GB2155979A

GB2155979A - Lightweight lattice bridge

Info

Publication number: GB2155979A
Application number: GB08506241A
Authority: GB
Inventors: Paul Sigwalt
Original assignee: DIETRICH SA
Current assignee: DIETRICH SA
Priority date: 1984-03-12
Filing date: 1985-03-11
Publication date: 1985-10-02
Also published as: DE3508437A1; FR2560900B1; GB8506241D0; DE3508437C2; GB2155979B; FR2560900A1

Abstract

A lattice-work bridge supporting treadway (6), is characterised in that the treadway (6) is connected to two bottom bed members (8) and (9) by a flexible structure of articulated lattice-work composed of two vertical core edge lattices (18) and two constant-incline central lattices (19) according to two general directions which converge above the treadway, said constant incline being determined by the oblique flanges (14) of the section members (8) and (9) constituting the bottom bed. <IMAGE>

Description

SPECIFICATION Lightweight portable bridge of the latticework type by which mobile appliance S various vehicles can cross gaps The present invention relates to a lightweight lattice-work type of bridge to allow mobile appliances and various vehicles to cross gaps.

Various types of bridge are available, in particular lattice-work bridges. These are composed of a low linear structure of rectilinear metal elements: beams, rolled sections . . . and a treadway, connected by two edging lattices.

These edging lattices are formed from oblique metal elements which are repeated over the length of the bridge, the lattices having ends rigid on the one hand with the bottom linear structure and on the other with the treadway, the joints being made by welding, riveting, bolting or other method which provides the assembly with the rigidity desired.

This technique is likewise used on various works relating to road or rail crossings. For reasons of safety attaching to their intention and usage, such works are designed by applying the following principles.

Lightness does not in any way constitute an advantage for this type of application, by virtue of the fixed and immovable nature of these works. Indeed, the aim is to achieve maximum rigidity for the minimum of flexion which only the rigid nodal points of this type of structure can provide.

These rigid lattices result in constructions which are heavy for the loadings envisaged, constructions which can only be used as fixed installations.

In addition, there are lightweight structures having multiple lattices rigid with outer frameworks. In these structures, the outer frameworks are connected to one another along two or all lateral planes by edging lattices. This rigid outer assembly is completed by repetitive triangulation in successive transverse planes constituting the inner lattice or lattices.

The lattice-work elements are in this case likewise rigid with the frames at their ends to provide a compact and rigid assembly which permits of only a small amount of flexion in relation to the transverse nominal stresses involved.

Structures of this type are found mainly in metal constructions and on hoisting equipment used in building, such as for example the cranes of which the mast and jib are called upon to withstand considerable stresses without suffering any substantial deformation.

Indeed, in this field, the technical requirements indicate choosing structures of low deformation. This form of triangulation provides the desired rigidity while retaining a certain flexibility which makes it possible to tolerate moments of sudden overload.

The bridge according to the present invention has been designed with an eye to saving weight to produce a flexible structure which retains the basic qualities of strength and ruggedness and ability to withstand loads and torsional stresses.

As indicated, the object of the present invention is to impart to a bridge for crossing gaps an exceptional flexibility, remarkable lightness and easy installation while retaining the major qualities of strength and ruggedness.

The combination of these qualities is achieved by the bridge according to the invention which is characterised by the following features.

The treadway is connected to the two sole members by an articulated lattice structure composed of two vertical core edging lattices and two central lattices of constant inclination in two planes which converge above the treadway.

In contrast to prior constructions, the lattice cores do not intersect. They converge towards the central longitudinal zone of the treadway so that at regular intervals they constitute a double bearing point of variable spacing along inclined zones.

A structure erected to this design has made it possible to obtain the following technical performance: flexion approx. 600 mm for a span of 30 m, when carrying a 30-ton load, for a total inherent weight of not more than 4 tons. The desire to save weight led the inventor to provide a flexible structure inspired by a liana bridge which offers adequate mechanical strength to be able, with complete safety, to bear the considerable weight of an armoured vehicle, strength allied with exceptional flexibility, allowing it to be positioned by the cantilever method.

