Assessment of the Influence of Tunnel Settlement on Operational Performance of Subway Vehicles

In the realm of subway shield tunnel operations,the impact of tunnel settlement on the operational performance of subway vehicles is a crucial concern.This study introduces an advanced analytical model to investigate rail geometric deformations caused by settlement within a vehicle-track-tunnel coupled system.The model integrates the geometric deformations of the track,attributed to settlement,as track irregularities.A novel“cyclic model”algorithm was employed to enhance computational efficiency without compromising on precision,a claim that was rigorously validated.The model’s capability extends to analyzing the time-history responses of vehicles traversing settlement-affected areas.The research primarily focuses on how settlement wavelength,amplitude,and vehicle speed influence operational performance.Key findings indicate that an increase in settlement wavelength can improve vehicle performance,whereas a rise in amplitude can degrade it.The study also establishes settlement thresholds,based on vehicle operation comfort and safety.These insights are pivotal for maintaining and enhancing the safety and efficiency of subway systems,providing a valuable framework for urban infrastructure management and long-term maintenance strategies in metropolitan transit systems.

Dynamic response limit of high-speed railway bridge under earthquake considering running safety performance of train

Due to the wide railway network and different characteristics of many earthquake zones in China,considering the running safety performance of trains(RSPT)in the design of high-speed railway bridge structures is very necessary.In this study,in order to provide the seismic design and evaluation measure of the bridge structure based on the RSPT,a calculation model of RSPT on bridge under earthquake was established,and the track surface response measure when the derailment coefficient reaches the limit value was calculated by referring to 15 commonly used ground motion(GM)intensity measures.Based on the coefficient of variation of the limit value obtained from multiple GM samples,the optimal measures were selected.Finally,the limit value of bridge seismic response based on RSPT with different train speeds and structural periods was determined.

Changes in ankle work,foot work,and tibialis anterior activation throughout a long run

Background The ankle and foot together contribute to over half of the positive and negative work performed by the lower limbs during running.Yet,little is known about how foot kinetics change throughout a run.The amount of negative foot work may decrease as tibialis anterior(TA)electromyography(EMG)changes throughout longer-duration runs.Therefore,we examined ankle and foot work as well as TA EMG changes throughout a changing-speed run.Methods Fourteen heel-striking subjects ran on a treadmill for 58 min.We collected ground reaction forces,motion capture,and EMG.Subjects ran at 110%,100%,and 90%of their 10-km running speed and 2.8 m/s multiple times throughout the run.Foot work was evaluated using the distal rearfoot work,which provides a net estimate of all work contributors within the foot.Results Positive foot work increased and positive ankle work decreased throughout the run at all speeds.At the 110%10-km running speed,negative foot work decreased and TA EMG frequency shifted lower throughout the run.The increase in positive foot work may be attributed to increased foot joint work performed by intrinsic foot muscles.Changes in negative foot work and TA EMG frequency may indicate that the TA plays a role in negative foot work in the early stance of a run.Conclusion This study is the first to examine how the kinetic contributions of the foot change throughout a run.Future studies should investigate how increases in foot work affect running performance.