"Device for the construction of platforms in water on foundation piles, and relative procedure"
The invention described below falls within the construction methods for reinforced concrete platforms, on foundation piles, partially or totally submerged in water; these platforms can have various civil applications, such as foundations for bridge piers, platforms for harbour areas and similar works (see Figure 1).
It is important to note how this invention can be applied in cases where bored piles with cast in-situ reinforced concrete are foreseen and with steel casing (the steel casing is always required for piles bored in water).
The current technology for the construction of reinforced concrete platforms in water mainly foresees the use of steel sheet piles of the "Larssen" type: they are driven around the design area and then the water is pumped out until the level is lower than that required to construct the platform. This system, however, requires rather lengthy execution times and high construction costs.
In comparison with this traditional system, the invention proposed herein is simple, practical and reliable to execute and construct, offering many advantages, both in economical terms and the construction time, especially in those cases in which the platform must be partially or totally submerged in water (obviously not beyond a certain limit).
To summarise, the invention described herein consists of a device composed of a disposable formwork, prefabricated in reinforced concrete, mounted on bored piles in water with a steel casing, and connected to the piles with a steel collar clamping system.
This device guarantees a fast connection between the platform and the piles, which means very short assembly time and, above all, the feasibility of this connection in water (other common connection systems, such as welding, cannot be carried out in water, unless very complicated operations are employed).
The invention also relates to the procedure to put into effect the connection of the device to the piles.
The attached drawings illustrate this written description, and in particular:
Figures 1 to 12 show the proposed system applied to the most typical case, i.e. the construction of a platform partially submerged in water.
Figure 13 briefly illustrates the system for the possible variant of a platform totally submerged in water, for which an additional operation is necessary (introduction and successive removal of a temporary formwork).
Figures 14-15-16 illustrate the details of the clamping collar.
Figures 17 and 18 show the details of the support and lowering systems of the formwork in respect of the piles.
The present device, therefore, comprises a prefabricated formwork (Figure 2), necessary for the construction of the platform.
This comprises a number of units, that depend on its size and on the lifting systems available on site (theoretically only one unit would be necessary in the case in which the site crane can lift and transport the entire formwork).
The base of the formwork must have holes with a diameter somehow larger than those of the piles on which it will be mounted, and the position of these holes should coincide with those of the piles already built in water (this operation will be possible thanks to a topographic survey of the built piles).
The base of the formwork must also be predisposed with some spacer elements (A) necessary for the connection during assembly of the various units of the formwork, with the same geometry with which they were built during prefabrication.
The prefabricated formwork is then connected to the piles with a system of clamping collars (Figure 14). Those comprise: anchor rods embedded in the base of the formwork (1), the formwork collar, connected to the anchor rods and made up of three round superimposed plates (2), the pile collar, comprising two half -rings with an "L" section (3) and the clamping bars (4).
The forces between the pile and the formwork are transmitted through the engagement between the elements 2 and 3, that create a kind of male-female joint.
Section 1-1 shows two special cases: one in which the collar is in a theoretically central position (CASE 1) and the other in which the collar is in an eccentric position (CASE 2) due to the non-eliminable construction tolerances (basically relating to the verticality of the pile, that, in any case, must be estimated for the development of the detailed design of the collar). The clamping force of the bars (4) depends on the calculations: the friction generated between the pile collar (3) and casing of the pile is used.
The clamping collar, therefore, comprises the following elements:
Element 1, shown in section 2-2, shown in Figure 15, consists of a steel rod with a hook, useful for improving the anchorage between the formwork and the collar in the limited concrete thickness.
Element 2, also shown in Figure 15, is formed by three circular, superimposed plates (two elements 2.1 and one 2.2). To facilitate construction and assembly, these circular elements are divided into two parts (but could also be formed by a single piece or be sub-divided into more parts). The internal cutting radius of element 2.2 is larger than that of 2.1 to guarantee the necessary engagement (X) with element 3.
Element 3, shown in Figure 16, consists of two plates (3.1 and 3.2) forming an "L" section.
The two pairs of plates are then joined together to create two half-rings. The thickness of plate 3.1 must be slightly less than that of element 2.2, in order to obtain a correct engagement between them. The element 3.1 must have at least one or more cuts (Y) to obtain a better fitting of the plate 3.2 around the pile (that can be slightly oval).
