• Tunnel and Underground Space
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• v.19 no.5
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• pp.388-396
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• 2009

Rock bolt is one of the most important supports for tunnelling to prevent excessive ground relaxation at the primary tunnel excavation stage. It forms a ground arch band by confining the ground around a tunnel. Rock bolt has various effects, such as support or hanging effect, internal pressure effect, arching effect, ground improvement effect etc. Most studies on rock bolt focused on the concept of support, but only a few researches on the ground reinforcing effect by pre-tensioning a rock bolts. In this study, large scale model tests are performed to investigate the ground reinforcing effect of rock bolts for regularly jointed rocks. Simple beam model was built to find out the reinforcing effect of jointed rocks, which was reinforced by pre-tensioned rock bolts. Settlement of model beam was analyzed through measuring its sagging for various installation intervals.

• Journal of Korean Society of Steel Construction
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• v.12 no.4 s.47
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• pp.445-455
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• 2000

This study proposed to beam-column joint model consisting of different type structural member to develop new structural system in the structural viewpoint as to a method to overcome various problem according to change of construction environment. This study promoted rigidity and capacity to stiffen reinforced concrete for steel structure end to increase rigidity of long spaned steel beam, and welt to steel flange to anchor U-shaped main bar of SRC structure end to easy stress flow between the different type structure. Through the series of experiments, proposed to possibility of this joint model, and investigated joint rigidity and capacity.

• Steel and Composite Structures
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• v.52 no.6
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• pp.609-620
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• 2024

The impact problem of imperfect beams is crucial in engineering fields such as water conservancy and transportation. In this paper, the low velocity impact of graphene reinforced metal foam beams with geometric defects is studied for the first time. Firstly, an improved Hertz contact theory is adopted to construct an accurate model of the contact force during the impact process, while establishing the initial conditions of the system. Subsequently, the classical theory was used to model the defective beam, and the motion equation was derived using Hamilton's principle. Then, the Galerkin method is applied to discretize the equation, and the Runge Kutta method is used for numerical analysis to obtain the dynamic response curve. Finally, convergence validation and comparison with existing literature are conducted. In addition, a detailed analysis was conducted on the sensitivity of various parameters, including graphene sheet (GPL) distribution pattern and mass fraction, porosity distribution type and coefficient, geometric dimensions of the beam, damping, prestress, and initial geometric defects of the beam. The results revealed a strong inhibitory effect of initial geometric defects on the impact response of beams.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.04b
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• pp.43-50
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• 2000

In the first-order shear deformation laminated beam theory (FSDT), the Kirchhoff hypothesis is relaxed such that the transverse normals do not remain perpendicular to the midsurface after deformation. Bending behavior of laminated composite thin-walled beams with singly- and doubly-symmetric open sections under uniformly distributed and concentrated loads is analyzed by the Timoshenko-type thin-walled beam theory. A closed-form expression for the shear correction factor of I-shaped composite laminated section is obtained. Numerical examples are presented to compare present analytical solutions by FSDT with the finite element solutions obtained by using three dimensional model. The effects of lamination of scheme and length-to-height ratio on the shear deformation of laminated composite beams with various boundary conditions are studied.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.541-546
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• 1998

The use of steel fibers in conventional reinforced concrete increases the strength and ductility under various loading conditions. In order to examine the possibility of the use of these combinations achieving required strength and ductility of a reinforced concrete beam, a refined optimization procedure based on nonlinear layered finite element method and nonlinear programming technique is developed in this study. Six design variables-beam width and depth, fiber volume fraction, amounts of tensile and compressive rebars, and stirrup, and stirrup spacing-are considered. The developed model can be used as a tool in determining the economical use of steel fibers in designing the reinforced steel fibrous concrete beam.

• Structural Engineering and Mechanics
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• v.61 no.5
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• pp.685-691
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• 2017

The free transverse vibrations of axially functionally graded (AFG) cantilever beams with concentrated masses attached at different points are studied in this paper. The material properties of the AFG beam, consisting of metal and ceramic, vary continuously in the axial direction according to an established law form. Approximated solutions for the title problem are obtained by means of the Ritz Method. The influence of the material variation on the natural frequencies of vibration of the functionally graded beam is investigated and compared with the influence of the variation of the cross section. The phenomenon of dynamic stiffening of beams can be observed in various situations. The accuracy of the procedure is verified through results available in the literature that can be represented by the model under study.