The various technical characteristics and other advantages of the present invention are set forth in the description which follows and in which reference is made by way of nonlimitative example to the accompanying drawings, in which: Figure 1 is a mixed perspective and plan view of the bridge according to the invention; Figures 2a and 2b are views of linear portions comprising the connecting joint between two portions and the beginning of the succession of elements which are formed as connecting rods; Figure 3 is a perspective view of a section showing the various connections and articulations at the level of a reinforcing cross-member, and Figures 4, 5 and 6 are cross-sectional views at three levels, one of which shows the central part and the other two a descending part, showing the remoteness of the central support points with the reduction in slope.

The description given hereinafter is of a three-section embodiment, two of the sections having a slope and the central section having a horizontal treadway. However, it goes without saying that this particular feature could not impart any limitative nature and that an embodiment having two sections designed according to the same general inventive idea would not depart from the scope of the present protection but, on the contrary, enters fully within the framework thereof.

Likewise, the width of the bridge described hereinafter could be adequate for the passage of the desired vehicles and consequently need not necessitate an additional bridge being used jointly with it, side by side.

Thus it is possible, using the same idea and the same technique, to construct a double width bridge which could be used for all the appliances and vehicles in a fleet, a group or an army corps.

As indicated, the bridge or the unitary crossing element according to the invention is composed of a central portion 1 having a horizontal top surface and two end portions 2 and 3 constructed as an inclined ramp, articulated inter se and completed by two removable flared trims 4 and 5. These flared trims constitute intermediate bearing members by which the bridge is in contact with the ground. If the slope is more pronounced, they form a transition between the soil and the body of the bridge. Similarly, the end portions act as access ramps to the central part.

Each portion has a treadway 6 consisting of reinforced rolled sections 7 disposed side by side and rigid with one another. The top face of these rolled sections is capable of constituting a treadway.

The bottom of the bridge is constituted by bottom bed members 8 and 9 which take the form of rolled sections 10 connected longitudinally inter se by double joints such as 11 for example with meshes 1 2 with linking plates made rigid by the use of cotter pins.

The rolled sections 10 have a straight section with a vertical flange 1 3 with, laterally in relation to it, an oblique flange 14 on which are mounted the elements of a lattice-work bearer structure 1 5. A vertical bottom flange 1 6 serves as a stiffener and for the fixing of cross-members 1 7.

The structure 1 5 consists of two groups of lattice structures articulated on the one hand on the lower bed members 8 and 9 and on the other on the cross-members provided on the underside of the treadway. There are a series of two edging lattices 1 8 which develop in vertical planes along the sides of each of the portions of the bridge.

The drawings also show a series of two central lattices 1 9 developing symmetrically in inclined oblique planes and converging above the treadway. The angle of inclination of these planes is determined by the incidence of the oblique flange 14 of the rolled sections 8 and 9 of the bottom bed members, which remains constant over the whole length of the structure.

The lattices are constituted by inclined straight edging elements 20 and central elements 21 in the form of tubes which have their top ends 22 formed as forks or other bifurcated members 23 each traversed by a spindle 24.

The bottom ends 25 are shaped and articulated directly and in the same way on the vertical flanges 1 3 and oblique flanges 14 of the rolled sections 8 and 9 of the bottom bed members.

For mechanical reasons, the elements of the lattice structures are replaced at the end of the section by double connecting rods 26 such as are shown in Figs. 2b and 6.

These elements converge alternately towards a top or bottom hinging point known as a nodal point of the lattice structure. For edging lattices, the drawings show upper nodal points 27 and lower nodal points 28 which are common to the edging lattices and the central lattices. The top ends of the central lattices, with their connecting elements, constitute bearing points to which reference will be made hereinafter.

As indicated, the elements 21 of the central lattices are articulated at the bottom part at a right-angle to the bottom nodal points 28 on the oblique flange 1 4. Also mounted at this point are the ends of cross-members 1 7 which, with the lattice elements, constitute succesive frames for the distribution of stresses.

The rolled sections 7 constituting the treadway 6 are joined transversely at intervals on the underside by reinforcing cross-members 29 consisting, for example of a profiled body of U-shaped cross-section and having vertical flanges. These cross-members comprise inner transverse plates 30 and outer transverse plates 31 provided between the flanges of the reinforcing cross-members 29 on which are articulated the ends of the elements 20 and 21 of the lattice structure.

The inner plates 30 are slightly inclined to respect the general direction of constant inclination determined by the oblique flanges 14.

