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Based on a recent review on blind bolted connections to concrete‐filled steel tubes, there is a need to improve the performance of anchored blind bolts in such composite connections. This paper presents a study on the pull‐out behavior of anchored blind bolts under applied tensile load in terms of stiffness, yield strength, ultimate strength and load‐displacement response. A finite element (FE) model with concrete damage plasticity model was developed for parametric study. Effects of key parameters, such as concrete strength, bolt grade, embedment length, tube thickness and tube grade, on the tensile behavior of the connection were studied to identify the key parameters influencing the behavior. Finally, a predictive model based on component method was proposed to estimate the structural behavior of the blind‐bolted connections. [ABSTRACT FROM AUTHOR]

Pre-stressed unbonded retrofit (PUR) CFRP strengthening of steel structures is becoming a common method of strengthening metallic structures. This paper presents a comprehensive study on the use of the PUR CFRP-strengthening method for strengthening a steel bridge in Melbourne, Australia. Finite element analysis is performed in this study to model the entire bridge and the strengthened element, and the model is validated using actual on-site measurements which showed the stress developments of two girders before and after strengthening when a fully loaded truck passed over the bridge. A parametric study is performed to investigate the stress development of steel girders strengthened with the PUR system under different girder-deck levels of rigidity. The results showed a perfect match between the finite element modelling and actual measurements, and the effectiveness of the PUR system under critical conditions such as different girder-deck stiffness connection levels. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study on the performance of concrete-encased concrete-filled steel tube (CFST) box columns subjected to eccentric axial loading. Finite-element analysis (FEA) was used to analyse the composite columns and experimental data reported recently by the authors was used to verify the FEA modelling. Analysis of the behaviour of the composite, including the full-range load versus lateral mid-height deflection, stress distributions, column failure modes and the interactions between steel and concrete, was carried out. The behaviour of the concrete-encased CFST box columns was compared with that of corresponding reinforced concrete columns and CFST built-up columns. Finally, a parametric study was carried out and the moment magnification approach adopted to propose design formulae for eccentrically loaded concrete-encased CFST box columns. [ABSTRACT FROM AUTHOR]

• Tests on concrete filled stainless steel tubes (CFSST). • Tests on T-stub to CFSST connections with various blind bolt types. • Finite element analysis of CFSST and T-stub to CFSST connections. • Discussion of effects of bolt type, tube thickness and layout of bolts on performance. • Formulas to predict the initial stiffness and capacity of CFSST and T-to-CFSST. Tension zone of a bolted steel beam-to-column connection can be represented by an equivalent T-stub to column connection under tensile load as recommended in Eurocode 3. This paper presents an experimental and theoretical study on equivalent T-stub to concrete filled stainless steel tube connections (T-to-CFSST) and the basic component (CFSSTs). Both stainless steel blind bolts and normal bolts were selected for the connections. Effects of various parameters, including tube thickness, bolt layout, bolt size, bolt type and bolting method, on the performance of T-to-CFSST and CFSST were investigated. Compared to hollow tubes, filling concrete could greatly enhance the stiffness and strength of the connections. Anchorage between bolts and concrete could be improved by setting studs at bolt ends. A finite element (FE) model was developed in this study and its accuracy was validated by the experimental results. Parametrical study was conducted to investigate the effects of parameters that cannot be covered in experiments, such as material type, tube length and T-stub thickness, on the behavior of CFSST and T-to-CFSST. Based on the experimental and numerical results, theoretical models were proposed to estimate the load–displacement curves of CFSSTs and their stiffness, yield capacity and ultimate capacity. By adopting the concept of component method, formulas were also proposed to predict the stiffness, yield capacity and ultimate capacity of T-to-CFSSTs. In general, the prediction matched well with the experimental results of CFSSTs and T-to-CFSSTs. [ABSTRACT FROM AUTHOR]

