Deck construction

Abstract

 Disclosed is a method of constructing a concrete deck (2) of a structure in which, in the finished construction, the deck is supported by spaced-apart pillars or piers (1), the method enabling concrete slipforming or jumpforming techniques to be used in the construction of the deck. In the method, members which when finally in-situ are to form a deck supported on spaced-apart uprights are formed in upright position (member 2E/F in Fig. 2) by one or other of these techniques each adjacent an upright (1 E) that is finally to support it, and the member is then pivoted (member 2D/E in Fig. 2) about its adjacent upright (1 D) to move it to its final position (member 2C D in Fig. 2).

Description

[0001] This invention relates to the construction of decks of structures where the deck is to be supported by spaced - apart upright pillars or piers. In particular the invention is concerned with the construction of bridge decks.

[0002] As is well known, concrete is a favoured constructional material and an advantageous method of constructing upright concrete pillars or piers is to utilise either the so-called slipforming technique, or the so-called jumpforming technique. An advantage of these techniques is that they avoid the need to use elaborate moulds and falsework such as is required, for example, when casting in-situ concrete deck parts which are to be supported by spaced-apart uprights and which have configurations that do not lend themselves to the use of slipforming or jumpforming. Even if the formation of such parts can be simplified by forming the parts away from what are to be their final locations, for example as proposed in British Patent Specification No. 1,000,949 to Paul Dupont, there remains the problem of moving the parts into their final positions. By the present invention the techniques of slipforming and jumpforming are extended to the construction of concrete decks, which when finally in-situ are supported on spaced-apart uprights, in such a way that movement of each member of a deck from an upright position in which it is slipformed or jumpformed into a final position is accomplished in a simple manner and with a minimum of additional equipment.

[0003] According to the present invention there is provided a method of constructing a deck in concrete comprising forming in upright position by the slipforming technique or by the jumpforming technique a plurality of members; characterised in that each member so formed is to be a member of said deck, and is so formed adjacent an upright that is to support it in its final position; and in that after its formation each so formed member is pivoted about the upright that is to support it for moving it into a final position in which it is to become a part of the deck. In this way the benefits of slipforming or jumpforming are.utilised in the formation of the deck members, and as each member so formed is formed adjacent an upright, the member only has to be pivoted into its final position and the major component required to effect this pivoting, i.e. the upright, is itself a part of the finished construction. Furthermore, pivoting is facilitated by the fact that it takes place above a point in a mid-way zone of the member.

[0004] For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-

Figure 1 is a side view, broken into three, of the approach part of a river bridge illustrating various stages in the construction of the bridge.

Figure 2 is a side view on a larger scale than Figure 1 further illustrating how this part of the bridge is erected.

Figure 3 is a side view on a still larger scale showing in greater detail the area ringed at III in Figures 1 and 2,

Figure 4 is a sectional view taken on the line IV-IV in Figure 3, and

Figure 5 is a sectional view taken on the line V-V in Figure 4.

[0005] The Figures relate to the approach spans of a road-carrying river bridge in which in the completed structure pairs of side-by-side uprights in the form of piers 1 carry a bridge deck 2. During construction the piers 1 are constructed in-situ, in conventional fashion (for example by slipforming or jumpforming) on previously driven piles. In the particular bridge illustrated a first span 2A and part of a second span 2B of the bridge deck are also constructed in-situ on trestling so that first and second piers 1A and 1B are spanned and in addition the deck extends towards the third pair of piers 1C. At the other end of the bridge approach a part span 2K is constructed in conventional fashion together with the main bridge spans. Construction of the bridge deck at the approach part of the bridge is carried out making use of either the slipforming technique or the jumpforming technique and will now be described with reference to slipforming.

