外包UHPC钢管混凝土叠合中长柱偏压性能试验研究

Experimental study on eccentric compression performance of UHPC-encased CFST compositemedium-long columns

为研究外包超高性能混凝土钢管混凝土叠合中长柱(简称“UC-CFST中长柱”)的偏压性能,以偏心率(0.52、1.04)和长细比(7.22~44.74)为主要参数,进行了18个UC-CFST中长柱的偏压性能试验,得到其破坏模式和偏压性能指标。结果表明:随着偏心率和长细比的增加,UC-CFST中长柱的破坏模式由材料强度破坏转变为失稳破坏,承载力显著降低;长细比不大于21.03的中长柱试件均表现出明显的材料强度破坏特征,小偏心受压试件的近载侧钢筋、钢管先发生受压屈服,大偏心受压试件的受拉区UHPC外包层开裂、钢管受拉屈服,在达到峰值荷载时大、小偏心受压试件的受压区UHPC均被压碎;长细比大于35.26的中长柱试件表现为弹塑性失稳破坏,长细比介于21.03~35.26之间时为塑性失稳破坏。同时,进一步研究了GB/T 51446—2021《钢管混凝土混合结构技术标准》建议的钢管混凝土叠合柱弯矩增大系数法计算UC-CFST中长柱偏压承载力的适用性,发现该方法会明显高估UC-CFST中长柱的偏压承载力。为此,结合UC-CFST中长柱的受力特点,推导得到了可用于计算UC-CFST中长柱偏压承载力的改进弯矩增大系数法,其计算结果与试验结果吻合良好。

To study the eccentric compression performance of UHPC-encased concrete-filled steel tube composite medium-long columns(referred to as‘UC-CFST medium-long columns’),the eccentricity(0.52 and 1.04)and slenderness ratio(7.22-44.74)were selected as the main parameters,and a total of 18 UC-CFST medium-long column specimens were tested under eccentric compression loads,and the failure mode and eccentric compression performance index were obtained.The results reveal that with the increase of eccentricity and slenderness ratio,the failure mode of UC-CFST medium-long columns changes from material strength failure to instability failure,and the bearing capacity of specimens is significantly reduced.The specimens with a slenderness ratio less than or equal to 21.03 exhibit obvious material strength failure characteristics.The steel bars and steel tubes on the near load side of the small eccentric compression specimens first undergo compression yielding,while the UHPC outer layer in the tensile zone of the large eccentric compression specimens cracks,and the steel tubes yield in tension.When the peak load is reached,the UHPC in the compressive zone of the large and small eccentric compression specimens is crushed.The specimens with a slenderness ratio greater than 35.26 are subjected to elastic-plastic instability failure,while a specimen with a slenderness ratio between 21.03 and 35.26 is subjected to plastic instability failure.Finally,the applicability of the bending moment amplification factor method for concrete-encased CFST columns proposed in GB/T 51446—2021‘Technical standard for concrete-filled steel tubular hybrid structures’to calculate the eccentric compression bearing capacity of UC-CFST medium-long columns is discussed.It is found that this method will significantly overestimate the eccentric compression bearing capacity of UC-CFST medium-long columns.Therefore,combined with the mechanical characteristics of UC-CFST medium-long columns,an improved moment amplification factor method which can be used to calculate the eccentric compression bearing capacity of UC-CFST medium-long columns is derived in this paper.The calculation results correspond well with the experimental results.