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Preliminary seismic evaluation of highway bridges in Istanbul
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 1995., 1995.) Zülfikar, A. Can.; Yüzügüllü, Özal.
In spite of the considerable developments in bridge engineering in recent years, substantial damages of highway bridges in recent earthquakes, have lead to an increasing awareness on the seismic performance of bridges. Seismic vulnerability of a bridge can be defined as the potential of a bridge to sustain significant damage or collapse. The seismicity at the location of the bridge is essential in the determination of its vulnerability. Istanbul is one of the most crucial cities in Turkey due to its historical, industrial and commercial importance. The main objective of the current study is to establish an inventory for the highway bridges on the 01 and 02 peripheral routes and the corresponding link roads in Istanbul and evaluate their seismic vulnerabilities according to a certain screening procedure. Such a preliminary screening procedure contemplates only the technical aspects of the problem and does not include political and economic considerations. In the preliminary screening process, Structural characteristics of the bridge, Importance of the bridge as a vital transportation link, Foundation and site characteristics of the bridge, are taken into consideration. In addition to the above studies, truck loading testing and a detailed analysis on a typical representitive bridge are presented. The results of this investigation are to be considered as the essential and basic step for the maintenance and rehabilitation of the ,highway bridges in istanbul under a future seismic activity.
Determination of earthquake performance of Süleymaniye Mosque
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 1999., 1999.) Kaya, Samiye Mircan.; Yüzügüllü, Özal.
Built between 1549-1557 by the great Turkish architect Mimar Sinan and named after the legendary Ottoman Emperor Siileyman the Magnificient, the Siileymaniye Mosque is considered to be the masterpiece of the Ottoman architecture. It is a fact that the research studies carried out up today towards the determination of the earthquake performance of this masterpiece of Otioman-Turkish Engineering is very limited. Within the framework of research activities being carried out at the Earthquake Engineering Department of Kandilli Earthquake Observatory and Earthquake Research Institute for the important historic edifices which was initiated with the Hagia Sophia, the present study on Siileyrnaniye Mosque is aimed at the exploration of the earthquake performance and dynamic characteristics of the structure. The three dimensional finite element model of the structure previously prepared by A.Selahiye was refined.Non-destructive material tests were carried out in the mosque in order to determine the material characteristics.The data obtained from the tests were used in the study and as a further step, the effects of different materials were investigated.At this stage the effects of different boundary conditions were also combined in the study. The earthquake records obtained from the strong ground motion accelerometers previously installed on Siileymaniye Mosque were also analysed to obtain the natural vibration frequencies and to compare the resulting values with those obtained by other methods.As a last stage of the study, the analysis of the improved model under a scenario earthquake for istanbul was carried out.
Seismic performance evaluation of the Sadabat 1 (V3) viaduct
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2002., 2002.) Önem, Göktürk.; Aydınoğlu, M. Nuray.
Sadabat V3 was designed in the late 1980's as a connector highway bridge in conjunction of Okrneydam and Hastal on ball-Sakarya motonvay route, which is a major component of the transportation system of Istanbul. The bridge shows some typical examples of old seismic design philosophy such as low level of design forces and lack of modem ductile detailing. Based on the visual inspection, any detrimental effects such as cracking or spalling of cover concrete due to corrosion could not be observed. Generally, it can be say that current condition of the bridge is good. The bridge is evaluated as a critical bridge because of the location on major traveled route. The bridge is expected to remain functional immediately following a destructive earthquake. Seismic performance of the bridge has been assessed by using nonlinear time history analysis and pushover analysis. At the end of the analysis, deformation demand determined fi-om the analysis has been compared with the predetermined component deformation capacity to obtain whether the bridge provides expected performance. Analysis shows that elastomeric; bearings, particularly located on flexible intermediate piers have insufficient displacement capacities in transverse direction to remain elastic. Displacement ductility of the piers are inadequate due to the poor detailing of the plastic hinge region. Because of the low ductility capacity, the piers are unlikely to tolerate cyclic displacement much exceeding yield in transverse direction. However, it can be concluded that the bridge response is essentially elastic in longitudinal direction.
