AU2018201264B2 - Building slab system - Google Patents

Abstract

A method of building construction, particularly suitable for reactive soils, where the reinforcing steel of the edge beams of a building slab is fixed to 5 load transfer plates on the tops of piles supporting the slab. The load transfer plates are selectively vertically adjustable relative to the upper ends of the piles ; but can be locked relative thereto to oppose both lateral and vertical movement of the soils. Typical External Wall 1/5 Slab Step Down Detail 2 Layers of stab Mesh 20 mm icpcove - 2 Layers osia M 30 mm otkvn covef Slab Mes0 to be pw 20 mmp by 2 Iu Mm n 10 lMat Ad ust abe Load " franster Plate Kaana Pie Load Bearing Wall Detail Load Bearing 2 Layers of stab Mesh Wall --- >__20 mm top cover 30 mm bottom cover Crushable oidForer 225 Water Proofing Membrane 30 Adjustable Load 80 RN SWL Transfer Plate Katana Pile Engaged Sction 150 Mm 2 Layers of stab Mesh 4roat 20 mm top cover 30 mm bottom cover RS Ugatures @200 C/cL. 200 -Water Prooig / / /' / Membrane AdUstableEdge Cage SIport (refer details Katama Ne

Description

BUILDING SLAB SYSTEM

BACKGROUND OF THE INVENTION:

1. Field of the Invention:

[0001] This invention relates to a building slab system.

[0002] The invention particularly relates, but is not limited to, a method of constructing a building slab, and a building slab, suitable for use with reactive soils.

2. Prior art:

[0003] Many geographical areas in Australia, including Adelaide, have reactive soils, typically containing a high clay content. It is not unknown for such reactive soils to be liable to vertical “heave” exceeding 30cm between fully dry and fully wet.

[0004] The ‘heave” of the reactive soils has resulted in damage to building foundations, and to vertical displacement of a building relative to adjacent facilities / utilities.

[0005] One solution used to try to overcome the effects of the “heave” has been the use of building slabs, supported on piers or piles anchored in underlying stable soil zones e.g. bedrock.

[0006] It has been known, however, that the “heave” of the reactive soils e.g. following rain after a long period of drought, has been so large as to raise the slabs from the supporting piers or piles. Furthermore, as the soils have dried, the slabs have reengaged the piers or piles, but horizontally offset from their original positions.

[0007] International Publication WO 2010/096883 A1 (= PCT/AU2010/000233 = AU 2010217205) (Trista Technology Pty Ltd) discloses a ’’Building Construction Method and System” where the perimeter beams of the building slab have sloped lower surface(s) to divert the swelling (i.e. reactive) soils away from the perimeter beams e.g. into voids. The slab is supported by a plurality of screw piles. The perimeter beams are tied to supports or cradles, positioned on the screw piles. Each screw pile is fitted with a pile cap such that a structural slip joint is formed between the pile cap and the slab.

[0008] This means that the slab can still move vertically as the soils swells. While the vertical movement of the slab is relatively controlled, such movement can lead to the failure of utilities (e.g. water pipes, sewage pipes, storm-water pipes, electricity cables

2018201264 21 Feb 2018 and telephone wires 0 fibre cables) connected to the slab or the building supported thereon.

OBJECTS OF THE PRESENT INVENTION;

[0009] It is an object of the present invention to prove a building slab construction where the slab, supported on piers or piles (hereinafter “piles”) is secured against vertical movement due to “heave” of underlying reactive soils.

[0010] It is a preferred object to prove a method for securing the building slab to the supporting piles.

[0011] Other preferred objects will become apparent from the following description.

SUMMARY OF THE PRESENT INVENTION;

[0012] In one embodiment, the present invention resides in a method of building construction, where a building slab is supported by a plurality of piles, wherein: reinforcing steel for at least one edge beam of the slab is fixed to respective load transfer plates on the piles.

[0013] Preferably, each load transfer plate is selectively vertically adjustable relative to an upper end of its respective pile, but is selectively lockable relative to the pile to oppose both lateral and vertical movement of the soil(s).

