Response of uncracked drywall joints and sheets to blast vibration and weather

Cracking is one of the concerns cited by owners of structures adjacent to construction or mine blasting. During the past decade a large number of measurements have documented the low level of crack response produced by typical, ground motions compared to those produced by climatological effects. These data support the observation that there is a level below which ground motions do not cause even cosmetic cracking. As with all new findings, these crack response measurements need to be thoroughly investigated for all possible alternative interpreta-tions.Among these alternatives is that uncracked locations are more affected than cracked locations. This article presents measurements to shed light on the influence of existing cracks and the response of uncracked, but weak locations. Blast and weather induced responses of cracked and uncracked areas of gypsum wall board are compared in two structures: one near a surface coal mine in Indiana, the other near a limestone quarry in Florida.The ground motions that excited one of the structures were unusual in that the dominant excitation frequencies of 5 Hz were near the structure's natural frequency and amplitudes exceeded 0.7 ips (18mm/s.