有平面外支撑的工形截面圆弧钢拱弹性稳定性能及支撑刚度设计

采用有限元特征值屈曲数值方法，对平面外支撑工形截面圆弧拱弹性屈曲荷载及其刚度取值进行研究。在考虑各种荷载条件与拱脚条件下，研究了支撑刚度，约束类型、数量以及作用位置对钢拱平面外屈曲性能的影响，对于设置等间距侧向支撑的情况，给出了侧向支撑弹性门槛刚度的拟合式，并提出了支撑点间拱段不发生平面外弹性失稳的条件。研究结果表明：平面外支撑越靠近拱顶，其防止平面外失稳的工作效率越高；设置侧向支撑的钢拱屈曲时，随着支撑刚度的增大其屈曲半波数逐渐增加，而仅在拱顶设置扭转约束时始终呈现1个半波失稳模式；从均匀受压圆弧拱的情况获得的等间距侧向支撑门槛刚度，应用在其他组合荷载作用下，同样可以获得足够的支承刚度；当工形截面钢拱的支撑点间拱段长度满足所提出的要求时，钢拱平面外失稳不先于平面内反对称整体失稳。     

Out-of-plane elastic buckling of I-section steel arches braced laterally and design of bracing stiffness

采用有限元特征值屈曲数值方法,对平面外支撑工形截面圆弧拱弹性屈曲荷载及其刚度取值进行研究。在考虑各种荷载条件与拱脚条件下,研究了支撑刚度,约束类型、数量以及作用位置对钢拱平面外屈曲性能的影响,对于设置等间距侧向支撑的情况,给出了侧向支撑弹性门槛刚度的拟合式,并提出了支撑点间拱段不发生平面外弹性失稳的条件。研究结果表明：平面外支撑越靠近拱顶,其防止平面外失稳的工作效率越高;设置侧向支撑的钢拱屈曲时,随着支撑刚度的增大其屈曲半波数逐渐增加,而仅在拱顶设置扭转约束时始终呈现1个半波失稳模式;从均匀受压圆弧拱的情况获得的等间距侧向支撑门槛刚度,应用在其他组合荷载作用下,同样可以获得足够的支承刚度;当工形截面钢拱的支撑点间拱段长度满足所提出的要求时,钢拱平面外失稳不先于平面内反对称整体失稳。     

大庆站房跨层重载桁架稳定承载力研究

大庆西站平面桁架结构跨越两层楼面,结构高度大,承载大,杆件与杆件之间采用刚性连接交织成网状,缺乏有效面外支撑,结构受力非常复杂,存在失稳破坏的风险。为研究大庆西站跨层重载平面桁架的整体稳定性,基于子结构分析法和大位移控制算法对跨层平面桁架结构的非线性稳定承载力进行分析,明确该平面桁架结构的失稳模式和稳定承载力,对结构的整体安全性进行评价。研究表明:跨层桁架的失稳模式表现为半波形面外鼓曲,桁架失稳后表现出"屈曲后不稳定"特性;非线性稳定分析得到的整体稳定系数均大于2,满足规范稳定承载力的要求。     

平面钢管桁架拱平面外稳定试验研究与有限元分析

对2个跨度为10 m的圆弧形平面圆钢管桁架拱模型进行全跨均布荷载作用下的静力试验研究,分析了平面钢管桁架拱的平面外稳定承载力。引入平面外转动弹簧单元、水平位移弹簧单元,建立弹簧-杆系有限元模型,对试验模型进行非线性有限元分析。试验和有限元分析结果表明：下弦杆无平面外支撑的平面钢管桁架拱,在极限状态时,受压上、下弦杆发生侧向弯曲失稳,并引起整体平面外弯曲失稳破坏;圆钢管相贯节点的平面外转动刚度对试验模型的平面外稳定承载力影响显著。弹簧-杆系有限元分析结果与试验结果较为吻合,可为同类型结构的平面外稳定分析、设计提供参考。     

