桁架约束型防屈曲支撑失稳机理及设计理论研究

Two types of truss-confined buckling-restrained braces (TC-BRBs), i.e. rigid-truss-confined BRB (RTC-BRB) and cable-truss-confined BRB (CTC-BRB) are proposed. These types of BRBs can be utilized in high-rise buildings and long-span spatial structures instead of common BRBs, solving the problems including: uneconomical design; difficulty in structural arrangement due to the large cross-sectional size; difficulty in transportation; unaesthetic appearance. Theoretical derivations, finite element (FE) simulations and quasi-static experiments are performed in this project to investigate the failure mechanism of the RTC-BRB and the CTC-BRB, thus proposing: ① The requirement of the restraining ratio to prevent the global buckling; ② The requirement of the restraining ratio to prevent the premature buckling of sub-segment before the global buckling; ③ The design method of lateral connecting bars to prevent the out-of-plane buckling of single confining truss; ④ The minimum pre-stress value of cables to prevent the pre-stress loss during loading. Furthermore, the structural formation and design check of end details of BRBs, longitudinal connection details of BRBs, as well as the lateral supports located at floors of high-rise buildings are investigated and validated by numerical simulations and experiments. The research results of this project can provide valuable references in practical design of the RTC-BRB and the CTC-BRB.

本项目提出两种新型桁架约束型防屈曲支撑，即刚性桁架约束型防屈曲支撑和索桁架约束型防屈曲支撑。这两类防屈曲支撑可作为大吨位超长防屈曲支撑应用于高层建筑或大跨度空间结构体系中，能够有效解决传统防屈曲支撑面对超长大吨位设计需求时可能产生的设计不经济、截面尺寸过大影响结构布置、运输困难、外形不美观等问题。采用理论分析、数值模拟、试验研究相结合的方式，对两类新型防屈曲支撑构件的失稳机理进行研究，提出：①构件整体不发生失稳的约束比限值；②构件节间段失稳不先于整体失稳对应的约束比条件；③保证单片约束桁架不发生面外失稳的横向联系杆布置方法；④保证受荷过程中拉索不发生松弛的最小预应力取值。此外，研究提出防屈曲支撑端部节点、分段连接节点及侧向支撑节点的构造方法，并获得数值分析与试验验证。本项目的研究成果可为桁架约束型防屈曲支撑的设计和应用提供依据。

本项目以防屈曲支撑(BRB)外围约束体系革新研究为主线，提出了两种新型全钢桁架约束型防屈曲支撑，即刚性桁架约束型防屈曲支撑(TC-BRB)和索桁架约束型防屈曲支撑(PCS-BRB)。上述附加约束（刚性或索桁架）与主约束套管形成整体约束体系，可有效约束内核的屈曲变形，用于超长和高承载力的防屈曲支撑设计可极大提高其约束效率、节约材料。在高层建筑和空间结构中应用，如外露设置可增加其欣赏及建筑美感。.首先，针对不同布置形式的外围约束桁架，分别对TC-BRB和PCS-BRB进行了弹性屈曲性能分析。对于TC-BRB，利用平衡法并考虑剪切变形的影响推导其弹性屈曲荷载表达式，其一阶屈曲模态呈现正弦单波形式；对于PCS-BRB，分别采用了平衡法、能量法以及基于索撑体系通用刚度系数的数值拟合方法得到其弹性屈曲荷载闭合解，随着索撑体系几何尺寸的变化，依据横隔数量及形式的不同，PCS-BRB的一阶屈曲模态会由单波对称转变为双波反对称或多波形式的屈曲模态。由此分别获得对应于TC-BRB和PCS-BRB的约束比计算表达式。.其次，通过大挠度弹塑性有限元数值分析，研究了上述两类桁架约束型防屈曲支撑约束比与其单调加载承载性能和反复加载滞回性能之间的相关关系，获得了相应的约束比门槛值，并揭示了两类桁架约束型防屈曲支撑的破坏模式。此外，通过有限元数值分析考察了初始预张力及组合初始缺陷对上述不同形式PCS-BRB承载性能的影响，并获得了考虑不同初始缺陷影响后对应于单调和反复拉压加载条件下的设计方法，包括相应的约束比门槛值和初始预张力的取值方法。.最后，对三榀刚性桁架约束型防屈曲支撑(TTC-BRB)进行了滞回性能的试验研究。试验结果表明刚性桁架约束型防屈曲支撑具有良好的整体稳定性能，并通过试验检验了端部构造设计的合理性。有限元分析与试验结果的对比验证了有限元模型的有效性和正确性，为该类防屈曲支撑的实际工程应用提供了可靠依据。