Structural evaluation and seismic vulnerability assessment of Reinforced Concrete (R/C) buildings have especially become the focus of many researches in Turkey and abroad especially after the August 17, 1999 earthquake causing major life and property losses. A devastating earthquake being expected in Istanbul-Marmara region raises many questions on how well the existing buildings are constructed and whether they can stand a major earthquake. Evaluation of existing buildings for seismic vulnerability requires time consuming input preparation (pre-processing), modelling, and post processing of analysis results. The objective of the study is to perform automated seismic vulnerability assessment of existing R/C buildings automatically over the internet by asking internet users to enter their building related data, and streamlining the modelling-analysis-reporting phases by intelligent programming. The internet based assessment tool is prepared for two levels of complexity: (a) the detailed level targets to carry out seismic evaluation of the buildings using a linear structural analysis software developed for this study / (b) the simplified level produces seismic evaluation index for buildings, based on simple and easy to enter general building information which can be entered by any person capable of using an internet browser. Detailed level evaluation program includes a user friendly interface between the internet user and analysis software, which will enable data entry, database management, and online evaluation/reporting of R/C buildings. Building data entered by numerous users over the internet will also enable formation of an extensive database of buildings located all around Turkey. 36 buildings from D&uuml / zce damage database, generated by the cooperation of Scientific and Research Council of Turkey (T&Uuml / BiTAK) and Structural Engineering Research Unit (SERU) after the 17 August 1999 Kocaeli and the 12 November 1999 D&uuml / zce earthquakes, are used in the analyses to identify relationship between calculated indices and observed damage levels of buildings, which will enable prediction of building damage levels for future earthquakes. The research is funded by Science Research Program (BAP 2003-03-03-03), NATO-SfP 977231, and TUBITAK ICTAG-I574 projects. The contribution of the research is composed of a) online building index -performance analysis/evaluation software which might be used by any average internet user, b) an ever-growing R/C building database entered by various internet users.

ABSTRACT VIBRATION FATIGUE ANALYSIS OF EQUIPMENTS USED IN AEROSPACE AYKAN, Murat M.Sc., Department of Mechanical Engineering Supervisor: Assoc. Prof. Dr. F. Suat KADIOgLU Co-Supervisor: Assoc. Prof. Dr. Mehmet &Ccedil / ELiK June 2005, 123 Pages Metal Fatigue of dynamically loaded structures is a very common phenomenon in engineering practice. As the loading is dynamic one cannot neglect the dynamics of the structure. When the loading frequency has a wide bandwidth then there is high probability that the resonance frequencies of the structure will be excited. When this happens then one cannot assume that the structures response to the loading will remain linear in the frequency domain. Thus to overcome such situations frequency domain fatigue analysis methods exist which include the dynamics of the structure. In this thesis, a Helicopters Self-Defensive System&rsquo / s Chaff/Flare Dispenser Bracket is analyzed by Vibration Fatigue Method as a part of an ASELSAN project. To obtain the loading (boundary conditions), operational flight tests with accelerometers were performed. The obtained acceleration versus time signals are analyzed and converted to Power Spectral Densities (PSD), which are functions of frequency. In order to obtain the stresses for fatigue analysis, a finite element model of the bracket has been created. The dynamics of the finite element model was verified by performing experimental modal tests on a prototype. From the verified model, stress transfer functions have been obtained and combined with the loading PSD&rsquo / s to get the response stress PSD&rsquo / s. The fatigue analysis results are verified by accelerated life tests on the prototype. Also in this study, the effect of single axis shaker testing for fatigue on the specimen is obtained.

Block shear is a limit state that should be accounted for during the design of the steel tension members. This failure mechanism combines a tension failure on one plane and a shear plane on a perpendicular plane. Although current design specifications present equations to predict block shear load capacities of the connections, they fail in predicting the failure modes. Block shear failure of a structural connection along a staggered path may be the governing failure mode. Code treatments for stagger in a block shear path are not exactly defined. A parametric study has been conducted and over a thousand finite element analyses were performed to identify the parameters affecting the block shear failure in connections with multiple bolt lines and staggered holes. The quality of the specification equations were assessed by comparing the code predictions with finite element results. In addition, based on the analytical findings new equations were developed and are presented herein.

