一级抗震预应力混凝土框架混合出铰机制下柱端弯矩增大系数研究

Research on moment magnifying coefficients at column ends of first seismic grade prestressed concrete frame with mixed hinge mechanism

按GB 50011—2010《建筑抗震设计规范》要求,对一级抗震预应力混凝土框架结构(简称"一级PC框架")进行"强柱弱梁"调整时,会出现中柱配筋面积过大及节点受剪承载力不足等问题。为降低中柱配筋,提出了一级PC框架结构"弱化中柱"、"强化边柱"的"强柱弱梁"调整方案,即通过弱化中柱配筋、强化边柱配筋,定义"强柱弱梁"框架为"罕遇地震作用下中柱和PC梁出现塑性铰,边柱除底层柱底外基本不出现塑性铰"的混合出铰有限延性框架。以4榀按抗震设防烈度8度(0. 2g)设计的不同跨数、层数的一级PC框架为研究对象,进行柱端弯矩增大系数研究。首先弱化中柱配筋,然后以控制边柱纵筋临界屈服为目标,对各个PC框架算例输入30条罕遇地震水准的地震波进行弹塑性时程分析,由梁实际配筋的正截面受弯承载力反算边柱所需的柱端弯矩增大系数,并经统计分析后提出具有明确概率意义的增大系数建议值。按照上述调整方案对算例进行再设计和弹塑性时程分析,结果表明,该调整方案能够避免结构在罕遇地震作用下出现整体和局部破坏,边柱除底层柱底外基本不出现塑性铰,上部楼层边柱总体安全储备较大,结构表现为以中柱和预应力梁出现塑性铰的混合耗能机制。

According to GB 50011-2010 ‘Code for seismic design of buildings’,‘strong column and weak beam’of first grade earthquake-resistant prestressed concrete frame( referred as‘the PC frame structure’) often results in overreinforcement of middle columns and insufficient shear resistance of middle joints. To reduce the reinforcement of the middle column,an adjustment measure had been proposed to weaken middle columns and strengthen side columns of PC frame structure,that is,weakening reinforcement of middle columns and strengthening reinforcement of side columns to redefine the ‘strong column and weak beam’frame which only makes middle columns,beams and side columns’ bottom sections of ground floor hinged under rare earthquakes. Four pieces first grade earthquake-resistant PC frames with different numbers of bays and sotries were designed under eight degree( 0. 2 g) of seismic fortification level to investigate the magnifying factor at column ends,where the middle columns were weakened to control the critical yield of the longitudinal reinforcement of side columns. The elasto-plastic analysis were carried out under the30 rare earthquake waves. The moment magnifying factors at side column ends were confirmed according to the actual flexural capacity of boundary beams and the recommended factors,which have an explicit probabilistic meaning,were given. Finally,according to the new adjustment measures,the PC frame were redesigned and the nonlinear analysis was carried out. Results show that the PC frame structures can avoid overall and partial damage;the side columns beyond bottom sections of ground floor are rarely hinged;the overall safety reservation of side columns in upper floors are enough;and structures exhibit the mixed energy dissipating mechanism where the plastic hinges occur at middle columns and prestressed beams.