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。     

门式刚架结构侧向支撑的强度和刚度研究

对于门式刚架结构,工程实际发现当构件截面尺寸、内力等超过一定范围时,檩条由于强度或刚度不足,致使隅撑对构件侧向支撑作用大大削弱,增大了构件的计算长度。本文结合国内外研究成果,总结出隅撑作为侧向支撑的最小刚度要求,并提供了当檩条刚度不满足最小刚度要求时构件侧向支承的解决方案。     

考虑隅撑作用的简支檩条设计研究

简支檩条的常规设计不考虑隅撑对檩条的作用,但隅撑与檩条的连接是客观存在的,隅撑对檩条的受力会产生影响。本文分析了隅撑对檩条的两种作用,即隅撑对檩条的支承作用和附加作用力,并指出隅撑作用下简支檩条的受力分析应当考虑活载不利布置以及各种不同的隅撑附加力工况。算例计算表明,考虑隅撑作用的简支檩条内力变化较大,常规设计偏不安全。     

考虑隅撑作用的简支檩条设计研究

简支檩条的常规设计不考虑隅撑对檩条的作用,但隅撑与檩条的连接是客观存在的,隅撑对檩条的受力会产生影响.本文分析了隅撑对檩条的两种作用,即隅撑对檩条的支承作用和附加作用力,并指出隅撑作用下简支檩条的受力分析应当考虑活载不利布置以及各种不同的隅撑附加力工况.算例计算表明,考虑隅撑作用的简支檩条内力变化较大,常规设计偏不安全.     

檩条设计中若干问题的探讨

檩条一般采用简支梁,假定屋面板能阻止其侧向失稳和扭转,则只计算其强度.仅就连续檩条以及隅撑对檩条的附加力导致檩条上翼缘受拉、下翼缘受压,失去屋面板对受压区的侧向支撑时等情况进行分析,希望对工程设计有所裨益.     

隅撑—檩条体系支撑的梁的弯扭屈曲讨论

本文简要介绍了隅撑-檩条体系支撑的梁的弯扭屈曲计算结构。     

轻钢结构中Z型连续檩条设计问题的探讨

针对我国现行钢结构规范中的不足 ,探讨Z型连续搭接檩条的结构性能 :荷载分布、搭接嵌套松动、内力计算、侧向稳定以及构件极限承载力等问题。此外 ,还讨论了带隅撑檩条的计算特点和双檩条的构造优点 ,提出了适合实际工程的算法 ,使冷弯薄壁型钢檩条设计更为经济合理。方法和结论可供设计人员参考     

轻钢门式刚架工程结构设计中存在的几个问题及探讨

分析轻钢门式刚架设计中，支撑、隅撑、檩条墙梁等系统存在的几个结构问题，提出了相应对策。     

隅撑支撑钢框架的试验研究和弹塑性受力分析

通过1∶2隅撑支撑钢框架模型的单调加载试验,研究了隅撑支撑钢框架的抗侧力性能和破坏机理。试验结果表明,在水平荷载作用下隅撑最先发生屈服,并具有很好的变形能力,结构具有很好的滞回耗能性能和延性。对隅撑支撑钢框架进行了弹塑性受力分析,并给出了其恢复力模型,从而为简化隅撑支撑钢框架的非线性分析提出了一种新的方法。     

隅撑对檩条受力的影响分析

为了对考虑隅撑作用的檩条受力情况进行分析,研究了隅撑对檩条产生的支承作用以及附加作用力,并通过算例加以验证,可知简支檩条在隅撑作用下的受力与常规檩条不同,在檩条设计中应加以考虑。     

Cyclic testing of a metal building moment frame system with web-tapered members

Cyclic testing of a full-scale metal building with built-up, web-tapered members was carried out as part of an effort to develop a seismic design procedure for this type of moment frame system. The test building was designed as an Ordinary Moment Frame (OMF) with bolted end-plate moment connection. Test results showed that the system had a very high deformability; the elastic behavior was observed up to more than 2% story drift. But the ductility of the test frame was limited; the system failed at 2.6% story drift due to lateral–torsional buckling of the web-tapered members with a significant strength degradation. The testing also revealed that improper flange bracing with slotted bolt holes could jeopardize the resistance of the framing system with premature lateral–torsional buckling. The experimentally derived member forces and the associated failure mode correlated well with the code provisions for strength evaluation of web-tapered members. The lateral bracing force of the rafter reached 2.6% of the nominal yield strength of the flange.     

