pier Commonly used as a general term for any type of structure located between a horizontal span and a foundation. However, from time to time, it is also used specifically for a concrete wall to separate it from a column or bent. From a structural point of view, a pillar is a member that opposes lateral force primarily by flexor action while a pier is a member that opposes lateral force primarily by a shear mechanism. A pier consisting of several columns is often called a Bent,
There are several ways to define pier types. By its structural connectivity to a superstructure is: monolithic or cantilever. The second is by its sectional shape: solid or hollow; Round, octagonal, hexagonal or rectangular. It can also be recognized by its framing configuration: single or multiple column bent; Hammerhead or pier wall.
The selection of the type of piers for a bridge should be based on functional, structural and geometric requirements. Aesthetics is also a very important factor in the selection as modern highway bridges are part of the city landscape. Figure 1 Shows a collection of cross section shapes typical for overcrossings and viaducts on land and line drawing number 2 Shows some typical cross section sizes for ferries for river and waterway crossings. Often, wharf types are mandated by government agencies or owners.
Many state departments of transportation in the United States have their own standard column sizes. concrete wall pierce, as shown in Fig-3a and Fig-4, are often used at water crossings because they can be constructed in proportions that are both thin and streamlined. These characteristics lend themselves well to providing minimal resistance to flood flow.
hammerhead pierce, as shown in fig-3b, are often found in urban areas where location limitation is a concern. They are used to support steel girders or precast prestressed concrete superstructures. They are aesthetically attractive. They generally take up less space, leaving more room for traffic underneath. Standards for the use of hammerhead piers are often maintained by individual transportation departments.
A column bent pier consists of a cap beam and supporting columns forming a frame. Column bent piers, as shown in fig-3c And Fig-5, can be used either to support a steel girder superstructure or as an integral pier where cast-in-place construction techniques are used. Columns can be either circular or rectangular in cross section. They are by far the most popular form in the modern highway system.
A pile extension pier consists of a drilled shaft as the foundation and a circular column extending from the shaft to form the substructure. An obvious advantage of this type of pier is that it occupies a minimum amount of space. In some instances the expansion of the pile may be required to widen the existing bridge as limited space precludes the use of other types of foundations.
Selecting the proper mooring type depends on several factors. First of all, it depends on the type of superstructure. For example, steel girder superstructures are typically supported by cantilever piers, whereas cast-in-place concrete superstructures are typically supported by monolithic bents. Second, it depends on whether the bridges are over the waterway. Wharf walls are preferred at river crossings, where debris is a concern and hydraulics guide it. Multiple pile expansion bents are commonly used on slab bridges. Lastly, the height of the piers also determines the selection of the type of piers. Tall piers often require a hollow cross section to reduce the weight of the substructure. Thereafter the load demand on the costly foundation is reduced. Table 1 Summarizes general type selection guidelines for different types of bridges.
Table 1 General Guidelines for Selecting the Type of Wharf
|over water||long pier||Wharf walls or hammers (T-piers) (Fig. 3a and b, Hollow cross section for most cases; cantilever; The base and stage of the pier wall can use hammerheads combined with tapered shafts|
|little pierce||Wharf walls or hammers (T-piers) (Fig. 3a and b, solid cross section; cantilever|
|on the ground||long pier||Hammerheads (T-piers) and possibly rigid frames (multiple columns bent) (Fig-3b and c, Hollow cross section for single shaft and solid cross section for rigid frame; cantilever|
|little pierce||hammerheads and rigid frame (Fig-3b and c, solid cross section; cantilever|
Precast Prestressed Concrete Superstructure
|over water||long pier||Wharf Walls or HammerheadsImage-4, Hollow cross section for most cases; cantilever; Can use hammerhead combined with pier wall base and step-tapered shaft|
|little pierce||Wharf walls or hammer tip; solid cross section; cantilever|
|on the ground||long pier||hammerheads and possibly rigid frames (multiple columns bent); Hollow cross section for single shaft and solid cross section for rigid frame; cantilever|
|little pierce||Hammerheads and Rigid Frame (Multiple Column Bent) (Figure-5a, solid cross section; cantilever|
Cast-in-Place Concrete Superstructure
|over water||long pier||Single Shaft Pier (Image-4, There would be the possibility of superstructure by traveling forms with balanced cantilever construction method; hollow cross section; monolithic; fixed on the floor|
|little pierce||pier walls (Image-4, solid cross section; monolithic; fixed on the floor|
|on the ground||long pier||single or multiple column bent; Solid cross section, monolithic for most cases; fixed on the floor|
|little pierce||single or multiple column bent (fig-5b, solid cross section; monolithic; pinned on|