Study On Structural Health Monitoring For Subway Stations

Subway station structures which have a long service period are inevitable to suffer from environmental corrosion, long term loading, fatigue effects, material aging and their coupling effects. In the wake of the damage accumulation, performance of the structures will degenerate, and even leading to structure failures under extreme loadings. If health monitoring for subway station is carried out, the possibility of accident will greatly decrease and the losses of accident also reduce. Therefore, the structural health monitoring technology for subway station will become an important technology to ensure structural safety.In this paper taking Guomao Station on No.10 subway line in Beijing as a case, structural health monitoring theories have been studied. The structural health monitoring system for Guomao Station has been installed firstly and the structural monitoring has been carried out for two years.Most of subway station soleplate structures are mass concrete. Cement hydration produces heat, which may provoke important temperature rises in massive structures. Such a high temperature may be a factor for cracking during a cooling phase. A simulation of the evolving temperature field for subway station soleplate is conducted by using the adiabatic temperature rise theory of concrete based on equivalent time. Temperature field simulated agrees very well with experiment data measured by fiber Bragg grating sensors and vibrating wire sensors. Parameters analysis of ambient humidity and thickness of slab which affect the difference of temperature between interior and exterior of concrete are carried out. It is shown that temperature increasesing leads to the difference of temperature between middle and upside of concrete increases, while the difference of temperature between middle and bottom of concrete decreases. Both the difference of temperature between middle and upside and the difference of temperature between middle and bottom of concrete increases.Based on creep theory of concrete, a structural health monitoring analysis is carried out in the paper. Using the double-power law for concrete creep, the strain of septi-slab is calculated. Experiment data measured by fiber Bragg grating sensors agree well with the calculated results, and the calculated results taking into account the earlyage creep are better in agreement with the measured data. Creep has very important effects on earlyage concrete, and the creep of earlyage concrete should be considered in the structural design and crack control. Based on the B3 model and the elastic continuation and plastic flow theory model for concrete creep, the long term creep of new impervious concrete structures is analyzed. The influence of ambient humidity, water-to-cement ratio and aggregate-to-cement ratio are studied with the B3 model.As restrained by earth, dynamic response of underground structures may not significant change from most surface structures. Its study has been ignored for a long time. Through monitoring and theoretical study for subway station, dynamic responses of a subway station are calculated under railway loads. Results show that railway loads have little influence on the stress of subway station structures.Temperature effects on the dynamic performance is a new study direction in structural dynamics. The paper deduces formulae for temperature effects on the natural frequencies of the beam and slab of specific boundary conditions. An artificial earthquake record with the Kanai-Tajimi model and trigonometric series superprosition method is generated. The artificial earthquake record is used to analyze seismic performance of the subway station structure. It is shown that the influences of the stresses of arch springing and basement are significant under horizontal direction earthquake. Under horizontal direction earthquake, the horizontal stresses of arch springing and basement are 1.46 and 1.61 times than the original stresses and their vertical stresses are 1.34 and 1.59 times than the original stresses. It is shown that the influences of the horizontal stress of soleplate and the vertical stresses of arch springing and basement are significant under vertical direction earthquake. Under vertical direction earthquake, the horizontal stresse of soleplate is 3.30 times than the original stress, while vertical stresses of arch springing and basement are 2.78 and 2.72 times than the original stresses. When temperature changes 20℃, the stress of structure changes about 9.6%, while stress amplitude reach 0.24MPa.Design methodology of health monitoring for subway stations is proposed firstly. According to the design methodology, the structural health monitoring system for Guomao Station has been installed to monitor temperature, strains, creep and cracks of the structure, obtaining a great deal of data, the data measured by fiber Bragg grating sensors and vibrating wire sensors of the system agree very well with each other. The change of structure strains at some special cases in the course of construction were obtained. It is demonstrated that the performance of the sensors are reliable and monitoring data are credible.A structural health monitoring system based on OpenGL and GIS which can collect, analyze, manage data and provide an alarm has been developed.