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(11) | EP 0 349 244 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Improvements in formwork elements |
| (57) An assembly of water stop (10) and threaded tie bar (12) for use in the casting of
concrete to provide concrete walls subject to water pressure is provided wherein the
water stop (10) comprises a moulded elastomeric annular flange portion (14) of greater
overall diameter than an integral boss (16). The water stop (10) may be initially
slid onto the tie bar (12) in the direction of thread advancement but will not slide
axially of the tie bar under the action of water pressure induced axial forces acting
on that face (20) of the flange portion (14) in a direction opposite to the direction
of thread advancement. Water pressure induced axial forces acting on the face (20)
cause compression and radially inward contraction of the boss (16) sealing and locking
the water stop to the tie bar thereby preventing water penetration past the water
stop. |
[0001] This invention relates to formwork as used in the construction industry for the casting of concrete walls or the like wherein liquid concrete is poured into a cavity between formwork shuttering, the concrete is allowed to set and the shuttering is then removed.
[0002] It is conventional practice to erect formwork with a plurality of vertical strongbacks at the outer surfaces of planar shuttering and to tie opposed sets of shuttering and strongbacks together by a plurality of tie bars connected between opposed strongbacks, or further interconnecting beams, and extending through the shuttering and the cavity defined between the opposed sets of shuttering within which concrete is to be poured. The interior walls of the cavity are provided by the inner opposed surfaces of the shuttering and the tie bars resist the outwardly extending forces acting on the shuttering induced by the mass of liquid concrete poured into the cavity.
[0003] Tie bars may be either threaded throughout their length or may only have threaded ends, the portion intermediate such threaded ends being unthreaded and straight apart from a central "kink" which is sometimes provided to locate a water stop. In use, each threaded end of a tie bar may be connected to a conical shell connector within the cavity and a further tie bar may then be connected to each such shell to extend through the shuttering for clamping connection to an associated strongback. Thus the length of tie bar within the cavity is usually less than the width of the cavity (by the combined lengths of the conical shells) and, after the concrete has set and the shuttering has been removed, this length of tie bar is retained within the concrete. The conical shells are removed and the conical recesses are filled with grout or like filler material plugs.
[0004] When cast concrete walls are exposed to water, as for example when used in dams or in underwater structures such as tunnels, it is essential to provide one or more water stops on each length of tie bar which is retained within the concrete. The water stops are provided to prevent seepage of water which could otherwise occur through the grout plugs and along the tie bar.
[0005] Various constructions of water stops have been proposed. For example, an annular elastomeric disc has been proposed for sliding onto an unthreaded tie bar with a force fit but such an arrangement does not permit the water stop to resist and seal to the tie bar against the water pressures to which it may be exposed with consequential risk of water seepage past the water stop. An alternative construction has utilised a centrally apertured metal plate welded onto a threaded tie bar intermediate its ends but this arrangement results in the introduction of additional potentially corrodible metal into the mass of concrete. A further arrangement has proposed the use of an annular elastomeric disc with an integral boss with a smooth central bore which can be slid onto a threaded or unthreaded tie bar from either end thereof and then clamped thereon by a metal clamping ring around the boss. Such an arrangement enables the water stop to seal to the tie bar and resist the water pressures to which it may be exposed but suffers from the disadvantage that the metal clamping ring itself may be exposed to moisture and hence eventually corrode within the concrete mass.
[0006] It is an object of the present invention to provide an improved water stop and assembly of such water stop and threaded tie bar which will overcome the disadvantages associated with prior art water stop devices.
[0007] In accordance with the invention there is provided a water stop mountable on a threaded tie bar for use in concrete formwork comprising an elastomeric flange portion and an elastomeric boss secured to said flange portion, the maximum exterior dimension of the boss being less than the maximum exterior dimension of the flange portion, the flange portion and the boss having an internally threaded bore extending therethrough of a thread form cooperable with that of the tie bar; the flange portion and the boss being so configured and arranged relative to one another that the stop may be either slid onto or screwed onto the tie bar in the direction of thread advancement but will not slide axially of the tie bar under the action of water pressure induced axial forces acting on that face of the flange portion remote from the boss in a direction opposite to the direction of thread advancement.
