PSI - Issue 62

Mariano Angelo Zanini et al. / Procedia Structural Integrity 62 (2024) 815–823 Zanini / Structural Integrity Procedia 00 (2019) 000 – 000

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From the analysis of the resulting risk ratings, MIT-GL indicates which structures needs further in-depth structural assessments, and those for which is sufficient to carry out periodical visual inspections. For the first subgroup, the analysis can be extended to a preliminary evaluation of the safety margin based on a simplified comparation of the demand acting on the structural elements considering the load model used for the original design and the current load model in force (Level 3), and a further structural assessment following the classic semi-probabilistic format aimed at quantifying the safety level of the existing structure with respect to current traffic load models or reduced loading schemes, newly introduced by MIT-GL (Level 4). After almost two years of research and application of the MIT-GL prescriptions, for the bridges characterized by the need of further structural assessment after the execution of the Level 2 screening it is frequent to observe the execution of a direct structural assessment (Level 4) rather than to the evaluation of the compliance in terms of structural demand (Level 3). In 2022 the Ministry of Infrastructures and Transports issued another technical standard (MIT 2022) specifically related to the safety check protocol to be adopted by infrastructure owners when an exceptional vehicle (EV) requires the transit authorization. For such specific conditions, even if the acting loads are significantly higher with respect to those characterizing ordinary vehicles and trucks, there is the advantage to be able to precisely know the amount of load and dimensions of the vehicle, and to preliminary define the loading scheme (i.e. number of axes and wheels, spacing), the transit speed, and the travel itinerary (i.e. number of bridges affected by the exceptional load). In this context, infrastructure owners are often asked to give permission to the transitability of the EV, and ofte n they don’t have time to carry out in-depth structural assessments. For such reasons, taking advantage of the standardization of the EV loading schemes provided by the Italian MIT, and considering also a set of exceptional vehicles used for such type of transports, the present work proposes a parametric comparative analysis of the structural demand induced by such loading schemes with those used on the original design of several configurations of simply-supported girder bridge decks. The results of such “Level 3 for exceptional transport loads” can be used by owners to get a quick response on the transitability of the requested travel itinerary and on the potential criticalities that can require alternative routes. 2. Exceptional transport loading schemes In this Section the exceptional transport loading schemes considered in this work are detailed. First, the loading schemes provided by the MIT EV standard (MIT 2022) have been adopted: this guideline defines a verification protocol for exceptional loads, starting from the definition of the individual EV load model and moving to the partial safety factors to be considered for this type of structural checks. The exceptional transport is defined according to the Italian road traffic regulations as a 108 tons total weight vehicle for eight-axle as maximum limit for roadways. The MIT standard considers two different situations and the consequent protocols to be followed by the owner to identify the load actions, as reported in the following: • Complete knowledge of load passing through including the vehicle weight distribution on each axle : in this case, the real arrangement and load distribution on the axles must be considered as a load model, for EV only (e.g. EV used for coil transport and for prefabricated products transports). • Only vehicle total weight knowledge or no knowledge of the load : in this case, only the total transiting load is known or no-load information is available, the MIT EV standard defines two different load models of exceptional vehicles namely 860/150 and 1080/135 (Fig. 1). In the event that the EV total weight is known, and it does not correspond with one of the two MIT EV standard loadin g schemes, it is possible to consider the vehicle composed by the same axles’ composition of the two model and appropriately scale the load in each axle. Furthermore, it must be considered that the Italian road traffic regulations allows the loads exceeding 86 tons transit only if the vehicle have at least 8 axles. The MIT EV standard introduces also different cases based on the transit vehicle mode, in order to standardize possible loading scenarios to be considered in the structural assessment. In detail, the four following cases can be defined: