Stuff to memorize Flashcards
3 Characteristics of a force
1) Point of application (the tip or tail of the arrow)
2) Direction (shown by an arrow pointing in the direction that the force would move the body)
3) Magnitude (represented with a number and units)
Mechanics is the branch or physical science that deals with ________ and _________ acting on ____________
Energies and forces
acting on Bodies
The line of action of a force is an imaginary line drawn to infinity along the arrow. In order to define the line of action we must know the following two characteristics of force
Point of Application
Direction
Two systems of units that may be used in structural analysis?
SI Units = The international system of units
Imperial Units = The imperial system of units
Unit forces are measured in
Newtons
The standard unit of force in the Imperial system is
Pound Force (Lbf)
One pound of force is equal to one pound of mass, or:
1 LBF = 1 LB
1 LBF = ? N
1 LBF = 4.448N
1 Kip = ? LBF
1 Kip = 1000 LBF
In structural design we typically refer to the forces applied to a building as
Loads
3 types of VARIABLE load
Live (L)
Wind (W)
Snow (S)
2 types of PERMANENT loads
Dead Load (D) - ie the weight of the building
Lateral Earth Pressure (H) - ie the horizontal pressure on the foundation of a house
1 type of RARE load
Earthquake (E)
What is the difference between MASS and WEIGHT
Mass = the amount of matter in a body
Weight = force due to gravity acting on the mass
What is the equation to calculate the force of gravity?
F=mg
F= force (N)
m= mass (kg)
g = gravity (9.81N/kg)
What are the steps in drawing an FBD
- Identify the body
- Draw the free-body
- Draw the external forces
- Draw unknown reaction forces an place of support icons
- Draw dimensions
Forces acting on a body are called?
Loads
The location of the reaction forces are called the?
Supports
The design procedure steps in making a building are
- Stability -
Statics is used to calculate the required forces in all members and their connections to the structure remains static under the load - Strength -
Once the forces are known then we use the principles of mechanics of materials to determine if the size and material of the structure will be strong enough to resist the forces - Stiffness -
A final design check is to ensure the size and material of the structure are stiff enough to limit the deformations of the building to within acceptable limits
The effect of a force is to move the body in the forces:
Line of action
Characteristics of a roller support
Can resist both pushing and pulling forces.
Hold the member to the surface, but allow it to slide along the surface.
Can be positive or negative
(one direction of force)
Characteristics of a PIN support
Holds the member in place at that point.
Prevents all translation of the member.
Does allow rotation.
Can be Positive or negative.
(two directions of force)
Characteristics of a Cable support
Can only provide tension (pulling) force.
Direction of the force will be in line with the cable.
Always positive
(one direction of force)
Characteristics of a Strut
A support with pins at both ends.
Can resist both tension (pulling) and compression (pulling)
(roller gives same type of reaction).
Can be positive or negative
(one direction of force)
Characteristics of a Fixed support
Prevents both translation and rotation.
Absolutely necessary if a member has only one support.
To prevent translation, shows horizontal and vertical force
To prevent rotation shows a moment reaction (circular arrow).
All forces can be positive or negative.
Characteristics of a Force Couple
a moment reaction (circular arrow)
Two forces with equal magnitude but opposite directions and separated by a distance
moment = force * distance
Total effect of the force of both directions is 0, but because they are separated they cause rotation.
