Replaceable Fuses in Earthquake Resistant Steel Structures: A Review

In earthquake-prone regions, steel structures are considered to be one of the best choices due to inherent material properties in terms of homogeneity and ductility. In the conventional seismic design of steel structures, prevalent specifications recommend that the column and joints should be strong enough such that the inelastic action or damage occurs in the beams in lateral load resisting frames. By following these design provisions, structural collapse can be prevented in the event of severe earthquakes to ensure occupant safety. However, repair and rehabilitation of damaged primary members is a challenging task and also time-consuming process, resulting in severe inconvenience to the occupants. To simplify the repair works in earthquake resistant steel structures after the event of severe earthquakes, recent research work is concentrated on designing structures to have localized inelastic damages at intended locations, which will dissipate the seismic energy and can be easily replaced after the event of a strong earthquake, so that normal life of the occupants can be restored immediately with lesser cost of repair. This paper presents a critical review of the state-of-the-art related to steel lateral load resisting systems comprising of replaceable fuses that help in the easy repair of steel structures following strong earthquakes.     

Plug and play type joints in steel and steel–concrete composite constructions: Development guide and design considerations

Traditionally, for countries in Western Europe, joints in steel frame structures are realised using bolts and welds. In the workshop, the components are made using welding end plates and attachments and drilling of the bolt holes. On site, these structural components are connected together using bolts and nuts. The activities on site mean a large physical effort of the steel construction workers who are not free from danger. Measures needed to ease the work and to make it safer for workers are increasingly expensive. There is a need to develop the so-called ‘plug and play’ connections which can be realised using remotely controlled techniques. The development of plug and play type joints is not only important to ease the work on site, but it can also reduce overall costs of the construction if the joint characteristics are taken into account at the design stage. Of the total costs of a steel structure, 50% of that amount is related to the joints whereas almost 90% of the total costs are already decided upon in the construction detailing phase. Optimisation in weight will not result in an optimal cost-efficient structure. Even semi-rigid and partial strength joints that result after the erection phase could lead to cost reduction. Some considerations are given to optimise the joint with respect to overall structural behaviour from a technical and economical point of view. Fast and safe construction methods with plug and play joints are required for the future. Structures need to be designed such that they are fit to be demounted and rebuilt easily. For these types of joints no specific design rules are available in Eurocode 3, Part 1.8: ‘Design of joints’ or in chapter 9 of Eurocode 4, Part 1.1: ‘Composite joints’. This article describes the basis of design for these joints.     

高强度结构钢研究现状及其在抗震设防区应用问题

近年来,随着钢材生产工艺的进步及一大批重点工程、标志性建筑的兴建,高强度结构钢在工程中的应用逐渐增长。高强度结构钢与普通强度钢材的力学性能存在明显差异,然而现有设计规范的制定是基于普通强度钢结构的试验与理论研究,其能否适用于高强度钢的结构设计有待进一步研究。首先介绍了高强度结构钢的经济性与其在国内外工程中应用的概况,然后总结了国内外关于高强度结构钢在材料性能、基本构件力学行为、连接与节点性能和抗震设计方面的研究成果与现状。已有的研究结果表明,随着钢材强度的提高,其伸长率下降,屈强比升高,延性变差,阻碍了高强度结构钢在抗震结构中的应用。最后对高强度结构钢在地震设防区应用所面临的问题进行讨论,提出了高强度结构钢在抗震结构中应用的两种思路,并指出未来高强结构钢应用仍需开展的研究工作。     

Analysis of steel storage rack columns

Storage rack systems are structures composed of cold-formed steel structural members that are used as columns, beams and bracing. The rack columns present peculiar features in their design because they have perforations to facilitate assemblage of the system, which makes them more difficult to analyze by cold-formed steel structures design codes. There are several design codes proposed by the manufacturers associations, as the specifications of Rack Manufacturers Institute (RMI), applied in the USA along with the specification of the American Iron and Steel Institute (AISI). These codes propose experimental stub columns tests for the determination of their resistance. In this work, the commercial software, ANSYS, is used for material and geometric non-linear analysis of these columns, and the results are compared with experimental data obtained by stub column tests, for a typical section of racks manufactured in Brazil.     

