双层纵向柱列支撑的设计要求

支撑体系的作用是保证柱列的几何不变性和减少柱子计算长度。本文从柱列整体稳定性出发,对双层纵向支撑体系的强度和刚度设计要求进行了研究,分别得到了横系杆完全刚性、交叉支撑完全刚性以及支撑构件有限刚度情况下,对支撑的门槛刚度要求;考虑实际柱列的初始缺陷,确定最不利初始缺陷组合情况下,使柱列极限承载力达到计算长度减半的欧拉荷载所需要的支撑的强度设计要求。     

竖向荷载作用下柱列支撑体系受力性能试验研究及有限元分析

为研究柱列支撑体系的受力性能和验证有限元方法分析该问题的可靠性,对带有不同初始几何缺陷分布的单层和双层柱列支撑体系进行静力模型试验研究。研究结果表明:由于试验模型中柱和水平撑杆的初始几何缺陷的随机分布,水平撑杆受压力或拉力也是随机的;双层柱列支撑体系的极限承载力高于单层柱列支撑体系的极限承载力,且双层柱列支撑体系中的水平撑杆减小柱的计算长度超过柱高的一半;柱列支撑体系的失稳破坏是由于单柱失稳破坏引发的。采用有限元模型对试验进行了模拟验证,计算结果与试验结果吻合良好。     

竖向荷载作用下厂房纵向支撑的受力分析

从保证厂房柱列纵向稳定性的角度,对柱顶撑杆的设计要求进行了研究。采用蒙特卡罗方法,考虑实际工程中柱子和柱顶撑杆初始缺陷的随机遇合,应用有限元程序ANSYS对承受竖向荷载作用的柱列纵向支撑体系进行了大量的仿真分析,得到了柱列纵向支撑体系的三种失稳模式;通过概率统计得到柱顶撑杆所受内力的三峰正态概率密度函数,发现柱子和撑杆初始缺陷的随机遇合作用导致柱顶撑杆受压、拉或零受力的随机性,降低了支撑力,据此确定了可用于实际工程设计的支撑力的大小,为传统的柱顶撑杆由纵向受力决定的设计方法补充了竖向受力分析的验算方法。     

柱脚刚接与铰接柱列支撑体系受力性能试验研究与有限元分析

为研究柱脚刚接与柱脚铰接柱列支撑体系的不同受力性能和验证有限元方法分析该问题的可靠性，对带有不同初始几何缺陷分布的柱脚刚接与铰接柱列支撑体系进行了静力模型试验研究。研究结果表明：柱脚铰接柱列支撑体系的极限荷载和柱中水平撑杆内力均高于柱脚刚接柱列支撑体系,且前者较高的极限荷载更大幅度地增加了柱中水平撑杆内力；由于试验模型中柱和水平撑杆的初始几何缺陷的随机分布，柱中水平撑杆受压力或拉力的情况是随机的；柱列支撑体系的失稳破坏是由于单柱失稳破坏引发的。采用有限元模型对试验进行了模拟验证，计算结果与试验结果吻合良好。     

Y形柱稳定性分析研究

Y形柱是机场航站楼屋盖支承体系中常采用的一种构件形式,作为主要承重构件,其稳定性决定了屋盖结构的整体承载能力。利用荷载-位移全过程跟踪技术,考虑几何非线性、材料非线性和初始几何缺陷,研究了在竖向和水平风、地震作用下薄壁Y形柱的稳定性。研究表明:竖向荷载作用下Y形柱以分叉段平面外屈曲为主要失稳模式;Y形柱对初始几何缺陷不敏感;水平风荷载对Y形柱稳定性不起控制作用;竖向和水平荷载作用下,发生面外失稳前柱子分叉处已经进入塑性变形,柱子强度问题先于整体失稳。     

柱脚刚接与铰接柱列支撑体系受力性能对比研究

为研究柱脚刚接与柱脚铰接柱列支撑体系的不同受力性能,采用蒙特卡罗方法,考虑柱子和水平撑杆初始几何缺陷的随机遇合,应用有限元程序ANSYS对柱脚刚接和柱脚铰接柱列支撑体系进行大量参数仿真分析。研究结果表明:柱脚刚接柱列支撑体系失稳时柱子呈两个半波的变化趋势,柱脚铰接柱列支撑体系失稳时柱子呈三个半波的变化趋势,因而后者的极限承载力和柱中撑杆内力均大于前者,且后者较高的极限承载力更大幅度地增加了柱中撑杆内力;柱子和水平撑杆初始几何缺陷的随机遇合作用导致柱中水平撑杆受压或拉力的随机性,降低了支撑内力,比GB 50017—2003《钢结构设计规范》中柱列支撑设计公式计算的支撑内力小许多。     

