Analysis of the response of temporary overhead sign structures subjected to overheight vehicle impact

Abstract

Overheight vehicle impact is the impact of a heavy dump truck with a rigid raised trailer on the beam of a light-weighted and flexible temporary overhead sign structure. The structure is initially not designed to resist overheight vehicle impacts and the impacts occurring during construction works with impact velocities up to 40 km/h result in total collapse of the structure and, consequently, high risks with respect to road users’ safety. These serious consequences in combination with the need for revised design specifications and calculations have led to the following main research question:

“Is it feasible to create a design for the temporary overhead sign structure which is able to resist the overheight vehicle impact of raised trailers of dump trucks in work zones?”

In this research study, a load analysis is performed in order to approximate the impact load for the impact problem analysed assuming viscoelastic behaviour. The analysis demonstrated that the impact response is barely influenced by the dynamic effects in the structure. The mass of the vehicle and the global stiffness of the structure dominate the impact response. The impact load can be approximated based on the quasi-static approximation.

The current temporary overhead sign structure is not able to resist overheight vehicle impacts since the tensile resistance of the bolts of the column base plate connection is much smaller than the internal tensile forces it is subjected to as a result of the large overturning moment and the small internal lever arm in the connection. The behaviour of the structure could be improved by redesigning the column structure while focussing on increasing the internal lever arm and simultaneously limiting the transverse stiffness of the column structure and with that limiting the magnitude of the impact load.

Some design considerations are analysed demonstrating that it is a challenging task to develop a design for the demountable temporary overhead sign structure which is able to resist the overheight vehicle impact with a mass of 20,000 kg while limiting the structural mass based on the design requirements as provided by Rijkswaterstaat. The possibilities are limited up to an impact velocity of 7.4 km/h after replacing the original column with a lattice column structure.

The study is based on viscoelastic behaviour of the structure neglecting the influence of plastic deforming of the structure and vehicle during impact which may be of significance. Moreover, the actions of the driver during impact are not taken into account. Including the influence of these aspects and developing an optimized design for the structure might somewhat increase the currently approximated critical impact velocity of 7.4 km/h.