WO2003066987A1

WO2003066987A1 - Stiffened flat metal deck as component of isotropic composite concrete slab

Info

Publication number: WO2003066987A1
Application number: PCT/ID2003/000001
Authority: WO
Inventors: Sindur P. Mangkoesoebroto; Irwan Kurniawan
Original assignee: Pt. Propenta Persisten Indonesia
Priority date: 2002-02-06
Filing date: 2003-01-31
Publication date: 2003-08-14
Also published as: AU2003244339A1

Abstract

A composite concrete slab comprising a flat metal decking sheet (1) with reinforcement in the form of a grid of stiffening elements each formed of longitudinal rebar (3) spaced from and parallel to the decking sheet (1) and a pair of diagonal rebar (4) welded between the longitudinal rebar (3) and the decking sheet (1).

Description

STIFFENED FLAT METAL DECK AS COMPONENT OF ISOTROPIC COMPOSITE CONCRETE SLAB

Description

Technical Invention

This invention is in regard to a stiffened flat metal deck as a component of isotropic composite slab constructions. The stiffened metal deck consists of a metal flat deck and a stiffening element. The isotropic composite concrete slab is capable of resisting bending in two directions. The purpose of this invention is to eliminate the use of temporary support or props that are commonly used with concrete slab constructions using conventional corrugated metal deck. The stiffened flat metal deck acts as permanent formwork, tensile and compressive reinforcements, and shear connectors, to produce a geometrically flexible composite concrete slab that will save concrete volume up to 20%. This invention is most suitable particularly for relatively large span composite concrete slab constructions. The stiffening element is general in nature; however, in a special case as will be described later in this document a stiffening rib will be introduced.

The Background of the Invention

Conventional metal decks as part of the composite concrete slabs that are presently available are generally made of 0.75~1.0 mm corrugated metal deck. Beside as permanent formwork, the deck acts also as the concrete reinforcement. However the corrugations are fashioned in such a way that tensile reinforcement action can only take place in one direction. This causes the conventional composite concrete slab can resist bending in one direction only, i.e., in the direction perpendicular to the corrugations. When necessary, shear connectors must be welded to the metal deck or to the supporting beams. The conventional corrugated metal deck has the following drawbacks:

1. As has been pointed out, the conventional corrugated metal deck can act as tensile reinforcement in one direction only, that is, the direction perpendicular to the corrugations.

2. Using metal sheet of 0.75-1.00 mm thick that is corrugated in a certain pattern has negative effect on the span. For span more than 2.5 meters, temporary props are required during the concrete casting and curing. The installation of these temporary props needs special attention, extra cost and time that are not insignificant, especially for bridge or flyover constructions that employ large span of concrete slabs.

3. Composite slabs made using conventional corrugated metal deck are limited geometrically to squares and rectangles. For circles, triangles or other arbitrary shapes, conventional corrugated metal deck is difficult to be used without special treatment.

Patent search iiv relation to this invention has been performed. Patent on metal construction decks

two-way reinforcement, this system still needs temporary props. Therefore it is entirely different from the deck construction invented in this document. Another patent number US4630414 discusses hollow core composite slab. These slabs are made of corrugated metal deck and special metal cover plates. The cover plates are fitted over the troughs so that it creates 'hollow space'. This hollow space serves as cable duct and air ventilation pathways without making holes or penetration through the floor surface. However, the tensile resistance parallel to the corrugations is reserved because the special cover plates and their connections to the corrugated deck are designed to carry tensile force that occurs. This deck system also is incapable of carrying its own weight during the concrete casting, which means that temporary props are required. Therefore, this patent is different from the invention described in this paper. Patent number US3763613 describes composite concrete slab consisting of panels that can carry bending in two directions as well as reducing the need of temporary props. The composite slab consists of two layers of concrete, i.e., bottom and top layers. The bottom layer is of prefabricated reinforced concrete, while the top is cast-in-situ. The bottom layer is equipped with inter-panel connection system that is specially designed to transfer load between panels and shear connectors to fix the connection between prefabricated bottom layer and the top cast-in-situ. This patent is clearly different from the invention in this document bearing in mind that the bottom layer in this invention is made of flat metal deck compared to that of the patent that is of prefabricated concrete panel.

