The Influence of Higher Modes and Support Gaps on the Seismic Response of Piping Systems Containing Snubbers

1997 ◽  
Vol 119 (4) ◽  
pp. 444-450 ◽  
Author(s):  
O. A. Abu-Yasein ◽  
C. Lay ◽  
M. A. Pickett ◽  
J. Madia ◽  
S. K. Sinha
Keyword(s):  
Seismic Response ◽  
Fundamental Frequency ◽  
Support System ◽  
Fundamental Mode ◽  
Support Condition ◽  
Higher Modes ◽  
Nodal Displacement ◽  
Piping Systems

In this study of flexible piping systems (0.6 to 6.6 Hz), it was shown that the fundamental mode was not always the most significant mode of vibration. This study also concluded that variations in support condition do not significantly influence response in terms of nodal stress, fundamental frequency, and contribution of higher modes. In terms of support stiffness, the ratio of the magnitude of the gap (the total of all the mechanical tolerances and deadbands in the snubber support system) to the magnitude of the support nodal displacement was found to be more important than the actual magnitude of the gap. Additionally, when the magnitude of the nodal displacement exceeded the gap magnitude by a factor of about five or more, support stiffness was found to remain relatively constant.

The Influence of Support Hardware and Piping System Seismic Response on Snubber Support Damping

1997 ◽  
Vol 119 (4) ◽  
pp. 451-456 ◽  
Author(s):  
C. Lay ◽  
O. A. Abu-Yasein ◽  
M. A. Pickett ◽  
J. Madia ◽  
S. K. Sinha
Keyword(s):  
Seismic Response ◽  
Fundamental Frequency ◽  
Damping Ratio ◽  
Damping Coefficient ◽  
Piping System ◽  
Nodal Displacement ◽  
Damping Coefficients ◽  
Fundamental Frequencies ◽  
Piping Systems

The damping coefficients and ratios of piping system snubber supports were found to vary logarithmically with pipe support nodal displacement. For piping systems with fundamental frequencies in the range of 0.6 to 6.6 Hz, the support damping ratio for snubber supports was found to increase with increasing fundamental frequency. For 3-kip snubbers, damping coefficient and damping ratio decreased logarithmically with nodal displacement, indicating that the 3-kip snubbers studied behaved essentially as coulomb dampers; while for the 10-kip snubbers studied, damping coefficient and damping ratio increased logarithmically with nodal displacement.

Effects of Column Stiffness on the Modal Contribution to Displacement Response of Singe-Column Bent Viaducts in the Transverse Direction

2011 ◽  
Vol 255-260 ◽  
pp. 1711-1715
Author(s):  
Liang Chen
Keyword(s):  
Mathematical Models ◽  
Seismic Response ◽  
Fundamental Mode ◽  
Comparative Evaluation ◽  
Transverse Direction ◽  
Contribution Ratio ◽  
Higher Modes ◽  
Displacement Response

The influence of column stiffness on the modal contribution in the transverse direction of singe-column bent viaducts in the nonlinear range is investigated in this paper. The modal contribution ratio is introduced as a measure of the importance of a mode after a bridge yields. Three typical mathematical models of irregular singe-column bent viaducts are selected for analytical seismic response. The comparative evaluation of modal contribution ratios are carried out when columns with different stiffness yielded individually. Results show that yielding of a stiffer column affects the contribution of the fundamental mode as well as that of the higher modes significantly while the yielding of a more flexible column affects the modal contribution of the fundamental mode only.

3-D elastic coupling vibration and acoustical radiation characteristics of cracked gear under elastic support condition

2015 ◽  
Vol 23 (9) ◽  
pp. 1548-1568 ◽  
Author(s):  
Shao Renping ◽  
Purong Jia ◽  
Xiankun Qi
Keyword(s):  
Dynamic Response ◽  
Support System ◽  
Three Dimensional ◽  
Elastic Support ◽  
Dynamic Responses ◽  
Tooth Root ◽  
Support Condition ◽  
Elastic Boundary ◽  
Root Crack ◽  
Elastic Disc

