SG181505A1 - Bracketted flat plate - Google Patents
Bracketted flat plate Download PDFInfo
- Publication number
- SG181505A1 SG181505A1 SG2012041000A SG2012041000A SG181505A1 SG 181505 A1 SG181505 A1 SG 181505A1 SG 2012041000 A SG2012041000 A SG 2012041000A SG 2012041000 A SG2012041000 A SG 2012041000A SG 181505 A1 SG181505 A1 SG 181505A1
- Authority
- SG
- Singapore
- Prior art keywords
- flat plate
- bracketed
- slab
- plate system
- concrete
- Prior art date
Links
- 239000004567 concrete Substances 0.000 claims description 27
- 238000010276 construction Methods 0.000 claims description 20
- 239000000463 material Substances 0.000 claims description 10
- 238000011065 in-situ storage Methods 0.000 claims description 6
- 238000005452 bending Methods 0.000 claims description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims 1
- 241001310793 Podium Species 0.000 claims 1
- 229910052799 carbon Inorganic materials 0.000 claims 1
- 238000004080 punching Methods 0.000 abstract description 16
- 230000008901 benefit Effects 0.000 description 5
- 238000004880 explosion Methods 0.000 description 5
- 230000000750 progressive effect Effects 0.000 description 5
- 230000002787 reinforcement Effects 0.000 description 5
- 238000009415 formwork Methods 0.000 description 4
- 238000009416 shuttering Methods 0.000 description 3
- 125000000174 L-prolyl group Chemical group [H]N1C([H])([H])C([H])([H])C([H])([H])[C@@]1([H])C(*)=O 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
- 229910000746 Structural steel Inorganic materials 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000011150 reinforced concrete Substances 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 235000012773 waffles Nutrition 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 238000005094 computer simulation Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
- E04B5/00—Floors; Floor construction with regard to insulation; Connections specially adapted therefor
- E04B5/43—Floor structures of extraordinary design; Features relating to the elastic stability; Floor structures specially designed for resting on columns only, e.g. mushroom floors
Landscapes
- Engineering & Computer Science (AREA)
- Architecture (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Civil Engineering (AREA)
- Structural Engineering (AREA)
- Conveying And Assembling Of Building Elements In Situ (AREA)
- Forms Removed On Construction Sites Or Auxiliary Members Thereof (AREA)
Abstract
The present invention provides a bracketed flat plate system, which satisfies the provisions of IS code, safe and economical. The bracketed flat plate system is designed by providing brackets on diagonals of columns in place of drop heads as in flat slabs, changing the load path mechanism from two way punching shear modes to one way shear at column location which is far safer as shown in Figurel. In this design, sudden failure due to punching shear is not a possibility.
Description
BRACKETED FLAT PLATE
This invention relates to a structural flat plate/slab system for large office and commercial buildings, wherein brackets are introduced at column slab junctions on its diagonals. This new system will be referred to and known as “Bracketed Flat Plate” hereinafter. }
The most common structural element in modern buildings is Concrete Slab, which may be either cast in-situ or post tensioned slab. In situ concrete slabs are built on the building site using form-work a type of boxing into which the wet concrete is poured. If the slab is to be reinforced, the rebars are positioned within the formwork before the concrete is poured in. Plastic tipped metal, or plastic bar chairs are used to hold the rebar away from the bottom and sides of the form-work; so that when the concrete sets it completely envelops the reinforcement. Structural slab system for large span office and commercial buildings are generally provided as an insitu slab reinforced concrete (RC) construction.
The following are the different types of structural system. : 01. Beam and slab system. - 02. Ribbed slab system. oo 03. Flat slab with drop head system = 04. Flat slab with Post tension system. 05. Waffle slab system : 06. Flat plate system (limited to 6mspans) : 07. Paneled slab system.
The other type of systems such as precast pre-tensioned system, structural steel metal deck slab system, hollow core slab system are not considered in this context as they are totally of different type of design and construction.
