组合梁负弯矩区UHPC接缝抗弯性能试验

为提高钢-混组合梁桥负弯矩区混凝土桥面板的抗裂性并简化现场施工工艺，提出新型钢-混组合梁桥负弯矩区超高性能混凝土（Ultra-high Performance Concrete，UHPC）接缝方案。以湖南省某桥为工程背景，进行1∶2缩尺模型抗弯试验研究；编制截面弯矩-曲率关系MATLAB程序，并与实测值进行对比，验证该程序可用于计算UHPC覆盖下的普通混凝土（NC）中钢筋应力；对现有NC裂缝宽度规范公式进行修正，提出考虑UHPC约束作用的组合梁负弯矩区NC最大裂缝宽度的建议公式；讨论钢-混组合梁桥负弯矩区UHPC湿接缝合理的纵桥向长度，分析UHPC层厚度及层内配筋对抗裂性能的影响。研究结果表明：新型UHPC接缝方案的抗裂性能和抗弯承载能力均满足工程要求，且接缝节点强度高于非接缝区预制部分强度；负弯矩作用下，试件沿梁高的应变较好地满足平截面假定，钢梁与混凝土板及UHPC与NC间的层间滑移量均较小；UHPC裂缝呈现“多而细”的特征，而NC裂缝呈现“少而宽”的特征，预制部分混凝土顶面最先开裂，之后UHPC-NC交界面、UHPC顶面、UHPC覆盖下的NC侧面依次出现裂缝；对于负弯矩区采用UHPC接缝的中小跨径钢-混组合连续梁桥，UHPC层的纵桥向长度宜为20%标准跨径，UHPC层厚度可根据实际工程设计要求确定，增大桥面板内钢筋直径可以提高负弯矩区混凝土的抗裂性能。

Experiment on Flexural Behavior of UHPC Joint in Negative Moment Area of Composite Bridges

To increase the crack resistance of concrete bridge decks in the negative-bending-moment area of steel-concrete composite bridges and simplify the site construction process, a new ultra-high performance concrete (UHPC) joint scheme of the negative-bending-moment area of steel-concrete composite bridges is proposed. A 1:2 scale-model bending test was carried out based on the background project on a bridge in Hunan province. A MATLAB program of section moment-curvature was developed and compared with the measured value. It was verified that the program can be used to calculate the stress of reinforcement in normal concrete (NC) covered by UHPC. Based on the modification of the existing NC crack width formula, a suggested formula for the maximum crack width of NC in the negative moment area of composite beams considering the restriction of UHPC is proposed. In addition, the reasonable longitudinal length of the UHPC wet joint in the negative moment area of the steel-concrete composite bridge is discussed, and the influence of the thickness of the UHPC layer and the reinforcement in the layer on the crack resistance is analyzed as well. The results show that the cracking stress and bending capacity of the new UHPC joint scheme can meet engineering requirements, and that the strength of the joint is higher than that of the prefabricated part of the non-joint area. Under the action of a negative bending moment, the strain along the beam height of the specimen satisfies the plane-section assumption, and the inter-laminar slippage between the steel beam and concrete slab and between the UHPC and NC is small. The cracks in UHPC are ‘more and thinner’, while the cracks in NC are ‘less and wider’. Cracks appear on the top surface of the prefabricated part of the concrete first and then occur at the interface of UHPC-NC, the top surface of the UHPC, and the side of the NC covered by UHPC, successively. For medium and small span steel-concrete-composite continuous girder bridges with the UHPC joints in the negative moment area, the longitudinal length of the UHPC layer should be 20% that of the standard span. The thickness of the UHPC layer can be determined according to the actual engineering design requirements. The crack resistance of concrete in the negative moment area can be increased by increasing the diameter of the reinforcement in the bridge deck.