Bridge Types
The five primary types of bridges are listed below according to their support mechanism:
1. Girder bridges
2. bridges with
arches
3. bridges with
cable stays
4. Bridges with
Rigid Frames
5. Bridges with
trusses
1. Girder bridges:
It is the most common and basic type of bridge. A girder bridge can be as basic as a log spanning a stream; the two types of girders most commonly encountered in steel girder bridges are I-beam and box girders. Examining the section of the I-cross Beam validates its name. The vertical plate in the middle is referred to as the web, while the top and bottom plates are called flanges.
A box girder takes on the shape of a box. Usually, a box girder has two webs and two flanges. Though this isn't usually the case, the presence of more than two webs results in a multiple chamber box girder. T-shaped girders and pi girders—so named because they resemble the mathematical symbol for pi—are two other examples of fundamental girders. Since most modern girder bridges are built with box or I-beam girders, we won't get into the specifics of these more unusual scenarios.
An I-beam is quite simple to design and build, and it functions very well in the majority of cases. Any curved bridge's beams are impacted by torque, which is just a synonym for twisting forces. The extra second web in a box girder increases stability and resistance to twisting forces. Box girders are therefore the greatest choice for bridges with any form of significant curvature. Box girders are often used for greater spans in instances where I-beams would not be strong or sturdy enough since they are more stable and can cover larger distances.However, the design and construction of box girders are more difficult than that of I beams. For example, to solder the internal seams of the structure, a human or a welding robot needs to be able to operate inside a box girder.
2. Arch bridges
After girder bridges, arch bridges are the oldest type of bridges with a traditional architectural style. In contrast to standard girder bridges, arches are excellent candidates for stone work. Arches are a wonderful option for spanning rivers and valleys because they don't need piers in the middle. One of the most exquisite forms of bridges can be an arch. The curved framework used by arches offers a strong resistance to bending forces. Because both ends of an arch are fixed in the horizontal direction (i.e., no horizontal movement is allowed in the bearing), unlike girder and truss bridges, arches can only be utilized when the ground or foundation is solid and secure. Therefore, horizontal forces arise in the arch's bearings when a load is applied to the bridge (such as when a car crosses it). In certain situations, the road may cross an arch or go through one, just like a truss.
There are four main arch-type bridges in terms of structure:
1. Without hinges
2. Two-faced
3. Three swung
around
4. Linked arches
The hinge-less arch does not have any hinges and does not permit foundational rotation. Because of the enormous force (bending, vertical, and horizontal) that is produced at the foundation, hinge-less arches can only be constructed in areas with extremely stable ground. But compared to other arches, the hinge-less arch is a much stiffer structure and experiences less deflection. Hinge bearings are used in the two hinged arch to enable rotation.
Only vertical and horizontal forces are produced at the bearings. This is probably the steel arches version that is utilized the most, and it's a pretty affordable design overall. An extra hinge is added to the top, or crown, of the arch in a three-hinged arch. If there is movement in one of the foundations (from sinking, earthquakes, etc.), the three-hinged arch is not affected too much.
On the other hand, the three-hinged arch deflects significantly more, and fabricating the intricate hinges can be challenging. These days, three-hinged arches are seldom ever employed. An alternative to the arch that permits building even in cases when the ground is not sufficiently firm to withstand horizontal forces is the tied arch. As the girder "ties" both ends of the arch together, it prevents the horizontal forces from being restrained by the foundation, hence the term "tied arch."
3. Bridges with cable stays:
The cable stayed bridge is an additional kind of bridge. A continuous girder bridge with one or more towers placed above piers in the middle of the span is a typical example of a cable-stayed bridge. Cables support the girder by extending diagonally from these towers, usually to both sides. Steel wires are incredibly flexible and robust. Because they enable a lighter, more thin structure that can still span large distances, cables are incredibly cost-effective. Even though there aren't many cables strong enough to hold up the entire bridge, they are vulnerable to a factor we don't often think about: the wind.
