GB2045848A - Improvements relating to plank bridges - Google Patents

Abstract

A girder unit for use singly or severally in the construction of a plank bridge comprises an elongated deck plate (1) having its central part secured to and supported by a vertical web (2) which extends beneath and longitudinally of the deck plate and has base support flanges (3, 4). Reinforcing channels (5) spaced from each side of the web (2) are secured to the underside of the deck plate (1) and extend longitudinally of it. Also a plurality of transverse stiffeners (6,7) are secured beneath the deck plate (1) at intervals along its length. Means preferably comprising lugs (10) with holes (11) and dowels (12) are provided along each side of the girder unit for enabling identical girder units to be attached alongside one another for obtaining different width bridges. Each plank end may be provided with a plurality of bearings 7 superfluous ones of which may be severed from the plank depending on the span. <IMAGE>

Description

SPECIFICATION Improvements relating to plank bridges This invention relates to plank bridges and more particuiarly to a girder unit for use in the construction of such bridges. The invention has been devised with the general object of providing a versatile girder unit of relatively simple form and construction and which alone or in combination with other similar girder units readily permits the construction of plank bridges of various desired widths.

In accordance with the invention, a girder unit for a plank bridge comprises an elongated deck plate having its central part secured to and supported by a vertical web which extends beneath and longitudin Jolly of the deck plate and which has base support flanges; reinforcing channels spaced from each side of the web secured to the underside of the deck plate and extending longitudinally thereof; and a plurality of transverse stiffeners fixed beneath the deck plate at intervals longitudinally thereof. Also attachment means, preferably associated with the stiffeners, will usually be provided for enabling identical units to be connected together side by side. Normally all components as above are connected together by line and fillet welds and preferably there are four spaced reinforcing channels arranged in pairs with one pair disposed to each side of the web.Preferably the attachment means comprise apertured plates intended to receive dowel pins.

Two kinds of stiffener may be incorporated in the girder unit, namely one which has a lower edge at the level of the top surface of base flanges of the web and another which itself has a base flange by which it can be supported on a pier or other bridge support.

The latter type of stiffener is desirably provided near the ends of the unit so that the unit can be shortened by a required amount by transverse cutting and thereafter be adequately supported on the stiffener base flange.

The nature of the invention should however become more clearly apparent from the following description by reference to the accompanying drawings, in which: Figure 1 is a fragmentary outline perspective view of a proposed plank bridge girder unit; Figure 2 is a side elevation of a simple plank bridge embodying a girder unit.

Figure 3 is an end elevation of the plank bridge of Figure 2; Figure 4 is a typical cross-section through a girder unit; Figures 5, 6, 7 and 8 are sections respectively on lines A-A, B-B, C-C and D-D shown in Figure 4; Figure 9 is a typical section of a different type of stiffener; Figure 10 is a side elevation of a more elaborate plank bridge including side rails; Figure ii shows a typical cross-section of the bridge of Figure 10.

Figure 12 is a detail view of part of Figure 11; and Figures 13 and 14 are respectively a typical section and an elevation of a plank footbridge utilising a girder unit according to the invention.

In Figure 1 there are shown the principal components of a typical plank bridge girder unit G in accordance with the invention, namely an elongated deck plate 1 centrally supported along its length by a vertical web 2 secured to horizontal base flanges 3, 4. On each side of the web 2 the underside of the deck plate 1 is stiffened by a pair of channels 5. At intervals along the length of the unit the deck plate 1 is supported by transverse parallel unflanged stiffeners 6. These stiffeners 6 are of increased depth at their centres and their reduced depth extremities 6a are provided with means for enabling units to be coupled together side by side. However at the extreme ends of the unit and at a short distance therefrom full depth base flanged stiffeners 7 are provided.In consequence of the provision of an inward one of the flanged stiffeners 7 it is possible to truncate the girder unit G by cutting it along the dashed line 8.

Conveniently but not of course necessarily the girder unit G is 12 metres in length 1.1 metres wide and 45 centimetres overall height. The overall width between the edges of the flanges 3 and 4 is 30 centimetres. The stiffeners 6 are at spacings of 2.4 metres along the unit whilst adjacent stiffeners 7 are spaced apart by 1.2 metres.

Figure 2 shows the ends of the girder unit G supported on and bolted to piers P and also shows the provision of lighting holes 2a at intervals along the web 2.

Referring now mainly to Figures 3,4 and 9 of the drawings the hatched parts thereof denote intermittent fillet welds which connect the various components of the unit permanently to one another.

