Damage assessment of Nepal heritage through ambient vibration analysis and visual inspection

The aim of this paper is to identify, both through microtremor analysis and visual inspection, the collapse mechanisms of the Nepalese wood-masonry monuments damaged by the 2015 seismic event that struck Kathmandu and its valley. The research analyses two case studies as the "Radha Krishna" temple located in Teku, a district in Kathmandu, and the "Pancha Deval complex" in Pashupati area. More specifically, after a careful anamnesis based on visual inspection and hypotheses on the temple's structural behaviour, global nondestructive testing (microtremor) was carried out for qualitative characterization of the structural system. The visual damage survey allowed to identify the recurring collapse mechanisms in the two case studies with the identification of typical Nepali expected damage. The case of Radha Krishna temple denotes a Nepali collapse mechanism typical in the corner of temples made of timber masonry, in which the mechanical contribution of the timber is manifested through columns and windows. The ambient vibration analysis carried out by tromograph device and microtremor evaluation allowed to dynamically characterize the two bases by identifying the peak frequencies both for Radha Krishna and for Pancha Deval complex. With the same device, the two historic constructions have been also studied in evaluating local modes and frequency. In the Pancha Deval complex, a relationship between damage, frequencies, and the amplification of the base was observed. In detail, the five buildings have similar damage and similar first frequencies (2.72-2.9 Hz). The most damaged sides are those with the frequencies close to the base (2.05-2.38 Hz).