Engineering survey of stone buildings after fire exposure

Introduction. Engineering survey forms a basis for making informed decisions regarding the operation of stone structures following exposure to high temperatures and fire. Aim. To determine the residual bearing capacity and to specify methods for reinforcing stone structures after a fire. Materials and methods. The impact of fire on stone structures depends on the size and material of the stone, the spatial arrangement of the walls, the thermal and prolonged effects of the fire, and the firefighting methods employed. Results. Stone buildings constructed in the late 19th and first half of the 20th century were predominantly 2–7 stories high, while those built in the second half of the 20th century ranged from 5 to 14 stories. The walls were primarily made of solid and hollow ceramic and sand-lime bricks. The mortar used for wall masonry in the late 19th century and throughout the 20th century was cement-lime based. The thickness of walls built in the late 19th to early 20th century typically comprised 2–2.5 bricks, while after the 1920s, it was generally two bricks. When exposed to thermal effects of a fire, ceramic brick masonry at temperatures up to 800 °C experiences spalling of the stone to a depth of no more than 5 mm, with vertical and inclined surface cracks appearing, while the bearing capacity remains unaffected. At temperatures between 800 and 1000 °C, fire damage penetrates to a depth of 5–10 mm, resulting in vertical and inclined cracks extending no more than two courses of masonry, with wall bulging not exceeding 1/6 of their thickness. The bearing capacity of the masonry decreases by 15–20 %. When masonry walls and columns made of ceramic bricks are heated from 1000 to 1200 °C, damage exceeds 10 mm in depth, with vertical and inclined cracks extending over two courses of masonry, and bulging of walls reaching one-third or more of the masonry thickness. The bearing capacity of the masonry declines by more than 20 %. Conclusions. All cracks must be classified according to their causes: overloading of wall sections, thermal effect, and uneven foundation settlement. This necessitates an inspection of wall sections adjacent to areas affected by fire. The type and condition of the mortar in the masonry are to be assessed. For comparison, joints in masonry adjacent to fire-damaged areas should be examined. The design resistance of brick masonry subjected to fire exposure, after cooling, is considered equal to the design resistance prior to the fire multiplied by a coefficient for reduced bearing capacity k mc .