[0014] In a second embodiment, the present invention resides in a building construction having a building slab supported on a plurality of piles, wherein:

reinforcing steel for at least one edge beam of the slab is fixed to respective load transfer plates on the piles.

[0015] Preferably, each load transfer plate is selectively vertically adjustable relative to an upper end of its respective pile, but is selectively lockable relative to the pile to oppose both lateral and vertical movement of the soil(s).

[0016] Preferably, each pile is a screw pile or blade pile, having:

a tubular shaft;

at least one helical screw or blade at or adjacent a lower end of the shaft; and a drive cap or nut, with a screw-threaded bore therethrough, at or adjacent an upper end of the shaft.

[0017] Preferably, each load transfer plate has:

2018201264 21 Feb 2018 a plate body to which the reinforcing steel is fixable e.g. by welding, clamping or tying; and a screw-threaded bolt or shank engageable in the screw-threaded bore;

at least one (optional) lock-nut selectively releasing or locking the bolt or shank relative to cap or structural nut, and thereby to the pile.

[0018] Other features of the present invention will become apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0019] To enable the invention to be fully understood, and to be able to be put into practical use, preferred embodiments will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a schematic sectional side view of the edge beam detail of a building slab constructed in accordance with a first embodiment in accordance with the present invention;

FIG. 2 is a similar view of the load bearing wall detail of the building slab;

FIG. 3 is a similar view of an external wall slab step down detail of the building slab;

FIG. 4 shows the details of FIG. 1 on an enlarged scale;

FIG. 5 shows a portion of FIG. 4 on a further enlarged scale;

FIG. 6 is a similar view to FIG. 4, of a second embodiment of the present invention;

FIG. 7 is a schematic end view of the fixing of the reinforcing steel, of the edge beam of FIG. 1, to a load transfer plate;

FIG. 8 is a top plan view of the load transfer plate of G FIG. 7; and

FIG. 9 is a schematic sectional side view of the engagement of a load bearing plate with an upper end of a pile.

[0020] NB: Any annotations on the drawings, including dimensions, comments, arrows, or the like, are for illustrative purposes only, and are not limiting to the scope of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

[0021] The building slabs, to be hereinafter described, may be supported on screw piles or blade piles, or suitably modified piers, hereinafter referred to as “piles”. The piles may

2018201264 21 Feb 2018 be in accordance with the piles disclosed in detail in AU 2013100623 (Patented Foundations Pty Ltd), the contents of which are incorporated by reference.

[0022] The crushable void formers, to be hereinafter described, may be formed of crushable material, e.g. cardboard, foamed plastics or the like, and/or incorporated crush zones and/or fold lines.

[0023] Before constructing the building slab over the reactive soil(s), it will be typical practice to:

a) scarify / plough the top surface of the reactive soil(s); and

b) wet the reactive soil(s);

so that the lower portion ofthe building slab will be above the top surface ofthe reactive soil(s) after the top surface ofthe reactive soil(s) has undergone vertical movement or “heave”.

[0024] Referring to the first embodiment illustrated in FIGS. 1 to 5, the building slab 10 is supported on a plurality of piles 70, with blade piles being preferred. The piles 70 are arranged in a pattern to support the edge beams 30 ofthe slab 10, together with other portions ofthe slab 10 supporting e.g. load bearing walls (see FIG. 2) or external walls adjacent a slab step down (see FIG. 3) [0025] The slab 10, formed of steel-reinforced concrete, has two layers of slab mesh 21 in the floor portions 20, connected to reinforcing steel cages 31 in the edge beams 30. Load-bearing walls LW are supported by the floor portions 20, while (cavity) external walls EW are supported by the edge beams 30 and slab step downs 30A.

[0026] The configuration of the underside of the slab 10 is, in part, defined by the positioning on the crushable void formers VF, which are overlaid with a water proofing membrane M before the concrete C is poured.

