International Journal of Steel Structures

In order to reveal more information and better understanding on the behavior and failure mechanisms of high strength steel (HSS) extended endplate connections at ambient temperature and after fire, an experimental and theoretical study has been conducted and presented in this paper. The provisions of Eurocode 3 are verified with the test results. Because strength of bolts decreases more rapidly than that of structural steels, failure modes of endplate connections may change after fire. Hence, a series of equations are proposed to predict failure modes of endplate connections after fire. Furthermore, FE simulations which can predicate the performance of HSS extended endplate connections with reasonable accuracy are adopted to study the behaviors of the connections after cooling down from various fire temperatures and to validate the accuracy of the proposed equations. Moreover, a parametric study is carried out to explore an optimization design method. It is found that the current provisions of EC3 can justifiably predict failure modes and plastic flexural resistances of HSS extended endplate connections both at ambient temperature and cooling down from 550 °C, but it is not the case for their initial rotational stiffness and rotation capacity. In order to avoid brittle failure mode of endplate connections after fire, appropriately increasing the diameter or grade of bolts in the design is suggested. What is more, the match of steel grade and thickness of column flange and endplate as well as beam should be considered in the optimization design of beam-column endplate connections.

This paper addresses the dynamic response of a continuous beam bridge with different levels of track irregularities under a single, moving high-speed train. The train is modeled as one-foot sprung masses. The bridge is described as an Euler-Bernoulli beam supported by several hinged supports. Rayleigh damping coefficients of the bridge are calculated by using the modal damping ratio. Random track irregularities are generated by power spectrum density functions. The interaction equation of motion is derived and then solved by using the Newmark-beta method combined with the Newton-Raphson method. The dynamic impact factors of a single-span simply supported bridge and a five-span continuous beam bridge under the same train are calculated and compared for verification. Additionally, a three-span continuous beam bridge with various damping ratios and track irregularities under a Korea Train Express (KTX) train is used as an example to investigate the dynamic impact factors at the midpoints of different bridge spans in both downward and upward directions, the deck rotations at the bridge supports, and the average maximum acceleration of the train bodies under different conditions.

Circular hollow steel sections are examples of members that are becoming increasingly popular. The demand of high strength with sufficient ductility for materials is increasing for design of long-span and high-rise structures. HSB 600 steel, High performance Steel for Bridge with minimum tensile yield strength, f y , of 480 N/mm2 for all thickness, was introduced in the Korea Building Code (KBC 2009, 2009). However, current design standards may not be applicable to circular hollow sections with HSB 600 steel since they have been established based on tests of steels with yield stress up to 355 MPa and a ductility ratio up to 0.8. Six full scale circular hollow section gap K-joints were tested and analyzed to investigate the applicability of current design standards. Two series using SHB600 and SS400 steel grades were tested. Three specimens in each series with various gaps between bracing members were evaluated. All chord members were 2,250 mm and brace members were 1,400 mm in length. All chord and brace members were 350mm in diameter and 12 mm in wall thickness. Based on the limited test and analysis results of this circular hollow section gap K-joint, the applicability to current standards, the possible elastic local buckling and gap effects of the different grades of steel are examined.

The fire accidents casually happen during operation of ship, which would influence the load carrying capacity of stiffened panel of ship structures due to the thermal load. The present paper aims to understand the influence of thermal loads on the collapse behaviour of stiffened panels under longitudinal compressive load. Considering the heating and cooling down processes, the collapse behaviours of the stiffened panels under combined in-plane displacement and heat loads representative of fire accident are simulated in the FE (finite element) analysis herein. Firstly, the thermal load is considered to investigate the stress state of the stiffened panels during heating and cooling processes. It is found that the stiffened panels would collapse during thermal loads for the structure with large heated zone. After that, the longitudinal compression loads are applied to assess the collapse strength of the stiffened panels. The parametric studies including different geometrical dimensions and areas of heat zone are performed in detail to quantify the effects of heat loads on the collapse behaviours of stiffened panels. It is found that the expansion could produce biaxial stress state that depends on not only in-plane stiffness but also collapse modes, and for stiffened panels with various heated area the cooling down to room temperature induce similar ultimate strength to that without considering heat loads.

