• Title/Summary/Keyword: dissipation test

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Seismic Behavior of Concrete-Filled HSS Bracing Members Reinforced by Rib (리브 보강된 콘크리트 충전 HSS 가새부재의 이력 거동)

  • Han, Sang Whan;Yeo, Seung Min;Kim, Wook Tae
    • Journal of Korean Society of Steel Construction
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    • v.17 no.1 s.74
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    • pp.53-62
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    • 2005
  • The purpose of this study is to improve the seismic behavior of the bracing members. Lee and Goel's (1987) concrete filling in the hollow structural section (HSS) reduced the severity of local buckling and increased the fracture life. However, concrete filling in the HSS did not prevent the occurrence of local buckling in the midsection of the bracing member, which resulted in continuous strength degradation. This study investigated the seismic behavior of the concrete-filled HSS bracing member, which is reinforced by ribs in the midsection of the bracing member. The main variable of the specimens is rib length. The test results showed that buckling mode, cyclic compression strength, and energy dissipation capacity of the bracing members were affected by rib length. Specimen reinforced with ribs with a length of 63% had better structural performance.

Experimental study of vibration characteristics of FRP cables based on Long-Gauge strain

  • Xia, Qi;Wu, JiaJia;Zhu, XueWu;Zhang, Jian
    • Structural Engineering and Mechanics
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    • v.63 no.6
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    • pp.735-742
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    • 2017
  • Steel cables as the most important components are widely used in the certain types of structures such as cable-supported bridges, but the long-span structures may result in an increase in fatigue under high stress and corrosion of steel cables. The traditional steel cable is becoming a more evident hindrance. Fiber Reinforced Polymer (FRP) cables with lightweight, high-strength are widely used in civil engineering, but there is little research in vibrational characteristics of FRP cables, especially on the damping characteristic. This article studied the two methods to evaluate dynamical damping characteristic of basalt FRP(BFRP) and glass FRP(GFRP) cables. First, the vibration tests of the B/G FRP cables with different diameter and different cable force were executed. Second, the cables forces were calculated using dynamic strain, static strain and dynamic acceleration respectively, which were further compared with the measured force. Third, experimental modal damping of each cables was calculated by the half power point method, and was compared with the calculation by Rayleigh damping theory and energy dissipation damping theory. The results indicate that (1) The experimental damping of FRP cables decreases with the increase of cable force, and the trend of experimental damping changes is roughly similar with the theoretical damping. (2) The distribution of modal damping calculated by Rayleigh damping theory is closer to the experimental results, and the damping performance of GFRP cables is better than BFRP cables.

Seismic damage assessment of steel reinforced recycled concrete column-steel beam composite frame joints

  • Dong, Jing;Ma, Hui;Zhang, Nina;Liu, Yunhe;Mao, Zhaowei
    • Earthquakes and Structures
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    • v.14 no.1
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    • pp.73-84
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    • 2018
  • Low cyclic loading tests are conducted on the steel reinforced recycled concrete (SRRC) column-steel (S) beam composite frame joints. This research aims to evaluate the earthquake damage performance of composite frame joints by performing cyclic loading tests on eight specimens. The experimental failure process and failure modes, load-displacement hysteresis curves, characteristic loads and displacements, and ductility of the composite frame joints are presented and analyzed, which shows that the composite frame joints demonstrate good seismic performance. On the basis of this finding, seismic damage performance is examined by using the maximum displacement, energy absorbed in the hysteresis loops and Park-Ang model. However, the result of this analysis is inconsistent with the test failure process. Therefore, this paper proposes a modified Park-Ang seismic damage model that is based on maximum deformation and cumulative energy dissipation, and corrected by combination coefficient ${\alpha}$. Meanwhile, the effects of recycled coarse aggregate (RCA) replacement percentage and axial compression ratio on the seismic damage performance are analyzed comprehensively. Moreover, lateral displacement angle is used as the quantification index of the seismic performance level of joints. Considering the experimental study, the seismic performance level of composite frame joints is divided into five classes of normal use, temporary use, repair after use, life safety and collapse prevention. On this basis, the corresponding relationships among seismic damage degrees, seismic performance level and quantitative index are also established in this paper. The conclusions can provide a reference for the seismic performance design of composite frame joints.

