Ambient vibration tests on New Zealand unreinforced masonry churches using low cost sensors

Churches are an important part of New Zealand's architectural heritage, and the extensive damage observed in stone and clay brick unreinforced masonry churches after the 2010-2011 Canterbury earthquakes has highlighted the need to appropriately describe their dynamic characteristics. Dealing with historical structures, characterized by a high level of uncertainty affecting both material properties and structural schemes, and given the paramount need of non-destructive investigation techniques, ambient vibration tests can be considered an effective tool. A test campaign was conducted on two churches located in Auckland and deemed to be representative of the New Zealand church portfolio. The structures were instrumented with low-cost tri-axial standalone accelerometer sensors based on Micro Elec-tro-Mechanical Systems (MEMS) technology. Despite such instrumentation being commonly used on more flexible structures and/or under higher service loads (such as the normal traffic on bridges), this technology potentially represents an affordable solution to provide information about the fundamental period of vibration of macro-elements of churches and bell-towers. The advantages and limitations of the adopted sensing technology, when applied to historic buildings exhibiting low response to ambient excitation, are discussed in the paper, based on the analysis of data collected.