不锈钢和CFRP混合配筋预应力混凝土梁的延性和变形性能

由于FRP(fiber-reinforcedpolymer/Plastics)材料直到拉断还表现出线弹性的力学性能,使得采用FRP配筋的混凝土结构延性较差,且已成为这类结构应用中人们所关注的一个主要问题。研究了不锈钢和CFRP(Carbonfiber-reinforcedpolymer/Plastics)混合配筋部分粘结、部分预应力混凝土梁的延性和变形特性。分析时假定这类梁的截面在加载过程中具有3折线的弯矩-曲率关系,而在卸载过程中截面的弯矩-曲率关系假定为线性,据此提出了这类梁受力全过程的非线性分析方法,并以试验结果验证了其适用性。基于能量耗散的观点引入了反映这类梁延性特性的延性指标,并利用所提分析方法对这类梁的延性进行了参数分析。分析结果表明:增加混凝土极限压应变和预应力束的无粘结部分长度可以有效地增加这类梁的变形性能,但对延性的增加却很有限,而且这两个参数对梁延性和变形性能的影响程度还强烈依赖于梁的破坏形态。

DUCTILITY OF CONCRETE BEAMS PRESTRESSED WITH CFRP TENDONS

One of the main concerns in the design of concrete beams reinforced and/or prestressed with fiber-reinforced polymer (FRP) materials is the lack of ductility due to the linear elastic behavior of such materials up to failure. The deformation of partially bonded, partially prestressed concrete beams with hybrid FRP tendons and stainless steel reinforcements has been studied by means of an analytical method. It is assumed that a section of the beam has a tri-linear type of moment-curvature relationship for its loading portion and a linear type for its unloading portion. The unloading part of moment-curvature relationship is necessary to determine the residual deflection of the beam from which the ductility index of the beam can be calculated using an energy concept. Predictions from the model are compared with the limited available test data, and reasonable agreement is obtained. A parametric study of the ductility of the prestressed concrete beams with hybrid FRP and stainless steel reinforcements has been conducted. It is observed from the parametric study that increasing the ultimate compressive strain of concrete and unbonded length of tendon can enhance the deformability more efficiently than the ductility of the beam, since only a limited effect on the ductility can be achieved. Moreover, it is seen that generally the influences of the parameters on ductility and deformability of the beam are dependent on the failure mode which may be tendon rupture or concrete crushing.