[0006] Adjacent the third pair of piers 1C slip forms are set-up on top of the pile cap on which the piers stand, or at beach level if there is a beach, in which case mass concrete walls or pillars are provided to carry loads down to the pile caps under the beach. The slip forms are positioned to form two side-by-side upright concrete box beams 2C/D each disposed about one metre from the adjacent face of one or other of the piers, which beams are to become members of the deck. In the initial stage of slipforming, temporary supports 3 are cast to some two or four metres in height. Thereafter each box beam 2C/D is cast on these supports.--For each beam 2C/D slipforming is carried out continously until the level of the top of the adjacent pier 1C is reached. At this point slipforming is stopped and a diaphram section 4 is cast in the beam. Up to this level the beam is free standing but at this stage temporary wind bracing 5 is installed to transfer wind loads to the top of the adjacent pier. After construction of the diaphragm section, slipforming is re-commenced to complete the box beam.

[0007] As the box beam is formed the inside shutters of the slipforming equipment are moved in and out to accommodate changes in flange and web thickness and the sliding members are steered as necessary to form any required overall curvature to the beam in the longitudinal plane. Pockets are formed for providing a number of prestressing anchorages spread along the beam.

[0008] After slipforming has been completed the beam is prestressed by straight bars or tendons inserted into ducts cast in the beam. This prestressing is carried out from platforms lowered and raised inside the beam after completion of the slipforming.

[0009] In a similar manner to that just described, pairs of upright box beams 2D/F, 2E/F, 2F/G..... are constructed adjacent each pair of piers 1D, IE, IF...... The overall. length of each beam is chosen in relation to the height-of the adjacent pier and the acceptance load that can be applied during 'transfer of the beam to its final position. Pairs of beams can be constructed at all the pairs of piers before further work is carried out (as shown in Figure 1), or further work at each pier pair can be commenced once the pair of beams at that pier pair is completed. It should here be noted that, for simplicity, Figure 2 in particular is drawn as if there is only one beam and one pier at each pier location (and such could be the case in some constructions, as, equally, there could be more than two beams and piers at each pier location).

[0010] Transfer of each beam to its final position is effected by pivoting the beam about the top of the adjacent pier on rocker bearings 6 installed at the diaphragm section 4. These bearings 6 are adjacent what will be the final position of permanent bearings constituted by plates 7 which serve as shear plates at the start of the pivoting operation.

[0011] When the beams are ready for transfer to their final position, and commencing with one of the beams of the pair nearest the constructed in-situ deck section at one end or the other of the bridge approach (Figures 1 and 2 illustrate the case where work is commenced at the deck spans 2A, 2B end), jacks (not shown) are installed at the bottom of the first slipformed box beam to be pivoted. Sets of cables 8 and 9 are connected to extend from an upper zone (in the case illustrated the top) of this beam (illustrated for one of the beams 2D/E in Figure 2) away from the already-constructed part of the deck down to the base of the pier (pier 1E in Figure 2) that is next adjacent the pier (1D in Figure 2) immediately adjacent the beams; and from a lower zone (in the case illustrated, the base) of the beam up to the free end of the already-constructed deck part. Further cabling 9A is installed between the free end of the already-constructed span 2B and the foot of the first free-standing pier 1C, this being left in place whilst the beams are transferred to their final positions and thereafter removed. The wind bracing 5 is removed and using the cables 8 and 9 and the jacks the beam is tilted so that the one metre gap between the beam and the immediately adjacent pier is closed at the top of the pier (see beam 2E/F and pier 1E in Figure 2). The rocker bearings 6 are installed, if not already fitted and any necessary adjustments made to them, to the bearing plates 7 and to landing stools 10 for the bearings 6 at the top of the pier. Levelling screws 11 are provided to facilitate such adjustment.

