Thin-walled Steel Structures Research Articles

Effective width method for distortional buckling design of cold-formed lipped channel sections

The aim of this paper is to improve the effective width method for distortional buckling strength of cold-formed steel lipped channel members using the energy method and the large deflection theory based on nonlinear post-buckling strength analysis of the partially stiffened element. The accuracy of the proposed method was verified using the finite element method. Comparison on post-distortional buckling strength is conducted between the energy method and the effective width method in the Chinese code Technical code of cold-formed thin-walled steel structures (GB50018-2002). The compared results show that the energy method is very efficient and the effective width method formula in Chinese code can be used to calculate the post-distortional buckling strength. Then, The half-wave length, elastic buckling stress of distortional buckling and the corresponding stability coefficient of partially stiffened elements are developed based on the energy method. With comparison on the calculated results of elastic buckling stress using the proposed method and the Finite Strip Method, suitability and good precision of the developed method are illuminated. Finally, a uniform formula for the stability coefficient of partially stiffened elements considering both local and distortional buckling effect is established. Comparison with experimental results and calculated results predicted with North America specification indicates that the proposed method is reasonable and has a high accuracy and reliability for the distortional buckling load carrying capacities of cold-formed lipped channel members.

Inelastic Test and Design Method of Cold-formed Steel Lipped Channel Members in Bending

The aim of this paper is to investigate the inelastic bending capacity and design method of cold-formed steel lipped channel bending members. The bending tests were conducted on 30 cold-formed steel lipped channel members. The nominal yield stress and the nominal thickness of the bending members were 235 MPa and 2mm. The theoretical global buckling stress was higher three times than the yield stress which can make sure the failure of members were in inelastic stage. For each specimen, an analytical analysis using Finite Element Method (FEM) was also conducted considering the influence of the boundary, the ultimate bending capacity, and the failure mode could also be captured. The test results show that the Chinese cold-formed steel specification Technical code of cold-formed thin-walled steel structures (GB50018-2002) is conservative for lipped channel bending sections in inelastic stage. The test results are used to put forward to a revised design method based on effective width method for the current Chinese cold-formed steel specification. The comparison on the bending capacity between the test results and the calculated results by using the proposed method, effective width method and direct strength method in North American cold-formed steel specification (AISI-S120-2016(draft)) shows that the proposed method can consider the inelastic reserve capacity of bending members well. The failure modes and bending capacity of bending members obtained using the idealized shell finite element model, which are close to the experimental results, shows that the idealized model is very well to model the buckling behavior and calculate capacity of bending members.

Crashworthiness design of quenched boron steel thin-walled structures with functionally graded strength

Thin-walled structures have been widely used as energy absorbers in industries such as automobile, shipping and aerospace. Different from recent well-studied columns consisting of aluminum, this paper introduced a kind of quenched boron steel column formed by hot stamping technology, with wall strength varying along the axial direction with a specific gradient, i.e. functionally graded strength (FGS). These FGS structures are found to have higher crashworthiness in terms of peak crash force (PCF) and specific energy absorption (SEA) compared with the counterpart structures with uniform strength (US). Based on a series of numerical simulation results, it revealed that the crashing behavior of FGS columns is significantly affected by both the strength gradient and the strength in the impact end. To optimize the crashworthiness (PCF and SEA) of the FGS structures, multi-optimization based on different metamodeling techniques such as response surface method (RSM), radial basis function (RBF) neural network model, kriging (KRG) model and optimization algorithm of non-dominated sorting genetic algorithm (NSGA-II) are performed. Pareto fronts of several alternative thicknesses were obtained to provide guidance for the FGS column design and give a good insight into actual crashing engineering. It is interesting to find that the gradient exponent is taken as the main design variable when the PCF is restricted below a certain value while the parameter of steel strength in impact end will be taken as the main design variable on the contrary. The comparison of Pareto fronts between the FGS and US columns showed that the FGS columns enhance the SEA and lower the PCF concurrently. Furthermore, among the three metamodeling techniques, the RSM models are proven to be the most suitable approach for the crashworthiness optimization of FGS structure.

The Effect of Conjunction Flexibility on the Local Stability of Steel Thin-walled Slab Beams

Influence compliance of node connections are not taken into account fully in the existing calculation methods. Basically, this is because of insufficient three-dimensional interference knowledge of elements of thin-walled steel frames. In practice, the structural analysis of the LSTC is usually made with the help of design diagrams with articulated or rigid joints connection elements, therefore, real behavior of structure is not taken into account, as the compliance units may lead to substantial redistribution efforts. Researches in clarifying the design diagrams allow to calculate the steel thin-walled structures with more accuracy and to improve the economic efficiency of design solutions. Thus, the purpose of the study is to determine the qualitative and quantitative characteristics on the basis of experimental and numerical studies that affect the loss of local stability in joints, taking into account the compliance of node connections.