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.     

拱墙结构平面外失稳机理与设计研究

拱墙是一种由拱、立柱、横梁组合而成的竖向平面结构，横梁上的竖向平面内荷载通过立柱传递到大跨度拱体中。为研究拱墙结构的失稳机理，采用有限元分析方法，对拱墙模型在弹性和弹塑性条件下的稳定性能进行了研究。分析结果表明：立柱侧向刚度及横梁侧向支撑刚度是影响拱墙稳定性能的主要因素，当横梁侧向支撑刚度小于其门槛刚度时，拱墙的屈曲模式表现为拱墙整体平面外失稳；当横梁侧向支撑刚度大于其门槛刚度而立柱的侧向刚度小于其门槛刚度时，拱墙的屈曲模式表现为拱体的平面外失稳；当横梁侧向支撑和立柱的侧向刚度均大于各自的门槛刚度时，拱墙的屈曲模式表现为拱墙整体平面内失稳。结合某火车站站房工程，建立了横梁位置施加侧向弹簧支撑和带纵向桁架的两种拱墙模型，分析了该拱墙结构的平面外稳定承载力。结果表明，纵向桁架为拱墙横梁提供的平面外支撑刚度远大于拱墙的侧向支撑门槛刚度，提高拱墙的平面外稳定承载力需通过增大立柱的侧向刚度和加强立柱两端的可靠连接实现。     

Experimental study of prestressed steel-concrete composite beams with external tendons for negative moments

Four groups of prestressed steel-concrete composite beams with external tendons in negative moment regions were tested, and the cracking behaviours and the ultimate negative moment resistances of the composite beams were investigated experimentally. It is found that in hogging moment regions, on adding prestressing to the composite beams with external tendons, the cracking resistance of the beams can be effectively increased; however, the incremental internal tendon forces of the prestressed composite beams are rather small, and therefore can be neglected in the evaluation of the negative moment resistance of the beams. In hogging moment regions, the ultimate resistance of a composite beam prestressed with external tendons is governed by either distortional lateral buckling or local buckling, or an interactive mode composed of the two bucklings. For a beam with a compact section, the negative bending moment can reach the plastic moment when the steel section is fully plastic, and for a non-compact section, the negative bending moment is limited to the yield moment at which the compression steel flange initiates yield. The method for evaluating the buckling resistance of the composite beams is discussed, and a tentative design method based on BS5400: Part 3 is proposed to assess the buckling resistances of the prestressed composite beams.     

Lateral bracing of I-girder with corrugated webs under uniform bending

Lateral-torsional buckling may occur in an unrestrained beam where its compression flange is free to displace laterally and rotate. This paper presents the results of the theoretical and finite element analyses of the lateral-torsional buckling of I-girders with corrugated webs and lateral bracing, under uniform bending. It is well known that an elastic lateral brace restricts partially the lateral buckling of slender beams and increases the elastic buckling moment. However, a full study of the effect of lateral braces on lateral-torsional buckling has not been made especially for I-girder with corrugated webs. This paper develops a three-dimensional finite element model using ANSYS [User’s manual, version 10.0] for the lateral-torsional buckling analysis of I-girder with corrugated webs and uses it to investigate the effects of elastic lateral bracing stiffness on the critical moment of simply supported I-girders with corrugated webs under pure bending. It was found that for plastic and inelastic I-girder with corrugated webs, the effect of bracing initially is increased to some extent as the lateral unbraced length increases and then decreased until the beam behaves as an elastic beam. In other words, the effect of bracing depends not only on the stiffness of the restraint but also on the modified slenderness of the I-girder. Also, the results show that Winter’s simplified method to determine full brace requirements cannot be applied to I-girders with corrugated webs. Therefore, a general equation is proposed to determine the value of optimum stiffness (K_opt) in terms of the I-girder’s slenderness.     

