• Geomechanics and Engineering
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• v.37 no.5
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• pp.453-465
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• 2024

This paper presents a logarithmic shear deformation theory to study the thermal buckling response of power-law FG one-dimensional structures in thermal conditions with different boundary conditions. It is assumed that the functionally graded material and thermal properties are supposed to vary smoothly according to a contentious function across the vertical direction of the beams. A P-FG type function is employed to describe the volume fraction of material and thermal properties of the graded (1D) beam. The Ritz model is employed to solve the thermal buckling problems in immovable boundary conditions. The outcomes of the stability analysis of FG beams with temperature-dependent and independent properties are presented. The effects of the thermal loading are considered with three forms of rising: nonlinear, linear and uniform. Numerical results are obtained employing the present logarithmic theory and are verified by comparisons with the other models to check the accuracy of the developed theory. A parametric study was conducted to investigate the effects of various parameters on the critical thermal stability of P-FG beams. These parameters included support type, temperature fields, material distributions, side-to-thickness ratios, and temperature dependency.

• Geomechanics and Engineering
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• v.38 no.4
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• pp.381-395
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• 2024

With the wide application of urban subway tunnels, the foundation pits of new stations and existing subway tunnels are becoming increasingly close, and even zero-distance close-fitting construction has taken place. To optimize the construction support scheme, the existing tunnel's vertical displacement is theoretically analyzed using the two-stage analysis method to understand the action mechanism of the construction of zero-distance deep large foundation pits on both sides of the existing stations; a three-dimensional numerical calculation is also performed for further analysis. First, the additional stress field on the existing tunnel caused by the unloading of zero-distance foundation pits on both sides of the tunnel is derived based on the Mindlin stress solution of a semi-infinite elastic body under internal load. Then, considering the existing subway tunnel's joints, shear stiffness, and shear soil deformation effect, the tunnel is regarded as a Timoshenko beam placed on the Kerr foundation; a sixth-order differential control equation of the tunnel under the action of additional stress is subsequently established for solving the vertical displacement of the tunnel. These theoretical calculation results are then compared with the numerical simulation results and monitoring data. Finally, an optimized foundation pit support scheme is obtained considering the pit corner effect and external corner failure mode. The research shows a high consistency between the monitoring data,analytical and numerical solution, and the closer the tunnel is to the foundation pit, the more uplift deformation will occur. The internal corner of the foundation pit can restrain the deformation of the tunnel and the retaining structure, while the external corner can cause local stress concentration on the diaphragm wall. The proposed optimization scheme can effectively reduce construction costs while meeting the safety requirements of foundation pit support structures.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.1
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• pp.561-568
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• 2014

A modular fish-bone girder pier consists of one main girder system named as "Spine Girder". Therefore, this pier can be most affected by torsion as well as flexural bending. The design considerations of the fish-bone girder pier are proposed to assure the reasonable design in this study. In order to investigate the behavior characteristics, structural analysis F.E model is developed, and the verification of the developed model is performed by comparison with experimental data. From the investigation of the structural behavior, the vertical stiffener is required at the bottom of bone-beams to prevent the excessive local stress. Also, it is found that the normal stress of the flange and the shear stress of the web and flange are dominantly affected by the warping torsion and pure torsion, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.1
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• pp.525-532
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• 2014

In this study, practical design method of coupling beams is proposed. The member forces varies according to the location of the members and the members at 25%~40% of building height shows large member forces. The 100mm increase of wall thickness causes 3~4% variation of member forces and the 100MPa increase of concrete strength decrease approximately 3% of member forces. The required strength of coupling beams is twice the resistant strength and 80% reduction of coupling beam stiffness is necessary to fulfill the design criteria. The stiffness reduction of coupling beams is not necessary over the entire stories and the strength reduction range can be estimated considering design requirements.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.3
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• pp.133-140
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• 2018

This paper is concerned with the 2-D micostructure generation for $Ni-A{\ell}_2O_3$ dual-phase composite materials and the numerical analysis of mechanical characteristic of hierarchical models of microstructure which are defined in terms of the scale of microstructure. The microstructures of dual-phase composite materials were generated by applying the mathematical RMDF(random morphology description functions) technique to a 2-D RVE of composite materials. And, the hierarchical models of microstructure were defined by the number of Gaussian points. Meanwhile, the volume fractions of metal and ceramic particles were set by adjusting the level of RMD functions. The microstructures which were generated by RMDF technique are definitely random even though the total number of Gaussian points is the same. The randomly generated microstructures were applied to a 2-D beam model, and the variation of normal and shear stresses to the scale of microstructure was numerically investigated. In addition, through the crack analyses, the influence of RMDF randomness and Gauss point number on the crack-tip stress is investigated.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.67-74
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• 2007

We perform an experimental study of concrete beam with pultruded fiber reinforced polymer(FRP) plank using as a permanent formwork and the tensile reinforcement. A satisfactory bond at the interface between the smooth surface of the pultruded plank and the concrete must be developed for the FRP plank and the concrete to act as a composite structural member. Two kinds of aggregate were bonded to the FRP plank using a commercially available epoxy. No additional flexural or shear reinforcement was provided in the beams. For comparison we test two types of control specimen. One control did not have any aggregate bonded to the FRP plank and the other control had infernal steel reinforcing bars instead of the FRP plank. The beams were loaded by central patch load to their ultimate capacity. The experimental results were compared to current ACI 318 (2005) and ACI 440 (2006) code predictions. This study demonstrates that the FRP plank has the potential to serve as formwork and reinforcing for concrete structures.

