Seismic performance of tubular structures with buckling restrained braces

In this study 36‐ and 72‐story framed and braced tubular structures were designed according to the current design code and their seismic performances were evaluated by nonlinear static and dynamic analysis. According to the analysis results, the tubular structures generally showed high earthquake‐resisting capability. The framed tube structure showed lowest stiffness and strength compared with the other model structures. The braced tube structures showed larger strength but lower overall ductility compared with framed tube structures. When buckling‐restrained braces were used instead of conventional braces, strength increased significantly compared with the framed tube, and ductility was enhanced compared with braced tube structures. As the load–displacement relationship estimated by static pushover analysis formed the lower bound of the dynamic analysis results, the response modification factors obtained based on the static pushover curve may safely be used for seismic design. Copyright © 2007 John Wiley & Sons, Ltd.     

Local buckling restraint condition for core plates in buckling restrained braces

Buckling Restrained Braces (BRBs) are commonly used as bracing elements in seismic zones. A key limit state governing BRB design is to prevent flexural buckling. However, when the wall thickness of the steel tube restrainer is relatively small compared to the cross-section of the core plate, the restraint conditions against the local buckling of the core plate can be critical for the stability and strength of the BRB. In this study, cyclic loading tests and numerical analyses of BRBs were carried out using various tube restrainer configurations to investigate the influence of local buckling of the restrainer on BRB strength and ductility.     

Overall buckling behavior of all-steel buckling restrained braces

One of the key requirements for the desirable mechanical behavior of buckling restrained braces (BRBs) under severe earthquake loading is to prevent global buckling until the brace member reaches sufficient plastic deformation and ductility. This paper presents finite element analysis results of the proposed all-steel buckling restrained braces. The proposed BRBs have identical core sections but different buckling restraining mechanisms (BRMs). The objective of the analysis is to conduct a parametric study of BRBs with different amounts of gap (between the core and the BRM) and initial imperfections to investigate the global buckling behavior of the brace. The results of the analysis showed that BRM flexural stiffness could significantly affect the global buckling behavior of a brace, regardless of the size of the gap. In addition, a minimum ratio of the Euler buckling load of the restraining member to the yield strength of the core, P_e/P_y is suggested for design purposes. This ratio is the principal parameter that controls the global buckling of BRBs.     

Local buckling and inelastic cyclic behavior of tubular members

Closed form expressions are obtained for the load-deflection behavior of the locally buckled circular tubular braces under the reversed loading conditions. These expressions are obtained by supplementing the deflected shape of the brace with closed form expressions for moment-curvature relationship of locally buckled circular tubular section. The developed closed form expressions are used to study the effects of the slenderness ratio and diameter-to-thickness ratio on the behavior of braces under reversed loading conditions.     

Local buckling and inelastic cyclic behavior of tubular sections

Moment-curvature relationship of a circular tubular section under reversed loading conditions is obtained. A simple kinematic model, proposed previously by the authors, is used here to obtain the local buckling branch of the moment-curvature relationship. Three types of closed form expressions are proposed to approximate the reversed loading branch of the computed moment-curvature curve of the locally buckled section. These expressions can be used to obtain the load-deflection relationship of a long circular tubular member/brace.     

Local buckling of steel plates in concrete-filled thin-walled steel tubular beam-columns

The availability of high strength steels and concrete leads to the use of thin steel plates in concrete-filled steel tubular beam-columns. However, the use of thin steel plates in composite beam-columns gives a rise to local buckling that would appreciably reduce the strength and ductility performance of the members. This paper studies the critical local and post-local buckling behavior of steel plates in concrete-filled thin-walled steel tubular beam-columns by using the finite element analysis method. Geometric and material nonlinear analyses are performed to investigate the critical local and post-local buckling strengths of steel plates under compression and in-plane bending. Initial geometric imperfections and residual stresses presented in steel plates, material yielding and strain hardening are taken into account in the nonlinear analysis. Based on the results obtained from the nonlinear finite element analyses, a set of design formulas are proposed for determining the critical local buckling and ultimate strengths of steel plates in concrete-filled steel tubular beam-columns. In addition, effective width formulas are developed for the ultimate strength design of clamped steel plates under non-uniform compression. The accuracy of the proposed design formulas is established by comparisons with available solutions. The proposed design formulas can be used directly in the design of composite beam-columns and adopted in the advanced analysis of concrete-filled thin-walled steel tubular beam-columns to account for local buckling effects.     

