GB1584744A - Reinforcement of concrete for security structures - Google Patents

Description

(54) IMPROVEMENTS RELATING TO THE REINFORCEMENT OF CONCRETE FOR SECURITY STRUCTURES (71) We, CEIUBB & SON'S Loa AND SAFE COMPANY LIMITED, a British Company, of 14 Tottenham Street, London W1P OAA, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to concrete for use in the construction of strongrooms, safes and other security enclosures and is particularly concerned with the nature of the reinforcement used in such concrete. The requirements for concrete for this purpose are set out in considerable detail in our earlier specification number 1,450,091 and can be summarised somewhat more briefly.

The requirement which is specific to this particular use is the ability to survive under condition of sudden shock, e.g. under attack by explosive or by means of cutting tools, particularly of the percussive type.

The main properties necessary to meet this requirement are the general quality of the concrete and its tensile strength, both of which can be developed on the basis of normal reinforced concrete design, and also the impact resistance which calls for specialised consideration.

The effect of sudden shock on steelreinforced concrete can be regarded as the equivalent of the transmission of a short train of longitudinal shockwaves, the speeds of transmission and rates of absorption of which differ markedly between steel and concrete. Consequently, if a wave train travelling through the cement matrix of the concrete meets a steel inclusion, some of the energy will be reflected, some will accelerate to the higher speed through the steel and the remaining component will travel alongside the steel inclusion through the body of the cement matrix. The difference of wavelengths in the steel and in the cement will means that the two components of the original wave train travelling alongside one another will rapidly become out of phase so that high stress across the interface will result.

In the past it was regarded as advisable to restrict the straight and continuous runs of steel reinforcing elements to lengths of the order of 4 centimentres to 6 centimetres for this reason, but this had the inevitable result of reducing the effectiveness of the tensile reinforcement provided by the steel. As described in our earlier specification referred to above, the resistance to attack by explosive of cutting tools is increased by the provision of fibrous reinforcement in the cement mix so that the tensile strength and impact resistance properties of the concrete are more nearly matched to those of the steel reinforcement, thus making it possible to use longer runs of steel reinforcing elements.

Despite this increased resistance to the effects of high stress at the interface between the steel reinforcement and the clement, the high stress itself still remains.

The present invention is based on the realisation that if the distance travelled by the component of the wave train in the steel reinforcement is increased in relation to that of the component in the cement, it is possible to compensate for the greater velocity of the wave train in the steel so that the phase difference at points spaced from the entry of the wave train into the steel reinforcement can be substantially eliminated.Thus, according to the present invention the walls of a strongroom or similar security enclosure are formed of reinforced concrete in which at least part of the tensile reinforcement is in the form of steel helices of which the ratio of pitch to diameter is approximately three, thus ensuring that the components of a shock wave which travel respectively along the helix and through the cement matrix are not substantially out of phase at points spaced from the entry into the helix.

Although the difference of phase may not be eliminated completely, it is reduced sufficiently to allow considerably greater lengths of steel reinforcement to be used and, in practice, helices extending for the full height of the wall of a strongroom may be used for reinforcement purposes without the risk of introducing excessive stress under conditions of shock. Still better results are obtained if fibrous reinforcement is included in the concrete. The use of polypropylene fibres is described in our earlier specification referred to above. In particular, a proportion of polypropylene fibres of about two percent by weight of cement used in the concrete mix is found to give excellent results. Glass fibres and more particularly steel fibres may also be used, the latter being particularly preferred.The use of helical reinforcement not only gives the required additional path length in the steel, but has the further advantage of acting as a local three-dimensional containing reinforcement, avoiding a plane of easy separation and giving sufficient metal to interfere with percussion and diamond drilling.

As mentioned above, the ratio of pitch to diameter needs to be approximately three in order to deal with the problem of phase difference, the best results being obtained if the precise value of the ratio is determined in accordance with the respective properties of the steel and concrete used; in other words if the ratio of path length along the helix to the axial length is made substantially equal to the ratio of the speed of the shock wave through the steel to that through the concrete. The diameter of the helix is by no means critical, but may, for example, be in the range of 50 to 150 mm with the spacing between centre lines of coils in a grid about twice the coil diameter. The diameter of the rod from which the coils are formed may, for example, be in the range 5 to 20 mm.