[0008] Also in accordance with the invention there is provided an assembly of water stop and threaded tie bar for use in concrete formwork wherein the water stop comprises an elastomeric flange portion and an elastomeric boss secured to said flange portion, the maximum exterior dimension of the boss being less than the maximum exterior dimension of the flange portion, the flange portion and the boss having an internally threaded bore extending therethrough in cooperating engagement with the threads of the tie bar intermediate its ends; the flange portion and the boss of the water stop being so configured and arranged relative to one another that the stop may be initially either slid onto or screwed onto the tie bar in the direction of thread advancement but will not slide axially of the tie bar under the action of water pressure induced axial forces acting on that face of the flange portion remote from the boss in a direction opposite to the direction of thread advancement.
[0009] Said flange portion and said boss of the water stop are preferably formed integral with one another as a moulding, conveniently an injection moulding, of ethylene propylene or other suitable elastomeric material capable of withstanding the water pressures to which it may be exposed within its operational temperature range without deterioration. The water stop is preferably capable of resisting said water pressure induced forces up to a pressure of at least two bar and preferably up to a pressure of four bar.
[0011] Other features of the invention will become apparent from the following description given herein solely by way of example with reference to the accompanying drawings wherein
Figure 1 is a side cross sectional view of a water stop constructed in accordance with the invention;
Figure 2 is a side part elevation, part cross sectional view of an assembly of water stop and threaded tie bar in accordance with the invention;
Figure 3 is a diagrammatic side cross sectional view through a concrete wall incorporating a water stop and tie bar assembly of the type shown in Figure 2;
Figure 4 is a diagrammatic side view showing how the water stop may be slid along the tie bar in the direction of thread advancement; and
Figure 5 is a diagrammatic side view showing how the water stop resists axial forces acting on it in a direction opposite to the direction of thread advancement.
[0012] Referring to Figures 1 and 2 of the drawings, there is shown an elastomeric water stop 10 (Figure 1) and an assembly of such water stop 10 on a threaded tie bar 12 (Figure 2). The water stop 10 comprises a moulding, conveniently an injection moulding, of an elastomeric material such as ethylene propylene in the form of a circular cross section flange portion 14 of an annular form and an integral circular cross section boss 16 also of annular form through which extends an internally threaded central bore 18; the thread form of the bore 18 cooperating with the thread form of the threaded tie bar 12. The overall diameter of the flange portion 14 of the water stop is considerably greater than the overall diameter of the boss 16. Both the flange portion 14 and the boss 16 have respective planar end faces 20, 22, 24; the planar end face 20 of the flange portion remote from the boss being the water pressure resistant face and the planar end face 22 of the flange portion adjacent the boss merging with the outer surface of the boss at a radius.
[0013] Although ethylene propylene is the preferred material for injection moulding the water stop, other suitable elastomeric materials may be employed provided that they are capable of meeting the water pressure resistance properties and temperature range properties which are required in use. For example, the water stop should be capable of resisting water pressures up to a pressure of at least two bar and preferably up to four bar within an operational temperature range of minus 40 degrees C to 120 degrees C.
[0014] In use, the water stop 10 may be either slid onto or screwed onto the threaded tie bar 12 in the direction of thread advancement to a position intermediate its ends as shown in Figure 3. In practice, it is convenient, since a tie bar may be 1000mms or more in length, to slide the water stop onto the tie bar in the direction of thread advancement i.e. in a direction from right to left as shown in Figures 2 and 3 with the planar face 20 leading and the boss trailing. It is found, as is shown in Figure 4, that flexing of the flange portion 14 resulting from pushing the water stop along the tie bar in the direction indicated by the arrows F expands the boss 16 radially outwardly away from the tie bar 12 creating a substantial line contact of the flange portion with the tie bar at the leading edge of the bore enabling such sliding movement as aforesaid.
