GB2223783A

GB2223783A - Bearing for a panel bridge

Info

Publication number: GB2223783A
Application number: GB8822096A
Authority: GB
Inventors: Paul Barrie Worthington
Original assignee: Thos Storey
Current assignee: Thos Storey
Priority date: 1988-09-20
Filing date: 1988-09-20
Publication date: 1990-04-18
Anticipated expiration: 2008-09-20
Also published as: GB8822096D0; GB2223783B

Abstract

A bridge made from pre-fabricated panels has a bearing at at least one of its supports, each bearing comprising a base member (18) for securement to the support and a rocker member (20) for connection to at least one panel. The base member (18) has an at least partially concave surface (22) in which a correspondingly shaped portion (24) of the rocker member (20) locates whereby the base member (18) supports the rocker member (20). The axis of the concave surface of the base member is parallel to the plane of the panels, in order to evenly transfer loads applied to the transoms of the bridge, A layer of resilient material (26) may be located between the curved surfaces (22, 24) of the base member and the rocker member. The rocker member (20) preferably has means for connection to two or more panels. <IMAGE>

Description

IMPROVEr\TS IN AND RELATING TO PANEL BRIDGES This invention relates to bridges and in particular to bridges constructed from prefabricated panels.

Bridges of this type comprise, in their simplest form, two parallel spaced girders each formed from a single row (or truss) of panels joined end to end, I-section cross girders known as transoms which span between the girders and carry the roadway and the roadway itelf which comprises a number of deck panels.

The deck panels comprise a series of parallel spaced I-section beams known as stringers to which is secured a deck plate of timber or steel. This arrangement can be varied as required by adding one or more rows of panels to each girder beside the original rows and cross bracing the rows and/or by bolting one or more further rows of panels on top of the row or rows of panels in each girder. Additionally reinforcing chords can be attached to the top and bottom of each panel.

When the girders comprise two or more rows of panels the transoms are secured to each panel in the girder to transmit loads on the bridge to each of the panels to which the transom is secured. When the bridge is loaded the transoms which are rigid supports try to rotate and therefore pull upwards on the connection between them and the outer panels. If the panels are not constrained in a vertical direction, that is if they are unsupported, the resultant stresses are not too great. However, when the transoms connected to the panels which are secured to the bridge supports are loaded, the load is not equally distributed between the trusses because of the rotation of the transoms; This results in the inner truss being overloaded.Moreover, the transoms and the transom seats by which they are connected to the panels are highly stressed at the connection points which can lead to their being damaged and weakened.

Known bearings for transferral of loads from the bridge to the bridge supports provide resistance in the longitudinal direction, that is in the direction in which the bridge extends, but do not reduce the loading effects described above which occur in bridges with girders which have two or more side by side rows.

A bridge constructed from prefabricated panels in accordance with the invention has a bearing at at least one of its supports comprising a bearing block, having a base member for securement to the support and a rocker member for connection to at least one panel, the base member having an at least partially concave surface in which a correspondingly shaped portion of the rocker member locates whereby the base member supports the rocker member, a layer of resiliant material being located between the base member and the rocker member.

Preferably the axis of the concave surface of the base member is parallel to the plane of the panels.

This arrangement means that when the bridge is loaded the transoms, panels to which they are secured and the rocker member to which the panels are secured can move as a whole relative to the base member. Thus when the transoms try to rotate under the effects of the loading, they can do so without overloading the inner panel or overstressing the transom seats.

It is the resiliant layer, which is preferably formed of rubber or a rubber composite, which, since it distorts as the transom rotates, allows the rocker member to rotate relative to the base member thus equalising the loads in the trusses.

The bearing can suitably be employed at each of the supports of single span or multi-span bridges, that is bridges with three or more supports. Suitably the rocker member has means whereby it may be connected to two, three or four panels.

Preferably the concave surface of the base member is an arc of a circle whose centre lies on the neutral axis of the transom which is secured to the panel to which the rocker member is connected. This means that the transom will rotate under the loading without unevenly loading either of the supports.

