Temel Türker

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.

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.

Structural Performance Evaluation of 90 RC Buildings Collapsed during the 2011 Van, Turkey, Earthquakes

AbstractThe structural performance evaluation is presented of 90 reinforced concrete (RC) buildings that collapsed during the October 23 (Ercis) and November 9 (Edremit), 2011, earthquakes in Van, Turkey. A total of 35,000 buildings are damaged or collapsed in the city center and surrounding villages after the Ercis and Edremit earthquakes. Almost all the RC buildings are affected in the region. To evaluate the structural performance of the collapsed buildings, the buildings are evaluated according to structural system properties, specification properties, material properties (concrete and reinforcement steel properties), and soil properties. The results showed that a large proportion of nonengineering RC buildings completely collapsed or were damaged heavily. Most of the RC buildings in the affected area are not designed and constructed in accordance with Turkish code. Also, it was found that 26% of the buildings do not have a building license, 66% of the buildings’ ground floors were used as a commercia...

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

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.

Finite-Element Model Calibration of Historical Masonry Domes Using Operational Modal Testings

AbstractThis paper aims to determine the dynamic characteristics, such as natural frequencies, mode shapes and damping ratios, of two different domed structures, namely Hamza Pasa Mausoleum and Kavak Meydan Fountain, built in the sixteenth century by experimental methods. The experimental dynamic characteristics are used to develop initial analytical models and update these models. Analytical models of the structures are constituted using finite element theoretical software, and dynamic characteristics are determined analytically. The experimental measurements are carried out by operational modal testing under environmental loads, which are wind and traffic loads, and the dynamic characteristics are identified experimentally. Vibration responses are collected from the dome’s outer surface for Hamza Pasa Mausoleum and the dome pulley’s inner surface for Kavak Meydan Fountain. Measurement time, frequency span, and effective mode number are determined by considering pretest measurement results. At the end of...

Dynamic Field Test, System Identification, and Modal Validation of an RC Minaret: Preprocessing and Postprocessing the Wind-Induced Ambient Vibration Data

The investigation of dynamic response for civil engineering structures largely depends on a detailed understanding of their dynamic characteristics, such as the natural frequencies, mode shapes, and modal damping ratios. Dynamic characteristics of structures may be obtained numerically and experimentally. The finite-element method is widely used to model structural systems numerically. However, there are some uncertainties in numerical models. Material properties and boundary conditions may not be modeled correctly. There may be some microcracks in the structures, and these cracks may directly affect the modeling parameters. Modal testing gives correct uncertain modeling parameters that lead to better predictions of the dynamic behavior of a target structure. Therefore, dynamic behavior of special structures, such as minarets, should be determined with ambient vibration tests. The vibration test results may be used to update numerical models and to detect microcracks distributed along the structure. The o...

Window opening effects on structural behavior of historical masonry Fatih Mosque

ABSTRACT 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.

Vibration based modal testing of a scaled reinforced concrete building for construction stages

The dynamic behavior of buildings can change during construction stages. The brick walls cause a considerable effect on the modal behavior depending on the wall configuration. In this paper, it is aimed to present the effects of construction stages (bare frame, brick-walled and coated cases) on the modal parameters of reinforced concrete (RC) buildings. For this purpose, a three-storey RC building model with a 1/2 scale was constructed in the laboratory of Civil Engineering Department at Karadeniz Technical University. The modal testing measurements were performed by using operational modal analysis method for the bare frame, brick walled and coated cases of the building model. Randomly generated loads by impact hammer were used to vibrate the building model; the responses were measured by uni-axial seismic accelerometers as acceleration. The building’s modal parameters at these construction stages were extracted from the processed signals using the enhanced frequency domain decomposition technique. The natural frequencies of the building model varied depending on the construction stages considerably. The frequencies decreased by increasing number of stories. But the brick walls caused a significant increase in the natural frequencies and affected the modal behavior that the longitudinal response occurred at first mode.

Seismic assessment of existing engineering structures using ambient vibrations

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.