In Vietnam, voided slabs are still considered a new structural solution bringing great benefits to users such as: fast construction, long spans, optimal architecture spaces and reasonable prices. The following article will help you understand more about flat-plate floor technology in Vietnam. 

Why are they called Voided Slabs?

Structural solution for floors is a very important in the building structure. It determines the costs, construction progress and use quality of the building. The two traditional floor structure solutions used for the building are Floors – beams and Floors – no beams – flat-plate floors.

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Beamless floors are a new trend in Vietnam

Compared with the structure of the Floor – Beam, Flat-plate Floors are a solution with outstanding advantages as follows:

– Short construction time and less labor in such stages as formwork erection, reinforcement installation and ceiling finishing. This is the biggest advantage of the flat-plate slab solution compared to slabs with beams

– The floor-to-floor heights are reduced by reducing the structural heights of the floors and thus the building height as well. In many cases, it is possible to increase the number of stories, therefore increasing the land use efficiency;

– The flat-plate slabs will not limit the position of the partition wall, thus allowing the Architect to arrange the use areas optimally;

– No need to install the false ceiling. If there is no technical system attached to the ceiling, it is not necessary to apply the false ceiling but still ensure aesthetics.

However, traditional flat-plate slabs have major disadvantages as follows:

– The thickness of the floor is larger as the span is longer, normally to ensure deflection in the middle of the span and shearing resistance at the top of the column, the thickness of the slab must reach H = 1 / 25L. This is the biggest disadvantage of flat-plate floors, resulting in the following problems:

– greater thickness causes great self-load, affecting column structure and foundation structure;

– The cost of the project is high, especially for multi-storey projects due to the high cost of concrete and reinforcement of the floors. Some technologies and solutions have been studied and applied to overcome the above disadvantages of traditional flat floors. We can summarize in the following solution groups:

Group 1 – Flat floor with pillar cap (mushroom floor) – Figure 2a: Column caps help to reduce the slab spans, thereby decreasing the thickness in the middle of span and still ensuring the shearing thickness at the top of the column. This solution overcomes the biggest disadvantage of flat-plate floors, but at the same time it also takes away the privilege of flat plate.

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Figure 2a: Slabs with column mushroom                                               Figure 2b: Prestressed slab

Group 2- Prestressed slab – Figure 2b: Using prestressed steel (pre-tensioned or stretched after pouring concrete) to create pre-compressive stress in the floor concrete, which helps the floor withstand large forces, allowing longer spans. However, this solution does not increase the shearing resistance of the floor at the column head positions, so either the floor thickness is still as large as the traditional solution or there must have a column cap and shearing steel reinforcement. Besides, the cost for the steel cables, post-tensioning, auxiliary, and professional construction workers significantly add up to the construction cost.

Group 3 – Hollow core floor – Figure 3: The principle of this solution group is to create a voided structural slab in the middle areas (core areas) that barely involve in bearing to lighten the weight of the floor. The voids are positioned so that after casting concrete, they will form a one- or two-way working slab system. Floors can be emptied up to 50% of its volume with significantly reduced slab weights compared to conventional flat-plate floors.

 What is a voided slab?, sàn phẳng không dầm lõi xốp, sàn lõi xốp, sàn xốp, sàn lõi rỗng, gạch không nung, gạch nhẹ, gạch chống thấm, gạch lõi xốp, gạch xây dựng

Hình 3: Structure of voided slabs

Compared with the groups of solutions 1 and 2, the hollow core floor solution (GP3) has very obvious advantages as follows:

– Still retaining the biggest advantage that the floor is completely flat;

– Ability to well withstand shearing at the top of the column due to ensuring the thickness of the concrete like solid floors;

– Although the stiffness of the floor is not significantly reduced compared to a solid floor of the same thickness, the weight is much more reduced. So, the voided slab is really good at bending and vibration resistance, allowing the floor to reach a longer span;

– Thick floor with many voids effectively insulates sound and heat;

For the above advantages, the voided slab casting technology has developed relatively fast, especially for the past 10 years and has become a very interesting choice when looking for an ideal solution for construction works.

What is a voided slab?, sàn phẳng không dầm lõi xốp, sàn lõi xốp, sàn xốp, sàn lõi rỗng, gạch không nung, gạch nhẹ, gạch chống thấm, gạch lõi xốp, gạch xây dựng

Many buildings use S-VRO voided core slab technologyMORE VIDEO OF FOAM CORE VOIDED SLAB S-VRO:

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