The column spacing that is generally adopted for commercial buildings varies from 6m to : 12m. The above structural systems are generally adopted taking into account the safety, economy and constructability. The most commonly adopted system is FLAT SLAB due to its ease of construction and for getting an unhindered space between the soffit of slab and false ceiling for all services. As the volume of. office / Information technology 10 . projects constructed is increasing in millions of square feet of built up area and the construction industry is looking for more and more cost effective designs thus this innovation. oo
Flat plates are elegant, simple, easy and faster to construct and provides uninterrupted : space for services allowing lesser floor to floor height of the structure. Flat plates/slabs are extensively used for offices, schools, warehouses, hospitals, hotels, car parking structures and commercial buildings. Flat plates are provided for smaller spans and flat
Bb slabs for larger spans. Two-way shear or punching shear as described is very brittle and is - instantaneous giving no time for escape. There may not be any indications of cracks and deflections in this type of failure, i.e., the failures are sudden ‘and also may lead to progressive failures. A failure at one column location may lead to large rotations of slabs and this flexural curvature may reduce the capacity of slabs to resist punching shear at the affected columns leading to progressive collapse. Providing shear reinforcement / shear stirrup cages are expensive and the shear capacity is limited to the overall capacity of concrete in taking up the shear with reinforcement. oC h + In flat plates the load path from the slab to the column is through two-way shear or : punching shear. The failure mode in punching shear is a truncated cone surface of concrete and the failure is very sudden and brittle, due to the very highly concentrated shear forces around columns. As the demand for large span and economical structures are increasing and secondary problems arising out of gas explosion, impact construction 2 oo errors, vibrations are also to be given due consideration, providing column drop heads, capitals have become more acceptable. :
A number of design options there are considered in accounting for these highly concentrated shear forces are as given below: : 01. Providing drop heads. oo 02. Usage of column capital. - 03. Column capital and drop heads. ° 04. Shear reinforcement in slabs including bent rebars, stirrup cages. 05. Structural steel — Shear connectors. -
Out of the above design -options most commonly used is a flat slab with column heads - which to a certain extent reduces the concentration of shear forces around column.
Column capital with drop heads improves the system to carry shear forces over an extended area. Shear reinforcement /shear connectors are some of the options to take advantage of the full capacity of the concrete sections adopted for the design. However in ~~ all the above systems the mode of transfer of loads is through two-way punching shear.
Hence the need for an improved, safe and economical approach £0 the design of flat slabs, necessitating a re-look at the load path at the column-slab junction. ~~ SUMMARY OF THE PRESENT INVENTION :
The object of the present invention is to provide a bracketed flat plate system, which is safer, economical and construction friendly. : )
In the present invention load is dissipated from flat slabs to columns through one-way shear and bending, rather than through punching shear as in the case of normal flat slab construction.
Structures constructed in recent times require that it shall be designed so that it will not be damaged by explosions, impact, consequences of construction errors and vibrations ~ apart from primary requirements of strength, stability and serviceability as per the IS codes. This implies that local failures must not lead to progressive collapse of the entire . structure either due to construction errors or. due to gas explosions and hence the need for solutions that could prevent such failures, which is a very significant one. The punching ~~ shear failure mode of the failure surface is in the form of a truncated pyramid cone around the column and is at 2 distance of D/2 where “D” is the thickness of the slab/drop ‘head. The punching shear capacity is thus governed by diagonal tensile strength of the concrete which occurs in the normal cases of loading; at 2/3rds of ultimate loads and the cracks around the column appear at this stage although it may not decrease the ultimate capacity of slab in punching shear. The mode of failure is attributed to the flexural curvature of the slab of compression zone at column junction.
The above theory thus clarifies that, the shear rebars, shear studs, shear strips does not give the desired results but still persist with the brittle punching shear failure. ~The research and requirements of the code to make the column slab junction a ductile one and avoid punching shear failure is made possible by providing brackets on its diagonals. + 20 The rebars in the brackets take up bending and tension 4nd the stirrups provided in the brackets take up shear forces.
