The supports transfer the loads from the beam to the foundations by compressing them vertically. The average weight of the beam bridges was 13.25 pounds since beam bridge number two contained 12 pounds. The first arch bridge weighed 21.5 pounds. Therefore, the second bridge could carry about 2 times its own weight.
Beam bridges are usually made of steel or concrete. The length of a beam bridge is usually more than 10 feet. The height depends on how high you want the bridge to be. A common height for a beam bridge is about 20 feet high. That makes it strong enough to support a lot of traffic. However, if you need a very long bridge, then it would be better to use several shorter beams instead.
There are three parts to a beam bridge: the head, the foot, and the web. The head and foot of the bridge connect at an angle. The top of the head connects to the top of the frame of the bridge structure while the bottom of the foot connects to the ground or some other surface. The web is the horizontal part that connects the head to the foot. It can be any shape such as V-shaped or Y-shaped but it must connect the head to the foot. There should be a firm connection between the head and foot because all the weight of the beam bridge will be transferred through this part of the beam.
The second arch bridge contained 21 pounds, bringing the total weight of the arch bridges to 21.25 pounds. The first truss bridge weighed 24 pounds. The second truss bridge contained 23 pounds, bringing the total weight of the truss bridges to 47 pounds.
These arch and truss bridge designs were used extensively in early America. Although they were not as strong as later designs, they were relatively inexpensive to build and easy to maintain. As a result, they remained popular into the 19th century.
An arch bridge is a simple but effective design that uses arches to support a deck over a rail or gutter line, enabling it to carry heavier loads than a culvert bridge. An arch bridge is built with two parallel supports (arches) that rise above a base plate called a bierstone. The space between the arches is called the arch gap. A horizontal beam called a king post spans the arch gap from one side of the bridge to the other. It is tied at its ends to the arches, preventing it from moving. On top of the king post are two more beams called queen posts. They too are tied together at their ends so they cannot move. The deck is laid over the whole structure, including the bierstone under the arches and the rails or gutters on which it rests.
Say it out loud: Weight Distribution on a Beam Bridge When weight is applied to a beam bridge, it is driven immediately downward, toward any below support, making the center section of the bridge the weakest. Vertical supports are used in beam bridges to secure the weight across greater lengths. The distribution of weight between vertical supports is critical to maintaining the structural integrity of the bridge.
Beam bridges spread their load over a large area, which reduces the stress on any one point. Since all beams are not loaded equally, cross-sections vary. The key to understanding how weight is distributed is to realize that as long as there is still room under the lowest point on a beam for another beam to be placed there will be no failure due to lack of space. If there isn't enough space under one beam, others above it take up the load.
The total weight of a beam bridge is divided into two parts: supporting and non-supporting. The term "supporting" means that the beam is bearing some portion of its weight. Any part of the beam not bearing weight is called "non-supporting." The burden on a beam bridge is evenly shared among those beams that carry supporting weight. The more weight that a single beam bears, the wider it is. A heavy object placed on top of a beam bridge will push down on all beams, causing them to bend a little bit unless they are able to support this extra load.
Determine how much weight the beam must hold. This is 25 pounds per square foot for a flat roof with snow loading in northern locations of the United States. It might be 50 pounds per square foot for frequently used spaces. The supporting area of the beam should be able'too large'ethis would cause stability problems.
The formula for calculating the load that a beam will support is:
Load = W x B x 0.25 where W is the load in pounds and B is the breadth of the beam in feet.
For example, if you need to support 250 pounds over a 10-foot-wide floor space, then the beam must be 15 inches deep.
See how your beam fits into this calculation. If it doesn't fit, then you need another beam or more floor space.
Loads on beams can be caused by its own weight or external forces such as people walking on the surface or moving objects being stored on the premises. Beams must be able to support these loads without failure. They do this by using strong materials, such as steel or wood, and by applying appropriate techniques during construction or renovation projects.
External forces may also cause beams to bend.
Weight restrictions are often stated on bridges because a structural member(s) within the bridge has deteriorated, limiting that member's structural capacity to withstand the pre-design loads. Bridges are often weight limited to avoid bridge beam degradation. The weight limit may be indicated by metal placards attached to the side of the vehicle near the center point of the vehicle's undercarriage.
Beam weight limitations can also be an issue when constructing new bridges. The load-bearing members of a bridge (girders and beams) must be able to support the total weight of all vehicles crossing the structure. If the girders or beams become too heavy, they may need to be replaced which can be expensive. Weight limitations also ensure that the remaining strength of the bridge is not exceeded which could lead to failure.
The weight of a single vehicle can greatly exceed the recommended maximum load for a bridge if the driver chooses poorly loaded trucks or cars, or if the bridge is very long. A typical car weighs about 2,500 pounds and most highways have a posted maximum load limit of 10 percent of body weight or less. Thus, a bridge cannot accept responsibility for any damage caused by vehicles weighing more than 150,000 pounds or so crossing it daily.
Heavy cargo or passenger buses can weigh up to 80,000 pounds empty and usually run on routes with high traffic volumes at good speeds.
Bending a beam allows it to carry vertical weights. The top of the beam bridge experiences horizontal compression as it bends. At the same time, horizontal stress is applied to the bottom of the beam. If the bending moment caused by the weight is greater than the supporting capacity of the structure, then the beam will fail by buckling.
When a beam is loaded in tension, it experiences maximum strain at its end supports. In compression, the strain is maximum at the midpoint between supports. The strain is equal to the fractional change in length divided by the original length:. The fractional change in length is the amount that the beam has been shortened (or lengthened) due to loading. For example, if you compress a beam by 50% and release it, then its fractional change in length is equal to. The strain is also called "local force" because it refers to the force required to cause that amount of shortening or lengthening at a particular point on the beam.
The total load carried by a beam can be calculated by adding the individual forces acting on each end. These forces include the weight of the object being supported, any other objects resting on the beam, and the torque resulting from any turning movement applied to the beam.