• Journal of Korean Society of Steel Construction
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• v.13 no.4
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• pp.419-431
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• 2001

This study was to investigate structural behavior of composite structure beams composed of end-RC. center-Steel according to respective reinforcing method for connection zone composed of different materials (SRC) while attaching main bars on steel-flange by welding. The main reinforcing methods are as follows ; non-reinforcing, vertical shear reinforcing (type-stirrup), inclined reinforcing(type-x), horizontal reinforcing(type-web, 0.3L), double horizontal reinforcing (type-web, 0.3L), vertical reinforcing (type-flange, 0.3L). Consequently, It showed little difference in structural properties like ductility and strength according to the attaching method of main bars. For Maximizing the structural properties of composite beam, the most effective methods were vertical reinforcing one and double horizontal reinforcing one.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.9 no.1
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• pp.59-69
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• 2001

The rotor blade is modeled using a composite box beam with arbitrary wall. The active constrained damping layers are bonded to the upper and lower surfaces of the box beam to provide active and passive damping. A finite element model, based on a hybrid displacement theory, is used in the structural analysis. The theory is capable of accurately capturing the transverse shear effects in the composite primary structure, the viscoelastic and the piezoelectric layers within the ACLs. A reduced order model is derived based on the Hankel singular value. A linear quadratic Gaussian (LQG) controller is designed based on the reduced order model and the available measurement output. However, the LQG control system fails to stabilize the perturbed system although it shows good control performance at the nominal operating condition. To improve the robust stability of LQG controller, the loop transfer recovery (LTR) method is applied. Numerical results show that the proposed controller significantly improves rotor aeromechanical stability and suppresses rotor response over large variations in rotating speed by increasing lead-lag modal damping in the coupled rotor-body system.

• Steel and Composite Structures
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• v.34 no.5
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• pp.625-641
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• 2020

The realistic modeling of the beam-column semi-rigid connection in steel frames attracted the attention of many researchers in the past for the seismic analysis of semi-rigid frames. Comparatively less studies have been made to investigate the behavior of steel frames with semi-rigid connections under different types of earthquake. Herein, the seismic behavior of semi-rigid steel frames is investigated under both far and near-field earthquakes. The semi-rigid connection is modeled by the multilinear plastic link element consisting of rotational springs. The kinematic hysteresis model is used to define the dynamic behavior of the rotational spring, describing the nonlinearity of the semi-rigid connection as defined in SAP2000. The nonlinear time history analysis (NTHA) is performed to obtain response time histories of the frame under scaled earthquakes at three PGA levels denoting the low, medium and high-level earthquakes. The other important parameters varied are the stiffness and strength parameters of the connections, defining the degree of semi-rigidity. For studying the behavior of the semi-rigid frame, a large number of seismic demand parameters are considered. The benchmark for comparison is taken as those of the corresponding rigid frame. Two different frames, namely, a five-story frame and a ten-story frame are considered as the numerical examples. It is shown that semi-rigid frames prove to be effective and beneficial in resisting the seismic forces for near-field earthquakes (PGA ≈ 0.2g), especially in reducing the base shear to a considerable extent for the moderate level of earthquake. Further, the semi-rigid frame with a relatively weaker beam and less connection stiffness may withstand a moderately strong earthquake without having much damage in the beams.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.2
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• pp.281-291
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• 2002

This paper describes the minimum cost design of prestressed reinforced concrete (PRC) hem with rectangular section. The cost of construction as objective function which includes the costs of concrete, prestressing steel, non prestressing steel, and formwork is minimized. The design constraints include limits on the minimum deflection, flexural and shear strengths, in addition to ductility requirements, and upper-Lower bounds on design variables as stipulated by the specification. The optimization is carried out using the methods based on discretized continuum-type optimality criteria(DCOC). Based on Kuhn-Tucker necessary conditions, the optimality criteria are explicitly derived in terms of the design variables - effective depth, eccentricity of prestressing steel and non prestressing steel ratio. The prestressing profile is prescribed by parabolic functions. In this paper the effective depth is considered to be freely-varying and one uniform for the entire multispan beam respectively. Also the maximum eccentricity of prestressing force is considered in every span. In order to show the applicability and efficiency of the derived algorithm, several numerical examples of PRC continuous beams are solved.