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Abstract: This paper presents a model test and numerical finite element analysis (FEA) on the mechanical behavior of a composite joint in a truss cable-stayed bridge. The model test with the scale of 1:2.5 for the truss joint was conduct to fully understand the safety and serviceability. In the experiment, stress distribution, crack resistance ability and shear resistance of headed studs were carefully measured to investigate the mechanical performance, force transmission of the joint part. The maximum strain of the steel plate and concrete chord remained in the linear elastic region until 1.7 times the design load, which means there is a significant safety margin for such composites. On the basis of the experimental results of composite truss joints, three-dimensional finite element models are established. The results of the finite element analysis are in good agreement with those of the tests in terms of strength and stiffness. It is also expected that the results presented in this paper would be useful as references for the further research and the design of composite truss bridges and composite joints. [Copyright &y& Elsevier]

The development of all-steel tube-in-tube buckling controlled brace (TinT-BCB) is presented. The efficiency of the TinT-BCBs is evaluated experimentally and numerically. The cyclic behavior and fracture life of TinT-BCBs was first investigated through physical testing, followed by FE-based simulations revealing the inherent correlation between fracture and peak cyclic strain in load-bearing braces. The cyclic strain in plastic zones was recorded up to 0.02 strain range during the cyclic tests, enabling the study to use the recorded strain in verifying the FE simulation models. The strain response of plastic zones was captured by the FE simulation up to fracture in conventional large-size braces. The paper concludes that (1) the TinT-BCB, developed based on the buckling-controlling concept, has demonstrated stable and symmetrical cyclic response, with global and local buckling controlled up to 0.035–0.04 story drift ratio; (2) the TinT-BCB is proven to be effective in elongating cyclic fracture life of conventional CBF from 2% SDR to 3.5–4% SDR by adding simple buckling controller. The cost for adding the buckling controller is low in comparison with the substantially increased lateral strength and energy dissipation capacity; and (3) the efficiency of the TinT-BCB in improving overall cyclic behavior in general and elongating fracture life of braces in particular is attributed to its ability in controlling highly concentrated strain in plastic zones of conventional braces. By spreading the concentrated strain demand throughout the entire length, the buckling controller is shown to reduce excessive peak strains in conventional braces by 7–8 times. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents experimental and numerical results of dynamic cyclic tests carried out on two full-scale specimens of welded beam-to-column connections. In order to simulate the nonlinear dynamic behaviour of tested specimens, a fibre-based finite element beam is used to model beam and column members and a nonlinear rotational spring is also used to model welded connections. The effect of strain rate on beam and column behaviour is taken into account for each constitutive fibre using the Perzyna law. The effect of strain rate on welded connection is taken into account by extending the static Richard model to simulate its dynamic behaviour. The Krawinkler–Zoheri model, expressed as a function of normalized cumulative plastic strain, is introduced to quantify damage and degrading behaviour in terms of the strain-rate effect. The finite element Drain-2dx software is first upgraded for this purpose to carry out numerical investigations. The analytical results obtained from the numerical simulation, taking the strain rate effect and damage accumulation into account, predict well the structural dynamic behaviour up to failure of welded connections when compared with available experimental data. [Copyright &y& Elsevier]

Abstract: This paper investigates the behaviour of pin-ended axially loaded concrete encased steel composite columns. A nonlinear 3-D finite element model was developed to analyse the inelastic behaviour of steel, concrete, longitudinal and transverse reinforcement bars as well as the effect of concrete confinement of the concrete encased steel composite columns. The interface between the steel section and concrete, the longitudinal and transverse reinforcement bars, and the reinforcement bars and concrete were also considered that allowed the bond behaviour to be modeled and the different components to retain their profile during the deformation of the column. Furthermore, the initial overall (out-of-straightness) geometric imperfection was carefully incorporated in the model. The finite element model has been validated against published experimental results. The main objective of the study was to understand the structural response and modes of failure of the columns and to assess the composite column strengths against current design codes. The study covered slender, non-slender, stub and long concrete encased steel composite columns. The concrete strengths varied from normal to high strength (20–110 MPa). The steel section yield stresses also varied from normal to high strength (275–690 MPa). Furthermore, the variables that influence the composite column behaviour and strength comprising different slenderness ratios, concrete strength and steel yield stress were investigated in a parametric study. It is shown that the increase in structural steel strength has a small effect on the composite column strength for the columns having higher relative slenderness ratios due to the flexural buckling failure mode. The composite column strengths obtained from the finite element analysis were compared with the design strengths calculated using the American Institute for Steel Construction AISC and Eurocode 4 for composite columns. Generally, it is shown that the EC 4 accurately predicted the design strength for the concrete encased steel composite columns having a concrete cylinder strength of 30 MPa and structural steel yield stresses of 275 and 460 MPa, which are in the limits of the code, which otherwise, was generally conservative. The AISC predictions were quite conservative for all the concrete encased steel composite columns. [Copyright &y& Elsevier]