[0015] Conversely, as shown in Figure 5, pressure applied to the planar end face 20 of the flange portion 14 of the water stop causes compression and radially inward contraction of the boss 16 sealing and locking the water stop to the tie bar against pressure induced axial forces acting in a direction opposite to the direction of thread advancement i.e. in the direction from left to right as shown by the arrows P in Figures 2, 3 and 5.
[0016] Figure 3 shows the assembly of water stop 10 and threaded tie bar 12 retained in position in a mass of cast concrete 26 after the concrete has set and after the conventional conical shell connectors have been removed from the ends of the tie bar and the resulting recesses filled with grout or other suitable filler material plugs 28. In a dam or underwater structure, that wall 30 of the concrete which is exposed to water pressure is that shown as the left hand wall in Figure 3 and seepage of water through the grout plug 28 and along the tie bar 12 will be resisted by the water stop 10 against further penetration along the tie bar since, as hereinbefore described, water pressure induced axial forces acting on the planar end face 20 of the flange portion 14 remote from the boss 16 will enhance the sealing and locking properties of the water stop relative to the tie bar and thus prevent water penetration past the water stop.
1. A water stop (10) mountable on a threaded tie bar (12) for use in concrete formwork
comprising an elastomeric flange portion (14) and an elastomeric boss (16) secured
to said flange portion, the maximum exterior dimension of the boss being less than
the maximum exterior dimension of the flange portion, characterised in that the flange
portion and the boss have an internally threaded bore (18) extending therethrough
of a thread form cooperable with that of the tie bar; the flange portion and the boss
being so configured and arranged relative to one another that the stop may be either
slid onto or screwed onto the tie bar in the direction (F) of thread advancement but
will not slide axially of the tie bar under the action of water pressure induced axial
forces acting on that face (20) of the flange portion remote from the boss in a direction
(P) opposite to the direction of thread advancement.
2. A water stop as claimed in Claim 1 further characterised in that said flange portion
and said boss are formed integral with one another.
3. A water stop as claimed in either one of Claims 1 or 2 further characterised in
that the stop is capable of resisting said water pressure induced forces up to a pressure
of at least two bar.
4. A water stop as claimed in any one of the preceding claims further characterised
in that the flange portion and the boss are moulded of ethylene propylene.
5. A water stop as claimed in any one of the preceding claims further characterised
in that said flange portion is of annular configuration.
6. A water stop as claimed in Claim 5 further characterised in that said boss is of
annular configuration.
7. An assembly of water stop (10) and threaded tie bar (12) for use in concrete formwork
wherein the water stop comprises an elastomeric flange portion (14) and an elastomeric
boss (16) secured to said flange portion, the maximum exterior dimension of the boss
being less than the maximum exterior dimension of the flange portion, characterised
in that the flange portion and the boss have an internally threaded bore (18) extending
therethrough in cooperating engagement with the threads of the tie bar intermediate
its ends; the flange portion and the boss of the water stop being so configured and
arranged relative to one another that the stop may be initially either slid onto or
screwed onto the tie bar in the direction (F) of thread advancement but will not slide
axially of the tie bar under the action of water pressure induced axial forces acting
on that face (20) of the flange portion remote from the boss in a direction (P) opposite
to the direction of thread advancement.
8. An assembly as claimed in Claim 7 further characterised in that said flange portion
and said boss of the water stop are formed integral with one another.
9. An assembly as claimed in either one of Claims 7 or 8 further characterised in
that the water stop is capable of resisting said water pressure induced forces up
to a pressure of at least two bar.
10. An assembly as claimed in any one of Claims 7, 8, or 9 further characterised in
that said flange portion and said boss of the water stop are moulded of ethylene propylene.
11. An assembly as claimed in any one of Claims 7 to 10 further characterised in that
said flange portion of the water stop is of annular configuration.
12. An assembly as claimed in Claim 11 further characterised in that said boss of
the water stop is of annular configuration.