EP4493770A1

EP4493770A1 - Precast shoe base and precast shoe

Info

Publication number: EP4493770A1
Application number: EP22714829.3A
Authority: EP
Inventors: Sayed DAHER; Ming Keat CHONG; Alvin DEVADAS
Original assignee: Leviat GmbH
Current assignee: Leviat GmbH
Priority date: 2022-03-15
Filing date: 2022-03-15
Publication date: 2025-01-22
Anticipated expiration: 2042-03-15
Also published as: EP4493770B1; CN119032213A; EP4493770C0; WO2023174514A1

Abstract

The invention relates to a precast shoe base (2) for a precast shoe (1) and a precast shoe, comprising such precast shoe base (2). The precast shoe base (2) has a front section (3) with a bolt hole (5) and with at least two threaded primary rebar holes (6). The precast shoe base (2) has a rear section (4) located opposite to the front section (3). The precast shoe base (2) has a generally flat plate shape having in the front section (3) adjacent to the bolt hole (5) a first plate thickness (t₁) and having in the rear section (4) a second plate thickness (t₂) being smaller than the first plate thickness (t₁). The precast shoe base (2) has a generally flat bottom surface (8). The cross-section of the precast shoe base (2) is tapered from the first thickness (t₁) adjacent to the bolt hole (5) to the second thickness (t₂) in the rear section (4). The precast shoe base (2) is made as a monolithic part of molded ferrous material. The precast shoe further comprises at least two separate primary rebars (19) being threaded to match the threaded primary rebar holes (6) of the precast shoe base (2).

Description

PRECAST SHOE BASE AND PRECAST SHOE

The invention relates to a precast shoe base and a precast shoe comprising such precast shoe base.

In the technical field of concrete building structures a variety of precast structure components are used to a wide extent, in order to save cost and time in the on-site building process. Such factory fabricated precast structure components comprise a number of metal precast shoes, which are cast-in into a concrete body, and which allow for bolting together such precast structure components on site.

According to the prior art, such precast shoes comprise a shoe base, to which a number of rebars (short for reinforcing bars) are connected. The shoe base has a front section facing the outer contour of the concrete structure and an opposite rear section being oriented towards the inner part of the concrete structure. Furthermore, the shoe base has in said front section a central bolt hole, which is accessible by the mounting personnel, and through which a threaded fastening bolt of an adjacent building structure is passed. The mounting personnel fixes and fastens the precast structure in the desired position by means of nuts and washers screwed onto the threaded fastening bolt.

The cast-in rebars are designed for force coupling and force transmittal from said fastening bolt through the shoe base into the precast concrete structure. At least one pair of cast-in primary rebars are located in close vicinity to the bolt hole, and carry the majority of the acting longitudinal loads. Due to some eccentricity between the bolt hole and the primary rebars resulting bending moments are involved as well. In order to cope with such bending moment at least one secondary rebar is connected to the shoe base at its rear section. While the combination of primary and secondary rebars allows for transmitting both longitudinal forces and bending moment, the shoe base of the precast shoe itself is subjected to said bending moment as well.

EP 1 057 950 Bl discloses numerous embodiments of such precast shoes each having a shoe base with a bolt hole, a pair of primary rebars in close vicinity to the bolt hole, and at least one secondary rebar in the shoe base's rear section. In each such embodiment the shoe base has a complex geometric shape formed of welded steel plates. Vertically arranged sheet metal parts are welded to a horizontally arranged base sheet metal part in order to act as reinforcement parts, thereby forming a three dimensional structure of the shoe base.

A common feature of all disclosed embodiments is the arrangement of vertically oriented sheet metal parts, providing the required bending stiffness and bending load bearing capability of the shoe base. In one type of such precast shoes, the rebars are welded to the shoe base, wherein the vertically oriented sheet metal parts additionally serve to provide sufficiently long welding seams. While such embodiments suffice to carry the acting loads, the process of manufacturing such welded structures is demanding and cost intensive. Furthermore, a fixed arrangement of shoe base and rebars is given, which requires extensive stock-keeping to cope with different geometric mounting requirements. In another type of such precast shoes, the rebars are screwed to the base sheet metal. The vertically oriented sheet metal parts serve as a reinforcement structure only, without supporting the rebars. The screwing connection of the rebars allow for some flexibility in adapting the precast shoe's configuration to the actual demand. However, the manufacturing effort of the welded shoe base's structure is still high. Furthermore, due to the limited thickness of the base sheet metal the screwed connection of the rebars is limited in its load carrying capability

The object of the present invention is to provide a shoe base with reduced complexity without compromising structural integrity. This object is solved by a shoe base according to claim 1.

