用于预测C形檩条横截面应力的简化模型

旨在提供并且验证一个简化模型,可用于预测C形檩条的纵向应力。首先,介绍一个关于弯曲应力的简单案例,其中外力施加在剪力中心,或者施加在双侧翼缘都有支撑的截面中。如通常在檩条-护墙板系统中发现的一样,当弯曲问题变得比较复杂时,即可取消对加载点和翼缘的约束,而仅仅考虑对受拉翼缘转动的约束。回顾并验证用于预测纵向应力的Winter模型,这个模型是为解决直接受拉问题而开发的,将该模型扩展,使其能解决受拉翼缘受限的弯曲构件的计算问题。从弯曲和约束扭转作用中得到的纵向应力,用于评估典型的檩条-护墙板系统的弹性稳定性能。最后,为现有的AISI方法提供了典型C形檩条的强度预测方法,并且利用该方法中预测的纵向应力分布为直接强度方法提出了新的扩展建议。     

Experimental and numerical investigation on cold-formed steel C-section flexural members

This paper presents an experimental and numerical investigation on the bending strength and behavior of cold-formed steel C-section flexural members with upright, inclined and complex edge stiffeners. A total of 24 specimens that divided into 12 tests including 6 pure bending tests and 6 non-pure bending tests have been conducted. Local buckling, distortional buckling and interaction between local and distortional buckling were observed in the tests. The experimental results show that the edge stiffener and buckling mode have great influence on member’s bending strength. Comparison of the bending strengths under the two bending states show that the bending strength under non-pure bending is higher than which under pure bending, but the increased magnitude is related to the buckling modes. Moment gradient effect has only a minor influence on local buckling, but has great influence on distortional buckling. The tests were simulated by finite element program of ANSYS and the simulated results show good agreement with the experimental results in terms of bending strength and buckling mode.     

Numerical simulation of high strength cold-formed purlins in combined bending and shear

The paper provides numerical nonlinear simulations, based on the finite element method (FEM) using the software package ABAQUS/Standard, of high strength C-section cold-formed steel purlins in shear and combined bending and shear. The simulations are compared with and calibrated against tests performed at the University of Sydney on a variety of section sizes and thicknesses. Studies of the effects of boundary condition, geometric imperfection, and element type as well as mesh size are included. Geometric imperfections are often taken as a scaled multiple of the eigenvalue modes. The selection of eigenmodes and their scaling is given in the paper. The accurate results of the numerical simulations show that finite element analysis can be used to predict the ultimate loads of thin-walled members including the post-buckling behavior of thin-walled sections in shear and combined bending and shear. It is demonstrated that finite element analysis can therefore be used to design and optimize thin-walled sections of high strength steel.     

A parametric study for distortional buckling stress on cold-formed steel using a neural network

The process of prediction of distortional buckling stress of cold-formed steel members is often cumbersome and it is also difficult to perform parametric studies in this field to investigate the effect of geometric parameters on Elastic Distortional Buckling Stress (EDBS). To overcome this difficulty a neural network based model and formulation which was presented in a companion paper by the author [Pala M. A new formulation for distortional buckling stress in cold formed steel members. Journal of Constructional Steel Research 2006;62:716-22] is proposed as an alternative approach to investigate the effect of geometric parameters on distortional buckling stress. The model considers the effect of web height, flange width, angle of lip, lip length and flange thickness. The results of the Neural Network model are quite satisfactory and are consistent with the literature.     

支撑筒角部钢柱抗拔锚固设计试验研究

大连国际会议中心的筒体采用"钢管角柱-钢桁架暗支撑架混凝土组合核心筒"。该结构各核心筒均根据建筑的需求开设了洞口,且整个结构质量、刚度分布不均,筒体受力较为复杂。在核心筒的抗震设计中,如何保证筒体角部钢管柱柱脚与混凝土基础具有良好的共同工作性能,保证结合部位的锚固性能,是其关键技术之一。对这部分钢管柱进行抗拔试验研究,以确保在地震作用下整个筒体以及结构的安全。试验表明,混凝土基础中配置竖向抗拔钢筋和水平分布钢筋均能有效提高抗拔柱的锚固承载力。     

Genetic programming-based formulation for distortional buckling stress of cold-formed steel members

The main purpose of the research is to develop formulations for estimating the Elastic distortional buckling stress (EDBS) of cold-formed steel member under compressive loading using Genetic programming (GP) which has not been applied so far. The required data used for the training and testing is collected from the literature. Two GP-based formulations are proposed to predict the elastic distortional buckling of cold formed steel C sections. The results of proposed GP formulations are compared with experimental and analytical results of different researchers and methods and found to be accurate. The results obtained from the formulas have shown that GP is a promising technique for predicting EDBS of cold-formed steel C sections.     

