SHEET DECKING

Abstract: A sheet decking (1) has a plurality of parallel transversely spaced-apart re-entrant dovetail corrugations (2) extending longitudinally along the sheet (1). An upper section (4) of each corrugation has a plurality of spaced-apart upper shear keys (10). Side walls (5, 6) of the corrugations (2) have a plurality of spaced-apart side shear keys (11). The combination of the re-entrant dovetail corrugations (2) and the upper and side keys (10, 11) give an improved mechanical bond between the sheet decking and conctrete.

Description: "Sheet Decking" Introduction The invention relates to cold formed, profiled sheet metal decking having engagement means for interlocking with concrete poured thereover to provide a composite floor decking. On setting, the concrete grips the profiled sheet to form a load-bearing floor slab. Many different sheet deckings have been produced with various arrangements of keying ribs. However, the problems with such known sheet decking include the fact that they are difficult to manufacture on a large scale and/ or do not sufficiently key with the concrete. This invention is therefore directed towards providing an improved sheet decking which will overcome at least some of these difficulties. Statements of Invention According to the invention there is provided a re-entrant sheet decking comprising a sheet having a plurality of parallel spaced-apart re-entrant dovetail corrugations extending longitudinally along the sheet, each corrugation comprising a generally flat upper section and a pair of inwardly converging inclined sidewalls extending from the upper section, the upper section having a plurality of spaced-apart upper shear keys and at least one of the inclined sidewalls having a plurality of spaced- apart side shear keys for keying, in use, to cementitious material. Preferably both inclined sidewalls of the dovetail corrugation have a plurality of spaced-apart side shear keys. The side shear keys may be located centrally or indeed randomly located between adjacent upper shear keys. The spacing between adjacent upper shear keys and the spacing between adjacent side shear keys may be similar. In a preferred arrangement the side shear keys are stretched out from the side wall of the dovetail corrugation. Ideally the side shear keys extend for between 50% and 85% of the length of the sidewall. Preferably the side shear keys extends for approximately 70% of the length of the sidewall. Preferably the depth to length ratio of the side shear keys is from 1:5 to 1:12, preferably approximately 1:9. In a preferred embodiment of the invention the side shear key has an outer face and a pair of outwardly diverging side faces. Preferably the side faces extend at an angle of between 100° and 140° to the outer face, most preferably at an angle of approximately 135°. In a preferred embodiment the upper shear keys are stretched out from the upper section of the dovetail corrugation. In a preferred embodiment of the invention the upper shear key has an upper face and a pair of outwardly diverging side faces. Preferably the side faces extend at an angle of between 100° and 140° to the upper face, most preferably at an angle of approximately 135°. In one embodiment of the invention the upper shear key has a width which is from 20% to 60% of the width of the upper section of the corrugation. Preferably the upper shear key has a width which is approximately 37.5% of the width of the upper section of the corrugation. In a preferred embodiment of the invention the depth to length ratio of the top shear key is from 1:3 to 1:8, ideally approximately 1:5. Brief Description of the Drawings The invention will be more clearly understood from the following description thereof given by way of example only with reference to the accompanying drawings, in which :- Fig. 1 is a perspective view of a sheet decking according to the invention; Fig. 2 is a cross sectional view of the decking of Fig. 1; Fig. 3 is a perspective view of a detail of the decking; Fig. 4 is a side view of a detail of the decking; Fig. 5 is a cross sectional view on an enlarged scale of a dovetail detail of the decking; Fig. 6 is a cross sectional view of a side shear key detail on the line VI - VI in Fig. 5; Fig. 7 is a cross sectional view of a top shear key detail of the decking; Fig. 8 is a cross sectional view of an overlap detail between adjacent sheet deckings; Fig. 9 is a perspective, partially cut-away view showing the decking; Fig. 10 is a perspective view of another sheet decking according to the invention; and Fig. 11 is a plan view of a detail of the decking of Fig. 10. Detailed Description Referring to the drawings and initially to Figs. 1 to 9 there is illustrated a reentrant sheet decking 1 of cold formed galvanised sheet metal material. The sheet 1 has a plurality, of parallel transversely spaced-apart re-entrant dovetail corrugations 2 extending longitudinally along the sheet 1. The sheet 1 has an inboard longitudinal side edge 3a and an outboard longitudinal side edge 3b which are overlapped in use, as illustrated in Fig. 8. There are three dovetail corrugations 2 and one part dovetail corrugation at the inboard side and one part dovetail corrugation at the outboard side illustrated in Fig. 