This project provides supplementary instrumentation to advance the state-of-the-art of construction blast vibration control, with the objective of reducing the cost of constructing urban buildings and facilities. It leverages ongoing measurements of building response to high frequency, blast induced excitation at a construction site in New York City. The additional instruments will be used to time correlate excitation and response motions, and to measure additional responses not required by construction regulations. Measurements enabled by this deployment of supplemental instruments will be used to test the hypothesis that urban structures are not perturbed as greatly as typically assumed, and thus vibration controls may be safely reduced. In dense urban areas old and modern high-rise buildings can coexist on the same street block. Project owners and contractors performing rock excavation are faced with restrictive vibration limits targeted for older buildings designated as historic, "Landmark", or fragile and in need of repair. For blasting projects, the presence of a single building perceived as "vulnerable" to cosmetic cracking from vibrations can severely restrict allowable vibration limits and constrain rock removal efficiency, thereby lowering overall productivity and extending the duration of the project. All of these negative construction consequences may unnecessarily increase construction costs. The potential economic benefit is large. In New York City alone over $17 billion in current transit projects involve construction blasting for excavations and tunneling in rock.
Time correlated rock excitation and structure response measurements are needed to advance the understanding of the response of urban structures to high frequency excitation. Time correlation of these measurements along a structure will allow increased accuracy in the calculation of building strains that are responsible for cosmetic cracking, the object of control by regulation. Current regulations and understanding are based upon measurements of the response of residential, 1 to 2 story single family structures when subjected lower frequency excitation. Extension of these observations by response spectrum analysis to taller structures when excited by higher frequency ground motions needs to be validated. Excitation frequency and strain based analytical techniques developed in Earthquake Engineering, Blast Protective Design, and Structural Dynamics should be applicable to these urban situations; however, validation by measurement has not occurred because of the difficulty of finding full-scale test sites. This site and these instruments provide that opportunity.
