APPARATUS FOR FABRICATION OF CONCRETE BEAMS

Abstract: The invention concerns a method and an apparatus for fabrication of concrete beams. The invention also concerns a beam construction. According to the invention, the concrete beams (14) are manufactured using a slip-form casting machine mounted stationary on a casting bed such as to make the feed pressure of the concrete propel a mold construction (3, 4) with the concrete extruded into the mold along the casting bed (2). The beam construction in accordance with the invention integrates a part of the mold (3, 4) as an integral reinforcing structure of the beam. Beams fabricated in accordance with the invention are compliant as to their thickness with conventionally used slab constructions.

Description: The present invention relates to a slipforming extruder for the implementation of a method for fabrication of concrete beams. The method and the device are based on those disclosed in AT-B-156911 and GB-A-984389. AT-B-156911 discloses a method of and a device for manufacturing concrete beams, in which at least a part of the casting mold structure corresponding to each beam remains as an integral part of the reinforcement of the beam, whereas GB-A-984389 discloses a method of and a device for casting concrete products, in which the casting mold structure comprises at least two parts, this mold being movable relative to a stationary casting bed as well as to feeding and compaction means and being propelled together with the fed concrete relative to the casting bed by the feeding pressure of the concrete mix. Up to now, production methods for fabrication of structural concrete elements have been characterized by a high volume of manual labor required and large variations in element design. Industrial scale mass-produced products, such as hollow-cored slabs, have been lacking from the marketplace. Also steel elements are used as frame constructions. The most frequently applied method of conventional technology applied in the production of pillars and beams has been mold casting in which the pillars and beams are cast into individually fabricated wooden or steel molds. The molds are almost invariably placed horizontally and casting is made, using a relatively fluid mix of concrete, by feeding the fluid mix from a hopper under manual control into the mold, whereupon the cast mix is vibrated by high-frequency vibrators that may be either manually operated or permanently mounted to the molds. Prior to casting, frogs and brackets are prepared into the molds. Further, any specific additional reinforcement required by the element design is preplaced into the molds. Disadvantages of prior art technology include, i.a., the necessity of using fluid mix due to the undeveloped compaction techniques. This results in both an increased hardening time and, moreover, a higher consumption of cement in order to achieve a high final strength. The reinforcement operation involves a high proportion of manual skills as well as the fabrication of molds. Bracket constructions required to form element frogs require a high amount of manual work on the molds in addition to the extra reinforcements required. Conventional production techniques are also inferior in fulfilling needs for dedicated design and production. The aim of the present invention is to overcome the disadvantages associated with the aforedescribed prior art technology, while being based, as already stated above, on fabricating beams with help of a stationary slipforming extruder into a desired mold in a continuous horizontal slip-form casting process by incorporating the casting mold into an integral part of the cast beam structure, which thus is formed into a composite structure. An advantageous casting method is implemented using extremely stiff concrete mix compacted by a shear compaction method, thereby disposing of the need of conventional high- frequency vibrators. More specifically, an apparatus in accordance with the invention is defined by the subject matter stated in the unique claim appended to this disclosure. The invention provides outstanding benefits. Implementation of the invention makes it possible to produce individually designed products on a production line equipped with automated manufacturing technology. Thus, each mold may be individually designed as to its shape, surface details, and dimensions. Since the production is implemented in a continuous slip-form casting method to produce long elements, the final products may be fabricated by cutting the hardened product, e.g., with a saw, to desired length. Due to the efficiency of the shear compaction method and use of extremely stiff concrete, pillars and beams fabricated according to the invention are of remarkably higher strength compared with those manufactured according to the prior art. Instead of the conventionally applied strengh grades of 20... 50 MN/m², grades up to 50... 150 MN/m² are achieved. Correspondingly, products manufactured in accordance with the invention are essentially thinner than those of conventional technology. Prestressing tendons are placed in a hollow-cored section of the concrete construction and their tensioning force is backed by an already hardened concrete. Consequently, stress losses in the tendons remain minimal. By virtue of the present invention, the manufactured products are of extremely high strength and accept, when required, relatively high stress forces and quantities of tensioning tendons. In the following, the invention is examined in detail with help of the attached drawings illustrating embodiments of the invention. Figure 1 shows a side view of a slipforming extruder and postprocessing apparatus in accordance with the invention. Figure 2 shows in detail a longitudinally sectional side view of the slipforming extruder illustrated in Fig. 1. Figure 3 shows a cross-sectional front view (from the direction of the beam) of the slipforming extruder illustraded in Fig. 1 and, particularly, a mold construction in accordance with the