete and 4.5m for reinforced concrete. The exact spacing of joints depends on several factors such as the size of the structure, the type of concrete used, the environmental conditions, and the type of loading the structure will be subjected to.

It is important to note that joints should be placed in areas of the structure where shrinkage is most likely to occur, such as corners, edges, and areas with large temperature differences. Additionally, the joint should be made by cutting the concrete and providing a clean, straight surface for the joint sealant to bond to.

Describe the following components of a Water Tank: i. Floors ii. Roofs iii. Walls

A water tank is an essential component of any water storage system, providing a large and accessible source of water for various uses. In a water tank, the various components work together to hold water securely and prevent leaks. These components include:

i. Floors: The floor of a water tank serves as the base of the tank, providing support and stability for the walls and roof. Floors are usually made of reinforced concrete, which is strong and durable. The thickness and reinforcement of the floor depend on the weight of the water, the height of the walls, and the ground conditions.

ii. Roofs: The roof of a water tank protects the water from exposure to the elements, including rain, wind, and sunlight. Roofs are typically made of reinforced concrete or steel, with a waterproofing membrane or coating to prevent leaks. The design of the roof should also account for thermal expansion and contraction and wind loads.

iii. Walls: The walls of a water tank provide the main structural support for the roof and floor, holding the water securely. Walls are typically made of reinforced concrete, with the reinforcement and thickness depending on the height of the tank, the water pressure, and the design load. The walls should also be designed to withstand seismic forces and wind loads, if necessary.

It’s important to note that the design of a water tank should follow the relevant codes and standards, such as the Indian Standard Code for Design and Construction of RCC Structures (IS 456). This will ensure that the tank is safe, durable, and fit for purpose.

Recall the Minimum Reinforcement in the Water Tank

In reinforced concrete construction (RCC), the minimum reinforcement in a water tank refers to the amount of steel reinforcement that is necessary to ensure that the concrete structure can withstand the expected loads and environmental conditions it will be subjected to over its lifetime. This reinforcement helps to distribute stress and strain evenly throughout the structure and prevent cracking, collapse, and other forms of failure.

According to the Indian Standard Code (IS Code), the minimum reinforcement in a water tank must meet certain criteria, including the minimum area of reinforcement, the maximum spacing of reinforcement, and the minimum cover for the reinforcement. These criteria are based on factors such as the size and shape of the tank, the type and magnitude of loads it will be subjected to, and the environmental conditions it will be exposed to, such as temperature fluctuations and exposure to water.

The specific minimum reinforcement requirements for a water tank are determined by an engineer or designer, taking into account the design load conditions and local building codes and standards. The reinforcement must be designed and placed in such a way that it is able to effectively transfer stress and strain throughout the structure, and prevent cracking and other forms of failure.

Describe the analysis of members subjected to Axial tension only.

The analysis of members subjected to axial tension only is a crucial aspect of the design of reinforced concrete structures, particularly in the design of water tanks. In this type of loading, the concrete members are subjected to pure tensile stresses, with no bending or shear forces present.

The calculation of the axial tensile strength of a concrete member involves determining the amount of reinforcement required to resist the applied tension. The amount of reinforcement required is proportional to the tensile strength of the concrete and the size of the cross-section of the member.

The concrete’s tensile strength can be determined by multiplying the compressive strength by a coefficient of tensile strength, which is typically around 0.2 to 0.3 for normal weight concrete. The size of the cross-section of the member can be determined using the dimensions of the member and the type and spacing of reinforcement.

Once the required amount of reinforcement has been determined, the design procedure involves determining the size and spacing of the reinforcement bars to be used. The reinforcement bars must be spaced in such a way as to provide adequate bond between the concrete and the reinforcement, while also ensuring that the bars are not too close together to cause congestion.

In summary, the analysis of members subjected to axial tension only involves determining the required amount of reinforcement, based on the tensile strength of the concrete and the size of the cross-section of the member, and then selecting the appropriate size and spacing of reinforcement bars to resist the applied tension.

Describe the analysis of members subjected to Bending moment only

Bending moment refers to the effect of forces that cause a structural member to bend and deform. When a member is subjected to a bending moment, it experiences both compressive and tensile stresses. The analysis of members subjected to bending moment only involves determining the magnitude and distribution of these stresses along the member.

There are several methods for analyzing members subjected to bending moments, including hand calculations, and numerical or computer-based methods. The most common method used for hand calculations is the Moment Distribution Method, which involves distributing the moments along the member and solving for the internal forces and deformations. The steps involved in this method are as follows:

- Determine the applied loads and the loading condition of the member.
- Determine the support reactions and calculate the end moments using static equilibrium.
- Distribute the end moments along the member using a consistent set of assumptions.
- Solve for the internal forces and deformations by considering the effects of the compressive and tensile stresses along the member.
- Verify the accuracy of the solution by checking for equilibrium and compatibility of deformations.

The results of the analysis are used to determine the size and reinforcement requirements of the member to ensure that it can withstand the applied loads. The analysis also provides information about the deflection and stability of the member.

Describe the analysis of members subjected to combined Axial, Tension, and Bending moments.

