卷边加强开孔的冷弯型钢受弯构件的性能、优化及设计

冷弯型钢(CFS)受弯构件的腹板常常开圆孔,用于通过管道、电缆、水管设施和安装横向支撑等。传统在冷弯型钢腹板上开孔的构件的翼缘是不带卷边的,最近研发出新型具有加劲卷边的C型截面冷弯薄壁型钢抗弯构件。然而,目前对于新型C型截面构件的研究尚不深入,有用的试验也有限。该文采用有限元分析方法分析加劲开孔的冷弯型钢薄板和典型C截面构件的稳定性。基于弹性屈曲分析方法得出孔洞的最佳剖面,并将其应用于标准C截面构件。采用屈曲后有限元分析方法确定构件的挠曲强度。结果表明加劲孔洞能够大大提高C截面CFS挠曲强度。计划提出新的设计准则以准确计算孔洞剖面最佳的新型C截面构件的挠曲强度。     

Cold-formed steel flexural member with edge stiffened holes: Behavior,optimization, and design

Circular holes are commonly found on the web of cold-formed steel (CFS) flexural members for piping, electric-wiring, plumbing, or installing lateral bracing, etc. Traditional holes on CFS members are flat bunched without edge lips. A new generation of CFS C-section flexural members with edge stiffened holes was recently developed by the industry. However, research on the new generation C-section members is underdeveloped and available test results are limited. This paper presents finite element analyses to study on the stability of cold-formed steel thin plates and typical C-section members when edge stiffened circular holes are placed on those plates or members. Based on the elastic buckling analyses, the optimized profiles of the holes are obtained and then applied to standard C-section flexural members. The post-buckling finite element analysis is utilized to determine the flexural strength of those members. The results indicate that the stiffened holes can significantly improve the flexural strength of CFS C-sections. New design provisions are proposed to accurately predict the flexural strength of the new generation C-section flexural members with the optimized hole profiles.     

Buckling of orthotropic plates with free and rotationally restrained unloaded edges

Solutions and parametric studies are presented for the buckling of rectangular plates whose axes of material orthotropy coincide with the axes of the plate. The results presented apply to homogeneous orthotropic plates, stiffened orthotropic plates, and laminated composite material plates having flexural orthotropy (i.e. single ply and multiply unidirectional, and symmetric cross-ply composite plates). The plates considered are subjected to uniform uniaxial compression and simply supported on the loaded edges. The boundary conditions are different on the two unloaded edges; one edge being free and the other edge being elastically restrained against rotation. Parametric studies showing the effect of the orthotropic properties of the plate materials, the plate aspect ratio, the rotational restraint of the one unloaded edge and the buckle half-wavelength are discussed. Results in the form of nondimensional buckling curves are given in terms of orthotropy ratios and in terms of properties of common unidirectionally reinforced composite material. The use of the solution in conjunction with experimental data to predict the edge rotational restraint coefficient for thin-walled composite material beams is described.     

Nonlinear bending analysis of thin circular plates by differential quadrature

The behavior of thin, circular, isotropic elastic plates with immovable edges and undergoing large deflections is investigated by the numerical technique of differential quadrature. Approximate results are determined with the aid of a symbolic manipulation computer program and a Newton-Raphson technique to solve the nonlinear systems of equations. Bending stresses, membrane stresses, and deflections are calculated for clamped and simply supported flexural edge conditions and for a uniform pressure load and a concentrated load at the center.     

Evaluation of elastic in-plane flexural rigidity of unstiffened multiplanar CHS X-joints

Tubular structures have been widely applied in offshore structures and civil buildings in past decades. Some research has been carried out on rigidity of unstiffened circular hollow section (CHS) joints with various types, e.g. T-, Y-, K- and X-joints by former researchers. However, limited investigations on the in-plane flexural rigidity of multiplanar CHS X-joints which are commonly used in single-layered latticed structures are found in available literatures. In this paper, first a finite element model was calibrated through comparison with test results, and then a numerical parametric study on elastic axial rigidity of multiplanar unstiffened CHS X-joints was carried out using the calibrated models with package ABAQUS. Based on the parametric results, an in-plane flexural rigidity formula for the joints was fitted. Finally, a comparison among the different formulae in predicting joint rigidity of unstiffened CHS X-joints was carried out, which indicated a good reliability of the proposed formula.     

