Effect of Geometry and Dimensions on the Upward Fire Spread in U-Shaped Structures

U-shaped structures are very common in the facade of buildings, which have a significant impact on fire spread. In this paper, the effect of the geometrical factor ( α ), the cross-sectional area ( A ), the height ( H ) on the upward fire spread in u-shaped structures are analyzed based on the fire spread rate ( V f ) and the pressure difference between the top and the bottom (Δ P ) through full-scale experiments and simulations. A dimensionless structure parameter α H / A is put forward to analyze the coupling effect of the structure size. It is found that V f increases in the form of logarithmic function as α increases. Δ P max increases in the form of exponential function as α increases; both V f and Δ P max decrease in the form of exponential function as A increases; V f is positively correlated with H linearly. Δ P max increases in the form of quadratic function as H increases; both V f and Δ P max increase in the form of Slogistic function as α H / A increases. When α H / A ≤ 17.2 or α H / A ≥ 38.8, α H / A has little effect on Δ P max . The V f in the non-overhead structure is very close to that in the overhead structure. This study can provide a theoretical guide for the fire protection design of u-shaped structures covered with insulation materials in practical engineering. Graphical abstract