Lateral Bracing System

Lateral Bracing System:

Lateral Bracing System is a world-wide concept to increase the strength of a building structure. This design is found in buildings where the first storey contains a parking garage or an open commercial area for stores and the upper floors for house or offices or apartments.

This design creates a discontinuity of strength and stiffness. If all stories are approximately equal in strength, the entire building would bend in an earthquake. If the first storey is softer, or more flexible than the other stories, the bending would concentrate there. Because the first floor is also the most highly loaded, the problem is compounded, thus possibly causing column failure.

This also will put additional stress on the connection between the first and second stories and can cause the building to collapse. Building configuration can have significant effect on how a building performs in an earthquake. Generally the simpler the design and the more balanced the building and its structural and non-structural components, the better the building will perform during an earthquake.

Lateral Bracing is a Lateral Support of any structure to resist the upcoming Lateral Earth Pressure due to Earthquake. Lateral bracing is the term to refer to any pieces on a structure that help keep the top chord from bending horizontally.

Figure-01 indicates a lateral bracing system between two columns,

Figure-01: Lateral Bracing System between two columns

According to Johnson. Mark. A, Senior Vice President, Code Council’s of Business and Product Development,“Bracing is one of the most critical, yet most misunderstood, safety elements in one- and two-family dwellings and townhouses constructed under the IRC.”

Different Types of Lateral Bracing System:

In the world there are different types of Lateral Bracing are used in structure. The most commonly used Lateral Bracing are as follows,

a)      Knee Bracing

b)      Cross Bracing

c)      K-Bracing

d)      V-Bracing

a)      Knee Bracing:

A knee-brace system is a structural component that transfers wind pressures exerted on the sidewalls and roof of a farm building to its foundation. This, of course, induces shear and bending in the stud or pole. Knee braces are an effective wind-bracing system for either pole or stud-framed farm buildings. Figure 2.8 shows Knee Bracing system.

Figure-02 indicates a Knee Bracing System between two columns,

Drawing by Engr. Snehashish Bhattacharjee (Tushar), seasoft022.blogspot.com

Figure-02: Knee Bracing System between two columns

  

b)      Cross Bracing:

Cross bracing is a construction technique in which braces are crossed to form an X shape to support a frame. Cross braces are often metal, but they can also be made of wood. Cross bracing is used on many different types of items including furniture, ship frames, walls and flooring. Virtually any type of frame can be strengthened with a cross brace – even building frames.

Figure-03 indicates a Cross Bracing System between two columns,

Drawing by Engr. Snehashish Bhattacharjee (Tushar), seasoft022.blogspot.com

Figure-03: Cross Bracing System between two columns

c)      K-Bracing:

K-bracing is that type of bracing system where braces connect to the columns at mid-height.

Figure-04 indicates a K-Bracing System between two columns,

Drawing by Engr. Snehashish Bhattacharjee (Tushar), seasoft022.blogspot.com

Figure-04: K-Bracing System between two columns

d)      V-Bracing:

Inverted-V-braced frames are one type of Concentrically Braced Frame (CBF), in which the centerlines of members form a vertical truss system to resist lateral forces. As more emphasis has been placed on increasing ductility and energy dissipation capability of all types of structures in modern codes, design provision for a new type of braced frame, labeled the Special Concentrically Braced Frame (SCBF), have been developed (Goel1992, Bruneau et al. 1998).

Figure-05 indicates a V-Bracing System between two columns,

Drawing by Engr. Snehashish Bhattacharjee (Tushar), seasoft022.blogspot.com

Figure-05: V-Bracing System between two columns

Importance of Lateral Bracing System:

The load from gravity is easy to understand and constant on every house. Lateral loads are just as constant, but they vary in force and are not as recognized. The most common and universal lateral load is wind, with design velocities that vary from 85 to 150 miles per hour across the United States. The strongest wind loads, tornados, are not predictable and randomly occur in every part of the country. While it is not affordable or reasonable to design structures to withstand the strongest tornados, experience has taught us how structures can resist wind speeds of up to 150 mph and protect not only the inhabitants but also the integrity of the structure.

Similar experiences with seismic activity have helped building codes develop methods that enable structures to survive earthquakes that used to cause damage beyond repair.

Lateral bracing serves to break the top chord into smaller sections, giving it more strength against any natural disaster.

A journal about the Importance of Bracing published on November 2002 written by Ian Giesler, of ICF Builders, involved with ICF's for many years with a lot of experience in design, engineering to construction.

According to Mr. Ian Giesler,

“A wall alignment bracing system is as much a standard tool for building with ICFs as a paintbrush is to a painter. If you think that you can build perfect walls without bracing systems, you're only kidding yourself. ICF walls may look plumb, square and level without bracing, but typically they aren't. In fact, many walls need even more than a wall alignment bracing system just to get them close to a tolerable level.”