Static structures (e.g. – buildings) – Openwork; e.g. – truss – trellis – grille – screen – frame – or... – Truss with unitary chord and web; e.g. – sheet metal
Reexamination Certificate
2003-03-12
2004-10-19
Friedman, Carl D. (Department: 3635)
Static structures (e.g., buildings)
Openwork; e.g., truss, trellis, grille, screen, frame, or...
Truss with unitary chord and web; e.g., sheet metal
C052S652100, C052S651100, C052S648100, C052S645000, C014S013000, C014S014000
Reexamination Certificate
active
06804927
ABSTRACT:
This invention relates to lattice panel structures, such as bridges of the “Bailey” type. The invention is particularly concerned with a modular lattice panel system.
In a typical “Bailey” bridge construction there is provided a main girder at each side of the bridge, transoms extending between the girders and a deck supported on the transoms. The girders are formed from prefabricated lattice panels of steel which are joined together longitudinally. Two or more sets of the lattice panels may be secured together in the vertical direction so as to provide the required depth of girder, and to this end the panels are generally of a rectangular configuration. A common type of lattice panel consists of upper and lower longitudinally extending chords which are joined together by a lattice of web members. These will generally include vertically extending web members and angled web members which may for example extend at an angle of about 45° to the chords. Various panel configurations are disclosed in GB-A-2 251 018, for example.
To join the panels together in end to end relationship to provide the required length of girder, pin and aperture joints are usually employed to ensure speed and simplicity of assembly on site. One end of each chord will be formed with a female portion and one with a male portion. These are mated when the panels are to be joined together and then a transverse pin is inserted through apertures in the portions.
Bridges of the above type are often used as temporary structures, for example to replace bridges destroyed by floods, earthquakes or acts of war. They are supplied as prefabricated components which are assembled on site. In one common method of construction, the bridge girders are assembled on one side of the gap to be bridged, such as a river or ravine, and pushed out and over to the other side.
In a conventional system, the lattice panels are provided as completely prefabricated units with the web members welded to the chords. Typically, a standard length prefabricated panel will be available, and the designer of a bridge will use the appropriate number of these, to be joined end to end, for the bridge.
A significant advantage of using prefabricated panels is that bridges can be constructed quickly with the minimum of on-site fabrication however, there are design constraints due to the limited number of panel configurations available. It is also necessary to restrict the length of the prefabricated panels used as the basic units, so that there is sufficient flexibility to achieve a desired length by joining a number together. however, the joins between adjacent panels can be expensive, particularly if they are of the pin joint variety requiring forgings. The more panel units are required to span a given length, the more joins are required a further problem is that prefabricated panels are bulky to transport.
An object of the present invention is to provide a modular system for constructing lattice panels which provides greater flexibility but which does not increase to an undesirable level the time spent on site to construct a bridge.
Viewed from one aspect the present invention provides a modular system for the construction of a lattice panel for a structure, comprising first and second elongate chord members and a plurality of web members for attachment to the chord members so as to hold them apart transversely, wherein each web member comprises three legs forming a triangle, a first leg being adapted to extend perpendicularly between the chord members, and second and third legs being joined to each other and to adjacent the ends of the first leg, and wherein there are provided the following means for interlocking each web member to the chord members and to like web members:
first interlocking means adjacent one end of the first leg to interlock with corresponding second interlocking means provided at intervals along the first chord member;
third interlocking means adjacent the other-end of the first leg to interlock with corresponding fourth interlocking means provided at intervals along the second chord member;
fifth interlocking means adjacent the join between the second and third legs; and
sixth interlocking means intermediate the ends of the first leg;
the arrangement being such that the fifth interlocking means of one web member is adapted to interlock with the sixth interlocking means of an adjacent like web member.
Thus, in use a lattice panel can be constructed with upper and lower chord members and a lattice of web members providing vertical legs extending between and connected to the chord members, and inclined legs which are joined to the vertical legs of adjacent web members. Such an arrangement provides a strong lattice panel.
It is a simple matter to provide lattice panels of desired lengths, by selecting chord members of appropriate lengths and a corresponding number of web members. To cover a certain distance it may be possible to use a single panel constructed from the modular components with long chord members, rather than two or more standard lattice panels joined end to end. From a manufacturing point of view, it is preferable to fabricate and store the modular components capable of forming lattice panels of various lengths, rather than complete lattice panels of various lengths. Furthermore, the conventional joints between lattice panels, typically involving forged components, are expensive. The ability to construct longer panels, simply and from prefabricated components, reduces the total number of panels required for a particular job and thus the number of expensive joints The end user will also have fewer inter-panel joints to assemble if longer panels can be used.
The fabrication of the lattice panels may be carried out at a manufacturing site once an order is received, for shipment to a place of use. Alternatively, the modules may be shipped to the end user for assembly into panels on-site. This may be preferable from a shipping point of view. It may also be possible for the chord members to be manufactured locally if their design is simple enough, this being discussed below, so that only the web members have to be shipped.
It is known for the upper chords of lattice panels to be joined by simple compression joints, for example using abutting flanges and threaded fasteners. These chords can be made on site relatively easily. The lower chord joints are in tension and conventionally they have been in the form of pin joints which provide the required tensile strength whilst being relatively quick and simple to assemble. The pin joints are expensive, forged items, and it is less feasible to manufacture the lower chords on site. In accordance with the present invention, however, it is practical to use longer chords and fewer chord joints. For example, a panel in accordance with the invention may be between three and four times the length of a conventional panel. It is thus feasible to use alternative chord joints for the lower chords, which are cheaper and easier to manufacture even though it may take longer to join two chords. Thus, in one proposed arrangement the lower chord joints are provided by splice plates and several threaded fasteners. An advantage of such a simple joint is that the chords only need to be provided with apertures for the fasteners and it is a more practical proposition for the chords to be made on site.
There may be a number of different chords that can be used For example, a stronger chord could be provided if required. This could be only at suitable positions, such as at the centre of a bridge span. This avoids the need to take a standard lattice panel and add a reinforcing chord to it. It is also possible to introduce camber by using chords of different lengths at the top and bottom of a panel. A longer upper chord will introduce positive camber, resisting the tendency of a bridge to sag in the middle.
The interlocking means should be such that the modules can be assembled in the required orientation and also provide for the transfer of forces. In a preferred embodiment, where two interlocking means
Forsyth Richard Charles Edward
Mabey Bevil Guy
Richardson John Meynell
Friedman Carl D.
Mabey & Johnson Limited
Thissell Jennifer I.
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