SONTUM, Fredrik (Aspehaugveien 15, Oslo, N-0376, NO)
CLAIMS
1. A building unit made from a light concrete material containing at least 50 % by volume expanded plastic material, said building unit (1,6) having substantially the form of a plate, c h a r a c t e r i s e d i n t h a t the building unit (1,6) is provided with lifting devices (3,8) which each are anchored to reinforcement (2,7) in the building unit (1,6) in at least six points.
2. A building unit according to claim 1, wherein the lifting devices (3,8) are bent at least partially around the reinforcement (2,7) to which they are anchored.
3. A building unit according to claim 1 or 2, wherein the lifting devices (3,8) are welded to the reinforcement (2,7).
4. A building unit according to one of the preceding claims, wherein the reinforcement (2,7) is constituted substantially of one or more reinforcing nets.
5. A building unit according to one of claims 2-4, wherein the building unit is a wall unit (1) having two lifting devices (3) arranged at an edge of the wall unit (1), each of the lifting devices (3) having the form of a steel rod bent at an angle and having bent free ends (4), said ends (4) being anchored in the reinforcement (2) at a depth which is preferably at least equal to twice the thickness of the wall unit (1).
6. A building unit according to one of claims 2-4, wherein the building unit is a roof element (6) having the reinforcement (7) arranged substantially as tensile reinforcement.
7. A building unit according to claim 6, wherein the roof unit (6) has a rectangular form and has the tensile reinforcement (7) bent upwards at least at the short sides of the unit (6).
8. A building unit according to claim 6 or 7, wherein each of the lifting devices (8) comprises a steel rod bent substantially like a U, the legs of the U having a portion (9) bent at an angle and arranged underneath the reinforcement (7) and preferably being attached thereto by welding.
9. A building unit according to claim 5 or 8, wherein the steel rod has a thickness in the order to magnitude 10 mm and forms a lifting eye (5,11) which is recessed into the surface of the building unit (1,6). |
A Building Unit
The present invention relates to a building unit made from super light concrete containing expanded plastic material in a proportion of at least 50 % by volume. Such a concrete has also been called polyconcrete since the plastic material often consists of expanded polystyrene.
As shown in EP 1747327, such building units have been used to build entire houses of polyconcrete wherein prefabricated wall units are raised on a foundation, which also preferably consists of cast polyconcrete, and are attached to each other, whereupon the house is provided with a roof of similar building units.
Due to the very low specific weight of the polyconcrete, the wall units may be made so large that they alone can constitute an entire wall surface. The wall units are lifted in place by means of straps which are slung under the lower edge of the wall unit and are attached to U-shaped lifting shoes clasping the lower edge of the unit. No reinforcement of the wall unit is necessary, thus permitting openings for windows and doors to be simply cut out of the wall after mounting on the foundation. For this purpose, the applicant has developed a special frame for guiding a common chainsaw for accurate cutting of the openings. The frame is the subject of Norwegian patent application 20062925.
The situation is different for roof units of polyconcrete. These must be provided with reinforcement in order to endure snow loads and satisfy regulations regarding maximum permitted deflection. In ordinary concrete, tensile reinforcement alone will serve the purpose, but since the polyconcrete has a low compressive strength, usually in the order of magnitude 100 N/cm 2 , one assumed that it would also be necessary to provide compression reinforcement in order to give the tensile reinforcement sufficient reaction. However, very surprisingly it was found that the use of tensile reinforcement in addition to the compression reinforcement led to a higher deflection than with the tensile reinforcement alone. The roof units are therefore made with tensile reinforcement only and with sufficient thickness to provide the necessary compression resistance.
The applicant has found that it would be advantageous to be able to lift the building units without the use of lifting straps. This is so both when the unit is removed from the form and in later handling on the building site. As regards building units of ordinary concrete, it is known to provide wall units with lifting devices in the form of e.g. ears, wire loops or attachment nuts for de-mountable eye hooks. Thus, from EP 0392610 A2
there is known a wall unit of ordinary concrete having insulation plates cast therein, where the concrete is reinforced and at its upper edge is provided with two nuts formed from channel iron for later attachment of eye bolts, where the channel iron nuts are anchored in the concrete by means of short loops of reinforcement rods or the like.
Such a lifting structure would have an insufficient attachment in a wall unit of polyconcrete due to the low strength of the latter. Nor have other previously known attachment devices for wall units of concrete been able to provide sufficient pull-out strength to serve the purpose in a unit of polyconcrete.