A further object of the present invention is to provide a precast shoe with a simple yet flexible design.

This object is solved by a precast shoe according to claim 14.

According to the invention a precast shoe base for a precast shoe is proposed, wherein the precast shoe base has a front section with a bolt hole and with at least two threaded primary rebar holes, and wherein the precast shoe base has a rear section located opposite to the front section. The precast shoe base has a generally flat plate shape having in the front section adjacent to the bolt hole a first plate thickness and having in the rear section a second plate thickness being smaller than the first plate thickness. Furthermore, the precast shoe base has a generally flat bottom surface, wherein the cross-section of the precast shoe base is tapered from the first thickness adjacent to the bolt hole to the second thickness in the rear section. The precast shoe base is made as a monolithic part of molded ferrous material.

In a further aspect of the invention, a precast shoe is provided, comprising such precast shoe base and at least two separate primary rebars being threaded to match the threaded primary rebar holes of the precast shoe base.

In a preferred embodiment of the precast shoe base the rear section is provided with at least one threaded secondary rebar hole. In the related preferred embodiment of the precast shoe said precast shoe further comprises at least one separate secondary rebar being threaded to match the threaded secondary rebar hole of the precast shoe base.

In the present application the terms "shoe base" and "precast shoe base" define the entire metal structure, to which the primary and optional secondary rebars are connected before being cast-in into the concrete material, and which together with the primary and secondary rebars forms the fully functional precast shoe.

The invention provides a number of advantages over the prior art. The threaded primary and secondary rebar holes allow for varying configurations of the precast shoe by simply screwing-in rebars of dimension according to the actual demand. Semi-finished precast shoe-bases may be kept in store with unthreaded holes, while such holes can be bored up to the required diameter and then tapped with the required thread. Based on that idea, a large variety of applications can be covered by using standardized Semifinished precast shoe-bases. The same applies to the rebars, which can be kept in store in a reasonable variety, and which can be chosen and connected to the shoe base as required. The threads of the rebar holes and/or of the rebars can also be manufactured according to the actual demand. They may be cut in a traditional way, but are preferably rolled threads, which leads to a high load bearing capability even at short thread engagement lengths. Such threads are formed by pressing dies into the rebar, which allows for the material to move or shape into threads, instead of being cut away. This type of cold forging process results in good thread strength and reduces possibility of thread stripping.

The inventive tapering of the plate thickness follows the mechanical load distribution within the shoe base: The loads are highest in the vicinity of the bolt hole and the primary rebars. The relatively large first plate thickness in this area copes in particular with said high loads, and also provides a significant length of the threaded primary rebar holes with related high load bearing capability. The comparably small second plate thickness is provided at a place, where primarily longitudinal forces are induced by the secondary rebar(s), while relative low bending moments are involved. The tapered plate thickness between both follows the increase of the bending load along the way from the rear section to the front section. The generally flat plate shape of the shoe base embodied as a monolithic part of molded ferrous material suffices for that, without the need of welded-on or otherwise fastened reinforcement structure. The tapered thickness of the monolithic design, and further advantageous form features as mentioned below, might be formed by forging iron or steel. Preferably, said monolithic part of molded ferrous material is cast iron or cast steel. In result, a material-saving design is found with reduced cost and weight, yet with full load bearing capability, which is easy to manufacture and easy to handle.

In an advantageous embodiment, the rear section is provided with at least one holding anchor being integrally formed by the monolithic part of molded ferrous material as a single piece. Said holding anchor is formed by the same and single casting or forging process as used for the remainder of the precast shoe base without additional effort. Such holding anchor can be used in the alternative to and as a replacement for the aforementioned secondary rebar, or can be used in combination therewith. In any case a compact yet highly reliable stress and force transmission between the precast shoe and the surrounding concrete is achieved by means of the cast-in holding anchor, in order to counteract the load eccentricity resultant from the distance between the anchor bolt and the primary rebars.

In a preferred embodiment, the precast shoe base has a top surface, wherein the top surface is provided with extension collars surrounding the threaded rebar holes. Thereby, the inner thread of the rebar holes is extended in its axial direction, covering both the thickness of the shoe base's main body plus the extension collar. The enlarged length of the rebar hole threads allows to keep the thickness of the shoe base's main body to a minimum without compromising the thread load bearing capability. Material and weight can be saved, which leads to reduced cost and improved handling.

