• Title/Summary/Keyword: span number

Search Result 550, Processing Time 0.028 seconds

A direct damage detection method using Multiple Damage Localization Index Based on Mode Shapes criterion

  • Homaei, F.;Shojaee, S.;Amiri, G. Ghodrati
    • Structural Engineering and Mechanics
    • /
    • v.49 no.2
    • /
    • pp.183-202
    • /
    • 2014
  • A new method of multiple damage detection in beam like structures is introduced. The mode shapes of both healthy and damaged structures are used in damage detection process (DDP). Multiple Damage Localization Index Based on Mode Shapes (MDLIBMS) is presented as a criterion in detecting damaged elements. A finite element modeling of structures is used to calculate the mode shapes parameters. The main advantages of the proposed method are its simplicity, flexibility on the number of elements and so the accuracy of the damage(s) position(s), sensitivity to small damage extend, capability in prediction of required number of mode shapes and low sensitivity to noisy data. In fact, because of differential and comparative form of MDLIBMS, using noise polluted data doesn't have major effect on the results. This makes the proposed method a powerful one in damage detection according to measured mode shape data. Because of its flexibility, damage detection process in multi span bridge girders with non-prismatic sections can be done by this method. Numerical simulations used to demonstrate these advantages.

Development of wind vortex shedding coefficients for a multisided cylinder structure

  • Chang, Byungik;Neill, Michael;Issa, Roy;Miller, Aaron
    • Wind and Structures
    • /
    • v.18 no.2
    • /
    • pp.181-194
    • /
    • 2014
  • A major problem with high-mast light poles is the effects that wind vortex shedding can have on the pole itself because of the lock-in phenomenon. It is desired that the coefficients in the AASHTO Standard Specifications ($5^{th}$ edition) for Structural Supports for Highway Signs, Luminaries, and Traffic Signals be analyzed and refined. This is for the belief that the span of the shapes of poles for which the coefficients are used is much too broad and a specific coefficient for each different shape is desired. The primary objective of this study is to develop wind vortex shedding coefficient for a multisided shape. To do that, an octagonal shape was used as the main focus since octagonal cross sectioned high-mast light poles are one of the most common shapes in service. For the needed data, many wind parameters, such as the static drag coefficient, the slope of aerodynamic lift coefficient, Strouhal number, the lock-in range of wind velocities producing vibrations, and variation of amplitude of vortex-induced vibration with Scruton number are needed. From wind tunnel experiments, aerodynamic parameters were obtained for an octagonal shape structure. Even though aerodynamic coefficients are known from past test results, they need to be refined by conducting further wind tunnel tests.

A study on the three dimensional turbulent flow analysis of wake flow behind rotating blade row between hub and midspan (허브와 중앙스팬 사이의 회전익 후류 3차원 난류유동해석에 관한 연구)

  • No, Su-Hyeok;Jo, Gang-Rae
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.21 no.7
    • /
    • pp.911-918
    • /
    • 1997
  • The turbulent viscous wake flows behind a single airfoil, two-dimensional stationary blade row and three-dimensional rotating blade row were calculated, and the numerical results were compared with experimental ones. The numerical technique was based on the SIMPLE algorithm using three turbulent closure models, standard k-.epsilon. model(WFM), low Reynolds number k-.epsilon. model(LRN) and Reynolds stress model (RSM). In the case of a single airfoil, WFM, LRN and RSM presented fairly good velocity distributions in the wake compared with experimental data. In the case of the stationary blade row, LRN and RSM presented better results than WFM for wake velocity distribution, and especially LRN showed best results among these three turbulent models. In the case of the rotating blade row, WFM and LRN showed fairly good agreement with experimental data of the three-dimensional velocity component distributions in the range from hub to mid span region. LRN was also superior to WFM in accuracy of prediction for the wake velocity distribution as same with the cases of a airfoil and the stationary blade row.

