GB2132660A

GB2132660A - Connecting concrete components

Info

Publication number: GB2132660A
Application number: GB08332481A
Authority: GB
Inventors: Klaus Matz; Gerhard Ritter; Klaus Ritter
Original assignee: AVI Alpenlaendische Veredelungs Industrie GmbH
Current assignee: AVI Alpenlaendische Veredelungs Industrie GmbH
Priority date: 1982-12-13
Filing date: 1983-12-06
Publication date: 1984-07-11
Also published as: FR2537632A1; GB8332481D0; GB2132660B; FR2537632B1; DE8335407U1; CH662387A5

Abstract

A reinforcement unit for bonding two structural reinforced concrete components comprises a mounting strip (1) having a pair of oppositely directed main faces (2, 3) and a plurality of connector rods (4) held firmly on the mounting strip. Portions of the connector rods (4) project at intervals along one side (3) of the mounting strip and the connector rods (4) have arms (5) bent to a knee shape, the arms (5) being positioned within the mounting strip (1). One of the main faces (2) of the strip on the side away from the projecting portions of the connector rods (4) defines at least two grooves (9) parallel with one another and extending in the longitudinal direction of the mounting strip (1). The grooves (9) have a width substantially equal to the diameter of the connector rods (4) and a depth at least equal to the diameter. The mounting strip (1) further includes holes (8) at intervals along its length, the holes extending from the bottoms of respective ones of the grooves (9) towards the opposite main face of the mounting strip. The connector rods (4) are disposed individually through the holes, and the arms (5) of the connector rods are arranged and held firmly within the grooves (9). <IMAGE>

Description

SPECIFICATION Bonding unit for reinforced concrete structural components The invention relates to a unit for bonding together two structural reinforced concrete components, the unit consisting of a mounting strip which holds firmly a number of connector rods and from which portions of the connector rods project at intervals along one side, whilst arms of the connector rods bent to a knee shape are enclosed inside the mounting strip.

Bonding units of this type are known from the AT-A-342396. These known bonding units include a piurality of connector rods bent like a stirrup, which serve for bonding the two adjacent structural components which may be in the form e.g. of slabs, each stirrup being substantially Ushaped, the arms of the U being bent at right angles to the plane of the loop at a predetermined distance from its bridge and embedded in a mounting strip of hardened foam and material.

In use, the strips of hardened foam material are nailed to the shuttering of the first of the two structural components, in such a way that the loops of the connector rods projecting out of the strips of foam material are surrounded by the concrete of the first structural part. After the concrete has set, the strips of foam material are broken away from the concrete of the first structural component and then the arms of the connector rods which were embedded in the strips are bent up in the direction perpendicular to the connecting face of the first structural component so that they form jumper reinforcement for the second of the structural components.The breaking out of the strips of foam material is just as troublesome and timewasting as the production of the connector rods themselves, which have to be bent in space, i.e., in two planes and which presupposes two separate working steps.

Other known bonding units use, as the mounting strip for the connector rods, a profiled strip having a cross-section the shape of a U and of metal, plastics or wood, which exhibits drilled holes through which the arms of stirruplike connector rods bent are pushed in such a way that these arms come to lie convergently with respect to one another and partially overlapping one another in the direction longitudinal to the strip within the cavity in the profiled strip. If necessary the profiled strip may be closed off by a coverplate (cf., e.g., DE-A-2944739). Instead of being formed of a single profiled strip each mounting strip may also be formed of two connected U-shaped profiled strips, one arm of each of the stirruplike connector rods then being received in the respective cavities in the two profiled strips (cf., e.g., CH-A-626676).

U-shaped profiled strips of metal or plastics are expensive to use as mounting strips for the connector rods, especially since the mounting strips form lost components which remain in the concrete of the components. On the other hand employing wood as the material of the mounting strips means that a great quantity of material has to be machined awa in order to create the cavity in the U-profile, and this constitutes a waste of material and leads to a considerable reduction in the moment of resistance of the wooden body, which has a very unfavourable influence upon its breaking strength when it is not yet embedded in concrete, that is during handling and transport.

