Case Study on Dynamic Effects of Blast and Collapse Loads on Nearby Buildings at Roof Level

Three structures were monitored during a nearby controlled implosion of two 13-story reinforced concrete buildings. The controlled implosion included localized blasts on alternate floor levels, which initiated the progressive collapse of the buildings. Instrumentation was placed throughout the three nearby structures as well as at the ground level, which recorded a peak ground acceleration (PGA) of $0.077\mathrm{g}$ and peak particle velocity of $16.3\mathrm{mm}/\mathrm{s}$. The controlled implosion yielded two distinct ground motions, which were separated by an approximately $1.5\text{-}\mathrm{s}$ temporal gap, where one ground motion was due to the localized blasts within the buildings and the other to the progressive collapse of the buildings. The finite time gap between the 2 ground motions is attributed to the redistribution of loads within the two 13-story structures before the onset of progressive collapse. The resulting ground motions and the response of the nearby structures to both the blast and the collapse are presented and analyzed in the time and frequency domains. The results emphasize the higher frequency content of the blast-induced ground motions compared to the collapse-induced ground motions. In addition, the two closest adjacent structures were analyzed with respect to the recorded ground motions at each site for both the blast-induced and collapse-induced ground motions. Despite large amplitudes during the blast-induced ground motions, the high-frequency content was insufficient to excite the nearby structures. On the contrary, the lower-frequency collapse-induced ground motions resulted in horizontal accelerations at the roof level of the nearby structures with fundamental natural frequencies between 2.6 and 4.9 Hz on the order of $0.07–0.08\mathrm{g}$.