柱顶受轴力的柱列支撑受力分析

采用蒙特卡罗方法,考虑柱子初始缺陷和撑杆初始缺陷的随机遇合问题,应用有限元程序ANSYS对柱顶受轴力的柱列支撑体系进行了大量的仿真分析,得到了柱列纵向支撑体系的两种失稳模式;通过概率统计得到柱中水平撑杆所受内力的双正态概率密度函数,据此确定了可用于实际工程设计的支撑力的大小。结果表明:当柱顶轴力相等时,采用《钢结构设计规范》(GB 50017—2003)中柱列支撑设计公式计算支撑力偏大;当柱顶轴力不等时,采用规范公式计算支撑力将更保守;柱子初始缺陷和撑杆初始缺陷的随机遇合作用导致柱中水平撑杆受压力或拉力的随机性,降低了支撑力。     

火灾下有支撑体系钢框架的倒塌特性

使用作者研发的静态-动态程序研究火灾下二维有支撑体系钢框架结构的连续倒塌机理。对20种不同火灾条件下不同支撑体系的钢框架进行综合分析,总结这些支撑体系的连续倒塌机理,并分析其刚度和强度。结果表明,柱的承载力丧失是连续倒塌的主要原因之一。尽管横向"帽桁架"支撑体系能够直接将屈曲柱的轴向荷载重新分配到邻近柱,它们支承高温楼板的能力仍然有限。另一方面,竖向支撑体系不仅加强了框架的侧向约束,也有效牵制了由局部到整体的倒塌进程。刚度较大的竖向支撑体系能够将屈曲柱的荷载重新分配到邻近柱。"帽桁架"和竖向支撑体系相结合能够尽可能提高框架性能,以防止高温柱屈曲时发生连续倒塌。     

节点刚度对四边支承单层柱面网壳稳定性的影响

利用ANSYS有限元软件建立了半刚性节点单元模型,对四边支承单层柱面网壳进行了几何非线性全过程分析,主要考察考虑初始几何缺陷和荷载不对称分布情况下,节点刚度变化对柱面网壳稳定性的影响规律.研究结果表明,四边支承单层柱面网壳当缺陷相同时,刚度减弱,极限荷载下降,且抗弯刚度的影响较强;缺陷增大,扭转刚度对四边支承柱面网壳的影响增强;同一刚度下,随着缺陷的扩大,极限荷载呈下降趋势,随着刚度的减小,缺陷对网壳极限荷载的影响程度减弱;荷载不对称分布导致四边支承柱面网壳结构极限荷载降低至对称荷载作用情况的80％左右,缺陷变化使得节点刚度对极限荷载的影响程度有所改变,但对承载力终值影响不大.     

单层组合加肋拱支网壳的稳定性

介绍了某相贯单层组合加肋拱支网壳结构在竖向荷载及风荷载作用下的整体稳定性。采用有限元软件MIDAS,在两种荷载工况下分别进行了此网壳结构的特征值屈曲、几何非线性屈曲分析,初始缺陷对网壳结构的整体稳定性影响分析。结果表明:网壳结构对初始缺陷较为敏感,初始缺陷会明显降低结构稳定性;不同的荷载工况下,失稳的情况亦不同且网壳结构稳定临界系数随着荷载的增大而降低。     

Stability and initial post-buckling behaviour of frame system with vertical bracings

Steel halls are assembled of plane thin-walled frames stiffened with vertical bracings consisting of two crossed rods in order to fulfil requirements concerning stability and stiffness of horizontal loads. In the paper, using stationary conditions of the total potential energy, a stability analysis and initial post-buckling behaviour of the construction are investigated. The hall construction is modelled by rigid plane frames, elastically connected on upper ends with the roof and in one or more spans with vertical bracings. It has been proved that the obtained bifurcation point is unsymmetrical and unstable, indicating that a reduction of the critical loads is possible due to some geometrical and loading imperfections.     

