GB2304360A - Reinforcing a masonry arch or bridge - Google Patents

Abstract

Masonry arches are reinforced by forming substantially horizontal grooves in the masonry above the arch, forming substantially vertical grooves in the masonry at each side of and/or above the arch, and embedding a reinforcing rod or bar in a grouting composition in each groove. Bridges are also reinforced by forming grooves longitudinally and transversely in the intrados, and embedding a reinforcing rod or bar in each longitudinal groove and in each transverse groove in a grouting composition. The transverse rods or bars reinforcing the intrados may be laid against a first layer of longitudinal rods or bars and a second layer of longitudinal rods or bars are laid against the transverse rods.

Description

REINFORCING MASONRY STRUCTURES This invention is concerned with techniques for reinforcing masonry structures, especially arched structures such as bridges.

It has already been proposed to reinforce masonry walls by embedding reinforcing rods in the horizontal bedding joints of the wall. The internal forces encountered in arches make the reinforcement of an arched structure a much more complicated task than that involved in reinforcing walls alone.

The present invention addresses that problem by adding to existing horizontal reinforcements by introducing vertical reinforcement in the vertical surfaces of the bridge, and also by forming a reinforcing network in the intrados of the bridge.

According to one aspect of the present invention, there is provided a method of reinforcing a masonry arch, which comprises forming substantially horizontal grooves in the masonry above the arch, forming substantially vertical grooves in the masonry at each side of the arch, and embedding a reinforcing rod or bar in a grouting composition in each groove. It is advantageous to allow at least one of the vertical grooves to overlap with at least one horizontal groove, so that the respective reinforcing rods also overlap and may be tied in to each other to increase the reinforcement.

In the context of reinforcing a masonry arch bridge, this aspect of the present invention comprises forming substantially horizontal grooves in each parapet and forming substantially vertical grooves in each spandrel and/or wing wall, embedding a reinforcing rod or bar in a grouting composition in each groove.

As a further aspect of the present invention, grooves are formed longitudinally and transversely in the intrados of a bridge, and a reinforcing rod or bar is embedded in a grouting composition in each longitudinal groove and each transverse groove. This aspect of the invention may be carried out independently of the first aspect, but in practice the reinforcement of the intrados will normally be carried out in conjunction with reinforcement of the vertical surfaces using the above-described horizontal and vertical grooves.

The horizontal grooves are normally formed in the outer surface of each parapet, and the vertical grooves are in the outer surfaces of the spandrels and/or wing walls. In this configuration it is advantageous to allow at least one of the vertical grooves on each side of the arch ring to overlap with at least one horizontal groove, so that the respective reinforcing rods also overlap and are tied in to each other by the grout to increase the reinforcement.

Similarly, the crossing rods in the intrados are linked together as a reinforcing mesh. In a preferred configuration, the transverse rods are laid against a first layer of longitudinal rods and a second layer of longitudinal rods are laid against the transverse rods to form a "sandwich"structured mesh or network.

Vertical grooves may also be formed above the arch, or in the parapet of a bridge, to cross the horizontal grooves, to provide further overlapping reinforcement when rods are embedded in the grooves. Advantageously further grooves are formed extending radially outwards from the arch ring to cross the horizontal and/or vertical grooves, as formed in the parapet, spandrel and/or wing walls in the case of a bridge. Preferably these further grooves extend substantially normal to a tangent to the arch ring at the point at which the groove starts from the arch ring.

In the context of a bridge, this allows reinforcing rods embedded in those grooves to tie the intrados reinforcing network to the network of rods on the outer vertical surface of the bridge. For example, by using rods or bars that are 'L'-shaped, the short arm of the wL' may be overlapped with the end of a transverse bar.

The grooves that receive the reinforcing rods or bars may be cut into the masonry, preferably utilising bedding joints where possible. Alternatively, where practicable, they may be formed by raking out bedding joints, most suitably for horizontal grooves in the parapet. Typically these bedding joints lie parallel to the line of the parapet, and so may not be truly horizontal throughout their length.

The reinforcing rods or bars are preferably embedded by first injecting into the groove a backing bead of grout. The rod is pressed into the bead and then further grout is injected to complete the embedment. When one rod is laid so as to cross or overlap another rod, the grout embedding the underlying rod is preferably scraped away at the junction before laying the overlying rod, to allow satisfactory tying in.

