CA1162036A

CA1162036A - Method of and apparatus for the manufacture of prefabricated prestressed concrete members

Info

Publication number: CA1162036A
Application number: CA000381862A
Authority: CA
Inventors: Peter Auer; Fritz Kluge; Helmut Lieske; Horst Wutzler
Original assignee: Dyckerhoff and Widmann AG
Current assignee: Walter Bau AG
Priority date: 1980-07-17
Filing date: 1981-07-16
Publication date: 1984-02-14
Also published as: ES506670A0; ES8301739A1; ES8205629A1; EG17071A; ES503980A0; IT8167984A0; IT1144389B; BR8104574A; MX156121A; CH651245A5; AU7237181A; ZA814441B; DE3027046A1; AU542898B2; IN153655B; DE3027046C2

Abstract

ABSTRACT OF THE DISCLOSURE
Prefabricated prestressed concrete members are formed on a stres-sing bed with a number of working stations arranged next to one another along the length of the bed. A frame forms the working stations and the frame is im-movable over the stressing bed. With a previously poured concrete member in one of the working stations, part of a form is placed in another working station and is filled with concrete. After the form part is completely filled and con-solidated, a second form part is placed downwardly on the filled part, complet-ing the form. A lifting member on the frame which placed the second form part on the filled part is then moved to the station containing the previously poured member which is still within the form. The form is stripped from the concrete member and the frame is then moved along with the lifting member, returning the stripped form to the working station where it is to be filled with concrete.
After the stripped form is moved the second form part is separated from the part to be filled with concrete and is moved into another working station where it is cleaned and readied for the next working cycle.