Abstract: Fiber reinforced polymer (FRP) materials were used to repair cracked non-load-carrying cruciform welded joints; and both the finite element method and the boundary element method were employed to study the fatigue crack propagation life of specimens repaired with FRP materials. The stress intensity factors (SIFs) were calculated for cracked welded joints that were unrepaired or were repaired with various FRP materials. The reduction of the SIFs for the repaired specimens was evident with the comparison of the control specimens. The fatigue life was then estimated with the NASGRO equation, which is modified from the Paris law. It was observed that the resulting fatigue improvement agreed with existing experimental data, indicating that fatigue strength can be upgraded with composite material repairs. The effects of various repair parameters on fatigue life were also examined. Single-sided repairs on cracked surfaces were more effective than double-sided repairs, due to the shift of the neutral axis. An increased modulus of FRP materials and adhesive achieved better fatigue performance. The use of more patch layers also had a positive effect, while increased adhesive thickness had a negative effect on fatigue life. [Copyright &y& Elsevier]

Abstract: Concrete filled double skin tubular columns (CFDST) have excellent structural behaviour. They have been used as transmission towers and have potential to be used as building columns and bridge piers. Performance of the CFDST columns under ambient temperature has been well studied, whereas fire resistance of such columns is still a major concern. A summary of a series of fire tests on CFDST columns conducted by the authors is briefly presented in the paper. A finite element numerical model is developed to analyse the fire behaviour of CFDST columns, namely thermal and structural responses under fire exposure. The model is verified by the test results and then used to perform parametric analyses. Parameters which have significant effect on the fire behaviour of CFDST columns are identified. Based on the parametric studies, suggestions on the fire resistance design of such columns are made. Practical design tables are derived for the fire resistance design of some typical CFDST columns. [Copyright &y& Elsevier]

Abstract: This paper reports an investigation into the behaviour of high strength SCC (self-consolidating concrete) filled steel tubular stub columns exposed to standard fire. A series of tests were carried out to obtain the temperature distribution, axial deformation, limiting temperature of steel and fire endurance of the SCC filled steel tubular stub columns. In addition, a finite element analysis (FEA) model was proposed and used to simulate the fire behaviour of the columns. In the FEA modeling, a sensitivity study was conducted to determine the concrete fracture energy and the contact property of the steel and concrete interface. The verified FEA model was used to analyse the structural behaviour of the columns under fire exposure, such as strain, stress, the load sharing between the steel tube and concrete and local buckling of the steel tube, to gain an insight into the failure mechanism of the columns. [Copyright &y& Elsevier]

Describes a series of tests on longitudinal fillet welds in high-strength, cold-formed rectangular hallow section members. Material properties and welding procedures; Application of finite-element analysis, a mathematical method and analysis; Conclusions.

Highlights • Dynamic behaviour of Hybrid Corrugated Members was investigated. • Axially pre-stressed UHS steel tubes were examined under transverse impact loading. • Advanced 3D nonlinear finite element models were developed and validated. • Corrugation geometry parameters effect on lateral impact behaviour was studied. • The performance of HC members was demonstrated compared to corrugated members. Abstract Latest development in material and manufacturing technologies make it possible to increase the yield strength of steel to more than 1200 MPa. These steel grades, suitable for structures prone to extreme loadings, give potentials for considerable weight reduction and a cost-effective way to produce energy-efficient members. Having analysed the impact behaviour of corrugated members recently, this paper now investigates the performance of hybrid corrugated (HC) sections consisting of mild-steel corrugated plates and ultra-high strength (UHS) steel tubes. Three different types of trapezoidal corrugated plates are considered so as to examine the effect of geometrical corrugation parameters on the performance of entire member. Along with this, in order to study the contribution of UHS tubes in the performance of HC members under impact loading, their performance is also examined separately. In combined lateral impact and axial loading scenario, the tube is initially compressed axially; thus an indenter perpendicularly impacts the specimen at mid-span. An advanced numerical model in which nonlinear strain-rate dependent material behaviour of steel is taken into account is also developed by using ABAQUS/Explicit. Thus, the residual deformations, time histories, global lateral deflection, and energy absorptions are discussed and compared with those of experimental results. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the results of a component-based model developed for an innovative type of connection, recently proposed by the authors, for beam-to-hybrid fabricated column (HFC) connections. The active constitutive components of the connection are identified and their relevant resistance and flexural stiffness are presented. The moment-rotation curve of the joint is reproduced using the assembly of these components. The failure point of the connection is also predicted using the failure modes observed in the experimental tests. The results obtained from the developed component-based model are then compared to those provided by a three-dimensional (3-D) finite element (FE) model and experimental tests. It is shown that the component-based model shows good accuracy in the prediction of the initial stiffness, rotation capacity and failure of the connection. Highlights • A component-based model for an innovative connection is developed. • The model can represent the moment-rotation curve of the connection precisely. • Component method results are compared to the results of FE and experiments. • Component method results are in close agreement with finite element results. • The model can be used for developing design guide-lines for the connection. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tubular (CFST) column-wall has a promising prospect in the construction field, especially for multi-story residential buildings. It is very important to have a thorough understanding of its mechanical behaviour and fire resistance. This is a companion paper that carries forward the work by the authors [1]. The previous paper focused on full-scale testing to determine the fire resistance of CFST column-wall, whereas this paper deals with finite element analysis and simplified design method for such composite structural elements. Heat transfer mechanism was analysed by comparing the temperature distributions of CFST column-wall sections with different fire exposures. Structural analysis, such as internal force distribution, strain and stress of different components, interfacial behaviour between steel and concrete was given to describe the deformation behaviour and failure mechanism of CFST column-wall. Based on the FEA model, parametric analysis was carried out to investigate the influence of geometric, load and physical parameters on the fire resistance of CFST column-wall. Since no specific design rules can be found for CFST column-walls, a simplified fire design method was proposed in this paper to calculate the fire resistance of CFST column-wall structure. [ABSTRACT FROM AUTHOR]

