Measurement and assessment of geometric imperfections in thin-walled panels

Thin-walled members may be subject to performance limitations arising through local or distortional buckling of slender elements comprising the cross-section of the member, or overall buckling of the member. The effects of structural instability may be aggravated by the presence of geometric imperfections in these elements. An investigation is presented into methods of measuring and assessing geometric imperfections in cold-rolled thin-walled steel panels. These methods can be used to characterise the geometry of prismatic thin-walled members that exhibit performance sensitivity due to geometric imperfections. The measurement procedures investigated include close-range photogrammetry, precise optical levelling, and the use of a co-ordinate measurement machine. The assessment procedure comprises a least-squares spectral decomposition of the measurements to characterise the imperfections existent in the panels under investigation, and estimates of the precision of the derived Fourier coefficients are used to inter-compare the three measurement procedures. The investigation has demonstrated that statistically significant imperfections may exist in thin-walled members at short and medium wavelengths, leading to a reduction in the load carrying capacity. Both optical levelling and the co-ordinate measurement machine technique can yield desirable results, but for high precision work, use of the co-ordinate measurement machine is recommended.     

Material and geometric nonlinear isoparametric spline finite strip analysis of perforated thin-walled steel structures—Analytical developments

This paper presents the analytical developments of the application of the Isoparametric Spline Finite Strip Method (ISFSM) to the material inelastic and geometric nonlinear analysis of perforated thin-walled steel structures. The general theory of the ISFSM is briefly introduced. The formulations of the kinematics, strain–displacement and constitutive assumptions are presented, and the tangential stiffness matrix is derived by applying the incremental equilibrium condition. The requirements for strip continuity and boundary conditions are also discussed. In particular, the plasticity theory and the methods to integrate the ‘rate equations’ are emphasized, and the related ‘backward Euler return method’ and use of a ‘consistent material modulus’ are highlighted. The present isoparametric spline finite strip analysis is verified against a number of analyses of perforated and non-perforated plates and plate assemblages, as described in the companion paper (Yao and Rasmussen, submitted for publication) [1], demonstrating its accuracy and efficiency for the predictions of the inelastic post-buckling behavior of perforated thin-walled steel structures.     

Material and geometric nonlinear isoparametric spline finite strip analysis of perforated thin-walled steel structures—Numerical investigations

The theoretical developments of a material inelastic and geometric nonlinear analysis by use of the isoparametric spline finite strip method (ISFSM) are presented in a companion paper (Yao and Rasmussen (submitted) [1]). In the present paper, the numerical implementation of the analysis is reported, including nonlinear solution techniques, inelastic material models, selective reduced integration strategies, convergence criteria, and solution procedures. The reliability and efficiency of the method are demonstrated by a number of numerical examples, including analyses of flat plates with different material plasticity models, a classical nonlinear shell problem, perforated flat and stiffened plates, and perforated stiffened channel section storage rack uprights.     

A simplified method for collapse capacity assessment of moment-resisting frame and shear wall structural systems

A simplified methodology for predicting the median and dispersion of collapse capacity of moment-resisting frame and shear wall structural systems subjected to seismic excitations is proposed. The method is based on nonlinear static (pushover) analysis. Simple mathematical models denoted as “generic structures” are utilized to model moment-resisting frames and shear walls. After examining a wide range of structural parameters of the generic structures, a comprehensive database of collapse fragilities and pushover curves (using ASCE 7-05 lateral load pattern) are generated. Based on the obtained pushover curves, closed-form equations for estimation of median and dispersion of building collapse fragility curves are developed using multivariate regression analysis. Comparing the estimates of the median collapse capacity calculated from the closed-form equations with the actual collapse capacities determined from nonlinear response-history analysis indicates that the simplified methodology is reliable. The effectiveness of this methodology for predicting the median collapse capacity of frame and wall structures is further demonstrated with two case studies of structural systems designed based on current seismic provisions.     

