# Bridge Expansion Joint in Road Transition Curve: Effects Assessment on Heavy Vehicles
## 2 Heavy Vehicle-Bridge Interaction: The Expansion Joint Role
The DIVINE project also demonstrated that dynamic vehicle models can accurately reproduce dynamic wheel forces, and many researchers have demonstrated that the bridge/vehicle interaction problem can be analytically solved [12]. Some tools permit developing and validating bridge models including both road profile and bridge natural frequency [16]. Figure 2: Schematic block diagram of dynamic bridge-vehicle interaction. The model proposed by [PERSON] and [PERSON] [10] consists of a single degree of freedom vehicle on a simply-supported bridge. It does not detail the nonlinearities of vehicle suspensions and the complexities of sprung mass motion, but it ensures a good representation of the problem. [PERSON] [13] and [PERSON] et al. [17] elaborated multiple-degree-of-freedom models to describe dynamic bridge-vehicle interaction and found good agreement with experiments carried out on highway bridges. In these approaches, road unevenness is modeled by artificial profiles that simulate the desired roughness level [18]. [PERSON] and [PERSON] [10] performed a parametric study based on previously literature works [19; 20; 21] and using the model proposed by [PERSON] [13]. The results of this study permit ascertaining when coupling is important and when it can be ignored. For highway bridges, the most important parameters are speed, frequency and initial vehicle excitation. Moreover, vehicle suspensions are important in determining the dynamic response of bridges under a single vehicle, as demonstrated both by the DIVINE results and by [PERSON] et al. [22]. Different suspension systems induce different dynamic loads on roads (i.e., amplitude and frequency content). For example, for roads in fair condition and at a speed of 80 km/h, the dynamic load induced by a truck fitted with airbag suspension is about 60% of the dynamic load induced by the same truck, but fitted with steel multi-leaf suspension [22]. This paper presents a case study of a highway BEJ with a big unevenness due to the torsion of the cross-section along a transition curve. After five years of service life, it had partial breaks and superficial cracks in the head cross beam where it was located. Asphalt pavement before and after the BEJ was affected by severe distresses (e.g., cracking and rutting). Indeed, the impulsive vibrating actions of the heaviest and quickest vehicles produced a surface wear of the joint so important that its service condition was very unsafe. The geometric configuration of the road section is such that the allowable vehicle speed is quite high, and the concomitant presence of the joint determined the cause of many accidents, even serious ones, which have affected both light and heavy vehicles [23]. The irregular circulation induced by the BEJ was causing hard braking and acceleration, which have environmental effects [24]. Moreover, the condition of the BEJ had required several maintenance works during its even short service life. The present work focuses on the geometric characterization of the BEJ and on the assessment of the effects on road traffic, with particular attention to heavy vehicles running on it. Specifically, safety and comfort analyses were carried out, evaluating also the dynamic increment of loads transmitted to the pavement (and then to the bridge) and the stress magnitude on vehicles' mechanical components. The importance of these analyses is that the interpretation of their results is useful to identify strategies and procedures for policies to guarantee minimum safety levels at roads.