低配筋UHPC中空短柱轴心受压力学性能

为研究低配筋UHPC中空短柱在轴心受压下的极限承载能力及其影响因素,以UHPC材料特性研究为基础,设计并制作18根不同壁厚、不同箍筋间距的低配筋UHPC中空短柱,开展轴心受压破坏试验研究及理论研究。采用控制变量法对比分析宽厚比、箍筋间距对低配筋UHPC中空短柱的极限荷载、破坏形态、轴向和横向变形的影响。研究结果表明:所有UHPC中空短柱在达到极限承载能力的70%之前,力学性能接近线弹性变化,侧向变形较小,在0.5 mm之内;随着变形的增大,试件出现微小裂缝并伴有钢纤维拔出声,细而密的裂缝显著增多,达到极限荷载时,试件均发出爆裂声;当设计宽厚比分别为5.67和3时,无箍筋UHPC空心短柱的极限承载力为理论计算值的70.88%和87.65%;随着箍筋间距加密,极限承载力有所提高,但加密至一定程度后,承载力不再增长,接近材料强度极限值;采用UHPC塑性损伤本构模型对构件进行数值模拟,分析结果与理论计算和试验结果符合较好,按照直接强度计算法得到的中空短柱极限荷载接近试验值,可供UHPC柱设计提供参考。

Mechanical Performance of Low-reinforced UHPC Hollow Short Columns Under Axial Compression Load

To investigate the factors influencing ultimate load capacity on low-reinforced ultra-high performance concrete (UHPC) hollow short columns, an impact analysis of width-to-thickness ratio and stirrup spacing was carried out. Based on a UHPC material characteristics study, 18 UHPC low-reinforced hollow short columns with different wall thickness and stirrup spacing were designed and fabricated. Then, axial compression tests and theoretical research was carried out. The influence of width-thickness ratio and stirrup spacing on the ultimate load, failure pattern, axial and lateral deformation of low-reinforced UHPC hollow short columns is analyzed by using the control variable method. The results indicate that all columns had linear elasticity and small lateral deformation within 0.5 mm before 70% Pu. As the deformation increased, small and dense cracks increased significantly in the specimens, and the sound of steel fiber pulling out was heard. When the ultimate load was reached, the specimens cracked with a loud cracking sound. The ultimate load capacity of UHPC hollow short columns without steel stirrups was found to be 70.88% and 87.65% of the calculated value, respectively, with width-to-thickness ratios of 5.67 and 3, respectively. With decreased stirrup spacing, the ultimate load capacity was improved. However, as the test load approached the limit strength of the material, the measured load capacity no longer increased by decreasing stirrup spacing. The capacity analysis was also simulated using the UHPC damaged plastic model, and the results are in strong agreement with the theoretical and test results. The calculated values are also very close to the test results when using the direct strength method for ultimate load capability calculations, which provides additional support for UHPC column design.