Thesis Statement:
UNDERSTANDING AND APPLYING HOW ARCHES AND ARCH BRIDGES ARE INFLUENCED BY DIFFERENT FORCES.
UNDERSTANDING AND APPLYING HOW ARCHES AND ARCH BRIDGES ARE INFLUENCED BY DIFFERENT FORCES.
ARCHES
Arch Bridges have been used since the Ancient Romans, and they are still standing today! They have been used for about 3000 years. Arch bridges are really strong and can withstand a lot of force.This type of bridge is now one of the most popular bridges in the world.
How it Works
Arch bridges are strong because arch bridges spread the weight out through the entire form. They have a curve design that does not push the load straight down but instead the load is conveyed along the curve of the arch to the abutments. One of the most important parts of the bridge is the keystone. This is what keeps the arch together.
Types of Bridges
Parts of the Arch
How Forces Act On Arches
QUESTIONS FOR EXPERTS
Basic Facts
Arch Bridges have been used since the Ancient Romans, and they are still standing today! They have been used for about 3000 years. Arch bridges are really strong and can withstand a lot of force.This type of bridge is now one of the most popular bridges in the world.
How it Works
Arch bridges are strong because arch bridges spread the weight out through the entire form. They have a curve design that does not push the load straight down but instead the load is conveyed along the curve of the arch to the abutments. One of the most important parts of the bridge is the keystone. This is what keeps the arch together.
Types of Bridges
- Corbel arch bridge – A Corbel arch doesn’t function in the same way as true arch bridges (they don’t distribute the load / forces across the arch), although some are created to look very similar like them. They are made by laying successive layers of masonry or stone with each having successfully larger cantilevers.
- Aqueducts and canal viaducts – To bridge large distances, ancient romans built series of supports which were connected with stone arches. These series of arched structures were built with several layers that could reach very impressive heights unlike ordinary bridges with one layer.
- Deck arch bridge – This is a common arch bridge in which the deck is situated on top of the arch instead of under.
- Through arch bridge – Arch Bridge in which the deck is not situated completely above the arch, but it travels in one part below the bridge and is suspended to it via cables or tie bars.
- Tied arch bridge – Also known as bowstring arch bridge, it incorporates a tie between two opposite ends of the arch.
Parts of the Arch
- The Abutment is the substructure at the end of a arch's span whereon the load or bridges superstructure rests.
- The Keystone is the most important part of the bridge; it is what holds the arch together.
- The Voussoir is the curved part of a arch in which the load rests on. This is the main part of the super structure
- The Impost is the part if a arch in which the lowest part/piece of the voussoir rests.
- The Extrados is typically the outer part of the voussoir in which the abutment rests on.
- The Rise is the vertical distance between the keystone and the impost
- The Clear Span is the distance between both imposts.
- The arch is always under compression. The force of compression is pushed outwards.
- The tension is negligible. It dissipates the force outwards therefore reducing the tension. Bigger semicircle = more tension
- The resistance is passed from stone to stone until it is eventually pushing on the keystone which is supporting the load
How Forces Act On Arches
- Distributes compression through the entire form
- It has a curve design that does not push the load straight down but instead the load is conveyed along the curve of the arch to the supports on each end
- The curve has the ability to dissipate force outwards which hence reduces the tension on the underside of the arch
- The greater degree of the curvature (the larger the semicircle of the arch) the more tension on the underside of the arch
- When building a big enough arch, the tension will overtake the strength of it
- The load at the top puts pressure that goes to the abutments. The abutments are in the ground. The ground around the abutments is squeezed and pushes back on the abutments. For every action there is an opposite and equal reaction. The ground pushing back on the abutments vs the force being put on the abutments. This creates resistance.
QUESTIONS FOR EXPERTS
- What considerations do you make to build an arch bridge?
- Which and why external and internal forces do you think about
- Have you considered any other materials to build arch bridges?
- Have you considered any other forms to build arch bridges?
- Why are arch bridges really strong and how?
- Is there any interesting facts that we could learn about arch bridges?
Basic Facts
- Very rigid
- Over 3000 years of use
- One of the most popular types of bridges
- Prominent in many bridges
- Semi circular structure
- Elegant
- Diverts weight onto its two abutments (the parts of the bridge that directly take the pressure)
- Like every other structure the arch cannot “withstand physics forever”
- Even though some arch bridges might look different, the basic structure doesn't change
- The ancient romans built bridges that are still standing today!
- The hard part is actually building it because the parts of the bridge do not have “structural integrity” until they meet in middle
- Arch bridges have the greatest natural strength
- History: they were originally built of stone and brick but with today’s new materials, we are able to make them even more sturdy
- The frame is built before the actual arch is built. This allows the stones (or other material) to be in the right place. The frame is taken off after the stone is in position.
- Arch bridges were originally built of stone or brick but these days they’re built of reinforced concrete or steel
- The meaning of an arch, in architecture and civil engineering, is a curved structure or component that is used to span or cover an opening and to support loads from above
- The arch was formed from the evolution of the vault
- The arch depends on the wedge design
- If a series of wedge-shaped pieces are set side to side, it is an arch.
- These wedged pieces are called voussoirs
- Each voussoir must be precisely cut so that it presses firmly against the surface of neighbouring blocks to carry the load above.
- The stone or piece at the center and top voussoir is called the keystone
- Where the two vertical sides of the arch rises, into the curved arch it becomes, is known as the spring or springing line
- During construction of an arch, there is a form of temporary wooden centring that supports the voussoirs until the keystone is placed
- The curve of an arch can be semicircular, segmental (consisting of less than a half of a circle), or pointed (two intersecting arcs of a circle)
- Arches have great advantages over horizontal beams and can support more
- This great capacity comes from the pressure downward on an arch that has the effect of forcing the voussoirs together instead of apart.
- These stresses tend to squeeze the blocks outward radially, loads divert these outward forces downward to exert a diagonal force, called thrust, that will cause the arch to collapse if it is not properly buttressed
- The vertical supports which an arch rests must be large enough to buttress the thrust and direct it into the foundation (as in Roman triumphal arches)
- Arches can rest on very light supports but when they occur in a row, because the thrust of one arch counteracts the thrust of its neighbours, and the system remains stable as long as the arches at either end of the row are buttressed
- This system is used in such structures as arched stone bridges and ancient Roman aqueducts
- Arches were known in ancient Egypt and Greece but were not suitable for monumental architecture
- The Romans used the semicircular arches in bridges, aqueducts, and large monumental architecture
- They did not use mortar, relying simply on the precision of their stone dressing
- The Arabs popularized the pointed arch, and it was in their mosques that this form first acquired its religious connotations
- Medieval Europe used the pointed arch, which composed a simple element in Gothic architecture
- The segmental arch was introduced in the late Middle Ages
- This form and the elliptical arch were a great use in bridge engineering because they permitted mutual support by a row of arches
- Modern arches of steel, concrete, or laminated wood are highly rigid and lightweight.
- The horizontal thrust against the supports is small, this thrust can be further reduced by stretching a tie between the ends of the arch