1. The corrugations 2 are of generally trapezoidal shape and comprise a generally flat upper section 4 and first and second side walls 5, 6 which extend from the upper section 4 and converge inwardly towards a base section 7 of the sheet 1. The upper section 4 has a plurality of spaced-apart upper shear keys 10 and at least one, and in this case both, of the side walls 5, 6 have a plurality of spaced- apart side shear keys 11. In use, cementitious material is poured over the sheet 1 and is keyed to the sheet 1 as will be described in more detail below. The sheet 1 also includes two longitudinally extending stiffeners 20 between adjacent corrugations 2. Each upper shear key 10 is of generally square shape in plan and is formed by stretching out the upper section 4 of the corrugation 2. The upper keys are approximately 15 mm wide and are spaced-apart along the upper section 4 at a centre spacing of pitch p u approximately 40 mm. As will be particularly apparent from Fig 7 each upper shear key 10 has an upper face 15 and a pair of outwardly diverging side faces 16. The side faces 16 extend at an angle of between 100° and 140°, most preferably approximately 135° to the upper face 15. The depth of the top shear key 10 is approximately 3 mm, the depth to length ratio of the top shear keys being from 1:3 to 1:8, most preferably approximately 1:5. The width of the upper shear key is from 20% to 60%, most preferably approximately 37.5% of the width of the upper section 4 of the corrugation 2. Each side shear key 11 is of generally rectangular shape and is formed by stretching out the side walls 5, 6 of the corrugation 2. The side keys are approximately 10 mm wide and 32 mm in height and are spaced-apart along the side walls 5, 6 at a centre spacing pitch p s of approximately 41.7 mm. As will be particularly apparent from Fig. 6 each side shear key 11 has an outer face 31 and a pair of outwardly diverging side faces 32. The side faces 32 extend at an angle of between 100° and 140°, most preferably approximately 135° to the outer face 31. The depth of the side shear key 11 is approximately 4 mm, the depth to length ratio of the side shear keys being from 1:5 to 1:12, most preferably approximately 1:9. Each of the side shear keys 11 extends from between 50% and 85%, most preferably approximately 70% of the length of the sidewalls 5, 6. The sheet 1 is of galvanised steel with an average coating thickness of 0.02 mm. The yield strength for material type Z28 is from 280 to 490 N/mm 2 , minimum 350 N/mm 2 for type Z35 and minimum 550 N/mm 2 for type Z55. Referring in particular to Fig. 9, in use, the floor decking 1 is generally supported on beams 30. The engagement between the decking 1 and the concrete 31 will be apparent. In order to fully appreciate the advantages of the invention it is necessary to highlight the disadvantages of concrete. Concrete has a very poor tension capacity and must be reinforced by a suitable material which will bond in the concrete in such a way that the relative strains between the concrete and that reinforcement will allow the tension force to be supported by the reinforcement material. With reinforced concrete, steel bars are imbedded in the concrete and bond to form a lattice of tension carrying members. With a steel deck, the deck is intended to provide the tension reinforcement. However, decks by nature are not imbedded and must be mechanically keyed to the concrete. The measure of the key to the concrete is called shear bond which comprises a capacity due to a mechanical bond of the deck shape into the concrete and a much smaller chemical bond of the cement to the zinc coating. The dovetail or re-entrant shape of the corrugations provides a profile which is a compromise between efficient use of material to support the concrete at the wet stage yet provides an upstand that can bond in to the slab after curing of the concrete. When the composite slab deflects it forms into a curve which has a tendency to force the dovetail harder into the concrete enhancing the mechanical bond. The upper shear keys 10 provide additional mechanical keys into the concrete increasing the load at which the deck would slip longitudinally in relation to the concrete. Because they are located only on the top face there is a limit to the force that they can transfer into the dovetail. The side shear keys 11 provide two actions. During the wet concrete stage they provide stiffening to the dovetail webs providing an increase in the decks capacity, especially in the thinner gauges. This is important as it is often the construction stage (when the concrete is wet) that controls the overall capacity of the floor slab. The provision of temporary props are sometimes provided to get over the limits of the construction stage however this is time consuming and expensive. The increase in the spanning capacity at the construction stage provided by the decking of the invention is therefore advantageous. If the dovetail webs buckle, the section loses much of its capacity. Thus, enhancing the web capacity is an important improvement to the overall section. In addition, when the deck cures the side shear keys provide additional mechanical bond and allow the tension force to be more uniformly transmitted into the dovetail