A TIE ROD FOR FORMWORK

The invention relates to a tie rod for connecting opposite sections of a casting formwork, especially formwork for concrete. More particularly, the invention relates to a tie rod formed with a mid portion which is arranged to form supporting abutment surfaces against the internal surfaces of the formwork to maintain a predetermined distance between the formwork sides, and the mid portion is arranged to be fixed in the set casting material to form anchoring points in the concrete in such a way that good adherence is ensured between the concrete and the tie rod in order to prevent moisture from entering along the rod and cause damage to the concrete, and by good thermal properties to prevent condensation at the end portion of the tie rod, the tie rod being formed in one piece of a non-corrosive material, preferably a composite material .

In what follows, the casting material is described as "con- crete", and in this description there are also used other casting-process-related terms known from the casting of concrete. Nevertheless, the invention is not limited to applying only to formworks, which are to be filled with concrete, but

also relates to formworks, which are used when pouring building structures with other casting materials.

When concrete is poured, tie rods must be used to keep the formwork in position, that is to say to prevent the distance between two opposite sections of formwork which are to define a wall, for example, from changing when the formwork is loaded in the supporting of or by the pressure from the plastic concrete which is filled into the formwork. Tie rods are set with relatively regular spacing and fix the opposite formwork sections with a distance determined by the dimension of the tie rod. At the same time, the tie rods are locked with wedges to braces extending along the external sides of the formwork.

Prior art tie rods are formed of steel with spacers which are arranged to bear on the internal wall surface of the formwork sections, made of plastic, slipped over the tie rod in the production process and positioned axially on the tie rod, each bearing on a respective widened portion of the tie rod or an equivalent item. After the concrete has set and the formwork is removed, the projecting end portions of the tie rods are broken by bending them at a weakened portion located at the spacers. The surface of fracture is exposed in the wall surface, and the spacers, which are often of a conical shape with their widest portions facing outwards, often fall out. The need arises for trowelling the wall surface at each tie rod, partly in order to cover the surface of fracture, partly to fill the recess from the spacer. This is laborious and costly. Still, the largest drawback of the prior art is that the tie rod or, more accurately, the remainder of the tie rod, which is inside the concrete structure, forms an entry gate for moisture. The moisture penetrates the concrete structure and comes into contact with the reinforcement,

which lies, in part, immediately adjacent to or in direct contact with the tie rod. The reinforcement corrodes, the reinforcing strength is weakened, the adherence between the concrete and reinforcement is weakened and the concrete scales off due to corroded steel (rust coating) swelling relative to non-corroded steel. Corrosion also occurs on the tie rod.

Also in conditions in which a concrete structure is not in direct contact with water, prior art tie rods will be of dis- advantage as the thermal properties of the steel will make the tie rod work as a cold bridge, so that at a great temperature gradient across the cross-section of the concrete structure, condensation will easily form on the warm side. This moisture creates various maintenance challenges caused by the moisture directly or by rust formation on the tie rod.

In concrete structures which are to retain a liquid, that is prevent the liquid from entering or escaping, the tie rods will often be a source of leakage along the tie rods because of, among other things, poor adherence between steel and con- crete.

Another problem of the prior art is the lacking possibility of the tie rods for accurate positioning of reinforcement in the axial direction of the rod when the reinforcement is placed directly on the tie rods. Prior art tie rods lack means for this .

From US 3,430,914 is known a formwork tie rod of metal provided with diabolo-shaped spacer members, in which the outer part of the spacer member can be removed as required, and the diabolo shape ensures that the spacer member cannot inadver- tently come loose from the wall. There is also described a plastic plug for sealing the centre hole of the spacer member

after the rod end has been removed in a known manner. There are also described conical filler plugs of wood and ceramics. The rod exhibits the drawbacks described above as regards corrosion.

From NO 19980475 is known a formwork tie rod, in which spacers of plastic exhibit one or more plane partial surfaces in the circumferential surface to bring about good adherence of finishing mortar when the holes from the spacer shims are to be sealed up. The rod exhibits the drawbacks described above as regards corrosion.

The invention has as its object to remedy or reduce at least one of the drawbacks of the prior art .

