Journal of Constructional Steel Research最新文献

To evaluate the changes in the state of pan transmission lines in mountainous areas under the combined action of icing and wind, a novel numerical computation method was developed using segmental catenary theory and the Runge-Kutta algorithm, which enables the handling of arbitrary three-orthogonal distributed and concentrated loads. Validation was performed through an example test and a comparison with two other numerical methods. Given the mountainous terrain, models for icing and wind loads were used to assess the combined effects on multispan lines. The conditions of non-uniform and uniform icing were compared, and the relationships of the unbalanced tension to the spatial parameters of the line are discussed. The results demonstrate that non-uniform icing causes more significant changes in the state of the line in the longitudinal direction compared to uniform icing, and the two icing conditions result in opposite trends in longitudinal unbalanced tension as the spatial parameters increase, suggesting the importance of considering the icing distribution on multispan transmission lines. The transverse changes in the line were primarily influenced by wind loading, which showed a weak correlation with icing conditions, whereas the transverse unbalanced tension exhibited a notable positive relationship with the spatial parameters of the multispan transmission line.

The macro-mechanical performances of CFST column at low temperatures can be significantly affected by three main factors: the change of meso-material properties, the filling and frost heave effects caused by pore ice, and the interaction between each meso-component. Therefore, a three-dimensional thermo-mechanical sequential coupling mesoscopic simulation method was established and verified by existing experimental results with the maximum errors within 10 %. The seismic performances of CFST columns with various cross-section sizes (200–800 mm) at different temperatures (20, −30, −60 and − 90 °C) were simulated and investigated, with focused on the damage mechanism and quantitative analysis of the low-temperature effect on various seismic performance indexes (i.e., hysteretic characteristic, nominal shear strength, ductility, energy dissipation and reparability) as well as the corresponding size effects. The results indicate that the low temperature can increase the nominal strengths (i.e., peak strength, yield strength and ultimate strength), but weaken ductility, energy dissipation capacity and reparability of CFST columns. With the increase of cross-section size, the reparability increases, while other seismic performance indexes decrease, showing the size effect, which tends to be more obvious at low temperatures. The size effect on peak strength at −90 °C is enhanced by 115.5 % than that at 20 °C, while 127.9 % for yield strength and 113.5 % for ultimate strength. Based on research results, a modified size effect formula for calculating shear strengths of CFST columns considering the influence of low temperature and structural size was developed, which can provide references for seismic design of large-sized CFST columns in extreme low temperature environments.

High strength steel (HSS) has a broad application prospect in the field of bridge engineering, better meets the lightweighting of bridges. However, there is still a considerable lack of research on the fatigue properties of HSS. In order to study the fatigue properties of welded joints (WJ) of Q690D HSS, high cycle fatigue tests on unequal thickness butt welds (UTBW) and cross fillet welds (CFW) of Q690D HSS were carried out in this paper. The corresponding S-N curves were fitted. The fatigue properties are also evaluated in comparison with the existing research results. The research results show that the UTBW and CFW of Q690D HSS have good fatigue performance. The fatigue strength of UTBW is 1.96 times higher than the recommended value of GB50017. The design curve of BS7608 can better predict the fatigue life of UTBW when the number of cycles is more than 50,000 times. The fitted curve of CFW is lower than the design curve of GB50017 in the high stress area, and the fatigue strength of 95 % guarantee rate is similar to the recommended value of GB50017. The fatigue displacement curves can be roughly divided into a flat growth phase and a fast growth phase, the flat growth phase accounts for more than 90 % of the fatigue life. The fatigue strength of WJ did not show a clear pattern of change with the improvement of steel strength grade, and the distribution of fatigue parameters m and C of different strength grades of steel is more discrete.

To mitigate the issues of concrete cracking in the negative bending moment region of traditional steel-concrete composite beams, the concept of a prefabricated steel-UHPC (ultra-high performance concrete) lightweight composite beam was employed. Taking advantage of UHPC's superior tensile properties, a wet joint for the negative bending moment region of the steel-UHPC composite beam that includes a normal concrete transverse beam and a UHPC bridge deck is proposed in this study. A 1:2 scaled model bending test was conducted to experimentally study the flexural performance of the proposed wet joint and demonstrate its feasibility. The test results revealed that the interface between the transverse concrete beam and the longitudinal steel beam was generally the weak zone where failure occurred, with the fracture of the UHPC deck slab and the yielding of the steel bars in the deck recorded as the major factors contributing to the failure of the proposed joint structure. Through an actual bridge analysis, the flexural capacity of the joint structure, which was 3.7 times higher than the design load of the bridge, was quantitatively verified to meet the design requirements for practical engineering applications. In addition, the calculation method for computing the ultimate bending capacity of the joint structure was also proposed, in which the connection between the transverse concrete beam and longitudinal steel beam is considered as the crucial zone – with the analytical results showing good agreement with the experimental data. Overall, the calculation method provides a worthy reference datum for the development of steel-UHPC lightweight composite beams and their wet-joint designs in the negative moment region.

