寒区近海混凝土桥梁性能衰退机理与损伤行为评估方法

受到周期性潮汐变化的影响，中国寒区近海混凝土桥梁长期遭受海水冻融及多种耦合腐蚀作用，这严重影响了桥梁的服役性能与使用寿命。为了准确预测桥梁的性能衰退规律，针对桥梁所处环境，分析了桥梁结构的性能退化机理，并借助近场动力学方法在多尺度方面的优势，利用MATLAB-ABAQUS联合仿真方法建立了桥梁劣化损伤预测与评估方法。在此基础上，从混凝土海水冻融损伤出发，考虑温度分布特性、临界饱和度模型、孔隙结晶规律与孔隙压力理论，结合不同孔隙的结晶温度与孔隙累积，通过孔隙变形加载方式建立混凝土微观尺度的冻融循环数值模拟计算方法。随后，根据混凝土微观尺度冻融损伤的计算结果，建立考虑冻融损伤分布的RC桥墩等效数值模拟计算方法。最终，设计制作了RC桥墩节段，进行了海水环境下RC桥墩的冻融循环试验，并利用超声层析成像技术，得到RC桥墩的海水冻融损伤分布。试验与计算结果表明：通过与超声层析成像试验结果的对比，混凝土微观尺度计算模型可以很好地模拟冻融循环过程中孔隙累积与孔隙转化引起的混凝土冻融损伤行为；受到温度分布与相对饱和度的影响，当冻融大于50次后，试件出现明显的冻融损伤界限（冻融深度），且随着冻融次数的增加，冻融深度的增速呈现先增大后减小的趋势。除此之外，等效计算模型的滞回曲线计算结果与试验结果吻合较好，随着冻融次数的增加，RC桥墩的峰值荷载逐渐减低，海水冻融对RC桥墩力学性能的影响极为严重，且建立的计算方法很好地预测了海水冻融作用下RC桥墩的力学性能退化。

Performance Degradation Mechanism and Damage Behavior Evaluation Method of Concrete Bridge in Cold Region Marine Environment

Due to the influence of periodic tidal changes, offshore concrete bridges in cold regions of China have long been subjected to seawater freeze-thaw cycles (FTCs) and multiple coupling corrosion, which seriously affects the service performance and service life of bridges. In order to accurately predict the performance degradation law of the bridge, the performance degradation mechanism of the bridge structure was obtained according to the environment of the bridge. With the advantages of Peri Dynamics method in multi-scale aspects, the MATLAB-ABAQUS co-simulation method was used to establish the bridge deterioration damage prediction and evaluation method. On this basis, starting from the FTCs damage of concrete, considering the temperature distribution characteristics, the critical saturation model, the pore crystallization law and the pore pressure theory, the numerical simulation method of concrete under FTCs from micro-scale was established by pore deformation loading. Subsequently, according to the calculation results of concrete micro-scale FTCs damage, the equivalent numerical simulation method of RC pier considering FTCs damage distribution was established. Finally, the section of RC bridge pier was designed and manufactured, and the FTCs test of RC bridge pier in seawater environment was carried out. The FTCs damage distribution of RC bridge pier in seawater was obtained by using ultrasonic tomography technology. The test and calculation results show that the micro-scale calculation model of concrete can well simulate the FTCs damage behavior of concrete caused by pore accumulation and pore transformation during the FTCs by comparing with the results of ultrasonic tomography. Under the influence of temperature distribution and relative saturation, when the FTCs were greater than 50, the specimen had obvious FTCs damage boundaries (FTCs depth), and with the increase of FTCs, the growth rate of FTCs depth first increased and then decreased. In addition, the calculation results of the hysteresis curve of the equivalent calculation model are in good agreement with the experimental results. With the increase of the number of FTCs, the peak load of RC piers gradually decreases, and the influence of seawater FTCs on the mechanical properties of RC piers is very serious. The established calculation method well predicts the degradation of mechanical properties of RC piers under seawater FTCs.