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Advance modelling and collapse risk estimation of a highway bridge
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2013., 2013.) Görk, Serkan.; Şafak, Erdal.; Aydınoğlu, M. Nuray.
In this study, collapse risk of a highway bridge is estimated analytically using advance mathematical model. The concentration of this study is on advance modeling of the bridge, including linear sticks of beams, nonlinear modeling of piers and abutments with their shear capacities, inelastic connecting members, inelastic foundations and inelastic soil springs. The structural data including all geometry and dimensions, configuration of structural members and connecting elements, reinforcement details for piers, and material properties are taken from ‘as-built’ drawings of the bridge from contractors. Two different mathematical models have been constructed with different foundation conditions for nonlinear response history analyses with enough numbers of earthquake records. Collapse fragility curves are obtained in terms of spectral acceleration corresponding to dominant natural period of the bridge. The integration of collapse fragility curves of models and corresponding hazard curve gives the collapse risk of the bridge. In the first chapter of this study, the scope of the work and general information about the bridge has been given. In the second chapter, the methodology of estimating collapse risk in an analytical way has been introduced. The steps of collapse risk estimation have been explained. In the third chapter, mathematical modeling of the structure has been given in details. Materials, nonlinear load-carrying members, beams, connecting elements, foundation and soil properties have been given in detail. In the fourth chapter, analysis objectives, modal analysis results, the earthquake records and hazard curves have been presented. In the fifth chapter, fragility curves are developed and the collapse risk has been calculated for these two models. In the last chapter, the conclusions are presented and suggestions for improving this study are proposed.
Alternate representations of dynamic properties and loading
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2014., 2014.) Gülenç, Caner.; Tanırcan, Gülüm.; Aydınoğlu, M. Nuray.
This study covers three main topics, which are directly related to dynamic behaviour of structures, namely, representation of mass, damping and loading. These three properties of equation of motion are generally represented by widely accepted approaches. In this thesis, such representations are discussed via comparisons with infrequently used representations and viability of them is investigated. For case study, 50-story core wall structure is chosen. First topic discussed here is mass representation. Indisputably, the most accepted assumption for mass representation is lumped mass approach, which is very practical to construct the matrix or, at least, easy to understand the concept of. Another representation, not common one, consistent mass approach derived by a similar procedure in the method for derivation of stiffness coefficients. Consistent mass matrix has off-diagonal terms as distinct from lumped mass matrix. Since the core wall has a continuous form, it is reasonable to represent its mass distribution with consistent mass approach, which takes into account coupling terms. Effects of consistent mass representation on dynamic response of a 50-storey core-wall tall building are investigated. Second one is damping property which may be evaluated as one of the most controversial aspects of structural dynamics. As it is not possible to derive a damping matrix from the element cross section properties and material properties directly, proportional viscous damping matrix is generally used instead, which is defined in terms of modal damping ratios at certain anchor frequencies. However, viscous damping model has a significant deficiency associated with the energy mechanism. Studies based on experimental data show that dissipated energy per cycle of an oscillating system is essentially independent of the excitation frequency as opposed to dependency inherent in the viscous damping model. Such damping model is called rate-independent or structural damping, which is conveniently modelled in the frequency domain through complex stiffness matrix. One of the aims of this study is to observe the effects of such an alternate damping model on the linear seismic response of a tall building. To this end, a 50-story core-wall tall building system is investigated. Drift and total acceleration response characteristics for a set of earthquake records are obtained from the analyses conducted through Fourier Transform. Last concept, probably the most innovative idea of this study, is related to loading part of equation of motion. It has been long applied that ground accelerations are used directly as force by multiplying floor masses, eventually, relative response quantities are obtained. The underlying idea of this loading concept is based on pseudo-static transmission assumption, which presumes that base displacement, in any time instant, is transmitted throughout building statically and naturally, such movement does not deform the structure. One of the aims of this study is to investigate viability of this concept. The motivation is based on the idea that if the building is tall enough, is it possible to be transmitted of base displacements throughout the building without generating any significant deformation? For this reason, absolute response and relative response quantities of the 50-story core-wall are obtained by using acceleration and displacement loading concepts respectively. Comparative results are given at the end.