Careful research is needed for longer span cable-stayed bridges to ensure that the cables and the bridge will remain stable in the wind. The bridge's decreased weight is advantageous during an earthquake even though it is a disadvantage in strong winds. Care must be given when planning the foundations, though, as the cable-stayed bridge may sustain damage if uneven settling of the foundations happens during an earthquake or over time. The cable-stayed bridge is a visually appealing and distinctive landmark due to its sleek and contemporary design.
The design of the bridge is an extremely difficult assignment because of the special qualities of the cables and the structure overall. Without the use of computers and computer analysis, the calculations for longer spans where winds and temperatures must be taken into account would be incredibly difficult and nearly impossible. Cable stay bridge construction is likewise a challenging process. The girders and towers' cable routing and attachments are intricate structures that need to be fabricated with precision. Cable-stayed bridges are not specifically categorized.
They may differentiate between them, nevertheless, based on
factors including the quantity of cables, girder type, spans, and towers. The
quantity and kind of towers, as well as the quantity and configuration of
cables, vary greatly. Single, double, portal, and even A-shaped towers are
frequently utilized. There are also wide variations in cable configurations.
Fan, star, harp, and mono arrangements are a few common types. Sometimes the
tower's cables are simply fastened to one side of the girder, with the other
side secured to a foundation or other counterbalance.
4. Sturdy bridge frames:
Mendes bridges are another name for rigid frame bridges. The piers and the girder are two distinct structures of a typical girder bridge type. On the other hand, a rigid frame bridge consists of a single, solid framework for the girder and piers.
In a rigid frame bridge, the beam cross sections are typically I- or box-shaped. Compared to basic girder bridges, rigid frame bridge design calculations are more challenging. Fabricating the junction between the girder and the pier can be challenging and demands precision and close attention to detail.
Even though there are other alternative forms, the pi-shaped,
batter post, and V-shaped frames are the ones that are utilized practically
entirely these days. Because piers tilted at an angle can straddle the crossing
more efficiently without necessitating the building of foundations in the
center of rivers or piers in deep valleys, the batter post rigid frame bridge
is especially well suited for crossing rivers and valleys. Foundations are
effectively utilized by V-shaped frames. By providing two supports for the
girder, each V-shaped pier lowers the number of foundations and gives the
profile a less cluttered appearance. Inner city highway piers and supports are
often constructed using pi-shaped rigid frame systems. These bridges have a
frame that both supports the elevated highway and permits vehicles to pass
directly beneath it.
5. Truss bridges:
Truss bridges are the most prevalent type of bridge and are typically found in steel bridges. A truss is made up of numerous tiny beams that work together to sustain a significant weight and span a considerable distance. Truss design, manufacture, and erection are often quite straightforward processes. Trusses, however, require more room once completed and may provide a traffic hazard in more intricate constructions. There are both simple and continuous trusses, just like in girder bridges.
A truss bridge is the best option for locations where huge sections or pieces cannot be supplied, or where large cranes and heavy equipment cannot be used during construction due to its small individual parts. Since the truss is a hollow skeleton, the road may run over or even through it, providing clearance beneath the bridge that is frequently not achievable with other kinds of bridges. The fundamental design that is employed also categorizes trusses. The Warren, Pratt, and Howe trusses are the most exemplary types of trusses. When it comes to basic and continuous trusses, the Warren truss is arguably the most widely used. No vertical members are employed for short spans, giving the construction a more straightforward appearance.
Vertical members are added for longer spans to provide additional strength. Typically, Warren trusses are utilized for spans of fifty to one hundred meters. The diagonal members of a Pratt truss all slant down and in toward the center of the span, with the exception of the very end ones. All diagonal members, with the exception of those close to the center, are solely exposed to tension stresses; compressive forces are handled by the shorter vertical members. Because of this, diagonal members can be made thinner, leading to a more cost-effective design. In contrast to the Pratt truss, there is the Howe truss. The diagonal elements support compressive forces and face the other way. Because of this, it is a very expensive design for steel bridges, and its application is uncommon.
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