摘要
为解决传统自复位防屈曲支撑变形能力不足的问题,提出一种碟簧-钢绞线组合自复位防屈曲支撑(Disc Spring-Steel Tendon Self-centering Buckling-restrained Brace,DT-SCB). DT-SCB采用串联的钢绞线及碟簧组成的复位系统提供复位能力,通过两个并联的一字型内芯耗散地震能量. 介绍了DT-SCB构造、各阶段工作机理及恢复力模型. 建立有限元模型,研究复位比率αsc、钢绞线与碟簧组刚度比K1、复位元件与耗能系统刚度比K2等参数对支撑滞回性能、自复位效果及耗能能力的影响. 研究结果表明:提出的DT-SCB恢复力模型与模拟结果吻合较好,所有DT-SCB支撑在最大加载位移(2.5%轴向应变)内未发生明显破坏,支撑滞回曲线呈旗帜型特征,且具有稳定的耗能能力. 相比于传统基于钢绞线的自复位防屈曲支撑,DT-SCB具有更强的变形能力. DT-SCB最大残余变形随复位比率αsc提高显著减小,而刚度比K1的增加会削弱复位比率对支撑残余变形的控制效果. 钢绞线与碟簧组刚度比过大(K1≥2.0)会导致碟簧组提前被压平,进而降低支撑的变形能力. DT-SCB耗能能力受刚度比K2影响较大,其等效黏滞阻尼比随刚度比K2的增大而降低. 罕遇地震下支撑-框架结构非线性时程分析结果表明,DT-SCB可以有效减少结构的最大层间位移角及残余层间位移角,提高结构抗震性能.
防屈曲支撑(Buckling-restrained Brace,BRB)作为一种抗侧力构件,不仅可以在地震作用下为主体结构提供抗侧刚度,还可以通过金属内芯的拉压屈服消耗地震输入的能
碟簧具有较好的变形能力及较高的承载力,近年来常被用于构建自复位阻尼
基于上述问题,本文提出碟簧-钢绞线组合自复位防屈曲支撑(DT-SCB). 其自复位单元由串联的预应力钢绞线和预压碟簧组成,耗能功能则由布置于内外套管之间的金属内芯实现,两系统并联组成DT-SCB. 本文首先介绍该支撑的构造、工作机理及理论滞回模型,然后通过ABAQUS建立DT-SCB支撑有限元模型并开展参数分析,讨论各关键参数对支撑滞回性能及自复位效果的影响.
1 DT-SCB受力性能分析
1.1 DT-SCB构造
DT-SCB具体构造如

(a) 耗能系统

(b) 自复位系统

(c) 完成效果
图1 DT-SCB构造
Fig.1 Configuration of DT-SCB
如
1.2 工作机理及恢复力模型
(1) |
(2) |
(3) |
式中:KI、KO、KSC1和KBRB分别为内管、外管、碟簧-钢绞线和耗能内芯的轴向刚度;Est、E分别为钢绞线及钢材弹性模量;Ast、Ac,y、Ac,s分别为钢绞线、内芯耗能段及加强段横截面积;l、Lc,y及Lc,s分别为钢绞线、内芯耗能段及加强段长度;kd为组合碟簧轴向刚度. 当外力超过激活荷载后(AB段),内外套管与碟簧-钢绞线变为串联关系,由于内外套管刚度远大于碟簧-钢绞线刚度,因此SC系统第二刚度KSC1由碟簧-钢绞线控制. 此时支撑仍处于弹性状态[

(a) 弹性状态

(b) 支撑受拉

(c) 支撑受压
图2 DT-SCB工作机理
Fig.2 Working mechanism of DT-SCB

图3 DT-SCB恢复力模型
Fig.3 Restoring force model of DT-SCB
当支撑达到最大变形并开始反向卸载时(CD阶段),支撑内芯为弹性状态,SC系统刚度取决于碟簧-钢绞线,因此该阶段卸载刚度为KB. 随着恢复力进一步降低(DE阶段),支撑内芯受压屈服并继续产生压缩变形,直至与其相连的内外套管与两侧的端板及反力构件接触,该阶段支撑刚度为KC,之后支撑完成卸载恢复至初始状态(EO阶段). 随后的反向受压[
2 数值模型及参数分析
2.1 有限元模型
采用有限元软件ABAQUS建立支撑实体模型如