Collapse risk estimation of reinforced concrete buildings
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2013., 2013.) Beyazoğlu, Tamer İzzet.; Şafak, Erdal.; Aydınoğlu, M. Nuray.
In this study, collapse risks of five-storey RC frame buildings are estimated analytically using advance mathematical model. The concentration of this study is on advanced nonlinear analysis of the building including nonlinear modeling of columns and beams with their shear capacities. Collapse fragility curves are obtained in terms of spectral acceleration corresponding to dominant natural period of the building. The collapse risk of the building is obtained through integration of collapse fragility curves of models and corresponding hazard curve. In the first chapter of this study, the scope of the work and literature survey have been given. In the second chapter, the methodology of estimating collapse risk in an analytical way has been introduced. The steps of the proposed methodology for collapse risk estimation have been explained briefly. In the third chapter, mathematical modeling of the buildings has been given in details in terms of non-linear material properties, lump and distributed plasticity approach for structural members. In the fourth chapter, objectives of the analysis, the strong ground motion records and hazard curves used in the analysis phase have been presented. In the fifth chapter, fragility curves are obtained and the collapse risk has been calculated for each building under consideration. In the last chapter, the conclusions are presented.
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.
Development and verification of seismic capacity and ductility demand estimation procedures for coupled core wall systems
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2014., 2014.) Vural, Eren.; Şafak, Erdal.; Aydınoğlu, M. Nuray.
Performance-based seismic design of tall buildings is of great importance as demands are increasing for incorporating structural safety in such challenging structures. Although a number of design guidelines and consensus documents have been published in the last few years regarding performance-based seismic design of tall buildings, there are still several issues need to be resolved. Coupled core wall systems composed of flanged (U, T, E or I shaped) walls coupled by coupling beams, represent the most commonly used structural system in tall buildings. Although experimental and analytical research is available regarding the behavior of coupled wall systems with rectangular walls, such systems are not representative of the current design practice. Efforts are necessary not only for a clear understanding of the behavior of coupled core walls both at the component and system levels, but at the same time for the implementation of research results into performance-based seismic design methodologies. In this study, capacity and ductility demand estimation procedures are developed for preliminary seismic design of coupled core wall systems. These procedures may be considered complementary to capacity design principles to be implemented during the preliminary design stage. Effective design parameters controlling the behavior of coupled core wall systems and relative importance of each design parameter are identified through verification studies of the proposed capacity and ductility demand estimation procedures as well as nonlinear response history analyses.
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.
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.
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 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.
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
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.
Seismic shear amplification in structural walls
(Thesis (M.S.)-Bogazici University.Kandilli Observatory and Earthquake Research Institute, 2009., 2009.) Düzgün, Emre.; Aydınoğlu, M. Nuray.
Earthquake resistant design of structural walls involves inhibiting brittle shear failure that would develop with the formation of plastic hinge at the base of the walls. During seismic action, recent studies demonstrate that maximum wall shear responses, during an earthquake depending on characteristics of the walls, are generally higher than the conventional code procedures, namely elastic analysis procedures, which can be attributed to the contribution of higher mode effects subsequent to the formation of plastic hinge at the base of the wall. In light of findings from analyses of structural walls, shear amplification factors have been proposed in Eurocode 8 EN1998-1 (CEN, 2004) to inhibit brittle shear failure occurrence in structural walls. Proposed relationships mainly depend on first mode period of wall and strength reduction factors. However, in Turkish Seismic Design Code, this issue has been handled by considering a constant base shear amplification of 1.5 regardless of first mode period and ductility level of the structural walls. Generic structural walls having four, eight, twelve, sixteen stories with different sectional properties have been analyzed in order to evaluate the dynamic shear amplification phenomenon. Responses of structural walls have been obtained through nonlinear analyses results such as base shear amplification factors, force and deformation responses. This study can be treated as an initial investigation for developing a sound procedure for shear design of structural walls in current code applications.
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.

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