Hollow Concrete Beam Floor

• Hollow reinforced concrete beams are precast in rectangular secton
• Concrete walls of these beams are from 15 to 20mm thick with the steel reinforcement cast in the lower angles of the beam .
• the sides of the beams are indented to provide a key for the concrete topping .
• The beams are usually 355mm wide, from 130 to 205mm deep and up to 6m long
• The depth of the beam depends on the superimposed loads and the span
• Because of their length and weight , lifting gear is necessary to raise and lower the beams into place
• The beams are placed side by side with the edge joints being grounted together and their ends bearing 1/2 B on or into brick load bearing walls
• IF the ends of the beams are built into walls , the ends should be solidly filled with concrete because the hollow beam is not strong enough to bear the weight of heavy brickwork
• THe wall of the beams are made thin so that they are light in weight for transporting and hoisting into position
• When beams have been placed , brickwork is raised to act as formwork for concrete
• !b walls
• ENds of beams built in must be filled with concrete
• Constructional concrete topping 50mm thick on top of beams
• Pre-cast hollow reinforced concrete floor beams
• The thin walls of the beams are not strong enough to carry the direct weight of furniture , a layer of constructional concrete topping usually 50mm thick , is spread over the beams to distrubute point loads
• THe constructional concrete topping is an integral part of this floor systemn
• THe concrete is miced on the buildin site and is spread and levelled on top of the beams
• THe hollow beams give a flat soffit ,which can be left in its natural state or be given a skim coat of plaster
• The voids in the units can be used to house the services

Advantage and disadvantages

• The units are self-centering , therefore temporary support is not required
• THe conctruction period is considerably shorter
• Generally the overall weight of floor is less
• THey are not considered suitable where heavy points loads are encountered unless a constructional concrete topping is used to spread the load over a suitable area

ALternative sign