CONCRETE PIPE WITH STEP

Abstract: A concrete pipe with a step is provided wherein a step member in the form of a straight bar can be supported directly, readily and with certainty on a cylindrical face of a concrete pipe without provision of any swollen portion on an inner wall face of the concrete pipe. An inner wall face (2) of a concrete pipe (1) is formed as a cylindrical face having no projection thereon but having a pair of left and right blind holes (3, 4) formed in an opposing relationship thereon, and at least one groove (5) is formed horizontally along the cylindrical inner wall face (2) contiguously at a rear end thereof to the hole (4). A step member (7) is in the form of a straight bar having a length corresponding to the length of a straight line interconnecting the left and right holes (3, 4) and has a projection (8) formed at least at one end thereof such that it extends in a direction intersecting an axial line of the step member (7) and can be removably fitted into the groove (5) when it is directed horizontally but can be fitted into the hole (4) at the rear end of the groove (5) only by way of the groove (5) when it is turned around the axial line of the step member (7). The step member (7) has a locking member (9) attached thereto for removably fitting in the groove (5).

Description: This invention relates to a concrete pipe for use in a vertical position with a step wherein a step member is attached to an inner wall face of said concrete pipe. Conventionally, a concrete pipe for a manhole which is employed commonly has a U-shaped step member, the opposite end portions of which are embedded into and fixed to the concrete pipe upon molding of the concrete pipe. An example of apparatus for forming such concrete pipe is disclosed, for example, in European Patent No. 0160170. As can be seen from the disclosure, an apparatus for fixing a step member upon molding of a concrete pipe is very complicated in structure and requires a large number of manhours for the production of a concrete pipe, and consequently, a high cost is required for the apparatus and also for the formation of a concrete pipe. Further, with a concrete pipe to which a step member is fixed in this manner, even if the step member is corroded, replacement only of the step member is actually impossible after installation of the concrete pipe. Also a method of attaching a step member after formation of a concrete pipe has been put into practical use. According to the method, at least one pair of through-holes are formed in a wall of a concrete pipe upon molding of such concrete pipe, and after molding of the concrete pipe, the opposite end portions of a U-shaped step member are inserted into the through-holes from the inside of the pipe, whereafter cement is filled into gaps of the step member in the holes and a pair of nuts are screwed to threaded portions of the opposite end portions of the step member outside the pipe to fix the step member to the concrete pipe. With a concrete pipe having a step member fixed thereto in this manner, however, since the opposite end portions of the step member extend through the through-holes of the concrete pipe, cement filled in the gaps of the holes and the concrete of the pipe around the holes likely suffer from cracking. If such crack takes place, then such problems will arise that the step member comes off readily and is likely corroded by ground water admitted into the concrete pipe through the crack. Therefore, it is dangerous if the step member is not replaced in a comparatively short period of time. However, since a step member must be fixed to the concrete pipe by means of nuts on the outside of the pipe, such replacing operation is not easy. A concrete pipe which eliminates such drawback as described above is disclosed, for example, in Japanese Utility Model Publication No. 20846/1979. In the disclosed concrete pipe, a pair of left and right vertically elongated swollen portions each having a downwardly bent groove formed on a vertical face thereof are formed on an inner wall face of the concrete pipe, and the opposite end portions of a step member in the form of a straight bar are inserted into the grooves of the left and right swollen portions until they reach blind or lower ends of the grooves and are then fixed to the swollen portions of the concrete pipe with a calking material. With such concrete pipe, replacement of the step member can be performed comparatively readily in the inside of the concrete pipe. However, the concrete pipe has the following drawbacks. Since a pair of left and right vertically elongated swollen portions each having a bent groove formed therein must be formed on the inner wall face of the concrete pipe, molding of the concrete pipe is difficult and the structure of a form is complicated. further, since the inside spacing of the concrete pipe is limited by the left and right swollen portions, upward and downward movement of an operator or a tool or the like in the pipe is restricted particularly where the diameter of the pipe is decreased toward an upper end of the pipe in a tapered profile as in the case of a concrete pipe which is used at an uppermost location of a