ABSTRACT
In the past decades the European highways have experienced a steady increase in daily vehicle numbers and axle weights. In Germany the total heavy freight traffic on roads has approximately doubled in the last 20 years. More than half of the bridges in the German highway network however have been constructed before the 1980s. They were designed with a traffic load model that consisted of a vehicle with a total weight of 600 kN as shown in Figure 1 a and a uniformly distributed load of 5 kN/m2 in the main lane and 3 kN/m2 in the remaining lanes according to DIN 1072:1967 [1]. (a) Traffic load model for 60 t vehicle according to the DIN 1072:1967 [<xref ref-type="bibr" rid="ref122_1">1</xref>] and (b) Traffic load model 1 according to EN 1991–2 [<xref ref-type="bibr" rid="ref122_2">2</xref>]. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig122_1.tif"/>
In contrast the traffic load model of the Eurocode 1991–2: Traffic Loads on Bridges [2] includes three vehicles positioned simultaneously on the bridge, distinguishing also three uniformly distributed loads for each lane as displayed in Figure 1b.
The recently introduced German national annex [2] defines the values of these loads as summed up in Table 1. A direct comparison of the loads is influenced by the fact that the German standards used to apply a global safety factor while the Eurocodes are based on the limit state concept with the partial safety factor method. Nevertheless it can be concluded, that the traffic loads have approximately doubled for both the concentrated and uniformly distributed loads. Adjusted characteristic values for Load model 1 according to EN 1992–1/NA [<xref ref-type="bibr" rid="ref122_2">2</xref>].
Location
Adjusted value of axle loads Q ik ⋅ α Qi [kN]
Adjusted value of UDL system q ik ⋅ α qi [kN/m2]
Lane 1
300
12.0
Lane 2
200
6.0
Lane 3
100
3.0
Other lanes
–
3.0
Besides new bridges, the assessment and the preservation of existing road bridges (esp. for the highway network) came into the focus of investigations and the need of developing a guideline for re-assessment of existing bridges has been identified. The guideline features a multi-stage approach where, in case the requirements for a specific stage cannot be met, in the next stage considerations which are more sophisticated verification may be carried out. Aspects of traffic loads which have to be considered depending on the real traffic volume will be covered as well as optimized verification formats e.g. for shear and fatigue.
The paper describes the procedure for the reassessment of existing road bridges according to the German guideline for Re-assessment of road bridges. Typical deficiencies will be highlighted dependent on the date of construction. Alternative verification formats (partially based on the new Eurocodes) will be presented to fulfill the future requirements. Finally the re-assessment procedure using on-site measurements and scientific based research results will be presented. Together with suitable compensation measures a further usage of old bridges with a minimum of limitations can be reached.