基于SMA装置的框架-受控摇摆墙结构抗震性能试验研究

该文提出一种新型的框架-受控摇摆墙结构实现形式,由SMA装置代替传统的预应力筋实现摇摆墙体的受控约束,在墙体与基础之间安装V形铰接支座实现墙体的摇摆及提供竖向支撑,并在墙体与框架柱间安装耗能连接件增强摇摆结构的耗能能力。通过一个对比框架试件和一个基于SMA装置的框架-受控摇摆墙试件的低周往复试验,对比研究所提出的新型结构形式的抗震性能、破坏模式和自复位特性。试验结果表明：基于SMA装置的框架-受控摇摆墙结构的刚度和承载能力得到显著提高,提高幅度分别达到150%和103%;耗能连接件有效地发挥延性变形特性,使结构的滞回耗能能力显著提高,提高幅度达到183%,有效地减轻主体结构梁端、柱端以及梁柱节点区的损伤;所研发的SMA装置有效地实现了预设的工作机制,为摇摆墙体的自复位提供了恢复力;摇摆墙、耗能连接件和SMA装置的参数匹配还需进一步深入研究。     

Analytical assessment of the structural performance of composite floors subject to compartment fires

The behaviour of composite steel–concrete building floors exposed to fire conditions is examined in this paper. The work represents part of a large project dealing with the numerical modelling and assessment of structural behaviour based on the fire experiments undertaken on a full-scale multi-storey steel-framed building at Cardington, UK. After providing brief details on the analytical tools and modelling approaches adopted in this investigation, the structural models constructed to simulate the fire tests are described and salient findings are highlighted. Although the detailed models provide some insight into key behavioural aspects such as the paramount influence of restraint to thermal expansion, the complex structural interactions that occur under fire conditions may not be readily demonstrated. In order to illustrate a number of underlying response mechanisms, the analytical results obtained from an idealised structural system, in which a single compartment is subjected to fire, are summarised. Assessment of the structural response using such simplified models provides a clear interpretation of the behaviour and, with further refinements, may be employed for undertaking detailed studies aimed at developing improved design recommendations.     

单层单向索结构玻璃幕墙的受力性能研究

利用大型有限元分析软件SAP2000介绍了单层单向索结构玻璃幕墙的组成,并对江苏省南通市中国近代第一城展览馆幕墙工程进行了风荷载研究,得出了一些有益的结论,为玻璃幕墙在今后的设计研究积累了丰富的资料。     

密肋复合墙体受力机理及抗震性能试验研究

密肋复合墙体是密肋壁板结构体系的主要受力构件,其受力特点与抗震性能不同于普通的混凝土构件,是密肋壁板结构体系计算理论与设计方法研究的基础核心。本文通过对密肋复合墙体在水平低周反复荷载作用下的试验研究,介绍墙体的主要破坏形态和破坏过程;分析墙体的受力特点;探讨墙体的承载能力、延性、耗能等抗震性能;提出墙体的恢复力模型。试验结果表明:墙体的破坏模式主要分为剪切型破坏、弯曲型破坏、剪切滑移型破坏、复合型破坏,其中剪切型破坏属于密肋复合墙体合理的破坏模式;墙体的破坏过程大体可分为弹性阶段、弹塑性阶段、破坏阶段,其对应不同的力学模型;墙体中肋梁、肋柱与内部填充砌块、墙板与外框具有良好的共同工作特性;墙体的恢复力模型可以采用退化四线型。研究表明:密肋复合墙体是一种轻质、高强、节能、抗震性能良好的结构受力构件。     

Effect of geometric and process variables on the performance of inclined plate settlers in treating aquacultural waste

Inclined plate settlers are used in treating wastewater due to their low space requirement and high removal rates. The prediction of sedimentation efficiency of these settlers is essential for their performance evaluation. In the present study, the technique of dimensional analysis was applied to predict the sedimentation efficiency of these inclined plate settlers. The effect of various geometric parameters namely, distance between plates (w(p)), plate angle (alpha), length of plate (l(p)), plate roughness (epsilon(p)), number of plates (n(p)) and particle diameter (d(s)) on the dynamic conditions, influencing the sedimentation process was studied. From the study it was established that neither the Reynolds criterion nor the Froude criterion was singularly valid to simulate the sedimentation efficiency (E) for different values of w(p) and flow velocity (v(f)). Considering the prevalent scale effect, simulation equations were developed to predict E at different dynamic conditions. The optimum dynamic condition producing the maximum E is also discussed.     