The reinforcement is preferably carried out using steel, especially stainless steel, rods. The rods may be shaped, for example of helical form or with protruding tabs, or roughened to provide a good key to the grout. Also bars may be used, and the bars may be shaped, for example angle bars, or slotted or aperture to improve the key. Alternatively other high strength reinforcing materials, such as rods of carbon fibre reinforced resin, may be used.

The grout may be based on a synthetic resin, such as epoxy, or of a conventional cementitious composition. In a preferred implementation of the method of the invention, the grout is formulated so that it remains flexible when set or cured, and so that it has a compressive strength comparable to the surrounding masonry. In a still further preferred embodiment, the grout is formulated so that it is of low density, to reduce the risk of the grout sagging or slumping as it cures in downwardly facing grooves such as in the intrados of a masonry arch. Low density may be achieved by incorporating lightweight fillers, such as hollow glass beads or microspheres. A particularly suitable grout is formulated to provide a epoxy/urethane hybrid resin on curing.This provides good adhesion to steel bars and to masonry, is flexible on curing and can be formulated to low density and appropriate compressive strength by incorporating a hollow glass bead filler.

Since a bridge in a state of disrepair is often of historic or architectural merit, it may be appropriate to colour the grout, or to finish the grooves with a coloured pointing composition to match the original pointing. In some parts of the bridge structure it may be possible to prepare brick slips from bricks matching the original masonry, and so hide the filled grooves with an outer layer of slips.

The above and further features of the invention will now be described in more detail with reference to the accompanying drawings, in which: Fig. 1 is a schematic side elevation of a masonry arch bridge with reinforcement applied in accordance with the invention; Fig. 2 is a sectional view along the line A-A of Fig 1; Fig. 3 is an enlarged partial cross-section of the area B shown in a broken circle in Fig 2; Fig. 4 is an enlarged partial cross-section of the area C shown in a broken circle in Fig 2; Fig. 4a is a similar view to Fig 4, showing use of a tie bar; Fig. 5 is a schematic isometric view of part of the reinforcement network in the bridge shown in Fig. 1.

The system of this invention will often be used on bridges in an advanced state of disrepair. Therefore it may well be appropriate, in addition to reinforcement with metal rods or bars in accordance with this invention, to stabilise the barrel by pressure grouting a cement-based thixotropic nonshrink grout through the open joints where the original joints and pointing have eroded and washed out over the years.

Fig 1 is a side elevation of a typical masonry bridge as found on the canal systems of the United Kingdom. The bridge has an arch ring 1 bounded by spandrels 2 and wing walls 3.

The bridge carries a roadway protected by parapets 4. Whilst the initial stabilisation grouting works are in progress, the preparation and installation of the system to the outer parapets, wing walls and spandrels can be carried out simultaneously as follows.

After erecting scaffolding to allow for safe working platforms on both sides of the bridge, profile strips, typically of 6mm x 75mm plywood, are fixed to the outer face of brickwork, for example fixed by 50mm screws and plugs, adjacent to the intended cut line, preferably along a horizontal joint. With a cutter, such as a double diamond bladed wall chaser, and using the profile timber as a guide, a cut is made into the joint approximately 50mm deep. A bolster or plugging chisel is used to carefully snap off the cored plug to leave a clean cut rebate approximately 10-15mm wide x 50mm deep centred on the horizontal bed joint. This is repeated as desired to form a series of substantially horizontal grooves 10 extending along the line of the parapet.

Using the same techniques as described above, only cutting vertically through the perpendicular joints where possible but also through the brick face of stretcher and header courses if needed, a series of substantially vertical grooves 11 are formed from the wing walls to the parapet.

All loose, friable material and dust is flushed out from the grooves, cut as above, with clean water. While the groove is still damp, a priming coat is applied by brush. A typical primer consists of a synthetic polymer, such as Ronaf ix SBR (styrene-butadiene rubber), and cement mixed in the ratio of 1:1. This is applied to the back of the cut rebates. Then, typically using a single diaphragm grout pump or a pressurised pointing vessel gun, an approximately lOmm thickness of grout is applied along the back face of the primed grooves. The grout may be a, preferably thixotropic, cement grout such as ABP "Thixopump.