Their spacing apart is variable according to their position on the slope line. The outer plates 31 constitute with the top ends of the elements 20 of the edging lattices, the upper nodal points 27.

The top ends of the central lattice elements 19, at the level of the inner plates 30, determine two bearing points A and B, the spacing apart of which varies according to the level of elevation on the oblique ramps, by virtue of their constant inclination determined by the oblique flanges 14 of the rolled sections 8 and 9 which go to constitute the bed.

This particular feature of the bridge according to the invention is illustrated in Figs. 4 to 6, corresponding to cross-sections at the bottom of the ramp, halfway up and at the top end of the ramp.

It will thus be appreciated that there is a central reinforcing zone 32 supported by bearing points A and B, the width of which diminishes progressively with the height.

This reinforcing zone 32, connected to the reinforcements provided in the rolled sections constituting the treadway 6, makes it possible substantially to increase the resistance to transverse flexion of the treadway, that is to say to achieve a remarkable resistance to spot impact from tyres.

The exceptional qualities of flexibility and resistance arise from the use of a double articulated lattice structure 1 5. To a certain extent, the joints may enjoy a movement tolerance allowing minimal movement while the triangulation and the frames for distribution of stresses constituted by the lattice elements and connecting members 1 7 achieve a distribution of stresses and multiple inter-reactions which contribute to the cohesion of the whole.

The offsetting forces engendered by a badly centered vehicle are thus completely absorbed.

The joints between two sections are provided by link joints 1 2 in the case of the bed sections and, for the treadways, by special reinforcing cross-members 33 having complementary shapes which fit into one another to constitute a pivoting axis.

To guarantee the rigidity of the connection, an additional vertical straight element 34 is articulatingly mounted between the reinforcing cross-member 33 and the bottom link joint 12.

In the definitive embodiment, it is envisaged to replace these connecting means by rapidly and automatically assembled joints of the snap-together type, for example.

It is interesting to note that the crossing means may be constituted by two bridges identical to those described hereinabove, each bridge constituting a passage for each wheel track.

The invention has been described in detail hereinabove; it is understood that various modifications and substitutions may be made which have no inventive contribution but which would not go beyond the scope of the present protection, entering instead perfectly well into its framework.

Claims

1. A lightweight lattice-work type of bridge to allow mobile appliances and various vehicles to cross gaps, characterised in that the treadway (6) is supported by an articulated lattice structure (15), edging sections (18) and central sections (19) articulatlingly mounted on the one hand on the rolled sections (8) and (9) of the bed, at regular intervals, at common points or lower nodes (28) and on the other on reinforcing cross-members (29) on the underside of the treadway (6) and in that the central lattices (19) are at a constant angle of inclination towards the treadway, all along the bridge, an angle of inclination according to two general directions which converge above the treadway (6).

2. Bridge according to Claim 1, characterised in that the rolled sections (8) and (9) constituting the lower bed comprise an upper vertical flange (13), an oblique flange (14) and a lower vertical flange (16).

3. Bridge according to Claim 1, characterised in that the central lattice elements (19) are articulated on the oblique flange (14) which determines their constant angle of inclination.

4. Bridge according to Claim 1, characterised in that the rolled sections (8) and (9) constituting the lower bed are connected transversely inter se by tie members (17).

5. Bridge according to Claim 1, characterised in that the ends of the edging lattice elements (18) and central lattice elements (19) are articulated at intervals at the top on one and the same reinforcing cross-member (29).

6. Bridge according to Claim 1, characterised in that the points of articulation of the central lattices (19) on the cross-members (29) determine two bearing points A and B which are spaced apart by a variable amount according to the position on the ramp of the inclined portions constituting the bridge.

7. Bridge according to Claim 1, characterised in that the reinforcing cross-members (29) provided on the underside of the treadway (6) are U-shaped rolled sections having vertical flanges connected inter se by inner plates (30) and outer plates (31) on which are articulatingly mounted respectively the ends of the elements of the central lattices (1 9) to constitute the upper nodes (27) and the ends of the edging lattice elements (18) to constitute the variably spaced apart articulating and bearing points A and B.

8. Bridge according to Claims 1 and 4, characterised in that the bottom ends of the elements (20) and (21) of the edging lattices (18) and central lattices (19) and the ends of the connecting members (1 7) terminate at intervals in a common zone on the rolled sections (8) and (9) of the bed to constitute the bottom nodal points (28).