A parametric study on the longitudinal stiffeners of web panels

Optimum location and dimensions of longitudinal stiffeners in web plates under in-plane bending are investigated. This parametric study is performed by numerical simulation utilizing finite element method. Several plates having various aspect ratios are analyzed and an equation for minimum required second moment of area of stiffeners is presented and compared to that recommended by AASHTO. Also, it is shown that the optimum location of stiffener mainly depends on its relative flexural rigidity.     

腹板纵向加劲肋的参数研究

采用有限元数值模拟方法,对处于平面内弯曲的腹板纵向加劲肋的最佳位置和尺寸进行研究。分析对象为具有各种不同纵横比的平板,提出计算最小次弯矩的公式,并将其与AASHTO推荐的计算方法对比。结果显示,腹板加劲肋的最佳位置主要取决于其相对抗挠刚度。     

Buckling analysis of skew laminate plates subjected to uniaxial inplane loads

Elastic stability of skew composite laminate plates subjected to uniaxial inplane compressive forces has been studied. The critical buckling loads of the skew laminate plates are carried out by the bifurication buckling analysis implemented in finite element program ABAQUS. The effects of skew angles, laminate layups, plate aspect ratios, plate thicknesses, central circular cutouts, and edge conditions on the buckling resistance of skew composite laminate plates are presented.     

冷弯型钢C形截面受弯构件平面内稳定性能研究

为了研究冷弯型钢受弯构件平面内的稳定性能,对直卷边和斜卷边的冷弯型钢C形截面受弯构件分别进行了试验研究和有限元参数分析。试验研究和有限元分析均包含构件纯弯和非纯弯两部分。研究结果表明,多数构件在非纯弯作用下的抗弯承载力高于纯弯作用下的,但也有部分以局部和畸变相关屈曲为主的构件在纯弯作用下的抗弯承载力略高。屈曲模式是影响构件抗弯承载力的重要因素,构件以畸变屈曲为主时,非纯弯作用下的抗弯承载力明显高于纯弯作用下的。     

Elasto-plastic analysis of circular concrete-filled steel tube stub columns

This paper presents a full-range elasto-plastic analysis using continuum mechanics on circular concrete-filled steel tube (CFT) stub columns under concentric loading condition, covering concrete strengths from 30 to 120 MPa and diameter-to-wall thickness ratio (D/t) greater than 20. Firstly, a constitutive model was employed for laterally-confined concrete under axial compression. A continuum mechanics model was then established and the corresponding elasto-plastic analysis was performed through a FORTRAN program. This model is able to present full-range stress-strain developments in axial, radial and perimeter directions and further clarify the load sharing pattern between the steel tube and the concrete core. Based on the proposed model, parametric analysis was conducted to investigate the effects of material strengths and sectional steel ratio on the triaxial stress-strain developments and the load sharing pattern. In addition, the model was simplified to predict the ultimate capacity and the load-axial strain relationship of CFT composite sections and the results are in good agreement with experiments. Further comparisons were made of the approach developed by Han et al. 2004 and the existing international standards.     

Buckling of annular plates elastically restrained against rotation along edges

The problem of elastic buckling of thin annular plates under in-plane radial loads along either free or simply supported with elastic rotational restraints at inner and outer edges has been analysed. A variant of the classical energy methods has been used to obtain a comprehensive set of new buckling results for several combinations of boundary conditions with partial rotational fixity. Results for the special case of simply supported full circular plates with elastic rotational restraint are also obtained by making the inner edge free and permitting the inner radius to become very small.     

Buckling analysis of thin circular FG plates made of saturated porous-soft ferromagnetic materials in transverse magnetic field

This study presents the buckling analysis of soft ferromagnetic FG circular plates made of poro material. Equilibrium and stability equations of a poro circular plate in transverse magnetic field are derived. This study analyzes the poroelastic instability of clamped edge ferromagnetic plates subjected to magnetic loadings. The geometrical nonlinearities are considered in the Love–Kirchhoff hypothesis sense. In this paper the effect of pore pressure on critical magnetic field of plate and the effect of important parameters of poroelastic material on buckling capacity are investigated. Also the compressibility of fluid and porosity on the buckling strength are being investigated.     

