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Showing 30 results for Vibration

Mivehchi Mahmood R., M.t. Ahmadi, Hajmomeni A.,
Volume 1, Issue 1 (9-2003)
Abstract

Ambient vibration test is an effective and economical method for identification of dynamic properties of structures such as dams. Mathematical models generally are developed for the design purpose. Structural and material parameter are assumed from similar projects or limited material tests. Therefore it is usually desirable to verify the results obtained from mathematical model by performing vibration test on the actual as-built structure and process its, data correctly. There are addressed in this paper. A modification of mathematical model could then be performed.
M. Mazloom, A.a. Mehrabian,
Volume 4, Issue 4 (12-2006)
Abstract

The objective of this paper is to present a new method for protecting the lives of residents in catastrophic earthquake failures of unreinforced masonry buildings by introducing some safe rooms within the buildings. The main idea is that occupants can seek refuge within the safe rooms as soon as the earthquake ground motions are felt. The information obtained from the historical ground motions happened in seismic zones around the globe expresses the lack of enough safety of masonry buildings against earthquake. For this potentially important reason, an attempt has been made to create some cost-effective seismic-resistant areas in some parts of the existing masonry buildings, which are called safe rooms. The practical method for creating these areas and increasing the occupant safety of the buildings is to install some prefabricated steel frames in some of their rooms or in their halls. These frames do not carry any service loads before earthquake. However, if a near field seismic event happens and the load bearing walls of the building destroy, some parts of its floors, which are in the safe areas, will fall on the roof of the installed frames consequently, the occupants who have sheltered in the safe rooms will survive. This paper expresses the experimental and theoretical work executed on the steel structures of the safe rooms for bearing the shock and impact loads. Finally, it was concluded that both the strength and displacement capacity of the steel frames were adequate to accommodate the distortions generated by seismic loads and aftershocks properly.
A. Foroughi-Asl, S. Dilmaghani, H. Famili,
Volume 6, Issue 1 (3-2008)
Abstract

Self-Compacting Concrete (SCC) is a highly fluid yet stable concrete that can flow consistently under its own weight, pass between bars, and fill in formwork without the need of compaction. The application of SCC effectively resolves the difficulties of concreting in situations with complicated formwork and congested reinforcements. In this paper, the bond between SCC and steel reinforcement was investigated. The bonding strengths of reinforcing bars were measured using cubic specimens of SCC and of normal concrete. The SCC specimens were cast without applying compaction, whereas the specimens of normal concrete were cast by conventional practice with substantial compaction and vibration. The results showed that SCC specimens generated higher bond to reinforcing bars than normal concrete specimens and the correlation between bond strength and compressive strength of NC is more consistent.
A. Kaveh, M. Najimi,
Volume 6, Issue 3 (9-2008)
Abstract

In this paper, the Rayleigh's quotient and the inverse vector iteration method are presented. The latter approach helps to obtain the natural frequencies and mode shapes of a structure. Inverse vector iteration method with shifting enables to determine the higher modes. Some basic theorems of linear algebra are presented and extended to study the free vibration of structures. The variation theorems are presented for predicting the eigenvalues and eigenvectors of the modified structures. These theorems reduce the number of cycles of the iterations used for calculating the eigenvalues and eigenvectors of the modified structures. Finally, an example is solved to show the ability of the present approach.
M.a. Goudarzi, S.r. Sabbagh-Yazdi,
Volume 7, Issue 3 (9-2009)
Abstract

