Estimating a Seismic Wave Velocity for Exciting the Greatest Anticipated Vertical Deck Displacement of a Cable-Stayed Bridge Subjected to Asynchronous Excitation

Bashar Hariri,Lan Lin 한국콘크리트학회 2021 International Journal of Concrete Structures and M Vol.15 No.2

The purpose of this study is to examine the effects of the seismic wave velocity on vertical displacement of a cable-stayed bridge’s deck under asynchronous excitation. The Quincy Bayview Bridge located in Illinois, USA, and four other generic bridges are selected for the study. Ten records obtained from earthquakes in US, Japan, and Taiwan are used as input for the seismic excitation in the time-history analysis. Two equations are proposed in this study to determine a critical seismic wave velocity that would produce the greatest vertical deck displacement. The critical wave velocity depends on the total length of the bridge, the fundamental period of the bridge, and the C-factor. The C-factor in this study is 0.72, which is based on analyzed results from the five selected bridges. The two equations and the C-factor are verified through application on two 3-span cable-stayed bridges studied previously by Nazmy and Abdel-Ghaffar. The proposed C-factor of 0.72 is recommended for use for typical 3-span cable-stayed bridges with a side-to-main span ratio of about 0.48. The methodology developed in the study, however, can be applied to any specific bridge to examine the excitation of the deck vertical displacement under the longitudinal seismic ground motion.

Time-resolved Fluorescence Studies of Carbazole and Poly(N-vinylcarbazole) for Elucidating Intramolecular Excimer Formation

부봉현,류수영,강희성,고상곤,박찬조 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.21

We have studied the excited-state properties of carbazole and poly(N-vinylcarbazole) (PNVC) by means of femtosecond time-resolved fluorescence and time-dependent density-functional theory (TD DFT) calculations. When we excite the polymer at 280 nm, the polymer is shown to exhibit normal fluorescence peaks at 351 and 362 nm and an excimer peak above 400 nm. The lifetimes of the normal and excimer S1 states for PNVC were measured to be tF = 5.34 ± 0.03 ns for normal fluorescence and tF = 6.98 ± 0.03 ns for excimer fluorescence. In the DFT calculation, the chromophores in the ground-state PNVC are shown to be parallel. Owing to the intramolecular hindrance, the chromophores in the singlet excited-state PNVC may not be parallel, giving rise to a slightly red-shifted excimer peak. TD DFT calculations indicate that the vertical excitation energies are almost independent of the conformational changes and the degree of polymerization.

Fragility assessment of RC-MRFs under concurrent vertical-horizontal seismic action effects

Ehsan Noroozinejad Farsangi,Abbas Ali Tasnimi,Babak Mansouri 사단법인 한국계산역학회 2015 Computers and Concrete, An International Journal Vol.16 No.1

In this study, structural vulnerability of reinforced concrete moment resisting frames (RC-MRFs) by considering the Iran–specific characteristics is investigated to manage the earthquake risk in terms of multicomponent seismic excitations. Low and medium rise RC-MRFs, which constitute approximately 80-90% of the total buildings stock in Iran, are focused in this fragility–based assessment. The seismic design of 3-12 story RC-MRFs are carried out according to the Iranian Code of Practice for Seismic Resistant Design of Buildings (Standard No. 2800), and the analytical models are formed accordingly in open source nonlinear platforms. Frame structures are categorized in three subclasses according to the specific characteristics of construction practice and the observed seismic performance after major earthquakes in Iran. Both far and near fields’ ground motions have been considered in the fragility estimation. An optimal intensity measure (IM) called Sa, avg and beta probability distribution were used to obtain reliable fragility–based database for earthquake damage and loss estimation of RC buildings stock in urban areas of Iran. Nonlinear incremental dynamic analyses by means of lumped-parameter based structural models have been simulated and performed to extract the fragility curves. Approximate confidence bounds are developed to represent the epistemic uncertainties inherent in the fragility estimations. Consequently, it’s shown that including vertical ground motion in the analysis is highly recommended for reliable seismic assessment of RC buildings.