Design of Drilled Shafts Foundation by LRFD in Incheon Bridge Project (인천대교 민자구간의 대구경 현장타설 말뚝기초의 LRFD 설계 적용 사례)

  • Kim, Jeong-Hwan;Lee, Hyun-Gun;Shin, Hyun-Yang;Youn, Man-Geun
    • Proceedings of the Korean Geotechical Society Conference
    • /
    • 2006.10a
    • /
    • pp.551-561
    • /
    • 2006
  • Incheon bridge project is to construct total 12km long bridges on the sea consist of 800m span length cable stayed bridge, approach bridge and viaduct bridge based on LRFD design specification. To design pile foundations by RCD of each bridge unit, total 4 number of preliminary full scale pile load tests with Osterberg cell method were carried out on the piles for testing. The test load was planned to more than the expected design ultimate capacity and about 29,000tons maximum load was recorded. From the interpretation of test results, design parameters are evaluated and applied to the design. Preliminary pile load test plan and detailed execution of pile load tests are introduced and summarized. The resistance factors are presented for pile design of Incheon Bridge Project in LRFD considering variation of ground conditions and number of test piles.

  • PDF

A Study on the fatigue deformation behavior of granitic stone in Korea (국내화강석재의 피로변형거동에 관한 연구)

  • 김재동;정윤영;장보안
    • Tunnel and Underground Space
    • /
    • v.6 no.2
    • /
    • pp.144-156
    • /
    • 1996
  • The deformation behaviors under uniaxial compressive cyclic loading were investigated for fresh rocks and freeze-thaw cycled samples. The Pocheon granite which is one of the most popular building stone in Korea was selected for tests. 0.5 Hz and 50% of dynamic strength were used as test conditions for frequency and fatigue span, respectively. For freezethaw procedure, sample were frozen for 3 hours under the temperature of -2$0^{\circ}C$ and then followed 3 hours thawing under the temperature of +2$0^{\circ}C$. Twenty seven samples were used as untreated and seventy three for freeze-thaw samples. No failure occurred up to 15000 cycles at the stress level of 60% of dynamic strength, indicating that the lowest strees level for fatigue failure may be around 60% of dynamic strength. Permanent strain and damping capacity curves show that there were three stages when rock behaves like under creep. Young's moduli were increased and Possion's ratios were decreased with the increase of the number of cycles. Possion's ratios varied more rapidly than Young's moduli did with the increase of the number of cycles. This may represent that most microcracks developed by fatigue stress are parallel to the axis of loading. The deformation behavior of freeze-thaw cycled samples were almost the same as that of untreated samples. However, the result of freeze-thaw cycled samples showed lower regression constant, indicating that the physical durability of rock is much lowered because of cyclic temperature variation.

  • PDF

Fundamental periods of reinforced concrete building frames resting on sloping ground

  • De, Mithu;Sengupta, Piyali;Chakraborty, Subrata
    • Earthquakes and Structures
    • /
    • v.14 no.4
    • /
    • pp.305-312
    • /
    • 2018
  • Significant research efforts were undertaken to evaluate seismic performance of vertically irregular buildings on flat ground. However, there is scarcity of study on seismic performance of buildings on hill slopes. The present study attempts to investigate seismic behaviour of reinforced concrete irregular stepback building frames with different configurations on sloping ground. Based on extensive regression study of free vibration results of four hundred seventeen frames with varying ground slope, number of story and span number, a modification is proposed to the code based empirical fundamental time period estimation formula. The modification to the fundamental time period estimation formula is a simplified function of ground slope and a newly introduced equivalent height parameter to reflect the effect of stiffness and mass irregularity. The derived empirical formula is successfully validated with various combinations of slope and framing configurations of buildings. The correlation between the predicted and the actual time period obtained from the free vibration analysis results are in good agreement. The various statistical parameters e.g., the root mean square error, coefficient of determination, standard average error generally used for validation of such regression equations also ensure the prediction capability of the proposed empirical relation with reasonable accuracy.

Influence of seismic design rules on the robustness of steel moment resisting frames

  • Cassiano, David;D'Aniello, Mario;Rebelo, Carlos;Landolfo, Raffaele;da Silva, Luis S.
    • Steel and Composite Structures
    • /
    • v.21 no.3
    • /
    • pp.479-500
    • /
    • 2016
  • Seismic design criteria allow enhancing the structural ductility and controlling the damage distribution. Therefore, detailing rules and design requirements given by current seismic codes might be also beneficial to improve the structural robustness. In this paper a comprehensive parametric study devoted to quantifying the effectiveness of seismic detailing for steel Moment Resisting Frames (MRF) in limiting the progressive collapse under column loss scenarios is presented and discussed. The overall structural performance was analysed through nonlinear static and dynamic analyses. With this regard the following cases were examined: (i) MRF structures designed for wind actions according to Eurocode 1; (ii) MRF structures designed for seismic actions according to Eurocode 8. The investigated parameters were (i) the number of storeys; (ii) the interstorey height; (iii) the span length; (iv) the building plan layout; and (v) the column loss scenario. Results show that structures designed according to capacity design principles are less robust than wind designed ones, provided that the connections have the same capacity threshold in both cases. In addition, the numerical outcomes show that both the number of elements above the removed column and stiffness of beams are the key parameters in arresting progressive collapse.