The tapered thickness of the shoe base can be varied in a large range. Preferably, the second plate thickness is less than two-thirds and in particular less than 50% of the first plate thickness, which lead to a desired balance between material saving and structural integrity. In a further preferred embodiment, the precast shoe base has in the vicinity of the primary rebar holes a first width and in the vicinity of the secondary rebar hole a second width being smaller than the first width. Preferably, the second width is less than two- thirds and in particular less than 50% of the first width. Thereby, the outer contour of the shoe base follows the mechanical load distribution in a manner comparable to tapering thickness distribution, which supports the related and above described advantages. This is further supported by a preferred embodiment, wherein between the primary rebar holes and the secondary rebar hole and/or wherein between the primary rebar holes and the bolt hole sidewalls of the precast shoe base are provided with concave cutouts.

In a further preferred embodiment, in its front section the precast shoe base is provided with a guide plate having frontal positioning edge. Said frontal positioning edge allows for easy alignment of the precast shoe with the outer wall of cast mold. Preferably, the guide plate has at least one and in particular two beveled corner positioning edges. These are helpful when aligning the precast shoe with an inner comer of cast mold. Said guide plate is not subjected to high working loads. It is therefore desired to keep the thickness of the guide plate to a practical minimum. In particular, the guide plate has a third plate thickness, while that the third plate thickness is less than 25% and in particular less than 15% of the first plate thickness. Despite such reduced thickness the guide plate can still be reliably formed by casting or forging, and has sufficient strength to fulfill its alignment task under the rough conditions of manufacturing precast concrete structures.

In an advantageous embodiment, the a removable mounting access former or recess former is provided to form a mounting recess during casting-in the precast shoe, wherein the mounting access former is embodied in a two-part form by a spacer former and a recess former, and wherein the spacer former is positioned between the recess former and the frontal positioning edge of the precast shoe base. Said two-part form takes into account the geometrical complex upper surface of the shoe base by means of the spacer former. The spacer former allows for a precise positioning of the recess former relative to the frontal positioning edge without being influenced by the remaining irregular shoe base geometry. After the processes of casting-in the precast shoe both the spacer former and the recess former can easily be removed from the hardened concrete, leaving a clearly defined mounting recess and a more or less fully cast-in metal structure of the precast shoe.

An example embodiment of the invention is described hereinafter under reference to the drawing. Therein,

Fig. 1 discloses two concrete structure elements, one of which is equipped with four inventive precast shoes before connection with cast-in threaded bolts of the other concrete structure element,

Fig. 2 discloses an exploded view of one individual precast shoe of Fig. 1 showing details of the involved metal components including a precast shoe base, two primary rebars and one secondary rebar,

Fig. 3 discloses a perspective view of the precast shoe base according to Fig. 2 showing a bolt hole, two threaded primary rebar holes, one threaded secondary rebar hole and a beveled guide plate within a monolithic cast iron part,

Fig. 4 discloses a top view of the precast shoe base according to Fig. 3 with details of its footprint contour,

Fig. 5 discloses a side view of the precast shoe base according to Figs. 3, 4 with details of a tapered cross section thickness distribution,

Fig. 6 discloses a perspective view of the precast shoe according to Fig. 2 in a ready- to-use assembled state, Fig. 7 discloses a side view of an inventive precast shoe variant with a bent secondary rebar for generating an undercut,

Fig. 8 discloses a side view of a further inventive precast shoe variant with a shortened secondary rebar and a screwed-on anchor head for generating an undercut,

Fig. 9 discloses a side view of a still further inventive precast shoe variant with a forged secondary rebar having a monolithically formed anchor head for generating an undercut,

Fig. 10 discloses a side view of a still further inventive precast shoe variant with monolithically formed holding anchors in replacement of a screwed-in secondary rebar, being inclined relative to the bottom plane,

Fig. 11 discloses a side view of a precast shoe variant according to Fig. 10 with monolithically formed holding anchors having a double bend relative to the bottom plane,

Fig. 12 discloses a top view of the precast shoes according to Fig. 11 with the holding anchors being aligned at a spreading angle within the bottom plane,

Fig. 13 discloses a top view of a precast shoe variant according to Fig. 12 with the holding anchors having hook-shaped bends within the bottom plane,

