GB1568828A - Precasting elongated concrete members - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO PRECASTING ELONGATED CONCRETE MEMBERS (71) We, NEDERLANDSE SPAN BETON MAATSCHAPPIJ B.V., a Dutch body corporate of Alphen a/d Rijn, the Netherlands, 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 a method of prefabricating elongated, concrete structural members having accurately fitting contact surfaces at their sides, and intended to be assembled to form a reinforced concrete structure pre-stressed in the longitudinal and transverse directions thereof.

There are various conventional method,s,, known by the name of the "contact method", for producing such longitudinally pre-stressed concrete members, the object being that, on the site, such members, such as girders, are accurately fitted in side-by-side relationship, and are united to form one slab by means of tendons threaded through the members in the transverse direction thereof and which compress the members together with great force. The transverse tendons can be mounted rapidly and in a simple manner on the site.

When such a slab is used, for example, to span the space between two successive piers of a bridge, this system offers the additional advantage that on each slab thus assembled to form one whole, the slab for the next span can be assembled. This is especially beneficial in case the site is difficult of access and the like.

A further advantage of such a system is that the slabs may be mounted so as to be removable. In that case the tendons used for the transverse reinforcement are not embedded in the ducts formed in the side-by-side members by injecting grout therein, but, for example, provided with a bituminous coating and anchored in tensioned condition against the outermost members. If desired, the tendons can then be removed after releasing the tension, and the slab can be disassembled.

In the method described in German patent specification 2,257,004, at least some of the elongated concrete members to be assembled on the site to form one slab, are made in one batch in side-by-side relationship in one broad mould in the casting works. Adjacent members in the mould are kept separate by thin steel sheets, and it has been found in practice that this leads to excellent contact faces being formed on the sides of the members. One obvious advantage in precasting only a number of the members in one batch is that less space is required.

If the total number of members to be assembled in side-by-side relationship is greater than the number of members precast in one batch, it is proposed in said German patent specification 2,257,004 to place, in a separate step, the last member of each batch of finished members side-by-side with the first member of the next batch of finished members with some interspace between them. A thin steel sheet is then positioned approximately in the middle of the interspace, and contact-joint concrete for the two members is cast against the sheet from opposite sides thereof. A concomitant advantage is that, for different cases, the contact joints may be made of different widths. In this way, using essentially uniform members, the total width of the structure may be varied to some extent.Also, to some extent, the total structure may in this way be given a nonuniform width by giving the contact joint a somewhat wedge-shaped configuration over the length of the member.

However, owing to the relatively small number of places where such contact-joint concrete is cast on, relative to the total width, these possibilities of adaptation are rather limited.

A further drawback of the prior method is that, as a number of members are cast at the same time, the reinforcement which has to give the members the required longitudinal pre-compression cannot be applied, or at any rate cannot be tensioned, until after completion of the casting. Such post-tensioned reinforcement is considerably more ex pensive per ton of pre-stressing force than pre-tensioned tendons, for one thing by reason of the materials and equipment required and for another because the application, tensioning and injecting of post-tensioned reinforcement requires more work.

It is an object of the present invention to provide a method of prefabricating elongated, concrete structural members of the kind referred to, whereby the disadvantages of the prior art are eliminated.

According to the present invention a method of prefabricating elongated, concrete structural members arranged to be assembled together side by side to form a reinforced concrete structure having contact surfaces adapted to fit accurately with one another when assembled in the said side by side relationship comprises the steps of forming a series of elongated concrete castings with pre-tensioned reinforcement in their longitudinal direction, the width of said castings at least at their upper portions being less than the width of the structural members needed in the finished structure, placing said castings in side-by-side positions accurately corresponding to the relative positions of the structural members in the finished structure, with the portions of narrower width forming spaces between adjacent castings, filling up the said spaces between the adjacent castings with concrete, and allowing the concrete to bond to the surfaces of one member bounding the space, a release coating having been applied to the surface or surfaces of the other adjacent member bounding the space so the concrete bonds to the one member and not to the other member and allowing the concrete to harden to produce a series of prefabricated accurately fitting concrete members.