Experimental investigation of cold-formed lean duplex stainless steel beam-columns

This paper describes a test program on cold-formed lean duplex stainless steel members in combined compression and minor axis bending. The test specimens were cold-rolled from flat strips of lean duplex stainless steel grade EN 1.4162. In this study, square and rectangular hollow sections were compressed at different eccentricities, in order to obtain a beam-column interaction curve for each series of tests. Initial overall geometric imperfections of the members were measured prior to testing. The ultimate loads and the failure modes of each specimen were obtained. The observed failure modes include local buckling, flexural buckling and interaction of local and flexural buckling. The test strengths obtained from this study and other available data were compared with the design strengths predicted by the American Specification, Australian/New Zealand Standard and European Code for stainless steel structures. It should be noted that these specifications do not cover the material of lean duplex stainless steel. Therefore, the suitability of the beam-column design rules in these specifications for lean duplex stainless steel is assessed in this study. Generally, these specifications are capable of predicting the beam-column strengths of the lean duplex stainless steel test specimens, and the design rules in the specifications are considered to be reliable. It is observed that the European Code generally provides quite conservative predictions for the beam-column specimens compared to the American Specification and Australian/New Zealand Standard predictions.     

矩形钢管混凝土桁架设计

根据国内外矩形钢管和矩形钢管混凝土结构规范、规程和有关研究成果 ,提出了矩形钢管混凝土桁架设计的构造要求、桁架杆件和节点设计与计算方法 ,可供工程技术人员设计时参考 ,并为我国《矩形钢管混凝土结构技术规程》的编制提供了参考依据     

冷弯薄壁型钢双肢拼合构件轴压承载力研究

目前我国相关规范对冷弯薄壁型钢组合截面构件的承载力设计方法比较粗略。基于已有的卷边槽形截面构件和由其组成的组合箱形截面构件的轴心受压承载力试验研究结果,通过有限元模拟和理论分析研究了此类构件拼合前后的受力性能的差异。分析了安装误差和连接件间距对拼合构件承载力的影响。提出了针对组合箱形和工字形截面构件的轴心受压承载力设计方法。研究表明,组合箱形截面构件的整体屈曲和畸变屈曲承载力较单肢截面构件有一定提高,而组合工字形截面构件仅整体屈曲承载力有一定提高。设计承载力与试验结果的比较表明,所提出的建议设计方法基本合理,可为相关规范的编制提供参考。     

不锈钢结构构件稳定性的研究进展

不锈钢结构具有优良的耐腐蚀性能和耐久性能,可以从根本上解决普通钢结构的锈蚀问题,能够延长结构的使用寿命,降低维护成本。不锈钢材料的非线性应力-应变关系特性会导致构件的后期刚度降低,同时由于不锈钢材料单价较高,需要更为经济合理的截面设计,因此构件的稳定性需要特别关注。对当前国内外不锈钢结构构件稳定性研究的现状及进展进行总结,比较分析国外现行不锈钢结构设计规范中关于构件稳定性的设计思路与方法;针对国内不锈钢结构设计方法的空白,在总结当前国内外研究进展与国外现行设计规范的基础上提出相关意见和建议。     

冷弯薄壁型钢墙柱骨架的轴压性能试验研究和设计建议

由立柱和导轨通过自钻螺钉相连的冷弯薄壁型钢墙柱骨架是轻钢住宅系统中的竖向承重单元。本文对无支撑、钢带支撑、槽钢支撑和十字交叉钢带支撑的C型截面柱的墙柱骨架进行了在轴心压力作用下的足尺试验。试验结果表明:支撑试件比无支撑试件极限承载力最大提高20%,立柱的破坏模式为弯曲屈曲和弯扭屈曲。通过研究现行设计规范与试验结果的误差,提出了在导轨和支撑约束条件下C型截面立柱的计算长度系数可取为0.8。     

Data Parallel Neural Dynamics Model for Integrated Design of Large Steel Structures

We have two objectives in creating novel design theories and computational models: automation and optimization. These two aspects are particularly important in design of complex and large engineering structures. In this article, a robust data parallel neural dynamics model is presented for discrete optimization of large steel structures based on the AISC ASD or LRFD specifications. The computational model has been implemented on a CM–5 supercomputer and applied to integrated minimum–weight design of two steel high–rise building structures. The largest example is a 144–story modified tube–in–tube super–high–rise building structure with 20,096 members. Optimization of such a large structure subjected to the highly nonlinear constraints of actual design codes, such as the AISC LRFD code, where nonlinear second–order effects have to be taken into account, has never been attempted before. The computational model developed in this research finds the minimum–weight design for this very large structure subjected to multiple dead, live, and wind loadings in three different directions automatically. This research demonstrates how a new level in design automation is achieved through the ingenious use of a novel computational paradigm and new high–performance computer architecture.     

