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 (ΔP) through full-scale experiments and simulations. A dimensionless structure parameter \({{\alpha H} \mathord{\left/ {\vphantom {{\alpha H} {\sqrt A }}} \right. \kern-\nulldelimiterspace} {\sqrt A }}\) 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. ΔP_max increases in the form of exponential function as α increases; both V_f and ΔP_max decrease in the form of exponential function as A increases; V_f is positively correlated with H linearly. ΔP_max increases in the form of quadratic function as H increases; both V_f and ΔP_max increase in the form of Slogistic function as \({{\alpha H} \mathord{\left/ {\vphantom {{\alpha H} {\sqrt A }}} \right. \kern-\nulldelimiterspace} {\sqrt A }}\) increases. When \({{\alpha H} \mathord{\left/ {\vphantom {{\alpha H} {\sqrt A }}} \right. \kern-\nulldelimiterspace} {\sqrt A }}\) ≤ 17.2 or \({{\alpha H} \mathord{\left/ {\vphantom {{\alpha H} {\sqrt A }}} \right. \kern-\nulldelimiterspace} {\sqrt A }}\) ≥ 38.8, \({{\alpha H} \mathord{\left/ {\vphantom {{\alpha H} {\sqrt A }}} \right. \kern-\nulldelimiterspace} {\sqrt A }}\) has little effect on ΔP_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.