Bird-beak joints are a type of welded square hollow section (SHS) joint, the static strength of which is higher than that of conventional joints. Experimental analyses were conducted on the stress concentration factors (SCFs) of square bird-beak joints to obtain more information regarding their fatigue behavior. Twelve specimens, i.e., three conventional joints and nine square bird-beak joints, are separately tested by considering chord and brace axial force load cases. Both conventional and square bird-beak joints tested have a T-shape and are simply supported at their chord ends. Elastic strain distributions near the crown and saddle areas are measured, and strain concentration factors (SNCFs) at potential hot spots are calculated using an extrapolation approach. Quadratic extrapolation is suggested for the square bird-beak joints because linear extrapolation may underestimate SNCFs by up to 35%. Furthermore, critical locations are identified for square bird-beak joints subjected to chord and brace axial forces. A comparison indicates that the square bird-beak joints can produce lower stress concentration factors than the conventional or the diamond bird-beak joints with identical nondimensional parameters, especially when brace-to-chord width ratios are relatively small. [ABSTRACT FROM AUTHOR]

Ductile fracture of steel components cannot be avoided particularly due to large inelastic strain in extreme loading scenarios. Without considering damage model, conventional elasto-plastic constitutive material model cannot lead to accurate finite element (FE) modelling results when damage due to fracture exists. Metal fracture is a complex damage process in which damage onset, material deterioration and final fracture are related to development of material plasticity. Uniaxial tensile fracture and shear fracture are two typical failure modes of structural members. In this study, experimental investigations of monotonic tensile fracture and in-plane shear fracture under different strain rates in quasi-static loading range are presented for low-alloy structural carbon steel. The characteristic steel material properties are obtained insensitive to the chosen strain rate. A semi-empirical process is used to calibrate the damage properties (damage onset and softening criteria) through FE modelling of the coupon samples based on a continuum damage mechanics (CDM) model. Deterioration of the carbon steel properties was found related to the evolution of equivalent plastic strain, and particularly there is a linear relationship for the in-plane shear scenario. The verified damage onset and shear softening are then used for modelling of a welded steel tubular connection experiencing punching shear fracture phenomenon. It is shown that modelling result of the steel connection is significantly improved when the proposed fracture modelling is adopted. [ABSTRACT FROM AUTHOR]

Hybrid fabricated columns (HFCs) consisting of mild-steel thin plates connected to ultra-high strength thin-walled tubes at corners have exhibited superior performance compared to the equivalent conventional tubular columns. The higher load-bearing capacity, energy absorption, and post-buckling strength of these columns provide designers with new possibilities in the construction of high-rise buildings. Although several studies have been conducted on these columns, the connection between I-beams and this type of column is challenging. In this paper, using 3-D finite element modelling a numerical study is conducted to compare the behaviour of recently patented bolted modular M-HFC connection between I-beams and HFCs with the welded non-modular type of this connection (called as W-HFC). The performance of the W-HFC connection is also compared with four different types of common conventional connections currently in use in the industry. Moreover, a topology optimisation has been performed on the M-HFC connection in order to reduce the overall weight of the connection components while keeping the moment- rotation characteristics of the connection as close as possible to the originally proposed connection. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental investigations of the tensile properties of different types of CFRP plates. Coupon specimens of low, normal and ultra-high modulus CFRP plates were prepared and tested under tensile loading. Four different strain rates were used, including one low strain rate and three high strain rates. Two methods of capturing strain were used: image correlation photogrammetry and foil strain gauges. The results showed a significant increase in the tensile strength, ultimate strain and elastic modulus for coupons under high strain rates. The CFRP coupons were prepared and tested in accordance with the ASTM3039-08 standards. Finite element analysis was performed and the results agreed very well with the experimental results. [ABSTRACT FROM AUTHOR]

