In this paper three historical masonry minarets in Istanbul, Turkey, are assessed for the dependency between the input harmonic motion and structural response parameters. Their heights are 40, 73 and ...74 m, while the slenderness is 12, 6 and 12, respectively. The discrete element method is used in dynamic nonlinear analyses. Models were calibrated with measured natural frequencies. A series of sine-wave excitations is created for different frequency-amplitude pairs varying between 0.4 and 10 Hz, and between 0.1 and 1 m/s. From the results of dynamic simulations, a general trend was observed for masonry minarets. Especially, slenderness and wall thickness play an important role on their dynamic response and damage pattern. Dynamic behavior of these minarets cannot reliably be estimated by static non-linear analysis. Two engineering demand parameters (EDPs) are defined to characterize the displacement of the minaret top and the inter-ring shear displacements along the minaret body. Damage performance criteria for minarets are proposed based on four damage states and tentative limit values are given. We were able to identify the occurrence of those limit states as a function of frequency and amplitude of sinusoidal input motion.
Abstract This study presents a comprehensive seismic hazard assessment for Büyükçekmece, a district in Istanbul, Turkey, situated near the seismically active North Anatolian Fault (NAF). The study ...utilizes stochastic ground motion simulations with the validated EXSIM algorithm to understand the potential impact of medium to large-magnitude earthquakes (ranging from M W 6.3 to 7.42) on this vulnerable community. The research employs a site-specific approach, considering unique amplification factors for each location. By conducting 50 scenario-based simulations, the study assesses the seismic hazard, highlighting the importance of comprehending variations in ground motion, even when they are small, for a more precise hazard assessment. Furthermore, this study addresses the critical issue of uncertainty, particularly concerning stress parameters and hypocenter locations. The researchers demonstrate that variability in these factors can introduce substantial uncertainty in ground motion predictions. The study provides insights into the range of potential ground motion outcomes through probabilistic assessments involving multiple scenarios and stress drop values. Notably, the results indicate that ground motion levels vary with earthquake magnitudes and underscore the significance of accounting for this variability. This research emphasizes the seismic vulnerability of Büyükçekmece and the importance of accurate ground motion simulations, offering valuable insights for earthquake preparedness and mitigation efforts in the region.
The aim of using simulation techniques to provide generated ground motion data is to extend our knowledge on the effect of earthquakes and understanding their physical properties. High-frequency ...accelerations have incoherent behavior because of unpredictable irregularities and heterogeneities associated with faulting and wave propagation. Simulations of ground motions frequencies beyond > 1 Hz can be represented with stochastic methods using simplified model representations of source, path and site effects. In this paper, stochastic simulations are performed for the recordings of the 26 September 2019 Silivri, Istanbul earthquake, using a finite fault simulation approach with a dynamic corner frequency. The main target is to create a valid synthetic model database with consistent source, path, and site parameters in the region that can be implemented in future simulation efforts. In calibration, we have used the recordings at 59 widely distributed stations in Istanbul located on different site conditions with epicentral distances ranging from 23 to 101 km. Four different frequency-dependent Q models were tested to obtain the best fit with the observations. By comparing generated ground motions to the observed ones, optimum source parameters and crustal characteristics were estimated. The calibrated model parameters have been obtained from the set of best-fit data with observed ground motion in frequency domain. Synthetic PGAs have been compared with the NGA-West2 Ground Motion Models (GMMs). Furthermore, spatial distributions of the ground motion intensity parameters were obtained and compared with available damage observations in Istanbul due to this earthquake. In conclusion, the results of the simulation were in good agreement with the recorded ones, both in time and frequency domains. The results indicate that the proposed stochastic model can be used to simulate ground motion distributions in Istanbul and beyond from past and future events in the region.
•A scale model of a 15th century mosque is analyzed by discrete element approach.•Comparison of data from shake table program and nonlinear dynamic analysis results.•Good match of behavior in ...late-linear and early nonlinear ranges.•Prediction of zones and levels of damages in terms of inter-block displacements.•Global rocking of the upper part of minaret not well captured by numerical model.
The 1:10 scale model of the 15th century Mustafa Pasha Mosque in Skopje, that underwent a comprehensive shake table program, is modeled by the discrete elements approach. A rigid block model with nonlinear behavior concentrated at the joints was developed and calibrated by comparison with the observed response. Time domain analyses of the discrete model were performed under the various levels of dynamic excitation used in the shake table test. Under the lower levels of input, the time and frequency domain characteristics of the shake table experimental response were fairly well simulated by the numerical model. This model also predicted well the zones and the level of damages. For the higher input levels, the comparison was less satisfactory. Overall, the discrete element approach showed the capability to handle the dynamic nonlinear modeling of relatively complex masonry structures.
Istanbul today is probably unique in the world not only in terms of the recognition of its earthquake risk by its inhabitants and administrators, but also in terms of significant steps taken in a ...such a short time toward the mitigation of its earthquake vulnerabilities. This paper, however, deals with the issues that still remain unattended.