Description

1 16203~

The present invention is directed to a method of and an apparatus for mamlfacturing prefabricated prestressed concrete members having immediate bond and, in particular, to the formation of prestressed concrete ties. The concrete members are formed on an elongated stressing bed with the concrete members being formed in one or a number of side-by-side rows. Prestressing members extend along the stressing bed and are anchored in stationary abut-ments. Forms for producing the concrete members are made up of several parts and the prefabricated members are constructed in several casting or working stations located one after the other along the stressing bed. Concrete is poured into and consolidated within one of the form parts and then another form part is placed over the filled part to complete the concrete member.
Following the formation of a concrete member it is moved from one working station into another and the forms are removed from a previously constructed concrete member after the completion of the formation of the subsequently formed member.
It has been known to manufacture prestressed concrete ties on a long stressing bed with the ties located one behind the other and in several rows extending across the bed so that a large number of ties can be produced cor-responding to the length of the stressing bed. Accordingly, there must be as 2Q many individual forms as there are ties to be constructed along the entire length of the stessing bed. In this method, the ties are produced inverted from the normal position, with the form being shaped to afford the profile of the tie surface and the track support situated on that surface. Track attach-ment parts to be encased in the concrete of the tie are attached to the forms.
The concrete is poured into the forms and consolidated. When the concrete has set sufficiently, the fastening means for the concrete-encased track attachment parts are removed from the forms and then the forms are lifted off the ties.
Next, the prestressing members are detached rom the anchors on the stressing ~ ~.62036 bed, causing the stressing force to be transferrecl to the ties. After this, the prestressing members are severed between the individual ties and the ties are turned back into the normal position and the projecting ends of the pre-stressing members are removed.
In such a manufacturing operation there is the disadvantage that a large number of forms are required to produce the ties. Further, the consoli-dation of the concrete is not of sufficient intensity and, of necessity, the concrete consistency is such that it does not permit a quick stripping of the forms, which is needed for a quick reuse of the forms. ~s a result, the lQ quality of the concrete cannot be optimized as required because of the abrasion stress of the ballast bed, and the quantitative requirement of cement is rela-tively high. Moreover, this known method is not mechanized to the desired degree.
In the production of prefabricated prestressed concrete members with post-tensioning, especially in the formation of prestressed concrete ties, it has been known to choose the concrete consistency and to consolidate the conc-rete to such a high degree that the individual ties can be stripped immediately after the concrete is consolidated. This so-called instantaneous stripping process, however, cannot be applied to the formation of prefabricated prestres-2Q sed concrete members on a long stressing bed because the vibration oscillations developed during consolidation of the concrete are propagated throughout the prestressed members and affect the previously constructed and stripped ties.
In particular, there is the danger that the bond between the prestressing mem-bers and the concrete is lost.
To prevent the development of such vibration oscillations in the pre-stressed concrete members it has been known to provide devices along the stressing bed to fix the formed concrete members located immediately in front of and behind the member being fabricated in such a way that the vibration t 1162036 oscillations cannot be transmitted; note West German Patentschrift 26 14 036.
In this production procedure, these fixing devices, which must be provided along the stressing bed, cause an additional expense. ~urthermore, these de-vices prevent the forms in consecutive fabricating or working stations from being arranged closely together, limiting the effective utilization of the length of the stressing bed and causing a loss of prestressing steel.
Therefore, it is the primary object of the present invention, to provide a method of and apparatus for prefabricated concrete members on a long stressing bed which includes the immediate stripping of the forms from the formed member. As a result, the supply of forms needed -for the procedure is kept as small as possible and at the same time it is possible to provide op-timum use of the length of the stressing bed and of the prestressing steel.