Nonlinear sloshing in rectangular tanks under forced excitation

  • Zhao, Dongya;Hu, Zhiqiang;Chen, Gang;Lim, Serena;Wang, Shuqi
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.10 no.5
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    • pp.545-565
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    • 2018
  • A numerical code is developed based on potential flow theory to investigate nonlinear sloshing in rectangular Liquefied Natural Gas (LNG) tanks under forced excitation. Using this code, internal free-surface elevation and sloshing loads on liquid tanks can be obtained both in time domain and frequency domain. In the mathematical model, acceleration potential is solved in the calculation of pressure on tanks and the artificial damping model is adopted to account for energy dissipation during sloshing. The Boundary Element Method (BEM) is used to solve boundary value problems of both velocity potential and acceleration potential. Numerical calculation results are compared with published results to determine the efficiency and accuracy of the numerical code. Sloshing properties in partially filled rectangular and membrane tank under translational and rotational excitations are investigated. It is found that sloshing under horizontal and rotational excitations share similar properties. The first resonant mode and excitation frequency are the dominant response frequencies. Resonant sloshing will be excited when vertical excitation lies in the instability region. For liquid tank under rotational excitation, sloshing responses including amplitude and phase are sensitive to the location of the center of rotation. Moreover, experimental tests were conducted to analyze viscous effects on sloshing and to validate the feasibility of artificial damping models. The results show that the artificial damping model with modifying wall boundary conditions has better applicability in simulating sloshing under different fill levels and excitations.

Experimental Study on the Suppression of low Frequency Unstable Burning Occurred in a Gas Generator Using Bundle Cylindrical Grain (다발 원통형 그레인을 사용한 가스발생기의 저주파 연소불안정 소멸에 대한 실험적 연구)

  • Sung Hong-Gye;Byun Jong-Ryul
    • Journal of the Korean Society of Propulsion Engineers
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    • v.8 no.3
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    • pp.10-16
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    • 2004
  • Untypical unstable burning with very low frequency was observed at firing test of a gas generator using bundle cylindrical grain. The pressure unbalance between inside and outside of cylindrical grain brought such a low unstable burning. The grains were radially holed so that the high pressure gas inside of grain could quickly moved outward of gain, resulting dissipation of the pressure unbalance However too many holes were required to let the burning be stable for all operation regime from low to high temperature of grain and resultantly deteriorate the Progressive increase of gas amount produced by a gas generator. So another idea using grids located both sides of a bundle grain was applied to dissipate actively large vorticities enhanced by unbalance pressure distribution in a combustor. Finally stable burning with progressively increase of gas was established by application of 5${\times}$5 grid slightly away bundle grain to move bundle gain freely in case pressure unbalance were occurred inside of combustor.

Seismic Performance of Precast Beam-Column Joints with Thru-Connectors (관통형 연결재로 연결된 PC 보-기둥 맞댐 접합의 내진성능에 관한 실험적 연구)

  • Park, Soon-Kyu;Kim, Min-Hee
    • Journal of the Korea Concrete Institute
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    • v.22 no.4
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    • pp.441-450
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    • 2010
  • This is a preliminary study on the development of precast beam-column joints for dry construction methodology. Precast beam column joints with thru-connectors (BCJ_TC) using high strength bars or PS strands were developed and their seismic performance including strength degradation, stiffness degradation and energy dissipation capacity was experimentally evaluated. Test results showed that compressive failures at the end blocks of PC beam members occurred dominantly while PC columns including panel zones were free from any damage. However, the connections confined with CFRP at the end block showed much improved seismic performance than that of the unconfined connections. Connections with neoprene pad fillers between beam and column interfaces were better than the other connections in all the seismic performances except initial stiffness. To improve the seismic performances of BCJ_TC, compressive strength of the concrete at the end block need to be increased to compensate for the additional compressive stresses due to unbonded connectors and deformation of connectors should be controlled respectively.

