Key Factors for Torsional Wind Response of Tall Buildings

Key factors which govern the wind-induced torsional response, especially the torsional loads, 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 from case to case, the presented discussion is focussed on the floor plan geometry for torsional static loads, and natural frequency and dynamic coupling for the torsional dynamic loads. With definition of equivalent eccentricity, e, and load reduction factor, r, the magnitudes of torsional loads for several tall buildings are investigated with respect to the corresponding horizontal wind loads. The complicated nature of torsional response 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.