This paper deals with developing advanced, yet design-oriented expressions for ultimate strength of the newly developed hollow corrugated stub columns with or without ultra-high strength corner tubes under uniaxial compressive loading. This is achieved by individually analysing comprising self-strengthened corrugated plates using the effective width concept whilst the effect of corner enhancement is taken into calculation. For stiffened panels such as corrugated plates, the ultimate limit state design is equated to the lowest value among all collapse provisions. However, the finite element analyses show that Euler buckling state may govern the ultimate load capacity of corrugated plates used in the proposed columns. This is verified by comparing the results obtained from the proposed analytical formulations with those demonstrated by the finite element modelling and experiments. The results are also compared with the guidelines for design of corrugated panels available in the literature. Finally, several cases with different corrugation geometrical parameters are defined and the capacity of corresponding columns is evaluated and compared to each other. [ABSTRACT FROM AUTHOR]

Along with the rising application of high strength steel in civil engineering practice, it has become imperative to gain comprehensive understanding of the elastic and plastic behaviour of these materials under given strain or stress histories. For seismic analysis of structures in earthquake prone areas, this paper aims to analytically and theoretically study the cyclic behaviour of high strength steel tubes, with individual applications or incorporated in fabricated structural elements. Several low cycle tension-compression tests are conducted on high strength (grade 800) and ultra-high strength (grade 1200) steel coupons extracted from tubes. Parameters such as number of cycles, strain/stress amplitude and increment size are studied in the behaviour of cyclically strained material and its preserved mechanical properties. Numerical analysis is also conducted incorporating combined nonlinear hardening models. As opposed to conventional structural mild steel both grades of steels considered in this study exhibit cyclic softening with plastic straining having a more prominent strength reduction in higher strengths of steel. Cyclical damage applied on high tensile steel evidently influences the preserved mechanical properties of microstructure at fracture. Combined nonlinear plastic hardening and relevant parameters proposed in this study for two grades of high strength steel materials are calibrated and verified against hysteretic experimental results and proposed for further analytical and numerical modelling. [ABSTRACT FROM AUTHOR]

In recent years, the risk of damage or failure of axial load bearing structural members has increased rapidly due to increase of accidental vehicle/ship collision events. Therefore, suitable strengthening technique needs to be developed to minimise the casualty and economic loss caused by vehicular collisions with structural columns. In this study, numerical simulations are carried out to evaluate the effect of carbon fibre reinforced polymer (CFRP) strengthening of full scale concrete-filled steel tubular (CFST) columns under vehicular impact. Numerical models of bare and CFRP strengthened CFST columns were first developed and validated in a recent study of the authors. The validated finite element (FE) models are extended to full scale columns. Realistic vehicle behaviour is simulated with simplified mass-spring vehicle model. The outer diameter of steel section is kept same and the wall thicknesses are changed to account the slenderness effects of hollow steel sections. Both vehicle and column deformations are considered during the impact simulation as observed in practical situation. The dynamic impact analysis results show that adhesively bonded CFRP sheets provide enhanced impact resistance capacity of strengthened columns by reducing lateral displacement about 40% compared to ordinary CFST columns. A comprehensive parametric study is conducted by varying the vehicle velocity, vehicle mass, axial static loading, vehicle stiffness and CFRP bond length to observe the effects of these parameters on the structural responses of bare and wrapped columns. CFRP wrapping is found to be a promising strengthening technique to control global failure of full scale CFST columns subjected to vehicular impact. [ABSTRACT FROM AUTHOR]

