You are about to use a dangerous tool, the hot glue gun. To avoid workshop accidents copy in your notebook and make sure you understand the safety rules you will have to follow:
Do not touch the hot nozzle or hot glue
Never point the gun in the direction of another person
Be especially careful with the cable. Never touch the cable with the gun nozzle
Do not leave your glue gun plugged in an unattended place, other people may come in contact with the hot appliance.
Only use glue sticks that are recommended for your particular glue gun and never introduce any other object (paper, plastic, tools...) in the gun tube
Don’t pull glue sticks out from the glue gun once the gun is plugged in and glue has begun to melt
Be careful also after unplugging your gun, take into account it is still very hot.
One of the most amazing structures on Earth are Bridges.
We are a species of bridge builders. Since time out of mind, humans have engineered structures to solve obstacles, such as, say, Jiaozhou Bay. There, there is now a 42.5-kilometer bridge that links the busy Chinese port city of Quingdao to the Chinese suburb of Huangdou.
In addition to this we have tamed steel or stone in an effort to reach the places, people and things we desire.
Although the concept itself is as simple as felling a tree across a creek, bridge design and construction make artists, architects and engineers to reshape the very environment in which we live.
As a result, we inhabit a planet of bridges, some as ancient as Greece's 3,000-year-old Arkadiko bridge or as unchanged as India's 500-year-old Meghalaya living bridges, which are coaxed into existence from growing tree roots.
There are many types of bridges and we are going to study and classify so that you are able to understand how they work.
The main elements that bridge designers use to make a bridge successful are beams, arches, trusses and suspenders, and they make the pure types that we can find: beam, truss, arch and suspension bridges.
The key differences between the bridge types comes down to the lengths they can cross in a single span, which is the distance between two bridge supports, the physical braces that connect the bridge to the surface below. Bridge supports may take the form of pillars, towers or piers...
Types of bridges
Beam Bridge
If you want to build a beam bridge (also known as a girder bridge), all you need is a rigid horizontal structure (a beam) and two supports, one at each end, to rest it on. These components directly support the weight of the bridge and any traffic traveling over it. They are not very interesting to study because of its simple design, but some amazing new designs have a beam bridge as a part of it. Oresund Bridge in Sweden is an example of this.
Truss Bridges
In order to help the beam to be stronger engineers have developed several types of beams, all made with triangulated shapes.
The Forth Bridge in Edinburgh is a cantilever bridge, and you can see trusses in lots of the new designs.
Arch Bridges
After more than 2,000 years of architectural use, the arch continues in bridge designs and with good reason: Its semicircular structure elegantly distributes compression through its entire form and diverts weight onto its two abutments, the components of the bridge that directly take on pressure. Modern arch bridges like Garabit Viaduct, Yajiesha Bridge (Guangzhou) or Chaotianmen Bridge, are not pure arch but truss arch bridges
Suspension Bridge
As the name implies, suspension bridges, like the Golden Gate Bridge or Brooklyn Bridge, suspend the roadway by cables, ropes or chains from two tall towers. These towers support the majority of the weight as compression pushes down on the suspension bridge's deck and then travels up the cables, ropes or chains to transfer compression to the towers. The towers then dissipate the compression directly into the earth.
Examples of suspension bridges are Bosporus Bridge, Brooklyn Bridge or Golden Gate Bridge
Cable-stayed Bridge
At first glance, the cable-stayed bridge may look like just a variant of the suspension bridge, but don't let their similar towers and hanging roadways fool you. Cable-stayed bridges differ from their suspension predecessors in that they don't require anchorages, nor do they need two towers. Instead, the cables run from the roadway up to a single tower that alone bears the weight.
The tower of a cable-stayed bridge is responsible for absorbing and dealing with compression forces. The cables attach to the roadway in various ways. For example, in a radial pattern, cables extend from several points on the road to a single point at the tower, like numerous fishing lines attached to a single pole. In a parallel pattern, the cables attach to both the roadway and the tower at several separate points.
Millau Viaduct in France and Octavio Frias de Oliveira Bridge in Brazil are good examples
Draw-Bridge
Type of bridge that can be open to let boats or ships sail under their decks.
The Tower Bridge in London is a very famous example of this type and Gateshead Millenium Bridge is an incredible and original design.
