Patent Application
20050210793
This invention relates to load supporting structures of the type in which concrete deck panels are supported by laterally spaced beams.
The support of decks on laterally spaced beams is of course widely used primarily in bridge decks but also in many other constructions wherein a concrete deck is applied over supporting beams such as in a parking lot or other building.
Conventionally the deck is reinforced with steel so that the steel accommodates tensions in the concrete structure. Thus the conventional deck includes a layer or mat of supporting steel adjacent the bottom of the cast deck and a second layer or mat of reinforcing steel adjacent the top surface of the cast deck. The steel layers are in tension and are required since, as is well known, concrete is very weak under tension. Reinforcing steel has however the significant problem that it can corrode in the presence of chlorides thus reducing the life of the structure and requiring periodic expensive maintenance to repair or replace due to the corrosion.
In U.S. Pat. No. 5,339,475 (Jaeger) there is shown and claimed a technique in which tension members are connected across the beams to prevent expansion or movement of the beams in the transverse direction and the layer of concrete is cast over those tension members. Under load, within the structure of the concrete, is therefore formed a compressive arch so that loads from the upper surface of the concrete deck are transferred downwardly and outwardly to the girders and then to the ends of the tension members attached to the beams. The tension members are attached into the concrete by upstanding studs which are cast into the concrete so that the concrete is prevented by the tension members for moving outwardly at its bottom surface.
The compressive arch thus formed does not require that the deck itself be in any way arched since the compressive arch is formed in the body of the deck by compressing areas of the deck as required to accommodate the loading point relative to the tension points caused by the transverse tension member.
The compressive arch thus formed within the body of the deck thus generates areas of micro tension within the structure since some parts are compressed while other parts are not compressed. It is known therefore that the concrete may be reinforced by short length or staple fibers to transfer the micro tensions across the concrete and reduce cracking. This technique therefore obviates the necessity for the reinforcing steel within the structure of the deck since the loading within the deck is compressive rather than intention.
The tensioning members are generally steel straps, which are generally welded to the girders, but these are located at or immediately adjacent the bottom surface of the concrete deck so that they are much further from the corrosive chlorides which enter the top surface of the deck. Thus they are much less susceptible to corrosion. In addition it is in some cases possible to expose at least a part of the length of the steel straps underneath the bottom of the concrete deck, particularly in the central area between the two support beams.
This technique of forming a compressive arch using transverse tension members has been widely disseminated and is becoming accepted with a number of installations being tried.
The above technique as disclosed in this patent has the disadvantage that all the concrete must be cast in place with the disadvantages of forming and disassembling shuttering which is highly labour intensive and can be difficult when the deck is located in convenient location.
In U.S. Pat. No. 5,850,653 (Mufti) issued Dec. 22, 1998 is disclosed a modification of the above technique in which the entire deck is pre-cast. In this arrangement therefore the tension straps are embedded in the pre-cast concrete deck panel during the casting process. In order to attach the pre-cast deck panel to the beams, the beams have welded thereon a series of sheer transfer studs which can be welded as individual studs or as an array of studs with the pre-cast panel having cooperating recesses in the underside which are filled with grout to receive and retain the deck panel.
This arrangement has the disadvantage that it requires on site welding of the studs and the studs are located in grout rather than in the concrete itself. This technique has not achieved significant success.
It is one object of the present invention, therefore, to provide an improved load supporting structure, such as a bridge deck, which utilizes the above compressive arch technique to avoid the use of corrosive tensioning elements within the concrete and which has advantages of improved installation.
According to one aspect of the present invention there is provided a load supporting structure comprising:
Preferably each of the slab anchoring members and the panel anchoring members comprises an upstanding shear transfer stud with a bottom end fastened to the respective tension member.
Preferably each shear stud has a shaft and an upper head of greater transverse dimension than the shaft.
Preferably the tension member extends to a position beyond an outer edge of the panel and wherein the at least one slab anchoring member is located on the tension member at the position beyond the outer edge of the panel. This avoids on site welding.
Preferably the compressive arch in the panel and in the slab avoids the requirement for transversely extending tension reinforcement in the panel and in the slab. That is the conventional steel reinforcing bar which provides tension reinforcement can be omitted thus avoiding the corrosion problems associated with steel.
Preferably a lower surface of the concrete panel is recessed at a center area between the outer edge portions such that tension member is exterior to the panel at the center area. This reduces the weight of the panel and also removes material which is not associated with forming the compressive arch.
Preferably each of the beams has on its support surface a support pad, which may be formed of an elastomeric material, extending longitudinally along the beam and defining the support surface.
Preferably the tension member is free from fixed connection directly to the beam. This is no longer necessary since the cast slab may be fastened to the beams, or the slab may be continuous across a series of beams such as in the deck of a parking lot.
Preferably the beam has slab anchoring members thereon for connection of the slab to the beam for communication of forces from the compressive arch in the slab to the beam.
The concrete of the slab and the panel may contain staple fibers for micro-crack reinforcement due to the tensions in the concrete caused by the formation of the compressed arch in part of the concrete while other parts remain uncompressed. Alternatively the concrete may contain non-corrosive rebar material.
According to a second aspect of the invention there is provided a method of forming a load supporting structure comprising:
According to a third aspect of the invention there is provided a pre-cast concrete panel for mounting on laterally spaced apart beams defining a space therebetween comprising:
In the accompanying drawings, which illustrate exemplary embodiments of the present invention:
In
The beams 10 and 11 are shown as steel beams having a horizontal upper support surface 13 but the beam is maybe formed of other materials including concrete. The beams are generally of a conventional nature.