An approach is presented for the estimation of the parameters required to simulate the nonlinear monotonic (i.e., backbone) rotational response of Exposed-Column-Base-Plate (ECBP) connections subjected to moment and axial compression. A trilinear backbone curve is selected to represent the rotational response, defined by three deformation and two strength parameters; these properly represent the stiffness, strength, and ductility of the connections. This approach is accompanied by a tool to facilitate convenient estimation of the parameters. The approach is based on a combination of behavioral insights and physics-based models (for some parameters) as well as regression for other parameters, which are estimated from a dataset of eighty-four experiments on ECBP connections conducted over the last forty years in the United States, Europe, and Asia. Predictive equations are provided to estimate the various parameters defining the nonlinear response, and their efficacy is examined by comparing them with the test data; in addition, well-established techniques are implemented to avoid collinearity and the overfitting of regression models. The results show that the models presented in this work provide robust and accurate predictions for in-sample and out-of-sample data. Limitations are outlined.

Plate girders are primarily adopted for long spans that require higher load-carrying capacity like bridge girders and gantry girders. These sections however offer poor bending resistance in the plane of major axis i.e., about their minor axis. When unrestrained under loading, this leads to Lateral Torsional Buckling (LTB). In this study, the lateral rigidity of plate girders is improved by welding inclined rectangular plates to the compression flange of the plate girder. The combination of closed and open sections helps in improving the flexural and torsional rigidity of the girder. An attempt is also made to improve the flexural resistance by using steel of higher yield strength in the flanges. These hybrid girders further improved the strength-to-weight ratio of the girders. The cross-section of the test girders was proportioned as per AISC 360–16 such that their major mode of failure is lateral torsional buckling. The load-carrying capacity and failure modes of the test girders were studied numerically in ABAQUS before testing under single-point load in the laboratory. The response recorded experimentally is further compared with the theoretical investigation carried out with AISC 360–16, IS 800:2007 and EN-1993-1-5.

Static strain aging has significant effects on the mechanical behavior of steel materials and should be considered in the failure prediction of partially damaged welded steel connections. Micromechanical fracture models have been demonstrated to predict ductile fracture initiation in welded steel connections. This study investigates and updates the micromechanical fracture prediction model of structural steel and its weld metal affected by static strain aging. Q355B structural steel base metal, heat-affected zone (HAZ), and weld metal are adopted to manufacture 60 smooth round bar (SRB) and 126 notched round bar (NRB) specimens affected by different levels of static strain aging effect. The mechanical properties and true stress-strain curves affected by static strain aging are obtained for numerical analysis by conducting uniaxial tensile tests on the SRB specimens. The characteristic length and fracture toughness parameters of the micromechanical fracture prediction models are calibrated using uniaxial tensile tests and finite element analysis (FEA) of the NRB specimens. The applicability of the updated micromechanical fracture models to the three materials affected by strain aging is verified by introducing the calibrated micromechanical fracture models as fracture criteria into the user subroutine USDFLD in the ABAQUS FEA software. This study contributes to the ductile fracture analysis of partially damaged welded steel connections affected by strain aging using micromechanical fracture models.

Tie bars are commonly used in concrete-filled steel plate composite shear walls to connect the two steel faceplates. The present study focuses on the effective stress-strain relationships of the faceplates as they are indispensable in analyzing the seismic performance of composite members using fiber models. Elastic buckling analyses were first conducted using the finite element (FE) method. As the horizontal-to-vertical spacing ratio of the tie bars increases, the buckling mode changes from a single bulge in the region bounded by the tie bars and longitudinal edges to separated bulges between two adjacent columns of tie bars. Based on the calculated results, a simplified equation was developed for the elastic buckling stresses. Nonlinear FE analyses were then conducted on 207 models to obtain the effective stress-strain relationships of the faceplates with different yield strength and tie bar constraint conditions. The effective stress-strain relationships are primarily affected by the ratio of the steel yield strength to the elastic buckling stress. Still, they are significantly influenced by the initial geometric imperfections. Based on the FE analysis results, an effective stress-strain model was developed for the steel faceplates. Fiber model analyses of composite members with tie bars were also performed using the developed effective stress-strain model. The developed fiber models can reasonably simulate the behavior of the composite members.