A helix having a ratio of pitch to diameter of the order of three is a very coarse helix and is entirely different in its effect from the very fine helices which are commonly used in concrete reinforcement for entirely different purposes and of which the equivalent ratio is never greater than one and usually considerably less. With a fine helix of this kind, the path length along the helix is at least several times as great as the corresponding axial length and the use of such a helix has no benefit at all in reducing the effect described previously arising from differences of phase between the two components of the shock wave.

Generally speaking, the helical reinforcement needs to be supplemented by straight steel reinforcing bars in order to provide structural strength. These bars will, of course, be subject to the problems already discussed, but owing to the presence of the helical reinforcement, any disadvantage arising from this can be left out of account.

In order to obtain best results, the individual steel helices need to be arranged in a grid in which the lateral spacing between adjacent helices may be only slightly greater than the helix diameter. The precise arrangement of the grid or grids will depend on the thickness of the wall and the degree of security required. In a typical strongroom wall, a single grid of steel helices may be arranged approximately along the centre line of the wall with a grid of substantially straight reinforcing bars on either or both sides of the grid or helices. For a thicker wall a double grid of helices spaced symmetrically in relation to the centre line may be used and in particularly thick walls, a number of grids of helices lying in parallel planes may be inter-connected by further helices to form a three-dimensional array of helices.

Examples of construction in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a sectional view of a wall reinforced with a central grid of helices and a grid of straight reinforcing bars on either side; Figure 2 is a cross sectional view of a somewhat thicker wall having two spaced grids of helices; Figure 3 is a cross section of a wall similar to that shown in Figure 2, but with the components of the two grids not intermeshed; and Figure 4 is a cross section of an even thicker wall including three grids of helices interconnected by further helices to form a three-dimensional array.

The wall shown in Figure 1 is a comparatively thin one, e.g. of the order of 300 mm thick and includes a single grid of steel reinforcing helices. The wall itself is indicated at 1, but for clarity no separate indication of the concrete itself is included or of the fibrous reinforcement referred to previously although the concrete used in this wall and in those shown in subsequent Figures preferably includes such fibrous reinforcement. The open work nature of the helical reinforcement facilitates the placing of fibrous concrete in a densely consolidated mass.

The central grid shown in Figure 1 comprises a succession of vertically extending helices, one of which is seen at 2 and a succession of horizontally extending helices 3. The helices 2 conveniently extend for the whole height of the wall and the helices 3 may extend for the whole length of the wall or a proportion of it. Each helix has a pitch-to-diameter ratio of almost exactly three and, as can be seen, the spacing between adjacent helices 3 is slightly greater than the helical diameter. In a typical example, the diameter of the helix itself may be about 70 to 80 mm while the diameter of the steel rod forming the helix may be approximately 15 mm. Similar dimensions apply to all the illustrated examples.

Between the central grid of helices and each outer surface of the wall is a further grid consisting of straight steel reinforcing bars, the vertical bars being shown as 4 and the horizontal bar as 5. These bars are conveniently of the same diameter as the bars making up the helices.

The wall shown in Figure 2 is indicated generally as 8 and is approximately fifty percent thicker than that shown in Figure 1, e.g. 450 mm. In this construction, the grids of straight reinforcing bars are omitted, but there are two grids of helices, similar to the grid illustrated in Figure 1. The left hand grid is made up of a succession of vertically extending helices 9 and horizontally extending helices 10, while the right hand grid is made up of vertically extending helices 11 and horizontally extending helices 12. The characteristics of the helices themselves and of the bars forming the helices may be the same as described in relation to Figure 1.

The wall illustrated in Figure 3 and indicated generally as 14 is of a similar thickness to that shown in Figure 2 and again has two grids of helices. The difference is that the cross members of each grid, indicated by the same numerals as in Figure 2, instead of lying in substantially the same plane, are displaced laterally. Thus the horizontally extending helices 10 lie slightly to the right of the vertically extending helices 9 and the helices 12 lie slightly to the right of the helices 11.

The wall shown in Figure 4 as 16 is again thicker than those shown previously, e.g. 600 mm or more. In this construction, there are three spaced grids of helices, the components of each grid lying in the same general plane. These grids are made up of vertical helices 17 and horizontal helices 18, vertical helices 19 and horizontal helices 20 and vertical helices 21 and horizontal helices 22, respectively. In addition, these three grids are inter-connected by further horizontal helices 24 to form an interlocking, three-dimensional array.