Summary of the Invention

This invention is intended to overcome the drawbacks from using the conventional corrugated metal deck in composite concrete slab constructions as pointed out in the Background of the Invention. Flat metal deck used as a component of composite concrete slab in this invention, can serve as a two-way reinforcement, which is different from conventional corrugated metal deck that can only resist one-way tension. Furthermore, the flat metal deck will be permanently stiffened in its upper side by a stiffening element resulting in a stiffened flat metal deck. The stiffened flat metal deck is capable of resisting forces that arise during the concrete casting and curing. When the concrete has hardened and attained its full strength, the stiffened flat metal deck and the hardened concrete will form a composite concrete action to carry service load. In this way the need of temporary props, that requires extra resources can be eliminated, resulting in easier, faster, more economical, and safer construction method. With no further need for temporary props the use of this invention is especially effective in relatively large span structures, such as in bridges and highway flyovers. The use of the flat metal deck will cause the composite concrete slab to behave isotropically and thus able to resist bending in two directions. In this way the geometry of the composite slab can be flexible and no longer limited to rectangular or square

the need to have the ceiling. The construction method that is easier, faster, neater, more economica safer, make the invention in this document offers much more advantages than that of conventional corrugated metal deck.

As a special case, one kind of a stiffened flat metal deck is the ribbed flat metal deck. The stiffening rib is made of two pieces of zigzag or diagonal rebar that are welded at their toes to the longitudinal one. The toes at the other end are welded to the flat metal deck. When necessary, another stiffening rib may be constructed perpendicular to the former. The diagonal and longitudinal rebar can, respectively, resist shear and flexural compressive forces due to the weight of fresh concrete while being cast and cured. Later on, when the concrete has hardened, the diagonal rebar will serve as shear connectors.

Brief Illustration of the Figures

In general, the invention will be illustrated according to Figure 1 that presents the isometric appearance of flat metal deck (1) that is stiffened on its upper side by a stiffening element (2) to form a stiffened flat metal deck. During concrete casting and curing, the deck is capable of resisting its own weight and the weight of fresh concrete.

As a special case, components of the ribbed flat metal deck are illustrated in Figures 2 to Figures 6 and described as follows:

Figure 2: Presents the isometric appearance that shows diagonal rebar (4) that is zigzagged according to certain pattern. The toes of the diagonal rebar (4) are welded (5) to the longitudinal rebar (3) to form the stiffening rib.

Figure 3: The other toes of the diagonal rebar (4) of the stiffening rib are welded (5) to the flat metal deck (1) in the direction of L_\. These stiffening ribs are constructed every b apart for the span L_.

Figure 4: Similarly, the stiffening ribs may also be constructed in the direction of L , perpendicular to the formerly constructed in the direction of L_\, Figure 3. If L_\ is greater than L₂ then the elevation of the longitudinal rebar (3) in the direction of L_\ is slightly lower than that of the longitudinal rebar (3) in the direction of Li.

Figure 5: The diagonal rebar (4) that is bent by angle a with respect to the horizontal line connecting the toes of diagonal rebar (4) and then welded (5) to the flat metal deck ( 1 ) such that the plane that contains the diagonal rebar (4) forms an angle / with respect to the plane containing flat metal deck ( 1 ) and the distance of the plane containing the flat metal deck ( 1 ) to the apex of the diagonal rebar (4) is //. Similarly, the same procedure is applied to the adjacent diagonal rebar (4) that is welded (5) to the flat metal deck (1) at s apart so as to form an array of prisms. The longitudinal rebar (3) is then welded (5) to the prism at their apexes. Figure 6: Plan view of the flat metal deck (1), diagonal rebar (4) and longitudinal ii and £ , each at b spaced

Full Description of the Invention

According to Figure 1 and as explained in the Summary of the Invention, the stiffened flat metal deck as part of the isotropic composite concrete slab is designed to overcome the drawbacks of conventional corrugated metal deck that is oftenly used. The invention referred to in this document is intended particularly for composite concrete slab with relatively large span. The stiffened flat metal deck in this invention consists of a flat metal deck (1) and a stiffening element (2). The stiffening element (2) is attached to the upper side of the flat metal deck (1).

The stiffened flat metal deck will be monolithically cast with the concrete. The stiffening element (2) serves to resist compression and shear during concrete casting and curing. In the mean time, the flat metal deck (1) will resist tension. Therefore, it is no longer necessary to use temporary props, as are usually associated with conventional composite concrete slab, especially for relatively large span. In relatively long span constructions, for example bridges, the elimination of temporary props will reduce cost significantly as well as increasing the time efficiency considerably. When the concrete has achieved its full compressive strength, the stiffening element (2) will serve as shear connectors so that no special shear connectors are needed to guarantee the metal-concrete composite action.