The deck 12 is formed of a pre-cast panel 14 and a cast deck 15 which is cast over the pre-cast panel 14 in situ. The pre-cast panel is shown in
At the bottom of the cast panel 14 is cast in place a transverse tension member 16 in the form of a steel strap extending across the full width of the panel with end portions 16A and 16B projecting outwardly beyond the side edges 14D and 14C. As shown in
The strap 16 carries one or more steel transfer studs 17 at a position on the strap which is within the pre-cast panel 14. The studs 17 are of a conventional nature and include a shaft 17A and a head 17B with a bottom end 17C of the shaft welded to the strap. Thus the stud projects vertically upwardly from the horizontal strap with the head located within the body of the panel and the stud having a sufficient length such that it provides an effective anchor within the panel to transfer loading from the panel to the strap. In the arrangement shown in
Such studs are well known and the head at the top of the stud which is of greater transverse dimension than the shaft prevents any possibility of the panel lifting away from the strap under loading.
The first of the studs 17 closest the edge 14C or 14D is located above the edge of the surface 13 and just spaced from the edge over the top of the surface 13. The remaining stud or studs are located between the span of the beam so as to be located over the space between the beams.
The portions 16A of the tension strap carries two further shear transfer studs 18 which are located beyond the edges 14C and 14D respectively. These studs are of the same construction as the studs 17 but have a height greater than the studs 17 so they project above the top surface 14F of the panel 14.
In the arrangement shown in
In the finished construction of the deck, the cast in place concrete deck slab 15 is cast over the panel 14 using the panel 14 as a support for the casting without the necessity for additional shuttering. Thus the deck slab 15 is formed from cast concrete poured onto the panel 14 and poured onto the top surface 13 of the beams. The cast concrete deck 15 has a top surface 15A and has a surface 15B on top of the surface 14F of the panel. The cast concrete of the deck or slab 15 enters the area beyond the ends 14C and 14D of the panel onto the top surface 13 of the beams so as to encounter and engage the studs 18 on the straps 16. Thus the slab 15 is itself anchored to the tension members or straps 16.
The concrete forming the panel 14 and forming the slab 15 are both free from corrosive reinforcing tensioning members such as steel. The concrete may include staple fibers of a length and thickness and material as is well known to one skilled in the art sufficient to reinforce the concrete to prevent or reduce micro-cracking.
Some additional reinforcement may be provided of a non-corrosive nature such as a mesh or grid of a plastics material which simply assists in reducing cracking without providing any significant tensioning effects.
In the installation of the system, the beams are firstly installed and located at the required positions. The beams may be interconnected by suitable structural elements so as to ensure that they are located at the required spacing and are prevented from movement side to side beyond predetermined acceptable amounts.
With the beams in place, the pre-cast panel carrying the concrete material and the transverse tension straps is carefully placed onto the beams at the required position so that the side edges 14C and 14D are properly and accurately located just extending onto the surface 13. In this position the pre-cast panel 14 is itself sufficiently strong to accommodate loads using the compressive arch loading principal so that it can act to support the concrete to be cast in place including the necessary equipment to place that concrete. Thus with the panels in place, there is no necessity for any further structure elements or shuttering to receive the casting of the concrete. Thus with the panels in place, the structure is closed and can accommodate loading from the engineers and other operators passing over the panels.
With the panels in place, the concrete is simply poured to form the slab 15. The slab 15 can be terminated at the outside edges of the beams as shown in
In some cases it is desirable to provide additional studs 19 attached to the top surface of 13 of the beams. These studs are arranged either in clusters or in spaced array along the length of the beam and act to anchor the slab 15 to the beams. Thus if the anchors 19 are used, there is a connection between the slab and the beams. As the slab is connected to the panel by the anchors 18 and 17, this locates the whole structure onto the beam.
Whether or not the anchors 19 are used, there is no necessity to attach the tension strap 16 to the beam so that these are loosely placed on top of the surface 13 and there is no welding required for permanent attachment or for transfer of the loads. To provide a better support of the panel 14 on the surface 13, a resilient or elastomeric strip 20 can be provided which is relatively narrow in comparison with the surface 13 and is located under the edge of the panel along the length of the beam and along the length of the panel. A suitable material is neoprene, but other similar materials may be used.
As shown in
As shown in
Typical panels may have a width of 1.5 to 3.0 meters. The thickness of the panel may be of the order of 75 to 100 mm and the thickness of the completed deck including the cast slab and the panel will be of the order of 200 to 300 mm. The weight of the typical panel will such that it is simple to handle and can be readily positioned at the required location.
Further details relating to this invention may be found in the above references of Jaeger and Mufti, the disclosures of which are incorporated herein by reference.
While specific embodiments of the invention have been described in the foregoing, it is to be understood that these embodiments are only exemplary. Other embodiments of the invention are possible and are intended to be included within the invention. Thus, while the exemplary embodiments use steel straps in the tension members, the straps may be formed of any suitable tension-sustaining material. Where reference is made to non-metallic, reinforcing fibres, these may be any suitable material, for example aramid, polypropylene or glass. The invention is thus to be considered limited solely by the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2,460,643 | Feb 2004 | CA | national |
