A Brief Guide to Bridge Piers
Piers are essentially large, vertical supports to the superstructure above, like bridges or archs. The pers used to hold up a bridge is directly called the bridge piers. Note that columns do basically the same job, however, the difference between piers and columns are that the columns do not provide any aesthetic value and they are internal structures supporting slabs and beams. A pier, on the other hand, is exposed and is designed not only for load-bearing but also from an aesthetic point of view.
Generally having a cross-section of square, rectangular or round, piers are built to support both vertical and horizontal loads so that they can be built far apart so as the footprint of the superstructure remains pretty small on the highest region. This facilitates an unhindered flow of water or traffic under the bridge if the bridge is built above a water body or road or rail lines.
The materials that can be used to build bridge piers may be concrete, steel or other metal, or stone, or even a combination of these. Submerged piers are generally stone or concrete-based because they can weather any corrosive effects from water, whereas for their economic and aesthetic value land-based piers are preferably metallic.
Types of Bridge Piers
Based upon their structural designs, piers can be either the solid-type or the open-type. Discussing each below:
Solid Type Piers: Impermeable upright supports with no hollowed section, these piers are generally made of bricks, stone and concrete. They can be further subcategorised into:
Solid Masonry Piers: constructed from brick, stone and concrete, these pers have an inner shell of mass concrete and an outer shell of brick or stone masonry.
Solid Reinforced Concrete Piers: when the superstructure needs to be situated especially high, masonry piers become uneconomical. Then this specific type of pier having generally square cross-section and tall shape is used.
Open Piers: Hollow or spaced-apart structure that permits the passage of water through it. They are divided into:
Cylindrical piers: with a round cross-section, these are basically metal cylinders filled with concrete used for medium-height bridges.
Column Piers or Column Bent: For bridges that are of significant height, these piers are formed by using a cap beam above two-three columns, each having circular or square cross section on a solid footing. These are mostly used in overbridges and lifted approaches.
Multicolumn or Pile Bent: Similar to Column bent but having large distances between columns. These are used when there may be a problem about garbage collection at the foot of the columns. A cross-brace may be required.
Pile Pier or Pile Bent: Similar to above but used for short spans and low heights.
Trestle Pier or Trestle Bent: Composed of Bent cap at the top and columns below, they are used in firm solid riverbeds with slow current, or in flyovers.
Based on construction materials, bridge piers can be categorised in the following ways:
Masonry Piers: Comprised of stone and brick masonry, these are huge structures which may create obstruction of flow below and where the ground can take their massive load.
Mass Concrete Piers: Similar to above but built of solid concrete. Used where most of the structure is submerged.
Reinforced and Prestressed Concrete Piers: Having a smaller footprint than the above, these piers are preferred where there is considerable depth and span and there should be minimal obstruction below.
Fixed Piers: these have a fixed bearing and can support both-way stresses.
Free piers: similar to above but have free bearings and can support only axial stress.
Hammerhead/Cantilevered piers: a single solid concrete section supporting a steel girder or precast prestressed concrete superstructure section. Because of its small footing and aesthetic values these are highly popular in urban usage.
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