With bonding units just described the convergent arms of the stirrup-like connector rods, bent to a knee, do indeed make it possible to arrange the stirrups at short pitches because the arms from the knee of adjacent stirrups can partially overlap in the direction longitudinal to the mounting strip like the bones of a fish, but they demand elaborate bending operations and elastic deformation of the stirrups during introduction of the arms into the holes drilled in the strips. Further, with mounting strips which receive the arms of the connector rods in common cavities the positions of the connector rods are not exactly defined unless additional holders are provided for the parts of the rods passing through the drilled holes.Furthermore what is common to all known kinds of bonding units is poor adaptabiiity to different lengths of the faces of the two components.

An object of the invention is to simplify bonding units of the species specified initially as regards their overall construction and in doing so to create the possibility of eliminating the defects of the known bonding units described above.

In accordance with the invention, a unit for bonding two structural components of reinforced concrete and consisting of a mounting strip which holds a number of connector rods and from which portions of the connector rods project at intervals along one side, arms of the connector rods bent to a knee shape being enclosed inside the mounting strip, is characterized in that two or more parallel grooves running substantially longitudinally of the mounting strip are provided, on the main face of the mounting strip, away from from projecting portions of the connector rods, the width of the grooves being substantially equal to the diameter of the connector rods and the depth of the grooves being at least equal to this diameter, holes running from the bottom of the grooves towards the opposite main face of the mounting strip being provided at intervals along the mounting strip through each of which hole passes one of the connector rods, the arms of the connector rods lying in the respective groove.

In this way simple basic shapes result both for the connector rods and also for the mounting strips, so that these parts can also be easily combined, especially since stirrups having convergent arms are not necessary. The moment of resistance of the cross-section of the mounting strip is only slightly diminished by the grooves, but the arms of the rods bent to a knee may easily be held fast in the parallel grooves. Further, after embedding the parts of the connector rods projecting out of the mounting strip in a first reinforced concrete component, the arms of the connector rods previously bent at a knee can be bent unimpeded out of the grooves on the outside of the mounting strip and-if necessary after withdrawal of the mounting strip cmbedded in the second reinforced component.

Embodiments of units according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a first bonding unit; Figure 2a is a longitudinal section through a portion of a bonding unit; Figure 2b is a plan view of the Figure 2a unit; Figure 3a is a longitudinal section through a portion of another bonding unit; Figure 3b is a plan with respect to Figure 3a; Figure 4 is a cross-section with respect to Figure 2a or Figure 3a, showing on a larger scale a groove and the arm of the connector rod embedded in it; Figures 5a and 5b are a longitudinal section and an associated cross-section respectively through another embodiment of the invention; Figure 6 is a plan of the grooved main face of a further embodiment;; Figure 7 is a side elevation of a further refinement of the invention; Figure 8a is a side elevation of the right-hand end of a bonding unit similar to Figure 7, on a larger scale; Figure 8b is an associated plan of the underside of it; Figure 9a is a side elevation of the left-hand end of this bonding unit; Figure 9b is an associated plan of the underside of it; Figure 10 is an axonometric view of a further bonding unit; Figure 11 is a longitudinal section and Figure 12 is a cross-section through the bonding unit shown in Figure 10, bcth on a larger scale; Figure 13 is a view of yet another embodiment of a bonding unit; and Figure 14 is an associated cross-section on a larger scale.

In Figure 1 there may be seen a mounting strip 1 having main faces 2 and 3 lying opposite one another, out of which project the end portions of connector rods 4 bent, for example, into the shape of a hook. By means of parting lines 6, 7 arranged preferably at equal intervals from one another, predetermined points of break are formed in the mounting strip in order to enable the mounting strip to be adapted easily to different lengths of the joint at the bond between two structural components. In order to facilitate separation into sections, the parting lines are preferably incorporated into both the faces 2, 3 of the mounting strip, though the outer parting line 6 in particular should preferably be made as narrow as possible in order, as far as possible, to prevent the penetration of concrete on site.Mounting strips of wood, cane or pressboard may be nicked by means of a saw at the predetermined points of break; in the case of mounting strips of concrete oiled metal strips may be laid in the shuttering at the predetermined points of break.

Figure 2a shows a section through a portion of a first bonding unit which as a variant carries connector rods 4 bent merely at a right angle.

Each connector rod 4 passes through a regularly cylindrical drilled hole 8 which may be seen in Figure 2b, the diameter of which is only sufficiently greater in diameter than the connector rod 4 so that the connector rod can be pushed through the drilled hole without resistance. Reliable guidance of the connector rod 4 in the drilled hole is thereby guaranteed.