However, as mentioned above, preferred grouts are based on an epoxy/urethane hybrid resin, in which urethane linkages flexibilise an epoxy base resin. Such materials may be formulated as a two component grout, comprising a hardener component based on a polyamine, especially a cycloaliphatic polyamine, such as poly-cyclohexylamine, and a polymerisable resin component which is a blend of an epoxy resin, especially a bisphenol A and/or bisphenol F epoxy, with a blocked isocyanate. Each component can be filled with glass microspheres to form solvent-free compositions that can be easily blended on site in a simple 1:1 ratio to form a nonslumping, easily pumpable, structural adhesive.

A typical system has a specific gravity of about 0.89, and develops a compressive strength of about 11 N/mm2 after 24 hours, rising to about 21 N/mm2 after 7 days. The compressive strength can be varied to adapt to the masonry under reinforcement by adjustment of the filler content.

Suitable grout formulations are manufactured by NUFINS Ltd under the designation MARS structural adhesive. A structural adhesive of this type can be used as a grout without the need for a primer, if used on surfaces that are reasonably clean and dry.

To secure the parapets to the wing walls and spandrels reinforcing rods or bars 10' are inserted initially into the grooves 10 and pressed into the backing bead of grout, and then similarly rods 11 t into the grooves 11. Preferably, some of the vertical rods Ila' are laid across the horizontal rods, to tie the reinforced areas to each other.

Again by pressure grouting, more grout is fed into the grooves to completely encapsulate the reinforcing rods or bars in the grooves. This secondary grout is kept short so as to allow for reinforcing laps to be described below, as indicated on the accompanying drawings. Also the secondary layer of grout is raked back by about 15mm to 20nan behind the brick face to allow for the repointing of the joints to match the existing brickwork.

Additionally, as soon as the secondary grout layer has reached a firm enough set, the stretcher and header brick faces may be carefully removed by hand (hammer and chisel).

20mm brick slips, cut from bricks to match the existing bricks may be set into place with an epoxy adhesive along the previously cut rebate. These remedial works will camouflage the intrusion of the reinforcement into the pre-existing structure.

Whilst the works as described are in progress, it is desirable to carry out temporary works to stabilise the barrel during the insertion of the reinforcing system of this invention. As shown in Fig 2, to stabilise the brickwork locally adjacent to the intended cutting lines, steel hoopshaped straps 12 of about 50 x Smm section are fixed to the barrel 13 and abutments 14. The straps can be predrilled to accept a No. 10 screw fixing at about 750mm centres, and are fixed by being screwed through the joint or brick about 65mm deep.

Using the edge of the straps 12 as a cutting profile where possible, cuts are made longitudinally 15 and transversely 16 of the intrados using the techniques described above. On completion of the cuts, and leaving the steel straps in position, the core plugs are removed as described before.

For overhead work it may be desirable to construct a cradle within the arch to provide a mounting rail on which the cutter can be supported as it is tracked across the intrados.

The cradle also acts as a guide rail to provide a smoothly arcuate bed to the cut groove in situations where the intrados has an undulating surface.

After preparation of the grooves, longitudinal reinforcing rods 15' are installed with initial backing and encapsulating grout all as before described. The grout is raked out to expose the rods 15' at the intended intersection with subsequently applied transverse rods to allow for embedment.

As soon as the grout has reached its a satisfactory set (usually about 24 hrs), the steel strapping may be shifted to allow further rod positions to be prepared. On final set, the steel straps can be removed with any subsequent loading being transferred to the longitudinal rods.

Using similar techniques, further reinforcement rods 16' are placed transversely across the barrel and installed as before described. To prevent the rods 16' from falling downwards out of the grooves, it may be desirable to attach the transverse rods 16' to the previously applied longitudinal rods 15', using steel wire. Subsequently a second longitudinal rod 15 ' ' is installed in each groove 15, with occasional wiring to the transverse rods, so that each transverse rod 16' is sandwiched between a longitudinal rod 15' installed initially and the second longitudinal rod 15'', as seen in Figs 4 and 5.

It may be appropriate to pin the rods into the grooves, using steel tie bars with hooked ends, as shown in Fig 4a.

Preferably at the intersection of longitudinal grooves 15 and transverse grooves 16, a bore 20 is drilled into the arch ring to receive a tie bar 20'. The tie bar is secured in position, for example with a thixotropic resin, with its hooked end located around a rod to be secured, such as an outermost longitudinal bar 25''. In addition to extending the reinforcing matrix, the tie bars retain the rods 15', 16', 15'' in position in the grooves 15,16 until the grout has set.

