双折线先张预应力高强混凝土Ⅰ型梁抗弯性能足尺模型试验

Full-scale Model Test on Flexural Performance of Double-broken Line Pre-tensioned High-strength Concrete I-beams

作为桥梁快速建造中一种高效的装配式新结构,预应力混凝土Ⅰ型梁采用双折线先张法施工的密束预应力体系,具有预应力损失小、预压应力分布均匀、施工安全性好等特点。为检验该新型结构的抗弯性能,建立其正常使用极限状态及承载能力极限状态的抗弯能力设计及评价方法,开展了结构足尺模型的抗弯承载性能全过程加载试验,观察了结构在全截面工作阶段、开裂阶段和破坏阶段的结构形态、变形与受力特征及破坏模式。试验结果表明:在正常使用阶段,梁体工作性能良好,结构达到开裂荷载前,内力增量与荷载呈线性关系,应变分布满足平截面假定,受压区混凝土压应变、主梁挠度、主筋应变及预应力钢绞线内力增量均呈线性变化;继续加载时,结构内力及变形呈现明显的非线性特征,裂缝逐渐增多,应变增长速率加大,模型梁上翼缘应变横向分布差异性增大,呈现一定的剪力滞效应;随着裂缝深度发展,混凝土逐渐退出工作,预应力束不再与混凝土共同受力,直至梁体发生断裂;试验梁的计算破坏荷载与测试值的比例系数为1.08,静力延性系数为2.27,表明双折线先张预应力高强混凝土Ⅰ型梁的抗裂、抗弯承载能力计算模式具有较好的适用性和优异的抗弯静力延性。

As an efficient prefabricated new structure in accelerated bridge construction(ABC),the prestressed concrete I-beam by double-broken line pre-tensioning method belongs to dense prestressing system.The system has the advantages of small prestress loss,uniform prestress distribution,and good construction safety.To examine the flexural performance of the I-beams and establish the design and evaluation method during serviceability limit state and ultimate limit state,a full-scale loading test was carried out to record the whole process of flexural failure,observing the structural shape,deformation,mechanics characteristics and failure mode in the full section working stage,cracking stage and failure stage,separately.The test results show that in the serviceability limit state,I-beam has good working performance.Before the structure reaches the cracking load,the internal force increment has a linear relationship with the load,and the strain distribution satisfies the assumption of a plane section.The compressive strain of the concrete in the compression zone,the deflection of the main girder,the strain of the main reinforcement and the increment of the internal force of the prestressed steel strand all change linearly;when the loading continues,the internal force and deformation of the structure show obvious nonlinear characteristics,the cracks increase significantly,the strain growth rate increases,and the difference in the lateral strain distribution of the upper flange of the model beam increases,showing a certain shear lag effect;with the development of the crack depth,the concrete gradually withdraws from the work,and the prestressed beam no longer bears the force with the concrete until the beam body breaks;the ratio coefficient of the calculated failure load of the test beam to the test value is 1.08,and the static ductility coefficient is 2.27,indicating that the calculation model for crack resistance and flexural bearing capacity of double-broken line pre-tensioned high-strength concrete I-beam have good applicability and excellent flexural static ductility.