Accordingly, in the method of the present invention, a contact joint portion providing a contact surface is cast-on on one side of at least a large number of the members to be consecutively connected together in side-by side relationship in the finished structure, in contrast to the method of the prior art (German patent 2,257,004), in which cast-on contact joints are only made on the last of a group of members and on the first of the next group of members, and this in two layers, using a metal sheet between them.In the present invention, the contact-joint concrete present between two adjoining members consists of a single layer, formed during a second process step in the prefabrication in which it is cast monolithically with one member to link up properly with the side surface of an adjacent member, but prevented from being physically bonded to said surface through the release agent.

The term release agent as used herein is intended to cover any material that prevents the contact-joint concrete from being bonded to the concrete of the member to which the release agent is applied. There are a great many materials which are suitable for the purpose, which materials are well-known in the art. The choice of release agent is not critical, and does not constitute part of the present invention.

An important advantage of the method according to this invention is the possibility of widely varying the width and transverse con figuration of a prestressed concrete structure by means of the precast members.

Another important advantage is that the elongated members can be cast one by one in a pre-tensioning mould, owing to which post-tensioning of the longitudinal reinforcement is avoided.

A further advantage of the method according to this invention is that it may be possible to save one, or even more, prestressed member in assembling a structure by making the cast-on contact joints extra broad to the extent that the reinforcement provided in the casting is capable of taking up the load from a correspondingly broad, loaded strip in the completed structure.

According to a further elaboration of the method of this invention, the castings are formed with an integral rebate at one longitudinal upper edge, and the space between adjacent castings is filled with concrete using formwork extending from an adjacent casting that is provided with the release agent, said formwork having a free end movably supported on the bottom of the rebate.

Such bottom formwork is in particular advantageous when the cast-on contact joint is to be of varying width along the length thereof, although these may be made without using such formwork.

It is noted in this connection that a relatively low height of side contact surface may be of importance in erecting skew viaducts in that bending moments in the transverse direction may be limited and the occurrence of torsional stresses in the precast members may be avoided as much as possible.

If the side contact surfaces are of relatively low height, it is recommendable, in order to distribute concentrated loads over the structure assembled from a plurality of precast members made by the method of this invention, that the precast members should be made with the greatest possible torsional stiffness. This leads to the manufacture of relatively broad members which, for saving weight, are preferably made hollow.

As appears from the foregoing, the following important advantages are achieved by the contact method according to the present invention: - unlike the methods of the prior art, the precast elements may be made with pretensioned longitudinal reinforcement; -the number of precast members can be adapted to the required carrying capacity in the finished structure to a great extent; elongated castings can be made one by one in a first process step by a cheap industrialized, "long-mould" system with pre-tensioned tendons; -in the main, a relatively small assortment of formwork members in standard dimensions will suffice; -the precast members may be assembled to a structure having a varying width along the length thereof;; 9 structure having a barrel-shaped profile may be made by making the cast-on joint of somewhat trapezium-shaped cross-sectional configuration; -structures having a skew surface may be assembled from the precast members by giving the cast-on joints an appropriate configuration; straight tendons may be used for longitudinal reinforcement of the members, which during manufacture avoids buckling points and downward forces on head partitions at the ends of the moulds; as a consequence, the moulds may be less rigid and hence after in weight, and may be resiliently supported during vibration of the concrete without cornplications and without the risk of undesirable deformations; --pre-tensioned, straight tendons may be combined with unbonded, post-tensioned tendons which in the region of the supporting ends extend at the top, and at some distance from the ends slant downwardly to extend along the lower edge of the elongated member in the central region thereof.The unbonded tendons are then present at the top at both ends of the member, as a result of which the occurrence of unpermissible tensile forces, ia particular when the member is supported at points located a considerable distance from the ends, for example, during transportation, can be avoided; -by varying both the width of the cast-on joints during the second step of the method of this invention and the number of unbonded tendons, a very small assortment of standard types of prefabricated castings with identical, embedded, pre-tensioned longitudinal reinforcement will suffice to meet a great variety of requirements in practice. In this way, the tensioning mould in which the members are precast, in particular, can also be used economically and productively.

The present invention also relates to a series of associated, elongated, prefabricated members having accurately fitting contact surfaces at their sides, and made by the method descnbed hereinbefore.

