Forces Lab |
Materials Lab |
Loads Lab |
This lab simplifies the real-life conditions that affect structures, in order to illustrate key concepts.
Forces that act on structures are called loads. All
structures must withstand loads or they'll fall apart. In order to build a structure, you need to know what kinds of external forces will affect it.
The weight of the structure itself is called the dead load. Anything permanently attached to the structure is part of its dead load -- including the columns, beams, nuts, and bolts.
The weight of the stuff on the structure is called the live load. Things that move around in or on a structure, like people, furniture, and cars, are all examples of live load.
The beam failed because it could not support the heavy weight of the live load above it.
Thick Beam: The thicker a beam, the less likely it
is to bend. Thick beams are used in structures that
experience live and dynamic loads.
Thick Beam: The thick beam made this structure very
strong. Now the beam won't bend from the heavy weight
of the live load on top of it.
Loads that change over time are called dynamic loads. Dynamic loads -- from wind gusts to pounding objects -- create vibrations that can become bigger and more dangerous over time.
The beam was vibrating too much from the dynamic load. This kind of vibration would be unacceptable to people occupying a building or driving across a bridge.
Thick Beam: The thicker a beam, the less likely it is to bend. Thick beams are used in structures that experience live and dynamic loads.
Thick Beam: The thick beam absorbed the
vibrations caused by the dynamic load and
prevented the structure from bending and
galloping wildly out of control.
When wind blows on a structure, it is called wind load. Wind loads push horizontally on a structure.
The structure collapsed because it couldn't withstand the strong gusts of wind.
Cross-Bracing: Diagonal braces, usually made of steel,
are used to strengthen and stabilize all kinds of structures.
Cross-Bracing: Cross-bracing is an excellent way to stiffen a structure experiencing wind load. When the wind blows, the diagonal brace squeezes together and prevents the structure from flopping over.
When a structure expands or shrinks with the temperature,it is experiencing thermal load. The temperature causes the beams and columns to change shape and push and pull on other parts of the structure.
The intense sun made the beam expand, throwing
the entire structure out of whack.
Roller Joints: Roller joints are used in structures
that get really hot or cold. They give columns and
beams the freedom to expand and contract as the
Roller Joints: Thanks to this roller joint, the beam can swell in the sun and slide over the column without damaging the structure.
When the ground beneath a structure jerks back
and forth during an earthquake, the structure is experiencing an earthquake, or seismic load. Earthquake loads push and pull horizontally on
That was more rattling and shaking than this poor structure could handle.
Shear Walls: Solid walls of reinforced concrete or masonry -- called "shear walls" -- have great stiffness in the horizontal direction. They resist loads that push or pull horizontally on a structure.
Shear Walls: Shear walls can handle being pushed, pulled, rattled, and shaken during an earthquake. They're a great way to strengthen a structure prone
to earthquake load.
When the soil beneath a structure settles unevenly, it is called settlement load. Structures will sink and change shape when they experience settlement load.
This structure is in bad shape -- literally!
Deep Piles: Heavy concrete pillars, or piles, are used to support structures on soft soil. The piles rest deep in the earth on stable, solid soil and support the weight of the heavy structure above.
Deep Piles: The massive concrete piles, sunk deep
into the earth on hard, solid soil, keep the structure
safe and sound where it should be -- above ground!
Flash version of this lab