The main objective of this article is evaluation of the simplified models which have been developed for analysis and design of liquid storage tanks. The empirical formulas of these models for predicting Maximum Sloshing Wave Height (MSWH) are obtained from Mass Spring Models (MSM). A Finite Element Modeling (FEM) tool is used for investigating the behavior the some selected liquid storage tanks under available earthquake excitations. First, the results of FEM tool are verified by analyzing a liquid storage tank for which theoretical solution and experimental measurements are readily available. Then, numerical investigations are performed on three vertical, cylindrical tanks with different ratios of Height to Radius (H/R=2.6, 1.0 and 0.3). The behaviors of the tanks are initially evaluated using modal under some available earthquake excitations with various vibration frequency characteristics. The FEM results of modal analysis, in terms of natural periods of sloshing and impulsive modes period, are compared with those obtained from the simplified MSM formulas. Using the time history of utilized earthquake excitations, the results of response-history FEM analysis (including base shear force, global overturning moment and maximum wave height) are compared with those calculated using simplified MSM formulations. For most of the cases, the MSWH results computed from the time history FEM analysis demonstrate good agreements with the simplified MSM. However, the simplified MSM doesn’t always provide accurate results for conventionally constructed tanks. In some cases, up to 30%, 35% and 70% average differences between the results of FEM and corresponding MSM are calculated for the base shear force, overturning moment and MSWH, respectively.
M. Mazloom, A.a. Mehrabian,
Volume 7, Issue 4 (12-2009)
Abstract

Pullback test has no scrupulous theoretical establishment. It is based on the hypothesis that the response of

the structure can be related to the response of an equivalent single degree-of-freedom (SDOF) system. This implies that

the response is controlled by a single mode. In fact, the steel frame of each safe room, which is introduced within the

unreinforced masonry buildings for protecting the lives of residents in catastrophic earthquake failures, contains a

SDOF structural system. In pullback test, the steel frame carries its gravity load first, and then it will be pushed under

an incremental lateral roof displacement pattern, which is imposed to its center of mass. This paper expresses the

results of 13 pullback tests executed by the authors on the steel frames of safe rooms. The results show that pullback

test is a practical method for seismic performance evaluation of safe rooms. Also the performance of these frames

located in a collapsing three storey masonry building is presented with favorable conclusions. In fact, the results of

pullback test of the safe room located at the ground-floor level were compared with the requirements of Iranian code

for seismic resistant design and it was concluded that the steel frame had an acceptable performance against seismic

effects.


J. Sadeghi,
Volume 8, Issue 3 (9-2010)
Abstract

 Investigations on vibration behaviors of railway track systems were attempted in this research. This was made by conducting a comprehensive field investigation into the free vibration of track systems and response of tracks to train moving loads. In-situ modal analysis was used in a railway track field as an efficient method of investigating dynamic properties of railway track systems. Natural frequencies and mode shapes of the track system in different insitu track conditions were obtained for the fist time. The sensitivity of the natural frequencies of the track to the types of sleepers, fastening systems, ballast conditions, and rail joints were studied. Efficiency of rail welded joints in CWR tracks and the effects of replacing timber sleepers with concrete sleepers on dynamic behavior of a track were investigated. Advantages of flexible sleeper fastening system from the aspects of serviceability and passenger riding comfort were discussed. The effects of the track accumulative loading as a main indicator of ballast degradation on track dynamic behavior were studied. Rail deflections were calculated by using auto-spectra obtained from vibrations of the track under trainloads, leading to the development of a new mathematical expression for the calculation of the rail dynamic amplification factor.


A.a. Maghsoudi, Sh. Amohamadpour, M. Maghsoudi,
Volume 9, Issue 3 (9-2011)
Abstract

Considering normal concrete (NC) the type of concrete need to be vibrated after placing in the formwork, Lightweight

concretes have been successfully applied in the building constructions for decades because of their low specific weight in

connection with a high strength, a high capacity of thermal insulation and a high durability. The development leading to a self

compacting light weight concrete (SCLWC) represents an important innovative step in the recent years. This concrete combines

the favorable properties of a lightweight concrete with those of a self compacting concrete (i.e., the type of concrete need no

vibration after placing in the formwork). Research work is aimed on development of (SCLWC) with the use of light weight

aggregates " Light expand clay aggregate (Leca)". In this investigation, by trial and error procedure, different mix design of

SCLWC were caste and tested to reach a so called standard self compacting concrete in fresh matrix phase such as values of

slump flow, L-box, V-funnel and in hardened phase, the 28 day compressive strength. Based on the results obtained, for two best

so-called standard mix design of SCLWC the stress-strain diagrams are drawn and discussed. Also by three different methods,

the modulus of elasticity of SCLWC are obtained and discussed here. It was found that a brittle mode of failure is governed in

SCLWC.