Influence of modeling parameters on seismic response of steel moment resisting frames
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2003., 2003.) Gündüz, Ahmet Suat.; Aydınoğlu, M. Nuray.
The purpose of this work is to identify the building response to variations in modeling parameters and assumptions for the steel mid-rise buildings. The behavior and response of 9-story building in Los Angeles are studied. The building that was designed according to the UBC 1994 provisions was used in the analysis. Different models for this structure were developed and analyzed dynamically. The models investigated involved the use of centerline dimensions of elements, or clear length dimensions (rigid zone effect), nonlinear springs for the beam connections, and nonlinear springs for the panel zones. Also, P-delta effects on the system response to the ground motions were investigated. Nonlinear time-history analysis was used to assess the performance of buildings subjected to strong earthquake ground motions. The global (roof) and story level displacement demands, story drift ratio demands, beam and panel zone plastic rotation demands, location of plastic rotations of the systems, and the story shears were obtained by subjecting the six models to set of 10 ground motions representative of a 10150 (10% probability of being exceeded in 50 years) hazard level. The results are compared to evaluate the influence of modeling assumptions on the nonlinear dynamic response of the structures. As a result it is concluded that, the effect of analytical modeling is intrinsic to understanding the response of the structure. The overall effect of the different models can result in significant changes in the demands. Moreover, structure P-delta effects are found to have a potentially severe influence on the response of steel moment resisting structures.
Seismic evaluation of pile groups
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2003., 2003.) Beker, Hüseyin Afşin.; Siyahi, Bilge.
In certain regions of the country, designing deep foundations to withstand seismic loading is a reality. Seismic loading of structures and foundations reach a critical state as the laterally applied force increases. Especially liquefaction is the major effect on laterally loaded piles. So firstly, the liquefaction potential of the site has been evaluated to make the best seismic assessment, as studied in the following chapter. Since, liquefaction potential analysis is highly complex and is based on numerous variables such as moment magnitude, epicentrical distance, PGA, thickness of soil layers, overburden pressure and duration of motion etcetera. Most of the potential analysis methods are empirically based on the statistical measurements of known past earthquakes. Thus, firstly the liquefaction potential analysis of the site is evaluated. by means of these methods. Secondly, the effects of liquefaction-induced lateral spreading on piles have been studied. Then, after a brief information is given about the structure, which is chosen as the model, the capacity estimations of the piles and the superstructure are acquired. Then soil, piles and the superstructure are modeled together in the SAP2000 computer program. Liquefaction-induced lateral spreading, spectral analysis (for TSC-98) and non-linear time-history analysis, with three different earthquake records (two of them are simulated), are examined. Finally, the results of the most critically forced structural elements are illustrated and then compared both by the structural capacity and between the different methods of solutions used. This study also gives a general knowledge about the sufficiency of the Turkish Seismic Code for buildings within the vicinity of an active fault line.
Seismic performance evaluation of public school buildings in İstanbul metropolitan area
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2005., 2005.) Ekser, Burç.; Yüzügüllü, Özal.
Earthquake resistance of school buildings deserves special attention with respect to seismic safety because of their occupancy characteristics and their importance to immediate and long-term earthquake disaster relief and recovery efforts. The aim of the study is that the seismic performance evaluation of public school buildings in Istanbul. According to this, in Istanbul, three different types of projects are practiced and evaluated for public schools constructed due to different number of stories and different earthquake zones. besides, these kinds of porjects were analyzed in terms of 1975 and 1998 Turkish Codes. In addition to the seismic performance evaluation of public schools, a preliminary screening procedure was carried out in that study. To eliminate the losses caused by earthquakes, the earthquake resistance of the school building must be examined by quick and easy method which is Rapid Visual Screening Procedure prepared by Applied Technology Council. Actually, the method which was carried out, is classified the earthquake resistance resistance of the public schools and determined a detailed evaluation is required or not.
Strain based performance evaluation charts for rectangular reinforced concrete columns in nonlinear analysis of structures
(Thesis (M.S.)- Bogazici University. Kandilli Observatory and Eartquake Research Institute, 2005., 2005.) Şadan, Oğuz Bahadır.; Aydınoğlu, M. Nuray.
