Alemdar Bayraktar

Seismic Response of a Historical Masonry Minaret using a Finite Element Model Updated with Operational Modal Testing

This paper presents the earthquake response of a historical masonry minaret after a finite element model updating was undertaken using the information from full scale ambient vibration testing. The Iskenderpaşa historical masonry minaret dating back to the 16th century with a height of 21m located in the city center of Trabzon, Turkey is selected as an application. Analytical modal analysis is performed on the 3D finite element model of the minaret considering field survey and engineering judgments to obtain the analytical frequencies and mode shapes. The field ambient vibration tests on the minaret under natural excitations such as wind loading and human movement are conducted. The Peak Picking and the Stochastic Subspace Identification techniques are used to extract the modal parameters from the ambient vibration test. A good correlation was found among the modal parameters identified from the two techniques. The finite element model of the minaret is updated to minimize the differences between analytically and experimentally estimated modal properties by changing some uncertain modeling parameters such as material properties and boundary conditions. The analytical model of the minaret after finite element model updating is analyzed using the 1992 Erzincan earthquake record, which occurred near the area, to determine the earthquake behavior of the minaret. At the end of the study, maximum differences in the natural frequencies are reduced on average from 27% to 5% and a good agreement is found between analytical and experimental natural frequencies and mode shapes by model updating. Also, it is seen from the earthquake analysis that the displacements increase along the height of the minaret and the maximum and minimum principal stresses occur at the region of the transition segment and the cylindrical body.

EARTHQUAKE ANALYSIS OF GRAVITY DAM-RESERVOIR SYSTEMS USING THE EULERIAN AND LAGRANGIAN APPROACHES

In this study, the two-dimensional earthquake analysis of a gravity dam-reservoir system using both the Eulerian and Lagrangian approaches is performed. To this aim, the effects of the variation of fluid compressibility on the modal behavior were first investigated. Then, the earthquake response of a dam-reservoir system is investigated using the Lagrangian approach. Parametric studies are conducted on increasing the value of fluid bulk modulus. The results obtained for different values of the bulk modulus are also compared with the Eulerian solutions based on incompressible fluid assumption.

Asynchronous dynamic analysis of dam-reservoir-foundation systems by the Lagrangian approach

Abstract In this study, the asynchronous dynamic analysis of dam-reservoir-foundation systems is performed by the Lagrangian approach. Two-dimensional finite solid and fluid elements with various nodes based on the Lagrangian approach are coded, and incorporated into the MULSAP program to perform asynchronous dynamic analysis. The Sariyar concrete gravity dam is chosen for the analysis and the east-west component of the 1992 Erzincan earthquake is used in calculations. Propagation velocities of 250, 500, 1000, 2000, 4000 m s −1 and infinity are considered; the latter corresponds to classical dynamic analysis. Results obtained for various velocities of propagation are compared with each of the others. It is observed that decreasing the velocity of propagation produces greater stresses.

Finite-Element Analysis and Vibration Testing of a Two-Span Masonry Arch Bridge

This paper presents the analytical modeling, modal testing, and finite-element model updating for a two-span masonry arch bridge. An Ottoman masonry arch bridge built in the 19th century and located at Camlihemsin, Rize, Turkey is selected as an example. Analytical modal analysis is performed on the developed 3D finite-element model of the bridge to obtain dynamic characteristics. The ambient vibration tests are conducted under natural excitation such as human walking. The operational modal analysis is carried out using peak picking method in the frequency domain and stochastic subspace identification method in the time domain, and dynamic characteristics (natural frequencies, mode shapes, and damping ratios) are determined experimentally. Finite-element model of the bridge is updated to minimize the differences between analytically and experimentally estimated dynamic characteristics by changing boundary conditions. At the end of the study, maximum differences in the natural frequencies are reduced on average from 18 to 7% and a good agreement is found between analytical and experimental dynamic characteristics after finite-element model updating.

Finite element model calibration of berke arch dam using operational modal testing

This paper presents the finite element calibration of Berke Arch Dam by using Operational Modal Testing. Achievement of this purpose involves structural vibration characteristics of Berke Arch Dam using analytical and Operational Modal Analyses. Therefore, the study has two parts — analytical and experimental. In the analytical part of the study, the authors developed a 3D finite element model of Berke Arch Dam-reservoir-foundation system using ANSYS software, and analytically determined vibration characteristics such as natural frequencies and mode shapes. In the experimental part of the study, sensitive accelerometers were placed to several points of Berke Arch Dam, and ambient vibration tests were conducted over four days to obtain dynamic characteristics. The Enhanced Frequency Domain Decomposition technique is used to estimate natural frequencies, mode shapes and damping ratios of the Berke Arch Dam experimentally. Results showed that there were some differences between analytical and experimental natural frequencies of the dam. Therefore, an analytical model of Berke Arch Dam was calibrated to minimize these differences by changing material properties. Analytical results obtained from the calibrated model mainly conform to those of the experimental model.