manhole. However, if the amount of projection of the swollen portions into the inside of the pipe is decreased, then the swollen portions themselves will be reduced in thickness, which allows the swollen portions to be damaged readily, and besides, the thickness of portions of the concrete pipe between the bent grooves and the vertical surfaces of the swollen portions is reduced, which allows the portions to be damaged readily by a load applied to the step member. It is an object of the present invention to provide a concrete pipe with a step wherein a step member in the form of a straight bar can be supported directly on a curved face of a concrete pipe without provision of any swollen portion on an inner wall face of the concrete pipe and accordingly the concrete pipe can be molded very easily and the step can be replaced easily. It is another object of the present invention to provide a concrete pipe with a step wherein a step member can be held with certainty on an inner wall face of a concrete pipe. In order to attain the objects, in a concrete pipe for use in a vertical position with a step according to the present invention, an inner wall face of a concrete pipe is formed as a cylindrical face having no projection thereon but having a pair of blind holes formed in an opposing relationship at left and right portions thereof, and at least one groove defining a first and second end is formed on and extends horizontally along the cylindrical inner wall face of the concrete pipe in a contiguous relationship at said first end to one of the holes. A step member is in the form of a straight bar having a length corresponding to the lenght of a straight line interconnecting the holes at the left and right portions of the cylindrical inner wall face of the concrete pipe and has a projection formed at least at one end such that the projection extends in a direction intersecting an axial line of the step member and can be removably fitted into the groove when it is directed horizontally but can be fitted by way of the groove into the hole contiguous to said first end of the groove when it is turned around the axial line of the step member. The step member has a locking member attached thereto for removably fitting in the groove. The step member is received onto the inner wall face of the concrete pipe by inserting the opposite ends thereof into the holes at the left and right portions of the inner wall face. In this instance, the projection provided at the end of the step member can be inserted into the hole contiguous to the groove only by way of the groove. If the projection is turned around the axial line of the step member at the first end of the groove and fitted into the hole contiguous to the groove and then the locking member is fitted into the groove, then the projection of the step member is restricted within the hole. Further, since the step member has a length corresponding to the length of the straight line interconnecting the left and right holes, it cannot be moved in the axial direction with respect to the left and right holes, and after the locking member is fitted into the groove, the step member is locked with respect to the left and right holes and restricted from movement in any direction. The thus locked step member can be removed from the left and right holes by removing the locking member from the groove and then turning the projection back to the direction of the groove. Since the locking member is attached to the step member, there is no possibility that it may be lost inadvertently, and it can be handled conveniently for the storage and transportation. Where the groove is provided at only one of the left and right portions of the inner wall face of the concrete pipe, the projection is provided at only one end of the step member, and the other end of the step member is formed as a mere straight end so that it is inserted directly into the other hole. Where the groove is provided on each of the left and right portions of the inner wall face of the concrete pipe, the projection is provided at each of the opposite ends of the step member, and a pair of such locking members are provided on the step member so that the step member may be locked similarly on the left and right portions of the inner wall face of the concrete pipe. The locking member may be mounted for sliding movement in an axial direction on the step member in order to facilitate replacement of the step member.. The locking member may be formed from a resilient material and fixed to an end of the step member such that, when the projection is fitted into the hole contiguous to the first end of the groove, the locking member is resiliently contacted with the groove to restrict the projection within the hole. The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings. FIG. 1 is a horizontal sectional view of part of a concrete pipe for use in a vertical position having a locking member mounted on a step member showing a first preferred embodiment of the present invention; FIG. 2 is a perspective view showing part of the step member of FIG. 1 together with a hole and a groove of the concrete pipe; FIGS. 3 to 5 are perspective views showing different