• International Journal of Concrete Structures and Materials
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• v.11 no.1
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• pp.1-16
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• 2017

The compression or tension-controlled failure mode of concrete beams prestressed with unbonded FRP tendons is governed by the relative amount of prestressing tendon to the balanced one. Explicit assessment to determine the balanced reinforcement ratio of a beam with unbonded tendons (${\rho}^U_{pfb}$) is difficult because it requires a priori knowledge of the deformed beam geometry in order to evaluate the unbonded tendon strain. In this study, a theoretical evaluation of ${\rho}^U_{pfb}$ is presented based on a concept of three equivalent rectangular curvature blocks for simply supported concrete beams internally prestressed with unbonded carbon-fiber-reinforced polymer (CFRP) tendons. The equivalent curvature blocks were iteratively refined to closely simulate beam rotations at the supports, mid-span beam deflection, and member-dependent strain of the unbonded tendon at the ultimate state. The model was verified by comparing its predictions with the test results. Parametric studies were performed to examine the effects of various parameters on ${\rho}^U_{pfb}$.

• Structural Engineering and Mechanics
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• v.76 no.3
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• pp.413-420
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• 2020

Considering inverse cotangential shear strain function, the present paper studies nonlinear stability of nonlocal higher-order refined beams made of metal foams based on Chebyshev-Ritz method. Based on inverse cotangential beam model, it is feasible to incorporate shear deformations needless of shear correction factor. Metal foam is supposed to contain different distributions of pores across the beam thickness. Also, presented Chebyshev-Ritz method can provide a unified solution for considering various boundary conditions based on simply-supported and clamped edges. Nonlinear effects have been included based upon von-karman's assumption and nonlinear elastic foundation. The buckling curves are shown to be affected by pore distribution, geometric imperfection of the beam, nonlocal scale factor, foundation and geometrical factors.

• Steel and Composite Structures
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• v.47 no.5
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• pp.633-644
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• 2023

Taking a look at the previously published papers, it is revealed that there is a porosity index limitation (around 0.35) for the mechanical behavior analysis of the functionally graded porous (FGP) structures. Over mentioned magnitude of the porosity index, the elastic modulus falls below zero for some parts of the structure thickness. Therefore, the current paper is presented to analyze the vibrational behavior of the FGP Timoshenko beams (FGPTBs) using a novel refined formulation regardless of the porosity index magnitude. The silica aerogel foundation and various hydrothermal loadings are assumed as the source of external forces. To obtain the FGPTB's properties, the power law is hired, and employing Hamilton's principle in conjunction with Navier's solution method, the governing equations are extracted and solved. In the end, the impact of the various variables as different beam materials, elastic foundation parameters, and porosity index is captured and displayed. It is revealed that changing hygrothermal loading from non-linear toward uniform configuration results in non-dimensional frequency and stiffness pushing up. Also, Al - Al2O3 as the material composition of the beam and the porosity presence with the O pattern, provide more rigidity in comparison with using other materials and other types of porosity dispersion. The presented computational model in this paper hopes to help add more accuracy to the structures' analysis in high-tech industries.

• Advances in nano research
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• v.12 no.1
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• pp.73-79
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• 2022

Due to the extensive use of concrete structures in various applications, the improvement of their strength and quality has become of great importance. A new way of achieving this purpose is to add different types of nanoparticles to concrete admixtures. In this work, a mathematical model has been employed to analyze the vibration of concrete beams reinforced by graphene oxide (GO) nanoparticles. To verify the accuracy of the presented model, an experimental study has been conducted to compare the compressive strengths of these beams. Since GO nanoparticles are not readily dissolved in water, before producing the concrete samples, the GO nanoparticles are dispersed in the mixture by using a shaker, magnetic striker, ultrasonic devices, and finally, by means of a mechanical mixer. The sinusoidal shear deformation beam theory (SSDBT) is employed to model the concrete beams. The Mori-Tanaka model is used to determine the effective properties of the structure, including the agglomeration influences. The motion equations are calculated by applying the energy method and Hamilton's principle. The vibration frequencies of the concrete beam samples are obtained by an analytical method. Three samples containing 0.02% GO nanoparticles are made and their compressive strengths are measured and compared. There is a good agreement between our results and those of the mathematical model and other papers, with a maximum difference of 1.29% between them. The aim of this work is to investigate the effects of nanoparticle volume fraction and agglomeration and the influences of beam length and thickness on the vibration frequency of concrete structures. The results show that by adding the GO nanoparticles, the vibration frequency of the beams is increased.