Eser Çaktı

Recent Developments on Structural Health Monitoring and Data Analyses

The term “Structural Health Monitoring (SHM)” refers to continuous monitoring of a structure in order to track the changes in its dynamic characteristics and detect damage. In Civil/Structural Engineering, the majority of SHM applications are directed towards studying the response and damage from natural hazards, such as earthquakes and strong winds. The monitoring typically involves measuring continuously the vibrations of the structure by acceleration sensors. Some recent applications have also included GPS sensors, which provide superior accuracy for measuring displacements. Although a significant number of structures are now installed with SHM systems, the utilization of data for practical applications are still lacking. Some of the new findings resulting from SHM include the significant influence of environment on structural frequencies and damping, strong dependency of damping on amplitude and frequency, exponential decay in modal damping values with increasing building height, and the prevalence of 3D modes and non-proportional damping. A critical need in SHM is the simple tools and techniques for real-time data analysis and interpretation. Since data come continuously, the analysis cannot be done in batch mode; it should be done in real-time. This chapter summarizes the latest developments in SHM, with emphasis on data analysis and damage detection. The topics discussed include real-time analysis techniques, noise reduction in ambient vibration data, utilization of wave propagation approach as an alternative to spectral analysis, inadequacy of modal parameters for damage detection, applications of Seismic Interferometry for data analysis, and identification and damage detection for historical structures.

Ongoing Research on Earthquake Behavior of Historical Minarets in Istanbul

Minarets are slender structures. Old ones are mostly made of cut-stone-block masonry and occasionally of brick masonry, while the new ones are generally of reinforced concrete. They have suffered significant damage during past earthquakes, the most recent event being the 23 October 2011 Van, Turkey earthquake. Istanbul is home to many historical and contemporary minarets. Evaluation of their dynamic behavior is significant due to the expectation of a large event in the near future. In a recent study [1] we performed an extensive dynamic characterization campaign in 11 historical minarets in Istanbul, which allowed for the determination of frequencies, modes of vibration and damping. With the help of finite element modeling linear dynamic structural analyses of seven minarets were conducted to assess their earthquake risk level. Herewith we summarize our on-going studies on the same subject, which are: (1) The minaret damage that took place during the 2011 Van earthquake; (2) The new minaret campaign in Istanbul carried out in 30 historical and modern day minarets; (3) Earthquake damage assessment of the minaret of 16th century Mihrimah Sultan mosque based on discrete element modeling under simulated and real earthquakes; and (4) Permanent strong motion instrumentation of the Hagia Sophia Museum and Maltepe Mosque minarets.

EARTHQUAKE BEHAVIOR OF HISTORICAL MINARETS IN ISTANBUL

Minarets are slender structures. Old ones are mostly made of cut-stone-block masonry and occasionally of brick masonry, while the new ones are generally of reinforced concrete. They have suffered significant damage during past earthquakes, the most recent event being the 23 October 2011 Van, Turkey earthquake. Istanbul is home to many historical and contemporary minarets. Evaluation of their dynamic behavior is significant due to the expectation of a large event in the near future. In a recent study [1] we performed an extensive dynamic characterization campaign in 11 historical minarets in Istanbul, which allowed for the determination of frequencies, modes of vibration and damping. Finite element modeling and analysis of seven of these minarets were performed. Linear dynamic structural analyses were conducted to access their earthquake risk level. This paper summarizes our on-going studies on the same subject, which are: (1) The minaret damage that took place during the 2011 Van earthquake; (2) The new minaret campaign in Istanbul carried out in 30 historical and modern day minarets; (4) Earthquake damage assessment of the minaret of 16 century Mihrimah Sultan mosque based on discrete element modeling, and simulated and real earthquakes; (5) Permanent strong motion instrumentation of the Hagia Sophia Museum and Maltepe Mosque minarets.