Formulation for seismic response of a ship-block system

Kuchaksarai, Masoud Moghaddasi,Bargi, Khosrow Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.23 No.3

This paper presents a complete and consistent formulation to study the seismic response of a free-standing ship supported by an arrangement of n keel blocks which are all located in a dry dock. It is considered that the foundation of the system is subjected to both horizontal and vertical in plane excitation. The motion of the system is classified in eight different modes which are Rest (relative), Sliding of keel blocks, Rocking of keel blocks, Sliding of the ship, Sliding of both keel blocks and the ship, Sliding and rocking of keel blocks, Rocking of keel blocks with sliding of the ship, and finally Sliding and rocking of keel blocks accompanied with sliding of the ship. For each mode of motion the governing equations are derived, and transition conditions between different modes are also defined. This formulation is based on a number of fundamental assumptions which are 2D idealization for motion of the system, considering keel blocks as the rigid ones and the ship as a massive rigid block too, allowing the similar motion for all keel blocks, and supposing frictional nature for transmitted forces between contacted parts. Also, the rocking of the ship is not likely to take place, and the complete ship separation from keel blocks or separation of keel blocks from the base is considered as one of the failure mode in the system. The formulation presented in this paper can be used in its entirety or in part, and they are suitable for investigation of generalized response using suitable analytical, or conducting a time-history sensitivity analysis.

Dynamic Stability of Liquid in a Spherical Tank Covered with Membrane under Vertical Harmonic Excitation

Chiba, Masakatsu,Murase, Ryo,Nambu, Yohsuke,Komatsu, Keiji The Society for Aerospace System Engineering 2015 International Journal of Aerospace System Engineer Vol.2 No.2

Experimental studies were conducted on the liquid sloshing characteristics in a spherical tank covered with a flexible membrane. A spherical acrylic tank with 145.2 mm in radius was used as a test tank, and it was half-filled with water. Silicon membranes with 0.2 mm thickness were used as a test membrane with plane or hemispherical types. The test tank was harmonically excited in a vertical direction by an electro-dynamic exciter. In this case, a parametric instability vibration comes up when the excitation frequency is twice the natural frequency. Parametric instability regions of natural modes were measured for three cases, i.e. liquid surface is free, covered with plane membrane and hemi-spherical membrane.

직류전기장을 인가한 층류제트화염의 노즐 근접후류에서 부력 및 루이스 수에 의한 화염진동 특성

한종규(Jong Kyu Han),윤성환(Sung Hwan Yoon),박정(Jeong Park),권오붕(Oh Boong Kwon),김태형(Tae Hyung Kim),서상일(Sang Il Seo) 한국연소학회 2011 KOSCOSYMPOSIUM논문집 Vol.- No.43

A laminar attached free-jet flames with DC electric fields was experimentally investigated to determine distinct self-excitation regimes and explain the characteristics of individual self-excitations. The application of DC electric fields to jet flames was experimentally designed to suppress heat-loss-induced self-excitation. In the application of DC electric fields, the horizontally and vertically injected flames were designed to remove buoyancy effect and discriminate between Lewis-number-induced self-excitation and buoyancy-driven self excitation, respectively. The results show that buoyancy-induced self excitation due to a flame flicker causes the buoyancy-driven self-excitation due to the accumulation of partially premixed mixtures preheated in front of edge flame (observed by Chung’s group), and recognize that the buoyancy-driven self-excitation suppresses the Lewis-number-induced self-excitation. In addition, the individual phase diagrams in the distinct regimes are presented. The individual key characteristics for the self-excitations are also highlighted. The self-excitations obtained in laminar attached free-jet flames with DC electric fields were reasonably characterized by a functional dependency of the strouhal number upon related parameters.

선박의 수직방향 진동 감쇠를 위한 진동보상기의 개발

정민제 ( Min Je Jung ),김태옥 ( Tae Ok Kim ),안중환 ( Jung Hwan Ahn ),김화영 ( Hwa Young Kim ) 한국센서학회 2020 센서학회지 Vol.29 No.3

The aim of this study is to develop a vertical vibration compensator that attenuates the vertical vibration of ships. The vibration compensator was designed according to the principle of generating vertical excitation forces by rotating two eccentric bodies of the same mass in opposite directions at the same rotational speed. In addition, the structural stability was analyzed using the finite element method. The maximum stress in the drive shaft was 95.6 MPa, which was approximately 35% of the allowable stress of the shaft material (SM45C, 270 MPa). The acceleration signals of the vibrator compensator body and the testbed were determined to evaluate the efficiency of the vibration compensator and the designed excitation forces. Subsequently, the excitation forces were estimated based on the relationship between force and acceleration. The estimated results were very close to the theoretical values with an error of less than 3%.