后注浆抗拔桩在复杂地层下的试验及模拟研究

以郑州某工程抗拔试桩单桩抗拔承载力试验结果为基础,针对抗拔桩抗拔承载力不足的情况,采用桩端桩侧复式后注浆工艺来减小泥皮和沉渣对桩侧摩阻力和端阻力的影响,从而提高桩抗拔承载力.对注浆结果进行分析并用经验公式计算.结果表明通过试验验证,由《建筑桩基技术规范》(JGJ 94-2008)公式计算的注浆量可适当减小.分析了有泥皮...     

A new formulation for distortional buckling stress in cold-formed steel members

Distortional buckling of compression members usually comprises rotation and translation of each flange and lip about the flange-web connection in opposite directions. The present procedures for the calculation of elastic distortional buckling stress in the literature are very complex, cumbersome and have long expressions. In this paper a new neural network (NN) based formula is proposed for the determination of the elastic distortional buckling stress of cold-formed steel C-sections with both end sections pinned. The focus of this study is on the distortional buckling, for which existing results are for sections subjected to pure compression and/or pure bending only. The data used for training and testing NNs is taken from Schafer’s report. The NN-based estimates are compared with the experimental, numerical and analytical results of different researchers and methods. It was found that the proposed NN based-formula is practical in predicting the elastic distortional buckling stress of cold formed steel C-sections.     

冷弯槽钢受弯时长细比限值试验研究

非弹性设计方法与弹性设计方法相比,其截面的允许荷载值较大,这是由于屈服应力沿截面高度进行了重新分布。塑性设计方法使得截面的塑性能力和塑性铰的转动特性得到充分发挥,从而使结构设计更为经济合理。冷弯槽钢在农业和轻工/商业中广泛用于门式刚架结构,塑性设计方法对这类结构非常适用,然而目前仅采用弹性设计方法对其进行设计。为突破设计规范的限制,对冷弯槽钢的非弹性弯曲能力进行了试验研究和数值分析,以建立相应的设计准则。设计准则采用热轧钢分类方法,将截面分为紧凑型、非紧凑型及细长型(根据澳大利亚规范),或1,2,3,4级(根据欧洲规范)。澳大利亚规范所预测的超过弹性极限范围的冷弯槽钢弯曲能力精确可靠。     

Experiments on sheathed cold-formed steel studs in compression

The stability and strength of cold-formed steel lipped C-section columns (studs) with sheathing attached to the flanges is the subject of this paper. Stud configurations both with and without sheathing, either oriented strand board or gypsum board, are tested for failure in compression. A total of twenty-six tests covering short, intermediate and long specimens, varied sheathing configurations, and varied end boundary conditions are completed. Dimensions and geometric imperfections of the specimens are measured in detail. The measured geometric imperfections are reduced to scalar magnitudes consistent with local, distortional, and global buckling modes. During the testing, mid-height cross-section deformations are recorded using five position transducers. The deformations indicate the impact of the different combinations of sheathing, and of the end boundary conditions, on the strength and stability of the studs. Composite action between the stud and sheathing, and isolating direct loading of the sheathing, are shown to be significant in determining the strength and controlling limit state of the stud. Tested strengths are compared with existing North American (American Iron and Steel Institute) specification methods and potential improvements are explored.     

Behavior of thin gusset plates in compression

The use of cold-formed steel members for roof and floor truss applications is gaining widespread acceptance in the United States. However, there is little technical information regarding the behavior and design of thin gusset plates in compression. Thus, a study was initiated at the University of Missouri-Rolla aimed at investigating the behavior of thin steel gusset plates in compression. Key parameters that were considered in the experimental study were the thickness of the gusset plate, the width and length of the gusset plates, the fastener location, and the fastener pattern. Both a plate model and a column model were investigated for computing the strength of a thin plate in compression. Based on the findings of this study, design recommendations are proposed.     

地下结构抗浮设防水位和浮力计算刍议

大量地下车库、下沉式广场等地下建筑的兴建,使抗浮问题非常突出。针对地下结构设计时抗浮设计水位的确定和水浮力计算问题,分析了地下水赋存状态与渗流特性、基础埋深与地下水层关系,介绍了设防水位的合理选取及水浮力实用计算方法,最后给出了工程算例。     

Experimental investigation on laser welded connections for built-up cold-formed steel beams

A wide experimental investigation on laser welded connections based on both lap-shear and tension tests was performed at the University of Naples. The aim of the study was to assess the possibility of using laser welding in innovative built-up cold-formed steel beams. The experimental programme was designed in order to evaluate the effects of different parameters on the strength and ultimate displacement of the selected connections. In particular, the influence of sheet thickness, gap, loading direction, weld shapes and zinc coating were analyzed. The results of the experimental tests were compared with the predicted resistance values according to Eurocode 3, with the aim of validating for laser welding the mechanical models provided for spot welds.     