关于屈曲约束支撑在多遇地震作用下应用分析

介绍了屈曲约束支撑在结构中的工作原理,并结合某重点设防类医院建筑工程实例,阐述了屈曲约束支撑在结构中的具体应用过程,通过对多遇地震工况进行分析,得出两种软件计算指标一致,满足规范计算要求。     

钢棒防屈曲支撑受力性能研究

研发了一种钢棒防屈曲支撑(简称SBBRB),使得钢棒不仅能承受拉力,也可承受压力,从而提高钢棒的受力性能。通过对SBBRB足尺试件进行低周往复加载试验,研究其受力性能、破坏形态和耗能能力,并对支撑的应变和位移历程进行了全过程监测;采用ABAQUS分析软件建立了钢棒防屈曲支撑的有限元模型,并对试验工况进行模拟。研究结果表明:通过将钢棒内置于钢管套筒内,可使钢棒能够承受压力,试验得到的SBBRB受压极限承载力是钢棒受压临界荷载计算值的10倍左右;合理设计的SBBRB的钢棒屈服段在受拉和受压状态下均能充分屈服而不会发生支撑构件的屈曲破坏,具有较好的延性以及稳定的累积滞回耗能特性,在破坏之前滞回曲线始终饱满和稳定;可以通过监测钢棒受力,预先采取措施,从而保证结构安全; ABAQUS有限元分析结果与SBBRB试件按照预定加载制度进行加载的试验滞回曲线吻合较好,可为后续相关研究提供参考。     

Mesh modelling and analysis of cracked uni-planar tubular K-joints

In this paper, a new modeling method is proposed for a uni-planar tubular K-joint containing an arbitrary surface crack located along the chord weld toe. The crack is defined first in a 2-D plane and then mapped onto a 3-D curved crack surface. Subsequently, an automatic mesh generation is developed for producing the complete finite element mesh model. This technique can be realized by sub-dividing the entire structure into distinct zones. In each zone, the mesh is generated separately. After the mesh of all the zones have been completed, the complete model is obtained by merging the mesh of every zone. It has been proved to be efficient and effective in producing different quality mesh at different zones. In order to locate the likely crack initiation position, the hot spot stresses and hence the stress concentration factors (SCFs) need to be determined precisely. The hot spot stress correlated to the number of cycles, i.e. the S-N curve, has been used to predict the life of uncracked tubular K-joints. For a cracked tubular K-joint, its remaining service life depends on the fracture parameter called the stress intensity factors (SIFs). Two different methods, namely the displacement extrapolation and J-integral methods, are used to evaluate the SIFs along the crack front for different crack shapes in this study. Convergence tests for numerical analysis have been carried thoroughly to check the accuracy of the computed SIFs. The two sets of numerical results are in complete agreement. To evaluate the accuracy of numerical modeling, a full-scale fatigue test on tubular K-joint subjected to combined axial load and in-plane bending load was conducted. Comparison between the numerical and experimental results again shows a good agreement. Therefore, the proposed modelling and mesh generation methods demonstrate that the estimated stress intensity factors for any tubular K-joints are both accurate and reliable.     

屈曲约束支撑混凝土锚固节点力学性能试验研究

提出了一种用于混凝土框架结构中屈曲约束支撑连接锚固节点构造形式。通过8个对比试验,分别考察该节点在拉、剪、拉剪复合受力状态下的单调受力性能与滞回性能,分析了各种受力状态下节点的受力特点与破坏模式。试验结果表明,在各种受力状态下,节点屈服前位移均较小,对屈曲约束支撑耗能效率影响并不显著。通过试验结果与规范计算结果的对比发现,现行GB 50010-2010《混凝土结构设计规范》对单一受力状态下锚固节点承载力的计算比较准确,但对拉剪复合受力状态偏于保守;而采用JGJ 145-2004《混凝土后锚固技术规程》中的锚栓破坏相关方程能较为准确地估算拉剪复合受力状态下锚固节点承载力。另外,由于该锚固节点具有下锚固板,锚筋不会被整体拔出破坏,可取消现行规范中锚筋屈服强度取值小于300 MPa的限制。同时,在构造上应限制锚固板的弯曲变形,确保锚固钢筋共同受力,以使节点承载力在较小的位移下得以充分发挥。     

屈曲约束支撑在教学楼设计中的应用研究

结合某教学楼工程实例,分析了屈曲约束支撑在多遇地震及罕遇地震下对混凝土框架结构的性能影响,指出该支撑显著提高了结构的抗侧力,并且使结构的各项指标均满足规范,显著提高了结构的抗震能力。     

Experimental optimization studies on steel core lengths in buckling restrained braces