Several methods and criterion are being used recently in determination of the deformations occurred in structural elements of a building and performance evaluation of these structural elements under earthquake motion using nonlinear analysis. Performance evaluation of structures under nonlinear earthquake loading using material strains, rather than the rotations as commonly used in other seismic codes (FEMA356, ATC40, EUROCODE8 etc.) is the basic subject of this study. Performance evaluation using material strains is also being mentioned in Chapter 13 of New Turkish Seismic Code Dra3. For performance evaluation using member strains, Strain Based Performance Evuluation Charts for rectangular reinforced concrete columns have been formed which bring easiness by omitting several cross sectional analysis in order to transform rotations into strains. These Strain Based Performance Evaluation Charts are intended to be very useful for the structural engineers who will practice nonlinear analysis using New Turkish Seismic Code in the future. However it should be noticed that these charts are formed only for rectangular reinforced columns with limited concrete-steel grade combinations. Therefore further studies should be performed for other combinations and beams.
Seismic evaluation of Bolu viaduct 1
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake research Institute, 2006., 2006.) Candan, B. Tolga.; Aydınoğlu, M. Nuray.
A thesis is presented on the seismic evaluation of a viaduct using non-linear analysistechniques. The Bolu viaduct is a 2-3 km long seismically isolated structure with two parallelbridges each with a span length of 39.2 m and pier height of maximum 49 m that was nearly complete when it was struck by the 1999 Duzce earthquake in Turkey. With the design basedon AASHTO standards, it suffered complete failure of the seismic isolation system andnarrowly avoided total collapse due to excessive superstructure moment. After investigationsthe retrofit of the viaduct had been decided due to the study carried out by Michele Calvi and J. Nigel Priestley. This thesis concentrates on the retrofitted structure of Viaduct 1 by non-linear time historyanalysis.
Investigation of failure modes and mechanisms of Alibey Earth Dam by solid-fluid coupled nonlinear dynamic finite element simulation
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2006., 2006.) Parker, Ahmet Alper.; Siyahi, Bilge.
In this study, earthquake resistance of Alibey Earth Dam was investigated. Darn was modeled with four node plane-strain finite elements and displacement-pore pressure coupled finite element analyses were performed. Nonlinear material models such as pressure dependent and independent multi yield materials were implemented during the analyses. Transient dynamic finite element analyses were performed with Newmark method. Newton-Raphson solution scheme was adopted during the solution of the equations. Liquefaction and/or cyclic mobility effects were considered during the analysis. For the finite element analyses OpenSees (Open System for Earthquake Engineering Simulation) framework was adopted.
Shake table tests of a 1/4 scaled mass concentric three storey steel structure isolated by a hybrid passive control system
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2007., 2007.) Yenidoğan, H. Cem.; Uçkan, Eren.
Objective of this study is to investigate the effectiveness of a hybrid isolation system for a three-storey mass concentric steel structure. The isolation system consists of 2 elastomeric bearings and 4 flat sliding bearings, which are located below the central and corner columns, respectively. A 1,4 scaled isolated model of the structure has been tested on a shake table under real earthquakes and sinusoidal base motions. Measurements were taken at structural points and at base slab level. Two types of high damping elastomeric bearings, one with low shear modulus and the other with high shear modulus, were tested to see the effects of different target isolation periods. A numerical model for the structure was developed and calibrated by the data from the experimental studies. In this dissertation effectiveness of the hybrid isolation system is verified by comparing the results obtained from isolated and fixed base models.
Seismic performance assessment of Ortaköy V409 viaduct
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2007., 2007.) Öztürk, Ali Cem.; Aydinoğlu, M. Nuray.
The Ortakoy V409 carries 1st Peripheral Highway and has constructed in 1973. The V409 is the last approach viaduct of First Bosphorous Bridge and has a specific role on transportation of stanbul. The existing condition, which is investigated on site, clearly shows that there are significiant damages like corrosions and etc. at whole structure due to lack of maintenance. The existing condition of structure has been evaluated by inelastic analysis method. In this dissertation, in part 1 the general descriptions have tried to be explained. In part 2; The existing conditions like dimensions and etc. have stated according to the site investigations and existing drawings. In the following part; the methods that were used in calculations explained. In part 4 the modelling procedure with the appropriate softwares and the loads that were applied in analyses have exhibited. In the final part the conclusions have stated. As a result of the time history analyses, like mentioned above, the viaduct is vulnearable due to deficiencies of ductility and detailing concepts. Existing sections can not resist the shear forces and moments occured during the earthquakes.
