Seismic responses of base-isolated buildings: efficacy of equivalent linear modeling under near-fault earthquakes

Cenk Alhan,Murat Özgür 국제구조공학회 2015 Smart Structures and Systems, An International Jou Vol.15 No.6

Design criteria, modeling rules, and analysis principles of seismic isolation systems have already found place in important building codes and standards such as the Uniform Building Code and ASCE/SEI 7-05. Although real behaviors of isolation systems composed of high damping or lead rubber bearings are nonlinear, equivalent linear models can be obtained using effective stiffness and damping which makes use of linear seismic analysis methods for seismic-isolated buildings possible. However, equivalent linear modeling and analysis may lead to errors in seismic response terms of multi-story buildings and thus need to be assessed comprehensively. This study investigates the accuracy of equivalent linear modeling via numerical experiments conducted on generic five-story three dimensional seismic-isolated buildings. A wide range of nonlinear isolation systems with different characteristics and their equivalent linear counterparts are subjected to historical earthquakes and isolation system displacements, top floor accelerations, story drifts, base shears, and torsional base moments are compared. Relations between the accuracy of the estimates of peak structural responses from equivalent linear models and typical characteristics of nonlinear isolation systems including effective period, rigid-body mode period, effective viscous damping ratio, and post-yield to pre-yield stiffness ratio are established. Influence of biaxial interaction and plan eccentricity are also examined.

Seismic isolation performance sensitivity to potential deviations from design values

Cenk Alhan,Kemal Hisman 국제구조공학회 2016 Smart Structures and Systems, An International Jou Vol.18 No.2

Seismic isolation is often used in protecting mission-critical structures including hospitals, data centers, telecommunication buildings, etc. Such structures typically house vibration-sensitive equipment which has to provide continued service but may fail in case sustained accelerations during earthquakes exceed threshold limit values. Thus, peak floor acceleration is one of the two main parameters that control the design of such structures while the other one is peak base displacement since the overall safety of the structure depends on the safety of the isolation system. And in case peak base displacement exceeds the design base displacement during an earthquake, rupture and/or buckling of isolators as well as bumping against stops around the seismic gap may occur. Therefore, obtaining accurate peak floor accelerations and peak base displacement is vital. However, although nominal design values for isolation system and superstructure parameters are calculated in order to meet target peak design base displacement and peak floor accelerations, their actual values may potentially deviate from these nominal design values. In this study, the sensitivity of the seismic performance of structures equipped with linear and nonlinear seismic isolation systems to the aforementioned potential deviations is assessed in the context of a benchmark shear building under different earthquake records with near-fault and far-fault characteristics. The results put forth the degree of sensitivity of peak top floor acceleration and peak base displacement to superstructure parameters including mass, stiffness, and damping and isolation system parameters including stiffness, damping, yield strength, yield displacement, and post-yield to pre-yield stiffness ratio.

Probabilistic sensitivity of base-isolated buildings to uncertainties

Gazi, Hatice,Alhan, Cenk 국제구조공학회 2018 Smart Structures and Systems, An International Jou Vol.22 No.4

Characteristic parameter values of seismic isolators deviate from their nominal design values due to uncertainties and/or errors in their material properties and element dimensions, etc. Deviations may increase over service life due to environmental effects and service conditions. For accurate evaluation of the seismic safety level, all such effects, which would result in deviations in the structural response, need to be taken into account. In this study, the sensitivity of the probability of failure of the structures equipped with nonlinear base isolation systems to the uncertainties in various isolation system characteristic parameters is investigated in terms of various isolation system and superstructure response parameters in the context of a realistic three-dimensional base-isolated building model via Monte Carlo Simulations. The inherent record-to-record variability nature of the earthquake ground motions is also taken into account by carrying out analyses for a large number of ground motion records which are classified as those with and without forward-directivity effects. Two levels of nominal isolation periods each with three different levels of uncertainty are considered. Comparative plots of cumulative distribution functions and related statistical evaluation presented here portray the potential extent of the deviation of the structural response parameters resulting from the uncertainties and the uncertainty levels considered, which is expected to be useful for practicing engineers in evaluating isolator test results for their projects.