RECENT EFFORTS IN ISTANBUL TO PROTECT MUSEUM COLLECTIONS FROM DAMAGE DUE TO EARTHQUAKES

Abstract The city of Istanbul is located on two continents and has thousands of years of rich history, but it has also been affected by major earthquakes throughout this period and another significant seismic event is expected in the near future. Istanbul hosts numerous museums that make available a wide range of collections that represent universal heritage and most of these museums are located in historical buildings. Through the years earthquakes have caused significant damage to historical structures in Istanbul and an important issue is the protection of these buildings and collections now and in the future. Bogazici University, Kandilli Observatory and Earthquake Research Institute and the Museum Studies Graduate Program of Yildiz Technical University are leading institutions with respect to research and initiatives aimed at protecting museum collections from earthquake damage in Turkey. This contribution discusses improvements in the seismic protection of collections as well as recent efforts focusing on the development of a distance learning educational package being developed in Turkey that addresses seismic risk mitigation.

Long-term Dynamic Response of Hagia Sophia in Istanbul to Earthquakes and Atmospheric Conditions

This study investigates the long-term dynamic response of Hagia Sophia in Istanbul to earthquakes and atmospheric conditions. It is aimed to display the variation in frequency-domain dynamic response parameters of Hagia Sophia due to changes in the atmospheric conditions and to identify behavioral patterns that can be associated with them. Moreover, the time and frequency domain response of the structure to earthquakes that took place since 2008 are studied to identify anything that stand out and can be interpreted as possible local or general structural problems. doi: 10.12783/SHM2015/165

Engineering Implications of Source Parameters and 3D Wave Propagation Modeling for the 2004 Parkfield, California, Earthquake

Abstract The 2004 M w xa06.0 Parkfield, California, earthquake took place in a very well‐instrumented area, producing a substantial quantity of high‐quality near‐field recordings. Taking advantage of the rare luxury of having a large number of near‐field ground‐motion recordings distributed around the fault zone and the availability of various slip models as well as an Earth structure model of the region, we study the effects of various kinematic rupture parameters to derive implications for strong ground motion simulation in engineering applications. We model the 3D wave propagation resulting from this earthquake using the 3D staggered‐grid finite‐difference method. Using a grid spacing of 100xa0m in our fourth‐order explicit finite‐difference code, we could properly resolve frequencies of up to 1xa0Hz with a minimum of eight grids per wavelength for shear waves, except in the immediate vicinity of the fault where fault‐trapped waves dominate the records. We assess the effects of various simulation parameters such as slip model, rise time (constant or variable), rupture velocity, and the earth model (1D versus 3D) on the resulting waveforms. We also investigate the distribution of engineering parameters such as peak ground velocities, peak ground displacements, and spectral accelerations at specific periods on the Earth’s surface. An outstanding feature is that at high frequencies fault‐normal components near the edge of fault segments dominate the ground‐motion field. Fault‐parallel components are dominated by lower frequencies. The difference between fault‐parallel and fault‐normal components is clearly observed in such engineering parameters as peak ground velocity and peak ground displacement.

Recent Studies on Earthquake Performance Assessment of Hagia Sophia in Istanbul

Over the last 25 years there have been a series of academic efforts to understand the particulars associated with earthquake performance and vulnerability of Hagia Sophia. Linear and nonlinear structural analyses; literary investigations; non-destructive tests and investigations involving its construction materials, foundations and main structural elements; ambient vibration tests; monitoring its earthquake response with the help of an accelerometric network were among them. More recently the foci of efforts were the analysis of long-term dynamic response of Hagia Sophia to earthquakes and variations in atmospheric conditions, shake table testing of a scaled model of the structure, analysis of recently added tiltmeter recordings, evaluation of strengthening alternatives and monitoring of its static deformations via laser technology. This contribution presents an overall picture of the research efforts carried out so far on earthquake response analysis of Hagia Sophia, emphasizing the studies over the last 5 years.