steps of a process of attaching the step member to the concrete pipe of FIG. 1; FIG. 6 is an enlarged sectional view showing the step member of FIG. 1 in a locked condition; FIG. 7 is a horizontal sectional view of part of a concrete pipe including a step member having a pair of left and right locking members attached thereto showing a second preferred embodiment of the present invention; FIG. 8 is an enlarged sectional view taken along line X-X of FIG. 7; FIG. 9 is a horizontal sectional view of part of a concrete pipe including a step member having a resilient locking member attached to an end thereof showing a third preferred embodiment of the present invention; FIG. 10 is an enlarged sectional view taken along line Y-Y of FIG. 9; FIGS. 11 to 14 are perspective views showing different steps of a process of attaching the step member to the concrete pipe of FIG. 9; FIG. 15 is a sectional view showing a lining material disposed in a hole of a concrete pipe; FIG. 16 is a vertical sectional view of a manhole which employs a concrete pipe with a step according to the present invention; FIG. 17 is a vertical sectional view of a molding apparatus for molding a concrete pipe; and FIG. 18 is a horizontal sectional view of part of the forming apparatus of FIG. 17. Referring first to FIG. 1, there is shown a concrete pipe according to a first preferred embodiment of the present invention and for use in a vertical position. The concrete pipe 1 is molded in a cylindrical shape and has a cylindrical inner wall face 2 having a circular shape in plan and having no inner projection thereon. A pair of left and right holes 3 and 4 are formed, upon molding of the concrete pipe 1, in an opposing relationship to each other at the same height in a region of the inner wall face 2 of the concrete pipe 1 which is smaller than a half circle in plan. Further, a groove 5 is formed, similarly upon molding of the concrete pipe 1, contiguously to the right-hand side hole 4 at a right-hand side cylindrical face portion in FIG. 1 of the region of the cylindrical inner wall face 2. While the holes 3 and 4 and groove 5 are shown provided by one set in FIG. 1, the concrete pipe 1 actually has a plurality of sets of such elements provided in a predetermined spaced relationship in a vertical direction, that is, an axial or longitudinal direction thereof. While the left-hand side hole 3 has a mere circular shape and is provided independently, the right-hand side hole 4 has an obliquely rather elongated elliptical face as seen in FIG. 2 and connects to first end of the groove 5 having a second end opposite the first end. Preferably, the inclination angle of the hole 4 is smaller than 45 degrees with respect to a horizontal plane. The groove 5 extends laterally along the cylindrical inner face 2 in a rather downwardly inclined relationship toward the hole 4 while the hole 4 is depressed at said first end of the groove 5 such that a stepped portion 6 is formed on the boundary between a lower side inner face of the hole 4 and a lower side inner face of the groove 5. A step member 7 is in the form of a straight bar having a length equal to the length of a straight line interconnecting the left and right holes 3 and 4 so that it may be supported linearly and horizontally between the holes 3 and 4. The step member 7 shown in FIGS. 1 and 2 is formed from a round metal bar having a righth-hand end portion bent laterally therefrom and covered over the overall length thereof with a plastic film not shown. The step member 7 has a projection 8 formed only at the right-hand end thereof. The projection 8 extends in a direction intersecting an axial line of the step member 7 and is dimensioned and shaped such that it may be fitted closely in the right-hand side hole 4 of the concrete pipe 1. Since the length of the step member 7 is equal to that of the straight line interconnecting the left and right holes 3 and 4 as described above, the opposite left and right end portions of the step member 7 cannot be inserted into the left and right holes 3 and 4 at a time. Accordingly, in order to insert the opposite left and right end portions of the step member 7 into the left and right holes 3 and 4 of the concrete pipe 1, the left end portion of the step member 7 is first inserted into the left-hand side hole 3 as shown in FIG. 1, and then the projection 8 at the right end of the step member 7 is directed horizontally, whereafter the step member 7 is moved rearwardly to insert the projection 8 thereof into the groove 5 and is then moved obliquely downwardly from the first end of the groove 5 until the projection 8 is inserted into the right-hand side hole 4. A locking member 9 molded as a unitary member from a plastic material is mounted for sliding movement in the axial direction on and pivotal motion around the step member 7. The locking member 9 has a cylindrical sleeve 10 through which the step member 7 extends, a block 11 having such a size as to allow the same to be removably received in the groove 5, and a flange 12 provided on a circumferential edge of a side face of the block 11. The block 11 and flange 12 are both inclined with respect to the axial line of the step member 7 while