Study on distortional buckling performance of cold-formed thin-walled steel flexural Members with stiffeners in the flange

This paper presents a finite strip program CUFSM used to calculate and analyze the elastic distortional buckling of cold-formed thin-walled steel flexural members with stiffeners in the flange, which has different sectional geometric parameters. According to the classical buckling stress formula, the distortional buckling coefficient of the flange can be calculated so as to analyze the influence of changed sectional geometric parameters on it. On this basis, this study provides a simplified formula of distortional buckling stress to calculate 40 members with different sections which are selected from the Technical Code of Cold-Formed Thin-Wall Steel Structures of China but not contained in this paper. Compared with the analysis results of CUFSM, it shows that the two simplified formulas have quite high accuracy and wide applicability for general members provided by the specification. So it is suggested that they can be used for engineering design and standard revision.

Investigation of Residual Stresses in Thin-Walled Structure and Slender Web

Presented paper offers simplified equations for evaluation of residual stresses. Residual stresses are very important for evaluation of properties of steel thin-walled structures. They play a crucial role in definition of ultimate load and stiffness properties. Generally the residual stresses must be in equilibrium. In the case of statically determinate beam structures residual stresses do not have influence for natural frequency. But in case of plate structures situation is different. Relationship between residual stresses and natural frequency can be used as the base for preparation of non-destructive method for the investigation of residual stresses in thin-walled structures.

Mechanical Properties Prediction for Cold-formed Steel Angle Connection with Various Flange Cleat Thickness

Connection is an important element in structural steelwork construction. Eurocode does not provide adequate design information for mechanical properties prediction of top-seat flange cleat connection, especially for thin-walled cold-formed steel structures. Adopting hot-rolled design with neglecting thin-walled behaviour could lead to unsafe or uneconomic design. This research aims to provide accurate mechanical properties prediction for bolted top-seat flange cleat connection in cold-formed steel structures. The scope of work focuses on the effect of various thickness of the flange cleat to the rotational stiffness and strength behaviour of a beam-to-column connection. Experimentally verified and validated finite element modelling technique is applied in the parametric investigation. Two categories of flange cleat thickness, ranged from 2 mm to 40 mm are studied. From the developed numerical models, it is observed that Eurocode has overestimated the initial rotational stiffness prediction, calculated with component method. The over-estimation would influence the overall stiffness of structures and force distribution within the components. As a conclusion, a set of newly proposed accurate predictions for initial rotational stiffness and strength of cold-formed steel top-seat flange cleat connection, with the influence of the thickness of flange cleat is presented.

Buckling analysis of thin-walled cold-formed steel structural members using complex finite strip method

In this paper, a generalised complex finite strip method is proposed for buckling analysis of thin-walled cold-formed steel structures. The main advantage of this method over the ordinary finite strip method is that it can handle the shear effects due to the use of complex functions. In addition, distortional buckling as well as all other buckling modes of cold-formed steel sections like local and global modes can be investigated by the suggested complex finite strip method. A combination of general loading including bending, compression, shear and transverse compression forces is considered in the analytical model. For validation purposes, the results are compared with those obtained by the Generalized Beam Theory analysis. In order to illustrate the capabilities of complex finite strip method in modelling the buckling behavior of cold-formed steel structures, a number of case studies with different applications are presented. The studies are on both stiffened and unstiffened cold-formed steel members.

Effect of adhesive type on Strengthening-By-Stiffening for shear-deficient thin-walled steel structures

Strengthening-By-Stiffening (SBS) is a novel technique whose purpose is to improve structural strength by stiffening buckling-prone regions in thin-walled steel structures using pultruded composite sections. A proof of concept study showed that SBS can achieve gains in shear strength of up to 56% using glass fiber reinforced polymers (GFRP) sections. This paper presents experimental results showing the effect of adhesive type on the efficiency of SBS for shear-deficient thin-walled steel beams. Specimens strengthened with two adhesive types were tested; a generic type (Type I) that is typically used for FRP-strengthening of concrete structures and a relatively new type (Type II) that is particularly promoted for steel structures. Like most FRP-strengthened structures, a debonding failure mode was observed for SBS specimens strengthened using adhesive Type I. Conversely, specimens strengthened using adhesive Type II did not fail by debonding, but rather by buckling of the smaller (less slender) shear panels. The resulting ductile failure mode is uncommon for FRP strengthening techniques and can lead to new applications of FRP strengthening for steel structures that were not possible using more brittle adhesives with lower capacity to absorb inelastic energy.