One arm of each connector rod 4 bent to a knee rests in the groove 9 open to the lower main face 2 of the mounting strip 1, its depth in this case being a little greater than the diameter of the rod plus the radius of bend of the connector rod at the knee. The arm 5 of the connector rod 4 is held fast in this groove 9 by e.g., clips 10. With this choice of the depth of the groove the knee of the connector rod 4 lies in the groove 9.

A very similar embodiment is shown in Figures 3a and 3b. In this case, however, the depth of the groove 9 is only slightly greater than the rod diameter. The drilled hole 8 is instead made as an oblong hole, the plane of symmetry x-x of which coincides with the longitudinal central plane of the groove 9 running in the direction longitudinal to the mounting strip and moreover lies perpendicular to the parallel main faces 2,3 of the mounting strip 1. The width of the oblong hole 8 is again about equal to the rod diameter, whereas the length of the oblong holes is about equal to the radius of bend of the connector rod at the knee plus the rod diameter. Thus the knee of the connector rod can lie in the drilled hole 8.

As shown in Figure 4, tlie anchoring of the arm 5 of the connector rod 4, resting in the groove 9, onto the mounting strip 1 may also be effected by the groove 9 being made a little narrower than the diameter of the connector rod and the arm 5 of this rod bent to a knee being pressed into the groove 9 and then held fast in it by being a jam fit.

Figures 5a and 5b show a bonding unit having two grooves 9 and 9a parallel with the longitudinal centreline of the mounting strip, in which are arranged connector rods 4 and 4a.

Along each groove a number of drilled holes 8 are provided, arranged at intervals a which connect the bottom of the groove to the ungrooved main face 3 of the mounting strip 1. The drilled holes 8 are in this case made as oblong holes, the length of which is so dimensioned that the straight parts of the ready-bent connector rods may be passed through a drilled hole 8 and subsequently by turning the rod through 900 in the longitudinal central plane of the drilled hole may be brought into a position parallel with the groove 9 and be pressed into it.The connector rods 4 and 4a respectively associated with each individual groove 9 and 9a respectively and the drilled holes 8 and 8a respectively which receive them have a distance apart a, but the drilled holes in the adjacent grooves are offset, with respect to one another by the distance a divided by the number of grooves-that is, in the case of two parallel grooves they are offset from one another by 1/2.

In this way, for a given length of the arms 5 of the connector rods 4 resting in the grooves 9 and 9a respectively, the number of connector rods per unit length may be increased and hence also the force which can be transmitted along the butt joint between the two structural parts which are to be bonded.

Finally, it may also be seen from Figure 5b that the mounting strip 1 advantageously has a trapezoidal cross-section, the grooved main face 2 of the mounting strip 1 being wider than the ungrooved main face 3. Through this construction the mounting strip, after bending up the arms 5 of the connector rods 4 lying in the grooves, into a position perpendicular to the groove main face 2, can easily be loosened out of the surrounding concrete of the first or the two structural parts of reinforced concrete which are to be bonded, so that between the two structural parts there arises a kind of tongue-and-groove joint. In order further to facilitate the loosening of the mounting strIp 1 when desired, the mounting strip may be saturated for example, also with form oil.

A further possible embodiment of a bonding unit in accordance with the invention is shown in Figure 6. In the case of this embodiment the mounting strip 1 contains a plurality of grooves 9a, 9b ... running parallel with one another at an acute angle to the longitudinal central plane of the mounting strip, with each of which there is associated only one drilled hole 8a,8b... If these drilled holes are made as shown as oblong holes, the longitudinal central plane of the oblong hole must again coincide with the longitudinal central plane of the associated groove. This embodiment of the invention represents another possibility of providing a larger number of connector rods per unit length of the mounting strip than is possible if all connector rods are arranged one behind the other in a single groove.

Because of the considerable length of the arms of the connector rods bent to a knee and held fast in the grooves in the mounting strips, which is necessary for the frictional bonding of two adjacent structural components of reinforced concrete, an asymmetrical arrangement of the stirrup-shaped portions of the connector with respect to the centre of the mounting strip rods projecting out of the mounting strip inevitably results. If, for example, the arms of the connector rods held fast in the grooves in the mounting strip all extend towards the ieft from the drilled holes through which pass the connector rods, then at the righthand end of the mounting strip the first stirrup-shaped portion of a connector rod may be arranged very close to the right-hand end of the mounting strip.The last stirrup-shaped portion of a connector rod at the left-hand end of the mounting strip must on the contrary however have a distance from the left-hand end of the mounting strip, which is at least as long as the arm of this connector rod held fast in a groove in the mounting strip. The last stirrup at the righthand end of the mounting strip can therefore lie considerably nearer the end of the mounting strip adjacent to it than the last stirrup at the left-hand of the mounting strip.

