The present paper presents a stochastic seismic analysis of fluid and fluid–solid systems by using Lagrangian approach. For this reason, authors have programmed variable-number-nodes two-dimensional isoparametric fluid finite elements in fortran and have incorporated into a generalpurpose computer program for stochastic dynamic analysis of structure systems, stocal. For numerical examples, a rigid fluid tank and a fluid–solid interaction system are selected. Natural frequencies from the modal analyses of the fluid and fluid–solid systems are compared with those of analytical and numerical solutions. S16E component of the Pacoima Dam record of the San Fernando Earthquake in 1971 is used as a ground motion. The mean of maximum values from stochastic analysis are compared with deterministic analysis results
This study determines the water length effects on the modal behavior of a prototype arch dam using Operational and Analytical Modal Analyses. Achievement of this purpose involves construction of a prototype arch dam-reservoir-foundation model under laboratory conditions. In the model, reservoir length was taken to be as much as three times the dam height. To determine the experimental dynamic characteristics of the arch dam using Operational Modal Analysis, ambient vibration tests were implemented for empty reservoir and three different reservoir water lengths. In the ambient vibration tests, the dam was vibrated by natural excitations provided from small impact effects and the response signals were measured using sensitive accelerometers. Operational Modal Analysis software process signals collected from the ambient vibration tests, and Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification techniques estimated modal parameters of the dams. To validate the experimental results, 3D finite element model of the prototype arch dam was modeled by ANSYS software for empty reservoir and three different reservoir water lengths, and dynamic characteristics of each model were determined analytically. At the end of the study, experimentally and analytically identified dynamic characteristics compared to each other. Also, changes on the natural frequencies along to water length are plotted as graphs. Results suggest that reservoir water complicates the modal behavior of the arch dam significantly.
This paper demonstrates an application of the perturbation based stochastic finite element method (SFEM) for predicting the performance of structural systems made of composite sections with random material properties. The composite member consists of materials in contact each of which can surround a finite number of inclusions. The perturbation based stochastic finite element analysis can provide probabilistic behavior of a structure, only the first two moments of random variables need to be known, and should therefore be suitable as an alternative to Monte Carlo simulation (MCS) for realizing structural analysis. A summary of stiffness matrix formulation of composite systems and perturbation based stochastic finite element dynamic analysis formulation of structural systems made of composite sections is given. Two numerical examples are presented to illustrate the method. During stochastic analysis, displacements and sectional forces of composite systems are obtained from perturbation and Monte Carlo methods by changing elastic modulus as random variable. The results imply that perturbation based SFEM method gives close results to MCS method and it can be used instead of MCS method, especially, if computational cost is taken into consideration.
The present paper investigates the stochastic seismic responses of steel structure systems with Partially Restrained (PR) connections by using Perturbation based Stochastic Finite Element (PSFEM) method. A stiffness matrix formulation of steel systems with PR connections and PSFEM and MCS formulations of structural systems are given. Based on the formulations, a computer program in FORTRAN language has been developed, and stochastic seismic analyses of steel frame and bridge systems have been performed for different types of connections. The connection parameters, material and geometrical properties are assumed to be random variables in the analyses. The Kocaeli earthquake occurred in 1999 is considered as a ground motion. The connection parameters, material and geometrical properties are considered to be random variables. The efficiency and accuracy of the proposed SFEM algorithm are validated by comparison with results of Monte Carlo simulation (MCS) method.
Yapilarin dinamik yukler etkisindeki davranislari, her bir yapi icin karakteristik ozellige sahip dinamik parametreler kullanilarak belirlenmektedir. Bu parametreler yapinin mevcut yapisal ozelliklerine, malzeme ozelliklerine, sinir sartlarina ve hasar durumuna bagli olarak elde edilmektedir. Bina turu yapilar dikkate alindiginda, binanin insa asamalarina bagli olarak dinamik parametrelerin degisim gosterdigi bilinmektedir. Bu calismada, farkli insa asamalarindaki uc betonarme binanin dinamik parametreleri deneysel olcum yontemiyle elde edilmistir. Gerceklestirilen olcumlerden binalarin mevcut durumlari icin dogal frekanslari, mod sekilleri ve modal sonum oranlari belirlenmistir. Binalarin birinci dogal frekanslari standartlarda kullanilan yaklasik yontemlerle hesaplanmis, olculen ve hesaplanan frekans degerleri karsilastirilmistir. Bu calismada, incelenen binalarin dogal titresim frekanslari ve mod sekilleri mevcut durum icin elde edilmis ve beklenilen modal davranisin elde edildigi gorulmustur. Ayrica binalarin olculen birinci frekanslarinin hesaplanan degerlerden daha buyuk oldugu belirlenmistir
In recent decades there has been a trend towards improved mechanical characteristics of materials used in footbridge construction. It has enabled engineers to design lighter, slender and more aesthetic structures. As a result of these construction trends, many footbridges have become more susceptible to vibrations when subjected to dynamic loads. In addition to this, some inherit modelling uncertainties related to a lack of information on the as-built structure, such as boundary conditions, material properties, and the effects of non-structural elements make difficult to evaluate modal properties of footbridges, analytically. For these purposes, modal testing of footbridges is used to rectify these problems after construction. This paper describes an arch type steel footbridge, its analytical modelling, modal testing and finite element model calibration. A modern steel footbridge which has arch type structural system and located on the Karadeniz coast road in Trabzon, Turkey is selected as an application. An analytical modal analysis is performed on the developed 3D finite element model of footbridge to provide the analytical frequencies and mode shapes. The field ambient vibration tests on the footbridge deck under natural excitation such as human walking and traffic loads are conducted. The output-only modal parameter identification is carried out by using the peak picking of the average normalized power spectral densities in the frequency domain and stochastic subspace identification in the time domain, and dynamic characteristics such as natural frequencies mode shapes and damping ratios are determined. The finite element model of footbridge is calibrated to minimize the differences between analytically and experimentally estimated modal properties by changing some uncertain modelling parameters such as material properties. At the end of the study, maximum differences in the natural frequencies are reduced from 22% to only %5 and good agreement is found between analytical and experimental dynamic characteristics such as natural frequencies, mode shapes by model calibration.
