# Bridge Expansion Joint in Road Transition Curve: Effects Assessment on Heavy Vehicles
###### Abstract  
Properly-designed road surfaces provide a durable surface on which traffic can pass smoothly and safely. In fact, the main causes that determine the structural decay of the pavement and its parts are the traffic loads. These repeated actions can create undesirable unevennesses on the road surface, which induce vertical accelerations on vehicles, up to hindering contact between pavement and tire, with dangerous consequences on traffic safety. The dynamic actions transmitted by the vehicles depend on these irregularities: often, a bridge expansion joint (BEJ), introducing a necessary discontinuity between different materials, determines from the beginning a geometric irregularity in the running surface. Besides, some structural conditions could emphasize the problem (e.g., local cracking due to the settlement of the subgrade near the abutment or the discontinuity of stiffness due to the presence of different materials). When the BEJ is located in a transition curve, an inevitable vertical irregularity between road and joint can reach values of some centimeters, with serious consequences for the road safety. This paper deals with the analysis of a case study of a BEJ. Several test surveys were performed in order to fully characterize the effects on both vehicles and pavement. The three-dimensional representation of the pavement surface and the acceleration measurements on a heavy test vehicle were performed to analyze the joint behavior under traffic. Finally, a finite element model was implemented to evaluate the stress contribution on vehicle components induced by the vertical irregularities.  
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(e.g., a highway seismic joint), the vertical irregularity between road and joint can reach values of some centimeters.  
This undesirable local irregularity in addition to the construction unevenness can cause important dynamic actions on running vehicles, the bridge structure and joints [4; 5].  
In this case, dynamic actions induced by vehicle tires stress BEJ. Traffic running on bridges produces a stress spectrum, which may cause fatigue. The stress spectrum depends on various parameters: the geometry of the vehicles, the axle loads, the vehicle spacing, superficial characteristics of the pavement (unevenness) [6], the composition of the traffic and its dynamic effects. Several repetitions of these dynamic loads during the design life of the pavement can cause a rapid and general decay of the structure or local breaks in correspondence with the BEJ, although well-constructed [7]. A BEJ is anyhow a discontinuity of the pavement, and dynamic actions caused by heavy vehicles running on it cannot be overlooked. For this reason, in Eurocode 1 [8], where traffic loads on bridges are described, it is specified that in the proximity of expansion joints, an additional dynamic amplification factor should be applied. In this sense, the same Eurocode also suggests a conservative simplification consisting of adopting an amplification factor of 1.3 for any cross section within 6 m from the expansion joint.  
Following specific recommendations for the fatigue design of modular bridge expansion joints [7], it is possible to avoid BEJs' durability problems. In any case, the unevenness induced by the presence of a BEJ still remains, and in certain conditions (i.e., BEJ located in road transition curve), it can worsen.  
In particular, this paper focuses on the analysis of the detrimental effects induced by BEJ unevenness in terms of road safety, dynamic increment of wheel loads transmitted to the pavement and vehicle components' stress.