植筋参数对UHPC-石材界面抗剪性能的影响研究

在桥梁结构的加固工程中，植筋是最常用的界面连接增强措施。为明晰UHPC加固石砌结构植筋界面的力学性能，通过30个UHPC-石材组合试件推出试验，研究不同界面植筋率、植筋深度和植筋间距对UHPC-石材界面抗剪性能的影响，分析不同植筋参数下组合试件的裂缝开展及分布情况和荷载 滑移曲线特征。结果表明：①未植筋UHPC-石材组合试件的破坏模式均为脆性破坏，而植筋试件则主要表现为以界面滑移和石材局部劈裂为主要特征的延性破坏模式，石材表面裂缝形态均呈现“八”字形的斜向裂缝；②当植筋率小于0.29%时，组合试件的界面抗剪强度和延性随植筋率的增大而逐级提升，植筋率为0.09%、0.19%和0.29%的抗剪强度分别是未植筋组合试件的1.54倍、1.98倍和2.66倍；当植筋率继续增大时，UHPC-石材界面强度却出现降低的趋势；③植筋深度和植筋间距对组合试件界面抗剪强度影响较小，而对UHPC-石材界面延性影响较大；④基于试验结果和有限元分析，建议UHPC加固石砌体结构中带肋钢筋的最大锚固长度为10d(d为钢筋公称直径)，植筋间距取50～100mm较为合理；考虑安全和经济等因素，建议UHPC与石材的界面最优植筋率为0.29%，而UHPC加固层厚度以50mm为宜。

Effects of planting bar parameters on the shear resistance of UHPC-stone interface

When reinforcing bridge structures, planting bars shall be the most commonly used enhancement measure of interface connection. In order to clarify the mechanical properties of the UHPC-reinforced stone masonry structure with bar planted interface, 30 UHPC-stone composite specimens were tested to study the effects of bar planting rate of interface, planting bar depth and planting bar spacing on the shear performance of UHPC-stone interface, and then the crack development and distribution and load-slip curve characteristics of the composite specimens under different planting parameters were analyzed. The results show that: (1) The failure modes of the UHPC-stone composite specimens without planting bars are all brittle failures, while the specimens with planting bar are mainly characterized by ductile failure modes with interface slippage and local stone splitting. The crack morphology on stone surface presents diagonal cracks.  (2) When the bar planting rate is less than 0.29%, the interface shear strength and ductility of the composite specimens may increase step by step with the increase of the bar planting rate, and the shear strengths of specimens with the bar planting rate of 0.09%, 0.19% and 0.29% are 1.54 times, 1.98 times and 2.66 times that of the composite specimens without planting bars, respectively. However, when the planting bar rate increases continuously, the strength of UHPC-stone interface exhibits a decreasing trend. (3) The depth of the planting bars and the spacing of the planting bars have little effects on the interface shear strength of the composite specimen, but have a greater impact on the ductility of the UHPC-stone interface. (4) Based on the test results and finite element analysis, it is recommended that when UHPC is used to strengthen the stone masonry structure, the maximum anchorage length of the ribbed steel bar is 10 d (in which d is the nominal diameter of the steel bar), and the planting bar spacing of 50～100 mm shall be reasonable. In view of the factors such as safety and economy, it is recommended that the optimal planting bar rate for the interface between UHPC and stone is taken as 0.29%, while the thickness of the UHPC reinforcement layer should be 50 mm.