Business profile
masonry can be simulated. As a result, there are no restrictions to the arch bridge arrangements that can be considered, for instance the number of spans, rings and piers. Similarly any type of loading from highways, railways and even ground movements can be applied.
The application of FDEM represents a step change in the sophistication that can now be applied to the structural analysis of masonry arch bridges. Not only can it be used to accurately assess strength but also to determine bridge deformation, including important non-linear effects, making it possible to assess behaviour at both strength and serviceability limit states.
the shape and spaces within the walls, providing a mechanical bond.
The two viaducts have similarities and differences: Both have the Cintec anchor system tying the structure back together to form a single mass; both have in situ slabs. However, Crawick uses the existing haunch while Enterkin uses L-sections and its parapet is tied back. The project has used several site investigation techniques both traditional and new. All work was done by rope access and carried out without disrupting trains. A close relationship was established with the suppliers in developing the design, and the company has gained valuable experience that will stand it in good stead for tendering on viaducts requiring similar repairs .
Keith Haughes bridge
One of the first road over rail bridges to be strengthened using the Archtec system was Keith Haughes bridge in Scotland, a single-span brick masonry arch which carries a trunk road across a network rail line. Earlier assessments had indicated insufficient strength to provide the required trunk road live load rating. A further assessment, including SV196 abnormal loading, resulted in the selection of Archtec strengthening and, alongside other remedial work the project was completed in 2010.
Minimal disruption to road and rail traffic was key. Since it was a small-scale construction activity with no movement of bulk materials, the work could take place in short possession periods, and techniques such as laser scanning and 3D modelling enabled accurate planning.
Archtec technology now used for rail bridges
Archtec has been used on highway bridges for nearly 15 years. Now, the technology is being used for railway bridges and is set to introduce similar benefits.
The motivation for developing Archtec was the introduction of 40/44 tonne vehicle load rating - as a cost effective alternative to traditional assessment and
strengthening
routes.This drive continues, particularly overseas, but increasingly in response to rail traffic rather than road. It is now also recognised as an alternative, affordable and sustainable solution to traditional saddling, or in some cases bridge replacement, by improved use of mostly existing materials.
A significant research programme has been behind Archtec over the years, including advanced analysis, full-scale tests, monitoring of bridges, and importantly the formation of a team including academics, engineers/ analysts, project managers and specialist contractors to deliver the service. The team is a partnership of several specialists: Cintec International, Rockfield Software
Strengthening weak bridges Arches conventionally fail by the development of four hinges leading to a mechanism. The design basis for Archtec strengthening is to locate reinforcement, to improve bending strength where hinges are predicted to develop. By providing additional strength in this way the arch barrel is better able to resist live load, and peak compressive stresses in the masonry are reduced compared with similar un-strengthened cases. The same procedure is applied to more complex bridge arrangements including multi-span arches, although failure mechanisms and reinforcement positioning requires different locations to be considered in the design. The method of strengthening
and a team from Ramboll UK (formerly Gifford).
Internationally, around 250 bridges have now been strengthened, with many more assessed and found to be adequate.
Calculating the strength of arch bridges There are several existing methods of assessing the strength of ancient masonry arches but their generalised use is limited. Finite Element analysis has been used successfully but modelling materials to obtain realistic behaviour is challenging. Instead, the Finite/Discrete Element Method (FDEM), which involves the automatic computation of interacting bodies, is applied in the Archtec processes. As with the application of Finite Elements, the generalised approach also means that any geometric form of
involves the installation of Cintec anchors, which have been developed to allow the retrofitting of stainless steel reinforcement around the circumference of the arch barrel. The reinforcement is then grouted into holes precisely drilled into the bridge with a diamond coring rig to provide a shear connection with the masonry. It is this shear connection and method of grouting within a fabric sock that is vital to giving the required bond strength. Installation can be made from the road surface or, in the case of multi- span structures, from below.
Once the work is completed there is no evidence of major intervention to the bridge, a characteristic that is particularly important for historic structures. For more information tel: 01633 246614
www.cintec.com
March 2013 Page 101
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