Cold-formed thin-walled steel structures as vertical addition and energetic retrofitting systems of existing masonry buildings

According to the current trend for sustainable constructions in urban areas, the present paper deals with the analysis of vertical addition systems for energetic retrofitting of existing masonry buildings. Starting from the current European (EN 1998-3:2005) and Italian (NTC 08) technical codes for the seismic assessment of existing structures, first a FEM model has been implemented to investigate the structural performances of masonry units with variable storeys (1, 2 and 3) and material strength (fk = 1, 3 and 6 MPa). Later on, traditional (reinforced concrete, masonry and steel) and innovative (glued laminated timber and cold-formed thin-walled steel) technologies have been proposed as a solution for vertical addition of the studied buildings. Therefore, a numerical campaign of linear dynamic analyses has been undertaken on the examined structures aiming at selecting the best vertical addition solution. The achieved numerical analysis results have provided cold-formed steel systems as the dominant solution for improving the energetic behaviour of the inspected existing masonry buildings. Finally, the achieved numerical results have been confirmed by a consistent and reliable multicriteria decision-making (MCDM) TOPSIS method, where the proposed vertical addition systems have been compared with each other in terms of structural, environmental and economic performance parameters.

DISTORTIONAL BUCKLING STRENGTH OF COLD-FORMED THIN-WALLED STEEL MEMBERS WITH LIPPED CHANNEL SECTION

The half-wave length, the elastic buckling stress of the distortional-buckling of cold-formed thin-walled steel members with lipped channel sections and the corresponding stability coefficient of partially stiffened elements are developed, based on the energy method. With the comparison among the calculated results of elastic buckling stress using the proposed method and the finite strip method, the suitability and good precision of the developed method are illuminated. Then, a uniform formula for the stability coefficient of partially stiffened elements considering both local and distortional buckling effects is established. Finally, with examples’ analysis, it is shown that the proposed uniform formula has higher precision to calculate the stability coefficient of partially stiffened elements and the ultimate load-carrying capacity of cold-formed thin-walled steel members with lipped channel sections, comparing that of the current method provided by the technical code of cold-formed thin-walled steel structures (GB50018-2002).

Cold-Formed Thin-Walled Steel Framing Residential System

This paper briefly introduces the cold-formed thin-walled steel residential system, the mechanical behavior analysis on stress of cold-formed thin-walled steel structure residential vertical load and horizontal load, and through compared with cold-formed thin-walled steel structure residential and traditional residential structure, summarized the characteristics of cold-formed steel residential. It is significant that the cold-formed steel residential system will be promoted and applied.

Ultimate load-carrying capacity of cold-formed thin-walled columns with built-up box and I section under axial compression

The use of cold-formed thin-walled steel structures has increased in recent years, and some built-up section members are motivated and also widely used for their excellent structural behaviors. In this paper, a series of axially-compressed tests on built-up box section members composed of two C-section by self-drilling screws at flanges are conducted. The differences of global, local and distortional buckling behaviors between members with built-up and single sections are investigated at first. Then the effects of installation error and fastener spacing on ultimate load-carrying capacity of built-up members are analyzed. A strength estimation method for built-up members under axial compression is proposed based on the experimental investigation in this paper, as well as some existing experiments, and corresponding numerical analysis studies. Finally, the predicted capacity obtained by using the proposed strength estimation method is compared with experimental results and the nominal axial strength determined according to the AISI provisions, by which the suitability and accuracy of the proposed strength estimation method have been established.

Evaluation of fatigue life of thin-walled steel structures of mobile machines with a random complex stress state

The new technique is based on the fatigue life of metal elements of mobile machines, which experience in operation a random complex stress state when the stress tensor components are different in intensity and complexity of the asynchronous and incoherent random processes.

Comparison on Calculation Method for Post-Buckling Strength of Thin-Webbed I-Shape Member

The thin-webbed I-shaped members are used as the basic members for beams and columns of steel buildings in order to increase utilization ratio of steel. The local buckling can occur for these members because of the large width-thickness ratio and these members have a substantial post-buckling strength which can be used. Different codes in China have different estimation method for substantial post-buckling strength of thin-webbed I-shaped members. So it is very necessary to establish the same calculation method to consider post-buckling strength for different china codes. In this paper the effective width estimation methods of technical specification for steel structure of light weight buildings with gabled frames (CECS 102-2002), code for design of steel structures (GB50017-2003), technical code of cold-formed thin-wall steel structures (GB50018-2002), America specification (AISC: 2005), European specification (E3-1.5:2006), and Winter equation are introduced simply. The effective area of thin-webbed I-shaped members with different width-thickness ratio in web and slenderness ratio are estimated using these codes. Comparison of these estimated results show that CECS 102-2002, GB50017-2003, AISC: 2005, Winter equation, and E3-1.5:2006 may be conservative or unsafe for members with different slenderness ratio or width-thickness ratio of web. GB50018-2002 is applicable for members with different slenderness ratio or width-thickness ratio of web without considering interaction between flange and web of members and can be used to estimate the effective area of thin-webbed I-shaped members. At the same time, the calculated method of post-buckling strength of thin-webbed I-shaped members in CECS 102-2002 and GB50017-2003 could use the same method as GB50018-2002.