According to the actual working condition of the gear, the supporting gear shaft is treated as an elastic support. Its impact on the gear body vibration is considered and investigated and the dynamic response of elastic teeth and gear body is analyzed. On this basis, the gear body is considered as a three-dimensional elastic disc and the gear teeth are treated as an elastic cantilever beam. Under the conditions of the elastic boundary (support shaft), combining to the elastic disk and elastic teeth, the influence of three-dimensional elastic discs on the meshing tooth response under an elastic boundary condition is also included. A dynamic model of the gear support system and calculated model of the gear tooth response are then established. The inherent characteristics of the gear support system and dynamics response of the meshing tooth are presented and simulated. It was shown by the results that it is correct to use the elastic support condition to analyze the gear support system. Based on the above three-dimensional elastic dynamics analysis, this paper set up a dynamics coupling model of a cracked gear structure support system that considered the influence of a three-dimensional elastic disc on a cracked meshing tooth under elastic conditions. It discusses the dynamic characteristic of the cracked gear structure system and coupling dynamic response of the meshing tooth, offering a three-dimensional elastic body model of the tooth root crack and pitch circle crack with different sizes, conducting the three-dimensional elastic dynamic analysis to the faulty crack. ANSYS was employed to carry out dynamic responses, as well as to simulate the acoustic field radiation orientation of a three-dimensional elastic crack body at the tooth root crack and pitch circle with different sizes.

Seismic response and retrofit of industrial brick masonry chimneys

1992 ◽  
Vol 19 (1) ◽  
pp. 117-128 ◽  
Author(s):  
A. Ghobarah ◽  
T. Baumber
Keyword(s):  
Seismic Response ◽  
Ground Motion ◽  
Strong Motion ◽  
Brick Masonry ◽  
Wind Loading ◽  
Earthquake Ground Motion ◽  
Lumped Mass ◽  
Mass System ◽  
Higher Modes ◽  
Recent Earthquakes

During recent earthquakes, the documented cases of collapsed unreinforced brick masonry industrial chimneys are numerous. Observed modes of structural failure are either total collapse or sometimes collapse or damage of the top third of the structure. The objective of this study is to analyze and explain the modes of observed failure of masonry chimneys during earthquake events, and to evaluate two retrofit systems for existing chimneys in areas of high seismicity. The behaviour of the masonry chimney, when subjected to earthquake ground motion, was modelled using a lumped mass system. Several actual strong motion records were used as input to the model. The shear, moment, and displacement responses to the earthquake ground motion were evaluated for various chimney configurations. It was found that the failure of the chimney at its base is the result of the fundamental mode of vibration. Failure at the top third of the structure due to the higher modes of vibration is possible when the chimney is subjected to high frequency content earthquakes. Higher modes, which are normally not of concern under wind loading, were shown to be critical in seismic design. Post-tensioning and the reinforcing steel cage were found to be effective retrofit systems. Key words: masonry, chimneys, behaviour, analysis, design, retrofit, dynamic, earthquakes, seismic response.

scholarly journals Geotechnical characterization and seismic response of shallow geological formations in downtown Lisbon

2014 ◽  
Vol 57 (4) ◽  
Author(s):  
Paula Teves-Costa ◽  
Isabel M. Almeida ◽  
Isabel Rodrigues ◽  
Rita Matildes ◽  
Claudia Pinto
Keyword(s):  
Seismic Response ◽  
Fundamental Frequency ◽  
Linear Method ◽  
Ambient Vibration ◽  
Building Stock ◽  
Alluvial Deposits ◽  
Amplification Factors ◽  
Geotechnical Characterization ◽  
Geotechnical Database

<p> </p><p>The geological and geotechnical characterization of shallow formations is one of the main steps in performing a microzonation study. This paper presents an example of the usefulness of the information compiled in a geological and geotechnical database for the estimation of the seismic response of the shallower formations of the Lisbon downtown area of Baixa. The geotechnical characterization of this area was performed based on the analysis of Standard Penetration Test (SPT) data compiled in the geological and geotechnical database. This database, connected to a geoscientific information system (CGIS), allows, also, the definition of 2D geological profiles used for estimating the thickness of the shallower layers. The shear-wave velocities (V<span><sub>S </sub></span>) for each layer were estimated from empirical correlations using mean SPT values computed from the statistical evaluation of the compiled data. These V<span><sub>S</sub></span> values were further calibrated with ambient vibration recording analysis. The seismic response of Baixa’s superficial deposits was estimated by applying a 1D equivalent linear method to a set of soil profiles, regularly distributed across the area, and using synthetic accelerograms to simulate input motions associated with probable earthquake occurrences in Lisbon. The results are presented in terms of maps of predominant frequencies, with the corresponding amplification level, as well as spectral amplification factors for 1 Hz and 2.5 Hz. The results show that the fundamental frequency of the Baixa area is between 1.2 Hz and 2 Hz, for the whole central valley, reaching 3 Hz near the edges where anthroprogenic and alluvial deposits have less expression. Amplification factors up to 5 were obtained. These results were achieved regardless of the considered input motion. The similarity of the obtained fundamental frequency with the natural frequency of Baixa’s old building stock increases the probability of resonance effects in future earthquakes.</p><p><span style="font-size: medium;"><br /></span></p>

scholarly journals A Multimode Adaptive Pushover Procedure for Seismic Assessment of Integral Bridges