This asymmetry has a disadvantageous effect if along a long connecting joint between two adjacent structural components of reinforced concrete a number of bonding units must be put together in a row because then in every case in the region of abutment between two mounting strips the distance apart of adjacent connector rods or their stirrups becomes considerably greater than in the region within the mounting strips. The reinforcement is then distributed nonuniformly along the connecting joint between the two structural components. Figure 7 shows a bonding unit in accordance with the invention, in which the defect described above is eliminated so that uniform distribution of the reinforcement is possible also in long connecting joints which demand the placing of two or more bonding units together in a row.

In Figure 7 there may be seen again a mounting strip 1 having main faces 2 and 3 lying opposite one another, in which stirrup-shaped portions 4a, 4b, 4c of connector rods 4 project out of the main face 3. In the embodiment the stirrups 4a, 4b, 4c are U-shaped so that each stirrup has an arm 1 5 bent back in parallel, the straight portion of each connector rod 4 passing respectively through the mounting strip in drilied holes 8a, 8b, 8c which, as may be seen only in Figures 8b, 9b, are made as oblong holes and which connect the main face 3 to grooves 9a, 9b, 9c which are incorporated in the main face 2 of the mounting strips. The arms 1 5 of the stirrups lie wholly outside the mounting strip 1.

As may further be seen from Figures 8b and 9b the arms 5a, 5b of the connector rods 4 bent to a knee and held fast in the grooves 9a, 9b, all run from the drilled holes 8a, 8b in the direction towards the left-hand end El of the mounting strip.

The third groove 9c in the mounting strip 1 is connected to the main face 3 of the mounting strip 1 through the drilled hole 8c near to the lefthand end El of the mounting strip. A connector rod 4 passes through the mounting strip 1 in the drilled hole 8c. As may be seen from Figure 9b the arm Sc of this connector rod bent to a knee, extends from the drilled hole 8c away in the direction towards the right-hand end E2 of the mounting strip, that is, in a direction which is the opposite of that of the arms 5a, 5b bent into the grooves 9a, 9b.

As has been indicated at the left-hand end of Figure 7, by this measure it becomes possible in the region of abutment between two adjacent mounting strips 1, 1' to arrange the connector rods 4, 4' forming the stirrups 4c and 4a' at the same distance a apart as the rest of the mounting strips 1,1'.

When the stirrups projecting out of the mounting strip have a stirrup arm 15 bent back in the shape of a U, then the simplest arrangement is if the bent back stirrup arms 1 5 remaining wholly outside the mounting strips 1 and the arms 5a, 5b, Sc of the connecting rods 4 in question, held fast in the grooves 9a, 9b, 9c, lie on the same side of the straight portions of the connector rods passing through the mounting strip 1, as is shown in solid line in Figures 8a, 8b, 9a and 9b.

But in orde to achieve complete uniformity as regard the transmission of force, if the stirrup and the arm of each connector rod bent to a knee lie in one plane, then, preferably, in the case of the connector rod associated with the further groove 9c, the bent-back parallel arm of the U-shaped stirrup remaining outside the mounting strip 1 and the arm Sc of this connector rod held fast in the further groove 9c, are arranged on opposite sides of the straight portion of the connector rod 4 passing through the hole 8c drilled in the mounting strip 1,-as is indicated in Figure 9a by the stirrup 4c' and the arm 15' in dotted lines.

In the case of the embodiments of the invention described hitherto, each connector rod forms at one end a stirrup in single shear and at the other end an arm bent to a knee, where the rod is bent only in one plane, that is, the stirrup and the arm lie in one plane.

