A multi-resolution approach to robust time synchronization for lightweight seismic structural health monitoring

Accurate time synchronization among spatially distributed sensors is a prerequisite for reliable seismic structural health monitoring (S 2 HM), particularly for widely used lightweight S 2 HM systems that rely on inter-story drift ratios as the key damage-sensitive feature. In real-world S 2 HM applications, however, sensor measurements are inevitably affected by time delays arising from unreliable hardware- or protocol-induced synchronization. Such delays can lead to non-negligible errors in assessing inter-story drift outputs, even when the monitoring system operates under nominal conditions. This study proposes a progressive approximation time synchronization algorithm for practical lightweight S 2 HM systems under noisy measurement environments. Time synchronization is formulated as a sequentially constrained estimation problem, in which time delays are progressively estimated through cascading steps from coarse to fine alignment. The proposed algorithm is validated using shaking table tests of a full-scale ten-story reinforced concrete structure, where various time-delay scenarios representative of real-world monitoring conditions are conceived. The results show that the proposed algorithm can robustly reduce arbitrary inter-story time delays to within 5 ms, and constrain the relative error of peak inter-story drift estimations to within 1% from values exceeding 100%, even when the S 2 HM system is operated with the low-cost network time protocol synchronization.