upstand. The provision of the side keys allows the more efficient use of higher yield steels for the deck profile. Because the side shear keys are along the webs, when the slab deflects and curves as described above the side keys, because of the dovetail shape, are forced into a closer mechanical bond giving an overall better result. A range of static and dynamic bending tests has been carried out on the decking of Figs. 1 to 8. The results of these tests show a major advantage in improved composite action between the deck and the concrete. Interpretation of the results in line with BS5950 part 8 produced the regression line values of mr=291N/mm2 and kr=0 N/mm. While alternative interpretation in line with EC4 gives regression line values of m=280 Nmm 2 and k=0.07N/mm. Referring to Figs. 10 and 11 there is illustrated another sheet decking 100 according to the invention. The sheet decking 100 is similar to that described above with reference to Figs. 1 to 9 and like parts are assigned the same reference numerals. In this case the top shear keys 10 and side shear keys 11 are arranged so that the side keys 11 are located between adjacent upper keys 10. It will be appreciated that the decking may be of any suitable high tensile material which may have a suitable coating. The decking may be embossed with any desired pattern to strengthen the metal and/ or to enhance the bond to the concrete. An expanded mesh may also be used. It will also be appreciated that the decking may have any suitable number of reentrant dovetail corrugations. These corrugations need not all be the same size. For example, there may be a relatively wide corrugation towards the middle of the decking and two smaller ones to the side. The re-entrant dovetails may include a transverse reinforcement. For example, there may be a double wall in the dovetail and/ or the dovetail may be thicker than the main body of the sheet decking. Alternatively or additionally the re-entrant dovetail may be filled with a suitable filler such as foam or concrete. The invention is not limited to the embodiments hereinbefore described which may be varied in construction and detail.

Claims: Claims 1. A re-entrant sheet decking comprising a sheet having a plurality of parallel spaced apart re-entrant dovetail corrugations extending longitudinally along the sheet, each corrugation comprising a generally flat upper section and a pair of inwardly converging inclined sidewalls extending from the upper section, the upper section having a plurality of spaced-apart upper shear keys and at least one of the inclined sidewalls having a plurality of spaced apart side shear keys for keying, in use, to cementitious material. 2. A sheet decking as claimed in claim 1 wherein both inclined sidewalls of the dovetail corrugation have a plurality of spaced-apart side shear keys. 3. A sheet decking as claimed in any preceding claim wherein the side shear keys are stretched out from the inclined sidewalls of the dovetail corrugation. 4. A sheet decking as claimed in any preceding claim wherein the side shear keys extend for between 50% and 85% of the length of the sidewall. 5. A sheet decking as claimed in claim 4 wherein the side shear keys extends for approximately 70% of the length of the sidewall. 6. A sheet decking as claimed in any preceding claim wherein the depth to length ratio of the side shear keys is from 1:5 to 1:12. 7. A sheet decking as claimed in claim 6 wherein the ratio is approximately 1:9. 8. A sheet decking as claimed in any preceding claim wherein the side shear key has an outer face and a pair of outwardly diverging side faces. 9. A sheet decking as claimed in claim 8 wherein the side faces extend at an angle of between 100° and 140° to the outer face. 10. A sheet decking as claimed in claim 9 wherein the side faces extend at an angle of approximately 135° to the outer face. 11. A sheet decking as claimed in any preceding claim wherein the upper shear keys are stretched out from the upper section of the dovetail corrugation. 12. A sheet decking as claimed in any preceding claim wherein the upper shear key has a width which is from 20% to 60% of the width of the upper section of the corrugation. 13. A sheet decking as claimed in claim 12 wherein the upper shear key has a width which is approximately 37.5% of the width of the upper section of the corrugation. 14. A sheet decking as claimed in any preceding claim wherein the depth to length ratio of the top shear key is from 1:3 to 1:8. 15. A sheet decking as claimed in claim 14 wherein the ratio is approximately 1:5. 16. A sheet decking as claimed in any preceding claim wherein the upper shear key has an upper face and a pair of outwardly diverging side faces. 17. A sheet decking as claimed in claim 16 wherein the side faces extend at an angle of between 100° and 140° to the upper face. 18. A sheet decking as claimed in claim 17 wherein the side faces extend at an angle of approximately 135° to the upper face. 19. A sheet decking substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: ST QUINTON DAVID, ST QUINTON, DAVID
Applicants: ST QUINTON DAVID, WARD BUILDING COMPONENTS LIMIT, ST QUINTON, DAVID, WARD BUILDING COMPONENTS LIMITED
Application year: 1999
Main classification: E04B5
IPC codes: E04B5