张弦桁架面外支撑设置研究

设置面外支撑是提高张弦桁架面外稳定性的有效措施之一。以某实际张弦桁架工程为背景,采用线性屈曲法对该结构进行面外稳定性分析,研究了支座边界条件、弦杆局部失稳、面外支撑布置对结构稳定承载力的影响。研究结果表明,约束张弦桁架支座处截面扭转是必要的;当支撑系统刚度较大时,弦杆局部失稳将大幅降低结构稳定承载力;面外支撑布置方式的改变影响结构的失稳模式,该文的结论可为类似工程的面外支撑系统设计优化提供参考,并为后续结构的非线性稳定分析提供依据。     

侧向支撑对腹板开洞钢拱平面外弹性屈曲的影响分析

腹板开洞钢拱通过设置侧向支撑可以阻止钢拱发生平面外弯扭屈曲,支撑刚度的大小会对钢拱屈曲临界荷载产生影响.采用有限元方法分析了不同荷载、拱脚条件、支撑类型和位置对钢拱平面外屈曲稳定的影响.研究表明：在刚性支撑情况下,钢拱屈曲临界荷载随支撑刚度增大而增大,铰支钢拱屈曲半波随支撑数量的增加而增加,当支撑数量为n时,会出现n＋1个屈曲半波.两种支撑类型共同工作时,在侧向刚度支撑足够的情况下,扭转支撑对钢拱平面外屈曲临界荷载的影响有限.当侧向支撑刚度达到临界支撑刚度时,其屈曲临界荷载不再随支撑刚度的增大而增大.     

Warren型平面钢管桁架受压弦杆的面外稳定承载力

受压弦杆面外失稳是Warren型平面钢管桁架面外失稳的主要形式,其受力状态可以简化为支撑弹簧压杆。确定腹杆提供的支撑弹簧刚度是计算压杆面外稳定承载力的必要条件。考虑节点面外转动刚度的影响,推导了腹杆对弦杆支撑弹簧刚度计算公式。对4~15跨的支撑弹簧压杆建立了相应的标准化屈曲计算模型,进行有限元屈曲分析,得到不同跨数压杆的弹簧刚度与面外稳定承载力的数值关系表,通过计算支撑弹簧刚度可以方便地查表得到不同跨数Warren型平面钢管桁架受压弦杆的面外稳定承载力。通过数值算例比较,查表法简便可行,可以在实际工程设计中参考应用。     

铰接式斜撑平面桁架拱的平面外弹性屈曲性能

对设置连续和不连续斜撑的平面桁架拱的平面外弹性屈曲性能进行研究。首先,研究连续斜撑平面桁架拱,得到一个理论上的平面外弹性屈曲荷载的封闭解。通过有限元法分别研究不连续支撑平面桁架拱的两个重要参数——斜撑阈值刚度和相邻支撑间一段拱的平面外弹性屈曲荷载。此外,有限元结果显示,如果平面桁架拱由在腹杆与弦杆间使用相贯节点制作而成且受上弦杆约束,那么受刚度不足的影响,下弦杆的外平面屈曲可以完全避免平面桁架拱产生外平面屈曲,之后桁架拱会完全受上弦杆所约束。     

空间倒三角形管桁架的整体稳定研究

空间倒三角形管桁架的稳定性直接影响其承载力。针对不同跨度的空间倒三角形管桁架,按静力分析结果确定截面参数,然后以管桁架结构的高跨比和宽高比作为变量建立了96个结构模型,利用有限元软件进行特征值屈曲分析和非线性屈曲分析。结果表明:高跨比的增大可以提高管桁架的稳定承载力,但结构会出现静力承载力小于稳定承载力的现象;宽高比对管桁架的稳定承载力影响较小,当高跨比不小于1/15时,一定范围内其宽高比的减小可以增大管桁架的稳定承载力,当高跨比小于1/15时,宽高比的减小可以降低管桁架的稳定承载力;同时,对75 m跨度的管桁架设置了中部空间侧向支撑,结果表明侧向支撑能大幅提高结构的稳定性。     

