Challenge 8

1. What are piers and explain. Explain loads considered for calculating the total design force?

Answer:

Piers are vertical structural elements used to support and transfer the weight of a building or structure to the foundation or the ground below. Piers can be made of various materials such as concrete, masonry, or steel, and are commonly used in bridge and building construction.

In bridge construction, piers are typically built to support the weight of the bridge deck and any vehicles or loads that cross the bridge. Piers can be placed at regular intervals along the length of the bridge, and their size and shape will depend on the specific design of the bridge.

In building construction, piers are used to support the weight of the building's walls and roof. Piers can be built as independent columns or can be incorporated into the walls of the building. They can be designed to bear both compressive and tensile loads, and their size and strength will depend on the building's height, weight, and the soil conditions at the site.

In order to calculate the total design force that a pier must be able to support, several loads must be considered. These loads include:

1. Dead loads: the weight of the structure itself, including the weight of the walls, roof, floors, and any permanent fixtures or equipment.

2. Live loads: the weight of the people, vehicles, and equipment that will be using the structure.

3. Wind loads: the force of the wind on the structure, which can vary depending on the height, shape, and orientation of the building.

4. Seismic loads: the force of earthquakes or other ground movements on the structure.

5. Soil loads: the pressure exerted on the pier by the soil or rock beneath it.

By considering these loads, engineers can design piers that are strong enough to support the weight of the structure and any expected loads, and ensure that the building or bridge is safe and stable.

2. Explain about the DL, SIDL & LL considered for designing a pier of a metro viaduct? Also, what grade of cement is being used in the construction of piers

Answer:

Designing a pier for a metro viaduct requires consideration of various loads, including dead loads (DL), superimposed dead loads (SIDL), and live loads (LL).

1. Dead loads (DL): Dead loads refer to the weight of the permanent components of the structure, such as the weight of the pier itself, the weight of the track slab, and the weight of any other permanent fixtures. The dead loads are calculated based on the weight and dimensions of each component, and they are used to determine the size and strength of the pier.

2. Superimposed dead loads (SIDL): Superimposed dead loads refer to the weight of any additional components that are not considered permanent, but are still part of the structure. Examples of superimposed dead loads for a metro viaduct could include the weight of the electrical equipment, the weight of the cables or wires, and the weight of the ballast on the track slab.

3. Live loads (LL): Live loads refer to the weight of any moving or variable components of the structure, such as the weight of the trains, passengers, and any cargo or equipment being transported. The live loads are calculated based on the expected maximum weight and speed of the trains, and they are used to determine the dynamic response of the pier under varying load conditions.

In addition to the loads, the grade of cement used in the construction of the piers also plays an important role in their strength and durability. The grade of cement used in pier construction is typically based on the strength requirements of the pier, the soil conditions at the site, and any other relevant design factors. Commonly used grades of cement for pier construction include grades 33, 43, and 53, with higher grades indicating higher strength and durability. The specific grade of cement used in pier construction may vary depending on the local construction standards, materials availability, and design requirements.

3. Explain about the Braking & Traction effect and loads considered for designing a pier of a metro viaduct.

Answer:

Braking and traction are two important effects that need to be considered in the design of piers for a metro viaduct.

1. Braking effect: When a train brakes, it exerts a force on the track slab, which in turn exerts a force on the piers. The braking force is resisted by the pier, which needs to be designed to withstand this force. The braking force is typically calculated based on the maximum deceleration of the train, the weight of the train, and the coefficient of friction between the wheels and the track. The pier needs to be designed to resist the braking force without excessive deflection or damage.

2. Traction effect: When a train accelerates, it exerts a force on the track slab in the opposite direction of the train's motion. This force is resisted by the pier, which needs to be designed to withstand this force. The traction force is typically calculated based on the maximum acceleration of the train, the weight of the train, and the coefficient of friction between the wheels and the track. The pier needs to be designed to resist the traction force without excessive deflection or damage.

In addition to the braking and traction effects, several loads need to be considered in the design of piers for a metro viaduct. These loads include:

1. Dead loads: The weight of the pier itself and any permanent fixtures, such as the track slab, electrical equipment, and other components.

2. Live loads: The weight of the trains, passengers, and any cargo or equipment being transported.

3. Wind loads: The force of the wind on the structure, which can vary depending on the height, shape, and orientation of the pier.

4. Seismic loads: The force of earthquakes or other ground movements on the structure.

5. Temperature effects: The expansion and contraction of the pier due to temperature changes, which can cause additional stresses on the structure.

By considering these loads and the braking and traction effects, engineers can design piers that are strong enough to support the weight of the structure and any expected loads, and ensure that the metro viaduct is safe and stable.

4. Explain about the Centrifugal force & Wind load considered for designing a pier of a metro viaduct.

Answer:

Designing a pier for a metro viaduct also requires consideration of centrifugal force and wind load.

1. Centrifugal force: When a train takes a curve, it experiences a centrifugal force which pushes the train outward. This force is transmitted to the track slab, which exerts a force on the piers. The centrifugal force is resisted by the pier, which needs to be designed to withstand this force. The centrifugal force is typically calculated based on the radius of the curve, the speed of the train, and the mass of the train. The pier needs to be designed to resist the centrifugal force without excessive deflection or damage.

