Types of Structures and Loads

Why it matters

Understanding the types of structures and loads is crucial for civil engineers to design safe and efficient buildings and infrastructure. It helps in predicting how structures will behave under different conditions, ensuring stability and safety.

Key ideas

• Types of Structures:

  • Buildings: Residential, commercial, and industrial structures.
  • Bridges: Beam, arch, suspension, and cable-stayed bridges.
  • Dams: Gravity, arch, and buttress dams.
  • Towers: Communication and observation towers.
  • Shells and Domes: Used in roofs and large-span structures.

• Types of Loads:

  • Dead Loads (DL): Permanent static forces from the structure itself, including walls, floors, roofs.
  • Live Loads (LL): Temporary or movable forces, such as people, furniture, vehicles.
  • Environmental Loads:
    • Wind Loads: Forces exerted by wind pressure.
    • Snow Loads: Weight of accumulated snow.
    • Seismic Loads: Forces due to earthquakes.
  • Other Loads:
    • Thermal Loads: Expansion or contraction due to temperature changes.
    • Settlement Loads: Due to uneven settlement of foundations.

Formulas

• W = ρ·g·V
  • Where W is the weight (N), ρ is the density (kg/m³), and V is the volume (m³), and g is gravitational acceleration (m/s²).
• P = F/A
  • Where P is the pressure (Pa), F is the force (N), and A is the area (m²).

Worked example

Problem: Calculate the dead load of a concrete slab measuring 5 m x 4 m x 0.15 m. Assume the density of concrete is 2500 kg/m³.

1. Calculate the volume of the slab:

   • V = length × width × thickness
   • V = 5 m × 4 m × 0.15 m = 3 m³

2. Calculate mass using the density:

   • m = ρV = 2500 kg/m³ × 3 m³ = 7500 kg

3. Convert the weight to Newtons (N):

   • W = 7500 kg × 9.81 m/s² = 73575 N

Final Answer: 73575 N

Common mistakes

• Confusing dead loads with live loads.
• Ignoring environmental loads in design calculations.
• Incorrect unit conversions, especially from kg to N.

For GATE CE

Questions often involve calculating loads on different types of structures, understanding the effects of various loads, and determining the most critical load combinations. Practice problems on load calculations and understanding IS code provisions related to loads.

Quick check

1. What is the primary difference between dead loads and live loads?
2. Name two types of environmental loads.
3. How do you calculate the weight of a structure?

Answers: 1. Dead loads are permanent, live loads are temporary. 2. Wind loads, seismic loads. 3. Weight = mass density × gravitational acceleration × volume.