GB2518356A - Method of suspension bridge construction - Google Patents

Abstract

A method of constructing a suspension bridge whereby caissons, towers and bridge decks are constructed in sprayed and laminated ferrocement, laminated concrete and self-compacting concrete to form relatively lightweight cellular structures. The method comprises constructin9, using the above materials in a dry dock, of a floating caisson 4, two large pontoons (4, fig 3), two bridge towers 2 preferably each constructed in two halves in a mould (2, fig 3)) and a bridge deck 3. The caisson including two void spaces (2, fig 2) to accept counter balance tanks (2,fig 3) in the bridge towers and fulcrums (1, fig 2) about which the towers pivot when raised to vertical positions.

Description

METHOD OF SUSPENSION BRIDGE CONSTRUCTION.

DESCRIPTION.

This invention relates to the construction processes required to construct a bridge across an estuary or river and the use of sprayed and laminated ferrocement and laminated concrete and self-compacting concrete construction systems, to form relatively lightweight concrete cellular structures.

The invention relates to caissons, towers and bridge deck, being the major components of the bridge.

These cellular structures may become permanent shuttering for the subsequent placement of concrete.

The process is facilitated by the use of nearby available dry docks and by the transport of large elements of the bridge on pontoons, on the River or Estuary over which the bridge is built.

By constructing all the major elements of the bridge structure in one location, and then transporting these elements on the same river over which the bridge is being built, the logistics of the project are greatly improved.

By constructing in laminated ferrocement and self-compacting concrete together with innovations in stressing thin section concrete to produce high strength to weight ratio materials, the total material quantities and weights are reduced.

The inventions introduce novel means of constructing and placing a caisson, building and erecting towers, and assembly of a concrete box girder bridge deck by balanced cantilever construction.

The invention is further explained in stages of construction and is illustrated by drawings at each stage.

Stage 1 Construction in the dry dock, of a cellular concrete structure, to form a caisson. This is floated to the designed position and placed by a controlled sinking. This caisson forms a permanent shuttering into which mass concrete and reinforcements are placed to cast the foundations which subsequently support the bridge towers.

Stage 2 Construction in the dry-dock, of large laminated concrete pontoons and upon which large female moulds for construction of the bridge towers are assembled Stage 3 Construction of female moulds, made in two parts for each tower, to form the shape and dimensions of the suspension bridge towers. These moulds may be constructed in laminated ferrocement and steel tubular framing. One part of each mould to be made with bearing points to rotate it, in order to place the two parts together, thus making the complete tower. 2.

Stage 4 Construction in the dry dock, upon the pontoons, in the two female molds, of the two laminated ferrocement, concrete and steel towers required to support the suspension bridge. These towers will have large counter balance tanks incorporated into the base of each tower. These tanks are constructed into the tower structures to counterbalance lifting the towers from horizontal to vertical and from off the pontoons into the foundations.

Stage 5 Method of erecting temporary lifting capacity by installations of two luffing tower cranes on the centre line of the foundations / caisson. Together with jacking from pontoon and filling the counterbalance, these cranes are used to assist lifting the towers off the pontoons from horizontal to vertical and into the support caisson/foundations.

Stage 6 Method of transporting the completed towers to the caisson/foundation on the pontoons, and positioning the two pontoons with the two towers to abut the caisson /foundation.

Stage 7 Method of lifting bridge towers off pontoons and raising them from horizontal to vertical.

Stage 8 Return of pontoons to dry-dock and clearance of tower molds from pontoon decks. Preparation of new molds for manufacture of bridge segments on the pontoon decks.

Stage 9 Method of construction of segments of the bridge deck on the pontoons in the dry-dock.

Stage 10 Method of transporting bridge deck segments on pontoons and sequentially lifting into place to form a lightweight concrete box girder bridge by the balanced cantilever method.

Stage 11 Method of stressing together the bridge deck segments, by design of the segmental structure using horizontally casted laminated ferrocement panels as permanent shuttering to form the vertical full depth webs of the bridge segments both longitudinally and transversely.

Stage 12 Method of casting and stressing bridge deck segments using self-compacting concrete to fill the web sections and subsequently cast and stress the horizontal road deck of the bridge.