The drawings illustrate four typical arrangements of reinforcement, but a variety of other arrangements are possible, including combinations of those so far described. In particular, the arrangements of Figures 2, 3 and 4 may include one or more grids of straight bars, e.g. as illustrated in Figure 1.

WHAT WE CLAIM IS: 1. A strongroom or similar security enclosure having walls of reinforced concrete in which at least part of the tensile reinforcement is in the form of steel helices of which the ratio of pitch to diameter is approximately three.

2. An enclosure according to claim 1 in which the concrete also includes fibrous reinforcement.

3. An enclosure according to claim 1 or claim 2 in which the steel helices extend for the full height of the respective wall.

4. An enclosure according to any one of the preceding claims in which the steel helices are supplemented by straight steel reinforcing bars.

5. An enclosure according to any one of the preceding claims in which the steel helices are arranged in a grid.

6. An enclosure according to claim 5 in which the lateral spacing between adjacent helices is slightly greater than the helix diameter.

7. An enclosure according to claim 5 or claim 6 in which a number of grids of helices lying in parallel planes are interconnected by further helices to form a threedimensional array of helices.

8. An enclosure according to any one of claims 5 to 7, and also including at least one additional grid of straight reinforcing bars.

9. An enclosure according to claim 1 having one or more walls reinforced substantially as described and as illustrated with reference to any one of the Figures of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. Between the central grid of helices and each outer surface of the wall is a further grid consisting of straight steel reinforcing bars, the vertical bars being shown as 4 and the horizontal bar as 5. These bars are conveniently of the same diameter as the bars making up the helices. The wall shown in Figure 2 is indicated generally as 8 and is approximately fifty percent thicker than that shown in Figure 1, e.g. 450 mm. In this construction, the grids of straight reinforcing bars are omitted, but there are two grids of helices, similar to the grid illustrated in Figure 1. The left hand grid is made up of a succession of vertically extending helices 9 and horizontally extending helices 10, while the right hand grid is made up of vertically extending helices 11 and horizontally extending helices 12. The characteristics of the helices themselves and of the bars forming the helices may be the same as described in relation to Figure 1. The wall illustrated in Figure 3 and indicated generally as 14 is of a similar thickness to that shown in Figure 2 and again has two grids of helices. The difference is that the cross members of each grid, indicated by the same numerals as in Figure 2, instead of lying in substantially the same plane, are displaced laterally. Thus the horizontally extending helices 10 lie slightly to the right of the vertically extending helices 9 and the helices 12 lie slightly to the right of the helices 11. The wall shown in Figure 4 as 16 is again thicker than those shown previously, e.g. 600 mm or more. In this construction, there are three spaced grids of helices, the components of each grid lying in the same general plane. These grids are made up of vertical helices 17 and horizontal helices 18, vertical helices 19 and horizontal helices 20 and vertical helices 21 and horizontal helices 22, respectively. In addition, these three grids are inter-connected by further horizontal helices 24 to form an interlocking, three-dimensional array. The drawings illustrate four typical arrangements of reinforcement, but a variety of other arrangements are possible, including combinations of those so far described. In particular, the arrangements of Figures 2, 3 and 4 may include one or more grids of straight bars, e.g. as illustrated in Figure 1. WHAT WE CLAIM IS:

1. A strongroom or similar security enclosure having walls of reinforced concrete in which at least part of the tensile reinforcement is in the form of steel helices of which the ratio of pitch to diameter is approximately three.

2. An enclosure according to claim 1 in which the concrete also includes fibrous reinforcement.

3. An enclosure according to claim 1 or claim 2 in which the steel helices extend for the full height of the respective wall.

4. An enclosure according to any one of the preceding claims in which the steel helices are supplemented by straight steel reinforcing bars.

5. An enclosure according to any one of the preceding claims in which the steel helices are arranged in a grid.

6. An enclosure according to claim 5 in which the lateral spacing between adjacent helices is slightly greater than the helix diameter.

7. An enclosure according to claim 5 or claim 6 in which a number of grids of helices lying in parallel planes are interconnected by further helices to form a threedimensional array of helices.

8. An enclosure according to any one of claims 5 to 7, and also including at least one additional grid of straight reinforcing bars.

9. An enclosure according to claim 1 having one or more walls reinforced substantially as described and as illustrated with reference to any one of the Figures of the accompanying drawings.