Final Report Summary - IMPACT LOADS (Impact loads on concrete structures)
Impact loads on concrete slab track structures due to earthquake excitation
This research project was focused on the specific impact stresses in concrete structures caused by strong earthquakes. The research was combined with a practical background to investigate an earthquake-resistant slab track system for high-speed railways.
For high-speed rail systems, the stiffness and continuity of the track are extremely important for safety and operation quality. Furthermore, in seismic active regions the safe train operation has to be assured even in the event of an earthquake because a high-speed train derailment or overturning can lead to terrible accidents, as the past has shown. For a train travelling at 220 mph, the minimum breaking distance will be 2.8 miles and the minimum breaking time will be 1.5 minute, while the duration of ground shaking during an earthquake is normally less than a minute with the actual strong shaking lasting less than 10 seconds. If an earthquake impact hits a conventional concrete slab track while a train is operating on, a derailment is very probable.
In this research, a novel structural concept was developed for high-speed rail track systems to advance existing slab track design ideas to improve the seismic safety. The system consists of a longitudinally continuous slab track with seismic isolation along the longitudinal and transverse directions. The track slab is restrained by friction as well as gravitational force under normal service conditions, but it is isolated from seismic ground motions by allowing it to slide with respect to the supporting structure. It can be used at embankments as well as on bridges. It is designed to continuously cross movement joints of a bridge superstructure and accommodate potential moderate surface fault ruptures.
The slab track concept uses an isolation technology which is based on the same principle as the friction pendulum concept that has been used to protect buildings and bridges against earthquake loads. Similar concepts have already been used successfully but they need to be integrated and modified to arrive at a new system that will be a major step forward as compared to existing slab track systems. Investigations have been conducted to check the feasibility and practicality of the concept. On one hand, the track slab has to be strong and stiff enough to resist transverse forces induced by normal train operation, such as the centrifugal force due to train acceleration over a curved track, possible side impact, and wind without any additional bearings or support systems. On the other hand, it needs to have low enough resistance to slide with respect to the supporting slab to be isolated from earthquake ground accelerations.
The effectiveness of the isolation concept has been already demonstrated with computational investigations using MatLab and LS-Dyna. Under very low level motion (within the first seconds of the simulation), the two slabs move together, but with increasing acceleration or impacts, the track slab moves separately from the base and shows much lower acceleration, velocity and displacement. Further computational simulations with varying frequencies and amplitudes and with time histories of real earthquakes were carried out in the project to optimise the geometry, the material properties, and the cost of the rail system.
Based on those investigations the research groups at UCSD and Leibniz University Hannover will enforce the research work to improve the track slab system configuration and seismic isolation concept. Advanced analytical models will be developed to evaluate and validate the design concepts. Furthermore, it is planned to conduct experimental evaluation in two phases. The first phase will be focussed on the quantification of the physical characteristics of selected designs for the proposed track isolation systems while the second phase will involve large-scale shake-table testing for the proof of concept.
This research project was focused on the specific impact stresses in concrete structures caused by strong earthquakes. The research was combined with a practical background to investigate an earthquake-resistant slab track system for high-speed railways.
For high-speed rail systems, the stiffness and continuity of the track are extremely important for safety and operation quality. Furthermore, in seismic active regions the safe train operation has to be assured even in the event of an earthquake because a high-speed train derailment or overturning can lead to terrible accidents, as the past has shown. For a train travelling at 220 mph, the minimum breaking distance will be 2.8 miles and the minimum breaking time will be 1.5 minute, while the duration of ground shaking during an earthquake is normally less than a minute with the actual strong shaking lasting less than 10 seconds. If an earthquake impact hits a conventional concrete slab track while a train is operating on, a derailment is very probable.
In this research, a novel structural concept was developed for high-speed rail track systems to advance existing slab track design ideas to improve the seismic safety. The system consists of a longitudinally continuous slab track with seismic isolation along the longitudinal and transverse directions. The track slab is restrained by friction as well as gravitational force under normal service conditions, but it is isolated from seismic ground motions by allowing it to slide with respect to the supporting structure. It can be used at embankments as well as on bridges. It is designed to continuously cross movement joints of a bridge superstructure and accommodate potential moderate surface fault ruptures.
The slab track concept uses an isolation technology which is based on the same principle as the friction pendulum concept that has been used to protect buildings and bridges against earthquake loads. Similar concepts have already been used successfully but they need to be integrated and modified to arrive at a new system that will be a major step forward as compared to existing slab track systems. Investigations have been conducted to check the feasibility and practicality of the concept. On one hand, the track slab has to be strong and stiff enough to resist transverse forces induced by normal train operation, such as the centrifugal force due to train acceleration over a curved track, possible side impact, and wind without any additional bearings or support systems. On the other hand, it needs to have low enough resistance to slide with respect to the supporting slab to be isolated from earthquake ground accelerations.
The effectiveness of the isolation concept has been already demonstrated with computational investigations using MatLab and LS-Dyna. Under very low level motion (within the first seconds of the simulation), the two slabs move together, but with increasing acceleration or impacts, the track slab moves separately from the base and shows much lower acceleration, velocity and displacement. Further computational simulations with varying frequencies and amplitudes and with time histories of real earthquakes were carried out in the project to optimise the geometry, the material properties, and the cost of the rail system.
Based on those investigations the research groups at UCSD and Leibniz University Hannover will enforce the research work to improve the track slab system configuration and seismic isolation concept. Advanced analytical models will be developed to evaluate and validate the design concepts. Furthermore, it is planned to conduct experimental evaluation in two phases. The first phase will be focussed on the quantification of the physical characteristics of selected designs for the proposed track isolation systems while the second phase will involve large-scale shake-table testing for the proof of concept.