These stages are further explained in more detail and are illustrated by drawings. 3.

Example Stage 1 The Caisson.

Construction of floating caisson to support bridge towers. By design) a cellular structure formed by spraying and laminating ferrocement may be constructed upon the floor of a dry-dock. The caisson is constructed within a mould! form work to define the outside dimensions. Into the outer shell are passed the horizontally casted vertical plates of laminated ferrocement cell structure. These are concrete welded into the structure forming tanks, bulkheads and bearing/fulcrum points. The caisson may incorporate vertical tanks into its perimeter which may direct the positioning of conventional vertical steel piles or concrete piles. Vertical tanks will subsequently be filled with concrete and steel reinforcements to complete the bridge foundation.The caisson will incorporate two large central tank spaces which are required to subsequently accommodate the counterbalance tanks of the two tower constructions. The caisson will be designed with bearing points in line with the bridge deck. These points will form the fulcrum for rotating the subsequently constructed towers (constructed and carried upon large pontoons) from horizontal to vertical position. Upon completion, the caisson will be floated from the dry-dock to the required position and installed by a controlled sinking operation. The caisson may be constructed in several horizontal layers or rings depending on site conditions, water! mud depths etc. The caisson may incorporate a sleeve element around the perimeter to assist in sinking caisson to adequate depth and this sleeve may have a sharp edge of steel section to cut into the ground. By design some or all of the vertical cells of the floating caisson may have collapsible and removable temporary bottoms. These to permit the flooding of the cells and the removal of spoil materials from under the foundation as in conventional caisson works. The cells may also be used to accept concrete piles to penetrate the underlying ground and facilitate the landing' of the caisson. The caisson, with large void area to accept the counter balance tanks, may be bridged with temporary steel works to support the conventional equipment used to sink and place a caisson. Service/Ferry pontoons will be required to move plant, labour and materials to and from the foundation site.

The caisson is illustrated by Figure 2. Showing, for example, a structure 100 m long and 48 m wide,1.

with two void spaces 2. to accept the counter balance tanks. 3. Represents dock floor. On plan, the fulcrum are marked 1. And the counter balance tanks are marked 2.

Example Stage 2 Large Pontoons.

Within the dry-dock, two large laminated ferrocement and concrete pontoons structures will be built.

On the decks of which, variable surface female moulds, to define the form, shape and dimensions of the required towers, will be assembled. The two laminated concrete pontoon structures will be cast upon the dry dock floor within relatively lightweight and removable formwork which defines the dimensions of the pontoon structure. These pontoons will be cellular structures comprised of vertical elements cast in the horizontal position and then assembled vertically into a laminated ferrocement outer shell. The vertical webs and bulkheads will be joined by a sprayed concrete welding process. The decks of the pontoon will be stressed and reinforced to carry significant deck loads. Pontoons will be designed to support the bridge tower molds to be constructed upon them and subsequently transport the towers to 4.

the bridge site. The pontoon structures will be subdivided and fitted with pumping arrangements to facilitate flooding or ballasting. The pontoons will be built to class for potential future uses and will have usual fittings, fenders, mooring points etc.by design.

Example Stage 3 Bridge Tower Moulds.

Two female moulds, for two towers, will each be made in two parts and one part will be so designed to permit a rotation to join with the other part to form a complete rounded or rectangular tower structure.

These moulds will be made in sprayed and laminated ferrocement with steel reinforcements and high tensile steel wires.The moulds may have a tubular steel frame support to assist movement and rotation.

The internal surfaces of the moulds may be lined with materials to provide an imprinted pattern or a perfectly smooth surface to the mold. The internal mould surface will be reflected into the surface of the tower structure built within the mould. The mould may be created by conventional plug and mould making techniques. The laminated ferrocement cross sections of the mould structure may incorporate high tensile steel stressing wires. In the middle of the two parts, a substantial fabricated steel element which incorporates the many suspension cable fixing points, may be fabricated and positioned on the center line and between the left and right parts of the tower as formed in the female moulds. The moulds have a variable surface and profile to suit the design and are made so that one part may be rotated to fit upon the top of the other with the steel fabrication placed horizontally in between the parts. This horizontal steel fabrication, may by design, be made with vertical webs to add stiffness to the structure. The two parts of each tower may be joined by conventional bolted flanges or by concrete welding. At the bottom ends of the towers and built into the tower structures, are large counterbalance tanks. These are designed to be filled with water ballast to counterbalance the lifting and installation of the towers into the foundations. The counter balance is designed and shaped to fit into the void area of the foundation caisson. Thus the laminated concrete towers with a steel core and counter balance may be constructed upon the pontoons.