The Impact Mechanism of a Double-Layer Air Circulation System on the Indoor Thermal Environment in Light Steel Structure Residence

Based on the structural features of the cold-formed thin-walled steel structure residence, a green environmentally friendly double-layer air circulation system with the respiratory function has been developed to explore the impact mechanism of the system on indoor thermal environment. Various index properties and influencing factors including velocity field, temperature field, PPD-PMV distribution etc, from the various components of the air circulation system during operation by using 3D numerical simulation function of Fluent and Airpak, have been examined, whereby to evaluate the indoor airflow and air quality. Research shows that the buffer layer of air can provide good air source for both the inner and outer air layer; the outer layer of air can dynamically isolate indoor and outdoor heat by taking advantage of stack effect; under the premise of low energy consumption, the utilization of the entire double air circulation system can improve the indoor thermal environment as well as provide 24-hour fresh air for the indoor occupants, so that the purpose of energy saving and environmental protection could be achieved.

The Application of Plate Buckling Theory in the Steel Structures

Based on the width-to-thickness ratio of plates, four types of sections are proposed and post-buckling design, elastic design, elastic-plastic design and plastic design are employed respectively. Taking the post-buckling strength of plates into consideration, cold-formed thin-wall steel structures shall adopt calculation by effective width, also post-buckling design, and the restrain coefficient k1 of the plate groups shall be used. The direct strength method is quite convenient but needs the finite strip method. The computation of medially stiffened plates and distortional buckling has been figured out and thus further research and supplement are necessary.

Design Method on Shear Behavior of Single Tapping Screw Connections in Cold-Formed Thin-Wall Steel Structures

In order to investigate the design method of single tapping screw connections between steel plate and non-steel plate and the applicability of calculating the shear capacity of single tapping screw connections with sheet steel under 2mm according to Chinese code Technical code for design of cold-formed thin-wall steel structures(GB50018-2002),theoretical analysis was carried out on single tapping screw connections, which were distinguished by connection forms called steel plate-steel plate connections and steel plate-non-steel plate connections. The results show that: Chinese code GB50018-2002 is suited to calculate the shear capacity of single tapping screw connections with sheet steel under 2mm and the results are safe compared with test results. The design method of single tapping screw connections between steel plate and non-steel plate is given on the basis of test results.

Buckling analysis of thin‐walled steel structures using generalized beam theory (GBT): state‐of‐the‐art report

AbstractThis paper addresses the use of generalized beam theory (GBT) to analyse the local and global buckling behaviour of thin‐walled steel members and structural systems. After a brief historical perspective of GBT developments, the main concepts and procedures involved in performing buckling analyses are summarized in a systematic fashion. That is followed by a state‐of‐the‐art report concerning the most recent GBT formulations and applications that have been developed to assess the buckling behaviour of members, frames and trusses with various loading and support conditions. In order to illustrate the unique modal features and show the potential of the GBT approach to buckling analysis, numerical results and a few practical applications are presented and discussed; for validation purposes, most of these results are compared with values yielded by shell finite element analyses, performed in the ABAQUS and ANSYS programs. The paper closes with a few words on the future perspectives of GBT‐based buckling analysis.

Response of Water Tower on Wind Induced Vibration Considering Interaction of Fluid and Structure

The paper deals with the numerical analysis of forced vibrations of a slender water tower structure. The computation model has been developed using finite elements in the ANSYS program environment. For CFD (Computational Fluid Dynamics) analysis the CFX module was used. The computation model includes the precisely modeled thin-walled steel structure and two variants of fluid domain. Elements FLUID30 formulated for direct description of the fluid pressure field has been applied and Lagrange description FLUID80. The Raleigh’s model of energy dissipation has been used. Similarity of normal modes of vibration has been applied as the criterion for defining the relations between computed natural frequencies of the empty tank and filled with water. To obtain accurate wind induced forces the CFD model of air surrounding was modeled. From this model the relation between velocity of unaffected stream and vortex separation frequency. Forced vibrations of the tower excited by vortex shedding harmonic pulsations have been computed.