In accordance with the present invention, in addition to the forms required in each production step, a number of additional forms are needed which correspond to the number of prefabricated members being produced. While one or several prefabricated concrete members are being formed another group which were just produced are located in an adjacent working station. After the forms are filled and consolidated, the forms just previously produced are stripped and the working stations are rearranged to commence the next working cycle.
The basic feature of the present invention is that each of the pre-fabricated prestressed concrete members is not stripped immediately after the completion of the pouring and consolidation operation, rather, one additional single or group of forms is poured and consolidated before the previously poured member is stripped. Suprisingly, it has been found that when a highly consolidated prefabricated member is left in the form until the next one or series of members is poured and compacted, not only is it assured that the previously formed member is not damaged, but there is an intensification of 1 ~L~0~6 the consolidatlon of the prestressing members with the surrounding concrete which is comparable to a reconsolidation of the concrete in the area of the prestressing members.
Thus, the invention provides a method of manufacturing prefabri-cated prestressed concrete members having an immediate bond, such as prestres-sed concrete ties, including providing a form for shaping the concrete members to be manufactured, with each form made up of at least a first form part and a separate second form part, on an elongated stressing bed and arranging the forms in one or more side-by-side rows extending in the elonga~ed direction of the stressing bed, positioning prestressing members extending along the elon-gated direction of the stressing bed, arranging a first working station fol-lowed by a second working station and then by a third working station extending in the elongated direction of the stressing bed, with the third working station containing a previously poured and consolidated concrete member within the assembled form,and moving the forms along the stressing bed between working stations, wherein the improvement comprises arranging the working station to be movably displaceable in the elongated direction of the stressing bed, placing a first form part on the stressing bed in the second working station, filling the first form part with concrete and vibrating the first form part for consolidating concrete therein, removing the second form part corresponding to the first form part from the first working station to the second working station and attaching the second form part to~ the first form part, vibrating the as:sem~led first and second form parts, moving into the third working station and removing the form from the previously poured form located therein and moving the previously poured form relative to the stressing bed and placing the pre-viously poured form on the stressing bed so that the previously poured form is in the second working station and the subsequently poured form is in the third working station.

1 lB20~6 The invention also provides apparatus for manufacturing prefabricated prestressed concrete members having an immediate bond, such as prestressed con-crete ties, comprising an elongated stressing bed, means arranged to be suppor-ted on said stressing bed for forming the concrete members, said means includ-ing at least a first form part and a second form part, said form parts arranged to extend in one or more side-by-side rows in the elongated direction of said stressing bed, a framework extending in the elongated direction of said stres-sing bed and said framework having a first end and a second end spaced apart in the elongated direction of said stressing bed, a portal-like frame at each end of said framework, with said portal-like frame extending transversely across and over said stressing bed~ said framework being movably displaceable over said stressing bed in the elongated direction thereof, said framework having at least two adjacent working stations therein located above said stressing bed and each said working station extending in the elongated direction of said stressing bed, a carriage mounted on said framework and movable thereonin the elongated direction of said stressing bed, a lifting device supported on and extending downwardly from said carriage over said stressing bed and arranged to be connected to said second form par~ so that said second form part can be moved upwardly and downwardly relative to said stressing bed and also moved in 2Q the direction of said stressing bed, and coupling means on said lifting device for connecting said second form part with said lifting device.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. ~or a better lmderstanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illus-trated and described preferred embodiments of the invention.