双孔箱形框架式地道桥的结构分析及施工方法

以某下穿铁路钢筋混凝土箱形框架式地道桥为例,对其结构特点、内力计算、设计及施工方法等方面进行了研究,得出了具体的结论,以完善双孔箱形框架式地道桥的设计和施工,并推广其应用。     

内嵌秸秆板复合墙体热工性能测试及性能优化

将秸秆板装配在由肋梁和肋柱构成框格形式的墙体中,可作为一种新型装配式节能生态复合墙体应用于村镇住宅中。通过标定热箱实验方法直接进行墙体传热系数的测试,再基于有限元软件ABAQUS对该墙体进行一维稳态传热数值模拟。对比发现,数值模拟求得的传热系数与实测值相对误差仅为8.8%。最后再针对传热系数对复合墙体的保温隔热性能进行优化分析。     

钢板墙束柱受力性能试验研究及理论分析

对3个1/2缩尺钢板墙束柱试件分别进行单调和往复加载拟静力试验,研究其在水平荷载作用下的破坏机理、抗侧刚度、受剪承载力及滞回性能;对钢板墙束柱试件建立有限元分析模型,并按照试验加载制度进行数值模拟分析,得到了钢板墙束柱试件的力学性能;在试验和有限元分析的基础上,提出了钢板墙束柱的抗侧刚度及受剪承载力理论计算式。试验、分析及计算结果表明,单调荷载作用下钢板墙束柱试件抗侧性能稳定,层间位移角达到1/50时,加载后期试件承载力不下降,延性性能好;往复荷载作用下钢板墙束柱试件的滞回性能稳定,层间位移角达到1/50时承载力没有降低,滞回曲线平滑、饱满;钢板墙束柱的抗侧刚度及受剪承载力的理论计算结果与试验及有限元分析结果很接近。     

装配式混凝土框架-冷弯薄壁型钢复合墙板结构抗震性能试验研究

为研究装配式混凝土框架-冷弯薄壁型钢复合墙板(CTSC墙板)结构的抗震性能和破坏机理,对1榀装配式混凝土纯框架和2榀装配式混凝土框架-CTSC墙板结构进行了低周反复荷载试验。通过分析结构破坏模式、荷载-位移曲线、刚度退化特征、延性、耗能机理以及关键部位应变变化规律,探究了CTSC墙板内嵌式连接和外挂式连接对装配式混凝土框架抗震性能的影响。结果表明：CTSC墙板内嵌或外挂连接均安全可靠,可有效地保证地震作用下装配式混凝土框架与CTSC墙板的协同工作;与纯框架相比,采用内嵌和外挂连接形式时结构的水平承载力分别提高28.3%和15.0%,初始刚度分别提高38.4%和16.8%。基于等效拉压杆原理,提出了装配式混凝土框架内嵌CTSC墙板结构的抗侧刚度简化计算式,并验证了计算结果的准确性。     

超大型阵列光伏板体型系数遮挡效应研究

在我国新能源战略的大背景下,光伏发电得到快速发展,超大型光伏工程的光伏阵列可达数十列数十排。采用风洞试验和CFD数值模拟相结合的方法研究超大型阵列光伏板体型系数及群体遮挡效应。试验模型在风洞宽度方向满布,以实现大型阵列光伏板的二维绕流。采用大比例刚性模型上下表面同步测压技术确定倾角为12°时串列5片光伏板的风压系数分布、体型系数和遮挡效应,同时采用CFD的realizable k-ε湍流模型进行计算,与试验结果比对验证了计算方法的有效性。在此基础上,对串列16、24、32片光伏板进行CFD数值模拟,研究不同倾角及不同串列数对光伏板体型系数的影响,并给出了超大型阵列光伏板体型系数随光伏板串列数的变化规律。结果表明：倾角为20°时的遮挡效应明显大于倾角为12°时的遮挡效应,遮挡效应随着上游光伏板数量的增加而增大,当上游光伏板数量达到12片以上时,遮挡效应趋于稳定。结合试验和CFD模拟结果,将超大型光伏阵列分为边缘区、渐变区和稳定区,并给出各区体型系数取值建议。     

