Hollow Core Slab Dimensions

[Hortense Malovich]

KnightcoreHollowcore) plank is a precast, prestressed, concrete plank manufactured by a precision, extrusion process, from zero slump concrete providing outstanding dimensional control and uniformity. Slabs are cut to length to assure dimensional accuracy and smooth end finish.

The underside of hollowcore plank is steel form smooth, and can be either left as is or painted with a textured paint. In many floor applications, hollowcore plank may be used without concrete topping. Joints between slabs are grouted and feathered, suitable under-layment or padding applied, and finishing carpet, wood floor, or tile installed.

Hollowcore plank meets the requirements for the restrained and unrestrained fire ratings of ASTM E119 and is listed by Underwriters Laboratories, Inc. for two hour fire resistant classifications (untopped), restrained and unrestrained conditions. Three and four hour ratings are also available with field-cast toppings.

The use of hollowcore plank structural floor and roof slabs will result in a lower total construction cost for your next project. The time and weather delays of on-site forming and curing of poured concrete are eliminated.

For this specific case your slab needs to be 200 mm thick so that it matches the thickness of the template. The hollow core templates can be found at this location: C:\ProgramData\Autodesk\Structural Precast for Revit 2018\Families\en\Custom Slabs . For more information about this please visit the help page:

Hi everybody. I have also the same problem. I want to use hollow core slab 220mm, so I set structural floor as 220mm thickness. I also set in precast configuration minimum width 220mm but no way. I try also upgrade the family inside the folder structural precast, but don't work.

Thank you for the info. I created custom hollow core family with width 220mm (I started from original family and just change dimension to 220 in the front view, other parameter I didn't change) and work it. Now I understand how the module work

A hollow core slab, also known as a voided slab, hollow core plank or simply a concrete plank is a precast slab of prestressed concrete typically used in the construction of floors in multi-story apartment buildings. The slab has been especially popular in countries where the emphasis of home construction has been on precast concrete, including Northern Europe and former socialist countries of Eastern Europe. Precast concrete popularity is linked with low-seismic zones and more economical constructions because of fast building assembly, lower self weight (less material), etc.

Slabs in prestressed concrete are usually produced in lengths of up to 200 meters. The process involves extruding wet concrete along with the prestressed steel wire rope from a moving mold. The continuous slab is then cut to required lengths by a large diamond circular saw. Factory production provides the obvious advantages of reduced time, labor and training.

Another fabrication system produces hollow-core floor slabs in reinforced concrete (not prestressed). These are made on carousel production lines, directly to exact length, and as a stock product. However, the length is limited to about 7-8 meters. Especially in Belgium, this method is widely used in private housing.

To meet modern standards (both hollow-core and massive slab) of soundproofing the floor needs to be covered with a soft floor covering that is able to dampen the sound of footsteps or a floating floor screed should be installed. An alternative is to put a strip of rubber underneath the floor slabs.

Hollow-core slabs and wall elements without prestressed steel wire can be formed by extruders. The size of these elements will typically range in width from 600 to 2400 mm, in thickness from 150 to 500 mm, and can be delivered in lengths of up to 24 m.[1]

The Type TC is a quick and easy to install toggle clamp designed for service suspension from pre-cast hollow core slabs (minimum core depth 75mm). FM approved (Size M10 only) for applications with moderate loadings. Manufactured from zinc plated steel strip.

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The idea to reduce the self-weight of concrete slabs by putting voids in the centre of the cross-section, dates to the beginning of the previous century. Several inventors from different countries applied for patents on various systems. The present article is mainly based on an analysis of patents published during the first half of the 20th century, and personal experiences from 1960 on. Patents usually offer a complex description of inventions (claims). Reconstructing the history of hollow core slabs based on these patents is a laborious but fascinating exercise. This article aims to give a general overview and is not meant to be exhaustive.

In general, these manufacturing methods can be used for the production of reinforced slabs as well as for the production of pre-stressed slabs. They are mostly in normal dense concrete, but there are also examples of structural light weight concrete.

