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Load model (40 tonne-traffic) for the assessment of existing road bridges (AGB1999/154)

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Network and traffic management systems (NTM)
Infrastructure (INF)
Transport mode
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Background & Policy context

40 tonne-trucks will circulate throughout the Swiss road network. This raises questions about certain bridges on cantonal and local roads designed for a traffic limited to 28 tonnes. Cantonal authorities therefore need to assess existing bridges for 40 tonne-traffic and an appropriate load model is thus urgently needed.


The objective of this research is to develop a load model for Swiss traffic which will be limited to a legal gross weight of 40 tonnes. The model will be established for the assessment of existing bridges with two traffic lanes (bi-directional traffic) and is therefore not intended for motorways or transit roads. For these cases, the traffic load models in the Swiss Code SIA 160 or the Euro codes should be used.


The first stage of this research consisted of analysing these measurements in order to
define a traffic model which approximates, as closely as possible, the real traffic. A program for the analysis of the measurements was developed towards this end.

In the second stage of this research, a traffic simulation program offering high configuration flexibility was developed.

In the third stage, the results of the simulations were compared with the internal force values calculated according to the SIA 261 code.


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


"Swiss" load model for assessment of current bridges with a load of 40 tons trucks.

The proposed updated model involves the application of the SIA 261 load model with updated α coefficients. These coefficients were established on the basis of comparisons between the simulated internal forces and those calculated according to the code, taking into account the suggested correction. The various results obtained being relatively constant, it was possible to provide a simple updated model. The proposed α coefficients are in fact independent of the span, the type of effort, and the road type. Only the effect of the bridge type was differentiated.

Technical Implications

This study shows that the use of the SIA 261 code for the evaluation of existing road and highway bridges with two lanes is conservative for the traffic expected in the next 15 to 20 years.


Lead Organisation
EU Contribution
Partner Organisations
EU Contribution


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