a base end face of the block 11 is formed as such an inclined face 13 as shown in FIG. 6. The locking member 9 can be mounted onto the step member 7 from the left end of the latter. The step member 7 is received in the following manner into the left and right holes 3 and 4. The left end portion of the step member 7 is first inserted into the left-hand side hole 3 as shown in phantom in FIG. 1, and then the projection 8 thereof is directed horizontally and inserted into the groove 5 until it comes to the first end of the groove 5 as shown in FIG. 3, whereafter the step member 7 is turned around its axis to direct the projection 8 obliquely downwardly as shown in FIG. 4 so as to fit the projection 8 into the hole 4. Subsequently, the locking member 9 is moved slidably along the step member 7 toward the projection 8 to fit the block 11 into the groove 5 until the flange 12 is contacted with and stopped by the inner wall face 2 of the concrete pipe 1. When the block 11 is in such fitted position, the inclined face 13 thereof engages with a side face of the projection 8 received in the hole 4 so that the projection 8 is restricted within the hole 4 by the locking member 9. Accordingly, the step member 7 is prevented not only from moving in the axial direction and in the forward and backward directions but also from turning around its axis, and it is kept with certainty in the left and right holes 3 and 4. It is to be noted that, if necessary, a gap which may appear between the left end portion of the step member 7 and a wall of the hole 3 or between the locking member 9 and a wall of the groove 5 is filled suitably with a calking material such as mortar or a plastic to make such keeping of the step member 7 further sure. Preferably, the sleeve 10 of the locking member 9 is reduced in size as small as possible so that the extent over which it is projected inwardly from the inner wall face 2 when the block 11 is fitted in the groove 5 is minimized. The step member 7 may be in the form of a square bar or may not be covered with a plastic. Referring now to FIGS. 7 and 8, there is shown a concrete pipe according to a second preferred embodiment of the present invention. The concrete pipe of the present embodiment also denoted at 1 is a modification to the concrete pipe 1 of the first embodiment described hereinabove and is different in the following points from the concrete pipe 1 of the first embodiment. In particular, such projection 8 as in the first embodiment is provided at each of the opposite left and right ends of the step member 7, and a pair of left and right locking members 9 are mounted in the opposite directions to each other on the step member 7. Meanwhile, a hole 4 and a groove 5 similar to the hole 4 and groove 5 of the concrete pipe 1 of the first embodiment are provided on the opposite left and right portions of the cylindrical inner wall face 2 of the concrete pipe 1. In the case of the concrete pipe 1 of the present embodiment, the projections 8 at the opposite left and right ends of the step member 7 are fitted into the left and right holes 4 by way of the left and right grooves 5 and then the blocks 11 on the left and right locking members 9 are fitted into the left and right grooves 5 to lock the left and right ends of the step member 7, respectively, in a similar manner as in the first embodiment. Since the projections 8 are provided at the opposite left and right ends of the step member 7 in the present embodiment, if the sleeve 10 of each of the locking members 9 is formed so as to have a perfect cylindrical shape as in the first embodiment, then the locking members 9 cannot be mounted on the step member 7, and accordingly, a cutout portion 10a is formed on the sleeve 10 of each of the locking members 9 as shown in FIG. 8 so as to allow mounting of the locking member 9. If the flanges 12 of the locking members 9 extend comparatively long, then openings of the holes 4 and grooves 5 can be closed up with the flanges 12 as seen in FIG. 8. Referring now to FIGS. 9 to 14, there is shown a concrete pipe according to a third preferred embodiment of the present invention. The concrete pipe of the present embodiment is also denoted at 1 and is another modification to the concrete pipe 1 of the first embodiment described hereinabove. The concrete pipe 1 of the present embodiment is different from the concrete pipe 1 of the first embodiment principally in that a projection 14 at the right-hand end of a step member 7 in the form of a round bar is formed by merely bending a right end portion of the step member 7 laterally into an L-shape, and a resilient locking member 15 is securely mounted on the projection 14. The right-hand side hole 4 formed on the inner wall face 2 of the concrete pipe 1 is further elongated comparing with that in the first embodiment so as to allow the projection 14 of the step member 7 to be fitted into the hole 4. The locking member 15 is formed from hard rubber or a metal plate having suitable resiliency and has a base end portion adhered by a bonding agent or welded to an outer periphery of the projection 14 such that most part thereof is projected substantially straightforwardly from an end of