Fig. 14 discloses a perspective explosion view of a concrete precast formwork for a precast column with multiple mounted-in precast shoes having foam formers to form mounting recesses, Fig. 15 discloses a perspective view of a formwork for on-site casting of a concrete structure with multiple cast-in anchor bolts being held in place by an anchor positioning frame,

Fig. 16 discloses a side view of the concrete structure elements according to Fig. 1 at the beginning of the mounting process,

Fig. 17 discloses a side view of the arrangement according to Fig. 16 with the upper precast column being brought in place during tightening of the screw connection,

Fig. 18 discloses a side view of the arrangement according to Fig. 17 during casting in the screw connection,

Fig. 19 discloses a top view of a precast concrete structure with a rectangular cross section and with a total of six cast-in precast shoes according to Fig. 6,

Fig. 20 discloses a top view of a precast concrete structure with a circular cross section and with a total of five cast-in precast shoes according to Fig. 6, and

Fig. 21 discloses a variant of the arrangement according to Fig. 1 with a mixed application of inventive precast shoes and grout couplers.

Fig. 1 shows in schematic perspective view a precast concrete structure element 31, shortly before being connected to a second concrete structure element 32. Both concrete structure elements 31, 32 are indicated by their outlines only to allow visibility of castin connection elements as described below. In the present example, the precast concrete structure 31 is a precast concrete column with upright orientation. However, the precast concrete structure can be of any other orientation, shape and/or function including wall or floor elements. The precast concrete structure element 31 has rectangular cross section with an outer circumferential wall 36 and with four corners at its base surface facing the second concrete structure element 32. At each comer, each one inventive precast shoe 1 is cast-in into concrete material, using appropriate formwork or molds in the factory. The accordingly prepared precast concrete structure element 31 is transported to the construction site in a read-to-assemble state, and is mounted to another structure on-site as shown in Fig. 1.

In the present example, the schematically indicated second concrete structure element 32 is an on-site cast concrete foundation of a building, featuring a number of upright anchor bolts 33 corresponding to the number and orientation of the precast shoes 1 of the precast concrete structure element 31. The anchor bolts 33 are cast-in into the concrete material of the second concrete structure element 32. Instead of a building foundation, the second concrete structure element 32 can also be another precast concrete column to form multi-story building, or any other precast concrete structure. In the alternative, the precast concrete structure element 31 may also be connected to a steel substructure or any other suitable structure by means of the cast-in precast shoes 1 together with suitably arranged anchor bolts 33.

Fig. 2 shows an exploded view of one individual precast shoe 1 of Fig. 1 together with the top end of the related anchor bolt 33. In the shown example, the precast shoe 1 comprises a precast shoe base 2, two primary rebars 19, and one optional secondary rebar 20. At their ends adjoining the precast shoe base 2 the rebars 19, 20 feature threads that are "roll-threaded", instead of "cut-threaded". Corresponding thereto, the precast shoe base 2 has two threaded primary rebar holes 6 and one threaded secondary rebar hole 7 to receive the threads of the rebars 19, 20. At its end adjoining the precast shoe base 2 the anchor bolt 33 is threaded as well to receive nuts 34 and washers 35. The precast shoe base 2 comprises a bolt hole 5 to receive the threaded end section of the anchor bolt 33. The precast shoe 1 is fastened to the anchor bolt 33 by clamping its shoe base 2 between each one nut 34 and each one washer 35 on the anchor bolt's 33 threaded end section. The threads of the rebar holes 6 and 7 and of the anchor bolt 33 are also cold forged or rolled as mentioned in the context of the rebars 19, 20.

Fig. 3 shows a perspective view of the precast shoe base 2 according to Fig. 2. The precast shoe base 2 is made as a monolithic part of molded ferrous material. Said ferrous material covers both iron and steel with or without alloy components, and may be formed by forging. In the shown embodiment, the precast shoe base 2 is a monolithic cast iron single piece having a generally flat plate shape with a front section 3 and a rear section 4. The meaning of "front" and "rear" will become apparent further below in the context of the description related to Figs. 19 and 20. The bolt hole 5 and the pair of threaded primary rebar holes 6 are located in the front section 3, while the threaded secondary rebar hole 7 is located in the rear section 4.