Bonding units are also already known having connector rods in the form of stirrups placed transversely in double shear, in which the two arms of the stirrup are bent to a knee perpendicular to the plane of the stirrup. Such connector rods bent in space to have stirrups in double shear, demand indeed an increased expenditure of energy in the bending, because bending processes must be performed in two lines perpendicular to one another. However, compared with connector rods bent only in one plane with stirrups in single shear they offer various advantages. In particular their consumption of material in the case of equal force to be transmitted per unit length of the joint is less because of the very good anchoring action of the stirrup in double shear.Furthermore, the attachment of the bonding unit on the shuttering of one of the structural components is also simplified, by means of one wide mounting strip for applying to the shuttering and containing the stirrups in double shear, or by means of two narrower mounting strips with a gap between and connected by the stirrups in double shear.

Bonding units in accordance with the invention may now in accordance with Figures 10 to 14 also be equipped with connector rods bent in space to form stirrups in double shear.

In the embodiment of Figures 10 to 12, stirrups 4B and 1 4B in double shear are arranged transverse to the mounting strip 1 at intervals longitudinally, being formed of bent connector rods 4 and 14 following one another alternately in the direction longitudinal to the mounting strips.

Each connector rod consists of five portions 4a to 4e and 1 4a to 1 4e respectively. The homologous portions 4b, 1 4b and 4d, 1 4d respectively of successive connector rods 4 and 14 respectively pass through holes 8b, 1 8b and 8d, 1 8d respectively drilled in the mounting strip and arranged at equal intervals alternately along each of the two pairs of associated lines 8B,8D,18B, 1 8D which run parallel with the longitudinal direction of the mounting strips.

The portions of rod 4b, 4d and 1 4b, 1 4d projecting out of the mounting strip 1 at right angles to the main face 3 are completed by bridge portions 4c and 1 4c respectively running transversely to form transversely placed stirrups 4B, 1 4B in double shear, which are offset alternately a little towards the right-hand and lefthand edges respectively of the strip.

In the main face 2 of the mounting strip 1 and below the centrelines 8B,8D,18B,18D, grooves 9a, 9e and 19a, 19e are provided, which receive respectively the arms 4a, 4e and 1 4a, 1 4e of the connector rods 4, 14 bent to a knee. The inside width of these grooves corresponds generally to the diameter of the connector rods. The bent arms of these rods are held fast in the grooves either by being a jam fit or by clips or the like.

Through the provision of separate grooves for the arms of successive connector rods the stirrups 4B, 1 4B, as may be seen in figure 10, may be arranged along the mounting strip 1 at intervals which are less than the length of the arms 4a, 4e and 1 4a, 1 4e respectively because these arms can overlap unimpeded in adjacent grooves.

As is revealed in particular in Figure 11, the two arms 4a, 4e and 1 4a, 1 4e respectively of each connector rod 4 and 14 respectively can easily be introduced simultaneously into the associated oblong holes 8b, 8d and 1 8b, 1 8d respectively in the mounting strip.

For the transmission of higher loads in shear it is preferable if instead of one relatively wide mounting strip two separate weaker mounting strips are employed, which are held together at a predetermined distance apart by the connector rods forming stirrups in double shear, because then two tongue-and-groove bonds are created simultaneously per connection during concreting.

In spite of the employment of two mounting strips the stiffness of such a bonding unit against parallelogramwise shifting of the two strips relative to one another is very high because of the arm portions bent to a knee and held fast in the grooves so that they cannot twist.

In this sense in the case of the embodiment of Figures 13 and 14, instead of one common mounting strip, two mounting strips 1 and 1' are provided, arranged in parallel with one another at a distance apart, and between which a gap 20 is left open. During concreting this gap is filled with concrete so that tongue-and-groove bonds arise in the connecting face of the structural components.

The rest of the arrangement, of the grooves 9a, 9e, 1 9a, 1 9e, of the drilled holes 8b, 8d, 18b, 1 8d as well as the connector rods 4, 14 with the stirrups 4B, 1 4B and the arms 4a, 4e, 1 4a, 1 4e, bent to a knee, is as in the embodiment of Figures 10to 12.

The embodiments described allow of various modifications. Thus, for example, instead of connector rods equal with one another, and which form stirrups of equal width in double shear, two different connector rods may be employed, which form stirrups of different width in double shear.

These stirrups of different width can then be arranged alternately in succession in the direction longitudinal to the mounting strips, that is, symmetrically about the centre of the mounting strips, where the arms of the connector rods forming the wide stirrups engage in the outer grooves in the mounting strips and the arms of the connector rods forming the narrow stirrups engage and are held fast in the inner groove.

