阅读说明：本技术 一种大跨度钢桁组合连续梁结构及其施工方法 (Large-span steel truss combined continuous beam structure and construction method thereof ) 是由 李前名 邹向农 王旋 龙俊贤 牛军辉 马行川 范昕 于 2019-11-14 设计创作，主要内容包括：本发明提供了一种大跨度钢桁组合连续梁结构,包括混凝土桥面板、两组钢桁架、边跨支点及中支点；钢桁架包括上弦杆和下弦杆,上弦杆和下弦杆之间连接有多根腹杆；上弦杆为水平直杆结构,两根上弦杆之间设上平联,混凝土桥面板与钢桁架的上弦杆连接,下弦杆呈抛物线形状,边跨全长及中跨负弯矩区域内的两根下弦杆之间设混凝土底板,中跨剩余区域的两根下弦杆之间设下平联。该发明采用钢桁梁作为主受力结构,混凝土桥面板与上弦杆结合,边跨及主跨部分区域内设置混凝土底板并与下弦杆结合,充分发挥钢结构轻质、高强的特性,能够适应更大的桥梁跨度,且该组合梁残余徐变下挠值非常小,结构总高度小于其他混凝土组合结构桥梁。(The invention provides a large-span steel truss combined continuous beam structure, which comprises a concrete bridge deck, two groups of steel trusses, an edge-span fulcrum and a middle fulcrum; the steel truss comprises an upper chord and a lower chord, and a plurality of web members are connected between the upper chord and the lower chord; the upper chord is of a horizontal straight rod structure, an upper parallel connection is arranged between the two upper chords, the concrete bridge deck is connected with the upper chords of the steel truss, the lower chords are in a parabola shape, a concrete bottom plate is arranged between the two lower chords in the side span total length and the mid-span negative bending moment area, and a lower parallel connection is arranged between the two lower chords in the mid-span residual area. The steel truss girder is used as a main stress structure, the concrete bridge deck is combined with the upper chord member, the concrete bottom plate is arranged in the side span and the partial area of the main span and is combined with the lower chord member, the characteristics of light weight and high strength of the steel structure are fully exerted, the steel truss girder can adapt to larger bridge span, the residual creep and downwarp value of the composite girder is very small, and the total height of the structure is smaller than that of other concrete composite structure bridges.)

1. The utility model provides a continuous beam structure of large-span steel purlin combination which characterized in that: the concrete bridge deck comprises a concrete bridge deck, two groups of steel trusses which are oppositely arranged and used for supporting the concrete bridge deck together, and two side span supporting points and two middle supporting points which are used for supporting the steel trusses; the steel truss comprises an upper chord member and a lower chord member which are arranged along the direction of the bridge in a through-length mode, and a plurality of web members are connected between the upper chord member and the lower chord member; the upper chord is of a horizontal straight rod structure, the upper chords of the two groups of steel trusses are connected with the upper chords of the two groups of steel trusses in an upper parallel connection mode, the two sides of the transverse bridge of the concrete bridge deck are connected with the upper chords of the two groups of steel trusses respectively, the lower chords are in a plurality of parabolic shapes which are connected continuously, the two ends of each lower chord are supported on two side span supporting points respectively, the lowest point of each lower chord is supported on a middle supporting point, a concrete bottom plate is arranged between the lower chords of the two groups of steel trusses in a negative bending moment area of the middle span and in a side span full-length area, and the lower parallel connection is arranged between the.

2. The long-span steel truss composite continuous beam structure of claim 1, wherein: many web members between last chord member and the lower chord member are connected in order end to end and are formed the sawtooth configuration, and connect through the gusset plate between two adjacent web members.

3. The long-span steel truss composite continuous beam structure of claim 2, wherein: the steel truss adopts the all-welded structure, the gusset plate adopts full circular arc transition structure.

4. The long-span steel truss composite continuous beam structure of claim 1, wherein: the upper parallel connection comprises a plurality of upper cross beams arranged between the two upper chords at intervals along the bridge direction and upper inclined struts arranged between the two adjacent upper cross beams; the two ends of the upper cross beam are respectively fixed on the two upper chords, the upper cross beam extends along the horizontal cross bridge direction, and the bottom of the concrete bridge deck is connected with the upper cross beam.

