预应力混凝土框架结构“强柱弱梁”设计方法研究

针对预应力混凝土框架梁设计方法的特殊性,本文以8度区(0.2g)抗震等级为二级的多层多跨预应力混凝土框架结构为例,研究规范对预应力混凝土框架结构柱端弯矩增大系数取值的合理性,提出以梁端实际抗震受弯承载力调整柱端弯矩的方法进行预应力混凝土框架结构设计.分别以梁端地震组合弯矩和梁端实际抗震受弯承载力调整柱端弯矩设计8榀预应力混凝土框架,在OpenSees中建立其基于纤维梁柱单元的数值分析模型,并对其进行静力弹塑性分析与动力时程分析.研究表明:按现行规范设计的预应力混凝土框架结构,在罕遇地震下底层柱端出铰严重,提高其柱端弯矩增大系数,可以有效地改善结构屈服机制;04规程中柱端弯矩增大系数的取值偏小,规程修订时应给予适当提高,对抗震等级为二级的预应力混凝土框架结构,其柱端弯矩增大系数的取值≥2.0;本文建议二级PC框架按梁端实际抗震受弯承载力调整柱端弯矩,其取值为1.4.

Research on the Design Method of Strong Column and Weak Girder of Prestressed Concrete Frame

For the particularity of design method of prestressed concrete frame beam, this paper took a prestressed concrete frame structure in the 8-degree (0.2g) seismic grade district as an example to study the rationality of moment amplification factors at column ends in the current code, and a design method that the prestressed concrete frame columns could be designed on the basis of the actual seismic flexural moment of the beam was also proposed. Eight prestressed concrete frames were designed according to the combined moment and actual seismic flexural moment. The static elasto-plastic analysis and dynamic elastic-plastic analysis were then carried out for the frame structures in OpenSees using fiber elements. Research shows that the prestressed concrete frame designed by using the current code has serious hinges at the first floor columns under rare earthquake. The seismic performance of yield failure mechanism of the structures was effectively improved with the increment of the factor. Moreover, as the value of moment amplification factors at column ends is low in 04 specification, it should be improved in the new specification. This paper recommends that for the prestressed concrete frame with second level seismic requirement, the moment amplification factors at column ends should be increased in the revision of code for seismic design of prestressed concrete structures, and on the basis of the combined moment at beam ends, the factor should be higher than 2.0, while on the basis of the actual seismic flexural moment, the factor should be 1.4.