• The Journal of Sustainable Design and Educational Environment Research
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• v.9 no.3
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• pp.34-40
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• 2010

In this study, vibration characteristics of reinforced concrete slab in large span educational facilities were evaluated. A 21.75m X 14.4m full scale reinforced concrete slab specimen was constructed with pre-flex hybrid beams. Vibrations were generated by three different methods such as free falling method of a 6kg sand bag, a 70kg person walking method and impact method by impulse hammer. Vibrations were generated more than 3 times at single location. Vibration characteristic data were collected by SA390 signal analyzer machine at 5 different locations.

• Interaction and multiscale mechanics
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• v.4 no.4
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• pp.273-289
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• 2011

The vibration response of the bridges under the moving vehicular load is of importance for engineers to estimate the serviceability of existing bridges and to design new bridges. This paper deals with the three dimensional vibration analysis of prestressed concrete bridges under moving vehicles. The prestressed bridges are modeled by four-node isoparametric flat shell elements with the transverse shearing deformation taken into account. The usual five degrees-of-freedom (DOFs) per node of the element are appended with a drilling DOF to accommodate the transformation of the local stiffness and mass matrices to the global coordinates. The vehicle is modeled as a single or two-DOF system. A single-span prestressed Tee beam and two-span prestressed box-girder bridge are studied as the two numerical examples. The effects of prestress forces on the natural frequencies and dynamic responses of the bridges are investigated.

• Computers and Concrete
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• v.25 no.3
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• pp.215-224
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• 2020

In the present study, according to the important of porosity in low specific weight in comparison of high stiffness of carbon nanotubes reinforced composite, buckling and free vibration analysis of sandwich composite beam in two configurations, of laminates using differential quadrature method (DQM) is studied. Also, the effects of porosity coefficient and three types of porosity distribution on critical buckling load and natural frequency are discussed. It is shown the buckling loads and natural frequencies of laminate 1 are significantly larger than the results of laminate 2. When configuration 2 (the core is made of FRC) and laminate 1 ([0/90/0/45/90]_s) are used, the first natural frequency rises noticeably. It is also demonstrated that the influence of the core height in the case of lower carbon volume fractions is negligible. Even though, when volume fraction of fiber increases, the critical buckling load enhances smoothly. It should be noticed the amount of decline has inverse relationship with the beam aspect ratio. Investigating three porosity patterns, beam with the distribution of porosity Type 2 has the maximum critical buckling load and first natural frequency. Among three elastic foundations (constant, linear and parabolic), buckling load and natural frequency in linear variation has the least amount. For all kind of elastic foundations, when the porosity coefficient increases, critical buckling load and natural frequency decline significantly.

• Advances in concrete construction
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• v.15 no.4
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• pp.269-286
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• 2023

In the present study, we aim to utilize the numerical solution frequency results of functionally graded beam under thermal and dynamic loadings to train and test an artificial neural network. In this regard, shear deformable functionally-graded beam structure is considered for obtaining the natural frequency in different conditions of boundary and material grading indices. In this regard, both analytical and numerical solutions based on Navier's approach and differential quadrature method are presented to obtain effects of different parameters on the natural frequency of the structure. Further, the numerical results are utilized to train an artificial neural network (ANN) using AdaGrad optimization algorithm. Finally, the results of the ANN and other solution procedure are presented and comprehensive parametric study is presented to observe effects of geometrical, material and boundary conditions of the free oscillation frequency of the functionally graded beam structure.

• Journal of Korean Society of Steel Construction
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• v.16 no.2 s.69
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• pp.225-233
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• 2004

Composite action is generally achieved by providing shear connections between steel top flange and concrete topping. Composite sections have greater stiffness than the summation of the individual stiffness of slab and beam. Therefore, they can carry larger loads or similar loads with appreciably smaller deflection and are less prone to transient vibration. T-type Steel Composite beam (TSC-beam) was developed to increase these advantages. Ten specimens were tested for this study. During the experiment, crack pattern and deflection of beam were investigated. The examined results of TSC beam system were compared with results from the typical composite beam and RC beam.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.3
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• pp.129-137
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• 1999

Reinforced concrete structures using early age concrete were result in the degradation of structural performance due to crack, overload, unexpected vibration and impact load. It demands urgently that reinforced concrete structure using early age concrete should be improved the serviceability and structural performance with the application of new fiber materials. Therefore specimens, designed by the test varibles, such as with or without stirrup and percent of steel fiber incorporated, were constructed and tested to evaluate and develop the structural performance of reinforced steel fiber concrete beam. Based on the test results reported in this study, the following conclusions are made. Specimens, designed by the over 0.75% of steel fiber incorporated, were showed the ductile behavior and failed slowly with flexure and flexure-shear. Comparing with the load-displacement relationship of specimen BSS, designed by the recommendations of the Ministry of Construction and Transportation, reinforced steel fiber concrete beam using early age concrete, over 0.75% of steel fiber incorporated, gets enough load carrying capacity and ductility. Increasing the percent of steel fiber incorporated(0.25~2.0%), the ultimate shear stress of each specimen were increased 12~40% than that of control specimen SSS.