The precast shoe base 2 has a top surface 9, from which extension collars 10, 11 extend in an upward direction. Each extension collar 10 functions as a length extension of each one primary rebar hole 6 including its inner thread. Analogous thereto, the extension collar 11 extends the length of the secondary rebar hole 7 including its inner thread. The rebar holes 6, 7 are through-holes passing through the entire thickness of the precast shoe base 2 including the extension collars 10, 11. The same applies to the respective inner threads, which extend through the entire thickness of the precast shoe base 2 including the extension collars 10, 11, thereby providing an extended thread engagement length for the respective rebars 19, 20 (Fig. 2, 6).

Furthermore, in its front section 3 the precast shoe base 2 is provided with a thin guide plate 16 as part of its monolithic structure. The guide plate 16 has a frontal positioning edge 17 and two beveled corner positioning edges 18. From the top view of Fig. 4 it can be seen, that said frontal positioning edge 17 extends perpendicular to a longitudinal axis 21 of the precast shoe base 2, while the two beveled corner positioning edges 19 are inclined thereto by 45°, encompassing an opening angle of 90° between both of them. The top view according to Fig. 4 also shows, that the precast shoe base 2 extends along said longitudinal axis 21 in a mirror-symmetric fashion. Both the bolt hole 5 and the secondary rebar hole 7 are located on the longitudinal axis 21, while the two primary rebar holes 6 are symmetrically located on each side of the longitudinal axis 21. In the vicinity of the primary rebar holes 6, the precast shoe base 2 has a first width w which is the maximum width. In the vicinity of the secondary rebar hole 7 it has a second width w₂, which is smaller than the first width w The second width w₂ is preferably less than two-thirds of the first width w_b and is in the shown preferred embodiment even less than 50% of the first width w

The synopsis of Figs. 3 and 4 further reveals, that the massive base body of the precast shoe base 2 excluding the thin guide plate 16 is framed in the rear section 4 by sidewalls 12 and in the front section 3 by side walls 14. Between the primary rebar holes 6 and the secondary rebar hole 7 sidewalls 12 of the front section 3 are provided with concave cutouts 13 on each side of the longitudinal axis 21. Furthermore, between the primary rebar holes 6 and the bolt hole 5 sidewalls 14 of the front section 3 are provided with concave cutouts 15 on each side of the longitudinal axis 21.

Fig. 5 shows in a side view the precast shoe base 2 of Figs. 2 to 4. In this side view it can be seen, that the precast shoe base 2 has a generally flat bottom surface 8, while said top surface is not flat to provide a varying base thickness as follows: In the front section 3 and adjacent to the bolt hole 5 the precast shoe base 2 has a first plate thickness t In the rear section 4 and adjacent to the secondary rebar hole 7 it has a second plate thickness t₂. The second plate thickness t₂ is smaller than the first plate thickness t_b In between, the top surface 9 is inclined to the flat bottom surface 8 such, that the crosssection of the precast shoe base 2 is tapered from the first thickness ti to the second thickness t₂. The second plate thickness t₂ is preferably less than two-thirds of the first plate thickness t and is in the shown preferred embodiment even less than 50% of the first plate thickness t Compared to the afore-described thicknesses of the shoe base's 2 main body the guide plate 16 is significantly thinner. The guide plate 16 extends from said main body in the forward direction as defined by the location of the front section 3 relative to the rear section 4. The flat and planar bottom surface 8 extends under both said main body and said guide plate 16. Apart from said main body, the guide plate 16 has a third plate thickness t₃. The third plate thickness t₃ is preferably less than 25% of the first plate thickness t_b and is in the shown preferred embodiment even less than 15% of the first plate thickness t

Upon comparing Figs. 4 and 5 it can be seen, that the maximum thickness of the shoe base 2 being the first thickness t₃ is significantly smaller than its maximum width being the first width w_b According to the above definition of the shoe base as having a generally flat plate shape, the first thickness ti is preferably smaller than one half and even more preferable smaller than 40% of first width w

Fig. 6 shows a perspective view of the precast shoe 1 according to Fig. 2 in an assembled state. The primary rebars 19 are screwed into the primary rebar holes 6, while the secondary rebar 20 is screwed into the secondary rebar hole 7 of the shoe base 2, thereby forming a ready -to-use precast shoe 1. It has to be noted, that within the invention a higher number of primary rebars 19 and/or a higher number of secondary rebars 20 might be screwed into an appropriately adapted shoe base 2.