invention. Figure 4 shows a cross-sectional front view (from the direction of the beam) of a slipforming extruder illustrated in Fig. 1 and another mold construction in accordance with the invention. Figure 5 shows a detailed perspective view of the mold construction illustrated in Fig. 3 together with its clamping mechanism. Figure 6 shows a front view of an alternative mold construction. Figure 7 shows a lower mold construction in accordance with the invention. Figure 8 shows a side view of a method for connecting a beam construction in accordance with the invention to a pillar construction. Figure 9 shows a section A-A of Fig. 8. Figure 10a... 10e show another method for jointing a beam construction in accordance with the invention to a pillar construction. Figure 11 shows a side view of an apparatus in accordance with the invention for fabrication of beams. Figure 1 illustrates a typical beam extruder for fabrication of a continuous beam structure in a horizontal slip-form casting process. The apparatus comprises a stationary casting station 1 resting on a floor 2 of an industrial hall. In contrast, mold parts 3 and 4 are movable upon the hall floor 2 during the casting process. The actual casting process is started when a concrete mix feeding hopper 5 of the extruder 1 is filled with stiff mix 6. Then, the first auger 7 of the extruder 1 is started into rotation, driven by a rotational drive motor 8, and commences feeding the mix towards a rear part 9 of the extruder, where the actual formation and compaction of the continuous beam takes place. The final compaction of mix takes place in the rear part 9 of the extruder 1 with help of a second feeding/compacting auger (not shown). The second auger is rotated by the same drive motor 8 as the first auger 7. The second auger flight is rotated and subjected to a longitudinal reciprocating movement by means of an eccentric drive motor 10. When the second auger (called the extruder auger) forces the stiff mix into a closed mold space 3, 4 while simultaneously performing a longitudinal movement of compacting action, the stiff mix is compacted in a continuous slip-form casting process into a desired shape. The auger is followed by a tubular extension mandrel (not shown) that promotes further compaction and creates a duct in a desired location of the continuous beam structure. The duct may later be utilized for insertion of reinforcement steel tendons. The movement and shape of the mandrel may be adapted to achieve a desired shape of the duct, which provides at a later state an improved adhesion of injected concrete to the concrete of the beam. The actual lower part of the mold for the beam in the continuous slip-form casting is provided by a module-dimensioned steel plate 3, profiled in the desired shape of the beam structure's bottom surface. Correspondingly, the other part of the mold forming the upper part is provided by a steel plate 4 profiled in an equal manner. During the continuous slip-form casting process, the steel parts 3 and 4 of the mold are clamped together either before the extruder station 1 or underneath it so that the clamping is performed by means of quick-mounting clamps (not shown) before reaching the actual casting point. The steel upper part 4 of the mold, which is profiled to the shape of the beam's upper surface, is assembled above the extruder 1 before reaching an actual compaction point 9. The lower part 3 of the mold and the upper part 4 of the mold are later clamped together by quick-mounting clamps to be described later so as to form a tight, continuous tubular space about the second auger of the extruder. Concrete mix is slip-form cast into the tubular mold space by extrusion with help of the auger in a continuous slip-form casting process so that the mix is compacted into a shape determined by the lower and upper mold structures whereby the cast structure glides forward in the form of a continuous, integral, cast combination mold/beam construction supported by separate bearing blocks 11 mounted on a casting bed 2. The moving of the beam on the casting bed 2 is actuated by the back pressure exerted by the second auger of the extruder. Furthermore, when required, the glide movement actuating force may be increased by supplying an auxiliary force of, e.g, constant speed or constant force into the steady movement of the continuous beam by means of, e.g., pulling actuators placed between the mold bed and the beam structure. After the actual casting operation, a protective shield in the form of a blanket (not shown) can be extended over the integral cast beam structure in order to protect the casting bed from heat losses during heat treatment. According to Fig. 1, the dismantling of individual elements is started by first folding the protective blanket away from above the mold structures to allow dismantling of the mold structures 3 and 4. Dismantling is done by removing the quick-mounting clamps and then stripping the upper part 4 of the mold, which is transferred to the vicinity of the extruder 1 for reuse. Correspondingly, the lower part 3 of the mold is stripped in a recess 12 located in the casting bed 2. If the upper or lower part of the mold is to remain an integral part of the final structure of the beam, then this mold part will not be dismantled at this stage from the concrete section of the beam structure. After hardening of concrete, the elements are cut into individual products to customer specifications by means of a cutting saw 13. Following the cutting operation, elements 14 can be transferred by means of a separate clamping hoist 15 to an intermediate storage. Figure 2 illustrates in detail the construction of the extruder 1. As shown, a second auger 16 together with its tubular extension mandrel is arranged to form an extension of a first auger 7 on the same drive shaft. A possible adaptation of the augers is to provide independent operation of the augers by powering them with separate drive motors. An eccentric drive motor 10 is connected