5. The large-span steel truss composite continuous beam structure of claim 4, wherein: the concrete bridge deck slab is characterized in that longitudinal and transverse wet joints are respectively arranged in the longitudinal direction and the transverse direction of the concrete bridge deck slab, the longitudinal wet joints are arranged on the top surface of the upper chord, the longitudinal wet joints are connected with the upper chord through shear nails, the transverse wet joints are arranged on the top surface of the upper cross beam in parallel connection, and the transverse wet joints are connected with the upper cross beam through shear nails.

6. The long-span steel truss composite continuous beam structure of claim 1, wherein: the lower horizontal connection comprises a plurality of lower cross beams arranged between the two lower chords at intervals along the bridge direction and lower inclined struts arranged between the two adjacent lower cross beams; two ends of the lower cross beam are respectively fixed on the two lower chords, and the lower cross beam extends along the horizontal transverse bridge direction.

7. The long-span steel truss composite continuous beam structure of claim 1, wherein: the thickness of the concrete bottom plate is the same as the height of the lower chord, and the concrete bottom plate is connected with the lower chord through the shear nails.

8. The long-span steel truss composite continuous beam structure of claim 1, wherein: and a plurality of longitudinal prestressed reinforcements are arranged in the concrete bridge deck.

9. The construction method of the long-span steel truss combined continuous beam structure as claimed in any one of claims 1 to 8, comprising the steps of:

1) the construction of the bridge pier is completed, and meanwhile, the concrete bridge deck and the steel truss girder segment are prefabricated in a factory;

2) symmetrically and synchronously installing steel truss girder segments from two middle supporting points to two sides until the steel truss girders are folded;

3) the method comprises the following steps of (1) taking a steel truss girder as a support, adopting a concrete bottom plate between two lower chords in a hogging moment area of a mid-span and a side span full-length area of a hanging basket cast-in-place, and welding shear nails at corresponding positions of an upper chord and an upper parallel top surface;

4) and (3) mounting prefabricated concrete bridge deck boards above the steel trussed beams one by one, and constructing longitudinal and transverse wet joints on the top surfaces of the upper chords and the upper parallel upper cross beams to complete the connection of the concrete bridge deck boards and the steel trussed beams.

10. The construction method of a long-span steel truss combined continuous beam structure as claimed in claim 9, wherein the age of the concrete bridge deck is more than 6 months before being transported to a site for installation.

Technical Field

The invention belongs to the technical field of bridge design and construction, and particularly relates to a large-span steel truss combined continuous beam structure and a construction method thereof.

Background

The high-speed railway has very strict requirements on deformation and settlement of bridges and roadbed, which is one of the key control factors for the type selection of high-speed railway bridges. The prestressed concrete beam has the advantages of high rigidity, good dynamic performance and convenience in maintenance and repair, and is a preferred beam type of the railway bridge. However, the concrete structure has the characteristics of shrinkage and creep, and the mid-span deflection gradually increases along with the time. At present, the maximum span of the high-speed rail prestressed concrete continuous beam is about 135m, theoretically, when the maximum span exceeds 150m, the residual creep downwarping value after track laying is difficult to control within the range of 20mm (L/5000) allowed by the specification. Meanwhile, the nonlinear problem brought by the large span has more remarkable influence and the structural risk is increased.

In order to avoid the problems, the existing domestic high-speed railway main span 150-300 m concrete beam type bridge generally adopts a combined structure system, such as a beam-arch combined structure, a beam-truss combined structure, a short-tower cable-stayed bridge and the like. The systems all use a concrete beam as a main stress structure, an arch, a truss and a tower-stayed cable as stiffening structures, and the stiffening structures are used for controlling the downwarping of a main span and reducing the stress level of the concrete main beam.

However, the high-speed railway composite structure system bridge has some problems: (1) the suspension rods, the stay cables and the like are of a multi-time statically indeterminate structure, the tension force influences the line shape of the bridge deck, and the construction precision requirement is high; (2) the replacement of the hanger rod and the stay cable has great influence on railway operation; (3) the height above the bridge deck is large, and the aviation height limit can be broken through; (4) when the concrete bridge deck is stiffened by the steel truss, the appearance is poor, and the maintenance and coating operation of the steel structure above the bridge deck can be only carried out in skylight points.