The elements 3.3, 3.4 and 3.5 welded to element 3.2, and suitably shaped (as shown in figure
16), are necessary for the abutment of the nut of Element 4.
Lastly, Element 4 (Figure 16) comprises a bar threaded at the ends, where the clamping force is exercised through the terminal bolts.
Below is a description of the assembly of the device.
After prefabrication of the formwork units, they are assembled on the piles (using a crane)
(Figure 3); the units are mounted above water level and suspended on the piles themselves with a support system (A); this employs (Figure 18) a beam (1) with a section formed by two "C" profiles (as shown in Sections C-C and D-D), that permit the intermediate passage of the support beams (2), anchored to the formwork base (as shown in Section Y-Y).
Once the support system on the piles is terminated (Figure 4), concrete is then cast (A) for the closure of the formwork units.
The jacking system is then assembled (Figure 5) as is the system to lower the formwork (A): this uses (Figure 17) two beams (1) with a section formed by two "C" profiles (as shown in the Sections A-A and B-B), that permit the intermediate passage of the support beams (2), anchored to the base of the formwork (as shown in Section X-X).
For the lowering operation, three control positions are sufficient; the figure 5 shows four positions in correspondence with the four corner piles, but two positions are connected hydraulically to each other, in such a way to have only three hydraulic control points, because otherwise a redundant support state would be created.
At this point the formwork is lowered using the jacking system (Figure 6). This operation will only be possible after having removed the temporary support systems (B).
The clamping collars (A) are mounted on the various units, but are still not tightened.
When the formwork enters the water, the water will obviously penetrate through the spaces that exist between the piles and the formwork.
The proposed lowering system (Figure 7), consists of a series of cycles that will bring the formwork to the desired level.
Each cycle is composed of 6 phases:
- Phase 0: assembly of the jacking system formed by jacks (C) and superior beam (D); the lower nuts (B) are loaded while the top ones (A) are in contact but not yet loaded. The jacks are assembled with a piston stroke "X" (depending on the jacking system used), lower than the available maximum stroke.
- Phase 1: the jacks are loaded and, therefore, the top nuts (A*) work whereas the lower ones (B*) are unloaded; at the end of this phase, the jacking piston is lengthened by "dx"
and, therefore, also the formwork is lifted by the same amount.
At the end of this phase the temporary supports of the formwork without jacks, present on the other piles, must be removed.
- Phase 2: the lower nuts (Β') are lifted by "X" amount.
- Phase 3: the jacks are lowered by "X+dx" and, therefore, the formwork is also lowered by the same amount; at the end of the run, the lower nuts (B**) are once again loaded, while the top nuts (A**) are once again unloaded.
- Phase 4: the top nuts (Α') are lifted by "X" amount.
- Phase 5: This phase coincides with Phase 0: the jacks lift the top beam (D) by "X" amount until the top bolts touch (Α').
The number of cycles needed "N" will be the same as the total lowering "Y" divided by the lowering achieved for each cycle ("X").
When the formwork has reached the final position (Figure 8) and after checking the levelling of the platform floor, the clamping collars are closed (A).
The lowering systems (B) can be removed, as the formwork support is now guaranteed by the connection of the clamping collars.
The lean concrete is then poured (Figure 9) (A) in water around the piles. After approximately one day, the lean concrete will have set and the waterproofing of this joint will be guaranteed.
The water can then be pumped out (Figure 10) of the formwork (A) and operation proceeds (Figure 11) with the cutting of the pile steel casing (A) and the lopping of the piles with removal of the top concrete (B).
The reinforcement of the platform can then be assembled (Figure 12) and the concrete poured (A) inside the formwork. This figure shows the case of building a platform for a bridge pier; the predisposition of the reinforcement for the relative piers (B) for successive pouring of concrete is also shown.
The entire cycle described above can be applied to another particular case (Figure 13): when the platform remains totally submerged in water at the end of construction. This is possible
due to the use of a temporary formwork and its removal after pouring the concrete for the platform base (A). Before removal, it will be necessary to cast all the parts in concrete that, at the end of all the operations, will remain submerged in water: in this case, the bridge piers (B).
We wish to underline the fact that, during the elaboration of the invention described above, its practical application was experimented and it gave more than satisfactory results and confirmed its feasibility.