The effects of the uniform and spatially varying ground motions on the stochastic response of fluid-structure interaction system during an earthquake are investigated by using the displacement based fluid finite elements in this paper. For this purpose, variable-number-nodes two-dimensional fluid finite elements based on the Lagrangian approach is programmed in FORTRAN language and incorporated into a general-purpose computer program SVEM, which is used for stochastic dynamic analysis of solid systems under spatially varying earthquake ground motion. The spatially varying earthquake ground motion model includes wave-passage, incoherence and site-response effects. The effect of the wave-passage is considered by using various wave velocities. The incoherence effect is examined by considering the Harichandran-Vanmarcke and Luco-Wong coherency models. Homogeneous medium and firm soil types are selected for considering the site-response effect where the foundation supports are constructed. A concrete gravity dam is selected for numerical example. The S16E component recorded at Pacoima dam during the San Fernando Earthquake in 1971 is used as a ground motion. Three different analysis cases are considered for spatially varying ground motion. Displacements, stresses and hydrodynamic pressures occurring on the upstream face of the dam are calculated for each case and compare with those of uniform ground motion. It is concluded that spatially varying earthquake ground motions have important effects on the stochastic response of fluid-structure interaction systems.
Seismic assessment of existing engineering structures in earthquake zones is very important. This paper presents seismic assessments of a highway bridge and an arch dam using non-destructive tests under ambient vibrations. Firstly, finite element models of these structures are developed and analytical dynamic characteristics are attained. Secondly, experimental measurements under ambient vibrations are performed and dynamic characteristics are extracted using Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods. Experimental and analytical dynamic characteristics are compared and finite element models are updated to eliminate the differences. Lastly, the seismic assessments of the selected structures are performed using the updated finite element models under earthquake ground motions.
Abstract Natural stone masonry mosques with wooden roof are the most widespread historical building of Eastern Black Sea Region in Turkey. The main walls of buildings are made with the combination of natural stone, lime, soil or horosan mortar and their roofs are constituted with wooden elements. Within the scope of this study, it is aimed to determine the dynamic characteristics of masonry stone mosques with wooden roof in the Eastern Black Sea Region in Turkey with nondestructive experimental methods. For the purpose of practice, Rize Gulbahar Mahallesi Buyuk Mosque, Artvin Hopa Sundura Mahallesi Mosque and Trabzon Merkez Tavanli Mosque are selected. Selected mosques have recently been restored and their geometries and properties are similar. The dynamic characteristics such as natural frequency, modal damping ratios and mode shape of the mosques are determined with the Ambient Vibration Test by using the seismic accelerometer. The results of nondestructive experiments obtained from the mosques are compared with each other and the frequency interval for the control of the analytic models of masonry stone mosques with wooden roof is given. Key Words: Mosques with wooden roof, masonry stone mosques, the Ambient Vibration Test,nondestructive test method, Eastern Black Sea Region. Oz Ahsap catili dogal tas yigma camiler, Turkiye’nin Dogu Karadeniz Bolgesinde siklikla rastlanan tarihi eserlerdendir. Camilerin beden duvarlari dogal tas, kirec, toprak veya horosan harci birlesimi ile yapilmis ve catilari ahsap elemanlarla teskil edilmistir. Bu calisma kapsaminda, Dogu Karadeniz Bolgesinde bulunan ahsap catili yigma tas camilerin dinamik karakteristiklerinin hasarsiz deneysel yontemlerle tespit edilmesi amaclanmistir. Uygulama amaciyla, Rize Gulbahar Mahallesi Buyuk Camii, Artvin-Hopa Sundura Mahallesi Camii ve Trabzon Merkez Tavanli Camii secilmistir. Secilen camiler, yakin zamanda restorasyonu yapilmis eserler olup, geometrileri ve ozelikleri benzerdir. Camilerin frekans, sonum orani ve mod seklinden olusan dinamik karakteristikleri sismik ivme olcerler kullanilarak Cevresel Titresim Testi yontemiyle belirlenmistir. Soz konusu camilerden elde edilen hasarsiz deneysel sonuclar birbirleriyle karsilastirilmis ve ahsap catili yigma camilerin analitik modellerinin kontrolu icin frekans araligi verilmistir. Anahtar Kelimeler: Ahsap Catili Camiler, Yigma Tas Camiler, Cevresel Titresim Testi, Hasarsiz Deneysel Yontemler, Dogu Karadeniz Bolgesi.
