Influence of cross-section parameters of cast-iron tubbings of metro tunnel lining on their fire resistance

Introduction. Nowadays, cast-iron is used in the field of metro construction for the production of special products — tubbings of metro tunnel finishing. There is an urgent need to take into account the possibility of a fire in the metro tunnel and its impact on the tubbings. At present, there are no ways to predict the behaviour of tubbings in fire conditions.

Aim. Assessment of the influence of the nature of the cross-section of cast-iron tubbings of metro tunnel lining on their fire resistance.

Objectives. Development of methods and carrying out of experimental and analytical assessments of the fire resistance of cast-iron tubbings; determination of the correlation of fire resistance from the cross-section parameters of cast-iron tubbings lining of metro tunnels.

Objects of research. As an object of research, fragments of tubbings of metro tunnel lining, made of cast-iron SCh20, were considered.

Research methodology. In the course of experimental evaluation the deformation of specimens under fire action was assessed. In the course of analytical evaluation — calculation of the strength of the tubbing cross-section with the assessment of the strength condition fulfillment — the critical temperature at which the bearing capacity is preserved was determined, the limiting load on the tubbing at which the strength is preserved was assessed.

Results and discussion. Experimental and analytical methods on fire resistance were chosen for the study. In the course of the experimental assessment of fire resistance, the deformation of the specimens was assessed, which also served as an indicator of the achievement of the limit state of the specimens, the temperature on the unheated surface of the specimen was estimated for further use in the analytical assessment of fire resistance. During the analytical assessment of fire resistance, the strength of the tubbing section was calculated with an assessment of the fulfillment of the strength condition, the critical temperature at which the bearing capacity is preserved was determined. Based on the calculation, the maximum load on the tubbing was estimated, at which the strength is maintained. As a result of the experimental and analytical assessment of fire resistance, critical load values for the selected specimens were obtained.

Conclusion. Experimental dependencies of deformation and heating of cast-iron lining tubbings on the time of fire exposure, as well as the time of reaching the limit states for the loss of bearing capacity, were obtained. The values of the maximum loads on the tubbings are determined, at which after 90 minutes from the beginning of the fire impact, the limit state for the loss of bearing capacity occurs. The mathematical dependence of the value of the maximum vertical load on the specimens, at which the limit state for the loss of bearing capacity is achieved, on the reduced thickness of the section of the tubbings of metro tunnel lining is obtained.

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