图4 DT-SCB有限元模型
Fig.4 Finite element model of DT-SCB
2.2 参数设定
本文研究主要参数包括支撑复位比率αsc、钢绞线与碟簧组刚度比值K1、复位元件及耗能内芯轴向刚度比值K2. 复位比率αsc是影响支撑复位效果的一项重要指标,定义为碟簧组(或钢绞线)的预压力(或预拉力)与考虑随动强化与硬化效应的耗能内芯恢复力之比,即:
(4) |
式中:F0为自复位系统的初始预压(拉)力,fcy为耗能内芯的屈服应力,σ0为自复位系统的初始预压(拉)应力,Ac为耗能内芯的横截面积,ω为防屈曲支撑内芯应变强化系数,β为支撑拉压不平衡系数. 钢绞线与碟簧组刚度比K1表示为:
(5) |
复位元件与耗能内芯轴向刚度比K2表示为:
(6) |
根据以上分析及各参数定义,确定有限元模型编号及主要设计参数如
模型编号 | 内芯/(mm×mm) | 钢绞线预拉应力σ0/MPa | 钢绞线截面面积Ast/m | 碟簧组初始 预压力F0/kN | 碟簧组刚度kd/(kN·m | 复位比率αsc | 刚度比K1 | 刚度比K2 |
---|---|---|---|---|---|---|---|---|
BRB | 32×6 | — | — | — | — | — | — | — |
SC | — | 319 | 660.0 | 188 | 24.3 | — | 2.6 | — |
T-SCB | 26×6 | 600 | 404.4 | 243 | — | 1.8 | — | 4.5 |
DT-SCB-1.8-1.3-1.9 | 26×6 | 600 | 404.4 | 243 | 29.9 | 1.8 | 1.3 | 1.9 |
DT-SCB-0.9-0.9-1.6 | 32×6 | 507 | 287.2 | 146 | 35.8 | 0.9 | 0.9 | 1.6 |
DT-SCB-0.9-1.3-1.6 | 32×6 | 361 | 403.0 | 146 | 30.0 | 0.9 | 1.3 | 1.6 |
DT-SCB-1.3-0.9-1.6 | 32×6 | 732 | 287.2 | 210 | 35.8 | 1.3 | 0.9 | 1.6 |
DT-SCB-1.3-1.3-1.6 | 32×6 | 522 | 403.0 | 210 | 30.0 | 1.3 | 1.3 | 1.6 |
DT-SCB-1.5-0.9-1.6 | 32×6 | 845 | 287.2 | 243 | 35.8 | 1.5 | 0.9 | 1.6 |
DT-SCB-1.5-1.3-1.6 | 32×6 | 602 | 403.0 | 243 | 30.0 | 1.5 | 1.3 | 1.6 |
DT-SCB-1.5-2.0-1.9 | 26×6 | 375 | 525.6 | 197 | 25.4 | 1.5 | 2.0 | 1.9 |
DT-SCB-1.5-2.0-1.3 | 38×6 | 548 | 525.6 | 289 | 25.4 | 1.5 | 2.0 | 1.3 |
DT-SCB-1.5-1.0-1.6 | 32×6 | 692 | 350.4 | 243 | 33.9 | 1.5 | 1.0 | 1.6 |
DT-SCB-1.5-2.0-1.6 | 32×6 | 462 | 525.6 | 243 | 25.4 | 1.5 | 2.0 | 1.6 |
DT-SCB-1.5-3.0-1.6 | 32×6 | 346 | 700.9 | 243 | 22.6 | 1.5 | 3.0 | 1.6 |
DT-SCB-1.5-4.0-1.6 | 32×6 | 277 | 876.0 | 243 | 21.2 | 1.5 | 4.0 | 1.6 |
DT-SCB-1.5-1.3-1.0 | 32×6 | 600 | 404.4 | 243 | 29.9 | 1.5 | 1.3 | 1.0 |
DT-SCB-1.5-1.3-0.5 | 32×6 | 600 | 404.4 | 243 | 29.9 | 1.5 | 1.3 | 0.5 |
DT-SCB-1.5-1.3-0.25 | 32×6 | 600 | 404.4 | 243 | 29.9 | 1.5 | 1.3 | 0.25 |
注: 模型BRB及SC分别对应DT-SCB支撑移除复位系统及耗能系统后的支撑模型;T-SCB为仅采用钢绞线为复位元件的自复位防屈曲支撑模型;DT-SCB后缀的三个数据分别代表复位比率αsc、刚度比K1和刚度比K2.
3 结果与讨论
3.1 恢复力模型验证及滞回曲线
基于1.3节提出的恢复力模型,采用MATLAB编制了DT-SCB滞回响应分析程序,并与实体有限元模型模拟结果进行对比分析,结果如

图5 数值模拟与理论恢复力模型计算结果对比
Fig.5 Comparison between simulation result and hysteretic curve from theoretical restoring force model

图6 DT-SCB有限元模型滞回曲线
Fig.6 Hysteresis curves of DT-SCB finife element models

(a) K1=0.9

(b) K1=1.3
图7 DT-SCB、SC及BRB系统模型骨架曲线
Fig.7 Skeleton curves of DT-SCB,SC and BRB system models
3.2 复位比率
为评价DT-SCB支撑自复位能力,定义残余变形率为支撑残余变形与每级加载位移幅值比值.各支撑残余变形率与加载位移幅值关系曲线如

