• Steel and Composite Structures
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• v.30 no.4
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• pp.393-403
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• 2019

Cold-formed steel (CFS) has a great potential to meet the global challenge of fast-track and durable construction. CFS members undergo large buckling instabilities due to their small wall thickness. CFS beams with corrugated webs have shown great resistance towards web buckling under flexure, when compared to the conventional I-sections. However, the magnitude of global imperfections significantly affects the performance of CFS members. This paper presents the first attempt made to experimentally study the effect of global imperfections on the structural efficiency of various strengthening schemes implemented in CFS beams with corrugated webs. Different strengthening schemes were adopted for two types of beams, one with large global imperfections and the other with small imperfections. Strength and stiffness characteristics of the beams were used to evaluate the structural efficiency of the various strengthening schemes adopted. Six tests were performed with simply supported end conditions, under four-point loading conditions. The load vs. mid-span displacement response, failure loads and modes of failure of the test specimens were investigated. The test results would compensate the lack of experimental data in this area of research and would help in developing numerical models for extensive studies for the development of necessary guidelines on the same. Strengthening schemes assisted in enhancing the member performance significantly, both in terms of strength and stiffness. Hence, providing an economic and time saving solution to such practical structural engineering problems.

• Steel and Composite Structures
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• v.42 no.4
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• pp.447-458
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• 2022

Cold-formed steel (CFS) sections are thin-walled, therefore, more susceptible to different types of geometric imperfections. Global type of geometric imperfections has a significant impact on the load-carrying capacity of flexural members. This paper reports an experimental study that discusses the influence of global imperfections on the flexural response of CFS built-up I-beams composed of two lipped channels, with simply supported ends, under four-point loading. Global imperfections of magnitude over eight times the maximum permissible ones were induced in the specimens, leading to their distress. Using various simple stiffening schemes, the capacity and stiffness of the distressed specimens were improvised. The performance comparisons were made based on the maximum loads resisted, flexural stiffnesses offered, and failure modes experienced by the specimens. As experimental data on such distressed specimens are currently lacking in the literature, the test results of the present study will provide the necessary data needed by future researchers to numerically extend this study further, which will help in the development of necessary design guidelines for the same. The stiffening schemes significantly improved the structural efficiency of distressed specimens in terms of strength and stiffness, by over 60%. As a result, an effective and time-saving solution to such realistic structural engineering problems is given.

• Steel and Composite Structures
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• v.6 no.5
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• pp.401-415
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• 2006

Based on a non-linear model taking into account flexural-torsional couplings, analytical solutions are derived for lateral buckling of simply supported I beams under some representative load cases. A closed form is established for lateral buckling moments. It accounts for bending distribution, load height application and pre-buckling deflections. Coefficients $C_1$ and $C_2$ affected to these parameters are then derived. Regard to well known linear stability solutions, these coefficients are not constant but depend on another coefficient $k_1$ that represents the pre-buckling deflection effects. In numerical simulations, shell elements are used in mesh process. The buckling loads are achieved from solutions of eigenvalue problem and by bifurcations observed on non linear equilibrium paths. It is proved that both the buckling loads derived from linear stability and eigenvalue problem lead to poor results, especially for I sections with large flanges for which the behaviour is predominated by pre-buckling deflection and the coefficient $k_1$ is large. The proposed solutions are in good agreement with numerical bifurcations observed on non linear equilibrium paths.

• Steel and Composite Structures
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• v.8 no.2
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• pp.145-158
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• 2008

In slender sections there is a substantial post-buckling strength provided after the formation of local buckling waves. These waves happened due to normal stresses or shear stresses or both. In this study, a numerical investigation of the behavior of slender I-section beams in combined pure bending and shear has been described. The studied cases were assumed to be prevented from lateral torsional buckling. To achieve this aim, a finite element model that simulates the geometric and material nonlinear nature of the problem has been developed. Moreover, the initial geometric imperfections were included in the model. Different flange and web width-thickness ratios as well as web panel aspect ratios have been considered to draw complete set of interaction diagrams. Results reflect the interaction behavior between flange and web in resisting the combined action of moments and shear. In addition, the web panel aspect ratio will not significantly affect the combined ultimate shear-bending strength as well as the post local buckling strength gained by the section. Results are compared with that predicted by both the Eurocode 3 and the American Iron and Steel specifications, AISI-2001. Finally, an empirical interaction equation has been proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.209-212
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• 2008