iv ABSTRACT SEISMIC DESIGN OF COLD FORMED STEEL STRUCTURES IN RESIDENTIAL APPLICATIONS Uygar, Celaletdin M.Sc., Department of Civil Engineering Supervisor: Prof. Dr. &Ccedil / etin Yilmaz May 2005, 82 pages In this study, lateral load bearing capacities of cold formed steel framed wall panels are investigated. For this purpose lateral load bearing alternatives are analyzed numerically by computer models and results are compared with already done experimental studies and approved codes. In residential cold formed steel construction, walls are generally covered with cladding material like oriented strand board (OSB) or plywood on the exterior wall surface and these sheathed light gauge steel walls behave as shear walls with significant capacity. Oriented strand board is used in analytical models since OSB claddings are most commonly used in residential applications. The strength of shear walls depends on different parameters like screw spacing, strength of sheathing, size of fasteners used and aspect ratio. SAP2000 software is used for structural analysis of walls and joint force outputs are collected by Microsoft Excel. The yield strength of shear walls at which first screw connection reaches its shear capacity is calculated and load carrying capacity per meter length is found. The nonlinear analysis is also done by modeling the screw connections between OSB and frame as non-linear link and the nominal shear capacities of walls are calculated for different screw spacing combinations. The results are consistent with the values in shear wall design Guide and International Building Code 2003. The other lateral load bearing method is flat strap X-bracing on wall surfaces. Various parameters like wall frame section thickness, flat strap area, aspect ratio and bracing number are investigated and results are evaluated. The shear walls in which X-bracing and OSB sheathing used together are also analyzed and the results are compared with separate analyses.

This study investigates the influence of the gravity load resisting system on the collapse performance of Special Steel Moment Frames (SMFs). The influence was quantified using the FEMA P-695 methodology. The buildings used for this study were a 2-, 4- and 8-story SMFs taken from the ATC76-1 project where their collapse performance was already evaluated without the gravity system. The main work of this dissertation has been divided in two parts. The first part studies the influence of the gravity system when it is incorporated explicitly as part of the lateral resisting system. Aspects of the gravity frame that were investigated include the contribution of stiffness and strength of beam to column connections, and the location of splices in the gravity columns. Moreover, this research investigates the potential for the development of inelastic deformations in the gravity columns, and the effect of such deformations on structural response. The results show that gravity connections and gravity column's continuity profoundly affect the computed response and collapse probability. The inelastic behavior in gravity columns has a less important effect but should be included in the analysis. The second part of the investigation looks more in depth at the role of the gravity columns on the collapse performance of SMFs. Using the 2-, 4- and 8-story SMFs, the gravity columns are incorporated using the approach where all the gravity columns are lumped into one elastic, pinned at the base and continuous element. The approach is first validated by checking different aspects such as: strength of gravity connections to induce yielding into gravity columns, difference between the explicit and lumping column approach, and required gravity column's splices to provide continuity. The stiffness of the element representing the gravity columns was varied in order to find the influence of the gravity columns. At the end of the study it was found that they have a significant influence on the collapse performance of SMFs, especially on taller structures like the 8-story model. Moreover it was concluded that an adequate stiffness of the gravity columns could be found by performing nonlinear static pushover analysis. / Ph. D.

This dissertation discusses the potential for using a conventional main lateral-force resisting system, combined with the reserve strength in the gravity framing, and or auxiliary collapse-inhibiting mechanisms deployed throughout the building, or enhanced shear tab connections, to provide adequate serviceability performance and collapse safety for seismic and wind hazards in the central and eastern United States. While the proposed concept is likely applicable to building structures of all materials, the focus of this study is on structural steel-frame buildings using either non-ductile moment frames with fully-restrained flange welded connections not specifically detailed for seismic resistance, or ductile moment frames with reduced beam section connections designed for moderate seismic demands. The research shows that collapse prevention systems were effective at reducing the conditional probability of seismic collapse during Maximum Considered Earthquake (MCE) level ground motions, and at lowering the seismic and wind collapse risk of a building with moment frames not specifically detailed for seismic resistance. Reserve lateral strength in gravity framing, including the shear tab connections was a significant factor. The pattern of collapse prevention component failure depended on the type of loading, archetype building, and type of collapse prevention system, but most story collapse mechanisms formed in the lower stories of the building. Collapse prevention devices usually did not change the story failure mechanism of the building. Collapse prevention systems with energy dissipation devices contributed to a significant reduction in both repair cost and downtime. Resilience contour plots showed that reserve lateral strength in the gravity framing was effective at reducing recovery time, but less effective at reducing the associated economic losses. A conventional lateral force resisting system or a collapse prevention system with a highly ductile moment frame would be required for regions of higher seismicity or exposed to high hurricane wind speeds, but buildings with collapse prevention systems were adequate for many regions in the central and eastern United States. / Ph. D.

