Correctional works and effective strengthening of a small masonry road bridge using the MARS system

This small bridge had suffered extensively from historic flood damage and had been ‘strengthened’ by reducing the span and constructing concrete infill under the damaged section of the barrel. We were commissioned by Calderdale Metropolitan Borough Council to carry out the correctional works and strengthen this small masonry road bridge.

The Problem 

Unfortunately this ‘strengthening’ not only reduced the aperture of the bridge, it also damaged the barrel when the wrought-iron beams supporting the infill were inserted. 

The inserted abutments reduce the clear carrying span but, unfortunately, they only act as props at the pivot points as shown below. They do not take the thrust out of the barrel i.e. they do not act as springing points. Thus, in theory, the span could not be taken as the distance between the inserted abutment walls. The action of the loading at the critical point of the barrel will deflect the centre downwards, pivoting about the inserted abutments. This will have the action of deflecting it away from the back of the abutment walls into the fill relying on lateral pressure from the fill for stability. The effective springings will thus be some way beyond the pivot points. 

Floodwaters had also loosened the stone voussoirs resulting in numerous stones that had dropped by up to 40mm. 

The Goldhawk solution 

Goldhawk removed the concrete infill and the corroded wrought-iron beams, jacked the voussoirs back into position, and grouted them in place. This brought the capacity of the bridge up to 3t GVW. The bridge serves an industrial depot and the MARS System was then installed to bring the capacity up to 44t GVW. Helifix Sockfix anchors were also used to tie the barrel to the abutment inserts. 

As the foundations do not exhibit any distress and there is no anticipated increase in applied loading, the foundations were deemed adequate. Also, as there had been no reported recent flooding in the area, it was not considered cost-effective to remove the inserted abutments. The carriageway over the bridge will be re-profiled by Calderdale MBC so the bridge will be good for at least another 100 years of life. 

The MARS installation not only is the cheapest and most environmentally friendly method of strengthening masonry bridges, in this case it opened up the aperture of the bridge to ameliorate flooding. 

These works will thus upgrade the bridge and hence avoid replacing it with a new structure with a large carbon footprint. The MARS System utilises the inherent strength of the arch barrel and thus minimises the unnecessary use of additional environmentally damaging materials. The System also has a minimal effect on the stiffness of the barrel. 

The integrity of the System can be easily inspected at routine inspections though there are no future maintenance costs associated with the system. If repairs are ever necessary, they can be simply carried out using readily available tools.