(a) K1=0.9

(b) K1=1.3
图8 DT-SCB支撑残余变形率对比
Fig.8 Comparisons of residual deformation ratio of DT-SCB

(a) K1=0.9

(b) K1=1.3
图9 DT-SCB支撑残余变形对比
Fig.9 Comparisons of residual deformation of DT-SCB
不同刚度比K1下DT-SCB支撑等效黏滞阻尼比ζ与加载位移幅值关系曲线如

(a) K1=0.9

(b) K1=1.3
图10 DT-SCB等效黏滞阻尼比-加载位移关系曲线对比
Fig.10 Comparisons of equivalent viscous damping ratio and loading displacement amplitude for DT-SCB
3.3 钢绞线与碟簧组刚度比K1
不同刚度比K1的DT-SCB骨架曲线如

(a) 骨架曲线

(b) 等效黏滞阻尼比-位移曲线
图11 刚度比K1对DT-SCB力学性能的影响
Fig.11 Effect of stiffness ratios K1 on the mechanical properties of DT-SCB
3.4 复位元件与耗能内芯轴向刚度比K2
刚度比K2对DT-SCB复位能力及耗能能力影响如

(a) 残余变形-位移曲线

(b) 等效黏滞阻尼比-位移曲线

(c) 滞回曲线
图12 刚度比K2对DT-SCB力学性能的影响
Fig.12 Effect of stiffness ratios K2 on the mechanical properties of DT-SCB
3.5 变形能力对比
当其余构造及参数均相同时,模型DT-SCB-1.8-1.3-1.9与仅采用钢绞线为复位元件的T-SCB滞回曲线对比结果如

图13 DT-SCB -1.8 -1.3 -1.9 与T-SCB滞回曲线对比
Fig.13 Comparison of hysteretic responses of DT-SCB -1.8 -1.3 -1.9 and T-SCB
4 结构抗震性能分析
4.1 原型结构及数值模型
选取6层钢框架进行非线性时程分析,结构 立面图及梁柱尺寸如


图14 结构模型(单位:mm)
Fig.14 Structural model(unit:mm)
楼层 | BRB | DT-SCB | |||||
---|---|---|---|---|---|---|---|
Py/kN | KBRB/(kN·m | Py/kN | Pat/kN | KSC/(kN·m | KSC1/(kN·m | KBRB/(kN·m | |
1~3 | 1 000 | 192.2 | 500 | 500 | 624.2 | 103.5 | 65.2 |
4~6 | 660 | 126.8 | 330 | 330 | 206.0 | 68.3 | 38.1 |
结构有限元模型采用OpenSees建模. 其中梁柱采用基于力的非线性梁单元,BRB及SC单元采用桁架单元模拟. 梁、柱及BRB钢材本构采用Steel02模型,SC单元采用ElasticMultiLinear模型. 时程分析时采用5%Rayleigh阻尼,并通过设置摇摆柱考虑框架竖向变形的重力二阶效应影响.
4.2 层间位移角响应
从太平洋地震工程研究中心(PEER)选取5条地震记录,并将其峰值加速度调幅至罕遇地震水平,对BRB及DT-SCB支撑框架结构进行动力时程分析,两种支撑框架在地震作用下的最大层间位移角和残余层间位移角分布如

(a) 最大层间位移角

(b) 残余层间位移角
图15 结构地震响应
Fig.15 Seismic response
5 结 论
本文提出了一种碟簧-钢绞线组合自复位防屈曲支撑,介绍了该支撑的构造和工作机理,建立恢复力模型. 通过构件及结构层次有限元模型分析了复位比率、刚度比K1和K2等关键参数对支撑滞回特性、自复位效果以及耗能能力的影响,主要结论如下:
1)采用本文提出的恢复力模型可准确预测DT-SCB的滞回响应,有限元分析结果显示DT-SCB支撑滞回曲线具有典型的“旗帜型”特征.
2)提升复位比率可有效减少DT-SCB残余变形,当复位比率αsc≥1.5时,DT-SCB支撑的残余变形已基本消除,而增加刚度比K1会削弱支撑对残余变形的控制效果.
3)各支撑等效黏滞阻尼比随轴向变形的增加而趋于稳定,说明DT-SCB具有稳定的耗能能力. DT-SCB等效黏滞阻尼比ζ随复位比率αsc、钢绞线与碟簧组刚度比K1及复位系统与耗能系统刚度比K2的提高而降低.
4)相较于传统的以预应力钢绞线为复位元件的SCBRB,采用串联的预应力钢绞线-碟簧组为复位元件的DT-SCB,既能够保证较好的复位效果,又可提高支撑的变形能力,从而充分发挥其抗震耗能能力.
5)结构非线性时程分析结果显示,DT-SCB可以有效控制结构的最大变形及残余变形,提高结构抗震性能,实现结构震后可恢复的设计目标.
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