The compressive behaviour of Concrete-Filled Double-Skin tubular (CFDST) sections consisting of corrugated plates is investigated numerically in this study. Finite element simulations are employed to decipher more details on the compressive behaviour of numerous archetypes with different geometries and material properties. The results of these simulations reveal how the ultimate static compressive capacity of the intended sections may be affected by changing the geometric and material properties. Different cross-section shapes, dimensions and heights within the practical range are considered for the proposed archetypes. In addition, a wide range of concrete compressive strength values are assigned to the concrete infill of the archetypes. The ultimate axial capacity of almost all the intended CFDST archetypes is mainly dominated by concrete compressive strength. In conjunction with numerical simulations, different design formulations are also employed to predict the ultimate axial load-bearing capacity of CFDST sections. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the behavior of CFDST members under low velocity lateral impact using ABAQUS, where nonlinear material behavior and strain rates of steel and concrete are included. The finite element analysis (FEA) models of CFDST members are described and verified using existing experimental results. Strain and stress states of concrete and steel tube in CFDST members are analyzed over the full loading range, followed by a parametric study investigating the influence of impact height, hollow ratio, nominal steel ratio, diameter-to-thickness ratio of inner steel tube and strength of materials on the impact force and global residual lateral deformation. Furthermore, the dynamic increase factor (DIF) of CFDST members under lateral impact is proposed, and the influence of the confinement factor on the dynamic increase factor (DIF) is analyzed. The results show that when the confinement factor is larger than 1.03, the dynamic increase factor needs to be considered to accurately estimate the dynamic resistance capacity of CFDST members subjected to lateral impact. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study on stress concentration square bird-beak square hollow section (SHS) welded joints. Both conventional and square bird-beak SHS joints considered have T-shapes and are simply supported at their chord ends. Refined finite element models are developed to obtain the strain/stress concentration factors (SNCFs/SCFs) of square bird-beak joints with various dimensions. The FE models are validated by comparing with the experimental data. The SNCF differences among considered hot spots are analyzed for the identification of critical locations. The influences of three major non-dimensional parameters, i.e., brace/chord width ratio β , chord wall slenderness ratio 2 γ , and brace/chord wall thickness ratio τ , on the stress concentration factors (SCFs) of square bird-beak T-joints are revealed on the basis of numerous parametric studies. Comparisons of joint types are finally made. The results indicate that, in case of identical non-dimensional parameters, square bird-beak SHS T-joints provide SCFs smaller than conventional SHS T-joints in most occasions, especially when β is small; and SCFs of square bird-beak T-joints are expected to be lower than CHS T-joints with small β and large 2 γ and τ . [ABSTRACT FROM AUTHOR]

This paper presents the behaviour of circular concrete filled double skin tubes (CFDST) subjected to local bearing forces. This is an extension of a previous work on concrete filled steel tubes (CFST). A series of tests were conducted where some key parameters were varied, including loading angle, hollow ratio, chord wall thickness, as well as brace to chord diameter ratio. A finite element analysis (FEA) modelling was established and verified by the test data. Comparative analysis was conducted between the full-range behaviour of CFDST and CFST under local bearing. It was found that the performance of CFDST is considerably affected by the interaction of the outer tube, inner tube and the sandwiched concrete, whilst its bearing capacity depends on the hollow ratio. Finally, based on the load-transfer mechanism analysis, simplified formulae for predicting the strength of CFDST under local bearing forces are presented. Reasonable agreement between the predicted and measured values is achieved. [ABSTRACT FROM AUTHOR]

This paper focuses on the development of much-needed numerical and experimental models for understanding the mechanical behaviour, section capacity and energy absorption of the innovative fabricated columns consisting of corrugated mild-steel plates. The corrugated square columns proposed in this paper are fabricated by welding four corrugated plates which are originally produced from 3 mm thick flat mild steel plates. The experiments consist of applying a compressive axial force to the columns to determine load–displacement curves of the fabricated sections. The effects of geometric parameters such as inclination angle and corrugation height are also investigated experimentally by considering three different types of corrugated columns. Moreover, a finite element model in which the effects of material and geometric nonlinearities as well as residual stresses are taken into account is developed using ABAQUS. The experimental results are also compared with those given by the finite element (FE) model whilst a good agreement is achieved. A cost analysis is also conducted in which the cost of the innovative columns proposed in this research is compared to those of conventional welded columns currently available in the civil engineering market. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a finite element analysis (FEA) of circular concrete filled steel tubular (CFST) members under local bearing forces applied either perpendicularly to the member or at an angle of 45°. The established FEA modeling was verified by the experimental results that have been published in an international journal. The FEA modeling was then used to perform analysis on the typical failure modes and full-range load-deformation relations of CFST subjected to local bearing forces. Finally, simplified formulae for calculating the strength of CFST under local bearing forces was presented. Practical guidance was also given to avoid premature local buckling of brace member and premature fracture of chord member. [Copyright &y& Elsevier]

