Numerical and experimental analysis of a new conception of road restraint systems

Today, differently from other countries, the use of restraint systems for hazardous singularities on Italian roads is not widespread. This lack is mainly due to a missing design consciousness of the roads passive safety importance and to a deficiency in terms of safety analysis and safety review procedures. Furthermore, present Italian Standards does not support the engineer with satisfactory guidelines for restraint systems design and positioning and in addition, difficulties for placement and repairing are not unusual. The increasing number of accidents involving roads singularities like cusps, bridge piers, pillars, tunnel portals and so along, is sufficient to highlight the scale of this issue. In this paper, moving from a wide analysis of existing restraint systems classified by either their geometry, or construction characteristics and absorbing energies related with their constitutive materials, a new type of device is presented. If existing systems are mainly built with a steel confining structure filled with stress absorbing elements performing a plastic behaviour, the proposed one involves the use of expanded clay, opportunely graded, bound with high strength thermoplastic polymers. These device present some advantages, like reduced number of pavement anchoring, high energy absorption, low costs and easy replacement. Physical-mechanical characteristics of the constitutive material have been determined as first step, by means of laboratory tests conducted on reduced scale specimens. Step two needed standardized impacts numerical analysis made with a specific kineto-dynamic software able to reproduce different impact scenarios. An optimal system configuration has been identified in terms of cushions number, shape and position as well as material characteristics. The evaluation was conducted with regard to the vehicle and attenuator behaviour during the event and to the values of the ASI, THIV and PHD parameters.