Sources of Torsional Wind Loading on Tall Buildings: Lessons from the Wind Tunnel

Torsional wind loading on buildings is not as well understood as lateral or overturning loads, and is not as amenable to analytical treatment. Because of this, many designers—and indeed most codes of practice—ignore this aspect of the load, and simply apply the lateral load at the geometric or elastic center of the structure. Wind-tunnel tests on model buildings have revealed that torsional loads usually exist, and span a great range of significance. Several causes of the torsion can be identified, and this categorization aids the designer in providing methods to either reduce or manage the loading. This paper identifies some common sources of torsional loading in terms of building shape, interfering effects of nearby buildings, and dynamic characteristics of the structural frame. In addition, it is shown that torsional loading is routinely larger than that provided for in most standards.