Seismic performance evaluation of dual reinforced concrete systems design according to Turkish seismic code, 2007
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2007., 2007.) Kârcı, E. Yeşim.; Aydınoğlu, M. Nuray.
The aim of this study is to investigate the dual reinforced concrete frame systems of mixed ductility level which are described in Turkish Seismic Code, 2007, (TSC '07) by using Nonlinear Static Analysis (Pushover Analysis) for evaluating the seismic performance of these reinforced concrete buildings. For this purpose, a sample reinforced concrete structure is used accordihg to Turkish Seismic Code, 2007, (2.5.4.1(c)), to evaluate the performance where the ratio of the sum of base shear developed at the bases of solid structural walls under seismic loads to the total base shear developed for the entire building is between the values 0.4 and 213 (0.4
Characterization of response spectra for near field conditions by earthquake ground motion simulation
(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2007., 2007.) Şeşetyan, Karin.; Erdik, Mustafa.; Madariaga, Raul.
Strong ground motion estimation tools such as empirical ground motion prediction equations rely mostly on recorded data. Good quality strong motion data became available mostly in recent years and are still sparse for near field conditions. Strong ground motion records on the other hand contain them several characteristics such as source, path and especially local site effects. These features can sometimes be hardly differentiated when one is willing to study only one of them. As such, realistic simulation of the 3D wavefield generated by a fault rupture in a heterogeneous medium becomes critical for the study of strong ground motion. Particularly features such as intra-event and inter-event spatial and temporal variability of ground motion can be studied in detail. With increasing computational power and newly emerged methods such simulations become increasingly feasible. In this study I use kinematic simulation with 3D Staggered Grid Finite Difference method to study the characteristics of near source effects of strong ground motion. I also aim to prove that kinematic simulation with 3D Staggered Grid Finite Difference method (3DFD) is a useful tool to analyze and estimate the characteristics of long period strong ground motion. For this purpose first a simulation model has been set for the 2004 Mw=6.0 Parkfield earthquake. Making use of the available 3D crustal velocity structure of the region and several slip models of the earthquake over 40 near source recordings produced by the event have been simulated. Encouraged by the very good agreement between observed and simulated waveforms, 3DFD has been used for the characterization of directivity effects in the near source region. Eleven earthquakes covering a magnitude range from 6.0 to 7.4 have been modeled using one or more slip models for each of them. Eight of these events had a strike-slip mechanism whereas the remaining ones were dip-slip events. Resulting spatial distributions of fault parallel, fault normal and average response spectral accelerations at longer periods have been analyzed to derive general formulations for the modification of the response spectral values found from earthquake hazard analysis to include near source directivity effects. With recently emerging structural design methods, engineering studies concentrate more and more on the long period characteristics of strong ground motion. The present study validates kinematic simulation tools, particularly the 3DFD method used herein as a useful method for the simulation of low frequency strong ground motion in realistic earth media for engineering purposes.
A seismic vulnerability analysis procedure for urban loss assessment
(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2008., 2008.) Tüzün, Cüneyt.; Aydinoğlu, M. Nuray.
