• Steel and Composite Structures
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• v.11 no.2
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• pp.93-114
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• 2011

Flange and web local buckling in beam plastic hinge regions of steel moment frames can prevent beam-column connections from achieving adequate plastic rotations under earthquake-induced forces. This threat is especially valid for existing steel moment frame buildings with beams that lack adequate flange/web slenderness ratios. As the use of fiber reinforced polymers (FRP) have increased in strengthening and repair of steel members in recent years, using FRPs in stabilizing local instabilities have also attracted attention. Previous computational studies have shown that longitudinally oriented glass FRP (GFRP) strips may serve to moderately brace beam flanges against the occurrence of local buckling during plastic hinging. An experimental study was conducted at Izmir Institute of Technology investigating the effects of GFRP reinforcement on local buckling behavior of existing steel I-beams with flange slenderness ratios (FSR) exceeding the slenderness limits set forth in current seismic design specifications and modified by a bottom flange triangular welded haunch. Four European HE400AA steel beams with a depth/width ratio of 1.26 and FSR of 11.4 were cyclically loaded up to 4% rotation in a cantilever beam test set-up. Both bare beams and beams with GFRP sheets were tested in order to investigate the contribution of GFRP sheets in mitigating local flange buckling. Different configurations of GFRP sheets were considered. The tests have shown that GFRP reinforcement can moderately mitigate inelastic flange local buckling.

• Journal of Korean Association for Spatial Structures
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• v.4 no.1 s.11
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• pp.77-86
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• 2004

It is the buckling of the compression portions of the deckplate that govern its behaviour under wet concrete construction loading. The size and position of intermediate stiffeners in the compression flanges of thin-plate steel decks exert a strong influence on the dominant buckling mode of the flange. Test sections composed of high-strength steel were brake pressed with a variety of Flat-hat intermediate stiffeners in the compression flange forming a progression from small to large stiffeners. The ABAQUS program to determine the effectiveness of intermediate stiffeners in controlling buckling modes is undertaken. A series of specimens are loaded with simple beam. Various buckling wave forms prior to ultimate failure through a plastic collapse mechanism. The experimentally determined buckling stresses are found to be comparable with studies performed using the ABAQUS program analysis and using each country code.

• Steel and Composite Structures
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• v.28 no.2
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• pp.251-266
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• 2018

Compared to conventional flat web I-beams, the prediction of shear buckling stress of corrugated web steel beams (CWSBs) is not straightforward. But the CWSBs combined advantages of lightweight large spans with low-depth high load-bearing capacities justify dealing with such difficulties. This work investigates experimentally and analytically the shear strength of trapezoidal CWSBs. A set of large scale CWSBs are manufactured and tested to failure in shear. The results are compared with widely accepted CWSBs shear strength prediction models. Confirmed by the experimental results, the linear buckling analyses of trapezoidal corrugated webs demonstrated that the local shear buckling occurs only in the flat plane folds of the web, while the global shear buckling occurs over multiple folds of the web. New analytical prediction model accounting for the interaction between the local and global shear buckling of CWSBs is proposed. Experimental results from the current work and previous studies are compared with the proposed analytical prediction model. The predictions of the proposed model are significantly better than all other studied models. In light of the dispersion of test data, accuracy, consistency, and economical aspects of the prediction models, the authors recommend their proposed model for the design of CWSBs over the rest of the models.

• Steel and Composite Structures
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• v.2 no.1
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• pp.21-34
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• 2002

A model of the process of local buckling in tubular steel structural elements is presented. It is assumed that this degrading phenomenon can be lumped at plastic hinges. The model is therefore based on the concept of plastic hinge combined with the methods of continuum damage mechanics. The state of this new kind of inelastic hinge is characterized by two internal variables: the plastic rotation and the damage. The model is valid if only one local buckling appears in the plastic hinge region; for instance, in the case of framed structures subjected to monotonic loadings. Based on this damage model, a new finite element that can describe the development of local buckling is proposed. The element is the assemblage of an elastic beamcolumn and two inelastic hinges at its ends. The stiffness matrix, that depends on the level of damage, the yielding function and the damage evolution law of the two hinges define the new finite element. In order to verify model and finite element, several small-scale frames were tested in laboratory under monotonic loading. A lateral load at the top of the frame was applied in a stroke-controlled mode until local buckling appears and develops in several locations of the frame and its ultimate capacity was reached. These tests were simulated with the new finite element and comparison between model and test is presented and discussed.

• Structural Engineering and Mechanics
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• v.48 no.3
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• pp.367-382
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• 2013

Different types of long slender pile shall buckle with weak soil and liquefied stratum surrounded. Different from considering single side earth pressure, it was suggested that the lateral earth pressure can be divided into two categories while buckling: the earth pressure that prevent and promotes the lateral movement. Active and passive earth pressure calculation model was proposed supposing earth pressure changed linearly with displacement considering overlying load, shaft resistance, earth pressure at both sides of the pile. Critical buckling load calculation method was proposed based on the principle of minimum potential energy quoting the earth pressure calculation model. The calculation result was contrasted with the field test result of small diameter TC pile (Plastic Tube Cast-in-place pile). The fix form could be fixed-hinged in the actual calculation assuring the accuracy and certain safety factor. The contributions of pile fix form depend on the pile length for the same geological conditions. There exists critical friction value in specific geological conditions that the side friction has larger impact on the critical buckling load while it is less than the value and has less impact with larger value. The buckling load was not simply changed linearly with friction. The buckling load decreases with increased limit active displacement and the load tend to be constant with larger active displacement value; the critical buckling load will be the same for different fix form for the small values.

