Patent Application
20060272251
The present invention relates to composite floor systems, and more particularly the invention relates to a composite floor system with a floor slab positioned on one or more lower beams.
A composite floor system typically consists of a concrete floor slab positioned on several steel I-beams that extend in parallel. To act together in resisting loads, shear studs are typically resistance-welded to the top surface of the I-beams. The concrete that makes up the floor slab surrounds the shear studs, such that the entirety of each shear stud is embedded in the concrete.
When a vertical load is imposed on the floor system, a compressive load is developed in the concrete floor slab and a tensile force is developed in the I-beam. Such a system, however, typically has relatively low ductility. In general, systems having relatively lower ductility are less able to absorb energy from dynamic forces, such as those that occur during earthquakes, than systems with relatively higher ductility, such as pure steel structures.
In a first aspect, the invention is directed to a composite floor including at least one lower beam, a plurality of projections and a floor slab. The at least one lower beam is made from a metallic material. The at least one lower beam has a longitudinal direction. The at least one lower beam has an upper surface. Each projection has a connection to the upper surface of the at least one lower beam. Each projection extends upwards from the upper surface of the at least one lower beam. Each projection is metallic. The floor slab is made from a cementitious material. The floor slab is in contact with the upper surface of the at least one lower beam. Each projection has a first portion that is embedded in the floor slab. Each projection has a second portion that includes the connection. The second portion is spaced from the floor slab in at least a selected longitudinal direction.
The present invention will now be described by way of example only with reference to the attached drawings in which:
Reference is made to
The composite floor system further includes a plurality of projections 14 which extend upwards from each of the lower beams 12, and further includes a floor slab 16, which is positioned on the lower beams 12.
The lower beams 12 may be any suitable type of beam, such as, for example, I-beams or box beams. The lower beam 12 shown in
The lower beam 12 is made from a material that is ductile and resistant to catastrophic failure when experiencing tensile forces, such as can occur when the composite floor system 10 is loaded, and in particular during an earthquake or other event. An especially suitable material for the lower beam 12 is steel, however, other materials may be used.
The relative spacing between adjacent lower beams 12 may be selected at least in part based on the overall strength requirements of the floor system 10.
The projections 14 extend upwards from the upper surface 18 of the lower beam 12. The projections 14 may be positioned in a row along the longitudinally-extending, vertical-plane centerline, shown at CLvplong-lb in
Reference is made to
Around each projection 14 is an aperture 22 in the floor slab 16. The aperture 22 surrounds the projection 14 such that the projection 14 is spaced from the aperture wall, shown at 24 in the longitudinal direction by a distance Dlong. The aperture 22 may be circular, as shown in
The depth of the aperture 22 is selected so that a first portion 26 of the projection 14 is embedded within the floor slab 16, and a second portion 28 of the projection 14 is surrounded by the aperture and is therefore spaced from the aperture wall 24. The depth of the aperture 22 is shown at Dvert. It will be noted that the depth Dvert is the same as the length of the second portion 28 of the projections 14.
The projection 14 is made from a ductile material, and the connection 21 between the projection 14 and the lower beam 12 is a ductile connection, permitting a selected amount of deformation, including elastic and/or plastic deformation, prior to experiencing catastrophic failure. An example of a suitable material for the projections 14 is steel.
The projection 14 may be a stud, eg. a threaded rod, or may be some other member, such as, for example, a bolt.
The floor slab 16 rests on the upper surfaces 18 of the lower beams 12. As a result of the embedment of the projections 14 into the floor slab 16, the composite floor system 10 acts under load as a single, composite structure. The composite floor system 10 has a horizontal-plane centerline CLhp-fs that divides the floor system 10 into a lower half 30 and an upper half 32. In the absence of any pre-stressing of the components of the composite floor system 10, when the floor system 10 is under a bending load the bottom half 30 is in tension and the top half 32 is in compression. Preferably, the bottom half 30 of the floor system 10 includes substantially all of the lower beam 12, and preferably the top half 32 includes substantially all of the floor slab 16.
