FIELD OF THE INVENTION

The present invention relates to protective walls against blasts of bombs or missiles. In particular this invention is concerned with light-weight protective walls that can be added onto existing structures.

BACKGROUND OF THE INVENTION Bomb shelters are of course well-known to everyone. These generally comprise steel reinforced concrete structures, usually built underground, having thick walls. The recent Gulf War, with the accompanying missile attacks on urban centres and the constant fear of an imminent chemical attack, sewed utter confusion among the civilian population. This was due primarily because for protection against missile attack it is safest to be underground in a regular bomb shelter, whereas in case of a chemical attack it is best to be high up. Above ground bomb shelters are almost non-existent and are certainly not available in ordinary apartments and offices, particularly on upper floors. Constructing conventional bomb shelters in such places as apartments and offices presents several problems. First of all, the room designated to be a shelter will become significantly smaller, due to the thick concrete reinforced walls that must be erected.

^* | Secondly, such concrete reinforced walls present an acute

* weight burden on the floor of the structure and if a number of such walls are erected in a building, the

overall additional weight may cause unacceptable weakening of the basic structure, resulting in its collapsing.

SUMMARY OF THE INVENTION It is the object of the present invention to provide a bomb blast protective wall consisting of light-weight high enery absorbing hollow building blocks, placed in direct contact on top of and next to one another, said hollow blocks providing vertical and horizontal voids, said voids having disposed therein vertical and horizontal steel reinforced concrete beams, said reinforcements extending beyond said wall into a retaining frame structure.

Preferably the hollow building blocks are "Durisol" blocks composed of a mixture of mineralised wood shaving and concrete. These blocks are light— eight, in the order of about 0.9 tons per cubic meter, as opposed to 2.4 tons per cubic meter for concrete. They also have desirable characteristics with respect to fire resistance and sound absorption, as well as thermal insulation. Walls constructed with Durisol and having reinforced concrete beams are known as such in conventional construction. However, the use of this type of construction for providing blast-proof protective walls is unknown. Furthermore, it was surprisingly found that walls can be constructed with Durisol blocks in accordance with this invention as internal double walls in existing buildings, thus making it possible to provide blast shelters in every

apartment on every floor by merely constructing such a wall up against any outside wall in any room.

A further advantage of walls made from Durisol or similar blocks is the fact that they provide a decorative surface finish suitable for residential interiors, contrary to walls of poured reinforced concrete or cinder blocks.

BRIEF DESCRIPTION OF THE DRAWINGS Yet another aesthetic benefit from the use of the Durisol blocks is the fact that they are placed directly on top of and adjacent to one another without requiring any binder layer, such as grout or cement.

The invention will be better understood with reference to the drawings, in which -

Figure 1 is a frontal view of a protective wall constructed in accordance with this invention;

Figures 2a, 2b and 2c are respectively a perspective, top and side view of a Durisol block as known, which is used for constructing a wall according to this invention;

Figure 3 is a cross-sectional view of the front of the wall of Figure 1 ; and

Figure 4 is a cross-sectional view as seen from the top of the wall of Figure 12.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to Figure 1 , there is shown a wall 1 constructed with Durisol building blocks 2 which have a decorative finish. This wall is constructed within a

frame 3 of reinforced concrete all around the wall. The surface finish on the blocks 2 is naturally decorative enough to be suitable for the interior of an apartment, without requiring further finishing. The wall consists of blocks 2 placed on top of one another 4 and next to each other 5 without any spaces left between blocks, thus not requiring any caulking or grouting which would detract from the attractive natural surface of the wall.

For a better understanding of the construction of this wall, we refer to Figures 2a, 2b and 2c, which illustrate the basic building block suitable for the construction of wall 1. The Durisol blocks 2 are composed of a mixture of mineralised wood shaving and concrete, with high energy absorption capablity and light— eight.

They also have very good chacteristics with respect to fire resistance, sound absorption and thermal insulation.

These blocks 2 are similar to conventional blocks in dimensions and comprise front walls 10 and side walls 11 and generally have a centre partition wall 12, leaving two hollow sections 13. The side walls 11 and partition 12 have their upper ends grooved 14 to enable steel reinforcing rods to be placed therein. Side walls 11 further comprise a longitudinal extension 15 across about one half of the width of the wall, this extension serving as a tongue for fitting into a corresponding groove 16 when the blocks are placed alongside one another.

In constructing the wall according to this invention, for example in the case of a free—standing wall, there is first poured a reinforced concrete frame bottom ^' 20, as

shown in Figure 3, and the blocks 2 are placed thereon in a row adjacent one another. A steel reinforcing rod 21 is then placed horizontally within the trough formed by the adjacent grooves 14 of the blocks 2 extending 22 beyond the terminal blocks 2a and 2b. A second layer of blocks 2 is placed staggered on top of the first layer, so that the partitions 12 are aligned above the walls 11 of the blocks with the hollow sections 13 forming vertical cavities.

Further rows of blocks are added up to the desired height of the wall. Steel reinforcing rods 24 are introduced vertically into the cavities 13 and concrete is then poured into these cavities 13 to fill the voids and form a web of vertical and horizontal steel reinforced concrete beams within the blocks. The terminal ends 22 of the steel reinforcing rods are then embedded in concrete which completes the reinforcing frame 3 around the wall 1.

Alternatively, the vertical steel reinforcing rods 24 can be inserted into the cavities 13 of the blocks 2 after the first layer of blocks and horizontal steel rods 21 have have been placed in position and tied to the horizontal steel rods 21 where they cross each other 25. Subsequent layers of blocks are then slipped over the vertical steel reinforcing rods 24 and placed in position with the vertical and horizontal steel bars being tied together wherever they cross each other.

When such a protective wall is constructed in an existing apartment, the core is connected via the reinforcing steel to the reinforced concrete framework of the building

Additional strengthening of the protective wall may be accomplished by providing prestressing (post—tension) at the top and bottom and on either side of the wall.

This prestress strengthens the membrane (wall) formed by the Durisol blocks and also strengthens its connection to the framework.

Experiments were conducted to determine the resistance to blast of various walls constructed of different materials. Five types of walls were tested, including —

a) A wall consisting of conventional building blocks internally reinforced with steel bars;

b) A wall constructed of conventional building blocks to which plates of ferro—cement were glued on their inside surface to provide reinforcement;

c) A wall made of solid blocks of silicate.

d) A wall made of Itong blocks reinforced with beams; and

e) A wall made of Durisol blocks according to the invention.

All these walls were approximately 3.6 m long and 2.75 m high and reinforced with concrete beams all around. An

explosive device was detonated equidistant from all the walls. The results showed that the wall e) in accordance with the present invention had complete blast resistance and was far superior to the other walls a)—d) which underwent varying degrees of destruction.