In order to solve this problem, the applicant has taken the step of including an otherwise unnecessary reinforcement net in the wall unit and anchoring the lifting devices in the reinforcement net in such a way that the necessary pull-out strength is obtained. For roof units, the applicant has utilised the same idea and attached the lifting devices to the reinforcement for in this way to provide the roof unit with corresponding lifting devices.
The invention is defined in claim 1, and advantageous embodiments are defined in the dependent claims.
For a better understanding of the invention, it will be described below with reference to the exemplifying embodiments shown schematically in the appended drawings, where
Figure 1 shows schematically a perspective view of a wall unit according to the invention, and
Figure 2 shows in a similar manner a roof unit according to the invention.
In both the exemplifying embodiments the polyconcrete is shown partly transparent in order to show the location of the reinforcement net and the lifting devices.
The wall unit 1 in Figure 1 may have a thickness of e.g. 25 cm and has a reinforcement net 2 placed in the middle of the unit. The net may have the designation Kl 31 with a rod diameter of 5 mm and a centre distance of 150 mm.
The wall unit has two lifting devices 3, here consisting of a steel rod bent into a rounded V-shape, where the free ends are bent into a hook 4, which from the lower side of the reinforcement net is hooked up around a longitudinal rod of the reinforcement net. The lifting device, which e.g. may consist of a 10 mm serrated reinforcement rod, is welded
to the reinforcement net 2 before casting the wall unit, not only for holding it in place during the casting, but also in order to transmit the lifting forces to as large a part as possible of the reinforcement net 2.
The bend 5 of the lifting device 3 will lie flush with the top side of the finished wall unit. In order for a suitable part of the bend 5 to be exposed for attachment of lifting hooks or the like, a suitable screening is placed around the bend 5 before the casting in order to keep the casting mass away. Such a screening may be a plastic cup having a slot in the bottom which is pushed a suitable distance down over the bend 5.
It is important that the lifting devices 3 are located at the lower side of the reinforcement net 2 during the casting. This prevents them from being pulled out of the concrete if they are used in de-forming the unit before the form has been brought into a vertical position.
The example in Figure 1 shows a centred reinforcement net 2, but it will be understood that if the conditions of use make it desirable, it can be replaced by two reinforcement nets located closer to either side of the wall element. In this case the hooks 4 of the lifting devices are to be attached to one net each, and they have to be bent so that the free ends of the hooks point inwards in the wall unit 1. The two nets may be of the same type and dimension as the single, centric net mentioned above.
It will be seen that the hooks 4 of the lifting devices 3 are hooked around the longitudinal rod which is number five counted from the top side of the element.
Generally, the invention aims at locating the hooks at a depth from the top side which is at least twice the thickness of the wall unit, thus ensuring a safe anchoring of the lifting devices 3.
The roof unit 6 shown in Figure 2 has tensile reinforcement in the form of a net 7, which in most cases will be substantially stronger than the net used in the wall unit 1. The reinforcement net 7 is bent upwards along the short sides of the unit in order to improve the anchoring of the longitudinal rods, which carry the highest load, and increase the sheer strength in the supported areas of the unit. The thickness of the roof unit 6 may vary depending upon its length. For instance, a unit 6 metres long may have a thickness of 40 cm.
The roof unit 6 has four lifting devices 8 arranged symmetrically about both the longitudinal and transverse central axes. The lifting devices 8 have the form of an
elongated U, where the relatively longer part 9 of the legs of the U is bent through a suitably curved transition into a right angle, the relatively shorter part 10 of the U containing its base portion 11. The relatively longer part 9 of the legs of the lifting device 8 is placed underneath the longitudinal part of the tensile reinforcement 7 and crosses three of its rods.
Also in this case it will be advantageous to weld the lifting devices 8 to the reinforcement 7. Furthermore, it will be of advantage that the transverse reinforcement rods 12 lie above the longitudinal reinforcement rods 13.
It will be understood that when casting the roof unit 6, care is taken that the top portion 11 of the lifting devices 8 remains exposed even if its top edge lies at the same level as the top surface of the roof unit 6. Furthermore, it will be understood that the relatively longer part 9 of the legs of the U do not have to be parallel, but may diverge in a manner similar to that of the lifting devices 3 of the wall unit.
Even though the invention has been described above in relation to two specific exemplifying embodiments, it will be clear to the skilled person that the invention may be varied and modified within the scope of the appended claims.