Axial tensile mechanical properties and constitutive relation model of ultra-high performance concrete under cyclic loading
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摘要: 对具有不同拉伸应变特性(应变强化和应变软化)的超高性能混凝土(Ultra high performance concrete, UHPC)进行了单调和循环荷载作用下的直接拉伸试验。试验结果表明:应变强化UHPC基体开裂后进入多点微裂纹分布的应变强化段,达到极限抗拉强度后进入单缝开裂的应变软化段;应变软化UHPC基体开裂后直接进入单缝开裂的应变软化段;循环荷载下两种类型UHPC的轴拉应力-应变曲线包络线与单调荷载下的应力-应变曲线基本一致;基于刚度退化过程建立了两种类型UHPC的轴拉损伤演化方程,根据实测应力-应变曲线和试件的裂缝分布形态建立了两种类型UHPC的轴拉本构关系模型,与试验结果基本吻合;采用能量法研究了应变强化UHPC两阶段轴拉本构关系在数值计算时的等效方法。最后,通过无筋应变强化UHPC抗弯试验梁的数值模拟对本文建立的应变强化UHPC轴拉本构关系模型和损伤演化方程及相关假定进行了验证,结果表明本文建立的应变强化UHPC轴拉本构模型能较好地预测UHPC弯拉构件的极限承载力,轴拉损伤变量能在宏观层面上较好地反应试件的裂缝分布状态。
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关键词:
- 超高性能混凝土(UHPC) /
- 直接拉伸试验 /
- 循环荷载 /
- 轴拉本构模型 /
- 数值模拟
Abstract: The direct tensile tests under monotonic and cyclic loading were conducted on the ultra high performance concrete (UHPC) with different tensile strain characteristics (strain hardening and strain softening). The test results reflect that the strain hardening UHPC enters the stage of strain hardening with multi-point microcrack distribution after the cracking of UHPC matrix, and it enters the strain softening section with single seam cracking after reaching the ultimate tensile strength. The strain softening UHPC enters the strain softening stage with single seam crack after the cracking of UHPC matrix. The envelope of axial tensile stress-strain curves of the two types UHPC under cyclic load are generally consistent with that curves under monotonic load. Based on the stiffness degradation process, the axial tensile damage evolution equations of two types of UHPC were established. Based on the measured stress-strain curves and the crack distribution of the specimens, the axial tensile constitutive relation models of the two UHPCs were established. The test data are satisfactorily approximate to the proposed models. The equivalent method for the strain hardening UHPC with two-stage axial tensile constitutive relation in numerical calculation was studied by using energy method. Finally, the proposed axial tensile constitutive relation model and damage evolution equation of strain hardening UHPC were verified according to the numerical simulation of unreinforced strain strengthened UHPC flexural test beam. The results reveal that the proposed axial tensile constitutive model could precisely predict the ultimate bearing capacity of UHPC flexural-tensile members, and the axial tensile damage variables could generally reflect the crack distribution of the specimens. -
表 1 超高性能混凝土(UHPC)基体配合比(kg/m3)
Table 1. Mix proportions of ultra high performance concrete (UHPC) matrix(kg/m3)
Cement Silica fume Ground quartz Quartz sand Water Superplasticizer 745 223.5 223.5 998.3 179.0 13.1 表 2 钢纤维特征参数
Table 2. Properties of the steel fibres
Fiber shape Tensile strength/MPa Elastic modulus/GPa Length/mm Diameter/μm Density/(kg·m−3) Straight smooth 2500 200 16 200 7850 表 3 两种类型UHPC的基本力学性能
Table 3. Basic mechanical properties of two types of UHPC
Specimen type fc/MPa (Cov) Ec/GPa (Cov) Strain softening UHPC 127.8 (0.032) 47.4 (0.031) Strain hardening UHPC 135.2 (0.044) 48.9 (0.026) Notes: fc─Compressive strength; Ec─Elastic modulus. 表 4 应变强化(SH)UHPC轴拉应力-应变曲线特征参数
Table 4. Characteristic parameters of axial tensile stress-strain curve of strain hardening (SH) UHPC
Specimen Monotonic loading Cyclic loading fte/MPa εte/10−4 ftu/MPa εtu/10−3 fte/MPa εte/10−4 ftu/MPa εtu/10−3 SH1 9.62 2.2 11.71 4.11 9.75 2.1 12.08 3.49 SH2 9.76 2.1 11.28 3.72 9.42 2.3 11.65 4.55 SH3 8.71 2.3 12.01 3.82 10.19 2.1 12.18 4.45 Mean 9.36 2.2 11.67 3.89 9.79 2.2 11.97 4.16 Cov 0.06 0.6 0.03 0.05 0.04 0.7 0.02 0.14 Notes: fte─Elastic ultimate tensile strength; εte─Elastic ultimate tensile strain; ftu─Ultimate tensile strength; εtu─Ultimate tensile strain. 表 5 应变软化(SS)UHPC轴拉应力-应变曲线特征参数
Table 5. Characteristic parameters of axial tensile stress-strain curve of strain softening (SS) UHPC
Specimen Monotonic loading Cyclic loading fte/MPa εte/10−4 ftee/MPa ftee/fte fte/MPa εte/10−4 ftee/MPa ftee/fte SS1 9.09 2.2 8.45 0.93 9.01 2.4 8.32 0.92 SS2 9.28 2.8 8.83 0.95 8.69 2.2 8.52 0.98 SS3 9.47 2.2 − − 9.47 3.1 8.51 0.89 Mean 9.28 2.4 8.64 0.94 9.06 2.6 8.45 0.93 Cov 0.02 1.6 0.03 0.02 0.04 1.9 0.01 0.04 Notes: ftee─Equivalent tensile strength. 表 6 UHPC轴拉损伤演化方程中的参数
Table 6. Parameters for the evolution equation of axial tensile damage of UHPC
a0 t0 a1 t1 b Strain hardening UHPC 0.1048 3.1381 0.8541 0.0739 −0.0118 Strain softening UHPC 0.2037 3.3832 0.8076 0.0763 −0.0162 表 7 UHPC梁极限承载力的有限元计算和试验结果对比
Table 7. Comparison of ultimate bearing capacity between finite element calculation results and test results of UHPC beam
Beam Pu,test/kN Pu,FEA/kN Pu,test/Pu,FEA Numerical (10 mm) 127.23 131.27 0.97 Numerical (20 mm) 127.23 126.73 1.01 Numerical (30 mm) 127.23 120.81 1.05 Notes: Pu,test─Ultimate bearing capacity obtained from experiment results;Pu,FEA─Ultimate bearing capacity obtained from numerical simulation results. -
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