Experimental study on thermal bridge effect of steel-concrete-steel tunnel elements under fireproof board insulation schemes

Abstract

Steel embedded parts welded on the surface of steel-concrete-steel tunnel elements serve as thermal bridges in tunnel fires. Their influence on temperature field and macroscopic thermal damage of steel-concrete-steel structure were investigated through fire tests, and their heat transfer forms were analyzed. Then, a thermal bridge disposal scheme was proposed and examined. The results show that steel embedded parts significantly cause an increase and an uneven distribution of steel shell temperature in tunnel fires. As time exposed to fire increases, the extent and range of these influences grow. Thermal bridges raise the average temperature by 45.2 % inside the steel-concrete-steel structure, worsen the unevenness of temperature distribution in horizontal and vertical directions. Thermal bridges worsen surface macroscopic damage, lengthening cracks by more than 32.5 % and widening them by more than 22.6 times. Within a distance of 30 cm from the embedded part, heat provided by embedded parts accounts for over 79.9 % of the steel shell's total heat, and heat conveyed along the steel shell through thermal conduction accounts for over 53.7 %. GX-3 high-temperature adhesive is an effective method for thermal bridge treatment. These detailed findings offer new insights into the design of fire insulation schemes for the steel-concrete-steel structure.

Keywords

• Tunnel engineering
• Thermal bridge effect
• Thermal insulation scheme
• Physical model tests
• Steel-concrete-steel tunnel structure