• Magazine of the Korea Concrete Institute
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• v.9 no.6
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• pp.185-193
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• 1997

본 연구는 각종 제진재료를 이용하여 진동을 억제할 수 있는 콘크리트를 개발하여 각종 건설공사에서 흔히 발생할 수 있는 진동공해문제를 억제하고자 하며 아울러 폐기물의 재활용차원에서 폐자재를 이용하여 유용한 제진콘크리트를 개발하고자 하는데 그 목적이 있다. 우선, 제진재료를 이용한 압축강도 (200kg/$\textrm{cm}^2$)이상의 콘크리트 배합비를 찾기 위하여 24배치의 예비실험을 수행하였으며, 선정된 적정배합비에 따른 제진재료를 이용한9개의 진동시험체보를 제작하여 보의 구조적 및 재료적 동적특성 즉 1차 공명진동수와 동적 휨강성 및 감쇠비를 측정하여 제진효과를 조사하였다. 그리고 압축강도에 의한 각 시험체의 균열모멘트를 추정하여 재하하중과 균열모멘트비(M/Mcr)에 따른 하중단계별 동적특성값을 살펴보았다. 제진재료로서는 라텍스(Latex), 고무분말(Rubber Powder)그리고 플라스틱 레진( Plastic Resin)등을 사용하였고, 재료적, 구조적 진동감쇠효과를 파악하고자 KS F2437규정과 진동파의 속도법을 사용하였으며, 감쇠비 측정은 Frequency Spectrum 곡선에 대한 Polynomial Curvefitting 방법과 기하학적 해석방법을 이용하여 각각의 결과를 비교.분석하였다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.10a
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• pp.283-290
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• 1999

A practical damage identification scheme for PS concrete bridges via modal testing and system identification (SID) procedures is presented. The potential damage types are classified and the possible approaches which can be implemented into each damage type are designed. Damage identification algorithms are developed on the basis of the SID and modal analysis. The feasibility of the algorithms is verified from experimental tests to detect damage in PS concrete beam structures.

• Structural Engineering and Mechanics
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• v.67 no.3
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• pp.255-265
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• 2018

The prestress force effect on the fundamental frequency and deflection shape of Prestressed Concrete I (PCI) beams was studied in this paper. Currently, due to the conflicts among existing theories, the analytical solution for properly considering the structural behavior of these prestressed members is not clear. A series of experiments were conducted on a large-scale PCI beam of high strength concrete with an eccentric straight unbonded tendon. Specifically, the simply supported PCI beam was subjected to free vibration and three-point bending tests with different prestress forces. Subsequently, the experimental data were compared with analytical results based on the Euler-Bernoulli beam theory. It was proved that the fundamental frequency of PCI beams is unaffected by the increasing applied prestress force, if the variation of the initial elastic modulus of concrete with time is considered. Vice versa, the relationship between the deflection shape and prestress force is well described by the magnification factor formula of the compression-softening theory assuming the secant elastic modulus.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.5
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• pp.281-289
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• 2018

Existing reinforced concrete building structures have seismic vulnerabilities due to their seismically-deficient details resulting in non-ductile behavior. The seismic vulnerabilities can be mitigated by retrofitting the buildings using a fiber-reinforced polymer column jacketing system, which can provide additional confining pressures to existing columns to improve their lateral resisting capacities. This study presents dynamic responses of a full-scale non-ductile reinforced concrete frame retrofitted using a fiber-reinforced polymer column jacketing system. A series of forced-vibration testing was performed to measure the dynamic responses (e.g. natural frequencies, story drifts and column/beam rotations). Additionally, the dynamic responses of the retrofitted frame were compared to those of the non-retrofitted frame to investigate effectiveness of the retrofit system. The experimental results demonstrate that the retrofit system installed on the first story columns contributed to reducing story drifts and column rotations. Additionally, the retrofit scheme helped mitigate damage concentration on the first story columns as compared to the non-retrofitted frame.