南京金奥大厦巨型斜支撑异形铸钢节点试验研究

南京金奥大厦超高层建筑采用巨型支撑-筒中筒三重抗侧力结构体系,其中提供抗侧力刚度及支承外挂墙体的巨型钢斜支撑为此结构的一大特点。巨型钢斜支撑的节点采用异形铸钢连接节点,对其进行了在平衡和不平衡荷载工况下的3个足尺模型试验研究,利用ANSYS软件进行了有限元分析。有限元分析结果与试验实测值吻合良好。结果表明,节点应力分布不均匀,销栓孔壁承压区局部应力集中但无明显塑性变形,该节点基本处于弹性阶段工作,可以满足结构多道设防的性能化设计要求。     

超薄壁冷弯型钢矩形截面钢管墙架柱-楼层梁连接抗震性能试验研究

冷弯薄壁型钢结构的墙架柱与楼层梁连接构成空间受力体系,考虑柱的轴压比和楼层连接处不同构造方式,对3组共6个矩形截面镀锌钢管墙架柱与楼层梁的连接试件进行了低周往复加载试验。研究结果表明：墙架柱的轴压比从0.2增加到0.4时,规程JGJ 227-2011推荐的连接构造试件的屈服、极限和破坏荷载较角钢加强型连接构造试件均降低约20%,但对角钢加强型连接影响较小;所有连接均发生延性破坏,极限状态时墙架柱损伤很小;柱轴压比对延性、耗能能力均有一定的影响,因此将未加强的连接用于多层房屋结构时,要引起足够重视;在角钢加强型连接中,角钢厚度对连接试件的承载力影响显著,故建议对多层冷弯薄壁型钢房屋中的墙架柱与梁连接,采用厚t≥2 mm的角钢,与规程JGJ 227-2011推荐的连接方式相比,其承载力明显提高,累积耗能能力及屈服耗能能力均较强,破坏前试验所经历的荷载循环级数增加。     

Stability of thin-walled high-pressure cylindrical pipes with non-circular cross-section and variable wall thickness subjected to non-homogeneous corrosion

This paper proposes a method for determining the critical time of stability loss of thin-walled cylindrical pipes with non-circular cross-section and variable wall thickness along the directrix subjected to non-homogeneous corrosion from the inside. The method is based upon the model of a thin elastic cylindrical shell with a non-circular cross-section and variable wall thickness along the directrix. It is shown that the critical time can be established if the solution of the respective problem of the static stability loss for the non-circular cylindrical shell with variable wall thickness along the directrix, not subjected to corrosion, and the law of corrosion rate change are known. Numerical results are connected with the pipe of the elliptical cross-section.     

T形截面钢骨混凝土柱延性性能分析

利用大型有限元分析软件ABAQUS分析了T形截面钢骨混凝土柱在低周反复荷载作用下的受力性能,综合钢骨混凝土柱现有的试验研究成果,研究了T形截面钢骨混凝土柱在不同轴压比系数、配钢率、混凝土强度等级和长细比等参数对其延性的影响,得出了T形截面钢骨混凝土柱具有很好的延性性能,并提出了不同参数影响下T形截面钢骨混凝土柱满足一定延性要求的轴压比限值。     

Influence of initial distortion on the structural stress in 3 mm thick stiffened panels

This paper investigates the effect of initial distortion on the structural stress in 3 mm thick stiffened panels. The influence of initial distortion shape as well as magnitude is studied under axial tension and compression using geometrically non-linear finite element analysis. Different levels of structures are analyzed starting from the plate strips to an actual panel in order to understand how the structural response of thin initially distorted panel builds up. This way the difference between having initial distortion in one or two directions as well as the effect of boundary conditions becomes visible. The results reveal high non-linearity in the behavior of plate strip models and relatively linear behavior of actual plates and panel models in typical fatigue relevant ranges. This is due to support that the actual structures get from having initial distortion in two directions and from surrounding structures. In case of panels the most important effect on structural stresses near the transverse butt weld is the shape of the initial distortion. The second important is the magnitude of initial distortion and significantly less relevant is the straightening effect, i.e. decrease in structural to nominal stress ratio under loading.