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Main Functions of Buildings Provide a safe and comfortable environment for work and rest. (Protect us from wind, rain and the wild animals) Two types of loads act on a building structure : 1. Vertical force (Load from the weight of human, furniture or building itself) 2. Lateral force

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slide1

Main Functions of Buildings

  • Provide a safe and comfortable environment for work and rest. (Protect us from wind, rain and the wild animals)
  • Two types of loads act on a building structure:

1. Vertical force

(Load from the weight of human, furniture or building itself)

2. Lateral force

(Load from wind or earthquake etc.)

  • Basic requirements in building architecture:

1. For safety, a building will not collapse under great stress

2. For comfort, a building will not move excessively under great pressure

stress
Stress
  • Load acting on a structure will be shared by each component.

eg. For a load of 200,000 kg shared by 4 pillars, each

pillar has to bear 50,000 kg.

  • Stress = Force/Area

In the above case, if the area increases and the load remains unchanged, the stress will decrease.

  • The maximum stress that a material can bear is called the material strength.
slide3
Beam

L

  • A component used to bear the bending forces in a structure.
  • When stress is exerted, it has to bear a pressure from above and a pulling force from below. (see the figure above)
  • Under constant load (W), if the beam’s span (L) increases, it’s vertical displacement will increase and the stress it bears will increase.
  • The beam’s vertical displacement and stress will decrease if the thickness of the beam (H) increases.

H

W

building material
Building Material

1. Timber:

  • Light; cheap; easy to link up; has a high availability.
  • Used for buildings of one or two levels (common in Europe and America).
  • Low strength; easy to deform under stress or pressure; cannot be used in tall buildings or long bridges.

2. Steel bar:

  • High strength; high resistance to deformation; suitable for constructing tall buildings and long bridges.
  • Expensive
  • Difficult to link up (components are prepared in factory, rather in the building site.)
steel reinforced concrete
Steel-reinforced Concrete
  • Concrete can bear a very high pressure but is weak in bearing tension.
  • Steel lines are used to bear tension.
  • Cheaper than steel bars.
  • Can apply directly in working place; can be made into components for combination.
building structure
Building Structure
  • Vertical Force
    • Passes from the floor to the beam, then to the pillar, and finally to the base.
  • Lateral Force
    • The framework can bear the lateral force.
    • A shear wall is added to the structure of building with over twenty levels and thus the building can bear a greater lateral force.
slide11
A higher building suffers a greater lateral force, and therefore a tall building has to face a much greater lateral force than the vertical force.
  • Buildings having 40 to 50 levels (or more) require special designs :

1. Reduce the distances between the pillars and thicken the beams.

=>To increase the structural efficiency.

slide13

However, when the structural efficiency maximizes, the frame will become a box with many small holes on it.

eg. Jardine House

slide14

2. Super Frame

- Most of the external forces are taken by the super-sized structural components.

eg. Hong Kong and Shanghai Bank Building

acknowledgment
Acknowledgment:
  • Hong Kong University of Science and Technology (HKUST)
  • Dr. Christopher K.Y. LEUNG Associate Professor, Department of Civil Engineering, Hong Kong University of Science and Technology