Within the span range, the steel truss girder is a bridge type with high competitiveness, high rigidity, small later deformation and convenient and quick construction. The traditional railway steel truss girder is generally of a lower bearing type, namely a railway bridge deck is attached to a lower chord member and is surrounded on the inner side by a truss web member, and the view of passengers is blocked when the passengers take a bus; and the steel truss girder with large span and high height generally keeps the lower chord horizontal, the change of the girder height is realized by the change of the upper chord, and the modeling is not as simple and clear as that of a concrete continuous girder.

Disclosure of Invention

The invention aims to solve the problems that the existing long-span bridge taking a concrete beam as a main stress structure and a steel structure as a stiffening structure has higher construction precision requirement, larger overall height, limitation of aviation height limitation and inconvenience in steel structure maintenance.

Therefore, the invention provides a large-span steel truss combined continuous beam structure, which comprises a concrete bridge deck, two groups of steel trusses which are oppositely arranged and are used for supporting the concrete bridge deck together, and two side span supporting points and two middle supporting points which are used for supporting the steel trusses; the steel truss comprises an upper chord member and a lower chord member which are arranged along the direction of the bridge in a through-length mode, and a plurality of web members are connected between the upper chord member and the lower chord member; the upper chord is of a horizontal straight rod structure, the upper chords of the two groups of steel trusses are connected with the upper chords of the two groups of steel trusses in an upper parallel connection mode, the two sides of the transverse bridge of the concrete bridge deck are connected with the upper chords of the two groups of steel trusses respectively, the lower chords are in a plurality of parabolic shapes which are connected continuously, the two ends of each lower chord are supported on two side span supporting points respectively, the lowest point of each lower chord is supported on a middle supporting point, a concrete bottom plate is arranged between the lower chords of the two groups of steel trusses in a negative bending moment area of the middle span and in a side span full-length area, and the lower parallel connection is arranged between the.

Furthermore, a plurality of web members between the upper chord member and the lower chord member are sequentially connected end to form a zigzag structure, and two adjacent web members are connected through a gusset plate.

Furthermore, the steel truss adopts an all-welded structure, and the gusset plate adopts an all-circular arc transition structure.

Further, the upper parallel connection comprises a plurality of upper cross beams which are arranged between the two upper chords at intervals along the bridge direction, and upper inclined struts which are arranged between the two adjacent upper cross beams; the two ends of the upper cross beam are respectively fixed on the two upper chords, the upper cross beam extends along the horizontal cross bridge direction, and the bottom of the concrete bridge deck is connected with the upper cross beam.

Furthermore, the concrete bridge deck is provided with a longitudinal wet joint and a transverse wet joint in the longitudinal and transverse directions respectively, the longitudinal wet joint is arranged on the top surface of the upper chord, the longitudinal wet joint is connected with the upper chord through shear nails, the transverse wet joint is arranged on the top surface of the upper cross beam in the upper parallel connection, and the transverse wet joint is connected with the upper cross beam through the shear nails.

Further, the lower horizontal connection comprises a plurality of lower cross beams arranged between the two lower chords at intervals along the bridge direction, and lower inclined struts arranged between the two adjacent lower cross beams; two ends of the lower cross beam are respectively fixed on the two lower chords, and the lower cross beam is arranged along the horizontal transverse bridge direction.

Furthermore, the thickness of the concrete bottom plate is the same as the height of the lower chord, and the concrete bottom plate is connected with the lower chord through the shear nails.

Furthermore, a plurality of longitudinal prestressed reinforcements are arranged in the concrete bridge deck.

In addition, the invention also provides a construction method of the large-span steel truss combined continuous beam structure, which comprises the following steps:

1) the construction of the bridge pier is completed, and meanwhile, the concrete bridge deck and the steel truss girder segment are prefabricated in a factory;

2) symmetrically and synchronously installing steel truss girder segments from two middle supporting points to two sides until the steel truss girders are folded;

3) the method comprises the following steps of (1) taking a steel truss girder as a support, adopting a concrete bottom plate between two lower chords in a hogging moment area of a mid-span and a side span full-length area of a hanging basket cast-in-place, and welding shear nails at corresponding positions of an upper chord and an upper parallel top surface;

4) and (3) mounting prefabricated concrete bridge deck boards above the steel trussed beams one by one, and constructing longitudinal and transverse wet joints on the top surfaces of the upper chords and the upper parallel upper cross beams to complete the connection of the concrete bridge deck boards and the steel trussed beams.