by a lever 18 to the drive shaft of the augers 7 and 16 in order to achieve a reciprocating motion of the augers. Figure 3 illustrates a mold construction 3 and 4 of circular cross-section. Figure 4 illustrates a mold construction 3 and 4 of square cross-section. Figure 5 illustrates in detail the mold construction 3 and 4 of circular cross-section. The upper mold part 4 of a semi-circular cross-section includes flanges 19 extending in the direction of the mold's longitudinal axis and protruding radially outward at the ends of the semicircle. In additon, the upper mold part 4 has a seal lip 22 extending marginally over the flanges 19. Correspondingly, the lower mold part includes axially aligned, radially protruding flanges 20 and a groove 21, close to the corners of flanges 20, designed to mate with the seal lip 21. The mold parts are clamped on both sides with help of clamps 23, which can be, e.g., spring clamps. Figure 6 illustrates another preferred mold construction. Here, the lower mold part 3 is a planar plate, which rests on chains 24 of a chain conveyor while the chains 24 are gliding in chain troughs on the upper surface of the bed 2. The lower mold part carries the U-shaped upper mold part 4 incorporating clamping flanges 26. Figure 7 illustrates a U-shaped lower mold part 3, analogous to that of the embodiment illustrated in Fig. 6. Figures 8 and 9 illustrate the construction of a beam-to-pillar joint. Beams 36 are jointed to each other across a pillar 37 by bolting the beams to plates 38 embracing the pillar 37, with help of tensioned frictional bolts 39 extending through the beam. An alternative method for jointing the beams to the pillar is illustrated in Figs. 10a... 10e. The beam 36 is cut to a predetermined length in accordance with Fig. 10a so that the shell part 4 of the beam is flush with the beam end. According to Fig. 10b, a jointing plate 41 whose outer dimensions exceed those of the beam cross-section is welded to the end of the beam 36. The center of the jointing plate 41 is provided with a opening 42 for the pillar console and with holes 43 at the corners for securing bolts. The beam end is worked to have a recess compatible with the opening 42. The jointing plate 41 is also provided with a tube 48 which is inserted into a cavity 30 of the beam 36 in the installation phase. An advantageous length of the tube 48 is about 200... 500 mm. The joint of the cavity 30 and the tube 48 may be bonded by, e.g., grouting or epoxy resin. Illustrated in Fig. 10d is a side view of the jointing of the beams 36 to the pillar construction illustrated in Fig. 10c. The beams 36 are supported on a pillar console 44 of the pillar 37 by the opening hole 42 of the jointing plate 41, and the beams are jointed to each other across the pillar 37 by bolting the beams to the jointing plates 41 at both sides of the pillar with bolts 45. Mounting tolerances may be taken into account in the construction by using spacers 46 inserted between the beams 36 and the pillar structures 37. Figure 10e illustrates the pillar-beam joint viewed from the direction of the beam 36. The spacers 47 are installed between the pillar console 44 and the jointing plate 41. Figure 11 illustrates an alternative arrangement for fabrication of beam elements in accordance with the invention. Steel plate profiles 59, manufactured by, e.g., rolling from thin plate material, are placed on supports 61 on an elongated casting bed 60 so that the profiles 59 are displaced positively free from the casting bed 60. The thin-plate profiles 59 may be selected to be of a constant or modular length, e.g, as of 10... 12 meters. The length of the profiles 59 may go up to 20 meters, with the only limitation being principally dictated by the desired transportation and handling length. Furthermore, the steel profiles 59 may be joined together on the casting bed by welding into a continuous length profile that extends from one end of a long casting bed to the other end reaching lengths up to 50... 150 meters. Next, pretensioning tendons 67 are inserted in the steel profiles 59 and tensioned with a pretensioning apparatus 62 against prestressing anchor posts 63. Intended sawing points 64 of the beams may be complemented with a separate clasping reinforcement 65, which accepts cleaving stresses induced at the beam end by the prestressing tendons. The clasping reinforcements 65 may be inserted by 1... 3 pieces in the vicinity of each cutting point. Next to the insertion of the reinforcements, the mold construction 59 may be filled using any conventional casting method by feeding the concrete mix into the mold, vibrating the mix, and finally trowelling the upper surface of the cast concrete. After these operations, the cast concrete is covered by a protective blanket and heat cured until a sufficient release strength is achieved. The elements are cut to desired lengths while elevated on the supports 61, using a separate cutting saw 66 which is capable of sawing both the steel mold part, the prestressing tendons, and the cured concrete in one operation. Due to the supports 61, damage to the casting bed 60 is avoided during sawing. After cutting, the fabricated elements are ready for delivery to the construction site for installation.

Claims: 1. An apparatus for fabrication of concrete beams, comprising: a mold (3, 4) of a closed construction, feeding means (7) for feeding concrete mix into the mold (3, 4), and compaction means (16) for compacting the concrete mix fed into the mold (3, 4), wherein: the feeding (7) and compaction (16) means are mounted on a stationary bed (2), and the mold (3, 4) is arranged movable relative to the casting bed (2) and the feeding (7) and compaction (16) means, said apparatus being characterized in that the lower part (3) of the casting mold is arranged to rest on a chain conveyor (24, 25).

Inventors: TOMMINEN, HANNU
Applicants: LOHJA PARMA ENGINEERING LPE OY
Application year: 1988
Main classification: B28B23
IPC codes: B28B3, B28B23, B28B1, B28B19