The reliability of reinforced concrete (RC) columns decreases during long-term service, so there is an urgent need to develop seismic retrofitting methods. Ultra-high performance concrete (UHPC) has become a promising repair material due to its excellent mechanical properties, but it still requires suitable reinforcing materials to improve its ductility. In this study, a new method of using UHPC jackets reinforced with stainless steel mesh to retrofit the plastic hinge region of RC columns was developed, aiming to improve columns with insufficient seismic requirements due to the outdated standards design. Five circular columns, one of which is a control RC column and the others are retrofitted columns with various UHPC jacket heights, stainless steel mesh layers and axial compression ratios, were designed for quasi-static testing. To validate the availability of the proposed repair means, the failure modes, hysteresis behavior, ductility and self-centering capacity of the original RC column were compared to the retrofitted columns. The test results indicated that this repair method is an efficient and economical means to reduce the damage degree of the columns. For a specimen with a two-layer mesh and a 300 mm-height jacket, its ductility coefficient and cumulative energy dissipation could be enhanced by 36 % and 111 %. In addition, a three-dimensional solid numerical model was established and the seismic retrofitting mechanism of the retrofitted columns was analyzed. This model could reflect the load-displacement relationship and damage mode, which can be further used for designing the UHPC jackets for the retrofitted columns in real projects.

中文翻译：

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在塑料铰链区域使用不锈钢网加固的 UHPC 护套改造圆形 RC 柱


钢筋混凝土 （RC） 柱的可靠性在长期使用过程中会降低，因此迫切需要开发抗震改造方法。超高性能混凝土 （UHPC） 因其优异的机械性能而成为一种很有前途的修复材料，但仍需要合适的增强材料来提高其延展性。本研究开发了一种使用不锈钢网加固的 UHPC 护套改造 RC 柱塑性铰链区域的新方法，旨在改善因标准设计过时而抗震要求不足的柱子。五个圆形色谱柱，其中一个是对照 RC 色谱柱，其他是改装的色谱柱，具有各种 UHPC 护套高度、不锈钢网层和轴向压缩比，专为准静态测试而设计。为了验证所提出的修复方法的可用性，将原始 RC 塔的失效模式、滞后行为、延展性和自定心能力与改造后的塔进行了比较。试验结果表明，这种修复方法是降低塔体损伤程度的一种高效、经济的手段。对于具有两层网格和 300 mm 高度护套的试样，其延性系数和累积能量耗散可以提高 36 % 和 111 %。此外，建立了三维实体数值模型，分析了改造柱的抗震加装机理。该模型可以反映荷载-位移关系和损伤模式，可进一步用于实际工程中改造柱的 UHPC 导管架设计。