The analysis of members subjected to combined axial, tension, and bending moment is a complex task that involves multiple calculations and factors. It involves analyzing the behavior of the member under different loading conditions and determining the internal forces that are developed as a result of the applied loads. The internal forces include axial forces, shear forces, and bending moments. The designer must determine the size and type of reinforcement required to resist these internal forces and ensure that the structure is safe and stable.

In the analysis of members subjected to combined axial, tension, and bending moment, the following steps are typically followed:

- Determine the loads acting on the member: This involves considering the self-weight of the member, any imposed loads, and any live loads.
- Determine the axial forces: The axial forces are the forces that act along the length of the member. They can be either compressive or tensile.
- Determine the shear forces: The shear forces are the forces that act transversely across the member. They can cause failure in the form of shear failure or diagonal tension failure.
- Determine the bending moments: The bending moments are the forces that cause the member to bend and deform. They can cause failure in the form of yielding, local buckling, or tensile failure.
- Design the reinforcement: The designer must determine the type and size of reinforcement required to resist the internal forces. The reinforcement must be capable of carrying the tension and bending moments and preventing the member from yielding or failing.
- Check for safety: The designer must perform a safety check to ensure that the member is capable of resisting the loads acting on it and that the structure is stable and safe.

In conclusion, the analysis of members subjected to combined axial, tension, and bending moment requires a thorough understanding of structural mechanics and an in-depth knowledge of reinforcement design. It is an important aspect of structural engineering and plays a crucial role in ensuring the safety and stability of reinforced concrete structures.

Describe the design procedure for Circular water tanks

The design procedure for circular water tanks involves several steps to ensure that the tank can withstand the loads and forces it will experience during its intended use. Some of the steps include:

- Determine the purpose of the tank and its dimensions: The first step is to determine the purpose of the tank (e.g. storage of drinking water, industrial water, etc.) and its dimensions, including the height and diameter. This information will be used to calculate the required volume of the tank.
- Determine the design loads: The next step is to determine the design loads, including dead loads (the weight of the tank itself), live loads (any external loads, such as wind or water), and any other loads that may be imposed on the tank. This information will be used to calculate the required strength of the tank.
- Determine the permissible stresses: The permissible stresses for concrete and steel must be established for the design of the tank. The permissible stress for concrete is based on its resistance to cracking, while the permissible stress for steel is based on its strength.
- Design the walls: The walls of the circular tank must be designed to resist the axial and bending forces that are generated by the design loads. The thickness of the walls will depend on the height of the tank, the diameter, and the type of reinforcement used.
- Design the roof: The roof of the circular tank must be designed to resist the forces generated by the design loads. The roof must also be designed to provide adequate support to the walls and to prevent collapse in the event of a load failure.
- Design the floors: The floors of the circular tank must be designed to resist the forces generated by the design loads and to provide adequate support to the walls and roof. The thickness of the floors will depend on the height of the tank and the type of reinforcement used.
- Design the joints: The joints in the tank must be designed to allow for movement due to thermal expansion and contraction. The joints must also be designed to resist any forces that may be generated by the design loads.
- Check for stability: Finally, the stability of the circular tank must be checked to ensure that it will not tip over or collapse under the design loads. This step includes verifying that the centre of gravity of the tank is within its base, and checking the stability of the tank against sliding and overturning.

Overall, the design procedure for circular water tanks requires a comprehensive understanding of the loads and forces that the tank will experience, as well as the material properties of concrete and steel. It also requires careful consideration of the different components of the tank, including the walls, roof, floors, and joints, to ensure that the tank will be able to resist the design loads and remain stable over time.

Describe the design procedure for Rectangular water tanks

The design procedure for rectangular water tanks involves the following steps:

- Determining the capacity of the tank: The capacity of the tank should be determined based on the water requirement for the intended use.
- Selecting the dimensions: The dimensions of the tank should be selected based on the capacity and the available space. The aspect ratio of the tank, i.e. the ratio of its width to its length, should be selected to minimize the bending stresses and to avoid buckling of the walls.
- Designing the walls and floor: The walls and floor of the tank are usually made of reinforced concrete and are designed to withstand the weight of the water and any additional loads such as the weight of the people and equipment that will be used to access the tank. The minimum thickness of the walls should be determined based on the permissible stresses in concrete and steel.
- Designing the roof: The roof of the tank can be made of reinforced concrete or any other suitable material such as RCC slab or metal sheets. The roof should be designed to withstand the weight of the water, wind loads and any additional loads such as the weight of people or equipment.
- Designing the joints: The joints between the walls, roof, and floor should be designed to accommodate the expansion and contraction of the tank due to temperature changes. The spacing of the joints should be determined based on the size of the tank and the permissible stresses.
- Designing the reinforcements: The reinforcements in the walls, roof and floor should be designed based on the stress analysis of the members subjected to axial tension, bending moment or a combination of both. The minimum reinforcement in the tank should be determined based on the size of the tank and the permissible stresses.
- Calculating the stresses: The stresses in the members should be calculated using the theory of mechanics of materials. The stresses due to the weight of the water, wind loads and any additional loads should be taken into consideration.
- Checking the safety: The safety of the tank should be checked by ensuring that the calculated stresses are within the permissible limits. The load-bearing capacity of the tank should be verified and the tank should be designed to provide a sufficient factor of safety against collapse.