The tower, in the mould, on the pontoon is shown in Figure 3. 3 is a temporary strut arrangement to spread loads, on plan the moulds are shown on the pontoons 4. One mould is to be rotated to sit upon the other. The counter balance is omitted from the drawing for clarity.

Example Stage 4 Service pontoons and Luffing Tower Cranes as Sheer-legs.

Service pontoons are required to ferry plant equipment, labour and materials to and from the foundation site. These pontoons will be used to carry two tower cranes of the self-erecting type, to the caisson foundation. These cranes are off-loaded and erected onto the foundation side decks and positioned on the bridge center line. In a two leg configuration, they have two corner points from which to control the lifting operations of the towers from the pontoons. The two cranes are required to lift the towers and a special rig will be required to link the tops of the cranes to make them act as one and possibly may require buttress supports to permit the cranes to act as sheer-legs when raising the two very large towers from off the delivery pontoons. Special modifications will be required to the cranes so they can lift equally from both sides of the sheer-leg. 5.

Example Stage 5 Transport of bridge towers to site on Large Pontoons The first of the two large pontoons, carrying one of the completed bridge tower structures, will be floated from the dry-dock to the bridge construction site and positioned upstream of the bridge foundation caisson. It will be aligned at right angles to the bridge deck and in line with the fulcrum bearing points on the foundation caisson. Pontoon positioning will be controlled by cables and anchors.

They may be ballasted to account for tidal conditions and river depth. It may be designed to sit aground.

It may be positioned within piles to help maintain station. It may be ballasted down to sit upon the river bed. The first pontoon will be returned to dry dock to facilitate manufacture of tower two. Tower one will be left on bridge site in horizontal position on temporary supports until tower two is manufactured and delivered.

Example Stage 6 Lifting Bridge Towers off pontoons to vertical positions.

With the towers positioned upstream and downstream of the foundation caisson and the two towers, supported in the half moulds, may be rolled off the pontoons to sit their bearing points into the fulcrum plates prior to lifting off. With the aid of jacks and the two luffing tower cranes rigged as a fixed sheer-leg, a controlled lifting procedure will be commenced to raise the bridge towers into the vertical position and secure them into the foundation. To use the tower cranes in a two corner configuration to lift the bridge towers will require some special designs to join and brace the cranes, this will be a special rig to give a balanced lift to bring up the two large/long bridge towers from horizontal to vertical. This will be carried out by jacking the towers upwards from off the pontoons and simultaneously filling the counterbalance tanks. The lifting points of each tower will be from the central steel core which carries all the fixing points for the bridge suspension cables. By use of spreaders to these points the load will be spread into the structure. The lifting will be assisted by filling with water the counterbalance tanks at the base of the towers. The lifting process will be balanced between the two towers as they are raised from the pontoons. Lifting may be assisted by the tidal range. Upon completion of erecting the towers into the vertical position, the water ballast within the counterbalance tanks will be displaced with concrete and the void volumes will be grouted to secure the tower constructions into the foundation. The empty pontoons will then be returned to the dry-dock Figure 4 shows towers 1 and 2 erected with bridge 3, in between the towers, on the caisson 5 in river bed 5.The two luffing tower cranes are omitted from the drawing for clarity.

Example Stage 7 Pontoons Returned to dry dock.

With two large pontoons returned to the dry-dock and cleared of the moulds which formed and carried the bridge towers, the pontoon decks are now ready to receive new moulds to form the bridge deck segments. These segments when lifted and stressed together will form a lightweight laminated ferro cement box girder bridge which will subsequently be stressed as is common in bridge building practice.

They will be erected from the center point of the bridge by the balanced cantilever method of construction. 6.

The moulds for the bridge segments will be designed to the shape and dimensions required to build the bridge deck. The segments will be built upon the pontoons and de molded unit by unit to complete the required number for the bridge deck construction. They will be transported to site on the pontoons. A third large pontoon may be required to enable continuous production.

