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为获得体外预应力混凝土梁的正截面抗弯强度、必须首先确定体外预应力筋的极限应力。该文建立了分别以FRP和钢材为体外预应力时,构件的等效塑性区长度与破坏截面中性轴比值的转换关系式。并根据相关的试验研究数据,分析了以FRP为体外筋和以钢材为体外筋的情况下,等效塑性区长度与破坏截面中性轴比值的差异及变化。结果表明,对FRP体外预应力混凝土梁,这一比值比较稳定,并可取为常数。但该常数与以钢材为体外预应力筋的有所不同,需用该文建立的转换关系式进行转换。在此基础上,建议了既适用于简支梁,亦适用于连续梁;既适用于常规的体外预应力钢筋,亦适用于非常规的体外预应力FRP筋的体外预应力筋极限应力计算方法。
In order to obtain the normal section flexural strength of externally prestressed concrete beams, the ultimate stress of prestressed tendons must be determined first. In this paper, the relationship between the equivalent plastic zone length and the ratio of the neutral axis to the failure cross section of FRP and steel is established respectively. According to the relevant experimental data, the differences and changes between the equivalent plastic zone length and the ratio of the neutral axis of damaged section were analyzed under the condition of FRP in vitro and steel in vitro. The results show that the ratio of FRP externally prestressed concrete beams is relatively stable and can be taken as a constant. However, this constant is different from the prestressing steel made of steel in vitro and needs to be converted by the conversion equation established in this paper. Based on this, it is suggested that the method is suitable for both simple and continuous girders. It is not only suitable for conventional prestressed external tendons, but also applicable to the calculation of the ultimate stress of external prestressing tendons in unconventional prestressed FRP bars .