高强钢焊接箱形截面压弯构件局部稳定试验研究

为研究高强钢压弯构件的局部稳定性能，对5个Q460C和5个Q690D钢焊接箱形截面构件进行了单向偏压试验，分析了其破坏形式、局部稳定性能以及承载力；将实测承载力与欧洲规范EN 1993-1、我国标准GB 50017—2017和美国规范ANSI/AISC 360-16相关公式计算结果相比较，以验证各规范对Q460C钢和Q690D钢焊接箱形截面压弯构件屈曲后强度计算的适用性。研究结果表明：所有高强钢焊接箱形截面压弯构件均在柱中附近发生局部屈曲破坏；由轴向压力-轴向压缩变形或轴向压力-水平位移曲线可知，其为极值点失稳；构件的轴向压力-水平位移或轴向压力-应变曲线的形状和局部屈曲模式有关；在翼缘宽厚比为28.1～56.3、腹板高厚比为40.2～80.4、偏心距为20～50 mm范围之内，EN 1993-1和GB 50017—2017中的屈曲后强度计算公式仍然适用于Q460C和Q690D钢焊接箱形截面压弯构件，而ANSI/AISC 360-16中的相关公式需要进一步修正。     

高强钢焊接工字形截面压弯构件局部-整体相关屈曲分析北大核心CSCD

采用有限元法分析了Q460钢腹板高厚比超限(h w/t w=60,70,80,100,120)的焊接工字形截面压弯构件的极限承载力,研究了腹板高厚比、翼缘宽厚比、构件长细比和相对偏心率对其屈曲性能的影响,提出了计算Q460钢压弯构件局部-整体相关屈曲极限承载力的修正公式。研究表明,有限元法能很好地分析腹板高厚比超限的工字形截面压弯构件非线性屈曲性能;腹板高厚比增大,极限承载力提高,腹板屈曲后强度保持能力增大,延性增大。相反,翼缘宽厚比增大,构件极限承载力减小,腹板屈曲后强度保持能力减弱,延性降低;长细比增加,构件刚度明显减小,极限承载力降低,但延性却增大;相对偏心率增大,弯曲变形起主导作用,跨中挠度急剧增加,而轴力的变化相对变缓。提出的修正公式计算结果与有限元结果吻合很好。     

Q460高强度钢焊接工字形截面压弯构件局部和整体弯扭相关屈曲有限元分析

采用有限元法分析了高厚比超限的Q460钢焊接工字形截面压弯构件局部和整体弯扭相关屈曲的极限承载力,研究了腹板高厚比、翼缘宽厚比、构件长细比和荷载相对偏心率对其相关屈曲承载力的影响,提出了Q460钢焊接工字形截面压弯构件的局部和整体弯扭相关屈曲极限承载力修正计算公式。研究表明:有限元模型能够较好地模拟焊接工字形截面压弯构件局部和整体弯扭相关屈曲极限承载力;腹板高厚比、翼缘宽厚比、构件长细比及荷载相对偏心率增大均会导致构件无量纲化极限承载力降低;基于《钢结构设计规范》(报批稿)GB 50017提出的修正公式计算值与有限元计算值吻合较好。     

高强钢焊接薄壁箱形截面双向压弯构件的稳定承载力

采用ANSYS软件建立有限元模型分析了Q460钢焊接薄壁箱形截面双向弯曲压弯构件的极限承载力。分析中考虑几何缺陷和材料缺陷,以及几何非线性和材料非线性的影响。同时,研究了构件长细比和板件宽厚比对极限承载力的影响;探明构件达到极限承载力时真实的应力分布状态;提出了采用毛截面计算其承载力的简单计算公式;收集可获得的试验结果以验证提出的计算公式。研究表明,建立的有限元模型能够很好地模拟焊接箱形截面双向偏心压弯构件的局部-整体相关屈曲性能;在大部分情况下,无量纲极限承载力与构件长细比和板件宽厚比近似为线性关系;构件达到极限承载力时还处于弹性阶段;轴力和双向弯矩之间的相关曲线也近似为线性;引入屈服强度修正系数后,基于线性相关关系的计算公式能够很好地预测Q460钢薄壁双向压弯构件的极限承载力;该公式还可推广到普通钢构件和更高强度的钢构件。     

Q460高强钢焊接箱形压弯构件极限承载力试验研究

为研究Q460高强钢中厚板焊接箱形压弯构件的整体失稳极限承载力,采用11mm厚国产Q460高强钢中厚板制作7个焊接箱形压弯试件,试件截面宽厚比分别为18、12、8,长细比分别为35、55、80。试验内容包括:Q460低合金高强钢的材性试验,三种焊接截面残余应力测试,各试件初始几何缺陷测量及极限承载力试验,从而进行了面内整体失稳压弯构件的极限承载力试验研究;并且把试验结果与我国现行钢结构设计规范计算值相比较。试验研究结果表明:Q460低合金高强钢材性具有高强度,塑性性能良好等特点;Q460高强钢焊接箱形截面残余应力分布形式与普通钢材箱形焊接截面分布基本相同,但是残余应力比降低;压弯构件极限承载力试验结果明显高于现行钢结构规范设计公式计算值,所以应对Q460高强钢焊接箱形压弯构件进行近一步参数分析研究,并得出其实用设计方法。     