Numerical investigation on the behavior of SHS steel frames strengthened using CFRP

  • Keykha, Amir Hamzeh
    • Steel and Composite Structures
    • /
    • v.24 no.5
    • /
    • pp.561-568
    • /
    • 2017
  • Steel frames are widely used in steel structures. Exiting steel structures may be needed to strengthen for various reasons. Carbon Fiber Reinforced Polymers (CFRP) is one of the materials that are used to strengthen steel structures. Most studies on strengthening steel structures have been done on beams and steel columns. No independent study, to the researcher's knowledge, has studied the effect of CFRP strengthening on steel frames. This study explored the use of CFRP composite on retrofitting square hollow section (SHS) steel frames, using numerical investigations. Ten Finite Element (FE) models, which were strengthened with CFRP sheets, were analyzed under different coverage length, number of layers, and location of CFRP composite. One FE model without strengthening was analyzed as a control FE model to determine the increase of the ultimate load in the strengthened steel frames. ANSYS software was used to analyze the SHS steel frames. The results showed that the coverage length and the number of layers of CFRP composite have a significant effect on increasing the ultimate load of the SHS steel frames. The results also showed that the location of CFRP composite had no similar effect on increasing the ultimate load and the amount of mid span deflection of the SHS steel frames.

Development of the Computerized Mathematics Test in Korean Children and Adolescents

  • Lee, Eun Kyung;Jung, Jaesuk;Kang, Sung Hee;Park, Eun Hee;Choi, InWook;Park, Soowon;Yoo, Hanik K.
    • Journal of the Korean Academy of Child and Adolescent Psychiatry
    • /
    • v.28 no.3
    • /
    • pp.174-182
    • /
    • 2017
  • Objectives: This study was conducted in order to develop a computerized test to measure the level of mathematic achievement and related cognitive functions in children and adolescents in South Korea. Methods: The computerized Comprehensive Learning Test-Mathematic (CLT-M) consists of the whole number computation test, enumeration of dot group test, number line estimation test, numeral comparing test (magnitude/distance), rapid automatized naming test, digit span test, and working memory test. To obtain the necessary data and to investigate the reliability and validity of this test, 399 children and adolescents from kindergarten to middle school were recruited. Results: The internal consistency reliability of the CLT-M was high (Cronbach's alpha=0.76). Four factors explained 66.4% of the cumulative variances. In addition, the data for all of the CLT-M subtests were obtained. Conclusion: The computerized CLT-M can be used as a reliable and valid tool to evaluate the level of mathematical achievement and associated cognitive functions in Korean children and adolescents. This test can also be helpful to detect mathematical learning disabilities, including specific learning disorder with impairment in mathematics, in Korea.

Computation of Noise from a Rotating Cylinder (회전하는 실린더에 의한 공력소음의 계산)

  • Jang, S.W.;Lee, S.;Kim, J.H.;Han, J.O.
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
    • /
    • 2000.06a
    • /
    • pp.413-418
    • /
    • 2000
  • The noise sources from a rotating cylinder were identified to describe the blunt trailing edge noise. Firstly, LES formulation was applied to a non-orthogonal grid system and was tested with three-dimensional cross-flow over a cylinder with a yaw angle. The computed far-field noise showed peaks at Strouhal numbers ranging from 0.135 to 0.165 for the yawed cylinder flow with end-plates placed at both extremes under the yaw angle of $30^{\circ}$ and Reynolds number of $1.15{\times}10^4$. It was observed that the slantwise shedding at angles other than the cylinder yaw angle is intrinsic to inclined cylinder, with the result of shedding angles between $15^{\circ}$ and $31^{\circ}$. To study the trailing-edge wake thickness and unsteady lift-coefficient distribution in the span-wise direction of a rotating fan blade, the flows around rotating cylinder with 1,000 rpm were simulated and the far-field noise was exactly computed using the Ffowcs-Williams and Hawkings equation with quadrupole source term. The incoming velocities and stagnant zones were continuously distributed along the cylinder, and their changes made the Strouhal sheddings to occur at different phases even at almost same Strouhal number.

  • PDF