1 16203~

In the drawings:
Figure 1 is a side view of a portion of an apparatus embodying the present invention;
Figure 2 is a transverse sectional view taken along the line II-II in Figure l;
Figures 3a and 3b are transverse sectional views taken along the line III-III in Figure 1 each representing a different operating procedure of the present invention;
Figures 4a and 4b are transverse sectional views, on an enlarged scale, taken along the line IV-IV in Pigure 1 with each representing a differentoperating procedure of the present invention; and Figures 5a and 5b are transverse sectional views similar to Figures 4a and 4b through a different form arrangement for producing a prestressed concrete tie in a position inverted relative to its normal position.
In Figure 1 an apparatus is illustrated, in side view, for fabri-cating prestressed concrete tles on an elongated stressing bed 1. The long direction of the stressing bed is located in the plane of Figure 1. Stressing bed 1 includes a long continuous concrete foundation and prestressing wires 2 extend over the bed and are stressed between rigid abutments, not shown, lo-2a cated at the ends of the stressing bed. An oscillation-dampening covering 3 is placed over the surface of the stressing bed 1. Individual fabricating working stations are located along the stressing bed and one or several side-by-side tiescan be produced in the working stations. In Figure 3, three working sta-tions A, B and C are shown one following the other with two ties b~ing produced in each station, as can be seen in Pigure 2.
Along the opposite sides of and spaced outwardly from the stressing bed are tracks 4 on which a framework 5 travels. As can be seen in Figure 1, the framework 5 has a portal-like frame 5a, 5b at each of its opposite ends spaced apart in the length direction of the stressing bed so that the frames extend transversely across and over the bed. Longitudinal supports 5c connect the upper ends of the frames 5a, Sb while the lower ends are interconnected by longitudinal supports 5d. Mounted on each of the longitudinal supports 5c is a track 6 extending in the long directiorl of the stressing bed and a car-riage 7 with wheels 8 is movable along these tracks. Wheels 9 are located at the lower ends of the vertical posts of the frames 5a, 5b so that the entire framework 5 can be moved along the tracks 4 over the stressing bed 1.
A concrete storage hopper 10 is located along one side of the framework 5, note Figure 2, and concrete can be supplied from hopper 10 into a lower charging hopper 12 when a closure flap 11 at the bottom of the hopper 10 is moved into the opened position. Charging hopper 12 is supported on wheels 13 and can be moved in the transverse direction of the stressing bed 1 when it is displaced by a linkage 14 over the tracks 15 extending horizontally across and over the stressing bed. The linkage is operated via a cylinder-piston-unit, not shown.
Several cylinder-piston-units 16 are supported on the carriage 7 and include upqardly and downwardly movable piston rods 17 on which coupling members 18 are attached. Coupling members 18 hold the top part l9a of a form 19 used 2Q for constructing the prestressed concrete tie. The form 19, in addition to the top part l9a, includes a bottom part l9b. In the operating condition shown in Figure 1, the carriage 7 supporting the top parts l9a, is located in the working station A. Previously, the corresponding bottom parts l9b have been placed on the stressing bed 1 in the working station ~. This procedure is explained below.
A previously poured form 20 in the assembled condition including top part 20a and bottom part 20b is situated in the working station C.
To consolidate the wet concrete mix,used in forming the concrete ties, the top parts l9a and 20a of the form have external vibrators 21 and the lower parts l9b and 20b have external vibrators 22. Top parts 19a and 20a each have a catch 23 for connecting the top parts 19a and 20a to the corresponding bottom parts l9b and 20b of the forms. The forms 19 and 20 are of the same construc-tion.
Bottom parts 19b and 20b are connected to one another by transverse supports 24, note Figures 2 and 3. Clamping levers 25 are mounted on the frame-work 5 and are operated by means of cylinder-piston-units 26 for pressing the bottom parts 19b of the form 19 against the pressing bed 1. Rubber-metal ele-ments 27 are positioned between the levers 25 and the supports 24 and are pro-vided so that it is possible to vary the contact pressure of the bottom parts 19b against the oscillation-dampening covering 3 on the stressing bed 1.
Accordingly, it is possible to vary the oscillation behavior of the bottom parts 19b of the forms so that they enter into resonance with the vibration oscillations produced and the energy supplied for the consolidation of the concrete can be utilized in the most advantageous way.
While the ties are being poured in a working station, the framework 5 is locked in position relative to the tracks 4 by track clamps 28.
In the working station A, the framework 5 includes a working plat-form 29 for servicing thetop parts l9a of the forms, for example for cleaning and installing the track attachment part in the form. Working station A also includes sheet metal guide 30 for guiding the prestressing wires 2. In the working station C levers 31 are located on the framework 5 for Iifting the lower parts 20b of the form. The levers 31 are similar to the levers 25 and are oper-ated by cylinder-piston-units 32.
In carrying out the method of p~oducing the prestressed concrete ties in accordance with the present invention the method proceeds as follows:
In the operating procedure represented in Figure 1, the bottom parts l9b of the form have been placed on the oscillation-dampening covering 3 of the t 162~