Modal Analysis, Experimental Validation, and Calibration of a Historical Masonry Minaret

This paper describes a historical masonry minaret, its finite element modeling, modal testing, and finite element model calibration. Iskenderpasa historical masonry minaret located in Trabzon City Center, Turkey, is selected as an application. Modal analysis is performed on the developed 3-D finite element model of the minaret to obtain the analytical frequencies and mode shapes. The ambient vibration tests on the minaret under environmental excitations, such as traffic loads and wind, are conducted. The output-only modal parameter identification is carried out by using peak picking of the average normalized power spectral densities in the frequency domain and stochastic subspace identification in the time domain. Dynamic characteristics such as natural frequencies, mode shapes, and damping ratios are determined. The finite element model of the minaret is calibrated to minimize the differences between analytically and experimentally estimated modal properties by changing some uncertain modeling parameters such as material properties and boundary conditions. At the end of the study, maximum differences in the natural frequencies are reduced on an average from 27 % to 5 %. A good agreement is also found between analytical and experimental natural frequencies and mode shapes after model calibration.

Comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges

This paper presents a comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges. Boğaziçi (The First Bosporus) and Fatih Sultan Mehmet (Second Bosporus) suspension bridges built in Istanbul, Turkey, are selected as numerical examples. Both bridges have almost the same span. While Boğaziçi Suspension Bridge has inclined hangers, Fatih Sultan Mehmet Suspension Bridge has vertical hangers. Geometric nonlinearity including P-delta effects from self-weight of the bridges is taken into account in the determination of the dynamic behavior of the suspension bridges for near-fault and far-fault ground motions. Near-fault and far-fault strong ground motion records, which have approximately identical peak ground accelerations, of 1999 Chi-Chi, 1999 Kocaeli, and 1979 Imperial Valley earthquakes are selected for the analyses. Displacements and internal forces of the bridges are determined using the finite element method including geometric nonlinearity. The displacements and internal forces obtained from the dynamic analyses of suspension bridges subjected to each fault effect are compared with each other. It is clearly seen that near-fault ground motions are more effective than far-fault ground motion on the displacements and internal forces such as bending moment, shear force and axial forces of the suspension bridges.

Earthquake Behavior of Berke Arch Dam Using Ambient Vibration Test Results

AbstractThe Berke Arch Dam is the highest arch dam constructed in Turkey. The dam height is 201 m, and the crest length is 270 m. This paper describes the Berke Arch Dam, its finite-element modeling, ambient vibration testing, finite-element model calibration, and earthquake behavior before and after model calibration. First, three-dimensional (3D) models of dam-reservoir-foundation interaction were developed to obtain analytical dynamic characteristics, such as natural frequencies and mode shapes using the Ansys finite-element program. In the analyses, reservoir water was represented by a Lagrangian approach. Then, ambient vibration tests were conducted on the dam on 4 days in May 2009 to obtain experimental dynamic characteristics. In ambient vibration tests, the sensitive accelerometers were placed on several points on the arch dam, and signals were collected from accelerometers. The enhanced frequency domain decomposition technique was used in the extraction of experimental natural frequencies, mode s...

Determination of Water Level Effects on the Dynamic Characteristics of a Prototype Arch Dam Model using Ambient Vibration Testing

This study investigated the water level effects on the dynamic characteristics of a prototype arch dam model using ambient vibration testing were investigated. Achievement of this purpose involved construction of a prototype arch dam-reservoir-foundation model under laboratory. The dam body was constructed with 60 cm height. Ambient vibration tests on the arch dam estimated its natural frequencies, mode shapes and damping ratios for different water levels. In the ambient vibration tests, ambient excitations are provided from small impact effects and the responses of the arch dam are measured. It can be stated from the study that natural frequencies are not overly changed among 0–30 cm water levels; however they are increased for higher water levels. The difference between the first natural frequencies of the arch dam obtained from empty reservoir (H = 0 cm) and full reservoir (H = 60 cm) is about 20–25%.

Output-Only System Identification of Posttensioned Segmental Concrete Highway Bridges

This paper discusses the application of system identification of a highway bridge using finite-element method and ambient-vibration testing. The posttensioned Gulburnu Highway Bridge located on the Giresun-Espiye state highway was selected as a case study. A finite-element model of the bridge was developed using SAP2000 software, and dynamic characteristics were obtained analytically. During the test, sources of ambient excitations were provided by the traffic effects over the bridge. Ambient-vibration tests were applied to the bridge to identify dynamic characteristics. The selection of measurement time, frequency span, and effective mode number was considered from similar studies in the literature. Two output-only system identification methods, enhanced frequency domain decomposition and stochastic subspace identification, were used to estimate the dynamic characteristics of the bridge experimentally. The accuracy and efficiency of both methods were investigated and compared with finite-element results....