A suitable material for the floor slab 16 is a material that is strong in compression, such as, for example, a cementitious material. For the purposes of this disclosure, a cementitious material is any material that is a mixture of aggregate and matrix material such as, for example, concrete, Portland cement, or the like, that is known to a person skilled in the art for use in composite floor systems. Typically, such materials are poured into a form. They may be poured on site, or alternatively they may be poured and hardened first and subsequently shipped to the site for installation. The floor slab 16 has an upper surface 34, which may be covered with other layers to make up a floor having whatever physical or aesthetic properties are desired.
Referring to
There is a relationship between the longitudinal distance Dlong, the depth Dvert, the shape of the apertures 22 and the amount of longitudinal bending that can take place in the projections 14. Increasing the depth Dvert of the aperture 22 increases the lengths of the unembedded portions of the projections 14, ie. the lengths of the second portions 28, which in turn increases the energy absorption capability of the projections 14. However, care should be taken so that the embedded (ie. first) portions 26 of the projections 14 have sufficient length to meet the strength requirements of the installation.
In earthquake zones, a floor system may be required to be sufficiently strong to withstand a particular strength of earthquake, based on whatever regulations are applicable in the local jurisdiction. The ductility of the composite floor system 10 is a value that is related to the ability of the composite floor system 10 to absorb energy, such as the energy that would be imparted to the floor system during an earthquake. If a floor system is designed with sufficient ductility the strength of the floor system required by code can be reduced, because it is expected that such a floor system would be capable of absorbing a greater amount of energy than a rigid floor system without undergoing catastrophic failure in the event of an earthquake. As a result, the composite floor system 10 can be provided at less cost than a composite floor system without apertures around the projections, while still meeting the design requirements established by such regulations.
The longitudinal distance Dlong and the depth Dvert may be selected based at least in part on the overall ductility that is selected to be provided for the composite floor system 10. Additionally, or alternatively, the longitudinal distance Dlong and the depth Dvert may be selected based at least in part on a maximum selected bending load that the floor system is to withstand.
While it is preferable that the distance Dlong be equal to or greater than the aforementioned critical value, any spacing Dlong in combination with any depth Dvert permit some energy absorption to take place in the projections 14 and thus, provide some advantage over a composite floor system that lacks apertures around the projections.
The apertures 22 may be formed in the floor slab 16 by any suitable means. For example, in the case where the floor slab 16 is made from a material that is poured over the projections 14, a spacer 38 (see in particular
The spacers 38 may be made from a synthetic or natural polymeric material, such as, for example, a foam rubber. In embodiments where the spacers 38 are foam structures, they may include a projection aperture 40 (see
Other configurations for the spacers 38 would alternatively be suitable. For example, referring to
Adhesive or some other suitable bonding means may be used to hold the spacers 38 and 43 in place, so that they do not lift upwards when the material for the floor slab 16 is poured. For example, the spacer 38 may be bonded to the projection 14 with adhesive.
It is shown in
The particular composition of the steel or other ductile material used for the lower beams 12, connections 21 and projections 14 will be readily selectable by one skilled in the art based on the particular requirements of the installation of the composite floor system 10.
The apertures 22 formed in the floor slab 16 are shown in the figures as having walls 24 that extend directly vertically. It is alternatively possible for the aperture walls 24 to extend inwardly towards the projections 14 while extending upwards. Reference is made to
It is possible for the floor slab 16 to be manufactured prior to installation on the lower beams 12. In such an embodiment, the apertures 22 may be formed in the floor slab 16 by any suitable means, and they may remain empty, ie. with no spacer therein, after the floor slab 16 is installed on the lower beams 12. Suitable means, such as an adhesive paste could be provided in projection-receiving apertures in such a floor slab 16, for receiving the top, (ie. first), portions 26 of the projections 14 and for adhering the floor slab 16 thereto.
As will be apparent to persons skilled in the art, various modifications and adaptations of the apparatus described above may be made without departure from the present invention, the scope of which is defined in the appended claims.