It has to be further noted, that said ready -to-use precast shoe is solely formed by the single monolithic precast shoe base 2 and the rebars 19, 20 connected thereto. The structural and functional integrity of the precast shoe base 2 is achieved by the afore- described monolithic design, and no further reinforcement structures are welded or otherwise connected to the shoe base 2. In the example embodiment of Fig. 6 the secondary rebar 20 is straight and oriented perpendicular to the bottom surface 8 (Figs. 5, 7) of the precast shoe base 2. Fig. 7 shows in a side view a variant thereof, wherein the secondary rebar 20 is bent from its original straight form at a certain angle so as to extend in the plane of the bottom surface 8, for generating a positive locking undercut with the surrounding concrete in a cast-in state. By way of example the bending angle is shown to be 90°. However, different and/or multiple bending angles might be desirable. A further variant is shown in the side view of Fig. 8, wherein the secondary rebar 20 is kept straight, but is cut and shortened to a significant extent. For compensating the reduced length the secondary rebar 20 is provided with a screwed on anchor head 24 at its free end. In the alternative the anchor head 24 might be welded onto the secondary rebar 20 or connected thereto in any other suitable way. A further and similar variant is shown in the side view of Fig. 9, wherein the secondary rebar 20 is not made of regular endless reinforcing material, but is forged with a monolithically and one-piece formed anchor head 25.

The cast or forged design of the precast shoe base 2 allows for significant design freedom including one or more holding anchors being integrally or one-piece formed by the monolithic part of molded ferrous material. A first example of such a design variant is shown in the side view of Fig. 10 with monolithically formed holding anchors 22 in replacement of a screwed-in secondary rebar 20 of the above described embodiments. The holding anchors 22 are inclined relative to the bottom plane 8 and have an irregular form for generating a positive locking undercut with the surrounding concrete in a castin state. A variant thereof is shown in the side view of Fig. 11, wherein monolithically formed holding anchors 23 have a double bend relative to the bottom plane 8. In the shown example the double bend leads to a vertical and a horizontal portion of the holding anchors by means of 90° bends. However, different bending angles and orientations of the holding anchor portions might also be desirable within the scope of the invention. Fig. 12 shows in a top view the precast shoe 1 according to Fig. 11. It can be seen that a total of two holding anchors 23 are present being aligned relative to the longitudinal axis 21 at a spreading angle. The spreading angle may be chosen to any suitable value as required, including an orientation parallel to the longitudinal axis 21. Also, one single holding anchor 23 can be sufficient. Of course, three or more holding anchors 23 might be useful as well. The above comments to the holding anchors 23 apply to the holding anchors 22 of Fig. 10 in an analogous way.

In the embodiments of Figs. 10 to 12 the holding anchors 22, 23 are formed to have anchor heads 29 at their free ends for the desired positive locking undercut. In the alternative holding anchors 28 might be formed in any other suitable way with for example hook-shaped bends as shown in Fig. 13 to provide the desired positive locking undercut.

In the embodiments of Fig. 10 to 13 all holding anchors 22, 23, 28 are a replacement of the screwed-in secondary rebar 20 of the further shown embodiments. This means, that the holding anchors 22, 23, 28 fulfill the same purpose as the secondary rebars 20. However, within the invention a combination of anchors 22, 23 and/or 28 with secondary rebars 20 might be advisable as well.

In order to manufacture the precast concrete structure 31 (Fig. 1) in the precast factory, the precast shoes 1 as mounted and prepared according to Fig. 6 will be positioned in a precast formwork 40, namely in the bottom formwork of the column, as mentioned before in the context of Fig. 1, and as shown in the exploded view of Fig. 14. By way of an example a total of four precast shoes 1 are positioned in the four comers of the rectangular column base cross section. Within each precast shoe 1 one removable mounting access former is provided to form a mounting recess 37 as shown in Figs. 16 to 18 during casting-in the precast shoes 1. The mounting access formers are embodied in a two-part form each by a spacer former 26 and a recess former 27, and are made from foam plastic like expanded polystyrene or polyurethane. Other plastic materials or even materials like rubber, wood, steel or the like might be chosen as well. The recess formers 27 have the form of a solid block. The spacer formers 26 have a thin-walled L- shape, and are positioned between the respective recess formers 27 and the respective frontal positioning edges 17 of the precast shoe bases 2, as shown in the upper edge of Fig. 14. The such prepared precast formwork 40 is then filled with concrete. Shape and positioning of the spacer formers 26 allow for a more or less complete immersion of the precast shoes 1 in the poured-in concrete, while the recess formers 26 are held in place by the spacer formers during pouring and displace the poured-in concrete to form mounting recesses 37. After curing of the concrete the precast form work 40, the spacer formers 26 and the recess formers 27 are removed, thereby releasing a finished precast concrete structure 31 ready for assembly, as shown in Figs. 16 to 18.