The deck plate 1 has a thickness of 5 mm and is formed with a raised pattern non-skid top surface. It is secured to the top edge of the web 2 by a continuous weld. The pairs of reinforcement or stiffening channels 5 on either side of the web 2 extend from end to end of the unit. They are of frusto conical cross-profile and are secured to the underside of the deck plate 1 by continuous welds and to the stiffeners 6, 7, by fillet welds. The plates forming the base flanges 3 and 4 for the web are similarly welded to the web and the stiffeners 6 and 7. It will be noted by comparison of Figures 3 and 9 with Figure 4 that the stiffeners 7 are of essentially rectangular shape and formed with the base flanges 9, whereas the stiffeners 6 have a maximum depth and minimum width central portion and increase in width towards the top.

Attached by welding to the respective faces of each top side margin part of each of the stiffeners 6 is a laterally projecting rectangular lug 10. As can be seen most clearly from Figures 4 to 8 inclusive each lug 10 is formed with a hole 11 and has the base of a dowel pin 12 secured thereto.

The vertical distance between the axis of the hole 11 and the axis of the dowel pin 12 (50 mm) is the same for the lugs at both side edges of the stiffener 6 but the relative positions of the hole and the dowel pin are reversed on the right side lug compared with the left side lug so that adjacent units can be connected by causing respective dowel pins to enter respective holes. Each dowel pin 12 has a tapered end to facilitate its entrance into a hole 11 on the lug 10 of another unit.

The plank bridge which has been described above with reference to Figures 1 to 9 may comprise one or more girder units connected side by side. Figures 10, 11 and 12 illustrate a plank bridge suitable for a single track roadway comprising three girder units G connected side by side in the manner previously described and equipped at each side with a cranked side rail structure 5 attached by bolts 13 and dowels 14 to the outward side parts of the stiffeners of the outermost units. As shown most clearly in Figure 12 the joint between adjacent deck plates of adjacent units is filled with a layer of pre-compressed jointing material so as to compensate for expansion and contraction of the steelwork and to prevent spillage through the deck. For a double track roadway six girder units could be connected together by the system explained above.

Figures 13 and 14 show a single girder unit G constituting a footbridge. This footbridge has vertical side railing at each side with spaced stanchions 15 having brackets 16 welded onto their bottom ends, these brackets being secured by nuts and bolts to the stiffeners 6.

For any desired width of bridge, safety fenders and kerbs can be attached in like manner to the handrails.

Among the advantages of the girder unit there may be mentioned the following: 1. Three girder units can be transported to a bridge site on one lorry and placed in position providing a bridge in a very short space of time.

2. By locking the girder units together at points along their edges, torsional restraint is provided withoutthe use of cross members.

3. By locking girder units together the width of the bridge deck can be varied to suit requirements in increments of one girder unit deck width.

4. Removal of a greater or lesser part of a girder unit end by oxy-cutting provides spans of different lengths to allow rapid closure of a bridge gap for a number of lengths.

5. By cutting different lengths from three sections skew arrangements can be provided for shorter lengths of bridge.

Claims (8)

1. A girder unit for a plank bridge comprising an elongated deck plate having its central part secured to, and supported by, a vertical web which extends beneath and longitudinally of the deck plate and which has base support flanges, reinforcing channels spaced from each side of the web secured to the underside of the deck plate and extending longitu dinallythereof, and a plurality of transverse stiffeners fixed beneath the deck plate at intervals along its length.

2. A girder unit in accordance with Claim 1 having attachment means at each side for enabling it to be connected side by side to an identical girder unit.

3. A girder unit in accordance with claim 2 in which the attachment means are associated with the stiffeners.

4. A girder unit in accordance with Claim 3 wherein the attachment means comprise lugs projecting from the side margins of the stiffeners, each lug having a hole and an associated dowel, the positions of the lugs on the respective sides of the unit and the relative positions of the holes and dowels on the respective sides being complementary to one another whereby the left side of one unit is connectable to the right side of an identical unit and vice-versa by interfitting of complementary aligned dowels and holes.

5. A girder unit in accordance with any of the preceding claims in which stiffeners at or adjacent the ends of the girder unit, in contrast with the remaining stiffeners, have horizontal base flanges.

6. A girder unit in accordance with any of the preceding claims in which there are four reinforcing channels disposed in pairs one pair at each side of the vertical web.

7. A plank bridge comprised of at least one girder unit in accordance with any of the preceding claims.

8. A girder unit for a plank bridge substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.