预应力FRP筋增强RC梁受弯破坏模式研究

针对同时配有非预应力钢筋和有粘结预应力FRP筋的混凝土梁的受弯性能,分别以CFRP和AFRP作为预应力筋,研究对应于钢筋屈服和对应于FRP筋断裂的2类界限相对受压区高度大小关系的变化,进而研究FRP筋性能指标对受弯破坏模式的影响。研究表明,破坏模式与2类界限相对受压区高度大小直接相关,而2类界限相对受压区高度的大小又受FRP筋性能指标的直接影响,采用FRP筋短期性能指标和采用考虑了环境折减系数、徐变断裂折减系数、松弛提高系数和材料系数后的FRP筋长期性能设计值分别进行计算,结果存在着较大差异。4种破坏模式中,破坏模式I为设计预期的正常破坏模式,破坏模式II、III和IV应在设计时予以避免。极限延伸率相对较小的CFRP筋的张拉控制应力不宜过高,否则会在长期使用过程中先于结构中钢筋屈服发生断裂。

Analysis of Flexural Failure Mode of RC Beams Reinforced with Prestressed FRP Bars

The flexural performance of the beams reinforced with both non-prestressed bars and prestressed bonded FRP bars was theoretically analyzed.Both the CFRP bar and the AFRP bar were taken as the representatives in the study.Correlativity of two kinds of balanced relative depth of compressive area,respectively corresponding to the yield of steel bar and to the rupture of FRP bar,was investigated.Therefore the influence of performance parameters of FRP on the flexural failure modes was analyzed.The results indicate that failure modes and two kinds of balanced relative depth of compressive area are with direct correlation,and the latter is directly influenced by the performance of the FRP bars.Adopting the short-term performance parameters or the long-term performance parameters,which considers the environmental factor,creep fracture factor,relaxation factor and materials coefficiency,would have different results.Failure mode I is the ideal one,while the others should be avoided.Prestressed control stress of CFRP bars with low-ductility should not be too high,otherwise the rupture of CFRP bars will happen before the yield of steel bars.