Structural Joints
Section 3.2 p. 313-318
Learning Outcome
• Identify points in a structure where flexible or fixed
joints are required, and evaluate the appropriateness
of different types of joints for the particular
application
Deciding how to Join Building Material
• Ever have the following
• Ever had a door/cupboard come off it hinges, or the screws out of the setting?
• Ever had the arm of your glasses/sunglasses fall off?
• Ever built something to have it fall down the first chance it gets?
• No different than what building materials, or design of a structure, the
function must be considered when deciding how to join materials
together
• When deciding how to join materials together things that must be considered are:
• What external forces will be acting on it (how much snow, wind, etc..)
• What kind of safety factor needs to be built in?
Structural Joints
• A Joint is the place at which structural parts are joined
• Joints can be:
•
•
•
•
Rigid
Fixed
Flexible
Moveable
Joints that Rely on Friction
• Strength of force of friction depends on:
• Mass: how heavy something is
• Force of Gravity
• Roughness or smoothness of two surfaces (Concrete vs. Ice)
• Friction is the result of the one surface moving against the surface of another
object
• If you move a desk is it easier to move by itself, or with person on it?
• Explain using the terms above
• What about moving that same desk on concrete or linoleum
• Often friction is used to help increase the effectiveness of structural joints
Examples of Friction Joints
• Nails, Screws, Rivets, Tacks, Staples
• The friction between the metal and the material holds these joints together
• This is the most common type of joining used in modern construction
• A major advantage is that these materials can easily be removed for
dismantling of a structure
Interlocking Pieces
• You can increase the amount of friction by increasing the amount of
surface area
• This is used to join pieces together with out the help of screws, or nails
Mass
• Friction of an material increases as the weight of that object increases
• Therefore, big heavy objects like those found in solid structures are held in place due to
the increase of friction due to their mass
Sometimes Friction Can be Unwanted
• Friction can cause a wearing between the two surfaces joined
• It also creates heat
• When ever working with moveable joints, these two factors will want
to be avoided
• What happens if these are not successfully avoided?
Joints that rely on Bonding
• Another way to connect structural material is to use another
substance to bond them together
• i.e.
• Glue, Tape, Cement, Welds
Fixed or Movable
• Fixed Joints are rigid to prevent any movement
• They result from welding, cementing, gluing or nailing/screwing things
together
• Joined in such a way that there is no movement between the materials
• Movable Joints are flexible or mobile so that parts of the structure
can move as required
• Hinges, pin joints, and flexible rubber tubing are examples of movable joints
• Your body is made up of many movable joints
• Can you name some?
Designing Joints to last
• When designing a structure, the length
of time it is expected to survive must be
considered
• A skateboard ramp that only needs to last
the couple of months in summer
• Or a Gate on a fence that needs to last as
long as the fence does
• The proper joining technique must be
used to prevent fatigue, and even
failure (breakage)
• Consider your fridge
• How many times a day/week/year on average
is it opened
• How much weight is contained in the door
Your task
• You need to design a time capsule box (will be buried
for 100 years)
• Criteria
• Must be a door that can be opened when the time comes (100
years from now)
• The material must be able to survive the climate at the time
(buried)
• Material must be readily available, and fit the cost of the school
budget
• Must be Aesthetically pleasing