Wind tunnel tests were conducted in an effort to determine the magnitudes, power spectra and correlation of loads over the surface of a model of a tall building. The model was tested as a single element and also with an identical element upstream to provide an interfering flow. The work is presented in three parts which deal with the boundary layer simulation, the measurement technique using multiple transducers and the results of several model tests.

A turbulent shear layer similar to that found in the atmospheric boundary layer under strong wind conditions was generated in a wind tunnel with a short test-section by using a combination of sp:i,res and floor roughness elements. Flow properties were measured in detail at the model location, seven meters downstream of the spires. Properties measured included the mean velocity and turbulence characteristics for all three velocity components. Turbulence properties included intensities, some co-variances, integral length scales and power spectra. The flow was found to be two-dimensional across the central third of the tunnel and to be reasonably homogeneous in the flow direction. Measured flow properties were compared with estimates of full-scale properties for winds over urban areas as reported in review papers. The model flow was determined to be an acceptable simulation of atmospheric shear layer winds over urban areas for geometric scale ratios (between model and prototype) ranging from 1/400 to 1/600.

Resultant fluctuating loads were measured at several elevations throughout the height of a square cylinder having an aspect ratio of 8.33. Analog circuits using operational amplifiers were used to amplify and sum signals from numerous pressure transducers. The resultant signals directly represented resultant loads at the level where the transducers were located and consequently, simultaneous measurements of pressures at each transducer were not required. With this technique, fluctuating loads may be measured whether or not the model is moving, and it is the only method available for determining fluctuating twisting moments at various levels throughout the height of a model of a tall building.

Tests were conducted for numerous model orientations and configurations. Measurements were made of fluctuating normal forces and twisting moments at six elevations throughout the model height. Mean properties of the loads are presented for all configurations while spectra and coherence functions are presented for four illustrative cases. Test configurations included those involving a single instrumented model as well as cases where an identical model was placed upstream of the instrumented model. Load coefficients were found to vary throughout the height of the model. Spectra of the fluctuating loads for cases involving the single model indicate both periodic and random types of loading depending on the load component measured and the angle of orientation of the model. Both the power spectra of the loads and the correlation of the loads throughout the height of the model could be altered by the interference of an upstream model. Results indicate that the placement and orientation of neighboring buildings is critical to the aerodynamic stability of a particular building.