An analytical analysis of the full-range behaviour of grouted rockbolts based on a tri-linear bond-slip model

This paper presents an analytical solution for predicting the full-range mechanical behaviour of grouted rockbolts in tension based on a realistic tri-linear bond-slip model with residual bond strength at the grout–bolt interface. The full-range behaviour consists of five consecutive stages: elastic stage, elastic–softening stage, elastic–softening–debonding stage, softening–debonding stage and debonding stage. For each stage, closed-form solutions for the load–displacement relationship, interfacial shear stress distribution and bolt axial stress distribution along the bond length were derived. The ultimate load and the effective anchor length were also obtained. The analytical model was calibrated and validated against two pullout experimental studies. The predicted load–displacement curves as well as the distributions of the interfacial shear stress and the bolt axial stress are in close agreement with test results. A parametric study is also presented, providing insights into the behaviour of the rockbolts.     

往复荷载作用下矩形钢管混凝土构件力学性能的研究

以往 ,国内外学者对矩形钢管混凝土构件滞回性能的研究尚少见报道。本文以矩形钢管混凝土构件截面高宽比和轴压比为主要参数 ,进行了 3 0个构件滞回性能的实验研究。利用数值方法分析了矩形钢管混凝土构件的滞回性能 ,理论计算结果与实验结果吻合较好。利用数值方法 ,系统分析和考察了轴压比、长细比、含钢率、截面高宽比、钢材屈服强度和混凝土强度等参数对滞回曲线骨架线的影响规律 ,在此基础上 ,提出了矩形钢管混凝土构件弯矩 -曲率和P -Δ滞回关系模型 ,以及位移延性系数的简化计算方法。     

Experimental and numerical investigation of cold-formed lean duplex stainless steel flexural members

Experimental and numerical investigation of cold-formed lean duplex stainless steel flexural members is presented in this paper. The test specimens were cold-rolled from flat plates of lean duplex stainless steel with the nominal 0.2% proof stress of 450 MPa. Specimens of square and rectangular hollow sections subjected to both major and minor axes bending were tested. A finite element model has been created and verified against the test results using the material properties obtained from coupon tests. It is shown that the model can accurately predict the behaviour of lean duplex stainless steel flexural members. An extensive parametric study was carried out using the verified finite element model. The test and numerical results as well as the available data on lean duplex beams are compared with design strengths predicted by various existing design rules, such as the American Specification, Australian/New Zealand Standard, European Code and direct strength method for cold-formed stainless steel. Reliability analysis was performed to evaluate the reliability of the design rules. It is shown that these current design rules provide conservative predictions to the design strengths of lean duplex stainless steel flexural members. In this study, modified design rules on the American Specification, Australian/New Zealand Standard, European Code and direct strength method are proposed, which are shown to improve the accuracy of these design rules in a reliable manner.     

Flexural behaviour of stainless steel oval hollow sections

Structural hollow sections are predominantly square, rectangular or circular in profile. While square and circular hollow sections are often the most effective in resisting axial loads, rectangular hollow sections, with greater stiffness about one principal axis than the other, are generally more suitable in bending. Oval or elliptical hollow sections (EHS) combine the aesthetic external profile of circular hollow sections with the suitability for resisting flexure of rectangular sections, whilst also retaining the inherent torsional stiffness offered by all tubular sections. This paper examines the structural response of recently introduced stainless steel oval hollow sections (OHS) in bending and presents design recommendations. In-plane bending tests in the three-point configuration about both the major and minor axes were conducted. All tested specimens were cold-formed from Grade 1.4401 stainless steel and had an aspect ratio of approximately 1.5. The full moment-rotation responses of the specimens were recorded and have been presented herein. The tests were replicated numerically by means of non-linear finite element (FE) analysis and parametric studies were performed to investigate the influence of key parameters, such as the aspect ratio and the cross-section slenderness, on the flexural response. Based on both the experimental and numerical results, structural design recommendations for stainless steel OHS in bending in accordance with Eurocode 3: Part 1.4 have been made.     