the projection 14. A notch or depression 16 is formed on the locking member 15 so as to permit the locking member IS to be bent with respect to the end of the projection 14. With the concrete pipe of the present embodiment, the step member 7 is received in the following manner into and between the left and right holes 3 and 4. The left end portion of the step member 7 is first inserted into the left-hand side hole 3 as shown in phantom in FIG. 9, and then the projection 14 is directed horizontally and inserted into the groove 5 until it comes to the first end of the groove 5 as shown in FIG. 11, whereafter the step member 7 is turned forcibly around its axis to fit the projection 14 in an upwardly directed condition into the hole 4 as shown in FIGS. 13 and 14 while resiliently bending the locking member 15 at a portion around the notch 16 as shown in FIG. 12. After the projection 14 is put into the thus fitted condition, the locking member 15 is returned into an original condition due to its resiliency thereby to press against an upper side inner face of the first end portion of the groove 5 to restrict the projection 14 in the hole 4 as shown in FIG. 10. In order to assure such restricting condition of the locking member 15, a stepped portion 17 may be provided on the upper side inner face of the first end portion of the groove 5. It is to be noted that, in the case of the concrete pipes of the first and third embodiments, a cap-shaped lining member 18 made of a metal or plastic material may be embedded, upon molding of the concrete pipe, in the inside of the left-hand side hole 3 as shown in FIG. 15 in order to protect the left-hand side hole 3. FIG. 16 shows a manhole which is built with such concrete pipes 1 of any of the embodiments described hereinabove. Of whichever one of the embodiments the concrete pipes 1 employed are, the step member 7 of any concrete pipe 1 can be removed from and attached to the concrete pipe 1 by operation in the inside of the concrete pipe 1 at any time before and after the manhole is built. Further, since the inner wall face 2 of any concrete pipe 1 has no swollen or projected portion thereon and the step member 7 has the form of a straight bar, a wide spacing for operation can be assured in the inside of the manhole. Any concrete pipe 1 is molded so as to have a circular, elliptical or egg-shaped cross section in accordance with a shape of a manhole to be built. Referring now to FIGS. 17 and 18, there is shown a molding apparatus for molding any of such concrete pipes as described hereinabove. The molding apparatus includes a base plate 21, and a cylindrical inner mold core 19 having a closed top end and mounted vertically on the base plate 21 in an underground vertical shaft 20. A vibrator 22 is mounted in the inner mold core 19 on the base plate 21. When rotation of a motor not shown is transmitted to the vibrator 22 by way of a belt 23, the vibrator 22 is vibrated, and such vibrations are transmitted to the inner mold core 19 by way of a plurality of connecting members 24. An opening of the vertical shaft 20 is closed up with a lid plate 25 in order to prevent noises. Meanwhile, an outer mold jacket 26 is constructed for free movement, that is, is not located at a fixed position and may be inserted into the vertical shaft 20 through an opening 27 of the lid plate 25 by means of a crane or the like. A ring-shaped pallet 28 is removably attached to a lower end of the outer mold jacket 26 by known means. When the outer mold jacket 26 is inserted into the vertical shaft 20, the pallet 28 is removably fitted around an outer periphery of the inner mold core 19 with a predetermined fixed gap left between the inner mold core 19 and the outer mold jacket 26. A receiving seat 29 for receiving the pallet 28 thereon is provided at a lower portion of the outer periphery of the inner mold core 19, and when the pallet 28 is fitted onto the inner mold core 19 until it is received by the receiving seat 29, a flange 30 provided at the top end of the outer mold jacket 26 is received on the lid plate 25 with a plurality of vibration isolating members 18 interposed therebetween to hold the outer mold jacket 26 at a predetermined height or vertical position. Where the outer mold jacket 26 is set in such position, a forming spacing 32 which is closed at the bottom end thereof-with the pallet 28 is defined between the inner mold core 19 and the outer mold jacket 26. A pair of left and right air cylinders 35 and 36 are mounted horizontally in the opposite directions to each other on an inner periphery of the inner mold core 19 by way of a pair of brackets 33 and 34 as shown in FIG. 18. A forming mold element 38 for forming the left-hand side hole 3 of a concrete pipe of the first or third embodiment described hereinabove is attached to a piston rod 37 of the left-hand side air cylinder 35 while another forming mold element 40 for forming the right-hand side hole 4 and groove 5 is attached to a piston rod 39 of the right-hand side air cylinder 36. The left and right forming mold elements 38 and 40 are adapted to be fitted horizontally in a pair of left and right holes 41 and 42 formed in the inner mold core 19 such