[0027] As will be hereinafter described in more detail, the reinforcing steel cages 31 in the edge beams 30 are welded to the load transfer plates 80 mounted on respective piles 70; while the floor portions 20 are supported by load transfer plates 90, also supported by the piles 70. (NB: The slab mesh 21 in the floor portions 20 may also be welded, or otherwise fixed, to the load transfer plates 90.) [0028] As shown in more detail in FIGS. 4 and 5, the steel cages 31 are of substantially Z-shape and have parallel lower rods 32, 33, interconnected by lower cross-bars 34; parallel upper rods 35,36, interconnected by upper cross-bars 37; and vertical rods 38

2018201264 21 Feb 2018 interconnecting rods 33, 35.

[0029] The external formwork, not shown, and the void formers VF, defines the configuration of the edge beam 20 with vertical inner and outer faces 39, 40, interconnected by an inclined bottom face 41 (e.g. at 20° to the horizontal).

[0030] As shown in FIGS. 4,5 and 7, the lower rods 32, 33 are received within inwardlydirected sockets 83, 83 in the body 81 of the load transfer plate 80. This arrangement assists in preventing the steel cages 31 being released from the load transfer plate 80 under extreme vertical lifting loads, or “heave”, applied to the underside of the slab 20 by the reactive soil RS. These loads can occur when the void formers VF do not crush as designed, or all available crushing has occurred.

[0031] Referring to FIGS. 7 and 8, the load transfer plate 80 has an elongate slot 84 in the body 81, the slot 84 receiving the screw-threaded shank 86 of a bolt 85. A lock-nut 87, on the shank 86, enables the bolt 85 to be adjustably clamped in a range of positions relative to the body 81, to enable the sockets 82, 83 to be aligned with the lower rods 32, 33 of the steel cage 31.

[0032] As illustrated in FIG. 9, the shanks 86, 96 of the load transfer plates 80, 90 are screw-threadably received in threaded bores 74 through drive caps, or structural nuts 73, at the upper ends 72 of the shafts 71 of the piles 70. Lock-nuts 87, 97 may be provided to lock the shanks 86, 96 against rotation when the load transfer plates 80,90 have been adjusted to their respective desired heights. The drive caps may be in accordance with the disclosure in AU 2012101551 (Patented Foundations Pty Ltd).

[0033] The piles 70 are driven into the soils until the blades 75, adjacent the digging point 76 at the lower end 77 of the shaft 71, is engaged in a stable soil strata SS below the reactive soil strata(s) RS. The piles 70 are driven into the stable soil strata SS until the driving torque indicates the piles 70 can both support, and resist, vertical loads of e.g. 80 KN SWL.

[0034] When the reactive soils strata undergoes swelling, or “heave” the crushable void formers VF are crushed to take up the vertical movement of the top surface of the reactive soil strata(s) RS relative to the underside of the slab 20; while any upward movement of the slab 20 is rested by the connection of the steel cages 31 to the piles 70 via the load transfer plates 80, 90.

[0035] FIG. 9 illustrates a second embodiment, using an alternative steel cage 131

2018201264 21 Feb 2018 within the edge beam 130, where the lower rod 32 is omitted; the lower rod 133 lies adjacent a vertical flange 183 on the body 181 of the load transfer plate; and the lower cross-bar 134 and/or lower rod 133 are welded to the plate body 181.

[0036] In addition, a secondary steel cage 131A has an upper rod 135A received in a socket 182A on the underside of the plate body 181, and is connected to a lower rod 132A by vertical rods 138A. The upper rod 135A is preferably welded to the socket 182A.

[0037] As for the first embodiment illustrated in FIGS. 1 to 8, the connection of the steel cages 131, 131A to the piles 170, via the load transfer plates 180, resists any lifting forces on the slab 110.

[0038] The skilled addressee will appreciate that the configuration of the steel cages 31, 131, 131 A; and/or the number / spacing I load capacity of the piles 70, 170, can be varied to suit the particular building 10,110 to be erected and/or the characteristics of the reactive soil strata(s) RS and/or stable soil strata(s) SS.