Influence of concurrent horizontal and vertical ground excitations on the collapse margins of non-ductile RC frame buildings

T.Y. Yang,E. Noroozinejad Farsangi,A.A. Tasnimi 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.59 No.4

Recent earthquakes worldwide show that a significant portion of the earthquake shaking happens in the vertical direction. This phenomenon has raised significant interests to consider the vertical ground motion during the seismic design and assessment of the structures. Strong vertical ground motions can alter the axial forces in the columns, which might affect the shear capacity of reinforced concrete (RC) members. This is particularly important for non-ductile RC frames, which are very vulnerable to earthquake-induced collapse. This paper presents the detailed nonlinear dynamic analysis to quantify the collapse risk of nonductile RC frame structures with varying heights. An array of non-ductile RC frame architype buildings located in Los Angeles, California were designed according to the 1967 uniform building code. The seismic responses of the architype buildings subjected to concurrent horizontal and vertical ground motions were analyzed. A comprehensive array of ground motions was selected from the PEER NGA-WEST2 and Iran Strong Motions Network database. Detailed nonlinear dynamic analyses were performed to quantify the collapse fragility curves and collapse margin ratios (CMRs) of the architype buildings. The results show that the vertical ground motions have significant impact on both the local and global responses of non-ductile RC moment frames. Hence, it is crucial to include the combined vertical and horizontal shaking during the seismic design and assessment of non-ductile RC moment frames.

An ab initio Study of Excited States of C4H3 Radical

최중철,김갑수 대한화학회 2016 Bulletin of the Korean Chemical Society Vol.37 No.11

Carbon-rich radicals are important for understanding chemistry of flames as well as astrochemistry. However, they are elusive for both experiments and computations, due to the peculiarity of radicals. Here, we calculated excited states of the 1-buten-3-yn-2-yl (HCCCCH2, i-C4H3 ) and n-C4H3 (HCCCHCH) radicals with the state-of-the-art complete active space self-consistent field (CASSCF) and multi-reference configuration interaction (MRCI) methods using the 6-311 + G(3df,2p) and aTVZ basis sets. The vertical energies for the seven excited states of each of the two isomers were obtained with the MRCI method at the geometries optimized at the CASSCF/6-311G(d,p) level. The result using the aTVZ basis set has been more reliable than predicted with the 6-311 + G(3df,2p) basis set with the relative stability of the ground states of the two isomers better predicted in comparison to existing data. We believe that our results will be useful for understanding the chemistry of carbon-rich radicals.

Performance of under foundation shock mat in reduction of railway-induced vibrations

Javad Sadeghi,Ehsan Haghighi,Morteza Esmaeili 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.78 No.4

Under foundation shock mats have been used in the current practice in order to reduce/damp vibrations received by buildings through the surrounding environment. Although some investigations have been made on under foundation shock mats performance, their effectiveness in the reduction of railway induced-vibrations has not been fully studied, particularly with the consideration of underneath soil media. In this regard, this research is aimed at investigating performance of shock mat used beneath building foundation for reduction of railway induced-vibrations, taking into account soil-structure interaction. For this purpose, a 2D finite/infinite element model of a building and its surrounding soil media was developed. It includes an elastic soil media, a railway embankment, a shock mat, and the building. The model results were validated using an analytical solution reported in the literature. The performance of shock mats was examined by an extensive parametric analysis on the soil type, bedding modulus of shock mat and dominant excitation frequency. The results obtained indicated that although the shock mat can substantially reduce the building vibrations, its performance is significantly influenced by its underneath soil media. The softer the soil, the lower the shock mat efficiency. Also, as the train excitation frequency increases, a better performance of shock-mats is observed. A simplified model/method was developed for prediction of shock mat effectiveness in reduction of railway-induced vibrations, making use of the results obtained.