The assessment of seismic vulnerability of buildings in seismically active urban areas is of great importance in terms of engineering, economical and social aspects. In this study an analytical procedure has been developed in order to obtain the vulnerability functions of existing buildings. The building information included over all geometry of the structure, as-built dimensions and configuration of the structural members, complete with reinforcement details of beams and columns, which are extracted from the design dossiers available in the Bolu municipality archives. Totally 120 buildings, 20 from each class, are classified depending on their number of stories ranging from 2 to 7 story and nonlinear response history analysis has been performed in order to obtain damage distributions by using 20 spectrum compatible ground motions. In the first chapter a brief explanation of the role of loss estimation studies in urban planning, urban disaster management and mitigation has been given. In the second chapter, existing building vulnerability relationships have been evaluated and particular examples of studies that have made important contribution to the development are briefly cited. In the third chapter, basic steps of a standard derivation of analytical vulnerability functions are identified and the importance of each step in the process has been explained. In the fourth chapter, the procedure based on real building data has been explained in detail including the ground motion characterization, properties of building data, analytical methods used in the analysis, damage definition and quantification, statistical process and the determination of the vulnerability parameters. Results are presented in the form of lognormal vulnerability curves with respect to spectral acceleration or spectral displacement. In the fifth chapter, the conclusions are presented and the contribution of the study to the existing knowledge in the field has been evaluated
Dynamic shear amplification in seismic response of structural wall systems
(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2008., 2008.) Celep, Umut Utku.; Aydınoğlu, M. Nuray.
Previous research indicates that, shear force demand in yielding walls are not proportional to the design moments calculated by code procedures and higher shear force demands develop along the wall with respect to code predictions as a consequence of the higher mode effects after the plastic hinge formation at the base of the wall. 2007 version of the Turkish Seismic Design Code takes the dynamic shear amplification phenomena into account with a constant base shear amplification factor of 1.5 regardless of the first mode period and ductility level of the wall. However, results obtained from extensive non-linear time history analyses performed on generic walls in this study indicate that dynamic shear amplifications increase with increasing first mode period, Strength Reduction Factor (R) and ground motion intensity. A dynamic base shear amplification relationship as a function of the first mode period and strength reduction factor has been proposed for the Turkish Seismic Design Code (2007), based on the regression analysis of the non-linear time history analysis. A story shear force profile has been suggested for the Turkish Seismic Design Code (2007), which is intended for not only preventing shear failures at the base but also along the height of the wall. As a side product of the nonlinear time history analyses, a moment profile has also been proposed for use in the Turkish Seismic Design Code (2007). A modal decomposition technique is presented in this study for demonstrating the effects of the higher modes on the dynamic shear amplification phenomenon.
Deformation based seismic design of pile supported marine facilities
(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2008., 2008.) Polat, Şamil Şeref.; Aydınoğlu, M. Nuray.
Pile supported marine structures with batter piles comprise a considerable share in the modern marine structure stock built in seismic zones. Their stiff nature offers significant advantages to structural engineers in resisting non-seismic loads such as, berthing, mooring etc. On the other hand the poor performance of marine structures supported by batter piles in recent earthquakes has revealed certain disadvantages of these systems in resisting seismic loads. The general design approach for pile supported marine structures is to ensure that the cap-beam and the deck system will remain elastic and the yielding will occur either at the pile-to-cap beam connection or along the pile itself. Traditionally those structures were designed with force-based design methods to withstand seismic forces reduced by response modification factors or to a force equal to a fraction of the total weight of the structure. The past research in last decade have shown that the poor behavior of batter piles is mainly related to this force-based approach, which lack to identify the problems associated to post-yield behavior of these piles. When batter piles yield in tension, either in the form of pile-to-cap-beam connection or pile pull-out of soil pile-cap starts to pole vault over the compression piles as the structure deforms laterally. As the structure rises, substantial tension forces are developed both in the vertical and orthogonal batter piles and create additional shear and moment to the cap-beam. The non-linear analysis performed on generic pier frames in this study revealed that substantial amplifications in section forces have been observed at the pile-cap with decrease in strength and increase in batter. Even though section compactness is a well known requirement in steel design most of the modern marine structure design codes does not provide a compactness criteria. When the connection of the tension batter pile is designed to develop high axial forces, the compression piles with non-compact steel section have a tendency to yield under the action of earthquake induced bending moments and high compression forces at the pile-soil interface. The inelastic response history analysis performed on generic pier frames indicate formation of inelastic local buckling on compression piles results in partial or total collapse of the structure. Design recommendations are provided based on the results of the performed nonlinear analysis.
Strong motion simulation by empirical green's function method for Bursa Armutlu peninsula
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2008., 2008.) Savaş, Neval.; Tanırcan, Gülüm.
