Time Correlated Response of Multi-Story, Urban Structures to High Frequency Blasting Excitation

This paper presents measurement and analysis of the dynamic response of a five-story building to very-high frequency excitation (> 100 Hz) from blasting vibrations originating from a contiguous excavation of rock. Velocity response measurements, in the rock and on the structure, were employed to calculate time correlated dynamic displacement response of the building to blasting. Time correlated structure response measurements are needed to advance the understanding of the response of urban structures to high frequency excitation. Current regulations and understanding are based upon measurements of the response of one to two story residential structures by 10 to 40 Hz excitation. Extension of these observations to taller structures when excited by high frequency excitation needs to be investigated further. Measurements show that the amplification patterns at the ground level and top of the structure match or are lower than that observed by the US Bureau of Mines (Siskind, et al., 1980) for the shorter residential structures. They decrease with increasing peak particle velocity. From the measurements, the global transverse shear strains found by differentiating ground floor and top displacements were calculated to be 12 μstrains. Time correlated bottom and top of structure displacements show that building response may be more reflective of wave propagation up the structure than whole-structure inter story drift. In addition a 3D model was used to compare computed displacements and strains to measured results. Modeled responses varied considerably both in magnitude and location of the maximum strain. No conclusion can be made regarding the best 3D model to employ to simulate building response. More data such as motions measured at many points in the structure are needed. Maximum inter-story transverse shear strains calculated with the model were found through the acceleration excitation and were less than 12 μstrains for 37 mm/s rock motion excitation. The inter-story transverse shear strains calculated with rock displacement input were less than that found with the acceleration excitation.