Abstract: This paper presents a set of new test data for high strength concrete filled steel tubular (CFST) members subjected to transverse impact. A total of 12 circular CFST specimens and reference hollow steel tubes were tested in a drop hammer rig. The cube strength of the concrete used for the CFST members is up to 75MPa. A finite element analysis (FEA) model is established to predict the impact behaviour of high strength CFST members, and the accuracy of which is then verified by the presented test results. Full-range analyses of the behaviour of CFST members under impact loading are then carried out using the FEA model to produce the force state, internal force distribution, and flexural capacity. Finally, a simplified model is obtained based on a parametric analysis to calculate the flexural capacity of CFST members under impact load. [Copyright &y& Elsevier]

Abstract: This paper presents a finite element analysis (FEA) on concrete filled steel tubular (CFST) members with square sections under both loading and chloride corrosion, the established FEA model was verified by the experimental results presented in the companion paper (Han et al., 2012) [1]. The FEA model was then used to perform mechanism analysis on the CFST stub columns and beams subjected to both loading and chloride corrosion. Full-range analysis on the load versus deformation relations was carried out. Finally, simplified methods for calculating the strength of CFST stub column and beam under long-term loading and corrosion were illustrated based on the parameter analysis. [Copyright &y& Elsevier]

Abstract: This paper reports the numerical simulation of both CFRP/steel double strap joints with 1 and 3 CFRP layers per side at quasi-static and three dynamic tensile loading speeds of 3.35, 4.43 and 5m/s. Simulations are implemented using both the implicit and explicit codes respectively using non-linear finite element (FE) package ABAQUS. In these analyses, failures of both CFRP sheet and adhesive are considered and a cohesive element is utilised to model the interface. The developed FE models for both types of joints were validated by comparing their quasi-static and dynamic findings with those obtained from previous experimental program. This comparison includes four different variables such as the ultimate joint strength, effective bond length, failure pattern and strain distribution along the bond length. It was found that FE models proved to be able to predict all these parameters for both quasi-static and dynamic analyses and their prediction matched well with test results. [Copyright &y& Elsevier]

Abstract: This paper studies the behavior of very slender thin-walled concrete filled steel tubular (CFST) columns under axial compression. A finite element analysis (FEA) was developed to carry out the behavior of compressive columns. Initial out-of-straightness imperfection was discussed. Generally good agreement was obtained between the predicted and measured results. The FEA model was then used to perform mechanism analysis on very slender circular CFST columns. Parametric studies were carried out and the ultimate strengths from tested results and design codes were compared and discussed. The reliability analysis method was used to calibrate the existing design formulas given in DBJ/T13-51-2010, ANSI/AISC 360-05 and Eurocode 4. [Copyright &y& Elsevier]

Abstract: This paper presents a finite element analysis (FEA) modeling to study the flexural performance of circular concrete-filled thin-walled steel tubular (CFST) beam. A set of test data was used to verify the FEA modeling; generally, good agreement was achieved. The FEA modeling was then used to investigate the stress and strain distributions across the composite section in the whole loading procedure. The composite action between the steel tube and its concrete core was analyzed. A strut–tie model was proposed for the load transfer mechanism of the circular composite member subjected to pure bending. [Copyright &y& Elsevier]

Abstract: Strengthening of steel structures using externally-bonded carbon fibre reinforced polymers ‘CFRP’ is a rapidly developing technique. This paper describes the behaviour of axially loaded flat steel plates strengthened using carbon fibre reinforced polymer sheets. Two steel plates were joined together with adhesive and followed by the application of carbon fibre sheet double strap joint with different bond lengths. The behaviour of the specimens was further investigated by using nonlinear finite element analysis to predict the failure modes and load capacity. In this study, bond failure is the dominant failure mode for normal modulus (240GPa) CFRP bonding which closely matched the results of finite elements. The predicted ultimate loads from the FE analysis are found to be in good agreement with experimental values. [Copyright &y& Elsevier]