Kwang-Suek Oh, Tae-Hyung Kim,
Volume 11, Issue 2 (11-2013)
Abstract

This study was conducted to determine the effect of vibration on the curing and compressive strength of lightweight air-trapped

soil (ATS). ATS is manufactured by mixing cement with water and sand and injecting bubbles into the mixture. It is light as

compared to regular soil, can reduce the weight on the ground, and has high fluidity. If ATS is used at construction sites with

many vibration sources, such as pile driving, blasting, and construction machinery, the effect of vibration needs to be seriously

considered. If a road is expanded using ATS to reduce traffic congestion, the ATS quality may decrease because of vibration

generated by traffic moving on the road. In particular, because ATS contains many air bubbles and needs time for curing, the

effect of vibration can be greater than expected. Therefore, the effect of vibration on ATS was evaluated during the curing process

by conducting unconfined compression tests on samples prepared with different values of variables including vibration velocity,

starting vibration time, and mixing ratio. Vibration velocities of 0.25 and 0.50 cm/s did not greatly affect the strength. However,

vibration velocities of above 2.50 cm/s significantly affected the decrease in strength, and the starting vibration time also had a

clear effect on specimens cured for less than 2 hours.


H. Zhou, L.m. Sun,
Volume 11, Issue 3 (9-2013)
Abstract

Damping of a full-scale cable with a pair of passive–on magnetorheological (MR) dampers was tested. A cable of 215.58m long with the first mode frequency of 0.658Hz was tensioned horizontally in cable prefabrication factory. Two MR dampers were attached to the cable in an angle in the plane perpendicularly to the cable axis in 5m length from the cable anchorage. The applied voltage level was 0V, 3V, 6V and 9V. The cable was excited manually to a certain amplitude level for the first three modes of vertical vibration. The free decay curves of the cable were then recorded. The damping of the cable was calculated from the measured anti-node vibration amplitude. The damping of the free cable was also tested for reference. It was found that the damping of the cable is still low when MR dampers were no voltage strengthened. However, the damping of the cable increased greatly for the other with MR damper cases compared to free cable. Further study showed that the damping of the cable with MR dampers were strongly depended on applied voltage level and vibration amplitude. There is an optimal damping value when MR damper is voltage strengthened. The dependence of the optimum damping on applied voltage level, vibration amplitude and vibration mode was further analyzed.
A. Tarighat,
Volume 11, Issue 3 (9-2013)
Abstract

Concrete bridge deck damage detection by measurement and monitoring variables related to vibration signatures is one of the main tasks of any Bridge Health Monitoring System (BHMS). Generally damage puts some detectable/discoverable signs in the parameters of bridge vibration behavior. However, differences between frequency and mode shape before and after damage are not remarkable as vibration signatures. Therefore most of the introduced methods of damage detection cannot be used practically. Among many methods it seems that models based on artificial intelligence which apply soft computing methods are more attractive for specific structures. In this paper an Adaptive Neuro-Fuzzy Inference System (ANFIS) is used to detect the damage location in a concrete bridge deck modeled by finite element method. Some damage scenarios are simulated in different locations of the deck and accelerations as representatives of response at some specific points are calculated. Excitement is done by applying an impact load at the center of the deck. In the proposed ANFIS damage detection model accelerations are inputs and location of the damage is output. Trained model by simulated data can show the location of the damage very well with a few training data and scenarios which are not used in training stage. This system is capable to be included in real-time damage detection systems as well.
H. Rahami, A. Kaveh, M. Ardalan Asl, S. R. Mirghaderi,
Volume 11, Issue 4 (12-2013)
Abstract

