SE2000043A1 - Self-locking filigree slab - Google Patents

Abstract

A filigree slab having one or more lateral surfaces provided with indentations.

Description

DESCRIPTION OF THE INVENTION (original version)SELF-LOCKING FILIGREE SLAB GENERAL DESCRIPTION The present invention relates to a self-Iocking filigree slab.

A filigree slab is a known precast thin plate-shaped element with regularand smooth lateral surfaces, comprising a layer of concrete reinforced witha mesh of orthogonal rebars and stiffening lattice steel girders, which actsas a self-supporting permanent formwork for pouring solid and/or non-solidReinforced Concrete (RC) slabs and bridge decks.

The use of filigree slabs is an effective solution for civil structures andinfrastructures since this construction system is economically efficient(i.e., it eliminates the need for traditional formwork), versatile andlabour/time-saving.

However, a technical disadvantage can be observed when such system isemployed for the construction of composite steel-concrete girder bridges.More precisely, the longitudinal shear strength of composite T-sectionswith precast permanent formworks is significantly reduced by the weaklateral connection between these latter and the cast-in-place concrete.This issue can be addressed by extending the mesh of orthogonal rebarsbeyond the formwork edges; nevertheless, such extension is not alwaysfeasible because of space limitations, as well as being uneconomical.

The instant invention overcomes this disadvantage by providing a filigreeslab with indented lateral surfaces interfacing with the surrounding cast-in-place concrete thus allowing a stronger interaction between the twostructural elements/materials.

The inventor is not aware of any prior art that anticipates or suggests thepresent invention.

The proposed self-Iocking filigree slab can be constructed in a variety ofembodiments without, of course, departing from the spirit of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES Fig. 1 is a perspective view of the present invention in a firstembodiment.

Fig. 2 is a top view of the present invention in the same embodiment as inFig. 1.

Fig. 3 is a schematic view of the configuration for the indentations.

Fig. 4 is a composite steel-concrete T cross-section made with precastpermanent formworks.

Fig. 5 is a cut-away perspective view illustrating a composite steel-concrete girder bridge deck constructed using the present invention.

Fig. 6 is a cut-away perspective view illustrating a precast concrete beambridge deck constructed using the present invention.

Fig. 7 is a cut-away perspective view illustrating a timber-concrete bridgedeck constructed using the present invention.

Fig. 8 is a perspective view of the present invention in a secondembodiment.

Fig. 9 is a perspective view of the present invention in a thirdembodiment.

DETAILED DESCRIPTION With reference to Figs. 1 and 2, the present invention is embodied in theform of a filigree slab having two opposite Iateral surfaces with prismaticindentations (1), comprising a RC layer (2) and five stiffening lattice steelgirders (3).

The schematic of the configuration of said indentation is shown in Fig. 3,where the cast-in-place concrete is poured around (4); it complies withFigure 6.9 in [l], geometric requirements for indented construction jointsin RC structures subjected to shear at the interface between concrete castat different times. ln order to explain how the indented Iateral surface works and itsadvantage, consider the longitudinal shear transfer mechanism in the slabof composite steel-concrete girder bridges. According to [2], the followingtwo statements hold: 1. The design longitudinal shear stress, vLEd, is determined from therate of change of the longitudinal force in either the steel or theconcrete element of the composite T-section, as well as across the width of its concrete flange (part of the slab which is effectivelycombined to the steel beam); and 2. The vLEd for any potential surface of longitudinal shear failure withinthe RC slab shall not exceed the design longitudinal shear strength,vtRd, of the shear surface considered, where the distribution of bothvcEd and vcRd is assumed to be uniform. lnterestingly, when the slab is made of a combination of prefabricatedelements (such as permanent formworks) and cast-in-place concrete, onecritical longitudinal shear failure surface is identified by a vertical planepassing through the interface between the two elements/materials (seeline a-a illustrated in Fig. 4). ln this case, the vLEd is divided into two parts,the stress acting on the prefabricated element/cast-in-place concreteinterface (5) and the stress acting on the cast-in-place concrete toppingflange (6); similarly, the respective vLRd is evaluated through two differentmethods, one invoking the shear resistance at said interface (see [1],Section 6.2.5) and the other based on the shear strength of said cast-in-place concrete topping flange (see [1], Section 6.2.4).

While, on the one hand, the vLRd of the cast-in-place concrete toppingflange is calculated by considering it as a system of compressive strutscombined with ties in the form of transverse tensile reinforcement(meaning that a certain amount of transverse tensile reinforcement isalways necessary for the shear strength to be generated), on the otherhand, the vtRd at the prefabricated element/cast-in-place concreteinterface is mainly derived from the frictional forces developed due tosliding and interlock, which depend on three factors: a) The interface roughness; b) Any external normal force across the interface that actssimultaneously with vtfd; and c) Any reinforcement crossing the interface with adequate anchorageat both sides of the interface.

With reference to point (a) above, it is not surprising that the use offiligree slabs with appropriate indented lateral surfaces instead of thetraditional ones with smooth edges results in a dramatic increase of saidinterface roughness, thus significantly enhancing the vLRd without the needto invoke any additional locking mechanism (see [1]).

Although the discussion above has been presented for composite steel-concrete girder bridges, it also applies to other composite systems, i.e., forexample, precast concrete beam bridges [3] and timber-concrete bridges[4]- ln Figs. 5 to 7 are shown cut-away perspective views of a compositesteel-concrete girder bridge deck, a precast concrete beam bridge deckand a timber-concrete bridge deck, respectively, constructed using thepresent invention. ln other embodiments of the present invention, the indentations may havedifferent shapes such as, e.g., parallelepiped or truncated cone (see Fig. 8and 9, respectively).

Claims (1)

1. A plate-shaped element used for the construction of solid and/or non-solid reinforcedconcrete slabs and bridge decks comprising a layer of either concrete or lightweightaggregate concrete, reinforced with either a rebar mesh or fibres or both and at least onestiffening lattice girder, characterized in that said plate-shaped element has as a minimumone lateral surface provided with indentations complying with the following requirements: 0 shape of a prismatoid or a solid of revolution; 0 depth, d, greater than or equal to 5 mm; 0 maximum base width, a, less than or equal to 10d; 0 sides/lateral surface inclined at angles of 0° to 30° with respect to the depth axis; and0 spacing ofthe indents, b, less than or equal to 10d.