The document provides information about structures and the collapse of the Tacoma Narrows Bridge in 1940. It discusses the requirements of structures, including safety, strength, stability, rigidity, resistance, durability and economy. It then summarizes the collapse of the Tacoma Narrows Bridge, noting that it collapsed after 4 months in use due to oscillations caused by wind speeds of 55-75 km/hr. No one was injured in the collapse. Engineers then investigated how to strengthen suspension bridges.

1. STRUCTURES Technologies 1st year ESO (Adapted from a presentation by Manuel Suarez Alvite)

7. STRUCTURES: Forces A “successful” structure must be able to withstand all the forces it will experience without collapsing. An understanding of the kinds of forces which can act on a structure is important to a designer. TENSION FORCES Forces which can cause a member to “stretch”. COMPRESSION FORCES Forces which can cause a member to be “squashed” or buckled.

8. STRUCTURES: Forces TORSIONAL FORCES When a turning force (or torque) is applied to a member, it may twist. BENDING FORCES They are forces which tend to make the object bend. SHEAR FORCES They act “across” a material in such a way that one part of the structure can be forced to slide over anoder

9. STRUCTURES: Activity Draw the following swing and write the name of the forces that are acting on it

10. STRUCTURES: Activity

11. Activity The bracket holding up the hanging basket is made of steel and fixed to the wall with a screw. Write the forces exerted on the following points What forces are acting on the screw used to fix the bracket to the wall?

13. Types of structures 2. FRAME STRUCTURES 2. Frame Structures They have a skeleton of strong materials, which is then filled and covered with other materials, supporting the overall structure. Most of the inside part of the structure is empty space. Buildings made of steel beams and columns are an example of frame structures. Sometimes the columns and beams are made of reinforced concrete instead of steel.

14. Types of structures 2. FRAME STRUCTURES Concrete is a mixture of cement and stone aggregate and mixed with a small amount of water. When steel bars are placed in concrete, the composite material is called reinforced concrete . It resists compression and bending.

15. Types of structures 3. TRUSSES 3. Trusses Trusses are frame structures formed by triangles. The triangle is the most rigid frame structure and many complex structures are based on triangles. The technique used in these type of structures is called triangulation .

16. Types of structures 3. TRUSSES When forces are applied to a simple four-sided structure, it can be forced out of shape. A structure which behaves in this way is said to be non-rigid By adding an extra bar the structure can no longer be forced out of shape, and is said to be rigid. The effect is known as triangulation

17. Types of structures 3. TRUSSES Alternatively, a frame structure can be made rigid by the use of gusset plates. A GUSSET is a piece of material used to brace and join the members in a structure.

18. Types of structures 4. SHELL STRUCTURES 4. Shell Structures Structures, which keep their shape and support loads, even without a frame, or solid mass material inside, are called shell structures. These structures use an outer layer of material to provide their strength and rigidity. The shape of a shell structure spreads forces throughout the whole structure, which means every part of the structure supports only a small part of the load, giving it its strength. Examples include: egg cartons, water containers, gas tanks and cars

19. Types of structures 5. SUSPENSION STRUCTURES 5. Suspension structures Suspension structures are those with horizontal planes (road decks, roofs, and even floors) supported by cables (hangers). Suspension bridges are good examples of these structures. In these bridges, cables suspended via towers hold up the road deck.

20. Types of structures 6. VAULTED STRUCTURES 6. Vaulted structures Vaulted structures are those formed with arches . They are usually used to provide a big space with a ceiling or roof. The weight of the ceiling is conducted through the vault into the pillars (or columns) that are supporting it, and from those pillars into the foundation of the building. Different shapes in the vaulted structures have been used through history and depending on the different cultures.

21. Types of structures 7. GEODESIC STRUCTURES 7. Geodesic structures Geodesic structures (usuaslly called geodesic domes) are a kind of shell structures in which the shell is formed by polygons (usually triangles).