Probabilistic sensitivity of base-isolated buildings to uncertainties

Hatice Gazi,Cenk Alhan 국제구조공학회 2018 Smart Structures and Systems, An International Jou Vol.22 No.4

Characteristic parameter values of seismic isolators deviate from their nominal design values due to uncertainties and/or errors in their material properties and element dimensions, etc. Deviations may increase over service life due to environmental effects and service conditions. For accurate evaluation of the seismic safety level, all such effects, which would result in deviations in the structural response, need to be taken into account. In this study, the sensitivity of the probability of failure of the structures equipped with nonlinear base isolation systems to the uncertainties in various isolation system characteristic parameters is investigated in terms of various isolation system and superstructure response parameters in the context of a realistic three-dimensional base-isolated building model via Monte Carlo Simulations. The inherent record-to-record variability nature of the earthquake ground motions is also taken into account by carrying out analyses for a large number of ground motion records which are classified as those with and without forward-directivity effects. Two levels of nominal isolation periods each with three different levels of uncertainty are considered. Comparative plots of cumulative distribution functions and related statistical evaluation presented here portray the potential extent of the deviation of the structural response parameters resulting from the uncertainties and the uncertainty levels considered, which is expected to be useful for practicing engineers in evaluating isolator test results for their projects.

Probabilistic behavior of semi-active isolated buildings under pulse-like earthquakes

Seda Öncü-Davas,Cenk Alhan 국제구조공학회 2019 Smart Structures and Systems, An International Jou Vol.23 No.3

Seismic isolation systems employ structural control that protect both buildings and vibration-sensitive contents from destructive effects of earthquakes. Structural control is divided into three main groups: passive, active, and semi-active. Among them, semi-active isolation systems, which can reduce floor displacements and accelerations concurrently, has gained importance in recent years since they don’t require large power or pose stability problems like active ones. However, their seismic performance may vary depending on the variations that may be observed in the mechanical properties of semi-active devices and/or seismic isolators. Uncertainties relating to isolators can arise from variations in geometry, boundary conditions, material behavior, or temperature, or aging whereas those relating to semi-active control devices can be due to thermal changes, inefficiencies in calibrations, manufacturing errors, etc. For a more realistic evaluation of the seismic behavior of semi-active isolated buildings, such uncertainties must be taken into account. Here, the probabilistic behavior of semi-active isolated buildings under historical pulse-like near-fault earthquakes is evaluated in terms of their performance in preserving structural integrity and protecting vibration-sensitive contents considering aforementioned uncertainties via Monte-Carlo simulations of 3-story and 9-story semi-active isolated benchmark buildings. The results are presented in the form of fragility curves and probability of failure profiles.

A New Approach to Objective Evaluation of the Success of Nasal Septum Perforation

Sinan Ozturk,Fatih Zor,Serdar Ozturk,Ozgur Kartal,Dogan Alhan,Selcuk Isik 대한성형외과학회 2014 Archives of Plastic Surgery Vol.41 No.4

Background: Perforations in the nasal septum (NSP) give rise not only to disintegration ofthe septum anatomy but also impairment in normal nasal physiology. The successes of thesesurgical techniques are usually equated to anatomical closure of the perforation. The goal ofthis study is to evaluate the subjective and objective results of our surgical technique forseptal perforation surgery. Methods: All NSPs in the six patients were closed by inferior turbinate flap. The NasalObstruction Symptom Evaluation (NOSE) instrument was used to evaluate the preoperativeand postoperative subjective sensation of nasal obstruction. Measurement of preoperative andpostoperative nasal airway resistance was performed using active anterior rhinomanometrywhich is an objective test. Wilcoxson signed rank test and Spearman correlation test were usedto analyze correlation between NOSE scores and rhinomanometric measurements. Results: The full closure of the septal perforations was noted in 100% of patients. The totalNOSE score was 14 preoperatively and one postoperatively. The improvement in NOSE scoreswas statistically significant (P≤0.002). The mean preoperative total resistance (ResT150) valuewas 0.13 Pa/cm3s-1, which is below the normal range (0.16–0.31 Pa/cm3s-1), while the meanpostoperative ResT150 value was 0.27 Pa/cm3s-1. The correlation between the improvement inNOSE scores and improvements in ResT150 values was statistically significant . Conclusions: Surgical approaches should aim to solve both the anatomical and physiologicalproblems of NSP. The application of subjective and objective tests in the postoperative periodwill help surgeons assess the applied techniques.

