Finnish Bridge Fatigue Load Model Calibration from Recorded Traffic Data in Kaarina

Abstract

In 2013, a new regulation was implemented that increased the allowable vehicle weights in Finland. However, heavier vehicles increase stress ranges, which can affect the fatigue life of bridges. Eurocodes provide five Fatigue Load Models for fatigue verification. However, these Load Models were derived from Central European traffic in the 1980s. Two of the Fatigue Load Models are used in this analysis, FLM3 and FLM4. Furthermore, this analysis includes recorded traffic data from two separate years, 2014 and 2016. The traffic data was measured in Southwest Finland during a larger measurement campaign. Eurocodes provide two fatigue verification methods. That is the cumulative damage method and the damage equivalent method. The first is used with the recorded traffic and FLM4, whereas the latter is used with FLM3.

The effect of the regulation change and the accuracy of the Fatigue Load Models are inspected for four case bridges with varying span lengths. The required elastic section modulus for each case bridge and span length is calculated. The section modulus obtained for the 2016 recorded traffic is compared with the ones obtained for 2014 traffic to see how the regulations have affected bridge fatigue. The comparison between Fatigue Load Models and actual traffic is done by comparing the section modulus obtained for FLM3 and FLM4 with the 2016 recorded traffic. A new Fatigue Load Model is also calibrated based on FLM3, given in the Eurocodes. The calibration is done using the 2016 measured traffic data.

The results obtained clearly show how the regulation change has affected bridge fatigue. The traffic recorded in 2016 requires a higher elastic section modulus than the 2014 traffic. This is due to heavier vehicles and a higher traffic volume, causing larger stress ranges and more stress cycles. The Fatigue Load Models give conservative results compared to actual traffic, even when the vehicle weights have increased. With the calibrated Fatigue Load Model, the accuracy improved substantially compared to measured traffic. This is due to the new FLM and fatigue vehicle representing the traffic they were calibrated from.