Shear reinforcement is commonly used to prevent a sudden catastrophic shear failure by enhancing the shear capacity of the structural concrete. The possibility for inclined shear fractures to spread between the shear links can be increased by increasing the space between the shear links.... Shear connectors, such as stirrups or cotters, can also be used to connect several pieces of reinforcing steel together in order to increase the strength of the structure. This is especially useful when building structures that are subject to large forces but small cross sections.
The most common cause of shared wall failures is insufficient spacing between vertical members. If the distance between joists or beams is less than about 12 inches (30 cm), then there is a risk of one section of the wall collapsing when another section fails. Joists or beams should be at least 16 inches (40 cm) on center to provide adequate support. Avoid using 2-by-4s or 2-by-6s as studs because they don't provide much lateral support. Use 2-by-10s or 2-by-12s instead.
Other factors such as the type of wood used as framing members, the quality of construction work, and the environment where the house sits can all contribute to whether or not a shared wall will fail.
Reinforcement in the shape of stirrups, for example, is used in reinforced concrete beams to improve the shear strength of the member. A material's shear strength is greatly influenced by its cross-sectional area. The shear strength of a component increases with its width and thickness. However, greater weight must be supported by such a beam.
Stirrups are used instead because they can be placed inside the concrete before it sets, allowing more time for the reinforcement to properly bond with the cement. They also prevent the top surface of the concrete from becoming uneven which could cause problems later if vehicles were to drive over it.
Stirrups are long bars that run parallel to the axis of the beam. They are placed at regular intervals down the length of the beam. Each set of stirrups should have one facing out toward the middle of the beam and one facing inward. The ends of the beam are then wrapped with wire to form a circle, and the beam is lifted into place. As the concrete cures, the stirrups and wire become part of the solid beam, increasing its strength.
The amount of reinforcement needed depends on how much stress the beam will face during use.
Stirrups are used to offer minimal shear reinforcement in beams. To withstand additional shear force caused by a live load to make concrete resistant to shrinking to resist initial tension, stirrups should be added to beams. Stirrups are attached to the beam with fasteners and fill the void left by the removed web plates.
The required amount of stirrups for a specific beam depends on its size. For example, a 20-ft. Long beam requires 40 stirrups to meet the 100-pound working load requirement. The number of stirrups needed increases as the depth of the beam increases. For example, a 30-ft. Deep beam would require 80 stirrups to meet the same working load requirement.
Beams are either hollow or solid. Hollow beams have open cross sections and are usually made from wood. Solid beams have closed cross sections and may be made from metal, wood, or concrete. Both types of beams can have stirrups added. Stirrups are added to strengthen thinned areas of the beam where there's no resistance to the spread of the concrete during pouring. This occurs at the top and bottom edges of the beam and where there are shallow angles in the curvature of the beam.
Shear failures in beams are produced by diagonal fractures near the support, which do not offer shear reinforcement. Beams break promptly when significant fractures occur in the high-shear zone near the beam supports. The amount of load that a beam will fail under pure tension is called its ultimate load. When combined with the area of the cross section, this value gives the total load that the beam can carry before failing.
Beam failures can be divided into two main types: simple and complex. In a simple shear failure, only the bottom chord fails; the top one remains intact. This type of failure usually occurs when the load on the beam is close to its supporting capacity, and there is no major problem with the construction of the building or site conditions that would cause it to fail in other ways first. Simple shear failures are most common in beams that have been built according to code requirements but not designed with sufficient strength for the expected loads. They often happen because the designer used an outdated version of the code when setting up the drawings for the structure. For example, if the code was based on a 50-year-old edition, then the beams were likely designed using lower strength materials than today's standards require.
In a complex shear failure, both top and bottom chords fail. This type of failure usually occurs when the load on the beam is far below its supporting capacity.