• Journal of Korean Association for Spatial Structures
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• v.18 no.4
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• pp.113-121
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• 2018

U-flanged truss beam is composed of u-shaped upper steel flange, lower steel plate of 8mm or more thickness, and connecting lattice bars. Upper flange and lower plate are connected by the diagonal lattice bars welded on the upper and lower sides. In this study the structural experiments on the U-flanged truss beams with various shapes of upper flange were performed, and the flexural and shear capacities of U-flanged truss beam in the construction stage were evaluated. The principal test parameters were the shape of upper flange and the alignment space of diagonal lattice bars. In all the test specimens, the peak loads were determined by the buckling of lattice bar regardless of the upper flange shape. The test results have shown that the buckling of lattice bar is very important design factor and there is no need to reinforce the basic u-shaped upper flange. However, the early lattice buckling occurred in the truss beam with upper steel bars because of the insufficient strength and stiffness of upper chord, and the reinforcement in the upper chord is necessary. The formulae of Eurocode 3 (2005) have presented more exact evaluations of lattice buckling load than those of KBC 2016.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.1
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• pp.123-134
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• 2019

This paper proposed a new design equation for the inelastic lateral torsional buckling (LTB) of singly symmetric stepped I-beams with non-compact flange sections. The proposed equation was generated using a finite element program, ABAQUS, and a statistical program, MINITAB. The parameters used were the stepped beams parameters; ${\alpha}$, ${\beta}$, and ${\gamma}$ and the length-to-height ratio ($L_b/h$) of the beam. The proposed equation was further validated by means of experimental test, where beams were subjected to four-point bending and supported by roller and lateral braces near the end supports. In addition, finite element models were simulated using the same parameters used in the experimental test to verify the results of the test conducted. It was proved that LTB capacity calculated from the proposed equation is accurate and conservative in comparison with the yielded values from the FEM and actual test, making it a reliable and safe approach in calculating the buckling capacities of singly symmetric stepped beams with non-compact flange sections.

• Steel and Composite Structures
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• v.50 no.6
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• pp.675-688
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• 2024

Cold-formed steel (CFS) is prone to buckling failure under loading. Lightweight concrete (LC) made of lightweight aggregate has light weight and excellent thermal insulation performance. However, concrete is brittle in nature which is why different materials have been used to improve this inherent behavior of concrete. The distortional buckling (DB) performance of cold-formed steel-lightweight concrete (CFS-LC) composite columns was investigated in this paper. Firstly, the compressive strength test of foam concrete (FC) and ceramsite concrete (CC) was carried out. The performance of the CFS-LC members was investigated. The test results indicated that the concrete-filled can effectively control the DB of the members. Secondly, finite element (FE) models of each test specimen were developed and validated with the experimental tests followed by extensive parametric studies using numerical analysis based on the validated FE models. The results show that the thickness of the steel and the strength of the concrete-filled were the main factors on the DB and bearing capacity of the members. Finally, the bearing capacity of the test specimens was calculated by using current codes. The results showed that the design results of the AIJ-1997 specification were closer to the experimental and FE values, while other results of specifications were conservative.

• Steel and Composite Structures
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• v.4 no.1
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• pp.1-8
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• 2004

Tests on steel tubular columns of square, rectangular and circular section filled with normal and lightweight aggregate concrete were conducted to investigate the failure modes of such composite columns. Thirty-six full scale columns filled with lightweight and normal weight aggregate concrete, eighteen specimens for each, were tested under axial loads. Nine hollow steel sections of similar specimens were also tested and results were compared to those of filled sections. The test results were illustrated by a number of load-deflection and axial deformation curves. The results showed that both types of filled columns failed due to overall buckling, while hollow steel columns failed due to bulging at their ends (local buckling). According to the above-mentioned results, and due to low specific gravity and thermal conductivity of the lightweight concrete the further interest should be concentrated in replacing the normal concrete by the lightweight aggregate concrete.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.51-55
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• 2004

A composite Iso-grid panel is manufactured and tested by compressive load. Vertical stringers and side stringers are joined with skin by secondary bonding using a liquid type adhesive. Bonding fixtures were developed to attach the stringers to skin. A-scan was done for inspection of secondary bonding region. The out of displacement field is visualized by shadow moire system. The strain and vertical displacement are measured by strain gages and L VDT (Linear Variable Differential Transformer). A local buckling is occurred at all grid sections. After that, the final failure is occurred. The strain of side stringer is much less than that of vertical stringer and skin. Due to the side stringer, the local buckling is delayed. Therefore the ratio of the first buckling to failure load is greater than that of vertical stringer stiffened panel.