Structural calculations are used in various fields and construction projects in the United Kingdom. Here are a few examples of when they are needed:

1. Residential and Commercial Buildings: When designing residential and commercial buildings, structural calculations are essential to ensure stability, durability, and safety of the structure. This applies to both new constructions and renovation or expansion of existing properties.

2. Bridges and Tunnels: For the construction of bridges and tunnels, structural calculations are crucial to ensure that the structure can withstand the loads from traffic, wind, and other external factors.

3. Road Infrastructure: In the case of roads, highways, and other road infrastructure, structural calculations help determine the thickness of pavement layers, drainage solutions, as well as bridge and viaduct structures.

4. Energy Investments: When building power plants, wind turbine towers, or other energy facilities, structural calculations ensure that the structures can handle the loads associated with energy production.

5. Industrial Construction: For production halls, warehouses, and other industrial facilities, structural calculations are necessary to ensure that the building can accommodate equipment and materials and withstand all relevant loads.

6. Public Utility Buildings: Structural calculations are also used in designing public utility buildings such as schools, hospitals, shopping centers, and sports facilities to ensure safety and comfort for users.

7. Specialized Structures: In some cases, such as underground structures, piers, or telecommunication towers, specialized structural calculations are needed due to unique conditions and requirements.

In practice, structural calculations are required in nearly every construction project where the key goal is to create a safe, durable, and functional structure that meets the client's requirements and complies with applicable regulations and standards.