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
Author(s):  
Ehsan Mohtashami ◽  
Ahmad Shooshtari
Keyword(s):  
Seismic Response ◽  
Demand Curve ◽  
Inelastic Response ◽  
Higher Modes ◽  
Seismic Performance Evaluation ◽  
History Analysis ◽  
Integral Bridges ◽  
Response History Analysis ◽  
Modal Mass ◽  
Adaptive Pushover

This paper presents a new adaptive pushover procedure to account for the effect of higher modes in order to accurately estimate the seismic response of bridges. The effect of higher modes is considered by introducing a minimum value for the total effective modal mass. The proposed method employs enough number of modes to ensure that the defined total effective modal mass participates in all increments of the pushover loading. An adaptive demand curve is also developed for assessment of the seismic demand. The efficiency and robustness of the proposed method are demonstrated by conducting a parametric study. The analysis includes 18 four-span integral bridges with various heights of piers. The inelastic response history analysis is employed as reference solution in this study. Numerical results indicate excellent accuracy of the proposed method in assessment of the seismic response. For most bridges investigated in this study, the difference between the estimated response of the proposed method and the inelastic response history analysis is less than 25% for displacements and 10% for internal forces. This indicates a very good accuracy compared to available pushover procedures in the literature. The proposed method is therefore recommended to be applied to the seismic performance evaluation of integral bridges for engineering applications.

Seismic Response of Long-Span Domes Supported by Multi-Storey Substructures

2020 ◽  
Vol 61 (2) ◽  
pp. 140-157
Author(s):  
Deepshikha Nair ◽  
Yuki Terazawa ◽  
Ben Sitler ◽  
Toru Takeuchi
Keyword(s):  
Seismic Response ◽  
Response Spectrum ◽  
Design Procedure ◽  
Mode Shapes ◽  
Vertical Acceleration ◽  
Vibration Modes ◽  
Higher Modes ◽  
Long Span ◽  
Excited Vibration ◽  
Buckling Restrained Braced Frames

This paper investigates the seismic response characteristics of long-span domes. The natural periods of the prominent modes are longer than medium-span domes, which leads to a greater contribution from the higher modes to the response of the long-span dome. The acceleration distributions, particularly the vertical acceleration distributions are sensitive to the dominant mode shapes of these higher modes. This leads to inaccuracies when applying the previously proposed response evaluation methods. The vibration modes of multi-storey supporting substructures also affect the excited vibration modes of the roof. In this paper, the dynamic characteristics and seismic response of 150m-span domes supported by multi-storey substructures are studied. The effects of the post- yield stiffness of multi-storey substructures are also analysed by considering two structural systems, buckling- restrained braced frames (BRBF) and damped spine frames. A simple design procedure to evaluate the equivalent static loads using amplification factors and incorporating the effects of higher modes is proposed based on response spectrum analysis and equivalent linearisation procedures. The accuracy of the proposed method is evaluated by comparing the responses with those obtained from non-linear response history analysis.

RADIAL PULSATION EIGENFREQUENCIES OF DIQUARK STARS

1993 ◽  
Vol 08 (07) ◽  
pp. 583-590
Author(s):  
PRADIP K. SAHU
Keyword(s):  
Equation Of State ◽  
Fundamental Mode ◽  
Radial Pulsation ◽  
Higher Modes ◽  
General Relativistic ◽  
Constituent Mass

We calculate the general relativistic pulsation eigenfrequencies of a mixture of constituent-mass quarks and diquarks stars. First we compute an approximation equation of state for pure diquarks and mixture of diquarks and quarks states and use it to obtain the range of periods for fundamental mode (0.2–0.6 milliseconds) and for higher modes (≤0.1 milliseconds).

Studies and Improvements on Modal Pushover Analysis and Application on Bridge

2010 ◽  
Vol 163-167 ◽  
pp. 4076-4082
Author(s):  
Ying Na Mu ◽  
Lei Shi ◽  
Zhe Zhang
Keyword(s):  
Seismic Response ◽  
Pushover Analysis ◽  
High Accuracy ◽  
Analysis Procedure ◽  
Bridge Structure ◽  
Higher Modes ◽  
Modal Pushover Analysis ◽  
Multi Mode ◽  
Inertia Forces ◽  
Modal Pushover

Because the traditional pushover analysis can not take the contributions of higher modes into account, To overcome this limitation, a modal pushover analysis procedure (MPA) is proposed by some researchers, which can involve the combination of multi-mode contributions to response. In this paper, much improvement on MPA procedure is made with consideration of the changes of seismic response after structural yielding and anew distribution of inertia forces. The method is verified by one example of bridge structure. It is concluded that the improvement part-sectionalized MPA presented in this paper has high accuracy.

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