Parts of a bridge
In its technical aspect, the engineering of a traditional bridge differentiates, in addition to the foundations, two essential parts: the superstructure and the infrastructure, and in them, the following basic components can be broken down:
• - Section: Part of the bridge that supports bastions or pilasters.
• - Bastion: In the substructure, support for a section.
• - Corbel: Traditional architectural resource to unload the excess weight of bastions and piles.
• - Filling or gravel "Grabble (construction)"): Retained by the abutments, it replaces the materials (earth, rocks, sand) removed, and reinforces the resistance of bastions, pilasters.
• - Seat: Part of the bastion on which a section rests, and in the case of piers the ends of two different sections.
• - Access slab: Surface of the bearing that rests on the bracket.
• - Light "Light (engineering)") (between bastions): Average distance between the internal walls of consecutive piles or bastions.
• - Bracing: System to give rigidity to the structure.
• - Deck "Deck (construction)"): Upper rolling base that also serves to distribute the load to beams and stringers, in special cases, the deck can be structured to support a railway track, a navigation channel, an irrigation channel, in these last two cases they are called "channel bridge"; or a pipe, in which case it is called a tube bridge").
• - Transverse beam: Connection reinforcement between the main beams (an example of a set is the "Lattice (engineering)" truss beams).
• - Supports: Plates and assemblies designed to receive, distribute and transmit reactions of the structure (examples of this type of support are rollers and rocker arms).
• - Lateral bracing or guy braces: They join the reinforcements and give them rigidity.
• - Siding "Siding (bridges)") or balcony: pedestrian stopping area or rest area on the margins of the road or deck.
• - Other sections: Hinges, expansion joints, rigid frames, connecting plates, beams of various categories and bearing surface.[7].
Regarding the architectural structure, in a bridge you can distinguish:
• - Platform.
• - Arcade (arches).
• - Cachado").[8].
• - Bridgehead.
• - Stirrups and handles").
• - Eye.
• - Pile, pillar, pile, zampa.
• - Parapet, acitara, parapet, railing.
• - Tajamar (see 20 on display).
• - Footing "Footing (foundation)").
Analysis and design
Unlike buildings, whose design is directed by architects, bridges are usually designed by engineers. This is due to the importance of the engineering requirements, that is, clearing the obstacle and having the necessary durability to endure, with minimal maintenance, in an aggressive outdoor environment.[9] Bridges are analyzed first; The distributions of the bending moment and the shear force due to the applied loads are calculated. For this, the finite element method is the most popular. The analysis can be one-dimensional, two-dimensional or three-dimensional. For most bridges, a two-dimensional plate model (often with reinforcing beams) or a bottom-up finite element model is sufficient.[10] Once the analysis is completed, the bridge is designed to resist the applied bending moments and shear forces, and section sizes with sufficient capacity to withstand the stresses are selected. Many bridges are built with prestressed concrete, which has good durability properties, either by prestressing the beams before installation or post-tensioning in situ.
In most countries, bridges, like other structures, are designed according to the principles of Load and Resistance Factor Design (LRFD). In simple terms, this means that the load is factored by a factor greater than unity, while the strength or capacity of the structure is multiplied by a factor less than unity. The effect of the factored load (stress, bending moment) must be less than the factored resistance to that effect. Both factors take into account uncertainty and are greater when it is greater.
Efficiency
The structural efficiency of a bridge can be considered as the ratio (quotient) between the load that the bridge can support and the weight of the bridge itself, given a certain set of materials. In a common challenge, some students are divided into groups and given a certain number of wooden sticks, a building distance, and glue, and then asked to build a bridge that will be tested to destruction by progressively adding load to its center. The bridge that resists the greatest load is the most efficient. A more formal measurement of this exercise is to weigh the completed bridge rather than measure a fixed quantity of provided materials and determine the multiple of this weight that the bridge can support, a test that emphasizes the economy of materials and the efficiency of glued assemblies.
The economic efficiency of a bridge depends on its location, the potential traffic it can handle, and the amount of savings involved in building the bridge (instead of, for example, a ferry, or a longer route) compared to its cost. Its useful life cost is made up of materials, labor, machinery, engineering, cost of money, insurance, maintenance, renovation and, finally, demolition and disposal of its associated, recycling and replacement, less the scrap value and reuse of its components. Bridges that employ compression only are relatively inefficient structurally, but can be highly efficient economically where the necessary materials are available close to their location and the cost of labor is low. For medium-sized bridges, braced or girder bridges are usually the most economical, while in some cases the appearance of the bridge may be more important than its cost efficiency. Larger bridges generally must be built suspended.
Aesthetics
Most bridges have a utilitarian appearance, but in some cases, the appearance of the bridge can be of great importance.[12] This is often the case with a large bridge that serves as the entrance to a city, or that crosses over the main entrance to a port. They are sometimes known as landmark bridges. Designers of bridges in parks and along greenways also tend to place more importance on aesthetics. Some examples are the stone bridges of the Taconic State Parkway in New York.
To create a beautiful image, some bridges are built much higher than necessary. This type, often found in oriental-style gardens, is called Moon Bridge, which evokes a crescent full moon. Other garden bridges may cross only a dry bed of stream-washed pebbles, with the sole intention of conveying the impression of a stream. Often in palaces, a bridge is built over an artificial waterway as a symbol of passage to an important place or state of mind. A set of five bridges crosses a winding waterway in an important courtyard of the Forbidden City in Beijing, China. The central bridge was reserved exclusively for the use of the Emperor and Empress, with their attendants.