This study presents a ground-motion selection and scaling procedure that preserves the inherent uncertainty in the modified recordings. The proposed procedure provides a set of scaled ground-motion records to be used in the response estimation of structural systems for a pre-defined earthquake hazard level. Given a relatively larger ground-motion dataset, the methodology constrains the selection and scaling of the accelerograms to the differences between individual records and corresponding estimations from a representative ground-motion predictive model. The procedure precisely calculates the distribution parameters of linear structural systems whereas it provides estimations of these parameters for nonlinear structural response. Thus this method is not only useful for ground-motion selection and scaling but also for probability based performance assessment studies. The proposed procedure is also capable of matching with a pre-defined target elastic response spectrum and corresponding variance over a period range. Case studies that compare the performance of the proposed procedure with some other record selection and scaling methods suggest its usefulness for the accurate verification of structural systems and rapid loss estimation studies.

In this study, the seismic fragility assessment of low-rise and mid-rise reinforced concrete frame buildings which constitute approximately 75 % of the total building stock in Turkey is investigated to quantify the earthquake risk. The inventory used in this study is selected from D&uuml / zce damage database which was compiled after the devastating 1999 earthquakes in the Marmara region. These buildings are not designed according to the current code regulations and the supervision in the construction phase is not adequate. The building database is divided into sub-classes according to the height and absence of infilled walls. Each building in the database is represented by an equivalent single degree of freedom system with three structural parameters: period, strength, and post-elastic stiffness ratio. The ground motion records are selected from different parts of the world covering a wide range of characteristics. The capacity of the structure is represented for each sub-class by the limit states. Hence, a set of fragility curves for low- and mid-rise reinforced concrete structures are developed by making use of the building characteristics in the database. The generated fragility curve set is referred as &ldquo / reference&rdquo / since it forms the basis of a parametric study. A parametric study is conducted to examine the influence of post-elastic stiffness ratio, simulation and sampling techniques, sample size, limit state definition and degrading behavior on the final fragility curves. Estimated damage distribution after two consecutive major earthquakes is compared with the actual field data in order to investigate the validity of the generated fragility curves.

Maximum interstory drift and the distribution of this drift along the height of the structure are the main causes of structural and nonstructural damage in frame type buildings subjected to earthquake ground motions. Estimation of maximum interstory drift ratio is a good measure of the local response of buildings. Recent earthquakes have revealed the susceptibility of the existing building stock to near-fault ground motions characterized by a large, long-duration velocity pulse. In order to find rational solutions for the destructive effects of near fault ground motions, it is necessary to determine drift demands of buildings. Practical, applicable and accurate methods that define the system behavior by means of some key parameters are needed to assess the building performances quickly instead of detailed modeling and calculations. In this study, simple equations are proposed in order for the determination of the elastic interstory drift demand produced by near fault ground motions on regular and irregular steel frame structures. The proposed equations enable the prediction of maximum elastic ground story drift ratio of shear frames and the maximum elastic ground story drift ratio and maximum elastic interstory drift ratio of steel moment resisting frames. In addition, the effects of beam to column stiffness ratio, soft story factor, stiffness distribution coefficient, beam-to-column capacity ratio, seismic force reduction factor, ratio of pulse period to fundamental period, regular story height and number of stories on elastic and inelastic interstory drift demands are investigated in detail. An equation for the ratio of maximum inelastic interstory drift ratio to maximum elastic interstory drift ratio developed for a representative case is also presented.

Turkey is located on a seismically active region and ranks high among all countries that have suffered losses of life and property due to earthquakes over many centuries. In addition, its building stock has usually poor construction quality with seismically improper structural systems. These lead to a need for rapid and reliable assessment and retrofit procedures. In the 2007 Turkish Earthquake Code, a new chapter is included for assessment and retrofit of existing buildings. The assessment procedures proposed in the Code are classified as linear elastic and nonlinear procedures. An engineer is allowed to choose one of these two procedures without any restriction. In this study, a research was undertaken in order to clarify the differences between the seismic assessment procedures in the 2007 Turkish Earthquake Code. For this purpose, two pairs of existing and retrofitted residential buildings were assessed according to the principles of both procedures proposed in the 2007 Turkish Earthquake Code. The assessment results were also compared with the actual performance observations from a 5-storey building which suffered damage during the 1999 D&uuml / zce earthquake. In addition, an anchorage design methodology was developed for the exterior coupled shear wall retrofit solution, and tested on a 6-storey case study building.