Ultimate strength of perforated steel plates under combined biaxial compression and edge shear loads

The present paper is a sequel to the author's papers [Paik JK, Ultimate strength of perforated steel plates under edge shear loading. Thin-Walled Structures 2007; 45: 301–6, Paik JK Ultimate strength of perforated steel plates under axial compressive loading along short edges. Ships Offshore Struct, 2007; 2(3): (in press)]. In contrast to the previous papers with the focus on edge shear or uniaxial compressive loads, the aim of the present study is to investigate the ultimate strength characteristics of perforated steel plates under combined biaxial compression and edge shear loads, which is a typical action pattern of steel plates arising from cargo weight and water pressure together with hull girder motions in ships and ship-shaped offshore structures. The plates are considered to be simply supported along all (four) edges, keeping them straight. The cutout is circular and located at the center of the plate. A series of ANSYS nonlinear finite element analyses (FEA) are undertaken with varying the plate dimension (thickness). Based on the FEA results obtained, closed-form empirical formulae of the ultimate strength interaction relationships of perforated plates between combined loads, which can be useful for first-cut estimations of the ultimate strength in reliability analyses or code calibrations, are derived.     

Whole-building behaviour of bonded post-tensioned concrete floor plates exposed to fire

This paper discusses the whole-building behaviour of post-tensioned concrete floor plates under fire conditions. Based on the results of eight fire tests on one-way spanning bonded post-tensioned concrete slab strips, recently conducted by the authors, a nonlinear finite element model was developed to model an entire typical concrete floor plate. The considered floor plate was post-tensioned using bonded tendons and was supported on traditional reinforced concrete columns. The overall objective of the study was to provide an understanding of the structural response and modes of failure of these floor plates under fire conditions. The mechanical and thermal material nonlinearities of the floor’s components, consisting of the concrete, grout, prestressing tendon, and the anchorages, as well as the reinforced concrete columns, have been considered in the model. The interface between the tendon and grout was also considered, allowing the bond behaviour to be modelled and the tendon to retain its profile shape during the deformation of the floor. The model has been validated against published finite element results on a floor plate under normal temperature conditions. The temperature distribution throughout the floor slab and supporting columns, together with the developed displacement and stress due to heating, and the overall fire resistance of the floor were predicted by the model. Furthermore, the variables that influence the structural behaviour comprising different natural fires, applied static load during fire, use of non-tensioned reinforcement, as well the difference between unbraced and braced frames were investigated in a parametric study. The study has shown that the failure mode of the floor under fire conditions is mainly due to tensile splitting along the tendons that extended to the top surface, while at ambient conditions the mode of failure is punching shear. The restraint provided by shear walls in the considered braced frame and the use of non-tensioned flexural reinforcement affected the vertical displacement behaviour under fire conditions, but did not affect the fire resistance due to the predicted tensile splitting failure mode. From the studies presented it is concluded that the design fire resistance of the floor specified in Eurocode BSEN1992-1-2 is acceptable, while that in the UK code BS8110 is unconservative and should be modified.     

Load–deflection behavior of thin-walled plates with multiple bolts in shearing

This paper presents a numerical and analytical study of the behavior of thin-walled plates connected by multiple bolts under shear. A validated finite element model has been used to perform a comprehensive set of parametric studies to investigate the effects of different design parameters on the connected plate behavior, including initial stiffness, ultimate resistance and maximum deformation at the ultimate resistance. The design parameters include edge and end distances, bolt spacing, number of bolts along and perpendicular to the loading direction and elongation limit of steel. It has been found that the existing methods for calculating the stiffness and ultimate resistance are directly applicable. The main focus of this paper is the maximum plate deformation at the ultimate plate resistance. Based on the parametric study results, it has been found that strain distributions around the bolt holes for different failure modes, as proposed by the authors for plate connected by a single bolt, are still applicable. However, it is necessary to modify the plate dimension ranges within which the different strain distributions apply to recognize the difference in failure modes for plates with different bolt arrangements.     

多螺栓连接薄壁板件抗剪(荷载-挠度)性能

对多螺栓连接薄壁板件的抗剪性能进行了数值分析。采用有限元模型对一系列复杂的参数进行分析,研究不同的设计参数对连接板件性能(包括初始刚度、极限承载力以及极限承载力状态下的最大挠度)的影响。设计参数包括:边界条件、约束条件、螺栓间距、沿加载方向和垂直于加载方向的螺栓数量以及钢材的断裂伸长率限值。结果表明:现有计算刚度和极限承载力的方法是可行的。研究重点在于极限状态下板件最大挠度。基于参数分析结果,发现了不同失效模式下螺栓孔周边的应变分布,表明作者所提出的单螺栓连接板件的应变分布仍然适用,但需要修改板件的尺寸范围,包括用于辨识不同螺栓排列下失效模式差异的应变分布。