In the early days, hollow core slabs were manufactured eitherin a plant, or on site. Often individual moulds were used and sometimes even long line beds, but in a discontinuous way. The compaction of the concrete was mostly carried out by tamping the fresh concrete. Here also a patent study could bring more insight, but it is not the main subject of the present article.

The most characteristic feature in the development of hollow core slabs was that they deviated strongly from the at that time existing design principles of reinforced and prestressed concrete, by which compression is taken up by concrete and tension by reinforcement. Indeed, in most cases, the developed manufacturing technique was only possible under the following conditions:

As a consequence, the tensile capacity of the concrete had to be taken into account in the design and new techniques for connections had to be developed. This was new especially with regard to transfer of forces at the support, shear capacity of the units, diaphragm action of the floors, transversal load distribution among adjacent units, non-rigid supports, floor openings, fire resistance, etc.

With regard to prestressed hollow core slabs, the fib Commission on Prefabrication played a crucial role in the development of the design. Extensive research and intensive field experience gathered from all over the world, learned that hollow core floors are perfectly able to fulfil all the needed structural functions, on condition that some elementary design principles are met. In 1988 the FIP Commission on Prefabrication published Recommendations for the design of prestressed hollow core floors. They have been used as a basis for national and international standards, for example the Eurocode 2 and the European CEN Product Standard EN 1168. An updated version of the FIB Recommendations 1988 will be published this year.

Wilhelm Siegler (Germany, 1906) can probably claim the first application of longitudinal void formers in concrete slabs [3]. His system to realize cores was based on prefabricated short moulding tubes in hardened mortar or another material, which were positioned on a scaffolding (Fig. 2). The length of the slabs was arbitrary. The tubes had lateral lugs at the bottom, serving as mould for the webs. They were placed either continuously in the longitudinal direction, or with short inter-distances at certain places to form transversal ribs. The longitudinal and transversal webs were reinforced in the classical way.

The question could be raised about the distinction between hollow core elements and box elements. The above variants still correspond to the definition of hollow core slabs given afore, but from a certain thickness on, they are to be classified as box slabs or beams. By the way, the inventors of the solutions of Table 1 are in the first place claiming for floor slabs, although they do not exclude in the patent description the applicability for box beams or even walls.

Today, this production technique is rather rare but is still used. After pouring a bottom layer, prismatic void formers, usually in polystyrene, are installed. Afterwards, a second layer of concrete is poured to shape the webs and the top layer.

In 1930, a patent is granted to the Belgian inventor Jules Heyneman for a precast floor slab with longitudinal voids [10]. These voids are formed by means of elastic moulds made of e.g. steel and held in place by wedges. When these wedges are removed, the cross-section of this mould is reduced, and the mould can be removed from the hollows in the beam without difficulty. Unfortunately, the drawings of the patent contain no details about these void formers. The number of voids in the cross-section could be modified. The floor units were in reinforced concrete. The patent describes mainly the product itself, without any detail about the manufacturing. The longitudinal joints between the units are indented and provided with transversal reinforcing stirrups. They were filled on site with mortar.

The inconvenience of the solution was of course the weakness of the flexible steel pipes. In 1939 a solution with pneumatic expansible and collapsible rubber core forms was patented by Walter H. Cobi (US) [11]. Fig. 4 shows a longitudinal

and transversal section of the system.

Charles Lethbridge (GB) [12] presented in 1940 an improved method with removable steel tubes of uniform cross-section extending longitudinally through the whole mould and conforming in shape to the cross-sectional form of the hollow core unit. After positioning of the desired reinforcement bars, the concrete was cast, and the mould vibrated as a whole. At the same time the core tubes were slightly moved relatively to the mould. When the concrete was sufficiently compacted to maintain its shape, the tubes were withdrawn via the end of the mould and the concrete was left to harden. By the employment of metal core members with a smooth surface and maintaining them in motion, the concrete was prevented from adhering to the tubes and the latter could be removed without difficulty. Preferably and for simplicity the core tubes were of circular cross-section which allowed for a rotary motion during casting.

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