The invention will now be further described by way of example with reference to the accompanying drawings in which: Figure 1 illustrates a support of a prior art bridge and Figure 2 shows a bearing in accordance with the invention.

The bridge, only details of one support of which is shown, comprises two girders each of which is formed from one or more parallel rows of prefabricated panels connected end to end. The panels each comprise an upper and lower chord spaced and connected by diagonal and vertical bracing members. The upper and lower chords are each formed from two back to back U channels.

1-section cross girders known as transoms span between the two girders and these support the deck panels. A transom is connected to each pair of panels in the girders adjacent the connection point of the panels to the next panel in the row.

Figure 1 illustrates a known bridge support arrangement The bridge girders each comprise two parallel rows of prefabricated panels which are cross-braced. One end vertical member 2 and the lower chords of a pair of panels 6, 8 of one of the girders are shown. A transom 10 is secured to the panels. The lower chords 4 are secured either directly to the supports 12 and 14 or via known bearings. When the transom 10 which is a rigid support is loaded, it rotates as shown by dotted outline 16. This results in an uneven distribution of loading on the panels 6, 8 that is the panel 8 closest to the bridge surface is overloaded. This can lead to weakening and/or damage to the panel 8. The same effect occurs with bridges whose girders comprise three or four side by side rows of panels.

The bearing 16 shown in Figure 2 prevents this problem from occurring. The bearing 16 comprises a base 18 and a rocker 20, the two parts being provided with co-operating curved surfaces, 22, 24. A suitably shaped layer 26 of rubber or rubber composite is provided between the two parts 18, 20. The rocker 20 hae plates 28, 30 secured to its top surface which include means whereby the pair of panels 6 and 8 may be secured thereto. The securing means may be, for example, bolt holes, so that bolts can be passed through the chord bolt sockets of the lower chords 4 of the panels 6 and 8 (which are provided in standard panels to allow additon of reinforcing chords) to connect these parts. The base 18 includes means (not shown) whereby it may be secured to the support 32.

The curved surfaces 22, 24 preferably form part of a circle the centre of which intersects with the neutral axis of the transom 10. The curved surfaces 22, 24 suitably extend in a direction parallel to the plane of the panels so that they are in fact part of a cylinder. The effect of the centre of rotation of the curved surfaces being on the neutral axis of the transom 6 is that rotation of the transom 6 under load will cause the rocker 20 to try to rotate. The rubber layer distorts readily under shear to permit the rocker 20 to rotate relative to the base 18 but allows transfer of vertical loads to the support. The rotation of the two parts of the bearings keeps the load on the panels 6 and 8 equal and prevents overloading of the inner panel 8.

A similar bearing may be provided when the number of panels is greater, with the rocker including means to mount the panels. The rubber layer 26 which provides resistance in a direction parallel to the plane of the panels and distorts in shear to equalise the loading on the panels no matter what number of rows of panels there are in the bridge girders.

Claims

CLAIMS:

1. A bearing for a bridge constructed from prefabricated panels comprising a base member for securement to a bridge support, and a rocker member for connection to at least one of the panels, the base member having a surface at least part of which is concave in which a correspondingly shaped portion of the rocker member sits, the axis of the concave surface of the base member being parallel to the plane of the panels.

2. A bearing as claimed in Claim 1 in which the concave surface of the base member is an arc of a circle the centre of which lies on the neutral axis of a transom which is secured to the panel to which the rocker member is connected.

3. A bearing as claimed in either Claim 1 or Claim 2 in which the rocker member has means for connection to two or more panels.

4. A bearing as claimed in any preceding Claim wherein resilient material is located between the base member and the rocker member.

5. A bearing as claimed in Claim 4 wherein the resilient material is in the form of a radiused rubber bearing pad.

6. A bearing as claimed in either Claim 4 or Claim 5 in which the resilient material is rubber or a rubber composite.

7. A bridge constructed from pre-fabricated panels in which a bearing as claimed in any preceding claim is provided at at least one support of the bridge.

8. A bearing substantially as described herein with reference to the accompanying drawings.