Bracing systems are an additional but vital component of a bridge's structure. A bracing system is used to support the main girders of the structure as well as to assist in the distribution of load-related effects and also to restrain chords or compression flanges, which could otherwise collapse laterally.
This article offers guidelines regarding designing bracing systems. Additional guidance is available within the Guidance Note 1.03 and Section 8.2 of SCI P356.
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What is a Braced Frame Structure?
A braced frame is extremely strong structural structure that is often used for structures that have to endure external loads like seismic pressure or wind. The components of a braced frame are usually composed of structural steel which is able to function effectively in compression and tension.
The columns and beams which make up the frame support vertical loads. The bracing system supports the lateral load. The location of braces however, is a challenge because they could hinder the style of the façade and the location of the openings.
Modernist and post-modernist buildings that adopt high-tech styles have responded by expressing bracing as an external or internal architectural element.
Benefits of Bracing Systems
The compression flange on the beam's main beam can be prone to stretch horizontally. Bracing systems prevent the buckle of the main beam.
The bracing system helps in spreading the horizontal and vertical load between the main beams.
Different Types of Bracing Systems
Majorly Bracing systems are categorized as:
- Horizontal Bracing System
- Vertical Bracing System
- Horizontal Bracing System
The bracing is done at every floor on the horizontal planes, thereby providing load paths to ensure that horizontal forces could be transferred onto the vertical planes of bracing.
The bracing system for horizontal use is also divided into two main kinds, namely:
Diaphragms as well as
Triangulated bracing in discrete
Certain floor systems offer a an excellent horizontal diaphragm. Others such as precast concrete slabs have particular steps. This can be seen in the example of steelwork as well as precast concrete slabs since they need to be joined properly in order to stop relative movement.
The use of triangulated discrete bracing is considered in cases where the floor system is unable to be utilized as an upright bracing system.
Vertical Bracing System
When vertical plans are used, there is bracing lines between columns that offer load paths utilized to transfer horizontal force to the ground. This system is designed to transfer the horizontal load to the foundations while minimizing the general swaying in the construction. The bracings are placed between two columns.
It is also possible to study in two different ways, namely:
- Cross bracing and
- Single diagonal.
Cross bracing is slim and able to withstand tension forces, but not compression forces. It is also able to provide the needed lateral stability based on the direction of the load.
In contrast to Cross bracing single diagonal bracing has been designed for resistance to both compression and tension forces. In thiscase, the structural members of the diagonal are placed into the rectangular regions of a structural frame . This helps to stabilize the frame.
In order to meet the requirement for a system that is relatively efficient bracing elements are positioned close to 45 degrees. This arrangement is durable and slim.
Vertical Bracing System is specifically designed to be resistant to:
- Wind power
- Equivalent horizontal forces
- The amount of vertical planes that need to be installed
Two vertical planes for each orthogonal direction is made available so that there is no disproportionate collapse.
Three bracings on the vertical side are included they provide enough resistance both in plan as well as against forces of torsion around the vertical direction of the structure's axis.
A greater proportion of bracing planes vertically can improve structural stability.
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Bracing Construction
A bracing system is a secondary but essential part of a bridge structure. A bracing system serves to stabilize the main girders during construction, to contribute to the distribution of load effects and to provide restraint to compression flanges or chords where they would otherwise be free to buckle laterally.
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