Concentric braced frames are commonly used in steel structures to withstand lateral forces. However, brace hysteretic behavior is asymmetric in tension and compression. These frames typically exhibit substantial strength deterioration when loaded in compression. Consequently, the concept of Buckling Restrained Brace (BRB) has been introduced to overcome this deficiency.The length of a BRB steel core could have a significant effect on its overall behavior since it directly influences the energy dissipation of the member. Furthermore, BRB could be effectively utilized as a damper to dissipate seismic input energy, particularly when used as a fuse within the brace in a frame. Modified BRBs with shorter lengths may be called damper BRBs, because they function as if a typical damper is utilized along any brace member. These damper BRBs are fabricated and tested in this study both experimentally and analytically. Useful insights into local retrofitting of core plates and connections are also provided.     

Guided local buckling (GLB) theory for short braces

According to recent earthquake experiences and experimental results, the local buckling is the most important parameter for limiting the ductility of short braces and prevents earthquake energy absorption in larger drifts. A new theory is introduced to prevent harmful effects of local buckling and use it as an energy absorption device in braced frames. According to this theory oblique stiffeners are provided inside braces section and it is expected to divide lateral drift of the system to smaller deflections inside stiffeners intervals. As much as number of local buckling along braces increases, more energy will be absorbed and the fracture life of the sections increases considerably. This theory is supported by half-scale experimental results and numerical modeling. The obtained results represent uniform and stable energy absorption and reasonable system ductility.     

Q235钢芯材屈曲约束支撑的超强特性研究

以国内外近年来的各类型屈曲约束支撑（BRB）的试验数据为基础,提出了与BRB承载力超强相关的应变硬化系数和拉压不平衡系数上限值的计算公式。设计并完成了7组Q235钢芯材BRB轴心受力试验,分析了超强系数与峰值应变和累积塑性应变之间的关系,研究了加载速率对超强系数的影响。结果表明：虽然离散性较大,但Q235钢芯材BRB的应变硬化系数和拉压不平衡系数均表现出随峰值应变的增大而增大的趋势。在设计中可采用建议的超强系数包络值以更加合理地考虑BRB的超强特性。BRB是位移相关型消能器,但试验中BRB试件在应变速率约为01/s的动力加载作用下的拉压不平衡系数明显大于相同峰值应变下静力加载试验结果,说明加载速率对BRB受压性能影响明显,对该现象有待深入研究。     

屈曲约束支撑在某会展中心工程中的应用研究

某会展中心采用钢管混凝土框架-屈曲约束支撑结构体系,主体结构跨度大、层高大且平面不规则.屈曲约束支撑作为耗能构件,分别应用在结构框架及大跨延性桁架两个部分.采用SAP2000软件进行动力弹塑性时程分析,考察罕遇地震作用下结构的性能.计算结果表明:屈曲约束支撑可以显著提高结构的侧向刚度、延性及耗能能力;结构在罕遇地震作用下具有良好的抗震性能,能够满足规范的要求.     

屈曲约束支撑在超限连体文化设施抗震中的应用

北京CBD核心区文化设施建筑功能复杂,主体结构为钢框架-支撑结构体系.由于存在竖向构件局部转换和局部抽柱形成大空间,多层楼板设较大洞口,东、西楼局部连体,以及平面不规则和竖向不规则等多项抗震超限内容,为超限项目.考虑项目结构体系特点,对项目进行了屈曲约束支撑设计,通过软件进行弹塑性时程分析对比,比较了采用屈曲约束支撑方...     

防屈曲支撑在某车间改造加固中的应用

以某工厂车间改造加固设计为案例,对防屈曲耗能支撑在建筑改造加固中的应用进行探讨,结合PKPM有限元软件进行计算分析,结果表明加防屈曲耗能支撑后,结构层间位移角满足规范要求,有效地改善了结构在地震作用下的扭转效应,具有良好的耗能减震性能,达到了预期加固效果.     

防屈曲支撑在双层柱面网壳中的减震性能分析

防屈曲支撑是一种效果良好的减震装置,由于其小震经济、中震不坏、大震易修的优点,有望成为新型的高性能装置从而应用于大跨度空间结构振动控制中.以一50m跨度的双层柱面网壳为实例,采用非线性时程分析的方法研究了柱面网壳结构在加入防屈曲支撑后的轴力及位移减震效果,通过不同的时程输入及不同支撑布置方式,得出了合理的支撑布置方式,在最优的布置方式下,位移减震效果可达27%,轴力减震效果可达47%,可见防屈曲支撑在双层柱面网壳中的减震效果较为理想,从而可以将其推广应用于其他形式的大跨度空间结构.