2 July 2019
Key Considerations of Building Bracing Plans
Bracing plans determine where to place the components of a bracing system to withstand wind loads and seismic pressure. Qualified, experienced and accurate partners are needed to provide architectural design drafting, with high quality and more detailed architectural CAD services, to ensure that bracing plans are beyond reproach.
To facilitate a robust seismic performance, certain precautions in developing bracing plans must be considered:
- They must run in two orthogonal directions. In timber-framed buildings, they must be parallel to the external walls.
- The lines must be spaced evenly, when possible.
- Lateral loads can be transferred between bracing lines in timber-framed floor and ceiling construction.
- Bracing lines should accommodate bracing elements anywhere on the lines.
There are two bracing systems that resist horizontal forces acting against the structure of the building: vertical and horizontal bracing. For both vertical and horizontal bracing, there are different types of bracing that can be used. They can be broadly categorised as follows:
Diagonal structural elements inserted into rectangular areas of a structural frame is called trussing, or triangulation, which helps stabilise the frame.
Cross-bracing (or X-bracing)
Two diagonal members cross each other in cross-bracing, or X-bracing. They are tension-resistant steel cables, and each brace resists sideways forces.
Typically, K-bracing connects to columns at mid-height and is thus more flexible to working around windows and results in reduced bending in floor beams.
Two diagonal elements are framed in a V-shape stretching down from the top two corners of a horizontal element and join at the centre of a lower horizontal element, or the two elements in the V meet at the centre of an upper horizontal element for an inverted V.
Centric bracing elements do not join at a centre point. There is a gap between them at the lateral connection, which absorbs energy from seismic activity.
Bracing System Design in a Nutshell
- Select the right beam section sizes.
- Select the right column section sizes.
- Calculate equivalent horizontal forces (EHF) for each floor.
- Calculate equivalent horizontal forces (EHF) of wind loads.
- Determine the total shear of the bracing base.
- Share shear appropriately between the bracing systems.
- Size bracing members.
- Determine frame stability.
- Ensure effectiveness of floor diaphragms in distributing forces to bracing system.
- Determine total force the bracing should resist locally.
- Ensure bracing can handle individual floor forces and external load forces.
Structural engineers and architects ensure effective bracing in a building. Software, such as GIB EzyBrace and Bracing software, with ArchiCAD, is used to determine how many bracing panels are required and where they should be placed. For cost-effective, accurate and timely delivery of bracing plans, many Western firms use the architectural CAD outsourcing services of a dedicated offshore CAD team, ensuring the structural fitness of the building.