The Mechanical Behavior Of Bridge Flexible Steel Tunnels Under The Impacts Of Rockfall In Mountainous Areas

In western regions of China, there is a high percentage of areas which are mountains, hills, or valleys, so the road construction in these areas is difficult, and the bridges and tunnels are often adopted. The rockfalls often happen in these areas because of the poor vegetation condition, perilous rock formation and frequent natural disasters such as earthquake and landslides. The rockfalls are energetic after a series of accelerated motion and the bridge may be destroyed under its direct impact. For example, small-sized rockfalls can puncture the deck of the beam, larger one may break the whole beam, which may lead to terrible bridge accidents. Thus, it is necessary to adopt passive methods to protect the bridges in dangerous sections. Similar to the tunnel, shed tunnels can be used to protect the bridges too. Since there is a strict limitation of loads in bridge design, flexible steel shed tunnels are often used in bridge projects due to the reasons of low self-weight and effective protection.At present, there is less research of the impacts of rockfalls on bridge flexible steel shed tunnels. This dissertation will study this topic and focus on the impact behavior of flexible steel sheds on the impact of rockfalls. This dissertation will begin with the theoretical analysis on the impacts behavior of rockfalls. Then, based on practical engineering background, computational models will be built to comparative analyze responses of the steel shed tunnel and bridge under the impacts with different levels of rockfalls energy and positions. Finally, the impact behavior of the steel shed tunnel will be summarized based on different sizes of sheds, types of rubberized cushion coat and conditions of thin-wall energy dissipater, and the optimized design scheme will be proposed as well. The following conclusions can be drawn according to this study:a) The higher energy of rockfalls, the worse destructive effects on the steel shed tunnel and bridge will be; b) When the rockfalls hit the girder of the steel shed tunnels, the worst bridge destruction scenario will be reached, c) To significantly alleviate the rock impacts on the bridge, it is better to adopt large-diameter steel shed tunnels, thicker girder steel plate, more rubberized cushion coats and thin-wall energy dissipater.