The deflection of beams and slabs must be controlled in accordance with operability requirements. Otherwise, slabs and beams will crack due to excessive deflection.
Furthermore, increased deflection in beams and slabs can lead to damage to non-structural components such as partitions, coverings attached to the structure, ceilings, etc.
Therefore, during construction it is necessary to control the deflection of the panels.
Several methods can be used to reduce slab and beam deflection.
- Increase the depth of beams and slabs
- Use alternative charging
- Increase traction reinforcement
- Increase compression gains
- Increase beam width
- Reduce gaps
- Use preload
Let's discuss each method individually.
Increase the depth of beams and slabs
The rigidity of the structural element is the main factor that affects the deflection of the element, as we cannot control the loads that act on the element and therefore must take them into account in the design.
There is no way to reduce loads on the structure except to consider changing the weight of non-structural elements.
The rigidity of the structural element can be increased by increasing the depth of the element.
Stiffness of beam elements proportional to OVO/L
Here “I” is moment 2 of the beam surface.
Me = bra 3/12
Where “h” is the height of the section.
Therefore, as the section height increases, the stiffness increases and, as a result, the deflection decreases.
A similar type concept is also used for plates.
Use alternative charging
Application to structural elements affects the deflection of the slab or beam.
Payload reduction is not possible for any reason. The structure must be designed for the loads that occur during its use.
However, we can reduce the dead weight of the structure.
Alternative materials reduce the weight of the structure. For example, using lightweight materials instead of heavy materials reduces the weight of the structure.
We can replace the internal partitions that we want to build from brick or block walls with dry partitions.
Furthermore, if we need a solid partition, we can use hollow blocks. This significantly reduces the weight of the structure.
Reducing the width of solid walls also has a significant impact on panel deflection.
We could also make an adjustment to the structure's own weight.
Increase traction reinforcement
Based on the applied loads, we calculate the bending and shear forces of the structural element.
We determine reinforcement requirements accordingly. Next, we check the element for deflection.
If we increase the reinforcement required for bending and shear, the stiffness of the beam increases.
As explained above, increasing stiffness reduces the deflection of the slab and beams.
Increase compression reinforcement
If we provide compression reinforcements where compression reinforcements are not required, we will increase the stiffness of the beam.
Even if we use compression reinforcement as Minimum steel also increases the stiffness of the beam or plate.
Increase beam width
There are limitations to increasing beam depth to control deflection.
If we cannot increase the depth, the deflection will be greater. In such situations, we need to provide more reinforcement to control the deflection as well as the design moment and shear forces.
To have more reinforcement we should have enough space. This could be achieved by widening the beam. This allows more reinforcement to be placed.
Reduce the margin
It's a very interesting topic of discussion.
Do we really need to reduce the gap to control deflection?
This must be decided based on the floor plan and taking other aspects into consideration.
Reducing the span results in a reduction in beam reinforcement and deflections.
In most cases, reducing the range does not make sense.
Use preload
Increasing the span of the beam or slab results in an increase in the height of the elements. At a certain level it is no longer economical to increase the panel thickness.
A slab span greater than 6-7 m is not economical if we build it as a normal reinforced concrete slab.
Therefore, options such as tensioning methods are used in panel construction.
If we use prestressing methods, the deflection will be significantly reduced.