In preparation of the construction site a choice of anchor bolts 33 is cast-in into the second concrete structure 32 (Fig. 1), as shown in Fig. 15. The total number of (here by way of example four) anchor bolts 33 corresponds to the total number of (here by way of example four) precast shoes 1 of the related precast concrete structure 31 of Fig. 14. In order to achieve a correct corresponding positioning, an anchor positioning frame 38 receives the anchor bolts 33 and positions them relative to an on-site formwork 41 of the second concrete structure 32. The such prepared on-site formwork 41 is then filled with concrete, while the anchor bolts 33 are held in place by means of the anchor positioning frame 38. After curing of the concrete the on-site formwork 41 and the anchor positioning frame 38 are removed, releasing a finished second concrete structure 31 ready for mounting the precast concrete structure 31, as shown in Figs. 16 to 18.

Figs. 16 to 18 show phases of the aforementioned mounting process. According to the side view of Fig. 16 lower nuts 34 and washers 35 are positioned on the threads of the anchor bolts 33. The lower washers 35 define the mounting plane for the precast concrete structure 31, and are adjusted to the desired height and horizontal orientation by turning the lower nuts 34. In the alternative or in addition, and in particular for heavy loads steel shims 42 can be used for the same purpose. In this state the free threaded ends of the anchor bolts 34 are protected by protection caps 43.

The prepared precast concrete structure 31 is positioned above said arrangement, as shown in Fig. 16, and is then in a next step lowered onto the washers 35 and/or the shims 42, as shown in Fig. 17. Thereby, the free ends of the anchor bolts 33 are passed through the bolt holes 5 (Fig. 6) of the precast shoes 1, and are accessible for the mounting personnel through the mounting recesses 37. After removing the protection caps 43 (Fig. 16), top washers 35 are passed onto said free ends, and top nuts 34 are screwed onto the same to provide a screw connection. The top nuts 34 are tightened through the mounting recesses 37 by the mounting personnel, using a suitable wrench 44.

After tightening said screw connection the entire seam area between the precast concrete structure 31 and the second concrete structure 32 may be surrounded by a finishing formwork 45 as shown in Fig. 18, and may be filled with appropriate high- strength low-shrink mortar, which in particular fills the gap between both concrete structures and also all the mounting recesses 37. As shown in Fig. 18 the mortar can be poured either from the side or, as indicated by dotted lines, more centrally with a cast-in pour pipe.

Figs. 19 and 20 each show a top view of further precast concrete structures 31', 31 ", with a rectangular base area in Fig. 19 and a circular base area in Fig. 20. In the embodiments of Figs. 1 and 19 it can be seen, that in each corner each one precast shoe 1 is positioned by aligning the beveled corner positioning edges 18 with the outer walls 36, 36' of the concrete structures 31', 31". Furthermore, according to Fig. 19 additional precast shoes 1 are placed in the middle of two opposing outer side walls 36', whereby they are positioned by aligning the frontal positioning edge 17 with the respective outer wall 36'. The latter principle of alignment can even be used for precast concrete structures 31" with a circular or curved base area, as shown by way of example in Fig. 20. Based on the afore mentioned alignment principles, more or less any precast concrete structure with more or less any base shape can be fitted with an appropriate number of precast shoes.

After positioning the precast shoes, the formwork will then be filled with concrete, whereby the precast shoes 1 will be cast-in into the concrete such, that only the portion of the bolt hole 5 is kept free from concrete, and is kept accessible for the mounting personnel. This is due to the fact, that the front section 3 with the bolt hole 5 is oriented towards the respective outer wall 36, 36', 36" of the respective precast concrete structure 31, 3 T, 31 ", while the opposing rear section 4 of the base plate 2 including the secondary rebar 2 is oriented away from the outer wall 36, 36', 36" towards the center of the precast concrete structure 31 , 3 T, 31 " .

The precast concrete structure 31 and the second concrete structure 32 can be connected by using only the arrangement of precast shoes 1 and anchor bolts 33 according to Fig.

