Elastic buckling of elliptical tubes

Hot-rolled and cold-formed structural steel tubular members of elliptical cross-section have recently been introduced into the construction sector. However, there is currently limited knowledge of their structural behaviour and stability, and comprehensive design guidance is not yet available. This paper examines the elastic buckling response of elliptical hollow sections in compression, which has been shown to be intermediate between that of circular hollow sections and flat plates. The transition between these two boundaries is dependant upon both the aspect ratio and relative thickness of the section. Based on the results of numerical and analytical studies, formulae to accurately predict the elastic buckling stress of elliptical tubes have been proposed, and shortcomings of existing expressions have been highlighted. Length effects have also been investigated. The findings have been employed to derive slenderness parameters in a system of cross-section classification for elliptical hollow sections, and form the basis for the development of effective section properties for slender elliptical tubes.     

Three-Dimensional Stress Analysis of Adhesive Butt Joints of Solid Cylinders Subjected to External Tensile Loads

This paper deals with a three-dimensional stress analysis of adhesive butt joints of similar solid cylinders subjected to external tensile loads. Similar adherends and an adhesive bond are replaced with finite solid cylinders in the analysis. Stress distributions on adhesive joints are analyzed strictly by using the three-dimensional theory of elasticity. The effects of stiffness, thickness and Poisson's ratio of the adhesive bonds and of external load distribution on the normal and the shear stress distributions are shown by numerical calculations. In addition, the analytical result is compared with the result obtained by F.E.M. It is seen that they are in fairly good agreement.     

Stress concentration analyses of bi-material bonded joints without in-plane stress singularities

The problem of stress concentration in bi-material bonded joint is investigated under the condition of without stress singularities. Disappearance conditions of stress singularity near interface corners and edges are determined based on analyses of eigenvalue equations. Straight-side and curved interface of materials are designed for the bi-material models to avoid singular stress fields around the interface corner and edge. Assuming that one stress component or combined stresses are responsible for failure at or near the interface, the stress concentration becomes critical for the design of bi-material joints with higher interfacial strength. Numerical results show that the stress state near the interface depends strongly on both the interface geometry and the combination of materials, and stress concentration may always occurs at or near the interface. Emphasis is placed on the necessity for geometric optimization of an interface in order to design singularity-free junction with higher interfacial strength.     

广西康密劳合资企业的技术进步

论述了技术进步与企业生存发展的关系。系统地回顾了广西康密劳成立以来 ,通过不懈努力 ,在实现技术进步方面所作出的努力及产生的积极效果     

高强度耐候钢Q355对接接头多次焊修力学行为研究

通过焊接工艺评定试验以及疲劳试验,分析高强度耐候钢Q355GNHD正常对接接头和3次焊修接头的显微组织、常规力学性能以及疲劳结果差异。结果表明:3次焊修接头熔合良好,显微组织未见马氏体;3次焊修焊接接头和正常焊接接头的拉伸、弯曲及硬度等常规力学性能未见明显差异;3次焊修接头过热区组织粗大,冲击功有所降低,但均满足标准规定的焊接接头技术条件;两种焊接接头的疲劳性能相近,符合设计要求。     

Joint optimization of spectrum sensing and accessing in multiuser multiple‐input single‐output cognitive networks

In this paper, a joint spectrum sensing and accessing optimization framework for a multiuser cognitive network is proposed to significantly improve spectrum efficiency. For such a cognitive network, there are two important and limited resources that should be distributed in a comprehensive manner, namely feedback bits and time duration. First, regarding the feedback bits, there are two components: sensing component (used to convey various users' sensing results) and accessing component (used to feedback channel state information). A large sensing component can support more users to perform cooperative sensing, which results in high sensing precision. However, a large accessing component is preferred as well, as it has a direct impact on the performance in the multiuser cognitive network when multi‐antenna technique, such as zero‐forcing beamforming, is utilized. Second, the tradeoff of sensing and accessing duration in a transmission interval needs to be determined, so that the sum transmission rate is optimized while satisfying the interference constraint. In addition, the aforementioned two resources are interrelated and inversive under some conditions. Specifically, sensing time can be saved by utilizing more sensing feedback bits for a given performance objective. Hence, the resources should be allocation in a jointly manner. Based on the joint optimization framework and the intrinsic relationship between the two resources, we propose two joint resource allocation schemes by maximizing the average sum transmission rate in a multiuser multi‐antenna cognitive network. Simulation results show that, by adopting the joint resource allocation schemes, obvious performance gain can be obtained over the traditional fixed strategies.Copyright © 2014 John Wiley & Sons, Ltd.     

相邻RC框架结构地震碰撞过程模拟与初步分析

相邻建筑物碰撞是指地震作用下其间距无法满足相对位移要求时造成的侧向撞击,常常导致或加剧结构破坏。选取Hertz-damp接触单元模型,推导了考虑碰撞的结构动力方程,模拟了相邻钢筋混凝土（RC）框架结构地震碰撞过程。分析碰撞过程,并利用梁柱单元破坏指数的变化解释了相邻RC框架结构地震碰撞破坏机理,指出地震碰撞破坏作用不完全随防震缝宽度的增加而降低。     

基于结构性黄土联合强度的邓肯–张非线性本构模型

基于Mohr–Coulomb强度准则建立的邓肯–张非线性本构模型可以较好地反映土体抗剪强度特性,但是不适宜反映土体的抗拉强度特性。为了合理反映结构性黄土的抗拉强度,首先,通过在邓肯–张非线性本构模型中引入联合强度准则,基于联合强度准则重新确定了土的强度(1 3?-?)f,从而对破坏应力比Rf进行了修正;然后,用修正后的破坏应力比Rf重新确定了切线变形模量Et;最后,用修正后的切线变形模量Et对切线泊松比νt进行了修正,从而建立了基于联合强度理论的邓肯–张模非线性本构模型,为邓肯–张非线性本构模型在结构性黄土边坡的稳定性研究中,合理考虑结构性黄土的抗拉强度特性的作用提供了一种新的方法和途径。     

沉管隧道–接头–场地土振动台试验研究

为了解沉管隧道及其接头在地震作用下的动力响应,以中国广州洲头咀沉管隧道工程为背景,在北京工业大学九子振动台台阵系统上开展了1∶60比例尺大型沉管隧道–接头–场地土振动台模型试验。试验中模型箱采用装配式连续体刚性模型箱,其尺寸为7.7 m(长)×3.2 m(宽)×1.2 m(高),试验中输入地震动时程采用El Centro、Taft、天津及广州人工地震动记录,输入方向为水平横向和水平纵向一致地震动激励。设计了用于模拟沉管隧道接头的构件,并利用拉压传感器和激光位移计测得接头处所受轴向力及变形。结果表明:不同段模型结构测得的加速度及其傅立叶幅值谱有差别,且隧道结构地震响应不是随其自身特性振动,而是服从于周围土体的地震响应;不同强度地震动激励下,不同接头的受力情况可以为沉管隧道的抗震设计提供有价值的参考;不同强度地震激励下,不同接头的位移变化趋势基本上遵循J1接头位移最大,J3接头位移次之,J2接头位移最小,由于J2接头位于中间,这样的变化规律使得整个隧道沿纵向变形更加协调;水平纵向和水平横向一致地震激励下,每个接头的正反方向位移变化趋势基本平行,本次试验结果换算到原型结构,隧道接头止水带处于安全范围不会漏水。