The invention will now be described in more detail with reference to the accompanying drawings, in which Fig. 1 shows diagrammatically, in plan view, a tensioning mould, showing three basic castings for prefabricated concrete members, succeeding one another in the longitudinal direction, during the first step of the method according to the present invention; Fig. 2 and 3 show, in cross-sectional view, preferred embodiments of prefabricated concrete girders, made by the method according to the present invention; Fig. 4 is a cross-sectional view, on a considerably smaller scale than Figures 2 and 3, showing a number of prefabricated concrete girders of external configuration substantially corresponding to Fig. 2, placed in side-by-side relationship;; Fig. 5 shows diagrammatically the use of cast-on contact-joints strips of a number of girders united to form a slab varying in width along the length thereof; Fig. 6 is a cross-sectional view on an enlarged scale, showing bottom formwork used in casting-on contact-joint concrete; and Fig. 7 is a diagrammatic, perspective view, showing a prefabricated concrete member according to Fig. 2, illustrating the configuration of the longitudinal tendons therein.

Referring to Fig. 1, there are shown three girders 1, 2 and 3, being made in a tensioning mould as "basic castings" in a first step of the method according to the present invention.

The girders are cast and vibrated, one behind the other in the longitudinal direction, in formwork moulds with tendons 5, pretensioned by means of tensioning legs 4 of the mould, as prestressed longitudinal reinforcement.

These basic castings may have a crosssectional configuration as shown, by way of example, in Figures 2 and 3, and respectively designated by 1 and 1', that is to say, with central longitudinal cavities.

The length of such girders may be in the order of several tens of metres. Girder 1 as shown in Fig. 2 will have a maximum height and a total width of approximately 90 cm, while the girder 1' will be about 65 cm high and about 120 cm wide.

Longitudinal cavities 6, 6' are interrupted by concrete partitions. Near the ends of the girders, these will be made of solid concrete over a length of approximately 50 cm to 150 cm, according to the length of the girder.

Furthermore recesses are formed at the tops of the girder ends for receiving jointing concrete or steel members between longitudinally successive girders or the girder end and an adjacent structure.

As shown in Figures 2 and 3, longitudinal rebates 7 and 7' are formed in an upper edge of the girders for receiving at least part of the width of a contact-joint strip, to be monolithically cast-on during a second step of the method according to the present invention. Pre-tensioned tendons, extending straight in the longitudinal direction of the girders in the bottom region of the crosssectional profile of the girders, are indicated in dash lines at 5 in Fig. 7. Accordingly, when girders 1, 2 and 3 of Fig. 1 are cast, tendons 5 have already been tensioned.

Furthermore, in each of girders 1, 2 and 3, unbonded tendons are included in the concrete in the sidewalls of the cross-sectional profile, that is to say, beside the cavities. These tendons extend as shown in dot-dash lines in Fig. 7 at 8. For the sake of clarity, the rear tendon is shown in part only. These tendons are surrounded with grease or another lubricant, as a result of which the concrete does not become bonded to the tendons 8.

When the concrete has hardened -- and has bonded to tendons 5 - but before tendons 5 are cut on the outside of each girders and the formwork is removed, at least some of the unbonded tendons 8 are tensioned and anchored against the end faces of the girders by known per se means. The remaining unbonded tendons will be tensioned later, for example, several months later.

In Figures 2 and 3, transverse ducts 9 and 9' are indicated in dot-dash lines in the upper region of the girders, which ducts have been formed using steel tubes. These ducts terminate in the bottoms of lateral recesses 10, 10' and 11, 11', respectively, shown in dash lines in Fig. 2 and 3. These recesses serve, inter alia, for receiving means for anchoring and, as the case may be, interconnecting the ends of transverse reinforcing members, to be applied later.

Castings 1, 2 and 3 are then laid in side-byside relationship in the casting works in positions accurately corresponding to those they are to occupy in the finished structure.

This arrangement is shown in Fig. 4, in which casting la is an edge girder with a slightly modfied contour at its outer edge (the left-hand one in the drawing), and Ib the first girder of a next series of girders Ib, 2b, 3b, made in the mould, corresponding to series 1, 2 and 3.

When a number, or possibly all, of the castings to be united on the site have been laid side by side in the works, bottom formwork 12, 13, etc, is placed in position in the interspaces -- where present between adjacent castings approximately at the level of the bottom of the rebates. Subsequently, bottom reinforcements are arranged in the spaces above the formwork for the contactjoint concrete 21, 22, 23 to be cast therein.