An M
W
4.5 earthquake took place on September 24, 2019 in the Marmara Sea. Two days after, on September 26, 2019, Marmara region was rattled by an M
W
5.7 earthquake. With the intention of compiling ...an ample strong ground motion data set of recordings, we have utilized the stations of Istanbul Earthquake Rapid Response and Early Warning System operated by the Department of Earthquake Engineering of Boğaziçi University and of the National Strong Motion Network operated by AFAD. Altogether 438 individual records are used to calculate the source parameters of events; namely, corner frequency, radius, rupture area, average source dislocation, source duration and stress drop. Some of these parameters are compared with empirical relationships and discussed extensively. Duration characteristics are analysed in two steps; first, by making use of the time difference between P-wave and S-wave onsets and then, by considering S-wave durations and significant durations. It is observed that they yield similar trends with global models. PGA, PGV and SA values are compared with three commonly used ground motion prediction models. At distances closer than about 60 km, observed intensity measures mostly conform with the GMPE predictions. Beyond 60 km, their attenuation is clearly faster than those of GMPEs. A frequency-dependent Q model is developed by using both events. Its consistency with existing regional models is confirmed.
The study presents probabilistic structural fragility assessment of public school buildings in Istanbul, which were constructed based on a standardized/typical project. The typical structure is a ...four-story, reinforced concrete shear wall building with moment resisting frames. Derivation of fragility functions rely on nonlinear dynamic analyses through Monte Carlo simulations. Nonlinear dynamic analyses are initially performed for a fully deterministic structural model based on the blueprints of the typical school building project. Uncertainties are introduced in different analysis cases following a modified version of the algorithm presented in Smyth et al. (2004) 21, which considers the effect of the random distribution of the parameters using a Monte Carlo approach. Aleatory uncertainties concerning material properties (i.e. compressive strength of concrete, yield strength of reinforcing steel and concrete density), geometrical characteristics (i.e. span lengths and story heights) and cross sectional dimensions of beams, columns and shear walls as well as epistemic uncertainty in the direction of ground motion excitation are considered. Statistical distributions for the parameters considered are obtained from in-situ measurements and material sampling tests. Fragility functions are produced in terms of peak ground acceleration and velocity as well as of the elastic spectral displacement at the first vibration period of the building. Mean damage ratios are calculated from the derived fragility functions. They are further compared to mean damage ratios calculated for similar building typologies provided in HAZUS-MH technical manual and in Istanbul building inventory.
•Probabilistic structural fragility assessment of typical school buildings is presented.•Uncertainties in material and geometrical properties; in the ground motion considered.•The uncertainties cause a significant variation in the resulting fragility functions and this would lead different loss estimations.Ultimately when extended to include other school types as well the results can be used to quantify the uncertainties in the damage estimation of school buildings in Turkey for earthquake loss scenario purposes.
This paper provides an investigation on the correlations between ground motion intensity measures (IMs) and engineering demand parameters (EDPs) through nonlinear dynamic analyses of MDOF systems ...under real earthquake recordings and then structural fragility curves are derived for the best correlated IM–EDP pairs. For this purpose, a parametric study on reinforced concrete (RC) buildings is carried out. Study buildings comprise 5-, 10-, 15- and 20-story, RC, code-complying, regular, moment-resisting frames designed for different strength reduction factors, e.g. R = 2, 4 and 6. The input ground motion dataset consists of 734 horizontal components of earthquake accelerograms. The best correlations between IMs and EDPs are computed by regression analysis. Sets of fragility curves in terms of maximum inter-story drift ratio, maximum plastic end rotation and maximum floor acceleration are derived based on log-normal distribution assumption. Fragility curves are presented not for a specific damage state such as slight, moderate etc. but for a range of damage thresholds on EDP.
The knowledge of frequencies of vibration of the first modes of minarets is essential to anticipate their behaviour under seismic loads. Masonry minarets are very slender structures with an extensive ...history of many centuries of construction and damages inflicted by earthquakes. Their construction techniques did not change much throughout the historical epochs, and only very recently, new minarets of the same type were built with Reinforced Concrete. Minarets lately have been the object of several studies because both the monitoring technologies for in-situ vibration observations and the existence of non-linear large-displacement software have become available. Many teams dedicated their attention to analysing frequencies of these structures and a few to study their behaviour. Several formulae were proposed to obtain frequencies as a function of their geometrical and mechanical characteristics, trying to arrive at some law valid for the set of minarets they studied. Others tried to extend their formulae to other slender traditional masonry structures such as towers, or chimneys. In this state-of-the-art review paper, the authors use a large set of data (79 Ottoman minarets) on frequency values as obtained by the authors as well as data compiled from the literature, to revisit this problem and discuss the details of how accurate the estimate of the frequencies might be. This large set confirms the trend of published formulae but includes uncertainties. A proposal for a simple formula, anchored on theoretical grounds, of the type
is presented with a minimum number of aggregated variables and better Coefficient of determination, R
2
.
Summary
A methodology for the interpolation of peak ground acceleration (PGA) from discrete array stations is developed. Limited number of accelerometers or difficulty of monitoring at unreachable ...locations often has a negative impact on the generation of the maps of shaking after an earthquake. In locations with no recordings, PGA is inferred from interpolation of recorded PGA. The presented methodology estimates PGA at an arbitrary set of closely spaced points, in a way that is statistically compatible with known or prescribed PGA at other locations. The observed data recorded by strong motion stations of Istanbul Earthquake Rapid Response System are used for the development and validation of the new numerical method. The estimated and recorded PGAs are compared. Biased ground motion prediction equations are also considered at the comparisons. Ground motion prediction equations underestimated both observed and estimated PGAs. It has been found that the methodology is very effective for highly vulnerable mega-cities and urban areas.
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