Knowledge-based global optimization of cold-formed steel columns

Cold-formed steel member cross-section shapes are difficult to optimize because of the nonlinear behavior of such members under buckling loads. Traditional gradient-based optimization schemes, employing deterministic design specifications for the objective function, are inefficient and severely limited in their ability to search the full solution space of member cross-sections. Herein, a new global optimization approach that is well suited for optimization of such cross-sections is introduced. There are two distinguishing characteristics of this approach: (1) it operates within a low-dimensional expert-based feature space rather than the high-dimensional design space of cross-section parameters; and (2) it uses a numerical implementation of the direct strength method (DSM) for the objective function. Through the use of Bayesian classification trees, the most significant coordinates of the expert-based feature space are defined; these coordinates are of low dimension and are in terms of features which provide insight into structural behavior. The classification trees are then used to efficiently generate candidate member cross-section prototypes for subsequent refined local optimization.Optimization results are presented for three structurally distinguishable length regimes to provide proof-of-concept of the proposed scheme. It is demonstrated that an expert-based feature space and its associated classification tree can effectively encapsulate the knowledge gained in the design optimization process and can be subsequently used as a starting framework for related design optimization problems. This is, in essence, a highly efficient knowledge transfer mechanism that is absent in most optimization schemes. Optimization of thin-walled members stands to benefit greatly from the combination of more flexible and general design methodologies (e.g., the DSM) and novel, emerging, optimization schemes such as the one presented herein.     

Strength and ductility of HPS flexural members

An experimental and analytical research program was recently completed that examined in detail the parameters affecting the strength and ductility of high-performance steel (HPS) flexural members. HPS is a term used to describe a new class of steels being produced under strictly controlled conditions that have high strength, usually greater than 448 MPa (65 ksi) and exceptional toughness and weldability. The mechanical characteristics of these steels are different from conventional steels, leading to concerns over their use in some structural applications. Under earthquake loading, flexural members are expected to deform inelastically, so members fabricated with HPS steels must possess adequate ductility. This paper discusses the inelastic behavior of welded, I-shaped flexural members fabricated from an HPS steel, HSLA-80, having a nominal yield stress of 550 MPa (80 ksi) and an ultimate strength between 610–690 MPa (90–100 ksi) and compares the results to similar flexural members fabricated from conventional A36 steel. The effects of material properties: yield stress, strain-hardening modulus, yield stress-to-ultimate strength ratio, and strain at ultimate stress; cross-section geometry: flange slenderness, web slenderness, and lateral slenderness; and loading condition: monotonic moment gradient, monotonic uniform moment, and cyclic moment gradient are described from the results of experimental testing and analytical modeling. The results are evaluated against the existing design criteria established in the AISC-LRFD specifications and recommendations are made for revising the specifications.     

Local buckling of steel equal angle members with normal and high strengths

Steel angle sections have been widely accepted with the development of steel structures, and such members made by high strength steel (HSS) sections are also increasingly used in buildings and bridges, and especially in transmission towers and long span trusses. Compared to normal strength steels, HSS exhibits different mechanical properties, which can cause different local buckling behavior. A finite element analysis (FEA) was performed in this paper to investigate the local buckling of steel equal angle members with different strengths under axial compression, where the residual stresses and the initial geometric imperfections of specimens were accurately described. Through this work, the relationship of the ultimate local buckling stress of steel equal angle members under axial compression as a function of steel strength and width-to-thickness ratio was established. By comparing the FEA results with the international design specifications (ANSI/AISC 360-10 and Eurocode 3), a modified design formula was developed and corresponding design suggestions were proposed, to take into account the effects of steel strength.     