Further, the age of the concrete bridge deck plate is more than 6 months, and then the concrete bridge deck plate is transported to the field for installation.

Compared with the prior art, the invention has the beneficial effects that:

(1) the large-span steel truss combined continuous beam structure provided by the invention adopts the steel truss as a main stress structure to fully exert the characteristics of light weight and high strength of the steel structure, can adapt to larger bridge span, and avoids the problems that the residual creep deflection of the large-span concrete beam after track laying is too large and the related technical requirements of high-speed rails cannot be met; and meanwhile, the concrete bridge deck is adopted, so that the defects of large vibration and large noise of the steel bridge deck are overcome, and the maintenance is more convenient.

(2) According to the large-span steel truss combined continuous beam structure, the concrete bridge deck, the concrete bottom plate and the steel truss beam form double combination, the rigidity of the bridge structure is increased, the side span concrete bottom plate plays a role in weighting, tension at a side span pivot is avoided, a tension support with a complex structure is not needed, meanwhile, the concrete bottom plate in a middle span negative bending moment area and the lower chord are pressed together, and the steel consumption of the lower chord is reduced; and longitudinal prestressed reinforcements are arranged in the concrete bridge deck and participate in stress together with the upper chord member, so that the steel consumption of the upper chord member at the middle supporting point is reduced.

(3) The large-span steel truss combined continuous beam structure provided by the invention adopts the deck type variable-height steel truss combined beam, the upper chord member is kept horizontal, the lower chord member is changed in a curve manner, the total height of the building is obviously smaller than that of other combined structures with the same span, and meanwhile, the web members are constructed by full-arc type node plates, so that the structure is transparent and attractive.

(4) The steel truss girder in the long-span steel truss combined continuous beam structure provided by the invention is arranged below the bridge floor, the position above the bridge floor is the same as that of a common concrete beam, and the coating and maintenance operation of the steel structure is below the bridge floor, so that the steel truss girder structure has no influence on railway operation.

The present invention will be described in further detail below with reference to the accompanying drawings.

Drawings

FIG. 1 is a schematic view of the vertical structure of the long-span steel truss composite continuous beam structure of the invention;

FIG. 2 is a schematic cross-sectional view of a bridge of the present invention where the concrete bottom plate is attached to the lower chord;

FIG. 3 is a schematic cross-sectional view of a bridge of the present invention where the lower chords are connected in parallel.

Description of reference numerals: 1. a concrete deck slab; 2. an upper chord; 3. a web member; 4. a lower chord; 5. a gusset plate; 6. an edge-span fulcrum; 7. a middle fulcrum; 8. a concrete floor; 9. upper parallel connection; 10. shear nails; 11. a longitudinal wet seam; 12. and (4) lower parallel connection.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it is to be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention. In the description of the present invention, the meaning of "plurality" or "a plurality" is two or more unless otherwise specified.

