复合螺旋箍筋约束混凝土柱偏压性能试验

采用复合螺旋箍筋约束混凝土柱,能在提高混凝土核心强度的同时,实现高延性,可支撑高地震设防烈度区重要结构的设计建造.以箍筋间距与轴向力偏心距为基本参数,完成了6根复合螺旋箍筋约束混凝土柱偏心受压试验,并与同条件下两类常规复合箍筋柱进行对比.获得了轴向力-侧向变形关系、轴向力-箍筋应变关系及轴向力-压区边缘混凝土压应变关系等,发现不同螺距/间距及偏心距下试验柱先后出现纵筋屈服与混凝土压碎的破坏模式.试验结果表明,破坏时采用不高于80 mm螺距/间距的复合螺旋箍筋柱正截面承载力及以柱高中点侧移定义的位移延性系数较常规螺旋箍筋柱有一定提高.结合试验结果,发现偏压复合螺旋箍筋柱破坏机制与螺旋箍筋强核心约束和外围方形箍筋次约束的复合作用明显相关,破坏主要是核心螺旋箍筋约束失效后混凝土压碎引起,而外围复合箍筋在峰值荷载后对混凝土仍具有一定约束作用.基于破坏机制,区分了两类约束区对柱承载力贡献,提出了复合螺旋箍筋柱偏压承载力计算方法.

Experimental investigation of reinforced concrete columns with composite spiral stirrups under eccentric loading

The application of composite spiral stirrups confined reinforced concrete columns can improve the core concrete strength and realize high ductility, which can be utilized to design and construct important structures in seismic zones of high intensity. A total of 6 concrete columns confined by composite spiral stirrups were tested under eccentric loading with different stirrup spacing and axial force eccentricities, and the results were compared with other two conventional composite stirrups confined columns under the same condition. The relationships of axial force with lateral deformation, stirrup strain, and compressive strain at the edge of the compression zone were obtained. Failure modes of longitudinal reinforcement yield and concrete crushing of the columns occurred successively under different spacing and eccentricities. Test results indicate that when the spacing is smaller than 80 mm, the composite spiral stirrups confined columns exhibited higher bearing capacity than conventional columns, the strength of the confined concrete is increased, and the defined displacement ductility is improved. Furthermore, the dual-confinement to the concrete consisted of core confinement by spiral stirrups and surrounding confinement by rectangular stirrups had significant effects on failure modes. The failure of the specimen was mainly caused by crushing and spalling of the concrete after buckling of longitudinal reinforcement. It was observed in the tests that the rectangular stirrups continuously provided a superior confinement effect on concrete even after the peak load while the spiral stirrups lost its efficacy. Based on the failure mechanism and the contribution of two different transverse reinforcement, spiral stirrups and rectangular stirrups, a calculation formula for eccentric bearing capacity of composite spiral stirrups confined concrete columns was proposed.