Concrete Filled Steel Tubes for Bridge Pier and Foundation Construction

Concrete filled steel tubes (CFSTs) are composite members that are commonly used in many countries today. CFST components are used in the United States, but they are more common in Asia, in part because the connections used in Asia are quite labor intensive and there are not standard connections in the U.S. In addition, US design specifications are prepared by separate groups for structural steel and reinforced concrete structures and so composite systems that use CFST components are not overseen by a single group and as such there are several conflicting design standards. In the US, steel tubes used for CFST are more slender (i.e., the diameter-to-thickness, D/t, ratio is larger) than some other countries, and labor practices (structural steel labor is different than reinforcing steel labor) also cause potential conflicts in construction. As a result, CFST has had some use in tall building construction in the US, but very limited use in bridge construction. A research program at the University of Washington has been in progress to address many of these issues with an eye towards universal design expressions, simpler, standardized connections and promotion of accelerated bridge construction (ABC). The research has resulted in recent changes to the American Association of State Highway Officials (AASHTO) bridge design specification as well as state departments of transportation (DOTs), which supports the increased use of CFST in bridge piers and pile and drilled-shaft foundations. An experimental research study which included 19 CFST pier-to-footing (or pile-cap) connection tests and 8 CFST pier column-to-precast pier cap tests was performed. These connections provide good performance under both seismic and gravity loads and address the concerns of US construction. These connections, their design rules and requirements, and their impact on composite behavior and system performance are discussed. These results permit rapid and economical construction of CFST bridge piers, piles and drilled shaft foundations. They encourage the use of more slender and economical tubes, while achieving the benefits of composite construction.     

基于仿生学的空间钢结构形体设计

结构的形态仿生主要从仿生学角度去研究结构的空间形体 ,形态万千的自然界蕴藏着无数优美的可供模仿的建筑造型 ,花卉、贝壳、晶体、蛛网、细胞结构 ,山川、森林、地形的形态乃至纯数学方程式都是空间钢结构形体设计可以借鉴模仿的对象。讨论了利用数学与仿生学原理进行空间钢结构形体设计的方法 ,并介绍了用CAD技术建构的几种形态的空间钢结构造型     

Overall buckling behavior of 460 MPa high strength steel columns: Experimental investigation and design method

Overall buckling behavior of compression columns is one of the most important research subjects in steel structures, especially for high strength steel which has been increasingly applied in recent years. An experimental investigation was carried out to study the overall buckling behavior of 460 MPa high strength steel compression members. Totally twelve columns including welded box and I-sections were comprised. The initial imperfections such as the residual stress, initial bending and loading eccentricity were all measured. Based on experimental results the buckling deformation and capacity were investigated. A finite element model was established and further validated by comparing with the test data in both present study and other previous researches, in which initial imperfections were taken into account. A large number of columns with various section dimensions and lengths were calculated by using the validated model, and their buckling capacities were compared with design values according to different steel structures specifications. It was found that the nondimensional buckling strength of such 460 MPa high strength steel columns were significantly improved compared to normal strength steel columns, and corresponding column curves and design formulae were suggested.     

某露天剧场看台预应力钢结构屋盖设计

预应力钢结构是应用于大跨度空间结构体系的重要结构形式,在国内外均具有十分广泛的应用前景。但该类建筑的结构形式往往较为复杂,各个结构之间的受力特点不尽相同,目前关于该结构的设计规范、技术规程等并不完善。通过对某露天剧场看台预应力钢结构屋盖设计过程的描述,详细介绍了预应力钢结构从结构选型、荷载计算到计算分析的全过程,为同类结构的设计提供有益参考。     

现代钢桥新型结构型式及其疲劳问题分析

随着各种形式的钢桥在我国得到大规模建设,特别是一些新型结构型式和制造工艺不断出现在现代钢桥中,钢桥构件的疲劳性能在设计时需特别关注。在对钢桥疲劳性能影响因素、钢桥疲劳设计关键参数以及疲劳荷载分析的基础上,对现代钢桥中的一些典型构造细节的疲劳性能进行了分析,并对防止钢桥疲劳的方法进行了总结,最后指出了目前我国钢桥疲劳研究中存在的一些问题,这对有效地防止钢桥疲劳破坏事故的发生,提高我国钢桥的设计和制造水平具有重要的意义。     

钢结构设计中若干问题的辨正

目前在钢结构设计中有几个基本问题 ,不少设计人员对此概念不清 ,而且在一些教材、设计手册甚至规范中对此论述也有不当之处。针对这几个基本问题进行了综合论述 ,提出了看法和意见 ,可供钢结构设计人员参考。