Concrete-filled Rectangular Hollow Sections have been tested under large-scale, far-field, air-blast loading for the first time. The concrete-filled, cold-formed steel tubes performed well under the blast loads, with a significant reduction in the global and local displacements compared to unfilled RHS members. The heavily instrumented tests provided a large quantity of response data that was used for the validation of numerical models. Numerical models of the concrete-filled steel tubes were first developed using explicit finite element methodologies. A parametric study was conducted with the validated finite element model to further characterize the response of the concrete-filled steel tubes under air-blast loading. The influence of several key variables on the response of the tubular members was determined and preliminary design guidance is provided. Finally, the test and finite element results were used to develop an idealized single-degree-of-freedom numerical model that is well-suited to future use in design problems. [ABSTRACT FROM AUTHOR]

This research investigated the stress concentration factor (SCF) superposition of bird-beak square hollow section (SHS) X-joints under asymmetrical axial brace forces. Three typical non-dimensional parameters (i.e., β = 0.6, 2 γ = 20, τ = 0.5) were employed for tubular joints. Finite element models of conventional, square bird-beak, and diamond bird-beak SHS X-joints were constructed by accurately considering the geometries of welds, and the structural hot spot stresses at weld toes were obtained using the extrapolation method. Numerical results show that, in case of single-side brace axial force, the stresses on the unloaded brace side of bird-beak X-joints are obviously higher the values at the corresponding locations of conventional X-joints, and as a result the SCF errors induced by the existing superposition formula of conventional joints are significant for bird-beak joints. The mechanism was revealed to be the interactions between adjacent walls of the chord by further investigating the compatible deformations of these joints. A modified superposition formula, in which a new load case considering both single-side brace axial force and reversed chord in-plane bending has been employed, was introduced as the solution. The SCF variations with non-dimensional parameters under the new load case were also identified by conducting parametric analysis. The proposed superposition approach gives reasonable predictions of SCF of bird-beak SHS X-joints under asymmetrical brace axial forces. [ABSTRACT FROM AUTHOR]

A diamond bird-beak T-joint is similar to a conventional T-joint except that the brace member and chord member both rotates 45°. Previous research demonstrated that the diamond bird-beak joint has better static and fatigue behaviour than a conventional joint. Experimental testing has been reported by the authors to determine the stress concentration factors (SCFs) of diamond bird-beak SHS T-joints. This paper fills the knowledge gap through FE analysis, parametric study and proposed SCF formulae for such joints. Three-dimensional finite element (FE) models were developed and validated by experimental data. The FE model was utilized for parametric study on SCFs for diamond bird-beak SHS T-joints to investigate the influence of key non-dimensional geometric parameters β (ratio of brace width to chord width), 2 γ (ratio of chord width to chord thickness) and τ (ratio of brace thickness to chord thickness). Finally SCF formulae were proposed for diamond bird-beak SHS T-joints under four loading cases, namely axial force and in-plane bending in the brace, as well as axial force and in-plane bending in the chord. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a finite element analysis (FEA) modeling to study the flexural performance of rectangular concrete filled steel tubular (CFST) members with compact, non-compact or slender element sections. Seventy test results are used to verify the FEA modeling. Generally good agreements were achieved in the ultimate bending capacity and the curvilinear trends of the moment versus mid-span deflection relations of the composite member between the experimental results and the FEA results. The FEA modeling is then used to investigate the residual failure patterns of the core concrete, the typical residual deformations of outer steel tube and the stress and strain distributions across the composite section in the whole loading procedure. Analysis results show that interaction of steel and concrete in the composite beam offers stress redistribution in steel and concrete which makes the rectangular CFST beam have high flexural capacity and ductility. Finally, the reliability analysis method is used to calibrate the existing design formulae on composite beam in EC4 (2004), AISC (2010) and DBJ/T13-51-2010 (2010). It was found that all the design formulae achieved adequate reliability index. [Copyright &y& Elsevier]

