This paper summarizes micro-inch response of cosmetic cracks in a typical slab-ongrade ranch style house to both construction equipment-induced vibration and environmental (weather) effects. This structure was instrumented, and its response studied as part of the development of an Autonomous Crack Measurement (ACM) system. ACM systems are intended to record-with a single sensor-micro-inch crack displacements from both long-term environmental changes and transient construction vibrations for comparison in an understandable fashion. Ground motions were measured with velocity transducers, and micro-inch crack displacements were measured with LVDT displacement sensors. Construction within 14 m (45 ft) of the house involved trackhoe excavation for a 10x12 ft. reinforced concrete box culvert , chain trencher excavation for an 8-inch water service line, and vibratory compaction of trench backfill and granular sub-grade. As with many other studies of this nature, it was found that the weather induced crack response far exceeded that produced by construction vibrations even when produced by vibratory rolling within 3 m (10 ft) of the structure.
This case history describes the instrumentation of a house near an aggregate quarry to assess the effect of changes in blast design on the house response. Velocity response was measured for the superstructure as well as walls and ceilings. Micrometer response of three cracks was measured as well. In all some 11 velocity transducers and 3 crack sensors measured excitation and response for each blast. Dynamic response of these cracks was compared to various measures of ground and/or structure motion to determine those with the best correlation. Variations in the ground motion and air pressure wave (air blast) reflected changes in the blast design. In addition dynamic crack response was compared to the long-term, weather induced crack response as well as the changes in temperature and humidity that produced the response. The study confirms the domination of long-term, weather induced crack response compared to the dynamic response produced by blast-induced phenomena.
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