European railways alone account for 200,000 bridges. These bridges form a vital asset and their replacement cost is almost incalculable. Despite being ancient in form, masonry arches are notoriously difficult to assess accurately. At all limit states their behaviour is complex, deriving their overall behaviour from the interaction of individual parts, blocks, bricks, mortar and fill.Archtec
Archtec is a partnership that links Cintec International, who manufacture and install masonry anchors (retrofitted reinforcement), Rockfield Software who produce Finite/Discrete Element (FDE) structural analysis software, ELFEN, and Gifford who carry out bridge assessment and design. This service was originally conceived for efficient, economic and sympathetic strengthening of arches, but the method of structural analysis can also provide accurate strength assessment of existing bridges. On many occasions it has been used to show that bridges do not need to be
Archtec is a novel method of strengthening masonry arch bridges, which firstly involves an accurate method of assessing bridge structural performance, and then the use of retrofitted reinforcement through the application of Cintec anchors. This type of strengthening has been described as ‘keyhole surgery’ for bridges because of the absence of any major intervention and the complete invisibility of the work. Generally, construction comprises retrofitting stainless steel reinforcement around the circumference of the arch barrel. The reinforcement is grouted into holes drilled in to the bridge with a diamond coring rig from the road surface or, alternatively in the case of multi-span structures, from below.
Arches conventionally fail by the development of four hinges leading to a mechanism. The design basis for the strengthening is to locate the reinforcement so as to provide bending strength at the critical locations, thereby resisting the development of the hinges. By providing bending resistance, the arch barrel is able to resist the critical loading conditions more efficiently and for a given live load, even reduce peak compressive stresses in the masonry. A similar procedure is applied to more complex arrangements including multi-span arches although failure mechanisms require anchors to be placed in different positions.Benefits
Compared with conventional arch bridge strengthening such as concrete saddling and lining, the Archtec service has several practical benefits.
- Through the use of FDE a good assessment of existing strength and bridge behaviour is obtained. This allows accurate matching of strengthening to the loading requirements if the bridge is under strength, thus minimising any intervention. Alternatively, strengthening may be avoided
- Strengthening is invisible, which is particularly important for historic and heritage bridges
- Construction is small scale and fast to implement
- Disruption to bridge users during strengthening is much less than saddling
- A more sustainable solution with lower environmental impact, embodied energy and carbon emissions
- Because displacement and strain is predictable, assessments and strengthening designs can be based on limit states other than purely ultimate strength
- The installation of each anchor provides a core of information that can be used to confirm the materials and internal arrangement of the bridge.
In many instances all these factors equate to reduced cost.Structural analysis
FDE is at the heart of all Archtec work, which involves the automatic computation
of interacting bodies and is, therefore, a natural choice for representing masonry and this type of non-homogenised structure. Like the conventional Finite Element method, being a generalised approach also means that any geometric form of masonry can be simulated.
Consequently, there are no restrictions to the arch bridge form, the number of spans, rings and piers that can be modelled. Also, unlike many simpler strength assessment methods, there is no adherence to predetermined failure mechanisms, for instance, a set number and pattern of hinges.Verification
Alongside commercial activities there has been a major development programme to verify the method of structural analysis, the design process and the implementation of strengthening on site. This has included full-scale laboratory tests, supplementary load tests on bridges in the field, monitoring programmes and verification of the arch bridge structural analysis.Summary
Archtec has now been used successfully for a decade on nearly 200 arch bridge assessment and strengthening projects, on bridges in the UK, United States of America, Australia and India. FDE is now recognised as a special assessment tool and Archtec has established itself as a leading bridge strengthening system.
For further information, please contact:
Cintec International Ltd
Tel: 01633 246 614