高强钢焊接方形截面偏压构件整体和局部相关屈曲承载力分析

采用有限元软件ANSYS分析了Q460钢宽厚比超限的焊接方形截面偏压构件的极限承载力,研究了板件宽厚比、构件长细比和偏心距对构件极限承载力的影响。基于数值模拟结果,提出了适用于Q460钢宽厚比超限焊接方形截面偏压构件极限承载力的计算方法。研究结果表明,考虑几何缺陷及残余应力的有限元模型能准确地预测焊接箱形截面偏压柱局部-整体相关屈曲的极限承载力;宽厚比超限的高强钢压弯构件的Pu/Py与Mu/Mp相关曲线基本为直线,且随着板件宽厚比(或构件长细比)的增大,Pu/Py和Mu/Mp不断下降。提出的建议计算方法与有限元计算结果符合良好。     

高强钢焊接箱形截面双向压弯构件屈曲后强度设计方法研究

相比于《钢结构设计规范》(GB 50017—2003),《钢结构设计标准》(GB 50017—2017)取得了较大的进步,允许板件先于构件发生屈曲,并利用了板件屈曲后强度。GB 50017—2017对轴心受压构件、受弯构件和单向压弯构件均给出了屈曲后强度计算公式,但对双向压弯构件却未给出计算公式。分析了已有的高强钢压弯构件屈曲后强度计算方法,基于GB 50017—2017中的压弯构件稳定承载力计算公式,提出了双向压弯构件屈曲后强度计算公式,收集已有高强钢焊接箱形截面压弯构件屈曲后强度的试验和有限元结果以验证公式的有效性。研究结果表明,提出的计算公式能在大部分构件长细比和板件宽厚比范围内偏于保守地预测名义屈服强度为460 MPa和690 MPa的高强钢焊接箱形截面双向压弯构件的屈曲后强度。     

高强钢焊接薄腹工形截面双向压弯构件的稳定性

应用ANSYS有限元,分析了Q460高强钢焊接薄腹工形截面双向压弯构件的稳定性能,提出了可供实际应用参考的设计公式。分析中考虑的主要参数有腹板高厚比,构件长细比,翼缘宽厚比及荷载偏心率。结果表明,对受压为主的构件,腹板局部屈曲对构件稳定承载力影响较大,而对受弯为主的构件,这一因素对构件稳定承载力影响较小。有限元分析结果与现行规范方法计算结果比较表明,目前规范方法尚不能较好地计算高强钢焊接薄腹工形截面双向压弯构件的稳定承载力,因而提出了修正直接强度法,该法精度较好且偏于安全。     

高强钢压弯和受弯构件计算模式不定性研究

介绍了《高强钢设计规程》(征求意见稿)中关于压弯构件和受弯构件计算的相关条款,并与我国现行GB 50017—2003《钢结构设计规范》进行了比较。收集了目前高强钢压弯构件、受弯构件的试验,对试验进行了有限元模拟。在此基础上,应用有限元模型对高强钢焊接截面880组压弯构件、460组受弯构件的极限承载力进行了计算。将极限承载力的有限元计算结果和规范公式的计算值进行了比较,对高强钢焊接截面压弯构件和受弯构件的计算模式不定性做了数理统计分析,得到了高强钢压弯和受弯构件计算模式不定性的统计参数,为下一步提出高强度钢材材料设计指标提供了依据。     

高强钢薄壁箱形截面压弯构件极限承载力研究

利用数值模拟方法分析了18Mn2Cr Mo BA高强钢薄壁箱形截面(由槽形钢板对焊而成)压弯构件的极限承载力,研究了长细比、翼缘宽厚比、截面边长比3个参数对薄壁箱形截面构件极限承载力的影响。在数值模拟计算和对轴心受力、受弯构件研究的基础上,提出了适用于18Mn2Cr Mo BA高强钢薄壁箱形截面压弯构件极限承载力的计算方法。研究结果表明:随着长细比的增大,弯矩-轴力相关曲线由上凸变为下凹,翼缘宽厚比、截面边长的增大都会降低构件极限承载力,各参数之间相互影响。提出的建议计算方法与有限元计算结果符合较好。     

Overall buckling behavior of all-steel buckling restrained braces

One of the key requirements for the desirable mechanical behavior of buckling restrained braces (BRBs) under severe earthquake loading is to prevent global buckling until the brace member reaches sufficient plastic deformation and ductility. This paper presents finite element analysis results of the proposed all-steel buckling restrained braces. The proposed BRBs have identical core sections but different buckling restraining mechanisms (BRMs). The objective of the analysis is to conduct a parametric study of BRBs with different amounts of gap (between the core and the BRM) and initial imperfections to investigate the global buckling behavior of the brace. The results of the analysis showed that BRM flexural stiffness could significantly affect the global buckling behavior of a brace, regardless of the size of the gap. In addition, a minimum ratio of the Euler buckling load of the restraining member to the yield strength of the core, P_e/P_y is suggested for design purposes. This ratio is the principal parameter that controls the global buckling of BRBs.     