stressing bed 1 and are pressed against the covering by the clamping lever 25, note Figu~e 2.
The bottom parts 19b of the form are filled with concrete from the charging hopper 12 which is movable over and across the stressing bed 1. The charging hopper 12 is open at the top and the bottom and is moved by a linkage 1~ over the bottom parts l9b. As the charging hopper 12 rolls over the tracks 15, the concrete is pushed over a sheet metal guide 15a. By moving the charging hopper 12 back and forth over the bottom parts 19b, the form parts are filled.
When the filling operation is completed, the charging hopper 12 returns to its initial position spaced laterally from the stressing bed and is refilled from the storage hopper 10. By switching on the vibators 22 on the bottom parts 19 for a short period, the concrete poured into them is preconsolidated.
A-fter such preconsolidation, the bottom parts l9b are completely filled and the charging hopper 12 is again returned to its starting position and the main consolidation step is carried out. The preconsolidation of the concrete makes it possible to vary the actual amount of concrete filled inb~
the form.
At the same time in the working station A, the necessary preparation of the top parts l9a of the form is carried out from the working platform 29.
Such form preparations include cleaning the top parts, spraying them with form oil, and placing the track fastening parts, which are to be encased in the concrete ties, in the top parts.
For the main consolidation operation, carriage 7 is driven along the framework 5 carrying the top parts l9a held by means of the coupling devices 18, into the working station B aligned over the bottom parts 19b of the form which have been filled with concrete. Top parts 19a are lowered by the cylinder-pis-ton-units 16 and pressed against the concrete in the bottom parts 19b. With the parts assembled together, the external vibrators 22 on the lower parts and _9_ ~ 1620~6 and the external vibrators 21 on the top parts are placed in operation.
By pressing the top parts l9a downwardly against the concrete in the bottom parts l9b, the surfaces 33 of the ties are formed with the track supports 35 located thereon. At this time, the track attachment parts are vibrated into the concrete forming the ties.
~ hen the desired consolidation of the concrete within the assembled form 19 has been acheived, the vibrators 21, 22 are turned off. Next, the top parts l9a are released from the coupling devices 18 on the carriage 7. The carriage 7 is driven to the next working station C and the coupling devices 18 are attached to the top parts 20a of the forms 20 which contain a tie that had just previously been poured. By operating the lever 31, bottom parts 20b are lifted slightly upwardly from the oscillation-dampening covering 3 until they are clear of the surfaces of the freshly poured concrete members, note Figure 3a. At this time, the catches 23 connect the bottom parts 20b to the top parts 20a of the form 20. The fastening means for the concrete-encased track attachment parts are detached and the entire form 20 is lifted upwardly, note Figure 3b. During the pouring procedure, the form 20 enclosing the previously poured concrete tie is not stripped until the pouring and consolidation of the concrete in the form 19 is completed. With the carriage 7 supporting the form 20, the framework 5 is moved to the right, as viewed in Figure 1, for a length of one working station, so that the middle portion of the framework 5 containing the working station B is positioned over free prestressing wires 2. At this point, carriage 7 supporting the form 20 is moved from the working station C
into the adjacent working station B and the form 20 is lowered onto the oscil-lation~dampening covering 3 of the stressing bed 1. By operating the clamping lever 25, the bottom parts 20b of the form 20 are pressed against the covering 3 and held in this position. Actually, the complete form 20 is positioned on the stressing bed, next, the catch 23 securing the top parts 20a to the bottom ~ 162~6 parts 20b is released. Top parts 20a held by thc coupling devices 18 on the carriage 7 are then moved into the working stat:ion ~ for cleaning and prepara-tion in the manner described above with regard to the top parts l9a of the form 19 which was previously poured.
The procedure for forming the ties is repeated in the same manner until the stressing bed is f:illed along its entire length with freshly formed ties 34. In accordance with the procedure of the present invention, it is as-sured that a freshly formed tie remains enclosed within its form until the next adjacent tie is constructed and it is only at that time that the previously formed tie is stripped.
In Figures 4a and 4b~ the form 20 is represented on a larger scale, in Figure 4a the form is shown in the empty condition without the top part 20a positioned on the bottom part 20b. In Figure 4b the form 20 has been complete-ly assembled and ;s filled with concrete 38.
In Figure 4a the empty bottom part 20b is shown with the attached external vibrators 22. Spaced upwardly from the bottom part 20b is the corres-ponding top part 20a. Secured to the top part 20a is the fastening means 36 for the track attachment part 37 which is to be encased in the concrete form-ing the tie. The track attachment part 37 can be a plastic corrugated dowel for a tie screw with which elastic and gauge-forming track attachment means can be attached on the prestressed concrete tie.
In Figure 4b a section is shown through the assembled form 20 filled with concrete 38, the form is made up of the top part 20a fitted downwardly onto the upper end of the bottom part 20b. At the upper end of the bottom part 20b, a vertical wall 20c extends along and in contact with a corresponding ver-tical wall 20d of the top part 20a. An inwardly facing bevel 39 is formed on the top part 20a. The concrete mass filled into the bottom part 20b is consol-idated, accordingly, it is possible that differences in the total height of the ~ 162036 tie may occur within acceptable tolerances. An exact transition from the top surface of the tie to its side surfaces is achieved so that each tie, in its upper region, has a vertical surface 40 of variable height formed by the cooper-ating vertical walls 20c, 20d on the bottom part 20b and top part 20a of the form 20.
Since air rises during the consolidation of the concrete in the bottom part 20b of the form, to assure that the surface 33 of the tie 34 is not very porous and unusable, the air must be able to escape or to be absorbed when the top parts 20a of the forms are placed on the bottom parts 20b. By inserting a covering 41 as the lower surface of the top part 20a, it is possible to absorb water and air with the covering being held by means of a vacuum or adhesion to the bottom side of the top parts 20a. The covering can be formed of paper or a textile material which is capable of affording the desired effect.
In the procedure described above and illustra~ed in Figures 1-4, the prestressed concrete ties are produced in the normal use position by utili~ing the method and/or apparatus of the present invention~ it is also possible to construct such ties in the inverted position. Similarly, other prefabricated prestressed concrete parts suitable for continuous production along a stressing bed can be formed. A form suitable for producing ties in the inverted position is represented in Figure 5. In Figure 5a, a tie 44 is shown in section before the bottom part 42a is stripped while in Figure 5b the tie 44 is shown with the bottom part 42b stripped away from the tie.
The form 42 displayed in Figure 5 is made up of the two bottom parts 42a, 42b which only serve to form the side walls 43 of the tie 44. The top surface 45 of the tie, the bottom surface as viewed in the drawing, is shaped by means of a profiled base 46 which rests on the oscillation-dampening cover-ing 47 which covers the stressing bed 48. In place of the top parts described in the other forms, in form 42 a plate 4~ acts as a surcharge on the top of the 1 1620~6 concrete. In the condition shown in ~igure 5b, the bottom part 42b has been stripped from the tie 44.