The grout length is kept short at each end of the transverse rods to allow for insertion of continuity 'L' rods 17', in grooves 17, or possibly bores, cut or drilled in the parapet, wing walls and/or spandrels substantially radially to the curve of the arch ring, as seen in Figs 2 and 5. The short arm of the 'L' is lapped against the end of one of the transverse rods laid in the intrados, so connecting the barrel to the wing wall and spandrels. The grooves or bore are filled with grout as before. These linking grooves are typically cut from the arch ring into the vertical surfaces of the bridge along a line that is substantially normal to the tangent to the arch ring at the point where the rod 17' will be lapped with a transverse rod 16'.

As shown in Fig 4, an upright groove 17 may be cut into the parapet, and if necessary continued by a bore 18 through coping stones. This allows an shaped rod 17 to be inserted in the groove and bore with its other arm lapped with a transverse rod 16'. Alternatively protruding ends of an over-length transverse rod 16' may be turned upwards to lie in a groove 17. After injection of grout, the groove 17 may be masked by a cover of brick slips 19.

Because of the close proximity to each other, centre to centre, of the longitudinal rods it is often not possible to remove the intruded brick face of the intrados and replace it with slip bricks, as described for the wing walls and parapet. To disguise the intrusion, it is possible to completely fill the rebate with grout, struck level to the brick surface, or endeavour to match the brick colour by adding a colour dye to the grout.

The reinforcing rods are suitably 6mm stainless steel rods, typically stainless steel grade 304515, but other corrosion resistant rods or bars, for example, carbon fibre rods, may be used if appropriate. The repointing described above may be carried out by applying 1:2:9 opc:lime:sand mortar (to BS 5628) to match existing pointing.

Claims (16)

1. A method of reinforcing a masonry arch, which comprises forming substantially horizontal grooves in the masonry above the arch, forming substantially vertical grooves in the masonry at each side of and/or above the arch, and embedding a reinforcing rod or bar in a grouting composition in each groove.

2. A method according to claim 1 in which at least one of the vertical grooves overlaps with at least one horizontal groove, so that the respective reinforcing rods also overlap.

3. A method according to claim 1 or 2 further comprising forming grooves longitudinally and transversely in the intrados, and embedding a reinforcing rod or bar in each longitudinal groove and each transverse groove in a grouting composition.

4. A method of reinforcing a masonry arch or bridge comprising forming grooves longitudinally and transversely in the intrados, and embedding a reinforcing rod or bar in each longitudinal groove and in each transverse groove in a grouting composition.

5. A method according to claim 4 in which the transverse rods or bars reinforcing the intrados are laid against a first layer of longitudinal rods and a second layer of longitudinal rods or bars are laid against the transverse rods.

6. A method according to claim 4 or 5 which comprises additionally forming substantially horizontal grooves in the masonry above the arch, and embedding a reinforcing rod or bar in a grouting composition in each groove.

7. A method according to claim 4, 5 or 6 which comprises additionally forming substantially vertical grooves in the masonry at each side of and/or above the arch, and embedding a reinforcing rod or bar in a grouting composition in each groove.

8. A method according to claim 7 in which at least one of the vertical grooves overlaps with at least one horizontal groove, so that the respective reinforcing rods also overlap.

9. A method according to claim 6, 7 or 8 in which the masonry structure is a masonry arch bridge, which comprises forming substantially horizontal grooves in each parapet and forming substantially vertical grooves in each spandrel and/or wing wall and/or parapet, and embedding a reinforcing rod or bar in a grouting composition in each groove.

10. A method according to any one of claims 4 to 9 in which further grooves are formed extending generally radially outwards from the arch ring to receive reinforcing rods or bars that cross the horizontal and/or vertical grooves.

11. A method according to claim 10 in which the radial reinforcing rods or bars are 'L' shaped and the short arm is lapped with the end of a transverse bar in the intrados reinforcing network.

12. A method according to claim 10 or 11 in which the further grooves extend substantially normal to a tangent to the arch ring.

13. Use of an epoxy/urethane hybrid resin as a structural adhesive or grout to bond reinforcing bars into grooves in a masonry structure.

14. Use according to claim 13, in which the resin is formed by mixing a cycloaliphatic polyamine hardener with a blend of bisphenol A and bisphenol F epoxy resins with a blocked isocyanate.

15. Use according to claim 13 or 14, in which the resin contains a lightweight filler.

16. Use according to claim 15, in which the filler is hollow glass beads or microspheres.