As shown in fig. 1, 2 and 3, the present embodiment provides a long-span steel truss combined continuous beam structure, which includes a concrete bridge deck 1, two sets of steel trusses oppositely arranged for supporting the concrete bridge deck 1 together, and two side span fulcrums 6 and two middle fulcrums 7 for supporting the steel trusses; the steel truss comprises an upper chord member 2 and a lower chord member 3 which extend along the bridge direction, and a plurality of web members 4 are connected between the upper chord member 2 and the lower chord member 3; the upper chord 2 is of a horizontal straight rod structure, the upper chords 2 of the two groups of steel trusses are connected with the upper parallel connection 9, the two sides of the transverse bridge of the concrete bridge deck 1 are respectively connected with the upper chords 2 of the two groups of steel trusses, the lower chord 3 is in a plurality of sections of parabola shapes which are continuously connected, the two ends of the lower chord 3 are respectively supported on the two side cross supporting points 6, the lowest point of the lower chord 3 is supported on the middle supporting point 7, a concrete bottom plate 8 is arranged between the hogging moment area of the middle span and the lower chords 3 of the two groups of steel trusses in the side span full length area, the concrete bottom plate 8 of the side span plays a role in weighting, tension force is prevented from appearing on the side cross supporting points 6, and a tension support with a complex structure; the concrete bottom plate 8 in the mid-span negative bending moment area can participate in compression together with the lower chords 3, so that the steel consumption of the lower chords 3 is reduced, and a lower parallel connection 12 is arranged between the two lower chords 3 in the remaining area of the mid-span so as to keep the steel truss beam stable transversely. In the embodiment, the steel truss girder with the upper bearing type variable height is used as a main stress structure, the characteristics of light weight and high strength of a steel structure are fully exerted, and the steel truss girder can adapt to larger bridge span, the concrete bridge deck 1 is combined with the upper chord 2 of the steel truss girder, and the concrete bottom plate 8 is arranged in the side span and the mid-span part area and is combined with the lower chord 3 of the steel truss girder, so that the steel truss composite girder has a very small residual creep and downwarp value and the total height of the structure is smaller than that of other concrete composite structural bridges, and the problems that the residual creep and warp of the existing large-span concrete girder after track laying are too large and cannot meet the related technical requirements of high-speed rails are solved; meanwhile, the steel truss girder is arranged below the concrete bridge deck 1, and the coating and maintenance operation of the steel structure is performed below the bridge deck, so that the railway operation is hardly influenced.

The embodiment that refines, concreties each other through web member 4 between upper chord 2 and the lower chord 3, and many web members between upper chord 2 and the lower chord 3 are connected in order end to end and are formed jagged structure, and connect through gusset plate 5 between two adjacent web members 4, connect into one whole with many web members 4 through gusset plate 5, have increased steel truss structure's vertical rigidity. Optimized, the steel truss adopts the all-welded structure, gusset plate 5 adopts full circular arc transition structure, has reduced with steel volume and structure dead weight, improves the stress concentration of node, and the steel truss segment can wholly transport and hoist and mount, has reduced on-the-spot welded joint, and lower chord 3 adopts curve (continuous secondary parabola) to change simultaneously, cooperates 5 structural designs of full circular arc formula gusset plate for the steel truss is handsome in appearance thoroughly, pleasing to the eye.

Specifically, the upper horizontal connection 9 comprises a plurality of upper cross beams arranged between two upper chords 2 at intervals along the bridge direction, and upper inclined struts arranged between two adjacent upper cross beams; the two ends of the upper cross beam are respectively fixed on the two upper chords 2, the upper cross beam extends along the horizontal cross bridge, and the bottom of the concrete bridge deck 1 is connected with the upper cross beam. The lower horizontal connector 12 comprises a plurality of lower cross beams arranged between the two lower chords 3 at intervals along the bridge direction, and lower inclined struts arranged between the two adjacent lower cross beams; two ends of the lower cross beam are respectively fixed on the two lower chords 3, and the lower cross beam is arranged along the horizontal transverse bridge direction. In the embodiment, the transverse stability of the upper part and the lower part of the steel truss girder structure is effectively ensured through the design of the cross beams and the inclined struts of the upper parallel connection 9 and the lower parallel connection 12.

In addition, in the embodiment, the concrete bridge deck 1 is prefabricated in a block manner, when the concrete bridge deck 1 is installed in a splicing manner, longitudinal and transverse wet joints 11 and transverse wet joints (not shown in the figure) are respectively arranged in the longitudinal direction and the transverse direction of the concrete bridge deck 1, the longitudinal wet joint 11 is arranged on the top surface of the upper chord 2, the longitudinal wet joint 11 is connected with the upper chord 2 through the shear nails 10, the transverse wet joint is arranged on the top surface of the upper cross beam 9, the transverse wet joint is also connected with the upper cross beam through the shear nails, and a steel-concrete combined system is formed by the upper chord 2 and the shear nails on the top surface of the upper cross beam and the concrete bridge deck 1. The thickness of the concrete bottom plate 8 is the same as the height of the lower chord 3, and the concrete bottom plate 8 and the lower chord 3 are connected through shear nails to form a whole. Optimally, the concrete bridge deck plate 1 is internally provided with not only common steel bars, but also a plurality of longitudinal prestressed steel bars so as to avoid tensile cracking of the concrete bridge deck plate 1; the concrete bottom plate 8 is mainly stressed or is under the action of smaller tensile stress, and the concrete bottom plate 8 is only provided with common steel bars without prestressed steel bars.