The object is achieved through features specified in the description below and in the Claims that follow.

The invention relates to a tie rod formed of non-corrosive materials, preferably composite materials, in which a mid portion, exhibiting opposite abutment surfaces arranged to rest supportingly on the inside of a formwork section, and a rod stem forms a continuous structure. In addition to exhib- iting said abutment surfaces the mid portion may also include supporting and securing portions for other building materials and also include elements, which increase the adherence to the surrounding concrete and/or reduce the possibility for water to enter along the tie rod. After the formwork has been removed, the projecting rod end portions may be cut off at any position with a cutting tool suitable therefore, for example cutting pliers.

Thereby the tie rod according to the invention exhibits improved properties in several areas : - no corrosion damage will occur in the part of the formwork tie rod which is left in the concrete structure;

the continuous, non-corrosive tie rod structure with good adherence to the surrounding concrete prevents water from penetrating into or through the concrete structure in channels formed along the tie rod, whereby the tie rod ac- cording to the invention thereby contributes to a concrete structure of better watersealing properties and a concrete structure exhibiting less risk of rust formation on the reinforcing steel; the mid portion of the tie rod may be shaped at minimal costs to form a large number of positioning and securing details for reinforcement and internal insulation in plate form, the mid portion of the tie rod may be formed with radial anchoring elements which prevent the tie rod, under torque strains, from coming loose from the surrounding, set concrete, and the through plug which is formed by the remaining part of the tie rod can thereby function as installation fixtures for external building materials, the through stem of the rod being suitable as a screw attachment, for example - the thermal conductivity of the rod materials is small in relation to that of the concrete structure, and the problem of condensation at the tie rods is eliminated; projecting end portions of the tie rod can be used for mounting external building materials, for example insulation material in plate form, as the material is slipped onto the projecting end portions and secured with locking elements suitable therefore, before excess lengths of the end portions are cut off? and after the formwork has been removed, there are no parts of the tie rod that can fall out of the cast structure and thereby create a need for surface repairs by trowelling hollows with mortar, putting in plugs etc.

Any fasteners for securing building materials to the tie rod are preferably also formed of a non-corrosive material .

More particularly, the invention relates to a tie rod for joining opposite side sections of a casting formwork, the tie rod being provided with a mid portion and two rod end portions, and there being formed in the transitions between the mid portion and either rod end portion at least one abutment surface which is arranged to bear supportingly on an internal surface of the side sections, the rod end portion including rests for wedges for securing the side sections of the casting formwork, characterized in that the tie rod includes a stem of large tensile strength and a surrounding mantle, the mid portion and the mantle of the stem being formed as a continuous structure, the stem, mantle and mid portion being formed of non-corrosive materials.

The tie rod is preferably formed of a composite material, the stem being fibre-reinforced in the axial direction of the tie rod.

The mantle and the mid portion are advantageously formed of the same type of material .

The mantle and the mid portion are preferably joined by fusion of the material forming the mantle and the material forming the mid portion. Alternatively the mantle and the mid portion are joined by gluing.

The mid portion is preferably provided with means for non- releasable engagement with a surrounding casting material when this has been poured into the formwork and has set .

The mid portion and the stem portion surrounded by the mid portion is advantageously arranged to form a watertight, non- releasable, through plug in a completed cast structure.

The abutment surface is preferably formed by the mid portion exhibiting a widened cross-section towards its abutment portions .

At least one portion of the mid portion advantageously exhib- its a cross-section exhibiting, when the cross-section lies perpendicularly to the centre axis of the tie rod, a non- circular shape.

The mid portion is advantageously provided with a plurality of concentric cross-sectional widenings .

The mid portion is advantageously arranged to receive and fix one or more locking means for a plate-shaped building material, for example an insulating material, substantially annular grooves being complementary to a portion of the locking means .

The locking means are preferably formed of a non-corrosive material.

The mid portion of the tie rod advantageously includes one or more means arranged to receive a reinforcing means, preferably in the form of one or more substantially annular grooves.

The substantially annular grooves advantageously have a trapezoidal cross-section with the smallest width at the bottom of the groove, the side edges of the groove exhibiting the same angle of inclination relative to the centre axis of the tie rod.

