Flexural Performance and Capacity Calculation of Unreinforced UHPC Slabs
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摘要:
为明确无筋超高性能混凝土(Ultra High Performance Concrete,UHPC)单向板和周边支承方板的受弯性能,分别对其进行了跨中局部荷载作用下受弯性能的破坏性试验. 基于本文及其他文献的试验结果,考虑钢纤维特征参数的影响,建立了UHPC材料的受拉本构. 通过数值分析,提出了无筋UHPC板截面受拉区等效均布应力折减系数k的计算公式. 根据试验和分析结果,建立了无筋UHPC单向板和周边支承方板抗弯承载能力的简化计算方法. 结果表明:无筋UHPC单向板和周边支承方板均发生由UHPC抗拉性能所控制的受拉破坏. 由于UHPC内钢纤维的增强作用,无筋UHPC板的抗弯承载能力和极限变形分别较相应的开裂荷载和开裂变形明显提高且表现出一定的延性破坏特征,但UHPC的受拉塑性尚不足以保证周边支承方板中完全塑性铰线机构的形成,塑性铰线法的上限解不适于预测周边支承方板的极限荷载,而静力法的下限解却能给出精度较高且偏于安全的预测结果;试验结果验证了所提无筋UHPC单向板和周边支承方板极限承载能力简化计算方法的适用性.
Abstract:
To investigate the flexural performance of unreinforced ultra high performance concrete (UHPC) one-way slabs and square slabs, experimental studies were conducted on the slabs under locally applied loads at mid-span, respectively. Based on the test results from the present study and other literature, the tensile constitutive model of UHPC was proposed in which the influence of the characteristic parameters of steel fiber was included. Through the nonlinear sectional analysis on the slabs, an equation was developed for determining the reduction factor k of equivalent uniform stress in the tensile zone of the unreinforced UHPC slabs at the ultimate. According to the test and analysis results, a simplified approach for calculating the flexural capacity of unreinforced UHPC one-way and square slabs was presented. The results show that all the unreinforced UHPC one-way and square slabs experienced a tension failure governed by the tensile properties of the UHPC. Owing to the enhancement by the steel fibers in UHPC, the unreinforced UHPC slabs exhibited a ductile failure mode with significantly greater loads and deformations at the ultimate state as compared to those at the initial cracking state. Because the plasticity of UHPC in tension is not enough to ensure the formation of a fully plastic mechanism in those unreinforced UHPC square slabs, the upper bound solution from the yield line theory is unsuitable to predict the flexural capacity of the slabs. However, the lower-bound one from the static method of limit analysis can give better predictive results with a safer margin, and the feasibility of the developed simplified approaches for predicting the flexural capacity of unreinforced UHPC one-way and square slabs are verified well by the test results.