玄武岩纤维筋海砂混凝土梁受弯性能试验研究

用玄武岩纤维(BFRP)筋替代钢筋作为未经淡化处理的海砂混凝土结构的受力筋材,进行了2种强度和4种配筋率的BFRP筋海砂混凝土梁的实验研究,包括海砂混凝土材料的抗压性能、海砂混凝土梁构件的受弯性能,对梁的开裂荷载、极限承载力、裂缝宽度、破坏形态、荷载-挠度曲线等进行了分析,探讨了混凝土强度和配筋率对梁承载力的影响,并给出设计建议。

Flexural behaviors of FRP strengthened corroded RC beams

The flexural behavior of eight FRP （ fiber reinforced polymer） strengthened RC （reinforced concrete） beams with different steel corrosion rates are numerically studied by Ansys finite element software. The influences of the corrosion rate on crack pattern, failure mechanism, ultimate strength, ductility and deformation capacity are also analyzed. Modeling results show that the beams with low corrosion rates fail by the crushing of the concrete in the compression zone. For the beams with medium corrosion rates, the bond slip between the concrete and the longitudinal reinforcement occurs after steel yielding, and the beams finally fail by the debonding of the FRP plates. For the beams with high corrosion rates, the bond slip occurs before steel yielding, and the beams finally fail by the crushing of the concrete in the compression zone. The higher the corrosion rates of the longitudinal reinforcement, the more the carrying capacity of FRP strengthened RC beams reduces. The carrying capacity of RCB-1 （the corrosion rate is 0） is 115 kN, and the carrying capacity of RCB-7 （the corrosion rate is 20% ） is 42 kN. The deformation capacity of FRP strengthened corroded RC beams is higher than that of FRP strengthened uucorroded RC beams. The ultimate deflection of RCB-1 and RCB-7 are 20 mm and 35 nun, respectively, and the ultimate deflection of RCB-5 （the corrosion rate is 10% ） reaches 60 ilUn.

Flexural behaviors of steel reinforced ECC/concrete composite beams

An engineered cementitious composite （ECC） is introduced to partially substitute concrete in the tension zone of a reinforced concrete beam to form an ECC/reinforced concrete （RC） composite beam, which can increase the ductility and crack resisting ability of the beam. Based on the assumption of the plane remaining plane and the simplified constitutive models of materials, the stress and strain distributions along the depth of the composite beam in different loading stages are comprehensively investigated to obtain calculation methods of the load-carrying capacities for different stages. Also, a simplified formula for the ultimate load carrying capacity is proposed according to the Chinese code for the design of concrete structures. The relationship between the moment and curvature for the composite beam is also proposed together with a simplified calculation method for ductility of the ECC/RC composite beam. Finally, the calculation method is demonstrated with the test results of a composite beam. Comparison results show that the calculation results have good consistency with the test results, proving that the proposed calculation methods are reliable with a certain theoretical significance and reference value.

Flexural behavior of steel reinforced engineered cementitious composite beams

In order to enhance the durability of steel encased concrete beams, a new type of steel reinforced engineered cementitious composite(SRECC) beam composed of steel shapes, steel bars and ECC is proposed. The theoretical analyses of the SRECC beam including crack propagation and stress-strain distributions along the depth of the composite beam in different loading stages are conducted. A theoretical model and simplified design method are proposed to calculate the load carrying capacity. Based on the proposed theoretical model, the relationship between the moment and corresponding curvature is derived. The theoretical results are verified with the finite element analysis. Finally, an extensive parametric study is performed to study the effect of the matrix type, steel shape ratio, reinforced bar ratio, ECC compressive strength and ECC tensile ductility on the mechanical behavior of SRECC beams. The results show that substitution concrete with ECC can effectively improve the bearing capacity and ductility of composite beams. The steel shape and longitudinal reinforcement can enhance the loading carrying capacity, while the ductility decreases with the increase of steel shape ratio. ECC compressive strength has significant effects on both load carrying capacity and ductility, and changing the ultimate strain of ECC results in a very limited variation in the mechanical behavior of SRECC beams.

FRP筋UHPC梁受弯承载力计算方法

目前国内外尚未提出纤维增强树脂复合材料(FRP)筋超高性能混凝土(UHPC)梁受弯承载力的显式计算公式。基于ABAQUS中的塑性损伤模型,建立了FRP筋UHPC梁的受弯性能非线性有限元分析模型,通过已有试验结果验证了该模型的有效性。开展了40根UHPC梁的参数分析,重点研究了截面尺寸、UHPC强度、FRP筋抗拉强度和配筋率等因素对梁受弯性能的影响规律。基于目前国际上最常用的法国NF P 18-710规范,对UHPC受拉本构模型进行了简化,推导了UHPC受压区和受拉区等效矩形应力图块系数,提出了FRP筋UHPC梁平衡配筋率的计算方法,建立了受压破坏和受拉破坏模式下梁截面受弯承载力的理论计算公式。该公式计算值与试验结果、有限元分析结果和条带法计算结果均吻合良好。