that they may partially extend into the forming spacing 32. Further, the forming mold elements 38 and 40 have end faces 43 and 44, respectively, which provide cylindrical face portions coincident with an outer peripheral face of the inner mold core 19. Molding of a concrete pipe proceeds in the following manner on the molding apparatus. The outer mold jacket 26 and the pallet 28 are first set in such a manner as shown in FIG. 17, and the left and right forming mold elements 38 and 40 are set so that they extend into the forming spacing 32 as shown in FIG. 18. Where such lining material 18 as shown in FIG. 15 is used, it is fitted on the left-hand side forming mold element 38. In this condition, stiff consistency concrete material or ordinary concrete material is thrown into the forming spacing 32 while vibrations are applied to the inner mold core 19 by way of the vibrator 22 to compact the concrete material. Then, an upper face of the thus compacted concrete material is compressed by a press 45 shown in FIG. 17 to level the same. After then, the left and right forming mold elements 38 and 40 are retracted by the air cylinders 35 and 36, respectively, until the end faces 43 and 44 thereof are registered with the outer peripheral face of the inner mold core 19 and then the concrete product is removed from the mold, thereby obtaining a concrete pipe of the first or third embodiment described hereinabove or a concrete pipe wherein the lining material 18 is further disposed in the left-hand side hole 3. Upon such removal of the concrete product from the mold, the outer mold jacket 26, pallet 28 and molded concrete pipe are first removed simultaneously from the inner mold core 19, and then the outer mold jacket 26 and the concrete pipe are separated from each other on the ground, or otherwise, the outer mold jacket 26 is first drawn up to the ground and then the concrete pipe is lifted to the ground together with the pallet 28. In order to mold a concrete pipe of the second embodiment which has the left and right holes 3 and 4 thereon, another forming mold element similar to the right-hand side forming mold element 40 should be attached to an end of the piston rod 37 of the left-hand side air cylinder 35. In any case, a concrete pipe according to the present invention can be molded very readily on such a molding apparatus of a simple structure as shown in FIGS. 17 and 18.

Claims: A concrete pipe for use in a vertical position with a step wherein a step member (7) is attached to an inner wall face (2) of said concrete pipe (1), characterized in that said inner wall face (2) of said concrete pipe (1) is formed as a cylindrical face having no projection thereon but having a pair of blind holes (3, 4) formed in an opposing relationship at left and right portions thereof, and at least one groove (5) defining a first and second end is formed on and extends horizontally along said cylindrical inner wall face (2) of said concrete pipe (1) in a contiguous relationship at said first end to one of said holes (4), that said step member (7) is in the form of a straight bar having a length corresponding to the length of a straight line interconnecting said holes (3, 4) at said left and right portions of said cylindrical inner wall face (2) of said concrete pipe (1) and has a projection (8) formed at least at one end such that said projection (8) extends in a direction intersecting an axial line of said step member (7) and can be removably fitted into said groove (5) when it is directed horizontally but can be fitted by way of said groove (5) into the hole (4) contiguous to said first end of said groove (5) when it is turned around the axial line of said step member (7), and that said step member (7) has a locking member (9) attached thereto for removably fitting in said groove (5). A concrete pipe with a step as set forth in claim 1, characterized in that said groove (5) is provided at only one of the left and right portions of said inner wall face (2) of said concrete pipe (1) while said projection (8) is provided at only one end of said step member (7). A concrete pipe with a step as set forth in claim 1, characterized in that said groove (5) is provided on each of the left and right portions of said inner wall face (2) of said concrete pipe (1) while said projection (8) is provided at each of the opposite ends of said step member (7), and a pair of such locking members (9) are provided on said step member (7). A concrete pipe with a step as set forth in claim 1, characterized in that said locking member (9) is mounted for sliding movement in an axial direction on said step member (7). A concrete pipe with a step as set forth in claim 1, characterized in that said locking member (9) is formed from a resilient material and fixed to an end of said step member (7) such that, when said projection (8) is fitted into said hole (4) contiguous to said first end of said groove (5), said locking member (9) is resiliently contacted with said groove (5) to restrict said projection (8) within said hole (4).

Inventors: SAKURAI, TOSHIHIDE
Applicants: SAKURAI KENZAI SANGYO KABUSHIKI KAISHA
Application year: 1990
Main classification: E06C9
IPC codes: E06C9