2. Wind load: Wind load refers to the force of the wind on the structure, which can vary depending on the height, shape, and orientation of the pier. Wind load is an important consideration in the design of piers for a metro viaduct, as strong winds can cause significant structural damage if the pier is not properly designed to withstand them. The wind load is typically calculated based on the wind speed and direction, the surface area of the pier, and the shape and orientation of the pier. The pier needs to be designed to resist the wind load without excessive deflection or damage.

In addition to these factors, other loads such as dead loads, live loads, seismic loads, and temperature effects, need to be considered in the design of piers for a metro viaduct. By considering all of these factors, engineers can design piers that are strong enough to support the weight of the structure and any expected loads, and ensure that the metro viaduct is safe and stable.

5. Explain about the Earthquake load & how the loadings are calculated as per code. Explain the three types where the seismic loads are considered.

Answer:

Earthquake load is an important factor to consider in the design of piers for a metro viaduct, especially in areas prone to seismic activity. Seismic loads are calculated based on the level of seismic hazard in the region, and the seismic loads must be taken into account to ensure the structure can withstand earthquakes without excessive deflection or damage.

Seismic loads are typically calculated as per the relevant building codes and standards, such as the International Building Code (IBC) or the Indian Standards (IS). These codes provide guidelines for determining the seismic hazard in a region and for calculating the seismic loads that structures must be designed to withstand.

The seismic loads are calculated based on the expected ground acceleration in the region, which is dependent on the seismic hazard, the soil conditions, and the proximity to active faults. The ground acceleration is converted into a seismic response spectrum, which is a graph showing the expected acceleration at different frequencies. The seismic response spectrum is then used to determine the seismic loads that the structure must be designed to resist.

There are three types of seismic loads that are typically considered in the design of piers for a metro viaduct:

1. Seismic weight: This refers to the weight of the structure and any permanent fixtures, such as the track slab and electrical equipment, that contribute to the seismic response of the structure.

2. Seismic force: This refers to the horizontal and vertical forces that are generated by the seismic response of the structure, including the inertia forces resulting from the mass of the structure and any dynamic effects caused by ground motion.

3. Seismic displacement: This refers to the deflection or displacement of the structure resulting from the seismic response, which can cause damage or failure if it exceeds the allowable limits.

The seismic loads must be considered in combination with other loads, such as dead loads, live loads, wind loads, and temperature effects, to ensure that the structure is designed to withstand all expected loads and is safe and stable.

6. Explain about the LWR forces & Derailment loads how the loadings are calculated as per code.

Answer:

Lateral Wheel/Rail (LWR) forces and derailment loads are important considerations in the design of piers for a metro viaduct. LWR forces refer to the lateral forces generated between the train wheels and the track, which can cause lateral deflection of the track and the piers supporting it. Derailment loads refer to the loads experienced by the piers in the event of a train derailment, which can cause significant structural damage.

The loadings for LWR forces and derailment loads are typically calculated as per the relevant metro codes and standards, such as the American Society of Civil Engineers (ASCE) Manual of Engineering Practice No. 79 or the Indian Standards (IS). These codes provide guidelines for calculating the lateral forces and derailment loads based on the characteristics of the train, the track, and the pier.

To calculate the LWR forces, the lateral force coefficient is used, which is a function of the train speed, the track alignment, and the characteristics of the train wheels and the track. The lateral force coefficient is multiplied by the vertical load on the wheel to determine the lateral force generated between the wheel and the track. The lateral force is then distributed to the track and the piers supporting it based on the stiffness and geometry of the track and the pier.

To calculate the derailment loads, the code specifies the loads and impact factors that the piers must be designed to resist in the event of a derailment. These loads are typically calculated based on the worst-case scenario for the train and the track, including the speed of the train, the type of train, and the curvature of the track. The loads are then applied to the pier in combination with other loads, such as the LWR forces, wind loads, and seismic loads, to determine the maximum loads that the pier must be designed to withstand.

By considering LWR forces and derailment loads in the design of piers for a metro viaduct, engineers can ensure that the structure is designed to withstand all expected loads and is safe and stable.

7. Explain the design combinations of the all the loads considered in a metro design through which we attain the factored BM from unfactored bending moments.

Answer:

In the design of piers for a metro viaduct, multiple loads are considered, including dead loads, live loads, wind loads, earthquake loads, braking and traction loads, and LWR forces and derailment loads. These loads are considered in combination to determine the maximum load that the pier must be designed to withstand.

The design combinations of loads are determined based on the relevant building codes and standards, such as the Indian Standards (IS) or the American Society of Civil Engineers (ASCE) Manual of Engineering Practice No. 79. These codes specify the load factors and load combinations that must be used to calculate the factored BM (bending moment) from the unfactored bending moments.

