Hollow board
The hollow board , also hollow concrete board or concrete board , is a single-axis reinforced precast concrete part with standardized dimensions that is manufactured in precast concrete plants. Today it is considered technologically obsolete. Hollow -floor ceilings were largely replaced by pre-stressed concrete ceilings and semi- prefabricated ceiling elements .
construction
Hollow core slabs are semi-finished components made of concrete quality controlled, on the construction site to the formwork of massive ceiling of reinforced concrete can be used. If you look at the cross-section of the rectangular concrete elements, round hollow chambers are arranged at regular intervals between the reinforcing bars, which extend through the entire length of the concrete element. This saves material and reduces its own weight. The longer the hollow plank (span), the stronger the elements are designed to increase their inherent stability.
Development and use
Hollow planks were developed to simplify the previously common, mostly wooden ceiling formwork for solid ceilings made of in-situ concrete . The time required to create the slab formwork was reduced and less concrete was required for the grouting. Concrete boards were mainly used in industrial and multi-storey buildings in basement, false and roof ceilings with regular axial dimensions . Due to the relatively low weight of the individual elements, they could also be assembled without heavy lifting equipment (cranes). With the development of frame formwork systems , individually prefabricated element ceilings or prestressed concrete prefabricated ceilings , hollow planks have lost a lot of their importance. A hollow-plank ceiling can only be economical on construction sites without the use of a crane, for example in private construction. The concrete planks, which are available in different lengths, are placed on or in steel girders ( beams ) that are positioned on the wall crowns according to a ceiling plan. The concrete elements are usually laid manually or with simple hoists and brought into the installation position. The resulting walk-on formwork is equipped with additional reinforcement according to the reinforcement plan, can be provided with pre-installations for plumbing, electrics or ventilation and is then poured with concrete to form a monolithic ceiling. In the case of smaller spans, the steel reinforcement in the hollow planks means that there is no need for additional support when grouting with the top concrete.
Prefabrication
The production takes place in a precast concrete plant in series production and monitored quality. The concrete boards, usually made in lengths of up to 160 cm (maximum 300 cm), are poured into corresponding molds, into which structural steel bars are inserted beforehand as reinforcement and molded bodies for the cavities. Depending on the span, the hollow planks have a thickness between 6 cm and 10 cm and weights up to about 100 kg (maximum about 180 kg) to enable processing without cranes. The width is uniformly 33 cm. After setting and partial hardening , the hollow planks are removed from the formwork and the moldings are removed, creating the characteristic round hollow chambers. After about 28 days, concrete has reached its final strength.
advantages
- More economical construction due to faster and support-free assembly compared to classic in-situ concrete formwork.
- Problem-free transport of the individual elements
- Can be used without heavy lifting equipment even in hard-to-reach places
- After grouting, monolithic ceiling without joints on the top
disadvantage
- The hollow planks and thus also the finished ceilings have a rough underside in contrast to element ceilings and pre-stressed concrete ceilings, the receiving iron girders remain visible. If this is undesirable, it must be cleaned or clad.
- The manual use during assembly is significantly higher than with the larger prefabricated elements, the assembly times are longer.
- Individual ceiling dimensions or recesses outside the board grid have to be laboriously created on the construction site by machining the hollow boards.
Web links
- Hoba building materials: Reinforced concrete hollow boards , hollow board range, accessed September 20, 2012
Individual evidence
- ↑ Boba: Stahlbeton-Hohldielen , accessed September 20, 2012