In recent years, steel or composite beam-column connections adopting blind fasteners have drawn increasing praise due to the rapid development of assembled steel structures. However, limited researches have paid attention to the experimental and analytical behavior of concrete filled double-skin steel tube (CFDST) column blind bolted joints. For investigating the structural performance and seismic behavior of this type of connection, cyclic tests on blind bolted joints to square CFDST columns were carried out to explore the effects of column hollow ratio and end plate type. Finite element analytical modelling of the semi-rigid joint was performed considering complex contact interactions and material models. Good agreement between the test and analytical results was observed in terms of the failure modes and the hysteretic behavior. Substantial parametric analyses were conducted on typical CFDST column connections to observe the influence of parameters including strength of steel tube, column hollow ratio and bolt pretension force. Furthermore, certain constructional measures commonly employed in engineering practice were also discussed. It was concluded that the CFDST column blind bolted to the steel beam joint has favorable seismic behavior and is feasible for application in high-intensity earthquake regions.

Thin-walled steel circular hollow section (CHS) is widely used in wind turbine towers, where the tube is subjected to axial load combined with bending moment. Understanding the behavior of axially loaded thin-walled tubes with large diameter-to-thickness (D/t) ratios is crucial for the design of such structures. To investigate the behavior of axially loaded thin-walled circular hollow section steel tubes, 16 stub columns were tested with the D/t ratio ranging from 75 to 300. The experimental results showed that the compressive strength decreased sharply with the increase of the D/t ratio. The experimental result indicated that the tubes with smaller D/t ratios failed with outward deformation without visible local buckling. With the increase of the D/t ratio, local buckling appeared at the peak load. The finite element method was used to model the behavior of axially loaded stub columns. The experimental results were used to validate the accuracy of the finite element results. Based on the finite element model, the influences of the D/t ratio, the initial geometric deformation and the initial residual stress were analyzed. Design guidelines in Eurocode3, AISC-LRFD, AS4100 and S16-9 on thin-walled steel members were used to compare with the experimental and calculated results. Among them, the results based on AS4100 were the closest to the experimental results.

The design of un-braced frames using wind-moment method (WMM) with cruciform column (CCUB) section as vertical member is presented here. Steel frames on a regular grid with approximately equal column spacings in the y-y and z-z direction using UC/UB sections has resulted in minor axis controlled the design, which leads to a significant loss in performance. The use of CCUB sections with equal I y and I z warrants an equal behaviour in both directions whilst ensuring that both the major and minor axis beam to column connections remain straightforward. The study has been conducted on 2-bay and 4-bay plane frames with 2, 4, 6 and 8 storey heights, and two different load cases are considered: minimum wind load in conjunction with maximum gravity load and vice versa. Structural design optimization of steel frames was conducted on the selection of steel sections for beam and column. The selection was carried out in such a way that the steel frame had the minimum weight while the performance of the structure was within the limitations described by BS EN 1993-1-1: 2005. Significant column weight savings (between 17–66%) was achieved by using CCUB section in the design, as compared to conventional UC sections.

This paper presents a series of bending tests performed on G550 high strength cold-formed steel Z-section members under pure bending and moment gradient. In tests, failure resulted from distortional buckling or the interaction between local and distortional buckling. The test results indicated that the bending strength for moment gradient is greater than that for pure bending. The increasing magnitude is closely bound up with the member’s buckling modes since moment gradient has a significant effect on distortional buckling but has a minor effect on local buckling. Moreover, finite element analysis was applied to verify the tests and the numerical results agree well with test data according to bending strength and failure modes. Furthermore, the test results were compared with the Direct Strength Method (DSM) formulas stipulated in AISI (2016), and it is found that the DSM provides a good agreement with the bending strength for distortional buckling but provides unconservative predictions for the bending strength for interaction between local and distortional buckling.