Structural Health Monitoring: Lessons Learned

Department of Earthquake Engineering of Kandilli Observatory and Earthquake Research Institute, Bogazici University (DEE-KOERI) has designed and been operating a significant number of structural monitoring networks in Istanbul. They are installed in a large number of historical structures (i.e., mosques, minarets, and museums), lifeline structures across the Bosphorus (i.e., suspension bridges and tunnels) and several tall buildings including the Sapphire tower, currently the tallest building in Europe. The structural monitoring networks record the dynamic motions of the structures continuously, and the data are transmitted in real time to the monitoring center at the DEE-KOERI. The majority of the systems use accelerometers for monitoring. Some structures are also instrumented with tiltmeters and GPS sensors. In-house real-time modal analysis software is used to process and analyze the data. The software includes data processing, spectral identification, and animation modules. The results are displayed in real time, showing the time variations of modal properties and the structure’s configuration. This chapter provides an overview of these monitoring systems in Istanbul. Moreover, it presents major findings related to the dynamic response properties of monitored structures particularly focusing on structural response to long-distance, long-period earthquakes; on the sensitivity of dynamic modal parameters to variations in atmospheric conditions; on structural response characteristics due to explosions; and on damping in tall buildings.

Earthquake risk assessment for the building inventory of Muscat, Sultanate of Oman

Earthquake risk can be quantified in terms of the estimated numbers of human casualties and of damaged buildings as well as the monetary losses. The information required for the assessment of earthquake risk in a given region includes the expected level of ground shaking intensity (i.e., the seismic hazard), inventory data for building stock at risk, identification of predominant building typologies and of their vulnerability characteristics, and spatial distribution of number of inhabitants. This study presents an indicative assessment of earthquake risk associated with the building stock in Muscat, the capital city of the Sultanate of Oman. For this purpose, building inventory and demographic data for the city are compiled in GIS environment. The buildings are classified to identify their damageability/vulnerability characteristics, and predominant building typologies are determined. For the estimation of casualties, Muscat population data are further analyzed to calculate number of occupants in the exposed building stock. Spectral acceleration–displacement based damage estimation methodology is implemented for risk calculations. Site-specific ground motions in terms spectral accelerations obtained from the probabilistic seismic hazard assessment for 475- and 2475-year return periods are considered for the representation ofxa0earthquake demand in damage analyses. Assessment of damage to buildings and estimation of casualties are obtained using analytical fragility relationships and building damage related casualty–vulnerability models, respectively. Earthquake risk maps illustrating the spatial distribution of number of damaged buildings at different damage states are presented for the considered levels of seismic hazard.

Identification of Energy Loss Due to Soilstructure Interaction from the Recorded Vibrations of Buildings

The vibrations of a building are due to the waves that travel up and down the building. When the ground below the foundation is not rigid (e.g., hard rock), a portion of the downgoing waves from the lowest story is transmitted back into the ground. This transmitted portion corresponds to the energy loss due to soil-structure interaction. This paper presents an approach to identify such energy losses from the recorded vibrations of buildings. The approach is based on the discrete-time formulation of wave propagation in multi-story buildings subjected to vertically propagating shear waves. The wave propagation in each story is characterized by the upgoing and downgoing waves at the top of the story. We derive equations for the 2x2 transfer matrices that relate the upgoing and downgoing waves in one story to those in the adjacent stories. The downgoing waves at the soil-foundation interface gives a measure of the energy loss due to soil-structure interaction. Starting from the top story, and by consecutive use of story transfer matrices, we can relate the upgoing and downgoing energies at the soil foundation interface to those at the top story. This relationship is also represented by a 2x2 matrix. The matrix is basically the product of 2x2 story transfer matrices from the foundation to the top story. The inspection of the elements of the matrix indicates that this relationship is equivalent to an IIR (Infinite Impulse Response) filter, which can be represented by an AR (Auto-Regressive) model between the foundation response and the top story response