地下空间混凝土顶板耐火性能试验研究OA

The concrete roof slabs of underground spaces,constructed with waterproof concrete and covered with soil on their surfaces,exhibit fire behavior and post-fire performance that differ from those of conventional concrete slabs.Four waterproof concrete two-way slabs with peripheral beams were tested for fire resistance under standard fire conditions with a constant load,as well as for post-fire residual bearing capacity.The effects of fire exposure time,the presence of a soil layer covering the slab,and the vertical deformation of peripheral beams on failure mode,temperature distribution,fire resistance,post-fire bearing capacity,and deformation development were investigated.The results indicate that covering the slab surface with soil significantly reduces the temperature of the concrete at the bottom of the slab.After 64 minutes of fire exposure,the temperature of the upper surface of the concrete slab remains between 103℃and 104℃.Explosive spalling is observed exclusively in the concrete slab covered with a soil layer,exhibiting a spalling depth of 19.5 mm and an area accounting for 4.4%of the bottom surface of slab.This condition leads to an 11.5%reduction in fire resistance compared to the concrete slab without soil coverage.Furthermore,restricting the vertical deformation of the peripheral beam significantly reduces the mid-span deflection of the concrete slab,thereby enhancing its fire resistance.The concrete slab with unrestrained vertical deformation of the peripheral beam reaches the fire resistance of 165 minutes due to excessive deflection.In contrast,the concrete slab with restrained vertical deformation of the peripheral beam attains a fire resistance of 181 minutes,primarily attributed to an excessive average temperature rise on the surface of the slab despite its small deflection.When the fire exposure duration is extended from 85 minutes to 165 minutes,the post-fire bearing capacity of the concrete slab decreases modestly by only 7.1%.In contrast,the post-fire bearing capacity of the concrete slab with soil cover diminishes further,resulting in a 12.1%reduction.