+ 25 Fig.l lustrates the bracketed flat plate of the present invention; -
Fig2A, 2B,2C Illustrate the sectional elevations of the bracketed flat plate of the present invention; :
Fig.3 Illustrates the isometric view of the bracketed flat plate showing two floors;
Fig.4 Illustrates the isometric view of the bracketed flat plate showing single : floor;
Fig.4a Hlustrate the arrangement of bottom rebars in X and Y direction:
Fig.4b Illustrate the arrangement of top rebars in X and Y direction: , Example: Fig. 05 Illustrate the bracketed flat plate of the arrangement of brackets on the column diagonals oo a
Example : Fig. 06 Illustrate the sectional elevations of the bracketed flat plate
Example: - Fig. 07 Illustrate the computer model of the bracketed flat plate
Example: Fig. 08 Illustrate the moment contour in X direction.
Example: Fig. 09 Illustrate the moment contour in Y direction.
Example: Fig. 10 Illustrate the deflection contour of the bracketed flat plate.
Example: Fig. 11 Illustrate the arrangement of bottom rebars in X direction:
Example: Fig. 12 Illustrate the arrangement of bottom rebars in Y direction:
Example: Fig. 13 Illustrate the arrangement of top rebars in X direction:
Example: Fig. 14 Illustrate the arrangement of top rebars in Y direction:
Example: Fig. 15 Illustrate the arrangement of top rebars in the bracket.
Example: Fig. 16 Illustrate the arrangement of rebars in the bracket - section at } intermediate column location. : IE
Example: Fig. 17 Illustrate the arrangement of rebars in the bracket - section at : edge/corner column location. : ~ DETAILED DESCRIPTION OF THE INVENTION
The present invention has diagonal brackets 1 which is tapered in depth at column-slab junctions and are extending upto length of L/4 from the center of the column 2 along X and Y axes and having depths of L/9 --L/10 at column end 2 and L/25 - L/28 at free end
CC 3, where “L” is the length spanning between the columns in X and Y directions. Columns 4 oriented diagonally with reference to Xand Y directions facilitate the construction and placement of rebars in brackets.
The brackets 1 which are tapered at the bottom look elegant and have all the advantages of flat slabs in providing the services under the ceiling. Brackets could be varied in depths and widths to accommodate design forces.
. Bracketed flat plates reduces the overall thickness 5 of the slab 6 thus saving substantial amount of concrete and rebar quantities when compared to flat slabs of similar span. ~~ Rebars used in the bracketed flat plate is placed the same pattern as flat slabs and the ~ rebars in bracket are placed diagonally within the beam and portion of the rebars are extended into the flanges thus avoiding congestion of steel at the column-bracket junction. The pouring of concrete within the bracket is also easier as only a small height of the column has to be poured directly from the top of the slab.
In high rise structure the grades of concrete varies in columns and slabs, higher grade being used in columns and lower grade in slabs. The columns are cast first with the higher grade of concrete followed by slab with concrete of lesser grade in order to reduce the cost of construction. As the dead load of the slabs including the bracket is reduced, there will be intangible benefit in column and foundation designs.
The flat slab construction may be of cast in-situ concrete with rebars or post-tensioned slabs with lesser quantity of rebars. Application of this invention can be in cast in-situ flat _ slabs, flat plates, post-tensioned slabs, waffle slabs, ribbed slabs, voided slabs and . foundations. oo
Application of the bracketed flat plate system varies with usage patterns, such as commercial, car parks, hotels, residential, hospitals and office structures and spans varying from 6m to 15m. Larger the spans this invention has advantages of minimizing : the materials used and thereby reducing the cost of construction. :
The following is the description of above discussion of providing “brackets” for flat slabs and comprises of:. 01. Providing diagonal brackets 1 at column slab junctions. - 02. Length of brackets on diagonals along X and Y axes is approximately L/4 - L/5, “L” being the length between the center to center of columns. oo 03. Depth of bracket varies from L/9 - L/10 at column end to L/25 - L/28 at free end. 04. Width of bracket maybe L/25 - L/28.