地震下可恢复框架结构冷弯型钢构件试验研究

对地震时作为多层建筑抗弯钢架能量耗散构件的薄壁冷弯型钢(CFS)进行了试验研究。试验采用6个螺栓连接的梁-柱节点,在连接区域的板件和梁的翼缘上使用不同的出平面加劲肋。CFS连接件的滞后性能表明其具有较高的耗能能力和足够的延性,满足抗震设计规范的要求。在连接区域的钢梁内使用出平面加劲肋,能够提高连接件的弯矩-转角特性,强度提高35%,延性提高75%。弹性周期后连接件的滑动使其具有较好的滞回性能,能量耗散能力提高了240%。连接件试样可以作为刚性连接,其全部或部分强度取决于连接加劲肋。     

Effect of longitudinal stress gradient on the ultimate strength of thin plates

When thin-walled sections are subjected to a moment gradient, the plates that comprise the section are themselves subjected to a longitudinal stress gradient. This paper analyzes the effect of longitudinal stress gradient on the ultimate strength of thin plates. Two types of thin plates are investigated: (1) plates simply supported on all four edges; and (2) plates simply supported on three edges, and with one longitudinal edge free. These two cases illustrate the influence of longitudinal stress gradient on stiffened and unstiffened elements of cold-formed steel sections, respectively. Nonlinear finite element analysis (ABAQUS) was performed to determine the ultimate strength of thin plates under a longitudinal stress gradient. The results indicate that the longitudinal stress gradient increases the strength of both types of thin plates, but has significantly more influence on unstiffened elements than stiffened elements. The beneficial effect of longitudinal stress gradients can be accounted for in design by using a plate buckling coefficient modified to account for the longitudinal stress gradient, an example of the impact of this change on a common cold-formed steel channel is provided.     

Lateral restraint forces in Z-section roof systems using the component stiffness method

The component stiffness method is a method to predict lateral restraint forces in roof systems supported by Z-sections. The method approximates a bay of Z-sections as a single degree of freedom system and uses a stiffness formulation to determine the contribution of the different components in the system to the resistance of lateral movement. The forces generated by the roof system requiring restraint are derived from mechanics.     

运用复合刚度方法对Z型构件支撑屋面系统的侧向约束力分析

复合刚度方法是一种可以预测Z型截面构件支撑的屋面系统侧向受力的方法。该方法将一系列Z型截面作为单自由度系统分析,并采用刚度公式计算系统中不同的构件对于抵抗侧向位移的贡献。从力学理论中推导出屋面系统所需的抗力。     

软土地区冲孔灌注桩抗拔承载力的研究

本文介绍了三根嵌入岩层并有桩端高压注浆的软土地区冲孔灌注桩的单桩竖向抗拔静载试验情况。分析了高压注浆、嵌岩深度、持力层性状对单桩竖向抗拔承载力的影响,对目前规范建议的桩端高压注浆侧阻力增强系数进行了探讨,可供类似工程参考借鉴。     

高强冷弯型钢受弯构件截面局部屈曲临界应力

介绍了求解截面的局部屈曲临界应力的意义,探讨了求解截面的局部屈曲临界应力cσrl的方法,并对实验值与理论值进行了比较,最后提出了有待进一步研究的问题,从而为直接强度法的顺利使用提供了理论基础。     

厚壁矩形中空截面冷弯型钢纵向残余应力试验研究

对壁厚超过6mm的厚壁矩形中空截面冷弯型钢进行试验研究。矩形中空截面采用两种成型方法:直接法(直接形成矩形)和间接法(先形成圆形,再转换成矩形)。采用两种方法(钻孔法和X射线衍射法)计算纵向残余应力的大小和分布。研究了沿截面周长方向和厚度方向的纵向残余应力的大小和分布。结果显示,沿厚度方向的纵向残余应力在外表面为拉力,内表面为压力,表现出类似于正弦曲线的非线性特性。此外,讨论了厚壁矩形中空截面冷弯型钢的成型过程和截面几何尺寸对残余应力的大小和分布的影响。最后,针对厚壁矩形中空截面冷弯型钢两种不同成型过程,分别给出相应的残余应力分布情况。