复式不锈钢管高强再生块体混凝土短柱轴压试验研究

Experimental Investigation on Composite-sectioned Stainless CFST Stub Columns Filled with High Strength Demolished Concrete Lumps Under Axial Compression

在方不锈钢管混凝土中配置圆碳素钢管,可以改善方不锈钢管对核心混凝土约束效应低、变形能力差的特点,使复式不锈钢管混凝土(concrete-filled steel tube,CFST)截面具有较高的承载力、变形能力和抗火性能,减少普通钢结构的防腐和防火施工工序;钢管的约束效应也有利于弥补添加再生混凝土块体所带来的不利影响。开展16根复式不锈钢管高强再生块体混凝土短柱的轴压试验,考察了再生块体取代率、约束效应系数和新旧混凝土强度等参数对试件轴压力学性能的影响。研究结果表明:复式不锈钢管再生块体混凝土短柱试件的轴压承载力随再生块体取代率的增加而降低,替代率20%时承载力最大降低幅度为6.8%;试件破坏过程及破坏形态与普通复式不锈钢管混凝土短柱相似;内部圆钢管混凝土呈腰鼓型和剪切型破坏两种类型;复式不锈钢管再生块体混凝土短柱具有良好的变形能力和剩余承载力,超过峰值荷载后,荷载–位移曲线经过短暂下降,基本维持水平或略上升,所有试件的剩余承载力达到峰值荷载的63%以上。最后,提出了复式不锈钢管混凝土截面中钢管截面对核心混凝土的约束效应的简化方法,采用4种承载力计算方法进行轴压承载力的计算并对比,结果表明,考虑圆形截面部分的承载力乘以折减系数的假定具有较好的适用性,所得承载力的计算结果与试验结果吻合较好。

A circular carbon steel tube was added to the core concrete inside square stainless-steel tubes,the constraint effect coefficient to the core concrete and the ductility of the composite CFST sections could be improved remarkably,as a result,the anti-corrosion protection and fire protection of traditional steel structures could be reduced,furthermore,the disadvantageous influence of the demolished concrete lumps(DCLs)in new concrete could also be improved.Sixteen composite-sectioned concrete-filled stainless steel tubular(CS–CFSST)stub columns filled with high-strength demolished concrete lumps(DCLs)were tested.The influence of factors such as the replacement ratio of the demolished concrete lumps,confinement factor,and different concrete strength of new or demolished concrete on the mechanical performance was investigated.According to the testing results,the axial bearing capacity of the CS–CFSST stub columns decreased with the increase of the mix ratio of DCLs,the maximum decreasing amplitude of the bearing capacity was 6.8%with the replacement ratio of 20%.The failure modes of the CS–CFSST stub columns were quite familiar with those of normal CS–CFSST stub columns filled with normal fresh concrete.Two types of failure modes,drum-shaped and shear failure modes were found in the inner circular CFST stub columns,and excellent ductility and residual bearing capacity were also found as the load-deformation curves kept horizontally or ascended slowly,the residual bearing capacity of all the specimens were higher than 63%of its bearing capacity.The simplified method of constraint effect coefficient in the CS-CFSST stub column was proposed,and four cal-culation methods of the bearing capacity of the CS-CFSST stub columns infilling with DCLs were compared,coincident results were obtained us-ing the calculation method considering the ultimate bearing capacity reduction of the circular CFST section.