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。     

简支Z型檩条在风吸力作用下应力分布及极限状态研究

轻钢工业厂房中,Z型檩条在其截面的非对称平面内承受风荷载,上翼缘受压型钢板连续约束作用而下翼缘自由,应力分布比较复杂,存在局部或整体稳定问题,是围护结构抗风设计的主要控制因素。基于薄壁杆件结构力学以及经典梁理论,分析了简支Z型檩条在风吸力作用时考虑压型钢板对檩条约束作用的应力分布,并依据相关试验资料,验证了分析方法的正确性。然后,针对檩条横截面应力分布、侧向位移及极限状态等力学性能进行定性参数分析。研究表明,该方法可以精确计算檩条横截面应力分布,压型钢板对檩条的扭转及侧翼约束作用分别影响檩条上、下翼缘的峰值应力,使得构件局部屈曲应力增大,而畸变屈曲应力降低,从而改变檩条局部失稳模式,使得檩条由局部屈曲失稳转变为畸变屈曲失稳。     

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.     

建筑物抗拔桩力学计算的实例分析

根据现行规范,阐明了抗拔桩的设计要点及注意事项,明确了抗拔桩设计的关键是配筋和裂缝控制,并且结合工程实例详细介绍了抗拔桩的设计思路,为地下建筑设计过程中结构抗浮设计工作积累了经验。     

加筋风砂土扩展基础的抗拔试验与位移控制计算

承受上拔荷载的扩展基础,可以用上拔位移或上拔荷载作为设计控制条件。在典型沙漠地区进行调研和现场采取土样,进行土工格栅与风砂土的摩擦特性试验,通过室内模型试验研究了上拔荷载作用下土工格栅加筋风砂土地基扩展基础的力学性能,包括荷载、位移、变形、破坏机理和承载能力的研究,提出了有效的土工格栅加筋形式:平铺一层和二层土工格栅。在上述研究基础上,对上拔位移机理进行了分析研究,提出了上拔位移计算模型和上拔位移控制的分析计算方法。     

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。     

砂土中扩底应力对深埋扩底抗拔桩承载力的影响

采用极限平衡法计算深埋扩底抗拔桩的承载力,需要确定破坏面的形状参数和应力条件。针对已有模型试验的研究结果,结合不同桩长扩底抗拔桩统一破坏模式,对上述问题进行了初步探讨。基于应力莫尔圆研究认为,仅考虑自重应力条件得到的破坏面法向应力明显小于扩底附近的实际破坏面应力条件,导致破坏面影响高度计算结果偏大。基于模型试验的试验结果,对扩底应力的增强系数进行了反算,该值在1.3到2.7之间,比被动土压力系数3.4要小,对扩底角度变化不敏感。只是初步的机理探讨,考虑到深埋扩底桩的埋深影响,该问题值得进一步深入研究。     

软土地基微型桩抗拔试验研究

微型桩具有布置形式灵活,施工机械小型化,经济环保等优点,针对杆塔基础交通不便、环保要求高、地质情况差等工程特点,微型桩的优势在杆塔基础中能够得到充分发挥。承受上拔荷载是杆塔基础的主要功能之一,而以往对软土地基上微型桩抗拔特性的研究较少。通过软土地基中微型桩单桩和群桩的抗拔试验,研究施工工艺对微型桩单桩抗拔承载力的影响,实测单桩桩身轴力和桩侧摩阻力的分布,研究微型桩荷载—位移特性、群桩效应系数等。试验结果表明采用二次注浆工艺能显著提高微型桩抗拔极限承载力,有效地减小抗拔桩位移;由于二次注浆对桩周土体加固作用,群桩的荷载–位移曲线呈"缓变型",桩土共同作用的群桩效应明显,实测群桩效应系数相对较小,这对于软土地基上杆塔基础的设计具有参考价值。     

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.     

上拔与水平力组合作用下加筋风积沙斜柱扩展基础试验

在土工格栅加筋风积沙、土工网垫加筋风积沙以及未加筋风积沙地基条件下,开展了3个不同尺寸斜柱扩展基础上拔水平力组合荷载作用下9个工况的现场试验。根据基础的顶部荷载与位移、基底土压力变化以及地表裂缝分布情况,分析了基础尺寸、加筋材料及其铺设方式对风积沙斜柱扩展基础承载性能的影响规律,研究了加筋风积沙地基的破坏机理。结果表明：加筋风积沙斜柱扩展基础上拔水平力组合荷载作用下①其承载机理是基础底板上方地基压缩挤密-塑性区出现并进一步发展-局部剪切破坏的渐进破坏过程,且地基破裂面具有不对称性;②土工格栅提高了风积沙地基的抗拔和抗倾覆的承载能力和抗变形能力,且铺设层间距越小,改善效果越好;土工网垫由于其易变形特点,不能提高甚至降低了风积沙地基承载能力;③降低基础露头高度、增加基础埋深、扩大基础底板尺寸均可有效提高基础上拔和水平承载力。     

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.     

深埋纯地下建筑不同抗拔桩型承载性状试验研究

通过对某沿海城市500 kV深埋地下变电站不同抗拔桩型的现场试验研究,对扩底抗拔桩和桩侧压浆等截面抗拔桩两种不同抗拔桩型的承载力性状进行了分析,研究了两种不同桩型的荷载传递规律和承载力提高机理。本文认为,对于含砂丰富地层且单桩承载力要求较高的长桩,宜优先选用压浆桩,而且在技术经济条件相当的情况下,选择桩侧压浆方案可以节省工期;对于以软土或黏土为主的地层或桩长较短的情况,扩底桩则比压浆桩更具优势。     

蚌埠隆起航磁构造特征和进一步找矿方向

蚌埠地区西贾庄铁金矿的发现,说明深部找矿也有广阔前景。利用1∶2. 5万航磁测量,获取区内基底、主干断裂信息;结合重力场信息,总结出磁力和重力高背景下的双低地段是酸性隐伏岩体的信息;磁异常对已知矿床反映明显,负背景场中的突出磁异常和剩余重力异常梯度带复合部位是成矿有利地区,异常带边部局部异常和鼻状突出部位是有利成矿地段。依据磁场信息和重力场信息,综合分析认为怀远—马头城一带、刘府—凤阳、刘府镇—大庙三地新发现磁异常,其找矿潜力很大,旧城—西阳集和万福—河溜镇两处覆盖区磁异常也是值得找矿地段,由此划分找矿远景区。所获取成果对进一步找矿具有指导意义。     

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.