Abstract: The tapered concrete-filled double skin steel tubular (CFDST) columns have been used in transmission towers with potential for other types of composite frame structures. However, the behavior of the tapered CFDST column under eccentric compression has not yet been studied, which will hinder the employment of such members. This paper reports an investigation on eccentrically loaded tapered CFDST columns with different load eccentricities. The numerical investigation was also carried out by using the finite element model to predict the behavior of the tapered member. Comparisons were made between the tapered and straight members on the strength and stress distribution. The stability of the tapered column was studied through numerical calculation. Finally, the load carrying capacity of the tapered CFDST column under eccentric compression was predicted using the concept of “equivalent column”. [Copyright &y& Elsevier]

Abstract: Recently, tapered concrete-filled double skin steel tubular (CFDST) columns have been applied in electricity transmission towers in China. However, there is still lack of information on the behaviour of such kind of members. This paper thus carried out the investigation on axially loaded tapered CFDST stub columns. The parameters included the tapered angle and the sectional profile. A finite element analysis (FEA) model was developed to predict the behaviour of the tapered member as well. The results showed that the steel tubes and the sandwiched concrete could work together well despite the tapered angle. The failure mode of the tapered CFDST stub column was similar to that of the straight one, and the failure occurred near the smallest section. The confinement effect of the tapered member was discussed by using the stress analysis. Finally, formulas were suggested for the calculation on the ultimate strength of the tapered CFDST stub column. [Copyright &y& Elsevier]

Abstract: This paper reports a finite element analysis of the compressive behaviour of CFDST stub columns with SHS (square hollow section) or CHS (circular hollow section) outer tube and CHS inner tube. A set of test data reported by different researchers were used to verify the FE modelling. Typical curves of average stress versus longitudinal strain, stress distributions of concrete, interaction of concrete and steel tubes, as well as effects of hollow ratio on the behaviour of CFDST stub columns, were presented. The influences of important parameters that determine sectional capacities of the composite columns were investigated. [Copyright &y& Elsevier]

Column-to-column bolted end-plate connections with stiffeners welded on the end plates and column side faces for steel modular buildings were investigated, to understand the effect of stiffener configurations on tensile capacity and stiffness. The connection performance was experimentally examined in tension, focusing on the flexure behaviour responses of the end plates, especially the yield lines on the end plates. Detailed finite element analyses (FEA) were also conducted to model the connection behaviours, considering bolt pretensions, contact behaviours and detailed bolt geometry, showing good comparison with experiments. The experimental and FE studies indicated that stiffeners at locations such as the corners of the steel tube could improve the tensile capacity by about 60%. On the basis of the FE modelling, a comparative study was subsequently performed to clarify the effects of stiffener configurations, end-plate thickness, and number of bolts on the tensile capacities and stiffness of such bolted end-plate connections. The effects of stiffener configuration on tensile capacity were also described in detail, based on yield-line theory. • Bolted end-plate connections with various stiffener configurations for tubular members. • Welded stiffeners for improving connection tensile performance. • Tensile failure of the connections governed by flexural yielding of the end-plates. • Detailed FE analysis parametric study for understanding of connection behaviour. • Yield line pattern on the end-plate analysed to clarify the effect of stiffeners. [ABSTRACT FROM AUTHOR]

This paper deals with the stress concentrations and fatigue behaviour of X-shape bird-beak joints under brace in-plane bending. Static load was first implemented to record the strain distribution along the hot lines, and then stress concentration factors (SCFs) were obtained through quadratic extrapolation method. Numerical analysis was then developed to further determine key parameters affecting SCFs and to propose corresponding SCF design formulas. During the subsequent high-cycle fatigue test, the fatigue cracking process including crack initiation, crack propagation, and fatigue lives, as well as the rigidity degradation were captured. Results show that crack initiation always occurred at the crown area where the SCFs are proved to be the greatest. The through-thickness lives may be utilized to conservatively represent the fatigue design lives of SHS bird-beak X-joints. Bird-beak SHS X-joints demonstrated better fatigue behaviors than those for traditional joints if the same service load is applied. • Stress concentration factors (SCFs) were measured for bird-beak X-joints under brace in-plane loading. • Finite element analysis was conducted to identify key parameters affecting SCFs. • Formulas were proposed for SCFs for bird-beak X-joints. • Fatigue tests were performed to determine fatigue life of bird-beak X-joints. • Joint stiffness degradation was recorded to explain fatigue failure process. [ABSTRACT FROM AUTHOR]