In the process of structural analysis we often come to structures that can be analyzed with simpler methods than the standard approaches. For these structures, known as regular structures, the matrices involved are in canonical forms and their eigen-solution can be performed in a simple manner. However, by adding or removing some elements or nodes, such methods cannot be utilized. Here, an efficient method is developed for the analysis of irregular structures in the form a regular structure with additional or missing nodes or with additional or missing supports. In this method, the saving in computational time is considerable. The power of the method becomes more apparent when the analysis should be repeated very many times as it is the case in optimal design or non-linear analysis.
H. Shakib, Gh. R. Atefatdoost,
Volume 12, Issue 1 (3-2014)
Abstract

An approach was formulated for the nonlinear analysis of three-dimensional dynamic soil-structure interaction (SSI) of asymmetric buildings in time domain in order to evaluate the seismic response behavior of torsionally coupled wall-type buildings. The asymmetric building was idealized as a single-storey three-dimensional system resting on different soil conditions. The soil beneath the superstructure was modeled as nonlinear solid element. As the stiffness of the reinforced concrete flexural wall is a strength dependent parameter, a method for strength distribution among the lateral force resisting elements was considered. The response of soil-structure interaction of the system under the lateral component of El Centro 1940 earthquake record was evaluated and the effect of base flexibility on the response behavior of the system was verified. The results indicated that the base flexibility decreased the torsional response of asymmetric building so that this effect for soft soil was maximum. On the other hand, the torsional effects can be minimized by using a strength distribution, when the centre of both strength CV and rigidity CR is located on the opposite side of the centre of mass CM, and SSI has no effect on this criterion.
M. Abbasi, A. H. Davaei Markazi,
Volume 12, Issue 1 (3-2014)
Abstract

An important factor in the design and implementation of structural control strategies is the number and placement of actuators. By employing optimally-located actuators, the effectiveness of control system increases, while with an optimal number of actuators, an acceptable level of performance can be achieved with fewer actuators. The method proposed in this paper, simultaneously determines the number and location of actuators, installed in a building, in an optimal sense. In particular, a genetic algorithm which minimizes a suitably defined structural damage index is introduced and applied to a well-known nonlinear model of a 20-story benchmark building. It is shown in the paper that an equal damage protection, compared to the work of other researchers, can be achieved with fewer numbers of optimally placed actuators. This result can be important from economic point of view. However, the attempt to minimize one performance index has negative effect on the others. To cope with this problem to some extent, the proposed genetic methodology has been modified to be applied in a multi-objective optimization problem.
A. Gholizad, P. Kamrani Moghaddam,
Volume 12, Issue 1 (3-2014)
Abstract

High performance and reliability of refurbish able knee braced steel frames has been confirmed in previous researches trying to get an optimal design for its configuration. Buckling of diagonal member which affects the hysteretic behavior of KBF under cyclic loadings has not been foreseen in previous evaluations of this system. This deficiency can be improved by utilization of adjustable rotary friction damper device (FDD) as knee element. Diagonal element buckling can be prevented considering a suitable value for FDD sliding threshold moment Mf. Lower values of Mf Lower energy dissipation rate in FDD and this leads to an optimization problem. Nonlinear time history analyses have been performed in addition to lateral cyclic loading analyses to evaluate the response of single story KBF subjected to seismic excitation. Optimal Mf in FDD has been chosen according to these analyses results. Roof displacement and acceleration, base shear and diagonal element’s buckling status have been compared in optimally designed KBF and FDD utilized KBF (FKBF) with different configurations. Nonlinear dynamic analyses have been performed for one, four, eight and twelve story frames under different seismic records with several PGAs. More than 60% displacement response reduction has been earned for the FKBF without considerable increase in base shear.
A. R. Habibi, Keyvan Asadi,
Volume 12, Issue 1 (3-2014)
Abstract