According to results of time dependent probabilistic hazard assessments, The fault segment extending between Gemlik-Bandirma and segment passing through the southern part of Iznik Lake have potentials of producing a magnitude 7.2+ event with 1000 year recurrence time and second highest hazard rate in Marmara Region. For future risk mitigation strategies, it necessitates preparing scenario earthquakes. Near-field generation of scenario events from mentioned fault segments was performed at nine BYTNET stations. Horizontal components of records with frequency range of 0.5-10 Hertz were used. Simulations were performed by using Empirical Green’s Function Method which essentially uses small events as Green’s function and sums them up to follow the omega-squared scaling law. Gemlik Earthquake was utilized as Green’s Function throughout analysis. As an initial calculation focal mechanism of Gemlik Earthquake was confirmed by simulating it with Mw= 3.3 event. For scenario case, assumption is that scenarios occur at the same location of Mw= 4.8 event with same focal mechanism. A single asperity model was adopted. Size of asperities was determined according to stress drop ratio equality between target and element event. Scenarios were defined by changing rupture initiation points. Near field effects at each scenario simulation were investigated via observing components perpendicular and parallel to fault plane. Various empirical attenuation relationships were compared with simulated peak ground accelerations and velocities. Simulated acceleration spectra pertaining to fault parallel and normal components were compared with Turkish Seismic Design Code. Finally, It was observed whether peak values were in harmony with attenuation curves or not.
Re-evaluation of earthquake performance and strengthening alternatives of Hagia Sophia
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2008., 2008.) Kırlangıç, Ahmet Serhan.; Durukal, Eser.
Static and dynamic linear analyses were carried out to evaluate the structural behaviour of and to propose strengthening strategies for Hagia Sophia. A Finite Element model of the structure was used for this purpose. While linear static self-weight and eigenvalue analyses were performed to ensure that the finite element model represents the structure, response spectrum analysis was used to obtain the deformation and stress distributions for determining the regions where intervention is needed. Response spectrum analysis revealed that main arches, semidomes and domebase exhibit high stress concentrations. These particular elements were the target zones for intervention. Two main strengthening strategies were considered: i) Retrofitting the main arches with post-tensioned bars, ii) Wrapping the structural elements with fiber reinforced polymers FRPs. These two strategies were modelled and changes in the structural behaviour were observed. The analyses revealed post-tensioning as a more effective approach as compared to wrapping the structural elements with FRP laminates.
Seismic strengthening of existing RC frame buildings by steel panels
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2008., 2008.) Sezer, Başak.; Mowrtage, Waiel.
Every major earthquake in Turkey causes a large number of building suffer moderate damage due to poor construction. If a proper and fast retrofit is not applied, the aftershocks, which may sometimes come days or weeks after the main shock, can push a moderately damaged building into a major damage or even total collapse. Retrofitting these poor constructed buildings using traditional methods may cost a lot of money, labor and time which make the choice of reconstruction better than retrofitting. This research presents a practical retrofit method for moderately damaged buildings, which increases the seismic performance of the structural system by reducing the displacement demand. Fabricated steel panels are used for the retrofit. They are light-weight, easy to handle, and can be constructed very quickly. Moreover, they are cheap, and do not need formwork or skilled workers. They can be designed to compensate for the stiffness and strength degradation, and to fit easily inside a moderately damaged reinforced concrete frame. To test the concept, a half-scale, single-story 3D reinforced concrete frame specimen was constructed at the shake-table laboratories of the Kandilli Observatory and Earthquake Research Institute of Bogazici University, and subjected to recorded real earthquake base accelerations. The amplitudes of base accelerations were increased until a moderate damage level is reached. Then, the damaged RC frames was retrofitted by means of steel panels and tested under the same earthquake. The seismic performance of the specimen before and after the retrofit was evaluated using Turkish seismic code (2007) standards, and the results were compared in terms of stiffness, strength, and deformability. The results have confirmed effectiveness of the proposed retrofit scheme. In order to make this retrofit method easy to comprehend for civil engineers a real structure from Zeytinburnu is chosen to test the panels in computer environment. Performance of the structure evaluated in the same way and effectiveness of the panels have confirmed again.
Evaluation of practice-oriented nonlinear analysis methods for seismic performance assessment
(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2008., 2008.) Önem, Göktürk.; Aydınoğlu, M. Nuray.