Claims

1. A unit for bonding two structural components of reinforced concrete and consisting of a mounting strip which holds a number of connector rods and from which portions of the connector rods project at intervals along one side, arms of the connector rods bent to a knee shape being enclosed inside the mounting strip, characterized in that two or more parallel grooves running substantially longitudinally of the mounting strip are provided on the main face of the mounting strip away from the projecting portions of the connector rods, the width of the grooves being substantially equal to the diameter of the connector rods and the depth of the grooves being at least equal to this diameter, holes running from the bottom of the grooves towards the opposite main face of the mounting strip being provided at intervals along the mounting strip, one of the connector rods passing through each hole, and the arms of the connector rods lying in the respective grooves.

2. A unit according to claim 1, in which all of the grooves run parallel with the longitudinal central plane of the mounting strip and a number of holes, arranged at intervals, are associated with each groove.

3. A unit according to claim 1, in which the grooves include acute angles with the longitudinal central plane of the mounting strip and only one hole is associated with each groove.

4. A unit according to any of claims 1 to 3, in which the arms of the connector rods are held fast in the grooves.

5. A unit according to claim 4, in which the arms are held in the grooves by clips.

6. A unit according to claim 4 in which the width of the grooves is slightly less than the diameter of the connector rods and the arms of the connector rods are held fast in the grooves by being a jam fit.

7. A unit according to any of claims 2, 4, 5 or 6, in which the holes are arranged at equal intervals a along each groove, the holes in each groove being offset with respect to the holes in the other groove or grooves by the interval a between the holes divided by the number of grooves.

8. A unit according to any of claims 1 to 7, in which the holes are oblong holes having a longitudinal central plane coinciding with the longitudinal central plane of the associates groove and lying perpendicular to the parallel main faces of the mounting strip, the width of the holes being substantially equal to the diameter of the connector rods and the length of the holes being at least equal to the radius of bend of the connector rods plus the diameter of the connector rods.

9. A unit according to any of claims 1 to 8, in which the connector strip consists of wood, pressboard or cane.

10. A unit according to any of claims 1 to 9, in which the connector strip has a trapezoidal crosssection, the grooved main face being wider than the parallel ungrooved main face.

11. A unit according to any of claims 1 to 10, in which the mounting strip is subdivided into sections along its length by predetermined points of break.

12. A bonding unit according to claim 1, in which the arms from the knees of the connector rods in at least two grooves in the mounting strip extend from the hole in the mounting strip, through which the connector rod passes, in the direction towards the same end of the mounting strip, the arm from the knee of the connector rod in at least one additional groove which has its hole adjacent the said same end, extending from the hole in the direction towards the other end of the mounting strip.

13. A unit according to claim 12, having connector rods each of which forms a U-shaped stirrup which lies in the same plane as the bent arm of the same connector rod, the arm held fast in the at least one additional groove and the respective stirrup being directed in opposite directions, the stirrup and the bent arms of the remaining connector rods extending in the same direction.

14. A unit according to claim 1, in which portions of the connector rods projecting out of the main face of a common mounting strip, together with a bridge section, form a double-shear stirrup lying transverse to the longitudinal axis of the mounting strip, so that homologous portions of successive connector rods pass through holes in the mounting strip which lie at intervals alternately on each of two associated centrelines parallel with the longitudinal direction of the mounting strip, the arms bent at right angles to the successive connector rods being held fast in associated pairs of parallel grooves formed in the opposite main face of the mounting strip.

15. A unit according to claim 1, in which portions of the connector rods projecting out of the main faces of a pair of mounting strips, together with a bridge section, form a double shear stirrup lying transverse to the longitudinal axis of the mounting strips, so that homologous portions of successive connector rods pass through holes in the mounting strips which lie at intervals alternately on each of two associated centrelines parallel with the longitudinal direction of the mounting strips, the arms bent at right angles to the successive connector rods being held fast in associated parts of parallel grooves formed in the opposite main faces of the mounting strips.

16. A bonding unit according to claim 14 or claim 15, in which the double-shear stirrups of successive connector rods have the same width and are offset alternately in opposite directions with respect to the longitudinal axis of the mounting strip or mounting strips.

1 7. A unit for bonding two structural reinforced concrete components, substantially as described with reference to any of the accompanying drawings.