1.同济大学 土木工程学院，上海 200092;2.上海临港经济发展(集团)有限公司 规划设计管理中心，上海 201306;3.同济大学 土木工程防灾国家重点实验室，上海 200092
夏 烨（1983—)，男，副研究员，硕士生导师，工学博士，主要研究方向为桥梁健康监测。E-mail: firstname.lastname@example.org
1.College of Civil Engineering, Tongji University, Shanghai 200092, China;2.Planning and Design Management Center, Shanghai Lingang Economic Development (Group) Co., Ltd., Shanghai 201306, China;3.State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
A long-term monitoring index system based on neutral axis（NA) position and the corresponding performance assessment method were proposed. Based on a detachable viaduct in Hebei expressway, a health monitoring system based on monitoring indicators was established, and the structural strain information was collected. Static response caused by traffic loads was separated from original strain signals by the multi-resolution wavelet analysis. The peak-valley pairs were picked in accordance with the designated peak prominence. Then the strain amplitude distribution was fitted and the measured NA arrays were derived. Finally, the neutral axis index was extracted from the accumulated data, and the statistical characteristics of different evaluation periods were compared and analyzed. The results show that the proposed neutral axis index in daily periods is less disturbed by the environment, which can represent the performance degradation of the structure in the long-term monitoring.