槽钢加劲钢板剪力墙受力性能研究

竖向槽钢加劲钢板剪力墙由内嵌钢板、边缘构件和墙板两侧对称布置的竖向槽钢加劲肋组成。槽钢加劲肋具有较高的抗弯、抗扭刚度,可为墙板提供有效的面外约束和轴向支撑作用。利用有限元分析软件ABAQUS对槽钢加劲钢板墙进行屈曲分析和静力弹塑性分析,研究槽钢距边缘构件距离、钢板宽厚比、高厚比、肋板刚度比和柱刚度对钢板墙及边缘构件力学性能的影响。结果表明,槽钢加劲肋至边缘构件的距离主要影响钢板墙的平面外变形,对钢板墙屈曲应力和承载力的影响较小。槽钢加劲肋可以有效提高墙板的屈曲应力。随着宽厚比和高宽比的减小,结构的承载力和刚度均显著提高。增大肋板刚度比可提高钢板墙的初始刚度和屈曲应力,肋板刚度比应大于20。为避免边框柱变形过大或过早破坏,边框柱应具有足够的刚度,增大柱刚度可以提高钢板墙的初始刚度,减缓墙板刚度的退化。     

Sensitivity analysis of critical forces of trusses with side bracing

The present research is devoted to the study of out-of-plane buckling of trusses with elastic side bracing. In this paper, a sensitivity analysis of critical buckling loads of a truss due to bracing stiffness is carried out. A method based on the sensitivity analysis for the determination of the threshold bracing stiffness condition for full bracing of a truss is proposed. The influence lines of the unit change of the bracing stiffness on the buckling load, for different initial bracing stiffness, are investigated. The approximations of an exact relation between the buckling load and bracing stiffness are found. The buckling length related to the side-support distance as a function of bracing stiffness is also determined. It is shown that the buckling length of truss chords with elastic side supports is larger than that assumed in design codes.     

Buckling of frames braced by flexural bracing

This paper investigates the buckling of multistory frames braced by vertical beams. The sectional properties of the frames and the bracing beam are assumed to vary linearly along the height; the axial forces in the columns and the bracing beam are also assumed to linearly change along the height. A relationship between the buckling load and the bracing rigidity is established. The threshold rigidity for the vertical bracing beam which is just enough to make the frames buckle in a non-sway mode is obtained. The result may be used as a rational basis for classifying sway frames and non-sway frames after taking the influence of initial imperfections and lateral loads into account.     

门式刚架中隅撑轴力强度的ANSYS分析

研究受到檩条和隅撑支撑作用的梁的弯扭,首先对檩条-隅撑体系提供结果的侧向支撑刚度进行了推导,然后考虑梁的初始侧移,研究了使梁的临界弯矩达到屈服弯矩时隅撑中的内力,这个内力即是对隅撑的强度要求。通过4个算例表明,隅撑轴力不到下翼缘屈服轴力侧向分量的1%,远小于《门式刚架轻型房屋钢结构技术规程》(CECS 102∶2002)中规定的支撑力。     

壁挂式冷弯型钢结构双层组合墙体抗震性能试验研究

为研究壁挂式连接冷弯型钢结构中双层组合墙体的抗震性能，对4个足尺双层墙体试件进行了水平低周往复试验，考虑了刚性斜撑、方钢管端柱加强、下部两层墙体抗侧刚度比等因素对墙体抗震性能的影响。结果表明：增设刚性斜撑墙体中V形刚性斜撑与墙面板蒙皮作用同时发挥抗侧作用，提高了墙体的受剪承载力及弹性抗侧刚度，但延性降低；采用方钢管截面端柱可避免端柱发生压屈破坏，其对墙体的抗侧刚度及受剪承载力提高幅度较小，但可以改善墙体的延性及变形性能；当底层与二层墙体抗侧刚度比大于1时，墙体属于弯曲型破坏。建议在多层冷弯薄壁型钢结构住宅抗震设计中，对底层墙体设置刚性斜撑、采用方钢管加强端柱以提高墙体受剪承载力及端柱抗压屈能力。     

壁挂式冷弯型钢结构双层组合墙体抗震性能试验研究

为研究壁挂式连接冷弯型钢结构中双层组合墙体的抗震性能,对4个足尺双层墙体试件进行了水平低周往复试验,考虑了刚性斜撑、方钢管端柱加强、下部两层墙体抗侧刚度比等因素对墙体抗震性能的影响.结果表明:增设刚性斜撑墙体中V形刚性斜撑与墙面板蒙皮作用同时发挥抗侧作用,提高了墙体的受剪承载力及弹性抗侧刚度,但延性降低;采用方钢管截面...     