Example Stage 8 Bridge deck Segments.

The Bridge deck segments,built on the pontoons, will be floated to the bridge position on the pontoons where they will be lifted to the box girder bridge by a traveling gantry crane and joined segment by segment to form the bridge by the balanced cantilever method. The first and middle segment may be rolled off the delivery barge onto the foundations beneath the towers before lifting into position.

Manufacture, delivery and erecting of bridge segments continues to complete the bridge. Temporary works and or lifting may be required to move segments from pontoon barge to land areas over which the bridge spans.

Bridge segments are, by example, illustrated in figures, which shows a segment 25 m wide and S m deep and 20 m of bridge deck length. The segment is 1.The five main horizontal webs 2, and transverse webs with lightening holes 3.

Example Stage 9 Bridge deck completions.

The bridge segments will be designed with vertical webs formed of precast ferrocement panels built into the segment as structure. These webs) while void of concrete, permit the passing of pre-stress cables over the length of the bridge deck and the vertical webs of the bridge. When all segments are placed to complete the bridge, subsequent stressing of cables and casting of the principal vertical webs of the bridge is carried out. Transverse vertical webs may be casted in a similar manner. The vertical panels of laminated ferrocement segment structure will form permanent shutters for the casting of concrete around stressing cables. Vertical laminated ferrocement panels also form permanent shuttering for the main vertical elements running the length of the bridge deck. The bridge vertical webs, through which stressing cables have been laid will now be stressed from bank buttress to bank buttress where the buttress's also act as mass anchors to the stressing cables. The bridge road decks are stressed as in normal practise.

Thus the bridge is completed.

The bridge is illustrated by Figure 1. 7.

Claims (13)

1. METHOD OF SUSPENSION BRIDGE CONSTRUCTION.CLAIMS.1. A method of spraying mortar and laminating reinforcements to form a relatively thin but highly reinforced cross section of concrete/ferrocement structural material.
2. 2. A method, as in claim 1, of applying fibres and concrete additive materials to enhanced the properties of the matrix.
3. 3. A method, as in claiml and 2, of applying expanded metal mesh materials, wire mesh materials and other reinforcements into a cross section of thin concrete/ferrocement to control cracking of the concrete and provide a high strength to weight ratio material.
4. 4. A method, as in claims 1,2 and 3, of constructing relatively light weight structural elements in laminated ferrocement to form cellular structures which may subsequently be filled with concrete.
5. 5. A method, as in claims 1,2,3 and 4,by which horizontally casted laminated ferrocement plates may be configured to form web frames and bulkheads of a pontoon structure or box girder bridge.
6. 6. A method, as in claims 1,2,3,4 and 5, of joining elements by sprayed concrete welding to lock reinforcements together.
7. 7. A method, as in claims 1,2,3,4,5 and 6, of spraying mortar and laminating reinforcements to vertical and horizontal surfaces of a mold to form the outer shell of a pontoon or segments of box girder bridge.
8. 8. A method, as in claims 1,2,3,4,5,6 and 7,of incorporating high tensile steel stressing wire into a thin cross section of laminated concrete.
9. 9. A method, as in claims 1,2,3,4,5,6,7, and 8, of constructing laminated ferrocement in female moulds, to form the shape and dimensions of tower structures or tubular structures or rectangular structures.
10. 10. A method,as in claims 1,2,3,4,5,6,7,8, and 9, of forming tower or tube structures in two parts in female moulds and rotating one part to sit upon the other to form a complete tower or tube structure.
11. 11. A method, as in claims 1,2,3,4,5,6,7,8,9, and 10, of creating a counterbalance to assist the lifting of a large/long tower or tube structure from the horizontal to the vertical position. 8.
12. 12. A method, as in claims 1,2,3,4,5,6,7,8,9,10, and 11, of creating a bearing and fulcrum about which a large tower or tube structure may be rotated from horizontal to vertical position.
13. 13. A method, as in claims 1,2,3,4,5,6,7,8,9,10,11, and 12, of creating permanent formworks within a structural element which may incorporate stressing wires for subsequent casting into the element when stressed and filled with concrete.