纤维混凝土梁受弯试验及开裂弯矩计算公式

Bending Test and Calculation Formula of Cracking Moment of Fiber Reinforced Concrete Beams

关键词:  纤维混凝土梁  开裂弯矩  塑性变形发展程度系数  玄武岩纤维  聚丙烯纤维

Key words:  fiber reinforced concrete beam  cracking moment  plastic deformation development coefficient  basalt fiber  polypropylene fiber

摘要:

通过受弯试验测得添加玄武岩纤维、聚丙烯纤维、混杂纤维和硅灰的不同混凝土梁开裂弯矩,利用开裂弯矩试验值及材性试验值推算出各混凝土梁的塑性变形发展程度系数k值,并绘出受拉区混凝土开裂时的应力分布;然后根据k值计算得到各混凝土梁的截面抵抗矩塑性影响系数,并推导出玄武岩纤维及聚丙烯纤维混凝土梁的开裂弯矩计算公式.结果表明：各混凝土梁均满足平截面假定,添加纤维可以提高普通混凝土梁及掺硅灰混凝土梁的开裂弯矩;相同体积分数下，玄武岩纤维对混凝土梁开裂弯矩的提升效果优于聚丙烯纤维;推算得到的k值为纤维混凝梁开裂弯矩的理论推导提供了参考,同时可作为评价纤维混凝土梁开裂时受拉区混凝土塑性变形能力的指标;混凝土梁的开裂弯矩受劈拉强度和塑性变形能力的共同影响;所提出的玄武岩纤维及聚丙烯纤维混凝土梁开裂弯矩计算公式可以作为二者开裂弯矩计算时的参考.

Abstract:

Firstly, different concrete beams reinforced by basalt fibers, polypropylene fibers, hybrid fibers and silica fume were experimentally tested for their cracking moments. The plastic deformation development coefficient k of each concrete beam was calculated based on the tested cracking moments and the measured material properties. Then the stress distributions of the tensile concrete subjected to cracking were described. After that, the plastic influence coefficient of the cross section resistance moment corresponding to each beam could also be calculated using k. Lastly, the cracking moment formulas for basalt or polypropylene fiber reinforced concrete beams were deduced based on the plastic influence coefficient. The analysis results indicate that the plane cross section assumption is basically satisfied for fiber reinforced concrete beams. The addition of fibers and silica fume increased the cracking moments of the concrete beams. The basalt fibers show better performance than polypropylene fibers under an identical volume fraction. Moreover, the coefficient k provides a reference for the theoretical deduction of the cracking moments of fiber reinforced concrete beams. It can be used as an index to evaluate the plastic deformation ability of tensile concrete subjected to cracking. The splitting tensile strengths, as well as the plastic deformation ability of tensile concrete, affect the cracking moments of concrete beams. The proposed formula for the cracking moments of basalt or polypropylene fiber reinforced concrete beams can be used as reference for relevant calculation.