Updated load models for short‐span road bridges in the range of 2‐15 m

In recent years, increased effort has focused on developing traffic load models for the safety verification of existing road bridges. In Switzerland for example, this was achieved by updating the alpha reduction factors in the Traffic Load Model 1 (LM1) for new bridges (analogous to the Eurocode LM1 alpha factors), providing a practica approach. The enveloping of the maximum simulated alpha factors, which were calculated by applying measured vehicles to different traffic scenarios, spans and bridge cross‐section types, resulted in the updated LM1 in the SIA 269/1 Standard for Existing Structures. The model development considered spans in the range of 10‐80 m and applied dynamic amplifications as a function of the gross vehicle weight. One limitation of the current updated LM1 is that, as a very high proportion of existing road bridges have spans of less than 15 m, the load effects in this short‐span range tend to be overly conservative. This paper studies the load effect behaviour in the longitudinal and transverse directions, based on actual traffic from Weigh‐in‐Motion (WIM) data. The study utilises all WIM data recorded in Switzerland over the last 10 years. Results from three new short‐span load models are presented which, together, envelope the extreme load effects. A parametric study is presented which highlights some conservatism in the existing code load models. Finally, a case study project is presented, in which these updated models were used to verify the structural safety of a historic road bridge.