Setback in elevation of a structure is a special irregularity with considerable effect on its seismic performance. This paper addresses multistory Reinforced Concrete (RC) frame buildings, regular and irregular in elevation. Several multistory Reinforced Concrete Moment Resisting Frames (RCMRFs) with different types of setbacks, as well as the regular frames in elevation, are designed according to the provisions of the Iranian national building code and Iranian seismic code for the high ductility class. Inelastic dynamic time-history analysis is performed on all frames subjected to ten input motions. The assessment of the seismic performance is done based on both global and local criteria. Results show that when setback occurs in elevation, the requirements of the life safety level are not satisfied. It is also shown that the elements near the setback experience the maximum damage. Therefore it is necessary to strengthen these elements by appropriate method to satisfy the life safety level of the frames.
Kaustav Bakshi, Dipankar Chakravorty,
Volume 12, Issue 2 (6-2014)
Abstract

A review of literature reveals that although singly curved conical shells applicable in many fields of mechanical engineering have been studied by many researchers but doubly curved conoidal shells which are very popular as civil engineering roofing units have not received due attention. Hence relative performances of composite conoidal shells in terms of displacements and stress resultants are studied in this paper under static and dynamic loadings. Free vibration frequencies are also reported. A curved quadratic isoparametric eight noded element is used to model the shell surface. Clamped and simply supported boundary conditions are considered. Results obtained from the present study are compared with established ones to check the correctness of the present approach. A number of additional problems of composite conoidal shells are solved for eight different stacking sequences of graphite-epoxy composite for each of the edge conditions. Uniformly distributed load for static bending analysis and step load of infinite duration for solution of forced vibration problem are considered. The results are interpreted from practical application standpoints and findings that are important for a designer to note, before he decides on the shell combination he will finally adopt among a number of possible options, are highlighted.
A. Kaveh, M. Maniat,
Volume 12, Issue 2 (6-2014)
Abstract

It is well known that damaged structural members may alter the behaviour of the structures considerably. Careful observation of these changes has often been viewed as a means to identify and assess the location and severity of damages in structures. Among the responses of a structure, natural frequencies and natural modes are both relatively easy to obtain and independent from external excitation, and therefore, can be used as a measure of the structural behaviour before and after an extreme event which might have led to damage in the structure. This paper applies Charged System Search algorithm to the problem of damage detection using vibration data. The objective is to identify the location and extent of multi-damage in a structure. Both natural frequencies and mode shapes are used to form the required objective function. To moderate the effect of noise on measured data, a penalty approach is applied. Varity of numerical examples including beams, frames and trusses are examined. The results show that the present methodology can reliably identify damage scenarios using noisy measurements and incomplete data.
A. Kaveh, M.s. Massoudi ,
Volume 12, Issue 2 (6-2014)
Abstract

Formation of a suitable null basis is the main problem of finite elements analysis via force method. For an optimal analysis, the selected null basis matrices should be sparse and banded corresponding to sparse, banded and well-conditioned flexibility matrices. In this paper, an efficient method is developed for the formation of the null bases of finite element models (FEMs) consisting of tetrahedron elements, corresponding to highly sparse and banded flexibility matrices. This is achieved by associating special graphs with the FEM and selecting appropriate subgraphs and forming the self-equilibrating systems (SESs) on these subgraphs. Two examples are presented to illustrate the simplicity and effectiveness of the presented graph-algebraic method.
M.e. Torki, M. Taghi Kazemi, S.b. Talaeitaba,
Volume 13, Issue 2 (6-2015)
Abstract

The effect of axial deformation of shell particles on the dynamic instability (flutter) of cantilevered cylindrical shells made of functionally graded materials (FGM) under an end axial follower force is addressed. To this end, at first, results for free vibration of FGM cylindrical shells were verified with previous outcomes and they were in very good agreement. Then, the effect of axial deformation of the shell, acting like a reducing linearly-distributed follower load, on the critical circumferential mode number and the flutter load of FGM shells was accounted for. Finally, the effect of axial deformation of the shell particles on the critical circumferential mode number and the flutter load of FGM shells were investigated. In this case, three homogeneous shells with different elasticity moduli and densities and two FGM materials were considered: nickel-stainless steel and stainless steel-alumina. Results include the increasing critical circumferential mode number and the increasing value of the flutter load due to axial deformation. The increase in the flutter load occurs in proportion to the whole elasticity modulus of the material, and thus it can be derived from the formula of mixture for an FGM.



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