1. The strength and stiffness of structures AHL Topic 9: Structures

2. Deflection and stiffness If an external load is applied to some part of a structure, that part will be deflected to an extent that depends on the size of the load and the stiffness of the structure.

3. Testing a product for stiffness Stiffness = Load Deflection Bending test Compression test TYPICAL COMPOSITION CURVE: This graph represents the deflection values measured at incremental load values.

4. How do you calculate the stiffness of a structure? Stiffness = Load Deflection

5. Bending moment The bending moment is the moment that a beam has to resist in bending at a particular section.

6. Moment arm The load X distance from the pivot is called the moment about the pivot. The distance between the load and the pivot is called the moment arm. The moment arm

7. Factor of Safety There is a need for a factor of safety in structural design. Structures are designed to take higher loads than those they are normally expected to support. For example: a children's slide needs to be able to withstand a higher load as you would normally need to account for larger children using it and account for misuse.

8. How do you calculate the factor of safety for a structure? Factor of safety = design load normal maximum load A factor of safety is simply the ratio of the quantitative value of a design factor divided by the normal expected value. For example... a cable that breaks under a load limit of 1000 pounds but is listed as having a maximum load limit of 100 pounds has a safety factor of 10.

9. Design context Evaluate the importance of strength and stiffness in the following structure: The Oresund Bridge

10. Building a single-purpose bridge is a complex engineering feat. Now add other complicating factors, like a bridge to carry both trains and cars. And join that bridge seamlessly with an immersed tunnel. These were the design requirements facing engineers when they began planning how to connect Denmark and Sweden across the Oresund Strait. Their solution was one of the largest infrastructure projects in European history: the $3 billion Oresund Fixed Link. Collectively, the Oresund Fixed Link is a miracle of modern engineering. It is the world's longest cable- stayed bridge for both road and railway. Its towers are 669 feet (204 meters) high and provide a navigational clearance of 187 feet (57 meters) under the main span. The bridge features two levels, with the railway running along the lower deck and the roadway on the upper.