[0039] Advantages of the present invention include, but are not limited to:

1. The piles are set attached to the building foundations by rigid (non- slip) joints;

2. The pile installation tolerance is not critical;

3. The piles are locked into the perimeter beams by use of the steel load transfer plates. This locks the piles into the edge beams, so as to resist uplift pressures of the clay / reactive soil(s) on the underside surface(s) of the edge beams;

4. The adjustable load transfer plate positions the steel reinforcing (Z-) cage, in to its correct position, and ensuring correct concrete cover;

5. The adjustable load transfer plate can be provided for all internal pile locations;

6. The adjustable load transfer plates are installed after positioning of water proofing plastic membrane over the void formers. This will enable the engineer to check for correctness as to location of the piles;

7. Enables a “Two Brick Rebate” same as a “Waffle Pod Edge Beam”;

8. Uses the same formwork as a “Waffle Pod Slab”;

9. Maintains a BCA visual “Termite Barrier”;

2018201264 21 Feb 2018

10. With a solid 80mm upper section of the void formers, one can obtain a R Rating for insulation of the slab;

.The fixed joint connections between the steel gages and the piles also ensures a larger lateral capacity for the foundations for the slab, in situations where there are “Slope Stability” issues i.e. where there are lateral loads transferred to the piles as a result of ground creep;.

12. There is an improved structural capacity of the slab, as joints are analysed as fixed, and not pins;

13. Line loads are easily designed in to the new system;

14. Due to the adjustable load transfer plates, the piles are sealed units, thus negating internal corrosion calculations, and extending the expected life ofthe piles to 120+ years.

[0040] The skilled addressee will appreciate the actual design / specification ofthe slab and piles will be varied to suit the particular intended building construction and the respective regulatory requirements / Standards.

[0041 ] Various changes and modifications may be made to the embodiments described and illustrated without departing from the present invention.

[0042] This application is a divisional application from Australian Application 2013222045. The full disclosure of AU2013222045 is incorporated herein by reference.

Claims (8)

1. CLAIMS:

   1. A method of building construction, where a building slab is supported by a plurality of piles, wherein:

   5 reinforcing steel for at least one edge beam of the slab is fixed to respective load transfer plates on the piles, and the reinforcing steel and the respective load transfer plates are located in the at least one edge beam.

   10
2. 2. The method of claim 1, wherein:

   at least one crushable void former is provided under the slab to at least partially absorb vertical movement, or “heave”, of soil(s) under the slab.
3. 3. The method of claim 1, wherein:

   15 each load transfer plate is selectively vertically adjustable relative to an upper end of its respective pile, but is selectively lockable relative to the pile to oppose both lateral and vertical movement of the soil(s).
4. 4. A building construction having a building slab supported on a plurality of

   20 piles, wherein:

   reinforcing steel for at least one edge beam of the slab is fixed to respective load transfer plates on the piles, and the reinforcing steel and the respective load transfer plates are located in the at least one edge beam.
5. 5. The construction of claim 4, wherein;

   at least one crushable void former is provided under the slab to at least partially absorb vertical movement, or “heave”, of soil(s) under the slab.

   30
6. 6. The construction of claim 4, wherein:

   each load transfer plate is selectively vertically adjustable relative to an upper end of its respective pile, but is selectively lockable relative to the pile to

   2018201264 03 Jul 2019 oppose the vertical movement of the soil(s).
7. 7. The construction of claim 4, wherein each pile is a screw pile or blade pile, having:

   5 a tubular shaft;

   at least one helical screw or blade at or adjacent a lower end of the shaft; and a drive cap or nut, with a screw-threaded bore therethrough, at or adjacent an upper end of the shaft.
8. 8. The construction of claim 7, wherein each load transfer plate has:

   a plate body to which the reinforcing steel is fixable e.g. by welding, clamping or tying; and a screw-threaded bolt or shank engageable in the screw-threaded bore;

   15 at least one (optional) lock-nut selectively releasing or locking the bolt or shank relative to cap or structural nut, and thereby to the pile.