Abstract: Material yielding is typically modeled either by plastic zone or plastic hinge methods under the context of geometric and material nonlinear finite element methods. In fire analysis of steel structures, the plastic zone method is widely used, but it requires extensively more computational efforts. The objective of this paper is to develop the nonlinear material model allowing for interaction of both axial force and bending moment, which relies on the plastic hinge method to achieve numerical efficiency and reduce computational effort. The biggest advantage of the plastic-hinge approach is its computational efficiency and easy verification by the design code formulae of the axial force–moment interaction yield criterion for beam–column members. Further, the method is reliable and robust when used in analysis of practical and large structures. In order to allow for the effect of catenary action, axial thermal expansion is considered in the axial restraint equations. The yield function for material yielding incorporated in the stiffness formulation, which allows for both axial force and bending moment effects, is more accurate and rational to predict the behaviour of the frames under fire. In the present fire analysis, the mechanical properties at elevated temperatures follow mainly the Eurocode 3 [Design of steel structures, Part 1.2: Structural fire design. European Committee for Standisation; 2003]. Example of a tension member at a steady state heating condition is modeled to verify the proposed spring formulation and to compare with results by others. The behaviour of a heated member in a highly redundant structure is also studied by the present approach. [Copyright &y& Elsevier]

In this paper, a new modeling method is proposed for a uni-planar tubular K-joint containing an arbitrary surface crack located along the chord weld toe. The crack is defined first in a 2-D plane and then mapped onto a 3-D curved crack surface. Subsequently, an automatic mesh generation is developed for producing the complete finite element mesh model. This technique can be realized by sub-dividing the entire structure into distinct zones. In each zone, the mesh is generated separately. After the mesh of all the zones have been completed, the complete model is obtained by merging the mesh of every zone. It has been proved to be efficient and effective in producing different quality mesh at different zones. In order to locate the likely crack initiation position, the hot spot stresses and hence the stress concentration factors (SCFs) need to be determined precisely. The hot spot stress correlated to the number of cycles, i.e. the S–N curve, has been used to predict the life of uncracked tubular K-joints. For a cracked tubular K-joint, its remaining service life depends on the fracture parameter called the stress intensity factors (SIFs). Two different methods, namely the displacement extrapolation and -integral methods, are used to evaluate the SIFs along the crack front for different crack shapes in this study. Convergence tests for numerical analysis have been carried thoroughly to check the accuracy of the computed SIFs. The two sets of numerical results are in complete agreement. To evaluate the accuracy of numerical modeling, a full-scale fatigue test on tubular K-joint subjected to combined axial load and in-plane bending load was conducted. Comparison between the numerical and experimental results again shows a good agreement. Therefore, the proposed modelling and mesh generation methods demonstrate that the estimated stress intensity factors for any tubular K-joints are both accurate and reliable. [Copyright &y& Elsevier]

This paper presents parametric equations to predict the stress concentration factors (SCF) of completely overlapped tubular K(N)-joints under lap brace axial compression. 192 finite element (FE) models of the joint have been created for the parametric study using a commercial FE package, MARC. In the analysis, both 8-node thick shell and 20-node solid elements are found suitable for modelling the joint. The comparison of strain concentration factors (SNCF) between the FE models and the tested specimen shows that the difference is less than 0.42. However, in view of the computational effort, the FE model with 8-node thick shell element is used for the parametric analysis. The study reveals that the effect of through brace to chord wall thickness ratio on SCF of the joint is most crucial. The maximum SCF occurs on the through brace saddle near the lap brace. The gap size on the through brace surface between the outer surfaces of the chord and the lap brace significantly affects the SCF. Based on the FE data, a set of parametric equations is derived to predict the SCF of the joint. The reliability of the equations has been verified against the requirement of the Fatigue Guidance Review Panel. [Copyright &y& Elsevier]