TOPIC 6 DESIGNING WITH FORCES
THREE KEY METHODS FOR WITHSTANDING FORCES
1. DISTRIBUTE THE LOAD THROUGHOUT THE
STRUCTURE SO THAT NO SINGLE PART IS
CARRYING MOST OF THE LOAD.
2. DIRECT THE FORCES ALONG ANGLED
COMPONENTS SO THAT THE FORCES HOLD PIECES
TOGETHER INSTEAD OF PULLING THEM APART.
3. SHAPE THE PARTS TO WITHSTAND THE SPECIFIC
TYPE OF FORCE THEY ARE LIKELY TO EXPERIENCE.
TOPIC 6 DESIGNING WITH FORCES
THREE KEY METHODS FOR WITHSTANDING FORCES
1. DISTRIBUTE THE LOAD THROUGHOUT THE
STRUCTURE SO THAT NO SINGLE PART IS
CARRYING MOST OF THE LOAD.
2. DIRECT THE FORCES ALONG ANGLED
COMPONENTS SO THAT THE FORCES HOLD PIECES
TOGETHER INSTEAD OF PULLING THEM APART.
3. SHAPE THE PARTS TO WITHSTAND THE SPECIFIC
TYPE OF FORCE THEY ARE LIKELY TO EXPERIENCE.
PROBLEM 1
Rectangular frames are easiest to build. Load forces can
easily push or pull them out of shape.
Explain Solution
Diagram
Triangle shapes are
stronger than
rectangles.
Share the load
Frame structures
contain many vertical
supporting posts
Problem 2
Load bearing horizontal beams supported only at the ends, may
bend in the center. This bending directs the forces outward on
the vertical beam.
Explain Solution
Arches can be rounded
and the stones shaped
to fit. The center stone
is shaped like a wedge
and called the keystone.
The keystone presses
harder on the stones
beside and transfers
the forces along the
other stones down to
the ground.
Diagram
Explain Solution
Diagram
Cantilever is a horizontal
board or span, supported
by a very strong column at
one end.
Double cantilever have
beams from the top of the
column that pull upwards
on the ends of the
cantilever and beams from
below that push upwards
on the cantilever.
Explain Solution
Braces can be added to a
structure to direct the
forces through the solid
part of the structure to
the ground.
Diagram
Problem 3
Large, solid beams are very strong. They are extremely
heavy and very hard to handle. They use a lot of
building material.
Explain Solution
Diagram
Beams
Cylindrical columns are very
strong but use less material
than square beams. Beams
in the form of I, L, T, or a
box use much less material
than a solid beam
Explain Solution
Corrugations
The wavelike shape give
strength but is lighter and
uses less material
Diagram
What is a flying buttress?
Columns on the outside of high wall connected at the top of
the wall to support the wall.
How does a flying buttress work?
The flying buttress supports the wall the way the sides of
an arch support each other.
What must engineers do when they design structures to make
them strong?
Engineers analyze structures in great detail to find out what
kind of internal forces are stressing each part of a structure.
The engineer must choose materials and shapes with the
strength to withstand each force.
What force was a problem with early railways and how did
they solve the problem?
Shear forces was a problem with the early railways. Tiny
cracks formed when the rail cooled quickly, which would
weaken the rail. With the weight of the loaded train, the
rails began to shear and could cause a serious accident.
Red hot rails were placed in a
steel box to cool slowly and this
produced strong, crack-free
rails.
What is the force that acts on your hand as you slide it
across your desk? Describe this force.
The force acting on your hand is friction.
Friction is a force that resists movement between two
surfaces that rub together.
Why is friction important in assembling structures?
Friction between the parts of the structure and the
fasteners in the structure hold the structure together.
The rougher the surfaces the greater the friction. Look at
the nails in the picture below. Which nail would create the
most friction?
Explain how friction is important to help hold a structure in
place.
Friction helps to hold the structure in place when the wind or
other forces act on it trying to move it.