Development of Passively Safe Post Using Momentum Principle and Crushing of Energy Absorbing Module

摘要

Roadside columns exposed to traffic without being properly shielded are severe hazards to the occupant safety of the vehicle impacting to the posts. In the case, passively safe columns should be used. Energy absorbing columns and breakaway ones are the most popular system. In this study, passively safe column of new concept is developed. It consists of a column having a special base plate with a key of inversed T shape and the foundation having guide trough of inversed T shape through which the column base key is inserted keeping the column stands against wind load, but moves in case of an impact. Part of the trough is filled with energy absorbing modules made of circular steel tube stub, which absorbs part of the impact energy remaining after the vehicle and column completes their plastic impact. In this system, energy dissipation takes place in two phases. In the first phase, it dissipates the impact energy by the linear momentum conservation principle while the plastic impact between the post and vehicle takes place, then, the second phase dissipation follows by the deformation of the energy absorbing modules embedded in the guide trough of the foundation. Energy dissipation mechanism is explained and simulations of impacts to the new column system are made using LS-DYNA program to investigate the vehicle response and occupant safety. The simulation results are used in tuning the dimension of the energy absorbing module for an impact of 0.9ton-80km/h. The simulation for the final design of the passively safe column shows its effectiveness to the proposed target impact of 0.9ton-80km/h.