05. The bracketed flat plate is modeled using the geometrical properties of columns, brackets and slab for the floor plate. 06. The bracketed flat plate is subjected to dead load plus live load analysis with lateral loads being resisted by shear/core walls. ; 07. Bracketed flat plate shall. be provided with a camber at the center of the panel equivalent to immediate dead load deflection. : 08. The analysis is carried out using commercial software ETAB-9.7 / STAAD 2007
Pro for dead load plus live load combinations. 09. The output from the analysis is scrutinized and designed for the critical load combinations. oo © 10. The deflection pattern and the maximum deflection and the secondary conditions defined are checked. : 11. The rebars so obtained is provided at the locations as per stress contours. © 12. Placement of shuttering may be standardized and repeated for the brackets. “15 ‘Aluminum formwork is preferred for a large number of repetitions. 13. Rebars shall be placed for brackets in-between the column bars, top rebars placed oo in the beam and a portion extended into the slab. 14. Stirrup shall be provided for brackets as per design. : oo 15. Bottom rebars as required by design are provided in brackets according to the profile of the shuttering. ~ 16. Top layers of slab rebars are provided on the top of the bracket rebars in : orthogonal direction. i 17. Slab rebars at bottom surface are provided orthogonally and are extended upto center of column and alternate rebars are curtailed upto L/4.5 on either side of the * column. oo 18. Concrete shall be poured in columns, brackets and slabs as per the grade of the concrete specified in designs.
10. The system transfers the slab loads onto the brackets and thus makes the square/rectangle area around the columns extending till the edge of the bracket into a zone of higher stiffness. oo 20. The stiffness thus obtained by providing the brackets will prevent the slab having a greater flexural curvature, thereby eliminating the brittle punching shear failure. 21. The bracketed flat plate effectively spans between the edges of the brackets thereby reducing the flexural behavior and thus reducing the thickness of the slabs. 22. The load path of the bracketed flat plate is effectively of one-way shear and bending mode at the column-bracket junction and thus it is a very different mode of transfer of forces than a flat plate/slab. 23. Bracketed flat plate facilitates ductile detailing at the column bracket intersection.
Structural slabs using the “Bracketed flat plate” invention has higher stiffness at column- bracket junctions, a more safer load path, avoids brittle punching shear failure, avoids progressive collapse due to gas explosions and construction errors, accommodates ~ openings around columns without going into detailed design, without affecting ‘the structural behavior and economizes the construction cost.
Example 1: : ~~ This Example describes the results of analysis and design of “Bracketed Flat Plate
System” for an office floor of Gird 10.8 x 10.8m.The designs are carried out as per the provisions of the Indian codes.
A 3x3 bay of a normal flat slab spans of 10.8mx10.8m and brackets are shown in Fig. 5.
The brackets are tapered varying from 1000mm depth at column to 400mm depth at edges and width of 450mm. The slab thickness provided is 200mm thick throughout, edge beams are 300mm x 900mm. In this example the slab is subjected to an imposed © 30 load of 300 kg/sqm, live load of 400kg/sqm apart from the dead load of slab and brackets. -
~The slab system is analyzed for Dead + Live load only using STAAD Pro / ETAB software. Fig — 05a — Indicates the sectional elevation details of edge beam 300x900m oo (A), Brackets depth varying from 1000 to 400mm, width 450mm (B) and (C).
This example subjected to the normal Dead +Live loads for a commercial building demonstrated the load path of the Bracketed Flat Plate system through essentially one - way shear and bending. The behavior of the system is within the limits of BIS of India.
This example when compared to the normal flat slab system has substantially reduced the consumption of materials which is as follows: Lo
SLParticulars Normal Flat Slab | Bracketed Flat Plate | Comparison of Materials | .
