Keyfactorswhichgovernthe wind-inducedtorsionalresponse, especially the torsionalloads, are discussed in this paper. These factors include building geometry of the floor plan and of the elevation, building surroundings, and structural dynamic properties. Due to the complication and variation of these factors fromcase to case, the presented discussionis focussed on the floor plangeometryfor torsionalstatic loads, and naturalfrequency and dynamic coupling for the torsional dynamic loads. Withdefinitionof equivalent eccentricity, e, and load reductionfactor, r, the magnitudes of torsional loads for several tall buildings are investigated with respect to the corresponding horizontal wind loads. The complicated nature of torsionalresponse also affects the precision of wind tunnel tests, although wind tunnel tests are still considered to be the most reliable approach. Normally, the torsional response cannot be measured with the same degree of completeness as for sway response using the wind tunnel force balance model. Selecting an appropriate wind tunnel method for torsional response is therefore also considered to be a key factor. With discussion on the recent developments in wind tunnel technique, guidance for selecting the wind tunnel method is suggested. Copyright ASCE 2004.
