Engineering Loads on Buildings

Loads Acting on a Building

• Loads are categorized into Static and Dynamic.
• Static loads are further categorized as Dead Loads and Live Loads.
• Dead Loads are stationary and include the weight of the building structure itself.
• Live Loads are dynamic and include occupants, furniture, and equipment.
• Building codes dictate the loads to be considered for different types of occupancies.
• This information comes from surveys of representative buildings to determine typical weight of furnishings and people.

Dynamic Loads

• Wind loads are a significant factor for buildings of all sizes.
• They include both pressure and suction.
• Wind pressure acts on the windward side of the building and suction occurs on the other sides and roof.
• Wind loads are particularly important for tall buildings due to their cantilever effect.
• Wind velocity is not constant, resulting in dynamic effects that need to be accounted for.
• Earthquakes are another type of dynamic load.
• They are sudden, jerky movements of the ground.
• The horizontal component of an earthquake can be particularly damaging.
• Local building codes define the anticipated earthquake intensity.

Equivalent Loads

• Result from temperature changes, moisture content fluctuations, and foundation settlement.
• Expansion joints are used to accommodate changes in size due to temperature and moisture.
• Uneven foundation settlement can induce stress in a building's superstructure.

Transmission of Loads

• Loads transfer vertically and horizontally towards the ground.
• The pathway of a load through structural members is known as the load path.
• Vertical load paths are handled through compression, tension, or bending.
• Horizontal load paths require lateral stability.
• There are three methods for providing lateral stability:
  • Triangulation
  • Shear panels or walls
  • Rigid frames

Effect of Forces on Materials

• Solid materials are held together by atomic bonds.
• These bonds can be extended or compressed, resulting in Elastic Deformation.
• As long as the bonds are not broken, the material recovers its original shape after force is removed.
• Stress is the force exerted on a material - calculated by dividing total force by the carrying area.
• Strain is the deformation of a material due to stress, expressed as a ratio of deformation to original dimension.
• The relationship between stress and strain is defined by Hooke's Law.
• The Young's Modulus of Elasticity is a constant for different materials.

Failure of Materials

• Beyond the Elastic Limit, atomic bonds start to break.
• This results in either Plastic/Ductile failure or Brittle failure.
• Ductile materials deform permanently before failure, allowing for some warning time.
• Brittle materials fail suddenly with little deformation.
• Buckling failure affects vertical members like columns and is caused by high compressive stress.
• Buckling leads to sideways bending due to compression.
• The bending causes further offset, increasing the bending moment until failure.
• Longer and thinner members tend to buckle easier than shorter and thicker members.