These reinforcements are not shown in the drawings, no more than connecting reinforcements embedded in the castings during the first process step to project from the castings on the right-hand side thereof as viewed in Fig. 4. These connecting reinforcements serve for connecting the castings and the cast-on contact-joint concrete.

Subsequently, so-called "ductubes" are threaded through the transverse ducts 9 of the castings to span the interspaces, and finally top reinforcements are placed in position in the interspaces, which are not shown in Fig. 4 either.

Boundary faces 32, 33, 34 at the top lefthand corner of the castings, as veiwed in Fig.

4, which each bound the interspaces for receiving the contact-joint concrete, have been provided with a release agent, which precludes the concrete from bonding to these faces.

Then concrete is cast in the spaces between adjacent castings defined by rebates 7, bottom formwork 12, 13, and the faces coated with the release agent.

After sufficient hardening, the ductubes are removed, and the members, i.e. the castings with a monolithic contact-joint strip, la, 21; 2, 22; 3, 23; etc., are ready and can be transported to a storage site.

If the members which are to be united in side-by-side relationship have not all been provided with a contact-joint strip in the manner shown in Fig. 4, but for example.

members la, 2 and 3 only, member ib of Fig. 4 can serve as the leftmost one of the next series of castings to be so treated.

Fig. 6 shows an embodiment of bottom formwork 18, which is secured to a right-hand casting 2c (in the situation according to Fig. 4) of a pair of adjacent castings, and the free end 19 of which rests on the bottom surface of the rebate of the left-hand casting lc. Fig. 6 shows three different positions of the free end 19, according to the width of the strip to be cast-on. Further variation of the width of the cast-on strips can be achieved using a limited assortment of formwork members of different widths.

The width of the cast-on strips can also vary along the length of the members, as indicated in Fig. 5 by reference numerals 21c, 22c and 23c for members lc, 2c, 3c, etc. As shown, these members together form a non-rectangular slab with slightly tapering side edges. It is also possible to make adaptations to slight differences in height of the upper surfaces of the members in the completed structure by adapting the shape of the contact-joint bodies.

Naturally, the invention is not limited to the embodiments described and shown in the accompanying drawings. Many alterations and modifications will readily occur to those skilled in the art without departing from the scope of the invention as defined in the accompanying claims.

WHAT WE CLAIM IS : - 1. A method of prefabricating elongated concrete structural members arranged to be assembled together side-by-side to form a

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

Claims (4)

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

   monolithically cast-on during a second step of the method according to the present invention. Pre-tensioned tendons, extending straight in the longitudinal direction of the girders in the bottom region of the crosssectional profile of the girders, are indicated in dash lines at 5 in Fig. 7. Accordingly, when girders 1,
2. 2 and
3. 3 of Fig. 1 are cast, tendons 5 have already been tensioned.

   Furthermore, in each of girders 1, 2 and 3, unbonded tendons are included in the concrete in the sidewalls of the cross-sectional profile, that is to say, beside the cavities. These tendons extend as shown in dot-dash lines in Fig. 7 at 8. For the sake of clarity, the rear tendon is shown in part only. These tendons are surrounded with grease or another lubricant, as a result of which the concrete does not become bonded to the tendons 8.

   When the concrete has hardened -- and has bonded to tendons 5 - but before tendons 5 are cut on the outside of each girders and the formwork is removed, at least some of the unbonded tendons 8 are tensioned and anchored against the end faces of the girders by known per se means. The remaining unbonded tendons will be tensioned later, for example, several months later.

   In Figures 2 and 3, transverse ducts 9 and 9' are indicated in dot-dash lines in the upper region of the girders, which ducts have been formed using steel tubes. These ducts terminate in the bottoms of lateral recesses 10, 10' and 11, 11', respectively, shown in dash lines in Fig. 2 and 3. These recesses serve, inter alia, for receiving means for anchoring and, as the case may be, interconnecting the ends of transverse reinforcing members, to be applied later.

   Castings 1, 2 and 3 are then laid in side-byside relationship in the casting works in positions accurately corresponding to those they are to occupy in the finished structure.