~ 1-3 -

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of manufacturing prefabricated prestressed concrete members having an immediate bond, such as prestressed concrete ties, including providing a form for shaping the concrete members to be manufactured, with each form made up of at least a first form part and a separate second form part, on an elongated stressing bed and arranging the forms in one or more side-by-side rows extending in the elongated direction of the stressing bed, positioning prestressing members extending along the elongated direction of the stressing bed, arranging a first working station followed by a second working station and then by a third working station extending in the elongated direction of the stressing bed, with the third working station containing a previously poured and cosolidated concrete member within the assembled form, and moving the forms along the stressing bed between working stations, wherein the improve-ment comprises arranging the working station to be movably displaceable in the elongated direction of the stressing bed, placing a first form part on the stressing bed in the second working station, filling the first form part with concrete and vibrating the first form part for consolidating concrete therein, removing the second form part corresponding to the first form part from the first working station to the second working station and attaching the second form part to the first form part, vibrating the assembled first and second form parts, moving into the third working station and removing the form from the previously poured from located therein and moving the previously poured from relative to the stressing bed and placing the previously poured form on the stressing bed so that the previously poured form is in the second working station and the subsequently poured form is in the third working station.

2. A method, as set forth in claim 1, including the steps of posi-tioning the second form part in the first working station, and preparing the second form part for placement on the first form part.

3. A method, as set forth in claim 2, including the steps of securing track attachment parts to the second form part in the first working station and, after placing the second form part on the first form part, pres-sing the track attachment parts into the concrete poured into the first form part.

4. A method, as set forth in claim 1 or 2, including the steps of vibrating the first form part for effecting a preconsolidation of the concrete poured into the first form part and, after placement of the second form part on the first form part, vibrating both parts of the form for effecting a final consolidation of the concrete poured into the form.

5. A method, as set forth in claim 1, including forming the concrete member in the inverted position relative to the normal position of the member when it is used.

6. Apparatus for manufacturing prefabricated prestressed concrete members having an immediate bond, such as prestressed concrete ties, comprising an elongated stressing bed, means arranged to be supported on said stressing bed for forming the concrete members, said means including at least a first form part and a second form part, said form parts arranged to extend in one or more side-by-side rows in the elongated direction of said stressing bed, a framework extending in the elongated direction of said stressing bed and said framework having a first end and a second end spaced apart in the elon-gated direction of said stressing bed, a portal-like frame at each end of said framework, with said portal-like frame extending transversely across and over said stressing bed, said framework being movably displaceable over said stressing bed in the elongated direction thereof, said framework having at least two adjacent working stations therein located above said stressing bed and each said working station extending in the elongated direction of said stressing bed, a carriage mounted on said framework and movable thereon in the elongated direction of said stressing bed, a lifting device supported on and extending downwardly from said carriage over said stressing bed and arranged to be connected to said second form part so that said second form part can be moved upwardly and downwardly relative to said stressing bed and also moved in the direction of said stressing bed, and coupling means on said lifting device for connecting said second form part with said lifting device.

7. Apparatus, as set forth in claim 6, wherein said lifting device includes cylinder-piston-units connected to said coupling means for lifting and lowering said coupling means.

8. Apparatus, as set forth in claim 6, wherein at least two said forms are positionable alongside one another in side-by-side relation on said stressing bed, and means are provided for connecting said side-by-side forms with said means extending transversely of the elongated direction of said stressing bed.

9. Apparatus, as set forth in claim 8, wherein clamping devices are mounted on said framework for clamping said first form parts onto said stressing bed.

10. Apparatus, as set forth in claim 9, wherein means are mounted on said framework in spaced relation to said clamping means for lifting said first form parts upwardly from said stressing bed.

11. Apparatus, as set forth in claim 10, wherein said means for lifting said first form parts comprises lever-like devices for engagement with said first form parts.

12. Apparatus, as set forth in claim 6, wherein an oscillation-dampening ring is provided over said stressing bed so that said first form parts are supported on said oscillation-dampening covering.

13. Appartus, as set forth in claim 6, wherein means are mounted on said framework for charging concrete into said first form part mounted on said stressing bed.

14. Apparatus, as set forth in claim 13, wherein said means for pouring concrete includes a storage hopper for storing concrete, said storage hopper having an openable bottom, and a charging hopper is located below said openable bottom and arranged to receive concrete therefrom so that the con-crete can be poured from said charging hopper to said first form part.

15. Apparatus, as set forth in claim 14, wherein said means for pouring concrete includes means for moving said charging hopper over said stressing bed transversely of the elongated direction thereof, said storage hopper being located along one side of said stressing bed, and said means being arranged to move said charging hopper from below said storage hopper across said stressing bed for filling concrete into said first form parts.

16. Apparatus, as set forth in claim 6, wherein said framework forms three said working stations, one following the other in the elongated direction of said stressing bed, a first said working station being arranged for preparing said second form parts, a second said working station being adjacent said first said working station and said second said working station being arranged for pouring concrete into said first form part, and the third said working station being arranged to receive a previously poured concrete member held within said first and second form parts.

17. Apparatus, as set forth in claim 6, wherein said first said form part is open at the upper end thereof, said second said form part being insert-able into the upper end of said first form part for support therein on the concrete poured into said first said form part.

18. Apparatus, as set forth in claim 16, wherein said first form part has vertically extending walls as the upper end thereof and said second form part has vertically extending walls disposable in sliding contact with said vertical walls of said first said wall part so that the height of the concrete member formed in said first and second form parts is adjustable in the range of said vertical walls of said first and second form parts.