The load factors are applied to the different types of loads to account for the uncertainties and variabilities in the loads. For example, dead loads are typically multiplied by a load factor of 1.5, while live loads are multiplied by a load factor of 1.25. The load factors for other loads, such as wind loads and earthquake loads, may vary depending on the severity of the load and the level of uncertainty in the load.

Once the loads are factored, the load combinations are determined by the code based on the different types of loads that are present. For example, the code may specify a combination of dead load and live load, or a combination of wind load and earthquake load. The code also specifies the load factors that must be applied to each load type in the combination.

By considering the load factors and load combinations specified in the code, engineers can calculate the factored BM from the unfactored bending moments. The factored BM is then used in the design of the pier to ensure that it can withstand the maximum load that it may experience during its lifetime.

8. Explain the reason behind the factored load of SIDL is higher than the factored load of DL in a design.

Answer:

In the design of structures, dead load (DL) and superimposed dead load (SIDL) are two types of loads that are considered. Dead load is the weight of the structure itself, including all of its components, such as the piers, beams, and decking. SIDL, on the other hand, refers to the additional weight that is imposed on the structure during its lifetime, such as the weight of the train, passengers, and other equipment.

In a design, the factored load of SIDL is typically higher than the factored load of DL due to several reasons. First, SIDL represents the additional weight that is imposed on the structure during its lifetime, which can vary significantly depending on the use and occupancy of the structure. For example, in the case of a metro viaduct, the weight of the train and the number of passengers can vary significantly, which can result in a significant variation in SIDL.

Second, SIDL is typically considered a more variable load than DL, which is typically a constant load. The variability in SIDL can result in a higher level of uncertainty in the load, which is accounted for by increasing the factored load. This ensures that the structure is designed to withstand the worst-case scenario of the load.

Third, the factored load of SIDL is also higher than the factored load of DL to account for the potential for long-term effects, such as creep and shrinkage, which can cause the structure to deform over time. These effects are not typically considered in the design of DL, but they can have a significant impact on the long-term performance of the structure.

In summary, the factored load of SIDL is typically higher than the factored load of DL in a design due to the variability in the load, the potential for long-term effects, and the need to ensure that the structure is designed to withstand the worst-case scenario of the load.

9. What are the basic design parameters considered for a RCC pier cap.

Answer:

In a metro project in India, the basic design parameters considered for a reinforced concrete (RCC) pier cap include the following:

1. Load carrying capacity: The pier cap must be designed to carry the loads imposed on it, including the weight of the superstructure, live loads such as the weight of the train and passengers, wind loads, earthquake loads, and braking and traction loads.

2. Span and height of the pier cap: The span and height of the pier cap are determined by the spacing and height of the piers that support it. The span of the pier cap should be sufficient to accommodate the width of the superstructure and the live load.

3. Bearing capacity: The pier cap must be designed to transfer the loads from the superstructure to the piers. The bearing capacity of the pier cap should be sufficient to ensure that the loads are distributed evenly across the piers.

4. Reinforcement detailing: The reinforcement detailing of the pier cap is critical to ensure that the structure can withstand the loads imposed on it. The reinforcement detailing should be such that it provides sufficient resistance against bending, shear, and torsion.

5. Durability: The pier cap must be designed to ensure long-term durability in the harsh environmental conditions of a metro viaduct. The concrete mix design and cover thickness should be selected to prevent corrosion of the reinforcement.

6. Constructability: The pier cap must be designed with consideration of ease of construction. The design should be such that it can be easily constructed within the project timeline and budget.

These design parameters are crucial in ensuring the safety and performance of the pier cap in a metro project in India.

10. Explain the reinforcement detailing from the result extraction in longitudinal & sectional views of a viaduct.

Answer:

Reinforcement detailing is a critical aspect of the design of a viaduct in a metro project, and it involves the detailed specification of the reinforcement steel bars to be used in the construction of the structure. The reinforcement detailing is usually done using the results extracted from the longitudinal and sectional views of the viaduct.

The longitudinal view shows the viaduct in a horizontal plane, and it is used to extract the results for the longitudinal reinforcement. The results extracted from this view include the clear cover, the number and diameter of the bars, the spacing between the bars, and the type of bars to be used. The clear cover is the distance between the surface of the concrete and the reinforcement bars. It is important to maintain an adequate clear cover to prevent corrosion of the reinforcement. The number and diameter of the bars, as well as their spacing, are determined based on the loads that the structure is expected to carry.

The sectional view, on the other hand, shows the viaduct in a vertical plane, and it is used to extract the results for the transverse reinforcement. The results extracted from this view include the size and spacing of the stirrups or ties, the type of stirrups or ties, and the clear cover. Stirrups or ties are used to provide resistance against shear forces and to hold the longitudinal reinforcement in place. The size and spacing of the stirrups or ties are determined based on the loads that the structure is expected to carry.

In summary, the reinforcement detailing for a viaduct in a metro project is a critical aspect of the design, and it involves the detailed specification of the reinforcement steel bars to be used in the construction of the structure. The results extracted from the longitudinal and sectional views of the viaduct are used to determine the clear cover, the number and diameter of the bars, the spacing between the bars, and the size and spacing of the stirrups or ties.