水平地震下钢-混凝土组合框架结构极限抗震与强柱构造

Ultimate Seismic Resistance and Strong Column Construction Measure of Steel-Concrete Composite Frame Structures Under Horizontal Earthquake

“强柱弱梁”是当前国际上主流的工程结构抗震设计理念,已有地震灾害调查表明,由于地震作用机制的复杂性以及对工程结构极限抗震认识的不足,强震作用后框架结构除出现梁铰的“强柱弱梁”破坏之外,还出现整体倒塌、柱铰以及局部楼层倒塌的“强梁弱柱”破坏。为合理认识各类破坏形式,首先对传统的塑性铰概念细分为“压铰”和“拉铰”,指出“拉铰”容易引发结构整体失稳;随后以钢-混凝土组合框架结构为对象,建立并采用实体单元与壳单元为主的组合框架结构有限元精细化抗震计算模型,开展组合结构极限抗震分析,初步探讨各水平地震波工况对组合框架结构位移、应力、轴压比等时程响应以及框架梁柱塑性耗能分配机制、塑性铰形成模式与失效机制的影响规律。分析结果显示:1)柱端拉筋减小了钢管与混凝土之间滑移,从而增大了柱和框架的刚度,降低了钢管和混凝土的应变水平,增大了钢梁的应力水平;620 cm/s^(2)及以上强度的地震波作用时,柱端拉筋构造可显著减小组合框架结构的最大层间位移角,在接近极限强度的水平地震波作用时,柱端拉筋屈服,框架梁端混凝土板纵筋一般不易屈服;2)“强梁弱柱”组合框架表现为“约束梁”与“耗能柱”,此时框架梁对框架柱约束较强,框架以框架柱耗能为主而梁端仅形成“压铰”,此时框架的耗能能力取决于框架柱;“强柱弱梁”组合框架表现为“耗能梁”与“承载柱”,此时框架梁对框架柱约束较弱,框架以框架梁耗能为主使得梁端先形成“压铰”,当梁端耗能至极限时形成“拉铰”引发框架柱长细比增大,导致框架加速失效,不利于发挥框架柱耗能潜力;3)柱端拉筋技术的“强柱”构造将提高组合结构的刚度、塑性耗能与抗倒塌能力,强柱构造对以柱耗能为主的6层框架抗震能力提升尤其显著。

“Strong column and weak beam”is the current international mainstream seismic design concept of engineering structures.The investigation of existing earthquake disasters have shown that due to the complexity of earthquake action mechanism and the lack of understanding of the ultimate earthquake resistance of engineering structures,frame structures after strong earthquakes will not only appear“strong column and weak beam”damage caused by beam hinges,but also“strong beam and weak column”damage caused by the overall collapse,column hinges and local floor collapse.In order to reasonably understand the various failure forms,the author first subdivided the traditional concept of plastic hinge into“compression hinge”and“tension hinge”,and pointed out that“tension hinge”is likely to cause the overall loss of the structure;then taking the steel-concrete composite frame structure as the object,the refined finite element seismic calculation model of composite frame structure based on solid element and shell element was established and used to carry out the ultimate seismic resistance of composite structure,and preliminarily discussed the effects of various horizontal seismic wave conditions on the displacement,stress,axial compression ratio and other time history responses of composite frame structure,as well as the distribution mechanism of plastic energy dissipation,the formation mode of plastic hinge and failure mechanism of frame beam column were preliminarily discussed.The analysis results show that:1)The tie bars stiffened column end reduce the slip between the steel tube and the concrete,thus increase the stiffness of the column and the frame,reduce the strain level of the steel tube and concrete,and increase the stress level of the steel beam.Under the action of seismic waves with intensity of 620 cm/s^(2) and above,the“strong column”construction of the column end tie bars can significantly reduce the maximum inter story displacement angle of the composite frame structure.The column end tie bars yield when the horizontal seismic wave is close to the ultimate strength,and the frame beam end longitudinal reinforcement of concrete slab is generally not easy to yield;2)The“strong beam and weak column”composite frame is shown as“constrained beam”and“energy dissipating column”,at this time,the frame beams strongly restrain the frame column,and the frame mainly consumes energy from the frame column.The beam ends only form“compression hinges”,at this time,the energy dissipation capacity of the frame depends on the frame columns.The“strong column and weak beam”composite frame appears as“energy dissipating beams”and“load-bearing columns”,at this point,the frame beam is weakly constrained to the frame column,the frame is based on the energy consumption of the frame beams so that the beam ends form a“compression hinge”.When the energy consumption of the beam ends reaches the limit,a“tension hinge”is formed,which causes the frame column slenderness ratio to increase,and then leads to accelerated failure of the frame,which is not conducive to the use of frame columns energy dissipation potential;3)The“strong column”construction of the tie bars stiffened column end technology will improve the stiffness,plastic energy dissipation,and anticollapse ability of the composite structure,in particular,the seismic capability of the 6-storey frame with energy dissipation column.