[0012] The jacks at the bottom of the beam are relieved of load and pivoting of the beam is then effected, utilising the cables 8 and 9, so that the beam pivots about the top of its adjacent pier with the bearings 6 rocking on the landing stools 10. At the completion of pivoting, the beam is jacked up so that the rocker bearings 6 can be removed and is then lowered so that the bearing plates 7 come to rest on permanent bearings (not shown) installed on the concrete pier. At this stage the beam is tilted sideways to obtain any camber required and is connected to the already-constructed deck part. It will be noted that this connection is made at approximately mid-span between piers. The connection is made utilising short lengths of prestressing bar after a tolerance gap has been filled, in-situ, with concrete. Each beam at a pair of piers is transferred to its final position in this way before transfer of the beams at the next pair of piers is commenced.

[0013] It is to.be noted that the beams do not exactly balance when they are pivoted, the degree of out of balance being chosen so that maximum use is made of the pier heights. The out-of-balance load is finally taken at the cantilevered end of the already-constructed deck part so that final stress is not increased. Temporary dead load bending moments do not exceed the dead load plus live load moments for which the deck as a whole is designed. As an example and considering, in the embodiment illustrated, one of the box beams 2D/E, the pier 1D is approximately 32.7 metres high and the overall length of the beam 2D/E is approximately 55.3 metres. The pivot point for the beam is at approximately 25.9 metres from what will be its cantilevered end so that the length of the beam on the other side of the pivot point is approximately 29.4 metres. The beam weighs approximately 1320 tons. For this beam the load in the cables 8 at the commencement of pivoting is 250 tons and is 0 tons at the end of pivoting (these cables being connected to what is then the cantilevered end of the beam). The load in the cables 9 is 0 tons at the commencement of pivoting, the load at this end of the beam immediately prior to making good its connection with the already-constructed deck part being about 70 tons.

[0014] Although construction of a bridge deck composed of side-by-side box beams supported on side-by-side pillars has been described it will be appreciated that other forms of deck could be constructed in the same way by forming in upright position by the slipforming technique a plurality of members, each member being formed adjacent an - upright that is to support it in its final position, and pivoting each so-formed member about the upright that is to support it into a final position in which it is to become a member of the deck. Furthermore, although slipforming has been referred to throughout this detailed description is is repeated that jumpforming can be used instead.

Claims

1. A method of constructing a deck in concrete comprising forming in upright position by the slipforming technique or by the jumpforming technique a plurality of members; characterised in that each member (2C/D, 2D/E, 2E/F... ) so formed is to be a member of said deck (2), and is so formed adjacent an upright (1C, 1D, IE...) that is to support it in its final position; and in that after its formation each so formed member (2C/D,2D/E, 2E/F...) is pivoted about the upright (1C, 1D, IE...) that is to support it for moving the member (2C/D, 2D/E, 2E/F) into a final position in which it is to become a member of the deck (2).

2. A deck construction method as claimed in claim 1, wherein each said member (2C/D, 2D/E, 2E/F....) is formed spaced from its adjacent upright (1C, 1D, 1E ...);and wherein prior to said pivoting, jacking means is installed at the bottom of the member, cables (8,9) are connected to extend from an upper zone of the member downwards and from a lower zone of the member upwards, and this jacking means and these cables are used initially to tilt the member to close the gap between it and the adjacent upright at the top of the upright.

3. A deck construction method as clained in claim 2, wherein afterinitially tilting the member, the jacking means is relieved of load and said pivoting of each member is effected utilising the cables.

4. A deck construction method as claimed in claim 1,2 or 3, wherein said pivoting of each member is effected with the member supported from the upright by bearings (6) carried by the member and rocking on landing stools (10)carried by the upright.

5. A deck construction method as claimed in claim 4, wherein after said pivoting has been completed each said member is jacked, said bearings are removed, and the member is lowered onto permanent bearings carried by the upright.

₆. A deck construction method as claimed in any one of the preceding claims, wherein during construction each said member is free-standing until it reaches the top of the adjacent upright, at which stage windbracing (5) is installed between the member and the adjacent upright and formation of the member is then continued, the windbracing being removed prior to pivoting the completed member for moving the member into its final position.

Drawing