1 ROMANS CHANGED THE MODERN WORLD How the Romans Changed the Modern World Nick Burnett, Carly Dobitz, Cecille Osborne, Nicole Stephenson Salt Lake Community College 2 Romans are famous for their advanced engineering accomplishments, although some of their own inventions were improvements on older ideas, concepts and inventions. Technology to bring running water into cities was developed in the east, but was transformed by the Romans into a technology inconceivable in Greece. Romans also made amazing engineering feats in other every day things such as roads and architecture. Their accomplishments surpassed most other civilizations of their time, and after their time, and many of their structures have withstood the test of time to inspire others. Their feats were described in some detail by authors such as Vitruvius, Frontinus and Pliny the Elder. Today our bridges look complex and so thin that one may think it cannot hold very much weight without breaking or falling apart, but they can. Even from the very beginning of building bridges, they have been made so many times that we can look at different ways to make the bridge less bulky and in the way, to one that is very sturdy and even looks like artwork. What allows an arch bridge to span greater distances than a beam bridge, or a suspension bridge to stretch over a distance seven times that of an arch bridge? The answer lies in how each bridge type deals with the important forces of compression and tension. Tension: What happens to a rope during a game of tug-of-war? It undergoes tension from the two opposing teams pulling on it. This force also acts on bridge structures, resulting in tensional stress. 3 Figure 1: Compression and Tension Compression: What happens when you push down on a spring and collapse it? You compress it, and by squishing it, you shorten its length. Compressional stress, therefore, is the opposite of tensional stress. Compression and tension are present in all bridges, and as illustrated in figure one, they are both capable of damaging part of the bridge as varying load weights and other forces act on the structure. It's the job of the bridge design to handle these forces (stress and strain) without buckling or snapping. Stress is a measure of how strong a material is. This is defined as “how much pressure the material can stand without undergoing some sort of physical change” (Google Dictionary). The yield stress is the level of stress at which a material will deform permanently (Google Dictionary). Stress causes strain. Putting pressure on an object causes it to stretch. Strain is a measure of how much an object is being stretched (Google Dictionary). Buckling occurs when compression overcomes an object's ability to endure that force. Snapping is what happens when tension surpasses an object's ability to handle the lengthening force. 4 The best way to deal with these powerful forces is to either dissipate them or transfer them. With dissipation, the design allows the force to be spread out evenly over a greater area, so that no one spot bears the concentrated brunt of it (How Bridges Work). We have four main types of bridges today: A Beam Bridge, Truss Bridge, the Arch Bridge, and a Suspension Bridge. The Beam Bridge (Figure 2): consists of horizontal beam supported at each end by piers. The weight of the beam pushes straight down on the piers. The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 250 feet. Beam bridges are often only used for really short distances because, unlike truss bridges, they have no built in supports. The only support for the bridge is provided by piers. Figure 2: The Beam Bridge The Truss Bridge (Figure 4): The Truss Bridge consists of an assembly of triangles. Truss bridges are commonly made from a series of straight, steel bars. The Firth and Forth Bridge in Scotland (Figure 3) in a cantilever bridge, a complex version of the truss bridge. 5 Figure 3: The Firth and Forth Bridge Rigid arms extend from both sides of two piers from both sides of two piers. Diagonal steel tubes, projecting from the top and bottom of each pier, hold the arms in place. The arms that project toward the middle are only supported on one side, like really strong diving boards. These “diving boards,” called cantilever arms, support a third, ventral span”. The bridge has triangle shapes in the frame, the triangles share the compression that an object exerts on the bridge so that one beam won’t support all the weight. Figure 4: The Truss Bridge The Arch Bridge: has great natural strength. Thousands of years ago, Romans built arches out of stone. Today, most arch bridges are made of steel or concrete, and they can span up to 800 feet. 6 Figure 5: The Arch Bridge The Suspension Bridge: can span 2000 to 7000 feet - way farther than any other type of bridge! Most suspensions bridges have a truss system beneath the roadway to resist bending and twisting (different types of Bridges). The suspension cables must be anchored at each end of the bridge, since any load applied to the bridge is transformed into a tension in these main cables. The main cables continue beyond the pillars to deck-level supports, and further continue to connections with anchors in the ground. Vertical suspender cables or rods, called hangers, support the roadway (Figure 6). In some circumstances the towers may sit on a bluff or canyon edge where the road may proceed directly to the main span, otherwise the bridge will usually have two smaller spans, running between either pair of pillars and the highway, which may be supported by suspender cables or may use a truss bridge to make this connection. In the latter case there will be very little arc in the outboard main cables” (Suspension Bridge, Wiki). 7 Figure 6: Suspension Bridge The Arch Bridge is also known as a Roman Bridge. Roman Bridges work the same way now as they did then, but with more modern technology. The Romans introduced stone arch technology over two thousand years ago. They applied to bridges they constructed across the known world and examples can still be seen today. The technology they used has stood the test of time and some Roman construction methods are still used today. The arch is a prime example of Roman technology that is still used world wide even though modern materials are now used. A wood frame was first constructed in the shape of an arch. The stonework was built up around the frame and finally a keystone was set in position. The wood frame could then be removed and the arch was left in position. Stone arch technology was used even on Roman monuments such as the Colosseum in Rome. Many of the monuments built with stone arch technology can still be seen today, such is the strength of the arch. 8 Figure 7: Arch Diagram Stone arches are not built entirely from stone. Stone is as expensive today as it was in Roman times. The Romans had a great understanding of material costs and consequently constructed stone bridges and viaducts from a combination of materials. The diagram above shows that accurately cut and shaped stone was used for the external walls. Gravel, sand and rough stone was used to fill all cavities. This filling was cheap to produce and use, compared to cut stone and it could be used by unskilled labor to fill the cavities of structures such as bridges and aqueducts (Typical Roman Stone Arch Construction). The arch is a curved beam that forms a half circular shape, which is made like this so it is prevented from straightening and spreading outward. The shape of the arch is formed from blocks or stones that have been carefully cut and put into place. Each one is wedge-shaped and once placed in its right position, the arch begins to take shape. 9 As the Keystone is pushed downwards by the load it carries, its wedge shape means that it pushes outward onto the sides, meaning that the forces are being spread sideways, rather than downwards. Therefore, the load on top that is crossing the bridge is partially transferred through the arch into the ground. Arch bridges have been in use for over 2000 years and are still in use. Over the years, engineers are finding ways to change the fashion of the bridge by changing the design or by using new materials that will make the bridge stronger and more efficient. As we have seen over the years, bridges have become more extraordinary, unique, and beautiful. 10 Roman dam building has received little attention from scholars compared to the attention given to other Roman engineering activities such as bridges and aqueducts; even though their expertise in dam building is as revolutionary as their water systems. The Romans built many dams for water collection, such as the Subiaco dams, two of which fed Anio Novus, the largest aqueduct supplying Rome. One of the Subiaco dams was reputedly the highest ever found or inferred. They built 72 dams in Spain, and many more are known across the empire. Roman masonry dams are very common in Britian, England, and North Africa. The Harbaqa Dam was a Roman gravity dam in the Syrian Desert between Damascus and Palmyra, dating to the 2nd century AD. It was built with a concrete core and ashlar. The reservoir served as a water source to nearby towns such as Palmyra.