Publications

Finite element model updating effects on nonlinear seismic response of arch dam–reservoir–foundation systems

Model updating effects on the seismic behavior of tall buildings under far and near-fault ground motions

The study investigates ambient vibration based model updating effects on the seismic behavior of a RC tall building subjected to far and near-fault ground motions. A 17-storey building built in Giresun, Turkey is selected as an application. Firstly, 3D initial finite element model of the selected building is created and determined analytical dynamic characteristics. Then, experimental dynamic characteristics of the building (frequencies, mode shapes, damping ratios) are determined by Operational Modal Analysis Method using the ambient vibration test data. According to experimental results, initial finite element model is calibrated by using boundary conditions and material properties. Initial and calibrated finite element models of the building are analysed under far and near-fault ground motions. Two models are compared with each other in terms of displacement, velocity, acceleration, base bending moment, base shear force, compressive and tensile stresses.

Evaluation of Damage Effects on Dynamic Characteristics of RC Buildings by Ambient Vibration Test

Abstract In this study, the dynamic behavior of a model building for different damage cases is studied based on the changes in the natural frequencies and mode shapes. The damage is assumed to occur on the walls and at the column-ends of the first story, because they are generally affected by earthquakes, explosions, etc. A ½-scale three-story reinforced-concrete (RC) building model is constructed in the laboratory. Different damage cases are applied to the model gradually by using mechanical cutting equipment. The wall damage is assumed to reach the interior of the walls and the column-end damage is created by removing the cover of columns. The ambient vibration tests are performed by using the operational modal analysis method under unknown random impact loads. The accelerometers are placed on the columns in the transverse and longitudinal directions to get the responses of the model in these directions. It is observed that the natural frequencies, corresponding mode shapes, and modal damping ratios of the building model vary depending on the damage location and damage extent. The natural frequencies show a decreasing trend with damage, and for the last damage case the natural frequencies are 60 % lower than for the undamaged case. In addition, the mode shapes are affected considerably by wall damage.

Dynamic Characteristics of an Arch Dam Model before and after Strengthening with Consideration of Reservoir Water

This technical note presents an investigation about the changing of dynamic characteristics of an arch dam model before and after strengthening considering reservoir water. To this end, an arch dam-reservoir-foundation model has been constructed in the laboratory. Ambient vibration tests have been performed on the damaged and strengthened arch dam models for empty and full reservoir to determine the effect of water on the dynamics characteristics. Enhanced frequency domain decomposition method has been used to extract the dynamic characteristics. Finally, the dynamic characteristics obtained from the damaged and strengthened dam models have been compared to with each other. Also, the natural frequencies for damaged and strengthened models are compared to detect the effect of strengthening application on the frequencies. Results indicate that the natural frequencies and damping ratios are changed with the full reservoir. However, mode shapes are not changed. Results also show that the natural frequencies of damaged dam considerably increase after strengthening applications.

Water length and height effects on the earthquake behavior of arch dam-reservoir-foundation systems

Reservoir water effects on earthquake performance evaluation of Torul Concrete-Faced Rockfill Dam

The Effect of the Spatially Varying Earthquake Ground Motion on Random Hydrodynamic Pressures

In this paper, the effects of the spatially varying earthquake ground motion on random hydrodynamic pressures are investigated considering dam-reservoir-foundation interaction by Lagrangian approach. 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 spatial variability of ground motion is taken into account with the incoherence, wave-passage and site response effects. As the effect of the wave-passage is investigated by using wave velocities of 1000 m/s, 1500 m/s and 2000 m/s, the incoherence effect is examined by considering the Harichandran-Vanmarcke and Luco Wong coherency models. The changing of the soil conditions from firm to soft soil types are selected for considering the site-response effect where the foundation supports are constructed. The effects of transient response and the water compressibility on hydrodynamic pressures are also investigated. The ground motion is described by filtered white noise and applied to each support point of the two dimensional finite element model of the dam-reservoir-foundation system in horizontal direction. It is observed that the spatially varying earthquake ground motion affects the mean of maximum values of random hydrodynamic pressures considerably.

ANALYTICAL AND OPERATIONAL MODAL ANALYSES OF TURKISH STYLE REINFORCED CONCRETE MINARETS FOR STRUCTURAL IDENTIFICATION

Seismic Performance of Bridge Expansion Joints with and without Viscous Dampers during the 6 February 2023 Kahramanmaraş Earthquakes

Expansion joints render bridge structures highly vulnerable to damage during strong ground motions. Failures of expansion joints triggered by earthquakes not only jeopardize the post-earthquake serviceability of the bridge but also have a significant impact on the bridgeâs overall seismic performance. Despite extensive investigations and efforts to integrate these measures into design specifications aimed at mitigating the consequences of relative movements between adjacent bridge spans, major earthquakes have still revealed instances of damage related to expansion joints. On 6 February 2023, strong earthquake sequences occurred in KahramanmaraÅ, Turkey, with magnitudes of M7.7 and M7.6. The fault lines and epicenters of these shallow earthquakes were near the city and town centers and caused severe structural damage to buildings and infrastructures. There are approximately 1000 railway and highway bridges in the earthquake-affected region. Although both highway and railway bridges have generally performed well, some bridges experienced structural damage during the KahramanmaraÅ earthquakes. A large number of damage on the bridges is due to pounding and opening relative movements in expansion joints. This paper presents a comprehensive seismic evaluation of expansion joint failure mechanisms on bridges without viscous dampers during the 2023 KahramanmaraÅ earthquake sequences and an in-depth investigation into the seismic performance of bridge expansion joints equipped with viscous dampers and shock transmission unit devices are implemented utilizing the strong ground motion data collected throughout the earthquake sequences. It can be stated that the near-fault induced significant directivity and fling effects, resulting in notable velocity pulses and permanent tectonic deformations, and that these effects contributed to the failures of expansion joints, viscous damper devices, pot bearings, and shear keys.