In the last decade, nonlinear static analyses based on pushover analysis have been developed as a simplified nonlinear analysis tool within the context of performance based design approach (ATC 40 and FEMA 356). Since nonlinear static analyses provide designers a practical analysis approach in estimating inelastic seismic demands, these methods have been widely used in engineering practice. On the other hand, recent research have clearly shown that simplified nonlinear static analyses, which consider single mode behavior of the structures, have serious limitations for high-rise buildings or buildings irregular in plan, where higher modes effects become important. In order to overcome these limitations and to enhance the feasibility of the pushover analysis in practice, a number of multi-mode pushover analysis methods have been developed. It should be noted that pushover analysis has not been provided with a firm theoretical basis and those methods are therefore based on various assumptions. In this study, development and codification of nonlinear static analysis as a tool for performance based assessment have been summarized. Piecewise linear representation of single-mode pushover analysis, which provides a non-iterative pushover analysis technique with an adaptive load or displacement pattern, has been presented in detail. A number of multi-mode pushover analysis methods have been investigated in detail and classified with respect to their assumptions. The emphasis of this study is to evaluate the validity of those assumptions and their limitations in terms of practical applicability. In addition, a parametric study is carried out in order to evaluate and understand the limitations of single-mode and multi-mode pushover analysis methods based on various assumptions. It has been observed that some multi-mode pushover analysis methods deal with estimating only structural capacity, resulting in a conventional pushover curve where higher modes effects are somehow considered. Thus these multi-mode pushover analysis methods can be regarded only as capacity estimation tools. However, the main objective of the nonlinear static analysis should be the estimation of the seismic demands under a given earthquake ground motion. It is interesting to observe that the number of multi-mode pushover analysis methods achieving this objective is very limited. Determination of relative modal contributions at each pushover step with an appropriate modal scaling procedure is a critical point in a multi-mode pushover analysis As a result of the investigation of multi-mode pushover analysis methods, it has been observed that there are mainly two types of modal scaling procedures generally adopted: (a) scaling based on instantaneous inelastic spectral displacements, (b) scaling based on instantaneous elastic spectral displacements or pseudo-accelerations. It has been identified that multi-mode pushover methods adopting modal scaling procedure based on instantaneous elastic spectral quantities would not work when P-delta effects are considered. The effectiveness of multi-mode pushover analyses has been tested for reinforced concrete frame and dual systems by comparing the results obtained from inelastic time history analysis (ITHA). Analysis results indicated that multi-mode pushover analyses, which combine multi-mode effects at each pushover step, provides relatively good estimates of inter-story drift and plastic rotation demands in the lower and middle stories of taller frames. At the upper story levels, where higher mode effects are significant, Incremental Response Spectrum Analysis (IRSA) developed by Aydınoglu (2003) and Modal Pushover Analysis (MPA) developed by Chopra and Goel (2001) give more accurate results as compared to the other methods. It has been observed that when P-delta effects are included in the analyses, the discrepancy between the results obtained from ITHA and all pushover analyses tends to increase as compared to the case without P-delta effects. For dual systems, multi-mode pushover analyses, which combine multi-mode effects at each pushover step, predicts reasonably well the changing height-wise variation of plastic rotation demands in the beams with building height, particularly for dual systems with smaller wall shear ratio. IRSA significantly predicts much more accurate plastic rotation estimates with respect to all other multi-mode pushover methods. Single-run multi-mode pushover analysis methods with single-load or single-displacement patterns based on combined multi-mode loading significantly underestimate shear force demands in the shear wall elements. Additionally, it has been observed that multi-mode pushover analysis methods provide much more accurate estimate of plastic hinge rotations and their locations at the base of the shear walls as compared to FEMA 356 lateral load distributions. Single-mode adaptive pushover analysis can predict plastic rotation demands accurately at the base of the shear walls in spite of the fact that only single mode was considered, whereas invariant single-mode pushover analysis cannot predict. This shows that adaptive pushover analysis provides a more reliable analysis technique, which is able to capture changing dynamic characteristics of dual systems and eventually plastic rotation demands at the base of the shear walls.

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