What is a Force???
A Force is any PUSH or PULL that acts on a structure. The images below show some of the extreme damage that can be done by natural forces of wind and water.
Forces can be classified into two main categories: INTERNAL and EXTERNAL forces. The above examples show EXTERNAL forces. Forces that act ON a specific structure from OUTSIDE of the structure. A simple example might include my fingers as I type on the keyboard, or my body pushing down on the chair I am sitting on.
Internal forces are those that the structure itself "feels". Balancing a couple of text books on your head, your neck, skin, shoulders all felt the force of the textbooks (external force) pushing down. The way YOU feel (as your body IS the structure) is the INTERNAL force. This particular feeling is that of COMPRESSION. See images below for the other types of Internal forces that a structure can feel. Some of these forces occur just because the structure itself is a force due to the weight of its own parts. (eg. Your feet feeling the weight of the body it is holding on top). Some of the forces occur because of external forces.
Internal forces are those that the structure itself "feels". Balancing a couple of text books on your head, your neck, skin, shoulders all felt the force of the textbooks (external force) pushing down. The way YOU feel (as your body IS the structure) is the INTERNAL force. This particular feeling is that of COMPRESSION. See images below for the other types of Internal forces that a structure can feel. Some of these forces occur just because the structure itself is a force due to the weight of its own parts. (eg. Your feet feeling the weight of the body it is holding on top). Some of the forces occur because of external forces.
When external forces exert pressure on a structure causing internal forces, sometimes the structure starts to break down. The images beside show some examples of this wearing down of the structure. Can you figure out what kind of internal force caused the damage you see here? | |
Loads: Static vs. Dynamic Loads
A LOAD is the mass of the thing that puts a force on a structure. This load can be external, such as the vehicles that travel across a bridge. This type of load is known as a DYNAMIC load because the load is constantly changing. When building a structure, engineers have to think about what the maximum dynamic load will be and build to support this external force.
The load can also be the weight of the structure itself! Think of a skyscraper. The lower levels have to be able to support all the levels above it. This is known as the STATIC Load. This load does not change unless there are modifications made to the structure itself. When deciding on building materials and the structural support needed, engineers need to consider not only the external dynamic load, but ALSO the static load of the structure itself!!!
TASK
With your table group think of 3 different types of structures (small, medium, and large) and describe what the dynamic load is.
The load can also be the weight of the structure itself! Think of a skyscraper. The lower levels have to be able to support all the levels above it. This is known as the STATIC Load. This load does not change unless there are modifications made to the structure itself. When deciding on building materials and the structural support needed, engineers need to consider not only the external dynamic load, but ALSO the static load of the structure itself!!!
TASK
With your table group think of 3 different types of structures (small, medium, and large) and describe what the dynamic load is.
- What considerations need to be made for dynamic and static loads of the structure?
- How have engineers designed the structure to resist these loads?