交叉支撑位置对被支撑柱数量的影响

工业厂房的支撑体系通常由交叉支撑和水平撑杆组成,当交叉支撑设置于柱列一端时,被支撑柱子的数量不宜超过8根。文中考虑柱子初始弯曲的随机性,应用有限元程序ANSYS对交叉支撑设置在柱列一端、柱列中间和柱列两端三种情况下的柱列支撑体系进行了大量的有限元参数分析。研究结果表明,当交叉支撑分别设置在柱列中间和柱列两端时,被支撑柱子的数量可分别增加至14和15根,说明可根据交叉支撑位置合理确定被支撑柱的数量,达到即安全又经济的目的。     

Experimental and numerical studies of practical system scaffolds

Scaffold design has become a popular research topic in recent years, likely because of the high rate of collapse for this structural form and its nature of under estimated loads close to the design loads, as opposed to permanent structures under remote statistical live and wind loads. This paper investigates the load capacities and failure modes of the system scaffold structure in various setups in construction and it is based on experimental tests supplemented by analyses. The parameters for system scaffolds studied in this paper include number of stories, ground heights, boundary conditions, presence of diagonal bracings and joint positions. The numerical studies quantify the load capacity of a system scaffold against addition of diagonal bracings. However, the load capacities of a system scaffold structure with varied spigot-joint positions on vertical props and with varied ground heights do not affect much the load capacity. Since the axial force of diagonal bracings on a system scaffold structure does not significantly increase with the vertical load, the diagonal bracings of the structure can be reduced in size for cost saving. A comparison between analyses and experimental tests conducted in this study confirmed the joint stiffness of different members used in the system scaffolds. Using the joint stiffness, the ultimate design loads of the system scaffolds with different number of stories were computed and quantified. The findings will be useful for accurate determination of the ultimate load capacity of complex system scaffolds used in construction sites.     

Inelastic buckling of torsionally braced I-girders under uniform bending: I. Numerical parametric studies

This study examines inelastic buckling of discretely braced I-girders by diaphragm bracings and torsional stiffness requirements to attain nominal flexural design strengths. To simulate the torsionally braced multi-girders, 2-girder and 4-girder systems interconnected with I-shaped cross-beams were numerically modeled by using 3D finite elements. Incremental nonlinear analyses considering the initial imperfections and residual stresses were conducted, and the effect of torsional bracing stiffness on inelastic lateral torsional buckling was evaluated. Based on the parametric analysis results, the torsional stiffness required attaining the inelastic buckling strengths specified by the AASHTO LRFD and Eurocode 3 was examined. It was found that the current design provisions suggested by AISC and SSRC overestimate the required torsional stiffness and may lead to an excessively conservative design. Improved information on the design criteria for the torsional bracings is provided.     

The use of single diagonal bracing in improvement of the lateral response of tall buildings

The improvement of the lateral response of tall buildings is a subject of great concern both in high wind areas and seismic regions. The lateral deflection of a tall building subjected to lateral loads can be decomposed into shear and bending components. Properly oriented single diagonal bracings are introduced in order to bring advantageous interactions between these two modes of deflection resulting in a reduction of the overall lateral deflection of the frame. The deflection of a panel with a single diagonal, when subjected to vertical downward load, has a lateral component caused by the axial force developed in the single brace, which, due to asymmetry, results in the lateral deflection. In order to restrict the panel from lateral deflection a compensating lateral force is required. By locating the single diagonal bracings in an improved manner, the vertical tension and compression on the opposite sides of the frame caused by the bending effect automatically generate the above mentioned lateral compensating force which opposes the inter story drift. A simple truss model is introduced to study the relationship between the vertical loading and the lateral load required to retain the vertical alignment of a panel with a single diagonal. This relation is then studied in detail and the optimal values of the height-to-width and brace-to-column stiffness ratios, needed to produce the maximum equilibrating lateral force are computed. Further, the single diagonal bracings are applied to typical building frames. Results from elastic analyses are compared with that of the conventional X-braced frame. Pilot analysis shows a reduction of about 2% in the lateral deflection of a typical 24 story braced frame building with rigid connections and five bays using the proposed bracing scheme.