Taking a continuous beam of a through-type variable-height steel truss combined beam with a span of (86 +172+ 86) m on a high-speed railway as an example, the height of the steel truss beam at the middle fulcrum is 15m, and the height of the steel truss beam at the middle and side-span fulcrum is 7.5m, and the specific construction process is as follows:

firstly, the construction of the bridge pier is completed, and the concrete bridge deck 1 and the steel truss girder segment are prefabricated in a factory. The concrete bridge deck 1 is prefabricated in blocks, the maximum block size is 6.8 multiplied by 2.8m, the thickness is 40cm, and the concrete bridge deck is stored for more than 6 months and then transported to the site for installation. The steel truss girder is manufactured in sections in a factory, an all-welded process is adopted, transportation and hoisting are carried out in a river channel shipping mode, the maximum size of the steel truss girder section is 17.2 multiplied by 15 multiplied by 8.7m, and the maximum hoisting weight is 180 tons.

Then, the steel truss girder segments are symmetrically and synchronously installed from the two middle supporting points 7 to the two sides until the steel truss girder is folded. And then, taking the steel truss girder as a support, adopting a concrete bottom plate 8 between two lower chords 3 in a hogging moment area of a midspan and a side span full-length area of a hanging basket cast-in-place, and simultaneously welding shear nails 10 at corresponding positions of the top surfaces of the upper chords 2 and the upper flat connector 9. Specifically, a concrete bottom plate 8 is arranged in the range from each side span 86m and the middle fulcrum 7 to the span center 52m, an L10 temporary angle steel cross brace is arranged between the lower chords 3 in the range, and a lower parallel connection 12 is arranged between the other two lower chords 3 in the range without the concrete bottom plate 8 in the span center; the thickness of the concrete bottom plate 8 and the height of the lower chord 3 are both 120cm, only common steel bars are arranged, and no prestressed steel bars are arranged.

Finally, the prefabricated concrete bridge deck slab 1 is installed above the steel truss girder piece by piece, the width of a longitudinal wet joint 11 is 60cm, the width of a transverse wet joint is 40cm, the longitudinal wet joint 11 is arranged on the top surface of the upper chord 2, the transverse wet joint is arranged on the top surface of the upper crossbeam, and a steel-concrete combined system is formed through the shear nails on the top surfaces of the upper chord 2 and the upper crossbeam, so that the connection of the concrete bridge deck slab and the steel truss girder is completed.

The concrete bridge deck slab 1 is installed after the steel trussed beams are erected and the concrete bottom plate 8 is poured, and the fixing process enables the concrete bridge deck slab 1 to bear the effects of second-stage constant load and live load only and not bear the effects of the steel trussed beams and the dead weight of the concrete bottom plate 8, so that the high-strength advantage of a steel structure is fully played, and the tensile force borne by the concrete bridge deck slab 1 in the hogging moment area near the middle fulcrum is reduced.

Optimally, a row of longitudinal prestressed reinforcements are arranged in the concrete bridge deck slab 1, and the prestress adopts 15-phi ^sThe transverse spacing of the 15.24 steel strands is 25cm, the cross section of the middle fulcrum is totally 40 prestressed steel bundles, and 8 prestressed steel bars are symmetrically anchored from the middle fulcrum to two sides at intervals of 17.2 m. The prestressed reinforcement bundle anchoring points are arranged at the positions without steel cross beams below the concrete bridge deck.

Through calculation and verification, after the track laying is finished, the residual creep deflection of the midspan and the side span is 3mm, the deflection under static and live load is 104mm, and the technical requirements of high-speed rails at the speed of 350km/h are met.

The above examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention, which is intended to be covered by the claims and any design similar or equivalent to the scope of the invention.