Seismic Experiment of Precast Concrete Exterior Beam-Column Joint Using Bolt Type Connection and Prestressing Method (볼트 접합 및 프리스트레스를 적용한 프리캐스트 콘크리트 보-기둥 외부접합부의 내진실험)

  • Lee, Dong-Joo;Lee, Ju-Dong;Oh, Tae-Soo;Kang, Thomas H.K.
    • Journal of the Korea Concrete Institute
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    • v.26 no.2
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    • pp.125-133
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    • 2014
  • In this study, experimental research was carried out to investigate the seismic and structural performance of precast concrete exterior beam-column joints using bolt type connection and prestressing method. A total of five full-scale exterior beam-column joints were constructed and tested under reversed cyclic loading, controlled by displacement. Results of the test are as follows: Energy dissipation capacity and pinching phenomenon of PC beam-column joints showed disadvantageous behavior compared to RC beam-column joints. However, drift capacity of the PC joint was excellent. Also, yield mechanism concentrated on embedded nuts was suitable as an exterior beam-column joint of lateral load resistance frame. Additional application of prestressing method was also very effective to control excessive pinching and cracking in the joint region, and thus improved an overall seismic performance of the PC joint.

Study on Consolidation Behaviors of Soft Ground by Plastic Board Drain Using Model Tests (실내모형실험에 의한 Plastic Board Drain이 적용된 연약지반의 압밀거동에 관한 연구)

  • You, Seung-Kyong;Hong, Won-Pyo;Yoon, Gil-Lim
    • Journal of the Korean GEO-environmental Society
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    • v.4 no.4
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    • pp.17-23
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    • 2003
  • Accurate prediction of consolidation behaviors of the soft ground improved by plastic board drains is not easy because the consolidation characteristics of the improved ground has not been fully elucidated yet. The shape of drains is one of the most important factors which affect the consolidation characteristics of the improved ground. In this paper, a series of model consolidation tests of soft clay ground improved by plastic board drain were carried out, in order to investigate the effect of both plastic board width and stress level on consolidation characteristics of the improved ground. As the results, behaviors of both settlement and excess pore pressure dissipation were elucidated. Also, the non-uniform distribution of water content in the model ground was obtained. Then, in order to investigate the effect of vertical drainage on the consolidation behavior in the model tests, the comparison between experimental consolidation behaviors and Barron's theoretical ones were carried out. As the results, it was elucidated that the consolidation behavior in the model tests was affected not only by radial drainage but also by vertical drainage.

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Evaluation of Surcharging to Reduce Secondary Consolidation for Kunsan Clay (군산점토의 2차압밀 감소를 위한 Surcharging 평가)

  • 주종진;임형덕;이우진;김대규;김낙경;김형주
    • Journal of the Korean Geotechnical Society
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    • v.18 no.4
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    • pp.127-135
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    • 2002
  • The accurate evaluation of settlement is important to every steps in the constructions involving soft soils. Relating with those constructions, especially, it has been emphasized recently that the influnce of secondary settlement is important. The ratio of $C_a/C_c$ and the surcharging tests can be applied collaboratively to predicting and reducing secondary consolidation. A series of incremental loading consolidation test and surcharging tests for undisturbed samples of Kunsan clay were performed in this study. As a result of the tests, the ratio of $C_a/C_c$ for the clay was found to be 0.0329. Also, the relationship between void ratio and $t/t_p$ was shown to be linear. Accordingly, the secondary compression index, $C_a for a long term loading had a constant value regardless of time. When the total surcharge ratio was 0.4 and the dissipation ratio of excessive porewater pressure was in the range from 80% to 100%, secondary settlement was effectively reduced for Kunsan clay.

Reflection Characteristics of Vortical Slit Caisson Breakwater (종 SLIT형 케이슨 방파제의 반사특성)

  • 이종인;조지훈
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.13 no.4
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    • pp.263-272
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    • 2001
  • Recently, some attempts to construct slit caisson-type breakwaters are made in Korea. Since slit caisson-type breakwaters are suitable for relatively deep sea areas, a lot of theoretical and experimental researches have been performed. In this study, the reflection characteristics of vertical slit caisson breakwaters are investigated based on the measured data in two-dimensional hydraulic model tests with irregular waves. The experiments were conducted for various cases; variation of porosity of perforated-wall, width of wave chamber, number of slits for single-and double-chamber, respectively. It is found that in the case when the wave steepness (H/L$_{s}$ ) is small, the reflection coefficients are large. The existing researches have shown that the wave reflection is minimized when the nondimensional width of wave chamber B/L is about 0.2~0.25 for the regular waves. However, for the irregular waves the reflection is lowest when $B/L_2$, is 0.13~0.15. For a same porosity condition, the wave dissipation is stronger as the width of s1it is larger. The double-chamber caisson is superior to single- chamber caisson in the wave dissipating effects.

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