A New Approach to Objective Evaluation of the Success of Nasal Septum Perforation

Ozturk, Sinan,Zor, Fatih,Ozturk, Serdar,Kartal, Ozgur,Alhan, Dogan,Isik, Selcuk Korean Society of Plastic and Reconstructive Surge 2014 Archives of Plastic Surgery Vol.41 No.4

Background Perforations in the nasal septum (NSP) give rise not only to disintegration of the septum anatomy but also impairment in normal nasal physiology. The successes of these surgical techniques are usually equated to anatomical closure of the perforation. The goal of this study is to evaluate the subjective and objective results of our surgical technique for septal perforation surgery. Methods All NSPs in the six patients were closed by inferior turbinate flap. The Nasal Obstruction Symptom Evaluation (NOSE) instrument was used to evaluate the preoperative and postoperative subjective sensation of nasal obstruction. Measurement of preoperative and postoperative nasal airway resistance was performed using active anterior rhinomanometry which is an objective test. Wilcoxson signed rank test and Spearman correlation test were used to analyze correlation between NOSE scores and rhinomanometric measurements. Results The full closure of the septal perforations was noted in 100% of patients. The total NOSE score was 14 preoperatively and one postoperatively. The improvement in NOSE scores was statistically significant ($P{\leq}0.002$). The mean preoperative total resistance (ResT150) value was $0.13Pa/cm^3s^{-1}$, which is below the normal range ($0.16-0.31Pa/cm^3s^{-1}$), while the mean postoperative ResT150 value was $0.27Pa/cm^3s^{-1}$. The correlation between the improvement in NOSE scores and improvements in ResT150 values was statistically significant. Conclusions Surgical approaches should aim to solve both the anatomical and physiological problems of NSP. The application of subjective and objective tests in the postoperative period will help surgeons assess the applied techniques.

Mirror Image Gerbode or Partial Atrioventricular Canal Defect?

Cem Ariturk, Ass.Prof.,Ahmet Umit Gullu, Ass.Prof.,Sahin Senay, Ass.Prof.,Eyup Murat Okten, M.D.,Fevzi Toraman,E. Hasan Karabulut, Prof.,Letisya Melengic, M.S.,Cem Alhan, Prof. 대한흉부외과학회 2015 Journal of Chest Surgery (J Chest Surg) Vol.48 No.6

Gebode defect, that can accurately be treated surgical repair, is defined as a true communication between left ventricle and right atrium. A 74-year-old woman with a worsening history of ortophnea and peripheral edema was hospitalised. A communication between right atrium and left ventricle was diagnosed using transeusophageal echocardiography. The defect was repaired and mitral valve was replaced with a biologic valve. It would be beter to tailor surgical strategy for each case with atrioventricular canal defect after preoperative transeusophageal echocardiography and peroperative direct sight.

Development of metal organic framework filled PDMS/PI composite membranes for biobutanol recovery

Aslıhan Çalhan,Sennur Deniz,Julio Romero,Ayça Hasanoğlu 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.9

Butanol is a second generation biofuel with high potential to replace fossil fuels in the future. The main drawbacks in biobutanol production are the low yields of operation and high cost of separation. In this study, n-butanol recovery from its aqueous solutions was carried out by pervaporation as an alternative separation process using polyimide supported polydimethylsiloxane membranes, which were especially prepared for this purpose. To enhance the separation efficiency of the membrane, metal organic framework fillers of MOF-199 were included in its structure. Several combinations of polyimide supported PDMS active layered membranes were prepared with the fillers in each layer of the membrane, in both layers of membrane and membranes without fillers. Thus, the effect of the fillers on the separation performance was investigated. It was found that the inclusion of MOF-199 enhances the membrane performance; meanwhile, the support layer also contributes to mass transfer of n-butanol. Furthermore, the effect of the process parameters on the pervaporation performance was investigated. Results of pervaporation tests indicate that the developed membranes have a good potential for n-butanol recovery from aqueous mixtures.

Non-preemptive Queueing Model of Spectrum Handoff Scheme Based on Prioritized Data Traffic in Cognitive Wireless Networks

Muhammed Enes Bayrakdar,Ali Çalhan 한국전자통신연구원 2017 ETRI Journal Vol.39 No.4

In this study, a non-preemptive M/G/1 queueing model of a spectrum handoff scheme for cognitive wireless networks is proposed. Because spectrum handoff gives secondary users an opportunity to carry on their transmissions, it is crucially important to determine the actions of primary users. In our queueing model, prioritized data traffic is utilized to meet the requirements of the secondary users. These users’ packets are categorized into three different priority classes: urgent, real-time, and non-real time. Urgent data packets have the highest priority, while non-real time data packets have the lowest priority. Riverbed (OPNET) Modeler simulation software was used to simulate both reactive and proactive decision spectrum handoff schemes. The simulation results were consistent with the analytical results obtained under different load and traffic conditions. This study also revealed that the cumulative number of handoffs can be drastically decreased by exploiting priority classes and utilizing a decent spectrum handoff strategy, such as a reactive or proactive decision-based strategy.