中小跨径桥梁数量多分布广，混凝土梁桥占比极高，其结构安全性和耐久性十分重要． 为评估此类桥梁的结构性能和安全储备，提出基于通用结构参数中性轴位置的监测方法，建立相应的指标体系与评估理论框架． 基于理论分析与有限元仿真分析，研究加筋混凝土梁在不同预应力下的中性轴指标在弹性、开裂、强化阶段的参数特性和退化规律．在实桥上针对中性轴指标设计健康监测系统，根据大量实测应变响应数据估计中性轴指标并进行统计分析，映射混凝土梁桥的结构行为． 结果表明，中性轴指标体系能够有效表征桥梁结构的性能退化和损伤发展，可指导设计与管理养护，具有较好的实用和推广价值．

Short and medium span bridges are widely spread and extremely large in number． The safety and dura- bility of concrete beam bridges，as a major portion of all bridge types，are very important． A neutral axis position based monitoring method is proposed，and the corresponding index system and evaluation framework are constructed to evaluate the performance deterioration and safety reservation． Through theoretical and finite element analysis，the parameter characteristics and deterioration law of neutral axis index are investigated regarding various stress state of reinforced concrete beam at different prestressing levels． A structural health monitoring system has been installed and operated in real bridges to evaluate the overall performance of neutral axis index system． Neutral axis index is estimated and statistical analysis is carried out based on the observed response data． Ｒesults show that the neutral axis index system can effectively characterize the degradation and damage development of the structure，and the proposed method can benefit for bridge design and management，thus has potential value for practical populariza- tion．