门式刚架梁隅撑设计的强度要求

研究了受到檩条和隅撑侧向支撑的梁的弯扭失稳问题。首先对檩条-隅撑体系对梁提供的侧向支撑刚度进行了推导,然后考虑檩条位置和隅撑支撑作用的特点,对梁的弯扭失稳临界弯矩与支撑刚度的关系进行了有限元分析,考虑梁的初始侧移和初始扭转,研究了使梁的临界弯矩达到屈服极限时隅撑中的内力,这个内力即是对隅撑的强度要求。通过4个算例表明,侧向支撑力小于下翼缘屈服轴力的1%,远小于《门式刚架轻型房屋钢结构技术规程》(CECS 102∶2002)中规定的支撑力。     

Lateral buckling of eccentrically braced RHS columns

Rectangular hollow section (RHS) is widely used as columns of agricultural greenhouse constructions. To enhance the resistance of these columns against the out-of-plane buckling failure, the bracing system is frequently adopted, typically composed of the bracing spans containing a two-layer x-brace at intervals of a number of spans and a horizontal bar connecting the mid-height sections of all columns of the same row. The horizontal bar provides the lateral brace to the columns between two adjacent bracing spans. Due to ease of installation and existence of glass at the outer face, the horizontal bar is usually connected to the inner face of the columns at the edges of the construction (side columns) using the overlapped joints, leading to the side columns being eccentrically braced by the horizontal bar. The present paper carried out an investigation into behavior of the eccentrically braced RHS columns, including the buckling load, failure mode, bracing eccentricity, bracing stiffness and the relationships between. Simple approximations of good accuracy are also provided for the normalized critical bracing eccentricity and buckling load, with which the hand-calculation method is only necessary in practical design. A worked example is given for side columns in greenhouse constructions following the procedure presented in this study.     

Comprehensive stability design of planar steel members and framing systems via inelastic buckling analysis

This paper presents a comprehensive approach for the design of planar structural steel members and framing systems using a direct computational buckling analysis configured with appropriate column, beam and beam-column inelastic stiffness reduction factors. The stiffness reduction factors are derived from the ANSI/AISC 360-16 Specification column, beam and beam-column strength provisions. The resulting procedure provides a rigorous check of all member in-plane and out-of-plane design resistances accounting for continuity effects across braced points as well as lateral and/or rotational restraint from other framing. The method allows for the consideration of any type and configuration of stability bracing. With this approach, no member effective length (K) or moment gradient and/or load height (C _b ) factors are required. The buckling analysis rigorously captures the stability behavior commonly approximated by these factors. A pre-buckling analysis is conducted using the AISC Direct Analysis Method (the DM) to account for second-order effects on the in-plane internal forces. The buckling analysis is combined with cross-section strength checks based on the AISC Specification resistance equations to fully capture all the member strength limit states. This approach provides a particularly powerful mechanism for the design of frames utilizing general stepped and/or tapered I-section members.     

The collapse behaviour of braced steel frames exposed to fire

Progressive collapse mechanisms of braced two-dimensional steel-framed structures, subjected to fire heating, are investigated using a robust static–dynamic procedure developed by the authors. 20 cases have been analysed to provide a comprehensive view of the mechanisms of progressive collapse for these frames, with different bracing systems under different fire conditions. The influences of stiffness and strength of the bracing systems are also analysed. The results indicate that the pull-in of columns is one of the main factors which generate progressive collapse. Horizontal “hat truss” bracing systems have limited capacity to avoid pull-in of columns supporting the heated floor, although they can directly redistribute the vertical load lost by buckling columns to adjacent columns. On the other hand, vertical bracing systems have the effect, not only of increasing the lateral restraint of the frame, which reduces the pull-in of the columns, but also of effectively preventing the collapse progressing from local to global. Stronger vertical bracing systems can redistribute load from a buckled column to its surrounding structural members. Frames with a combined hat and vertical bracing system can be designed to enhance the capability of the frame as much as possible to prevent progressive collapse when a heated column buckles.