The mid portion of the tie rod is advantageously arranged to receive one or more securing means for securing the reinforcing means .

The securing means for securing the reinforcing means is advantageously formed of a non-corrosive material.

The rod end portion is preferably arranged to receive one or more securing discs for securing a plate-shaped building material, for example an insulating material.

The securing disc advantageously includes means for releas- able connection to the mantle surface of the rod end portion.

The securing disc is advantageously provided with a plurality of resilient fingers extending from a circumferential portion and in a radial direction towards a centre opening.

The securing disc is preferably formed of a non-corrosive ma- terial .

The thermal conductivity of the tie rod is advantageously smaller than the thermal conductivity of the surrounding completed cast structure.

In what follows is described a non-limiting example of a pre- ferred embodiment which is visualized in the accompanying drawings, in which:

Figure 1 shows a perspective sketch of a tie rod according to the invention;

Figure 2 shows a perspective sketch on a larger scale of a locking disc for the tie rod according to the invention;

Figure 3 shows a perspective sketch of a securing disc for the tie rod according to the invention;

Figure 4 shows a perspective sketch on a smaller scale of a partially assembled formwork, in which the tie rod connects opposite formwork sections and positions reinforcement iron and insulating material;

Figure 5 shows, on a smaller scale, a completed cast wall section, in which a side surface has isolation material applied thereon, fixed by means of the tie rod according to the invention; and

Figure 6 shows a perspective sketch of a further exemplary embodiment of a mid portion of the tie rod according to the invention.

A tie rod 1 includes a stem 2 with a mantle 2a, a mid portion 3 and two rod end portions 5a, 5b. At either one of the tran- sitions between the mid portion 3 and the rod end portions 5a, 5b the mid portion exhibits a cross-sectional widening 7a, each forming an abutment surface 7.

The tie rod 1 is formed of a composite material, the stem 2 being reinforced in a manner known in itself with a fibre ma- terial of large tensile strength and surrounded by a bonding material forming the mantle 2a of the stem 2. The mid portion 3 may be formed of the same type of material as the mantle 2a.

In a first embodiment shown in figure 1, the cross-sectional widening forms a frustum of a cone, a bottom surface 7b facing the mid portion 3. The centre axis of the cone coincides with the centre axis of the tie rod 1. A top surface faces the adjacent rod end portion 5a, 5b, respectively, and is placed perpendicularly to the centre axis of the tie rod 1, forming the abutment surface 7. The bottom surface 7b exhibits a non-circular shape, four segment surfaces 7c lying parallel to the centre axis of the tie rod 1 in the direction towards the abutment surface 7 and extending into a side surface 7d. Two by two opposite segment surfaces 7c are parallel to each other, the bottom surface 7b forming a square with rounded corners .

In another embodiment shown in figure 6 the abutment surface 7 is formed as a first four-armed cross 57b. A second four- armed cross 57a of larger arm length is formed at a distance from the first cross 57b, and four ribs 58a projecting ra- dially and diametrically opposite, extend axially between the arms 59a, 59b of the crosses 57a, 57b. In addition this embodiment exhibits several concentric, circular cross- sectional widenings forming securing and sealing ribs 58b.

The mid portion 3 is joined in a sealing manner to the stem 2, liquid, for example water, being unable to enter in an axial direction from the end portion 5a, 5b towards the mid portion 3 due to the passage of the stem 2 through the mid portion 3 forming a tight connection. The tight connection is formed by fusion of the materials of the mantle 2a and the mid portion 3 in the production, or by joining them with, for example, glue forming a watertight joint between the stem 2 and the mid portion 3.

Either rod end portion 5a, 5b is provided at its outer end with a projecting rest 9 for a wedge device 11 for securing the side sections 23a, 23b of a formwork 21.

The mid portion 3 is provided with several grooves 3a extending round the entire periphery of the mid portion and arranged to receive a locking disc 13 for positioning and fixing a plate-shaped cast-in material 15, for example an insulating material.

