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Fatigue design of bridges with welded circular hollow sections (AGB1998/103)

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Vehicle design and manufacturing (VDM)
Infrastructure (INF)
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Background & Policy context

Numerous steel-concrete composite bridges with welded circular hollow section (CHS) trusses as their main load-carry members have recently been constructed (two of these in Switzerland). When compared to open structural sections such as I-beams, circular hollow sections offer several advantages: high strength-to-weight ratio, equal bending strength and stiffness in all directions, and an aesthetically pleasing form.

Architectural tendencies of today, as well as improvements in modern fabrication procedures will lead to an increase in the use of CHS members in structural engineering applications. The use of CHS members in bridges, however, is a relatively new concept. Little has been published on this subject and no specific research has been carried out in this area. Existing codes and standards used in the design of the recently constructed CHS truss bridges are incomplete, in particular the fatigue design of welded CHS joints. This results in overly conservative and penalising designs.


For this project new insights will be gained in the field of CHS bridges through measurements on two bridges of this type recently constructed. Furthermore experimental and numerical research on the fatigue resistance of welded CHS bridge joints will be carried out. A new fabrication method of welding on backing bars to ensure complete penetration welds will be examined.

Lastly, based on existing norms and standards, results of the project will be incorporated in a proposal for design rules.

Proposal of design rules for the design and fabrication of CHS bridge structures.

Promotion of this type of bridge construction.


Parent Programmes
Institution Type
Public institution
Institution Name
Swiss Government: State Secretariat for Education and Research
Type of funding
Public (national/regional/local)


Recommendation of design rules for bridges. The results can be directly put into practice. Tests on the finalised assemblies have shown an increase in fatigue resistance by 60%.


Lead Organisation
EU Contribution
Partner Organisations
EU Contribution


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