NO : 0 ones (Cum) | 311.60 1230.80 (260%
EB ebars (Mt)) | 25.50 122.50 (12.0% . [03 [Shuttering (Sqm) 1083.60 | 1147.30 +) 56%
The bracketed Flat Plate system not only assures a safer load path but also saves enough material. Co : (-) Indicates Reduction in material. (+) Indicates Additional in material. : ;
The advantages of the proposed system can be summarized as follows: 01. Bracketed concrete flat plate structure of the present invention provides all the . requisite clearances for services under the ceiling. ; : oo 02. Bracketed concrete flat plate of the present invention is safer and avoids brittle - punching shear. Bracketed concrete flat plate claims that the secondary requirements of avoiding progressive failure due to gas explosions, human errors in construction. : :
03. The openings around the columns may be provided and limitations as given for the flat plate/slab structures are not applicable in Bracketed concrete flat plate of the present invention. 04. Bracketed concrete flat plate of the present invention is more efficient in transfer of forces and uses fewer materials for construction. oo 05. A bracketed flat plate system the slab is cast in-situ the rebars or post-tensioned slabs with lesser quantity of rebars. 06. A bracketed flat plate system rebars used in the said plate is in the same pattern as flat slabs. : 07. A bracketed flat plate system the rebars in bracket are place diagonally within the - “beam and portion of the rebars being extended into the flanges to avoid congestion of steel at the column-bracket junction. 08. A bracketed flat plate system the plate structures are provided with lateral force resisting elements such as shear walls, core walls, braced columns to resist lateral forces due to wind and earth quake forces. -
Co 10
Claims (1)
- 01. A Bracketed Flat Plate system which is a concrete flat plate/slab structure for ’ construction of office, commercial, warehouse, car parking and podium + structures comprising of: oo a. A concrete flat plate/slab, structures with diagonal brackets at column- slab junction extending to L/4 - L/5 of spacing of columns, ~~ b. The depth of the bracket vary from column edge L/9 to L/10 to L/25 to L/28 at free edge,c. The width of the bracket being L/25 to L/28, and :d. The slab thickness varies from L/56 to L/54., wherein L being the length between the center to center of columns. - :02. A Bracketed Flat Plate system as claimed in claim 1, wherein the load path in the bracket flat plate system being different than concrete flat slab structure.03. A Bracketed Flat Plate system as claimed in claim 1, wherein the slab dead loads and live loads being transferred through one-way shear and bending.04. A Bracketed Flat Plate system as claimed in claim 1, wherein the deflections. which are with in the norms of the IS Codes and satisfies the criteria of stability, safety and serviceability. -05. A Bracketed Flat Plate system as claimed in claim 1, wherein the construction of : materials, concrete and rebars are substantially less.06. A Bracketed Flat Plate system as claimed in claim 1,-wherein due to substantially less consumption of materials there is less carbon emission.07. A Bracketed Flat Plate system as claimed in claim 1, ‘wherein due to reduction in consumption of materials the construction. will be faster. C1108. A Bracketed Flat Plate system as claimed in claim 1, due to reduction in dead loads the columns and footings sizes will be economical. oo09. A Bracketed Flat Plate system as claimed in claim 1, which is economical and consumes less concrete and rebar.10. A Bracketed Flat Plate system as claimed in claim 1, wherein the slab is cast in- situ the rebars or post-tensioned slabs with lesser quantity of rebars.11. A Bracketed Flat Plate system as claimed in claim 1, wherein the ductility " : ~~ detailing at the junction of column and bracket being provided unlike in the flat : © slab with drop head.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IN3009CH2009 | 2009-12-07 | ||
| PCT/IN2010/000766 WO2011070590A1 (en) | 2009-12-07 | 2010-11-26 | Bracketted flat plate |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| SG181505A1 true SG181505A1 (en) | 2012-07-30 |
Family
ID=43655680
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| SG2012041000A SG181505A1 (en) | 2009-12-07 | 2010-11-26 | Bracketted flat plate |
Country Status (3)
| Country | Link |
|---|---|
| MY (1) | MY164573A (en) |
| SG (1) | SG181505A1 (en) |
| WO (1) | WO2011070590A1 (en) |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB191013787A (en) * | 1910-06-07 | 1911-05-11 | John Edward Conzelman | Improvements in Concrete Construction. |
| DE3613627A1 (en) * | 1985-10-12 | 1987-04-23 | Borbely Gyoergy | Shell-type floor |
| EP0393091B1 (en) * | 1987-11-12 | 1992-07-22 | Rakennus-Ekono Oy | A load-bearing horizontal structural system for a building |
| AT505057B1 (en) * | 2007-01-17 | 2009-09-15 | Tech Universitaet Wien | FLAT CONCRETE STRUCTURE AND METHOD OF MANUFACTURING THE SAME |
-
2010
- 2010-11-26 WO PCT/IN2010/000766 patent/WO2011070590A1/en active Application Filing
- 2010-11-26 SG SG2012041000A patent/SG181505A1/en unknown
- 2010-11-26 MY MYPI2012002445A patent/MY164573A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| WO2011070590A1 (en) | 2011-06-16 |
| MY164573A (en) | 2018-01-15 |
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