Local buckling and post-local buckling redistribution of stress in slender plates and sections

Cold-formed open steel sections are comprised of component plates termed stiffened elements (webs) and unstiffened elements (flanges). The local buckling and post-local buckling behaviour of sections may be determined from the behaviour of the component plates. Much research effort has documented the theoretical elastic local buckling of plates and sections, however until recently few experimental studies have been reported on the local buckling and post-local buckling behaviour of unstiffened plates. This paper presents experimental and numerical studies of unstiffened plates and sections that contain them in both compression and bending, and in particular analyses the mechanism that provides post-buckling strength. It is shown that, as with stiffened elements, the mechanism is the post-local buckling redistribution of stress, however unlike stiffened elements this redistribution can occur to such an extent that tensile stresses commonly form in axially compressed slender elements. The stress distributions at ultimate are compared with current international cold-formed steel specifications.     

Interaction of local buckling and lateral torsional buckling of T-shaped cantilevering beams

The structural resistance of T-shaped cantilevering beams is governed by combined stability phenomena of lateral torsional buckling and local buckling. The aim of this paper is to show the applicability of the “general method” [1], to the prediction of the combined stability behaviour for single symmetric cross-sections. Since the approach is based on the modal shape and modal edge-moment distribution, it does not distinguish between local and lateral torsional buckling, but considers both phenomena in a single trail. A buckling curve for tapered T-shaped members is suggested and boundaries of applicability investigated.     

Local buckling restraint condition for core plates in buckling restrained braces

Buckling Restrained Braces (BRBs) are commonly used as bracing elements in seismic zones. A key limit state governing BRB design is to prevent flexural buckling. However, when the wall thickness of the steel tube restrainer is relatively small compared to the cross-section of the core plate, the restraint conditions against the local buckling of the core plate can be critical for the stability and strength of the BRB. In this study, cyclic loading tests and numerical analyses of BRBs were carried out using various tube restrainer configurations to investigate the influence of local buckling of the restrainer on BRB strength and ductility.     

Symmetries of elastic buckling

The paper explores the role of symmetry in the buckling of elastic structural systems, both at distinct points of bifurcation, and when such points coincide or interact. Arch, stiffened and unstiffened plate, and cylinder buckling models are introduced as examples.     

Inelastic beam buckling experiments

The paper describes a series of experiments on the buckling of simply supported laterally continuous I-beams in the inelastic range. Nine beams were tested in three groups of three, each group having a different predominant moment gradient. Points of load application were prevented from moving laterally and twisting. Measurements of geometrical and material imperfections are included in this report. Results of a number of subsidiary experiments such as plastic moment and stub column tests are also presented. The results add to the small amount of test data presently available on such beams and provide a comparison with theoretical predictions. In particular, support is shown for the theoretical curves of Nethercot and Trahair and for the current trend to multiple design curves based on moment gradient.     

A story buckling method for evaluating system buckling load of plane sway frames

With the intension of developing a simple method for system buckling analysis for engineering practice, a story buckling method for evaluating the system buckling load of a plane rigid frame is suggested. The method is developed based on the idea that at lower modes a plane sway frame buckles in story and story stiffness is getting to zero as the system getting close to the corresponding mode of buckling at that story. The stiffness of any story of a plane sway frame can be found with the stiffness without loading and then modified by a negative stiffness which represents the effect of vertical loads on the horizontal stiffness. P-Δ effect is first considered independently by letting the modified stiffness equal to zero and the system buckling load by first order analysis is obtained. To take P-δ effect into account, the buckling load from the first order analysis is modified with a modification factor and an estimation of buckling load of the whole system is obtained. Application examples are presented and the results are compared with those from FEA of the whole system. The simplicity and accuracy of the suggested method are demonstrated. The restraints of the method for application are discussed.     

Lateral-distortional buckling of tee-section beams

A fine element method that incorporates plate behaviour is developed for modelling the lateral-distortional buckling of tee-section beams. The method is shown to agree well with independent buckling results for tee-beams. Since relatively few elements are needed to obtain satisfactory convergence, the method is efficient computationally. The finite element analysis is used to study the elastic distortional buckling of tee-beams of practical geometry under moment gradient. The disparities found between the elastic flexural-torsional and distortional buckling moments are discussed.     

Distortional buckling of castellated beams

In previous studies of the structural behavior of castellated steel beams, different possible failure modes of these extensively used structural members have been identified and investigated. On the other hand, during the past 25 years or so, a proliferation of research work has been undertaken on the distortional buckling of steel members. Nonetheless, no studies are found in the literature on the distortional buckling of castellated beams. Accordingly, tests of six full-scale castellated beams are described, in which the experimental investigation of distortional buckling was the focus of interest. In addition to the test strengths, the accurate critical loads of the beams have been obtained using some extrapolation techniques, and ultimately a comparison has been made between the obtained test loads and some theoretical predictions.