Structures and Forces

Structures and Forces

1. Types Of Structures

   • Structures are objects that supports its self weight and external loads without collapsing and is able to hold different parts in the right place.
   • Man Made Structures
     • Structures made by humans. EG:: Houses Highways Bridges or Cans
   • Natural Structures
     • Forms that stand on their own, created from the Earthg's natural forces or through the efforts of animals but not made by human. Eg : beehives, rock arches, canyons, eggshells, bird's nests, coral reefs and naturally formed caves.
   • Shell Structures
     • A Structure that is held up by an outer shell and is usually hollow inside. Some Natural Shell Structures are the shells of animals such as turtles or lobsters , eggs , While some Man-Made shell structures include Vehicles such as Aeroplanes , Cars and boats.
   • Frame Structures
     • Frame Structures are structures that are held up by a series of frames . Some Natural structures are leaves while some man-made frame structures are Bus stops or buildings such as houses.
     • Open-Frame structures : no "skin" on them eg : spider's web
     • Frame Structures with skin EG: Leaves

2. Functions of structures

   • Support
     • Foundations of buildings or legs of tables
   • Span
     • Bridge or Shelf
   • COntain
     • Box
   • Protect
     • Foam Packaging or safety helmet

3. Forces acting on structures and are they dynamic or static?

   • Dynamic Forces
     • A load that changes size , position or direction
       • 1) Shear EG: Cutting paper with a pair of scissors
       • 2)Tension EG: String of a Tennis Racket
       • 3)Torsion: (Rotary or Twisting Force) EG: Ice Skater in air
       • 4) Compression EG: Legs of a Chair.
       • Bending (EXternal Force) EG::Jumping from a spring board
   • Static Forces
     • Static Force has a constant size , position and direction within a structure
       • Live Loads acting on a structure

4. Types of Loads

   • Static
     • Dead loads or static loads are static forces that are relatively constant for an extended time
   • Dynamic
     • live loads or dynamic loads are usually unstable or moving loads. These dynamic loads may involve considerations such as impact, momentum, vibration, slosh, dynamics of fluids etc.

5. Why is equilibrium important

   • Ah object at equilibrium has no net influences to cause it to move, either in linear motion or ratation.
     • The conditions of equilibrium are basic to the design of any load bearing structure such as bridge or building since such structures must be able to maintain equilibrium under load.

6. What are moments?

   • Products of force and perpendicular distance

7. Structural Failure

   • Causes of Structural Failure
     • no structural integrity, initiated when material stressed beyond stress limit, excessive deformation observe d
   • Structural properties of materials
     • Ductile Malleable Has a low melting point Good fluidity castability good machinability good resistance high strength to weight ratio resistant to corrosion and straining

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