Measure the Crack Instead of Construction Vibration

Charles H. Dowding

doi:https://doi.org/10.21985/N2N195

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Measure the Crack Instead of Construction Vibration

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Construction is omnipresent in modern-day America. It's the sound and vibration of a nation scrambling to keep up with its burgeoning population. In most states, allowable construction-induced ground motions range from 0.5 to 1.0 inches per second (in/sec) and under certain conditions up to 2.0 in/sec. However, ground motion as low as 0.02 in/sec can be perceived, and repeated motions throughout the day as low as 0.1 in/sec can cause annoyance. Even responsible construction activity produces motions that may startle people. Sharing close quarters with housing, businesses, and industrial complexes, construction activity often becomes a lightening rod for more complaints than it deserves. Many people incorrectly believe that construction vibration causes damage to their homes or buildings. What these people tend to focus on are cracks like that in Figure 1. Because many people interpret the response of buildings in their own terms, they tend to believe that if the vibration can be felt, it must be having a negative effect on the structure. The fact is, cosmetic cracking from construction vibrations has not been observed below peak particle velocities of 0.8 in/sec. Currently, complaints are addressed by measuring peak ground motions outside the structure with a blasting seismograph. These measured peak ground motions are then compared with a standard developed by the federal or state government. Motions that people truly believe are harmful usually turn out to be below the government standard. These standards, developed by some unknown government officials or researchers, are met with skepticism. Furthermore, it's difficult to convince skeptics that the "silent crackers" - temperature and humidity - produce more cracking than a phenomena that is felt and heard.

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