Flat metal deck (1) will also perform as permanent formwork and a two-way tensile reinforcement so that the composite concrete slab can behave isotropically and resist bending in two directions, one thing that cannot be achieved by conventional corrugated composite concrete deck. Because of this mechanism, the geometry of the slab in this invention can be formed rather arbitrarily such as circular, trapezoidal, or triangular, and not as limited as previously for only rectangular and square shapes. The use of flat metal deck (1) can also reduce concrete volume by up to 20% because the concrete cover is no longer necessary and is removed. Remembering also of a neat surface of the flat metal deck (1), it is no longer necessary to install the ceiling as is common in building that uses conventional corrugated metal deck, so that in addition to efficiency, more space volume can be obtained, or if required, the floor-to-floor height can be reduced to get more cost-effective building.

As a special case and shown in Figure 5, diagonal rebar (4) is bent by angle a with respect to horizontal line connecting the toes of diagonal rebar (4) and then welded (5) to the flat metal deck ( 1) in such a way that the plane containing diagonal rebar (4) form an angle /to the plane that contains the flat metal deck ( 1 ). The distance of the flat metal deck ( 1 ) to the apex of the diagonal rebar (4) is h. Similarly, the same procedure is applied to the adjacent diagonal rebar (4) that is welded (5) to the flat metal deck (1 ) at 5 apart from one to the other so as to form an array of prisms. The longitudinal rebar (3 ) is then welded (5) to the prism at their apexes to form a stiffened flat metal deck.

The diameter of the diagonal rebar (4), D_tl , and the diameter of the longitudinal rebar (3), D₍ , can be determined

where:

Where:

D,- is the diameter of the longitudinal rebar (3), ω_r is the buckling coefficient of the segment of longitudinal rebar (3), q_w is the service load due to concrete slab and the flat metal deck (l),

L is the span of the flat metal deck (l), h is the distance of the longitudinal rebar (3) to the flat metal deck (1), f_}, the yield strength of the metal, λ_c is the slenderness ratio of the rebar, k_c is the effective length factor,

£ is the segmental length of the longitudinal rebar (3), r₍ is the radius of gyration of longitudinal rebar (3),

E is the elastic modulus of the metal,

D_d is the diameter of the diagonal rebar (4),

(Dd is the buckling coefficient of the diagonal rebar (4), β, γ are the angles according Figure 5, d is the segmental length of diagonal rebar (4), ι\ι is the radius of gyration of diagonal rebar (4).

The stiffening rib shown in Figure 2 that consists of pair of diagonal rebar (4) and longitudinal rebar (3) is constructed for the span length L_\ at every b apart for total width Li on the flat metal deck ( 1) [see Figure 3]. Perpendicular to the direction L_\, or parallel to the direction L₂, another stiffening ribs may also be constructed at b spaced for total span L₂. If L_\ is greater than L₂ then the elevation of longitudinal rebar (3) in the direction of L_\ is less than that of longitudinal rebar (3) in the direction of L₂ [see Figure 4],

Longitudinal rebar (3) is supposed to resist flexural compressive force, diagonal rebar (4) is to resist shear force, and the flat metal deck (1 ) serves to carry flexural tensile force at construction period when fresh concrete is poured and cured. Therefore, there is no need to provide temporary props as it is always

deck(l).

Claims

2. The stiffening element (2) as noted in Claim 1 is welded to the flat metal deck (1) and together is monolithically cast with the concrete. The stiffening element (2) will serve as shear connector when concrete has hardened and achieved its full compressive strength.

3. Flat metal deck (1) as referred to in Claim 1 is metal sheet that is relatively flat but may have shallow pattern or flat and smooth, however, it is not corrugated by more than 20 times its thickness.

4. As a special case, the stiffened flat metal deck as noted in Claim 1 can be constructed of a flat metal deck (1) and stiffening ribs, shown in Figure 2.

5. The rib as noted in Claim 4 consists of two pieces of diagonal rebar (4) and one piece of longitudinal rebar (3). Each diagonal rebar (4) is bent through certain angle a to horizontal line connecting the toes of diagonal rebar (4). The bottom apexes of the diagonal rebar (4) are welded to the flat metal deck (1) forming two lines each contains apexes of the same diagonal rebar (4). The distance between the line is s. Top apexes of each diagonal rebar (4) are welded to the longitudinal rebar (3). The distance between the longitudinal rebar (3) from the flat metal deck (1) is h. The planes that contain the diagonal rebar (4) form an angle /to the plane that contains the flat metal deck (1).

6. The stiffened flat metal deck as noted in Claim 4 is constructed by running the stiffening ribs as noted in Claim 5 in the direction of L_\ and one to each other is b spaced to full span of L₂ as shown in Figure 3.

7. In addition to Claim 6, the ribs may also be run in the direction of L₂ and one-to-the other is b spaced for the full length L_\ as in Figure 4. If L_\ is greater than L , the elevation of the longitudinal rebar (3) in the direction of L_\ is lower than that of longitudinal rebar (3) in the direction of L .