Distortional buckling in braced-cantilever I-beams

This paper deals with distortional buckling of braced-cantilever monosymmetric I-beams under three types of load: a tip point load, a uniformly distributed load and a moment at the end. Top-flange and bottom-flange load positions are considered for the first two load cases. ABAQUS is used for the investigation. The effect of different types of bracing on buckling load is investigated. Results are compared with results from previous experimental investigations. It is also found that top lateral bracings are very effective for beam sections having larger bottom-flanges when a point load or a uniformly distributed load acts at the top-flange, and for the uniform moment case, except for the T-section or the inverted T-section cantilever beams. On the other hand, bottom lateral bracings are very effective for beam sections having larger top-flanges. When loads are placed at the bottom-flange, position of any kind of lateral bracing has practically no effect on the buckling capacity of a monosymmetric cantilever beam, except for the inverted T-section cantilever beams.     

Bracing requirements for inelastic castellated beams

Lateral-torsional buckling can be avoided by properly spaced and designed lateral bracing. Bracings are usually assumed to be elastic, and so may be characterized by their elastic stiffnesses. It is well known that an elastic lateral brace restricts partially the lateral buckling of slender beams and increases the elastic buckling moment. However, a full study of the effect of lateral braces on inelastic buckling has not been made especially for castellated beams, and it is not known whether the limiting stiffness for elastic buckling can be applied to castellated beams that buckle inelastically. This paper develops a three dimensional (3-D) finite-element model using a finite-element program and uses it to investigate the effect of elastic lateral bracing stiffness on the inelastic flexural-torsional buckling of simply supported castellated beams with an elastic lateral restraint under pure bending. It was found that for inelastic castellated beams, the effect of bracing initially is increased to some extent as the lateral unbraced length increases and then decreased until the beam behaves as an elastic beam. In other words, the effect of bracing depends not only on the stiffness of the restraint but also on the modified slenderness of the beam. Also, the results show that Winter’s simplified method to determine full brace requirements cannot be applied to inelastic castellated beams. Therefore, a general equation is proposed to determine the value of optimum stiffness in terms of the beam’s slenderness, applicable to all castellated beams under pure bending.     

Buckling of interbraced beam systems

Analyses of parallel beam floor support systems under both uniform beam moment and uniform spread load are carried out. The beams are braced by lines of braces which provide torsional and lateral support and which may be attached eccentrically. Charts illustrate the variation of the buckling load of this interconnected structure under different brace stiffnesses and eccentricities and, in particular, show the levels of stiffness at which ‘full bracing’ is achieved. The matrix equation which allows the uniform moment calculations to be quickly made is presented. Other cases employ a beam-column finite element.     

Coupled static and dynamic buckling of thin walled beam by spline finite element

For the coupled static and dynamic buckling of thin walled beam subjected to various forces, such as axial force, uniform bending moment, and bending moment due to concentrated and distributed lateral forces, the spline finite element method is employed to obtain the dynamic stiffness matrix. Second order effects of the axial force and moment are considered. A doubly symmetric cantilever beam with uniform cross-section is investigated. Extensive static and dynamic interaction diagrams are plotted. The effects of warping rigidity, torsional rigidity, axial tension and compression on moment buckling, moment on axial buckling compression, higher buckling modes are discussed in detail. The spline finite element method is proved to be very efficient for the present problem and many interaction diagrams can be plotted easily. Some new results are presented. The methodology is based on finite element formulation and therefore it can be easily extended to analyze structural frames.