1. However, within the scope of the invention said arrangement of precast shoes 1 and anchor bolts 33 might also be used in combination with other fastening means, as shown by way of example in Fig. 21. In such variant of the arrangement of Fig. 1, additional grout couplers 39 are used. The arrangement of precast shoes 1 and anchor bolts 33 is the same as in the embodiment of Fig. 1. In addition, both the precast concrete structure 31 and the second concrete structure 32 are provided with matching pairs of rebars 46. So called grout couplers 39 in the form of metal sleeves are slid of the ends of each rebar 46 pair, and are then filled with low viscosity grout. After hardening, a high strength connection between the rebars 46 is achieved, supporting the load bearing capability of the precast shoe 1 connection.

Claims

Claims A precast shoe base (2) for a precast shoe (1), wherein the precast shoe base (2) has a front section (3) with a bolt hole (5) and with at least two threaded primary rebar holes (6), wherein the precast shoe base (2) has a rear section (4) located opposite to the front section (3), wherein the precast shoe base (2) has a generally flat plate shape having in the front section (3) adjacent to the bolt hole (5) a first plate thickness (ti) and having in the rear section (4) a second plate thickness (t₂) being smaller than the first plate thickness (ti), wherein the precast shoe base (2) has a generally flat bottom surface (8), wherein the cross-section of the precast shoe base (2) is tapered from the first thickness (ti) adjacent to the bolt hole (5) to the second thickness (t₂) in the rear section (4), and wherein the precast shoe base (2) is made as a monolithic part of molded ferrous material. The precast shoe base according to claim 1, characterized in, that the rear section (4) is provided with at least one threaded secondary rebar hole (7). The precast shoe base according to claim 1 or 2, characterized in, that the rear section (4) is provided with at least one holding anchor (22, 23, 28) being integrally formed by the monolithic part of molded ferrous material. The shoe base according to one of claims 1 to 3, characterized in, that the precast shoe base (2) has a top surface (9), and wherein the top surface (9) is provided with extension collars (10, 11) surrounding the threaded rebar holes (6, 7). The precast shoe base according to one of claims 1 to 4, characterized in, that the second plate thickness (t₂) is less than two-thirds and in particular less than 50% of the first plate thickness (ti). The precast shoe base according to one of claims 1 to 5, characterized in, that the precast shoe base (2) has in the vicinity of the primary rebar holes (6) a first width (wi) and in the vicinity of the secondary rebar hole (7) a second width (w₂) being smaller than the first width (wi). The precast shoe base according to claim 6, characterized in, that the second width (w₂) is less than two-thirds and in particular less than 50% of the first width (wj. The precast shoe base according to one of claims 1 to 7, characterized in, that between the primary rebar holes (6) and the secondary rebar hole (7) sidewalls (12) of the precast shoe base (2) are provided with concave cutouts (13). The precast shoe base according to one of claims 1 to 8, characterized in, that between the primary rebar holes (6) and the bolt hole (5) sidewalls (14) of the precast shoe base (2) are provided with concave cutouts (15). The precast shoe base according to one of claims 1 to 9, characterized in, that in its front section (3) the precast shoe base (2) is provided with a guide plate (16) constituting a frontal positioning edge (17) of the precast shoe base (2). The precast shoe base according to claim 10, characterized in, that the guide plate (16) constitutes at least one and preferably two beveled corner positioning edges (18) of the precast shoe base (2). The precast shoe base according to claim 10 or 11, characterized in, that the guide plate (16) has a third plate thickness (t₃), and that the third plate thickness (t₃) is less than 25% and in particular less than 15% of the first plate thickness (t₃). The precast shoe base according to one of claims 1 to 12, characterized in, that said monolithic part of molded ferrous material is cast iron or cast steel. A precast shoe, comprising a precast shoe base (2) according to one of claims 1 to 13, and at least two separate primary rebars (19) being threaded to match the threaded primary rebar holes (6) of the precast shoe base (2). The precast shoe according to claim 14, characterized in, that the rear section (4) of the precast shoe base (2) is provided with at least one threaded secondary rebar hole (7), and that the precast shoe (1) further comprises at least one separate secondary rebar (20) being threaded to match the threaded secondary rebar hole (7) of the precast shoe base (2). The precast shoe according to claim 14 or 15, characterized in, that the threads of the rebar holes (6, 7) and/or of the rebars (19, 20) are rolled threads. The precast shoe according to one of claims 14 to 16, characterized in, that a removable mounting recess former is provided to form a mounting recess (37) during casting-in the precast shoe (1), wherein the mounting recess former is embodied in a two-part form by a spacer former (26) and a recess former (27), and wherein the spacer former (26) is positioned between the recess former (26) and the frontal positioning edge (17) of the precast shoe base (2).