Wind-Induced Torsional Loads on Low- and Medium-Rise Buildings

摘要

Proper building design against wind loads depends primarily on the adequacy of the provisions of codes of practice and wind load standards. During the past decades, much has been learned about along- and across-wind forces on buildings. However, studies on wind-induced torsional loads on buildings are very limited. The recent trends towards construction of more complex building shapes and structural systems can result in an increase of the unbalanced wind loads yielding an increase of torsional moments. Thus, re-visiting the wind load provisions is of an utmost concern to ensure their adequacy in evaluating torsion on low- and medium-rise buildings and to achieve safe, yet economic building design. It is noteworthy that most of the wind loading provisions on torsion have been developed from the research work largely directed towards very tall and flexible buildings for which resonant responses are significant. However, the dynamic response of most low- and medium-rise buildings is dominated by quasi-steady gust loading with little resonant effect. Moreover, the lack of knowledge regarding wind-induced torsion is reflected in having different approaches in evaluating torsion in the international wind loading codes and standards. udThe current research program undertakes the investigation of shear and torsional wind loads on low- and medium-rise buildings. The study demonstrates that North American and European Codes and Standards have quite different provisions for wind-induced torsion acting on low- and medium-rise buildings with typical geometries – namely, for horizontal aspect ratios (L/B) equal to 1, 2, and 3. In the experimental phase, several buildings with different configurations, i.e. different roof angles (0°, 18.4°, 45°) and heights (ranging from 6 m to 60 m) were tested in the boundary layer wind tunnel of Concordia University for different wind directions (every 15°). The measured shear and torsional loads were compared with the Canadian and American code provisions. The study found that NBCC 2010 underestimates torsion on low-rise buildings significantly, while discrepancies were found for medium-rise buildings. In addition, wind load combinations for low- and medium-rise buildings were studied. For flat-roofed buildings, it was found that maximum torsion for winds in transverse direction is associated with 80% of the overall shear force perpendicular to the longer horizontal building dimension; and 45% of the maximum shear occurs perpendicular to the smaller horizontal building dimension. Suggested approaches and load combination factors were introduced to enhance the current building codes and standards aiming at an adequate evaluation of wind load effects on low- and medium-rise buildings. ud