Hollow Concrete Slab Pdf

[Marylouise Colleen]

Ahollow 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]

Due to pre-stressing, the hollow core slab can span up to 23 m, easily in the range of 5.0 to 10.0 m for typical residential buildings. The number of vertical structural components, like column-beam or structural walls, can be reduced substantially using the pre-stressed hollow-core slabs.

Why use hollow core slabs? These pre-stressed floor slabs with either round or shaped voids are one of the most popular, efficient and long span floor construction components that exist today. Due to long spans, less load-bearing structures such as columns and inner walls are needed. This results in increased architectural and structural freedom and less raw materials used in a building. Continue reading to discover how to benefit from using precast hollow-core slabs.

One fascinating perspective to hollow core slabs is not often discussed. The slabs are made of two materials, the properties of which are taken almost to the extreme. Firstly, concrete: general wet cast concrete strength is C20 / 25, while hollow-core concrete strength is C40 / 50-C50 / 60. That is, more than twice as strong. Of course, special concrete with strength of 100-200 MPa, has been produced for specific purposes but now we are talking about basic construction.

However, hollow core slabs are not always used as horizontal structures. They can also be installed vertically as outer walls, dividing walls and noise barriers. This is enabled by the long spans and durable structure. Hence, they are especially beneficial for industrial buildings, where a high unified space is needed. On the other hand, the slabs are highly resistant to changing weather conditions and have efficient noise reduction, which makes them ideal noise barriers.

Not only do hollow core slabs enable construction of versatile buildings, they increase the usable floor area. How? The span of a hollow-core slab can be even up to 20 m without intermediate supports, which results in spacious rooms with less partition walls.

Think about it: if long-span hollow-core slabs are utilized for the floor of residential buildings, non-load-bearing partition walls can be placed inside of the flats. This gives freedom to the architects, because the floor layout can be easily modified. To enable this, the structure of the building should be designed so that the slabs are longer than the rooms or even apartments. Likewise, in commercial and public buildings, long-span hollow-core slabs enable less inner supporting structures, e.g. pillars, which can be rather annoying, for example, in parking halls. Thus, architects and structural designers have more freedom in designing well-functioning and visibly appealing spaces.

Moreover, the decreased need for load-bearing partition walls and columns results in lighter structures. Therefore, the weight of the whole building is reduced, which results in smaller and more affordable foundations. This is especially beneficial when designing and constructing buildings in seismic areas, because earthquake forces are proportional to the weight of the structure.

If you have a level in your model, but there is no view for it, go to "View" tab, then under "Plan Views" select type of the plan you need and after that select level for which to create selected plan(s).

Also, when drawing level, there is an option "Plan View Types..." in the options toolbar (usually under the ribbon) where you can select which plans Revit will create automatically when you draw your level.

It seems that this slab is missing "edit profile" capability: Now that I put one of these hollow core slabs on the second floor, I notice that it only could be lengthened but that this one instance put there cannot be conveniently modified with "edit profile", like some of the other generic floor types, to get an uneven floor shape. So that means that I will have to copy each one individually or array one to fill the entire floor, it seems. I also notice that I can change the widhts and revise the names of each new size accordingly with the "Edit Type" of Properties, which will make the creation of a complex floor laborius, but apparently I will have to do it that way.

The Hollow Core slab has a variety of uses, including floors and roofs for buildings and parking garages, decks for piers, and lagging for retaining walls. Cast-in-place, composite concrete topping is highly recommended to provide a smooth, level floor surface that serves as a horizontal diaphragm when properly reinforced.

All joking aside... You tell us that there will be "6 inch metal studs" attached to the underside of the pre-cast concrete floor system. Are you sure these are studs (vertical framing members)? Or perhaps you mean ceiling joists?

Ideally, the underside of the concrete will be insulated before any steel framing members (whether studs or joists) are installed. Once you attach steel to the concrete, you've got a thermal bridge that defeats the purpose of the insulation.

Martin, sorry for the confusion. The insulation would be in the 6" cavity under the precast slab, which is formed from securing studs to the underside of the planks. The precast planks are the full structure and the 'stud cavity' is for the insulation only. They are not structural. I could use treated 2x6's in lieu of the metal for a slightly better thermal break.

I suppose I could use a 2x4 on the underside, fill it with foam, and run a 1" or 2" layer of foam board on the underside of the 2x4 to thermally break the structural and then seal it with the gypsum board.

My concern is using open cell foam in this situation. I am thinking that vapor will makes it way to the underside of the precast plank and form condensation. So, thinking this though, maybe the best way is what I just said in the paragraph above. This is a building condition I haven't run into before and haven't seen addressed before.

The loss of headroom is the same. You will get continuous r-value at about 50% less than spray foam. The ceiling could be strapped and rocked or painted as is. You will probably need to bump up top pour to 4" , which will cost you 2" of headroom.

Nathan,

If you are talking about horizontal framing members that support the ceiling, I still think you're talking about ceiling joists, not studs. But that's a side issue. Ideally, the insulation needs to go between the concrete slab and the framing members -- especially if they are made of steel. If you switch to wood 2x6s, the thermal bridging problem still exists, but it won't be as egregious.

Precast concrete hollow-core slabs are often constructed with a cast-in-place concrete topping on site. Common construction practice includes applying cementitious grout between hollow-core units as a bonding agent. The cast-in-place concrete topping may contribute to the strength and stiffness of the hollow-core slabs if composite action is developed. The strength of the interface between the hollow-core units and the cast-in-place concrete topping largely depends on the surface condition of the slabs because it is not feasible to provide transverse reinforcement in these elements. The research presented in this paper primarily includes testing of two types of hollow-core units (dry mix and wet mix) to determine the interfacial shear strength between the units and the cast-in-place concrete toppings. Tests were conducted using push-off specimens designed to generate shear stresses at the interface. A parametric study is also conducted to identify the governing failure mode of topped hollow-core slabs as a function of span length.

12. ASTM Subcommittee C01.27. 2011. Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50 mm] Cube Specimens). ASTM C109. West Conshohocken, PA: ASTM International.

The concrete hollow core slabs have between four and six longitudinal cores running through them, the primary purpose of the cores being to decrease the weight, and material within the floor, yet maintain maximal strength. To further increase the strength, the slabs are reinforced with 12mm diameter steel strand, running longitudinally.

Currently we offer a range of five concrete slab depths; 200, 220, 300, 320 and 400 millimetre slabs. Depending on the project requirements, in particular span and loading performance, a particular slab depth is chosen.

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