Ölçeklendirilmiş Bir Kemer Barajın Laboratuar Modelinin Oluşturulması

Ambient Vibration Based Model Updating Effects on the Earthquake Response of Tall Buildings

Window opening effects on structural behavior of historical masonry Fatih Mosque

Structural walls of old historical structures are either blind or have openings for functional requirements. It is well known that in and out of plane responses of structural walls are affected by the size, locations, and arrangements of such openings. The purpose of this investigation is to study the window opening effects on static and seismic behaviors of historical masonry old mosques. Fatih Mosque, which was converted from a church, constructed in 914 in Trabzon, Turkey, is selected for this purpose. The mosque is being restored. Structural exterior walls of the mosque were made using stone and mortar materials. When the plaster on the walls was removed during the restoration, 12 window openings were found as blind on the exterior structural walls of the mosque. Within the scope of restoration works, it is aimed to open such blind windows. In order to investigate the effects of the window openings on the structural behavior of the mosque, 3D solid and finite elements models of the mosque with and without window openings are initially developed. The experimental dynamic characteristics such as frequency, damping ratio, and mode shapes of the current situation of the mosque, where some windows openings are blind, are determined using Ambient Vibration Testing. Then, the finite element model of the current situation of the mosque is updated using the experimental dynamic characteristics. The static and seismic time history analyses of the updated finite element model with and without window openings are carried out. Structural behaviors of the mosque with and without window openings are compared considering displacement and stress propagations.

Structural identification of concrete arch dams by ambient vibration tests

Modal testing, widely accepted and applied method for determining the dynamic characteristics of structures for operational conditions, uses known or unknown vibrations in structures. The method's common applications includes estimation of dynamic characteristics and also damage detection and monitoring of structural performance. In this study, the structural identification of concrete arch dams is determined using ambient vibration tests which is one of the modal testing methods. For the purpose, several ambient vibration tests are conducted to an arch dam. Sensitive accelerometers were placed on the different points of the crest and a gallery of the dam, and signals are collected for the process. Enhanced Frequency Domain Decomposition technique is used for the extraction of natural frequencies, mode shapes and damping ratios. A total of eight natural frequencies are attained by experimentally for each test setup, which ranges between 0-12 Hz. The results obtained from each ambient vibration tests are presented and compared with each other in detail. There is a good agreement between the results for all measurements. However, the theoretical fundamental frequency of Berke Arch Dam is a little different from the experimental.

Seismic safety assessment of eynel highway steel bridge using ambient vibration measurements

In this paper, it is aimed to determine the seismic behaviour of highway bridges by nondestructive testing using ambient vibration measurements. Eynel Highway Bridge which has arch type structural system with a total length of 216 m and located in the Ayvaclk county of Samsun, Turkey is selected as an application. The bridge connects the villages which are separated with Suat U<TEX>$\breve{g}$</TEX>urlu Dam Lake. A three dimensional finite element model is first established for a highway bridge using project drawings and an analytical modal analysis is then performed to generate natural frequencies and mode shapes in the three orthogonal directions. The ambient vibration measurements are carried out on the bridge deck under natural excitation such as traffic, human walking and wind loads using Operational Modal Analysis. Sensitive seismic accelerometers are used to collect signals obtained from the experimental tests. To obtain experimental dynamic characteristics, two output-only system identification techniques are employed namely, Enhanced Frequency Domain Decomposition technique in the frequency domain and Stochastic Subspace Identification technique in time domain. Analytical and experimental dynamic characteristic are compared with each other and finite element model of the bridge is updated by changing of boundary conditions to reduce the differences between the results. It is demonstrated that the ambient vibration measurements are enough to identify the most significant modes of highway bridges. After finite element model updating, maximum differences between the natural frequencies are reduced averagely from 23% to 3%. The updated finite element model reflects the dynamic characteristics of the bridge better, and it can be used to predict the dynamic response under complex external forces. It is also helpful for further damage identification and health condition monitoring. Analytical model of the bridge before and after model updating is analyzed using 1992 Erzincan earthquake record to determine the seismic behaviour. It can be seen from the analysis results that displacements increase by the height of bridge columns and along to middle point of the deck and main arches. Bending moments have an increasing trend along to first and last 50 m and have a decreasing trend long to the middle of the main arches.

Köprülerin Dinamik Karakteristiklerinin Operasyonel Modal Analiz Yöntemiyle Belirlenmesi

Linear and nonlinear response of concrete slab on CFR dam during earthquake

ASYNCHRONOUS AND ANTISYNCHRONOUS EFFECTS OF GROUND MOTION ON THE STOCHASTIC RESPONSE OF SUSPENSION BRIDGES

Assessment of semi-rigid connections in steel structures by modal testing