Bridge Construction Typology | The Piers
According to the definition, The Piers, are the vertical support structures of bridges. They are the intermediate supports, whose function is to transmit the forces they receive from the load-bearing elements to the foundations.
What type of piers are there?
There are many types of piers, and they vary according to structural design, aesthetic and economic factors. The variables that go into the design of the piers are therefore multiple: The size of the loads they receive from the deck, the height, the width of the deck, and the context in which they are located.
Before we start then, let’s identify the elements that make up the piers:
In civil works, piers can be classified according to 2 main characteristics: shape and section.
Let’s take a look!
Classification according to shape
Depending on their shape, these categories of piers can be identified:
- Straight piers: this is the simplest form of pier, i.e. with a square or rectangular cross-section, with no inclination or change of cross-section. High piers are often straight and sometimes do not have a lintel so as to simplify construction. For this type of pier, standard metal formwork is normally used for walls, and a climbing system is used to continue concreting at height.
- Curved Piers: curved piers have a circular or elliptical shape, and are mainly used when there is a hydraulic requirement (e.g., river piers), as this section reduces the dynamic pressure of the water. The formwork for this type of pier consists of standard circular formwork (circular piers) or special formwork, in case of elliptical or very large diameter piers.
- Special piers: it may happen that, due to aesthetic or functional requirements (lintel incorporated in the pier), the piers have a special shape, which requires an ‘ad hoc’ formwork study beyond the standard.
- Portico piers: this type of pier is characterized by the presence of an upper header that joins more piers. It can be used when the deck section is very wide, as the overhang of a lintel on a single pier would be too much.
Classification by section
Depending on the aesthetic and structural properties required by the project, there are many sections that bridge piers can have. In general, they can be divided into 2 macro typologies:
- Solid Section: the solid section is typical of piers that are not particularly high. It is the simplest type to execute, since it is only necessary to design the exterior formwork as if it were a large pillar or a wall.
- Hollow section: in this case, the section has an interior hollow section due to the need to lighten the pier itself and save concrete. It is mainly used for tall piers, where the impact of the concrete is significant, and where the rigidity at the top has to be reduced (due to thermal effects and concrete shrinkage).
The capital has the function of connecting the deck to the pier, transmitting the loads from the deck to the pier. For this function, the capitals can have neoprene or be directly embedded in the deck.
There are basically 4 types of capitals:
- Neoprene capital: this is the most commonly used type of capital: it comes in many shapes, depending on the width, the load of the deck and the aesthetics. Normally up to a height of 12 m, formwork is used, if possible, with shoring supported on the ground. For heights of more than 12 m, systems without floor support should be used (for example: SCAP system, Self Spanning).
- Capital recessed in the deck: in static systems with continuity between the deck and pier, the capital recessed in the deck, without supports, can be chosen at the design stage. In this case a fixed connection point is created.
- Pier without capital: especially in high piers, where the execution of the capital would be uneconomical in terms of cost and process, a solution without capital is usually chosen, supporting the deck directly on the pier.
- Lintel: in the case of portico piers, the solution is a lintel that transmits the loads to the piers. Normally, in these cases, the shoring is always supported on the ground, while the unsupported solution is more complicated.
We have taken a quick look, but the formwork system required for each type of pier depends very directly on a series of circumstances for each specific work, that is to say, on these main factors:
- Availability of cranes
- Possibility of support on the ground
- Maximum allowable pressure
- Pier height
- Climbing fill height
- Final finish
- Number of repetitions.
The specialist formwork company must investigate these details in order to offer the optimum formwork solution.
The correct technical advice, in the planning phase, is essential to ensure that the execution is carried out successfully.
If you have such a project, make sure of it!