Corrugated steel-concrete composite deck with I-beam welded is lighter and has higher load carrying capacity than RC slabs due to an I-beam embedded in the corrugated deck. The methods suggested from ACI and design standard of roadway bridge are used to evaluate effective moment inertia of RC structures. This paper presents evaluation and application of effective moment inertia for corrugated steel-concrete composite deck with I-beam welded by using the methods suggested from design standard of roadway bridge, ACI and CEB-FIP MC-90. In order to evaluate effective moment inertia, a series of flexural experiments were carried out. Five beams were built and the parameters considered in the experiments were studs, shape of the sections and connections of the beams. By using the aforementioned methods, effective moments of inertia was calculated and they were compared with the experimental results. As a result, The method suggested from CEB-FIP MC-90 yielded more satisfactory agreement than that from ACI. It was found that the beam has studs showed high load-carrying capacity and high effective moment of inertia.

• Steel and Composite Structures
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• v.4 no.1
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• pp.23-36
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• 2004

The inelastic lateral-distortional buckling of doubly-symmetric hot-rolled I-section beam-columns subjected to a concentric axial force and uniform bending with elastic restraint which produce single curvature is investigated in this paper. The numerical model adopted in this paper is an energy-based method which leads to the incremental and iterative solution of a fourth-order eigenproblem, with very rapid solutions being obtained. The elastic restraint considered in this paper is full restraint against translation, but torsional restraint is permitted at the tension flange. Hitherto, a numerical method to analyse the elastic and inelastic lateral-distortional buckling of restrained or unrestrained beam-columns is unavailable. The prediction of the inelastic lateral-distortional buckling load obtained in this study is compared with the inelastic lateral-distortional buckling of restrained beams and the inelastic lateral-torsional buckling solution, by suppressing the out-of-plane web distortion, is published elsewhere and they agree reasonable well. The method is then extended to the lateral-distortional buckling of continuously restrained doubly symmetric I-sections to illustrate the effect of web distortion.

• Structural Engineering and Mechanics
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• v.90 no.6
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• pp.611-633
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• 2024

This study intends to investigate the response of multi-cell (MC) beams to flexural loads in which the primary reinforcement is composed of both metallic and non-metallic materials. "Multi-cell" describes beam sections with multiple longitudinal voids separated by thin webs. Seven reinforced concrete MC beams measuring 300×200×1800 mm were tested under flexural loadings until failure. Two series of beams are formed, depending on the type of main reinforcement that is being used. A control RC beam with no openings and six MC beams are found in these two series. Series one and two are reinforced with metallic and non-metallic main reinforcement, respectively, in order to maintain a constant reinforcement ratio. The first crack, ultimate load, deflection, ductility index, energy absorption, strain characteristics, crack pattern, and failure mode were among the structural parameters of the beams under investigation that were documented. The primary variables that vary are the kind of reinforcing materials that are utilized, as well as the kind and quantity of mesh layers. The outcomes of this study that looked at the experimental and numerical performance of ferrocement reinforced concrete MC beams are presented in this article. Nonlinear finite element analysis (NLFEA) was performed with ANSYS-16.0 software to demonstrate the behavior of composite MC beams with holes. A parametric study is also carried out to investigate the factors, such as opening size, that can most strongly affect the mechanical behavior of the suggested model. The experimental and numerical results obtained demonstrate that the FE simulations generated an acceptable degree of experimental value estimation. It's also important to demonstrate that, when compared to the control beam, the MC beam reinforced with geogrid mesh (MCGB) decreases its strength capacity by a maximum of 73.33%. In contrast, the minimum strength reduction value of 16.71% is observed in the MC beams reinforced with carbon reinforcing bars (MCCR). The findings of the experiments on MC beams with openings demonstrate that the presence of openings has a significant impact on the behavior of the beams, as there is a decrease in both the ultimate load and maximum deflection.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.6
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• pp.53-60
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• 2008

