The deflection or the buckling It is the phenomenon that occurs in slender members when they are subjected to a compressive load. It is characterized by deformation, whether it is elastic or plastic, which involves a displacement perpendicular to the axis along which the compression is applied. This action is proportional to the horizontal moment generated by the eccentricity, and due to the slenderness of members such as beams, it becomes quite noticeable even with small eccentricities.
Consequences of Deflection in Beams
It is very important to identify the type of deflection that will have the greatest impact on beams and other structural elements, so that the necessary corrections can be made and failures can thus be prevented. Since the presence of deflections tends to cause damage to adjacent structural elements, and especially to non-structural elements such as tiling, flooring, and interior partitions in buildings...
These effects can be very noticeable—for example, severe cracking in the finishes—which can make building occupants feel unsafe. But they can also go beyond mere aesthetics, since depending on where the cracking occurs, it can cause water leaks or thermal bridges, leading to much worse consequences.
Types of Deflection
When conducting structural studies, calculations, and design, deflection can be evaluated in two main categories, which are the local one y the global. It is understood that “local” refers to the deflection analyzed from the perspective of the individual member, while “global” refers to the entire structural system.
Now, regardless of these two categories, Deflection, as a phenomenon, can occur or be studied in various ways. In fact, to verify a structural element during the design phase, its strength must be analyzed for several of these types of deflection simultaneously. These types are:
- Flexional: In this type of deflection, the member (the beam) bends laterally, but without any rotational movement about the longitudinal axis. Therefore, the cross-section of the member remains unchanged. This is commonly observed in columns and joists.
- Torsional: In torsional deflection, as the name implies, the cross-section of the member rotates about the member’s longitudinal axis or the center of any cross-section. This typically occurs in wide-flange beams with low torsional stiffness.
- Flexural-torsional: A type of deflection in which the beam experiences both of the types mentioned above simultaneously, causing the beam to be bent and twisted at the same time. However, there are no changes in the cross-section.
- Lateral-torsional: In these cases, deflection perpendicular to the plane of bending and rotation about the element's longitudinal axis occur simultaneously.
By understanding how deflection occurs in horizontal support members, such as beams, we will be able to not only identify the problem but also its possible cause. This gives us the opportunity to take action during the design phase or to implement remedial measures by applying the type of reinforcement as necessary, depending on the type of deflection that may occur in the structure under analysis.
