History
In the second
decade of the twentieth century, conventional systems that were used in decades
have progressed and classified. The use of slabs on the columns at this time
has been very much considered. Drop cap and Drop Panel were also added to the
construction technology. Focusing on the lightness of new buildings and slab
systems has led to the use of one-way roof systems. The slabs with joists and Waffle
Slabs also became popular in this period.
The presence of voids
at the bottom of the slab is the main characteristic of the waffle slabs.
Various shapes of the cube or cylinder create holes in the bottom of the slab
and. The shape of the formworks brings a special beauty to the finished
concrete surface. In many cases, concrete surfaces are used as the final
surface of the work.
The use of waffle
slabs to cover large spans in structures has been considered from the past.
Various types of this of slab have been used in the last century. But the
oldest and most famous example of the use of the hollow slab is the cover of
the 43-meter span of the ancient Roman Pantheon temple in the seventeenth
century.
Theory of waffle Slab
Waffle slab is
one of a kind of two way reinforced concrete slab that is made up of a thin top
slab based on joists with thin web. Characteristics of the slab waffle are as
follows:
- Web thickness in joists between 10 ~ 25 centimeters
- Top Slab thickness between 6.5 ~ 10 cm
- Low concrete rate between 18 ~ 25 centimeters per square meter
- Low reinforcements rate between 7 ~ 12 kg per square meter
can be used with other technology like prestressing
- Expose surface for
use in architecture porpuses
Waffle slabs are
one of the most used slabs in structures such as airports, multilevel parking,
industrial halls, commercial structures, etc. In
addition, the use of this slab as a foundation in high-rise structures will
have a great economic justification.
In
the waffle slab system, the upper slab acts as a flange of the joists. Since
there is a positive bending moment in the middle of the spans, the upper slab
plays a very positive role, but in the rigid areas where the bending moments are
negative, the lower fiber will be under pressure. Drop-cap, drop-Panel or Band
Beam is practically used in these areas.
