Available to all engineers who are members of the organization: The necessity of not placing the beam next to the main beam in the concrete structure

Notice to all the engineers who are members of the organization: The necessity of not placing the beam next to the main beam in the concrete structure

Question: Hello, what is the reason why it is said that the implementation of beams in concrete buildings next to beams is prohibited?
Is there basically such a ban?

Answer from Mr. Dr. Ahmedreza Jafari: Placing the beam next to the concrete beam if it is not separated from the concrete beam (for example, placing a few centimeters thick unilite between the concrete beam and the beam) will make the beam and the concrete beam become integrated. And in practice, the dimensions of the concrete beam will be bigger. This issue causes the following changes in the behavior of the concrete structure.

1. The hardness of the beam depends on its dimensions. Increasing the dimensions of the beam increases the stiffness of the beam, and this change in stiffness changes the behavior of the structure and changes the distribution of forces, which is not considered in the initial design of the structure.

2⃣ In reinforced concrete bending frames with medium and special ductility, there are limitations for beam width. Increasing the width of the beam due to the addition of the dimensions of the beam can cause the width of the beam to go out of the permissible range.

3⃣ In reinforced concrete bending frames with medium and special ductility, there are limitations for the distance between the axis of the beam and the axis of the column. If the beam is placed only on one side of the beam, it will change the axis of the beam and create a distance between the axis of the beam and the column, which may exceed the permissible value.

4⃣ If the longitudinal reinforcement of the beam at the top and bottom extends as much as the restraining length inside the column core and is restrained, this will increase the bending resistance of the beam.
As a result, the shear force corresponding to the formation of the plastic joint at both ends of the beam also increases.

Considering that this shear force is the basis of beam design in bending frames with medium and special ductility and is also effective in column shear design in special bending frame, the structure may not respond to this shear force in this condition. In addition, the increase in the bending strength of the beam in the special bending frame can be contrary to the reliability in the control of the ratio of the bending strength of the beam to the column (the rule of strong column – weak beam).

According to the above, if we want to install the beam next to the concrete beam, the beam and the beam should be properly separated.

This position can be done, for example, by using a few centimeters thick vertical monolith on the side of the beam at the distance between the beam and the beam. Of course, this separation should not be done in a way that causes a break between the concrete beam and the roof diaphragm. For this purpose, there must be a necessary connection between the concrete of the roof slab and the concrete beam.

Edited and edited by Khalil Dashti

National Regulations Channel – Engineering Rights

This post is written by amiralidashti93