Wind-induced forces on eaves of low buildings

Abstract

Wind standards and codes of practice specify design pressure coefficients for eaves of low buildings with gabled roofs of angles smaller than 10°. The paper presents the results of a recent experimental study on the effects of wind on eaves of gabled-roof buildings with higher roof slopes, namely 4:12 and 12:12. The experiments were carried out in the boundary layer wind tunnel of the Building Aerodynamics Laboratory of the Centre for Building Studies under conditions of simulated open country exposure. Both local and area-averaged pressures were measured for 36 azimuths. Simultaneous measurements of each pair of upper and lower surface taps were also carried out in order to evaluate the critical forces acting on various overhang zones. Area-averaged pressures were measured as well. The study has found that the 4:12-sloped overhang is the most severely loaded, particularly as far as suction on the upper surface near the gable is concerned. Positive pressures on the upper surface are higher for the 12:12 slope, as expected from wind flow considerations. However, lower eave surfaces are subjected to higher pressures and suctions for the 4:12 slope. The effect of building height on the pressure coefficients measured on either overhang surface is negligible, as also found previously for the case of eaves of almost flat roofs. Pressures measured on lower eave surfaces compare generally well with those measured on the walls, although some positive peaks are significantly higher under the eaves. Comparisons between actual uplift force coefficients and the presently used values show the significant overestimation that occurs in some cases when the current wind standards are used. The paper makes appropriate recommendations for design provisions.