• Structural Engineering and Mechanics
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• v.59 no.2
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• pp.243-259
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• 2016

This research develops a finite element code for the transient dynamic analysis of tapered fiber reinforced polymer (FRP) poles with hollow circular cross-section and flexible joints used in power transmission lines. The FRP poles are modeled by tapered beam elements and their flexible joints by a rotational spring. To solve the time equations of transient dynamic analysis, precise time integration method is utilized. In order to verify the utilized formulations, a typical jointed FRP pole under step, triangular and sine pulses is analyzed by the developed finite element code and also ANSYS commercial finite element software for comparison. Thereafter, the effect of joint flexibility on its dynamic behavior is investigated. It is observed that by increasing the joint stiffness, the amplitude of the pole tip deflection history decreases, and the time of occurrence of the maximum deflection is earlier.

• Structural Engineering and Mechanics
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• v.21 no.6
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• pp.677-698
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• 2005

In engineering practice, tubular connections are usually assumed pinned or rigid. Recent research showed that tubular joints may exhibit non-rigid behavior under axial or bending loads. This paper is concerned with establishing a new classification for tubular joints and investigating the effect of joint rigidity on the global behavior of CHS (Circular Hollow Section) lattice girders. Parametric formulae for predicting tubular joint rigidities are proposed, which are based on the finite element analyses through systematic variation of the main geometric parameters. Comparison with test results proves the reliability of these formulae. By considering the deformation patterns of respective parts of Vierendeel lattice girders, the boundary between rigid and semirigid tubular connections is built in terms of joint bending rigidity. In order to include characteristics of joint rigidity in the global structural analysis, a type of semirigid element which can effectively reflect the interaction of two braces in K joints is introduced and validated. The numerical example of a Warren lattice girder with different joint models shows the great effect of tubular joint rigidities on the internal forces, deformation and secondary stresses.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.1
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• pp.298-303
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• 2016

Owing to the advantages of reduced weight and wind effect, the space-framed towers that consist of vertical and horizontal members of circular hollow tubular sections have been adopted widely for various purposes. It is critical to guarantee the strengths of tubular joints where vertical and horizontal members are connected structurally to make the entire space-framed system behave as a single tower structure. In this study, a strength evaluation was conducted for T-type tubular joints subjected to the concurrent action of compression and bending. Three of the available design codes, i.e., AISC, Eurocode 3, ISO 19902 were investigated and a design equation was suggested for an ultimate strength interaction between the axial force and bending moment based on nonlinear finite element analyses by selecting the slenderness ratios at the joints as major parameters.

• Journal of Korean Society of Steel Construction
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• v.30 no.2
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• pp.115-126
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• 2018

Internationally representative steel design standards have forbidden or limited the application of high-strength steels to tubular joints, partly because of concerns about their unique material characteristics such as high yield ratio. Most of design standards stipulate that for steels whose yield strengths exceed 355 or 360 MPa, the strength equations cannot be utilized or strength reduction factor below 1.0 should be multiplied. However, the mechanical background behind these limitations is not clear. Experimental testing of high-strength steel CHS (circular hollow section) X-joints recently conducted by the authors also clearly indicated that the current limitations might be unduly conservative. As a continuing work, extensive, test-validated numerical analyses were made to investigate the behavior of high-strength steel CHS X-joint under axial compression. Three steel grades covering ordinary to very high strength steels were considered in the analysis. Again it was found that the high strength penalty to the joint strength in current standards is too severe and needs to be relaxed. The high-strength steel joints under the effects of chord stress generally showed higher strength than the ordinary steel joints and their strengths were conservatively predicted by current standards. It is also emphasized that current format of the CHS X-joint strength equation does not reflect observed behavior and needs to be recast.

• Steel and Composite Structures
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• v.18 no.3
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• pp.739-756
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• 2015

This paper presents investigations on the hysteretic behavior of concrete-filled circular tubular (CFCT) T-joints subjected to axial cyclic loading at brace end. In the experimental study, four specimens are fabricated and tested. The chord members of the tested specimens are filled with concrete along their full length and the braces are hollow section. Failure modes and load-displacement hysteretic curves of all the specimens obtained from experimental tests are given and discussed. Some indicators, in terms of stiffness deterioration, strength deterioration, ductility and energy dissipation, are analyzed to assess the seismic performance of CFCT joints. Test results indicate that the failures are primarily caused by crack cutting through the chord wall, convex deformation on the chord surface near brace/chord intersection and crushing of the core concrete. Hysteretic curves of all the specimens are plump, and no obvious pinching phenomenon is found. The energy dissipation result shows that the inelastic deformation is the main energy dissipation mechanism. It is also found from experimental results that the CFCT joints show clear and steady stiffness deterioration with the increase of displacement after yielding. However, all the specimens do not perform significant strength deterioration before failure. The effect of joint geometric parameters ${\beta}$ and ${\gamma}$ of the four specimens on hysteretic performance is also discussed.

• Journal of Korean Society of Steel Construction
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• v.22 no.2
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• pp.109-119
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• 2010

There are many restrictions in the application of high-strength HSSs, including yield strength and yield ratio for the 600-MPa steel. The AISC and Canadian codes recommend that the yield strength and yield ratio of HSS members be 360 MPa and 80%, respectively. It is important to understand the true buckling behaviors of HSSs using high-strength steel at the limit states. There are many experimental data regarding the rectangular HSSs, and the circular ones are not enough for high-strength steel. Therefore, this study was conducted to create a better understanding of the buckling behaviors of the 600- and 400-MPa steels based on the results of the finite-element analysis that was done before the experiment. To understand the structural behaviors of the aforementioned steels, the width-to-thickness ratios, the angle of the web members, the yield strength, and the gap of the web members were selected as the main parameters in this study, and ABAQUS, a general finite-element program, was used.As a result, the compression web member reached elastic buckling in the 600-MPa steel and inelastic buckling in the 400-MPa steel. A brittle fracture occurred in the case where the yield ratio was greater than 80%. At the same time, it was found that the limit strength determined via FEM analysis had a higher value compared to the code evaluation with the variation of the width-to-thickness ratio in the main code member. The change in the connection load in high-strength steels was not identified by the other factors.