The cross-sections of continuous multi-span beams sometimes suddenly increase, or become stepped, at the interior supports of continuous beams to resist high negative moments. The three-dimensional finite-element program ABAQUS (2007) was used to analytically investigate the inelastic lateral-torsional buckling behavior of stepped beams subjected to linear moment gradient and resulted in the development of design equations. The ratios of the flange thickness, flange width, and stepped length of beam are considered for the analytical parameters. Two groups of 27 cases and 36 cases, respectively, were analyzed for doubly and singly stepped beams in the inelastic buckling range. The combined effects of residual stresses and geometrical imperfection on inelastic lateral-torsional buckling of beams are considered. First, the distributions of residual stress of the cross-section is same as shown in Pi and Trahair (1995), and the initial geometric imperfection of the beam is set by central displacement equal to 0.1% of the unbraced length of beam. The new proposed equations definitely improve current design methods for the inelastic lateral-torsional buckling problem and increase efficiency in building and bridge design.

• Magazine of the Korea Concrete Institute
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• v.8 no.6
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• pp.173-182
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• 1996

An experimental research was carried out to investigate the effect of thc compressive strength of concrete on the stirrup effectiveness in shear behavior of concrete beams. For this purpose. total 24 beams of section dimension of $300{\times}600mm$ were tested: 4 specimens without web reinforcement and 20 specimens with web reinforcement in the form of vertical stirrups. Main variables were two levels(norma1 and high strength) of the compressive strength of concrete and six types of t h e shear rcinfor.cement ratios. Prior to experiment, for given sections and assumed material constants, the reference shear reinforcement ratio(${\rho}_vACI$) which leads to the flexure failure using the provisions of the ACI Building Code(AC1 318-95) was calculated. and the shear reinforcement ratios were relatively selected from the value of ${\rho}_vACI$. From test results, it was shown that thc safety factor of ACI eyuation for p1,ediction of shear strength was decreased with increasing the compressive strength of concrete in beams without stirrups. However. it was observed that as the amount of' stirrup is increased, the safety factor for high strength conci,ete beams with high stirrup ratio is ensured more than that for normal strength concrete beams. Therefore i t appears that the stirrup effectiveness of high strength concrete beams is greater than that of normal strength concrete beams.

• Steel and Composite Structures
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• v.43 no.4
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• pp.447-456
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• 2022

Recent experimental studies showed that deep steel I-shaped profiles classified as high ductility class sections in seismic design international codes exhibit low deformation capacity when subjected to cyclic loading. This paper presents an innovative retrofit solution to increase the rotation capacity of beams using bonded carbon fiber reinforced polymers (CFRP) patches validated with advanced finite element analysis. This investigation focuses on the flexural cyclic behaviour of I-shaped hot rolled steel deep section used as beams in moment-resisting frames (MRF) retrofitted with CFRP patches on the web. The main goal of this CFRP reinforcement is to increase the rotation capacity of the member without increasing the overstrength in order to avoid compromising the strong column-weak beam condition in MRF. A finite element model that simulates the cyclic plasticity behavior of the steel and the damage in the adhesive layer is developed. The damage is modelled using the cohesive zone modelling (CZM) technique that is able to capture the crack initiation and propagation. Details on the modelling techniques including the mesh sensitivity near the fracture zone are presented. The effectiveness of the retrofit solution depends strongly on the selection of the appropriate adhesive. Different adhesive types are investigated where the CZM parameters are calibrated from high fidelity fracture mechanics tests that are thoroughly validated in the literature. This includes a rigid adhesive commonly found in the construction industry and two tough adhesives used in the automotive industry. The results revealed that the CFRP patch can increase the rotation capacity of a steel member considerably when using tough adhesives.