Zhe Qu

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.

Torsional response remains an important concern in the seismic performance of base‐isolated structures. In this study, a full‐scale shake table test was conducted on a three‐layer FPB‐isolated structure, together with numerical simulations and bearing component tests, to investigate its torsional behavior and three potential sources of torsion: superstructure flexibility, pressure dependence of the friction coefficient, and bearing‐to‐bearing variability in the friction coefficient. The results show that, compared with the transient eccentricity ( ε _k ), the proposed effective transient eccentricity ( ε _s ) provides a clearer indication of torsional response because it directly represents the effective lever arm producing torsion. Superstructure flexibility increases ε _s by altering the instantaneous distribution of inertia forces, although the resulting torsional displacement amplification remains limited. The torsional response observed in the shake table tests is mainly associated with variability in the friction coefficient, whereas the pressure dependence of the friction coefficient has a relatively limited influence. These findings provide a mechanical interpretation of the torsional response of FPB‐isolated structures and highlight the importance of considering variability in individual bearing properties in torsional assessment.

Current seismic damage classification standards do not adequately capture the distinctive damage characteristics inherent to base‐isolated buildings. To bridge this gap, this study collects and analyzes empirical damage observations from 52 base‐isolated buildings affected by 11 destructive earthquakes globally. Operating within the framework of current Chinese seismic damage classification standards, the typical damage patterns of critical and vulnerable components in base‐isolated buildings are summarized, including isolation bearings, supplemental energy‐dissipation devices, nonstructural elements within the isolation layer, and the superstructure. On this basis, we propose a seismic damage classification framework for base‐isolated buildings, which incorporates postearthquake functionality, the conditions of the isolation layer, and the extent of nonstructural damage. The damage state of the isolation layer is derived from discrete damage states and damage rates of its constituent parts, which is subsequently integrated with the state of the superstructure to determine the overall building damage state. It offers a practical foundation for postearthquake field survey, damage statistical analyses, and the future revision of relevant standards.