1. External Forces:
* Gravitational Forces:
* Weight: The force exerted by the structure's own mass, pulling it downwards due to gravity. This is a primary force to consider in structural design.
* Earthquakes: Horizontal and vertical shaking forces caused by seismic activity.
* Wind Loads: Pressure exerted by wind on the structure's exterior, pushing or pulling it.
* Environmental Forces:
* Temperature Changes: Expansion and contraction of materials due to temperature fluctuations can put stress on the structure.
* Snow Loads: Weight of snow accumulating on roofs and other horizontal surfaces.
* Rain and Ice Loads: Weight and impact force of rain and ice.
* Human-Induced Forces:
* Live Loads: Forces from people, furniture, equipment, and other movable items within a structure.
* Traffic Loads: Forces from vehicles and pedestrians on bridges, roadways, and parking structures.
* Blast Loads: Pressure waves from explosions that can impact the structure.
2. Internal Forces:
* Stress: Internal forces that resist deformation within the structure.
* Strain: Deformation of the structure caused by stress.
* Shear Force: Forces acting parallel to a surface, causing it to slide or deform.
* Bending Moment: Forces that cause a structure to bend or deflect.
* Torsion: Forces that twist or rotate a structure.
Additionally:
* Accidental Forces: Unforeseen or unexpected forces, like collisions, explosions, or fires.
* Maintenance and Construction Forces: Forces applied during construction, maintenance, or repairs.
Understanding these forces is crucial for designing and constructing safe and durable structures. Engineers use various methods, like calculations, simulations, and material testing, to analyze these forces and determine the structure's ability to withstand them.