The locking disc 13 is arranged to be slipped onto the mid portion 3, preferably in a radial direction, as a sector opening 13a leads in to a circular centre hole 13b positioned substantially centrically. To ensure that the locking disc 13 will not fall off after having been fitted on the tie rod 1, the thickness of the locking disc 13 forms, at least at the

centre hole 13b, a press fit with the side edges of groove 3a of the mid portion 3 , or the periphery of the centre hole 13b forms a press fit with the bottom surface of the groove 3a.

The mid portion 3 is also provided with several grooves 3b extending round the entire periphery of the mid portion and having a transversal profile which is arranged to receive a reinforcing means 25 in the form of reinforcing steel or similar, the cross-section of the groove being trapezoidal, for example.

The tie rod 1 may expedient also include a securing disc 17 which is arranged to be secured to a cut rod end portion 5a, 5b projecting from a set casting material 31, for example a concrete wall, after the formwork 21 has been removed, the securing disc 17 being provided with a number of radially oriented, resilient fingers 17a extending from a circumferential portion 17b and in a radial direction towards a centre opening 17c, each finger 17a being separated from an adjacent finger by a slot 17d extending in a radial direction from the centre opening 17c to a circular opening 17e in the circum- ferential portion 17b of the securing disc. The centre opening 17c exhibits a diameter, which is smaller than the diameter of the rod end portions 5a, 5b to ensure that the securing disc 17 is retained in a prescribed position on the rod end portion 5a, 5b in that the fingers 17a are under ten- sion.

At least the projections 9 and the stem 2 of the tie rod 1, that is to say the rod end portions 5a, 5b and the through core of the mid portion 3, are formed of a composite material of a tensile strength which is great enough for absorbing the relevant tensile loads to which the tie rod 1 for a formwork 21 is subjected during installation and during pouring of the casting material 31, for example concrete, into the formwork

gap. The composite material has fibre reinforcement and a binder material, which do not convey water or corrode. The mid portion 3 and stem 2 are formed of a material which is suitable for securing a fastener, for example a nail or screw. The rod end portions 5a, 5b are arranged to be cut at any point between the projection 9 and the abutment surface 7 by means of a tool suitable therefore.

The entire tie rod 1 with projections 9 and mid portion 3 may be formed in one forming operation.

The locking disc 13 and the securing disc 17 are advantageously formed of a non-corroding material, for example a plastics material.

The tie rod 1 is installed in a manner known per se as the formwork 21 is being built, side sections 23a being put to- gether before the reinforcing means 25 then being positioned and locked relative to each other and the formwork 21. Insulating material 15, if any, for casting in, is fixed by means of the locking discs 13 before the opposite side sections 23b are mounted and the formwork is closed and secured by fitting the wedge devices 11 to the tie rods 1 within the projections 9 and tightening the tie rods 1. In the tightening the abutment surface 7 rests supportingly on an internal side surface 23c of the side sections 23a, 23b of the formwork 21.

After the casting material 31, for example the concrete, has been filled into the formwork and has set, the formwork 21 is removed in a manner known per se, and the projecting rod end portions 5a, 5b of the tie rods 1 are cut off.

If the rod end portions 5a, 5b are to be used for securing plate-shaped building materials 33, for example insulating plates, on one or both sides of the completed cast structure 31, these are secured by slipping the securing discs 17 onto

the rod end portions 5a, 5b into abutment on the plates 33 after the projection 9 and suitable lengths of the rod end portions 5a, 5b have been cut off.

If building materials are to be secured by screwing or nail- ing, for example, this may be done by securing the fasteners to the mid portion 3 through the centre of the abutment surface 7 which is level with the outer surface of the cast structure 31 and formed by the cut stem 2. Due to the unbroken axial extent and partly non-circular cross-section of the mid portion 3 they are held in a secure grip in the set casting material 31, both in axial strain and radial rotational strain.

Due to the choice of material the tie rod 1 will not corrode and lead water in to the cast-in reinforcement or through the cast structure. The means 3a, 3b, 13 ensure a better positioning of the insulating materials 15 and reinforcement 25 in the cast structure, which leads to a more efficient utilization of the materials and better quality of the cast structure.

The possibility of using the rod end portions 5a, 5b of the tie rod and the abutment surface 7 of the mid portion when fitting external building materials, adds favourable additional functions to the tie rod 1.