   This arrangement is shown in Fig. 4, in which casting la is an edge girder with a slightly modfied contour at its outer edge (the left-hand one in the drawing), and Ib the first girder of a next series of girders Ib, 2b, 3b, made in the mould, corresponding to series 1, 2 and 3.

   When a number, or possibly all, of the castings to be united on the site have been laid side by side in the works, bottom formwork 12, 13, etc, is placed in position in the interspaces -- where present between adjacent castings approximately at the level of the bottom of the rebates. Subsequently, bottom reinforcements are arranged in the spaces above the formwork for the contactjoint concrete 21, 22, 23 to be cast therein.

   These reinforcements are not shown in the drawings, no more than connecting reinforcements embedded in the castings during the first process step to project from the castings on the right-hand side thereof as viewed in Fig. 4. These connecting reinforcements serve for connecting the castings and the cast-on contact-joint concrete.

   Subsequently, so-called "ductubes" are threaded through the transverse ducts 9 of the castings to span the interspaces, and finally top reinforcements are placed in position in the interspaces, which are not shown in Fig. 4 either.

   Boundary faces 32, 33, 34 at the top lefthand corner of the castings, as veiwed in Fig.
4. 4. A series of elongated, prefabricated concrete members having accurately fitting surfaces at their sides, and made by the method according to any one of the preceding claims.

   4, which each bound the interspaces for receiving the contact-joint concrete, have been provided with a release agent, which precludes the concrete from bonding to these faces.

   Then concrete is cast in the spaces between adjacent castings defined by rebates 7, bottom formwork 12, 13, and the faces coated with the release agent.

   After sufficient hardening, the ductubes are removed, and the members, i.e. the castings with a monolithic contact-joint strip, la, 21; 2, 22; 3, 23; etc., are ready and can be transported to a storage site.

   If the members which are to be united in side-by-side relationship have not all been provided with a contact-joint strip in the manner shown in Fig. 4, but for example.

   members la, 2 and 3 only, member ib of Fig. 4 can serve as the leftmost one of the next series of castings to be so treated.

   Fig. 6 shows an embodiment of bottom formwork 18, which is secured to a right-hand casting 2c (in the situation according to Fig. 4) of a pair of adjacent castings, and the free end

   19 of which rests on the bottom surface of the rebate of the left-hand casting lc. Fig. 6 shows three different positions of the free end 19, according to the width of the strip to be cast-on. Further variation of the width of the cast-on strips can be achieved using a limited assortment of formwork members of different widths.

   The width of the cast-on strips can also vary along the length of the members, as indicated in Fig. 5 by reference numerals 21c, 22c and 23c for members lc, 2c, 3c, etc. As shown, these members together form a non-rectangular slab with slightly tapering side edges. It is also possible to make adaptations to slight differences in height of the upper surfaces of the members in the completed structure by adapting the shape of the contact-joint bodies.

   Naturally, the invention is not limited to the embodiments described and shown in the accompanying drawings. Many alterations and modifications will readily occur to those skilled in the art without departing from the scope of the invention as defined in the accompanying claims.

   WHAT WE CLAIM IS : - 1. A method of prefabricating elongated concrete structural members arranged to be assembled together side-by-side to form a

   reinforced concrete structure having contact surfaces adapted to fit accurately with one another when assembled in the said side-byside relationship, comprising the steps of forming a series of elongated concrete castings with pretensioned reinforcement in their longitudinal direction, the width of said castings at least at their upper portions being less than the width of the structural members needed in the finished structure, placing said castings in side-by-side positions accurately corresponding to the relative positions of the structural members in the finished structure with the portions of narrower width forming spaces between adjacent castings, filing up the said spaces between the adjacent castings with concrete, and allowing the concrete to bond to the surfaces of one member bounding the space, a release coating having been applied to the surface or surfaces of the other adjacent member bounding the space so the concrete bonds to the one member and not to the other member and allowing the concrete to harden to produce a series of pre-fabricated accurately fitting concrete members.

   2. A method according to claim 1, which comprises forming said castings each with an integral rebate at one longitudinal upper edge, and filling up the space between adjacent castings with concrete using formwork extending from each adjacent casting that is provided with said release agent, said formwork having a free end movably supported on the bottom of said rebate.

   3. A method of prefabricating elongated, longitudinally pre-stressed members, substantially as described herein with reference to the accompanying drawings.